DIY Subwoofer Project - A Premium Journey to the Low End
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    1. #1
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      DIY Subwoofer Project - A Premium Journey to the Low End

      I have started this thread to detail by effort to provide a first class bottom end to my 2011.5 XC60's Premium Audio System. While it took several weekends to complete this project it is not a difficult one and I hope others here give it a try by following these instructions. I will also offer support and welcome comments and questions in this thread.

      To start at the beginning in order to provide context, I admit I am a longtime audiophile and desire to have my daily commuting environment able to satisfy my wide ranging musical tastes. When originally evaluating the XC60, I was please to see the partnership with DynAudio as I was quite familiar and impressed by their home speakers. However, when I actually went to test drive one, I learned that the system had been changed mid-year and the dealer was not sure whether DynAudio was still involved or if not who replaced them. I also learned to my dismay that a subwoofer was not included as one of the 12 speakers in the Premium option though it was an additional option. Further I found out that this option was not available in the U.S. and in Europe was the equivalent of $1200. Even though I was disappointed overall the ne Premium system appeared capable and the car was on the top of my list for other reasons. so I went ahead and ordered it.

      After taking delivery and loading up my music and setting everything flat I was appalled by how emphasized the bass was. Even my wife commented on it. Fortunately the Premium system has a 5-band equalizer and by reducing the 60Hz seven steps and boosting the 200Hz by 2 steps, I got the sound reasonable but unfortunately there was no quality low bass in the 30-60Hz region. I will say with if this was the flat setting, most people would have little to complain about. Unfortunately, when it comes to music reproduction, I am not most people and thus began my journey to design a custom subwoofer for this deserving car.

      For those who want to see what they will get if they complete the project, here is a picture of the completed installation with the cargo floor removed (It does lie flat when installed):

      Completed Subwoofer Installation

      Since this was not going to be my first sub design, I knew from experience to put down my requirements first. Without a clear target one can forever be "tinkering" instead of enjoying. My requirements for the design and installation were the following:

      1. Extend seamlessly the existing system's response to the mid-30Hz range at low distortion and comparable dynamic capability.
      2. Stay comfortably within the XC60's alternator/battery capabilities
      3. Lose no significant cargo space.
      4. Make no irreversible changes or modifications to the car.
      5. Have the driver(s) protected from physical damage through normal use.
      6. Be within my capabilities to implement.

      For starters, I researched as much online information as I could regarding DynAudio's OEM subwoofer design. While I never have actually seen one, the pictures, diagrams and specs, I have found indicated that it was a vented bandpass design using 2 6.5" drivers side-by-side in an enclosure that ported forward into the rear seats. From the its size and knowing DynAudio's drivers I knew that while better than simply using the doors, simply reproducing that design was not going to give me the low end extension I was looking for. However, the existence of this option, did provide me with a candidate mounting location that would not interfere with cargo and was fully protected. I did consider the more "in fashion" approaches of building a custom fiberglass enclosure in either the spare tire wheel or on the side. I dismissed both due to the power needed to overcome the small enclosures and the requisite low-end signal boost to overcome its acoustical rolloff and the fact that it would be very difficult to physically protect the driver without interference. I also did not have significant experience working with fiberglass and did not want to farm it out due to cost. Bottom line, find a way to use the existing subwoofer space.

      One reason, DynAudio undoubtedly decided to use the vented bandpass design was that it provides bass gain where a sealed/vented design of the same size would have a bass roll-off. By placing the drivers face-to-face and wiring them out of phase in an isobaric configuration, I knew that I would get the extended low end of a box twice the size. Additionally I would get lower distortion due to harmonic cancellation as the drivers are working out of phase. The only problem then was to find drivers that were shallow enough to mount face-to-face in an enclosure that at best would have 5" of internal height. Fortunately I found a 6.5" sub from Earthquake Sound (SWS-6.5) that has only 1.75" of depth but has an inch of cone travel. Entering in its parameters into WinISD revealed that I could easily achieve my desired low end response with a 1 cu. ft. enclosure as long as the vent could be tuned to ~50 Hz which meant it had to be approximately 8" long by 2" in diameter. As one needs to have at least 1x Vent diameter in rear space, this meant the enclosure needed to be at least 10" plus the thickness of the rear panel deep. Best of all, these drivers are sold as a pair for less than $100.

      My next task was to figure out how to design the enclosure in such a way that it would be air-tight where it needs to be and still be able to have access to the drivers if I needed to replace one. Also since the tuning of this design is dependent on the volumes of the respective sealed and vented areas as well as the vent length I needed a tuning capability. By mounting the drivers and internal dividers on the front panel, and by making the panel initially a bit longer than required, I was able to tune it by sliding the panel thus changing the ratio of the two internal areas and also have a way to gain service access to the drivers. Below are pictures of the two pieces.


      Front of Top Plate resting on Enclosure


      Rear of Top Plate resting on Enclosure

      The construction diagrams for the enclosure:




      To construct the enclosure, I chose to used MDF for its stability and ability to hold an edge. The sides and interior are made from 3/4" MDF in order to have sufficient width to accept #10 x 1 1/2 wood screws edgewise. All joints should be glued and screwed every 3 to 4" Ensure that 1/8" holes are predrilled and that screws are placed so that orthogonal ones do not run into each other. Additionally the interior and front panel seams should be caulked to ensure an airtight enclosure. An adhesive-backed gasket should be applied to all of the edges that contact the front panel and interior pieces. This will take the place of the glue and caulk you will not be able to use. As this MDF is thick relative to the size of the pieces tolerances should held as precise as possible which means that the thickness of the saw blade must be taken into account on all cuts.

      The trickiest part is cutting the circles for the drivers and the vent. I used a circle jig and my router. A heavy duty jig saw can also be used if you have a steady hand. Neither circle needs to be pretty as they both will have their edges covered. Also the driver cutout does not have to be precisely centered. IMPORTANT, the drivers will need to be bolted together to either side of the MDF. There is not much clearance between the opening and the screw holes. Make sure you have enough distance to support the screws and flange.

      I chose a Precision Port 2" double flange part because it is not only well made and adjustable, but using flanges on both ends reduces the overall length required to reach the desired frequency. I chose to gasket and glue to to the front panel but it can be screwed as instead.

      This design requires that the drivers are connected in parallel but out of phase. What this means is that the positive (+) terminal of the sealed driver is connected to the Negative (-) terminal of the vented driver which is then connected to the Positive (red) terminal on the enclosure. The other negative wires are connected in the same way but in a N-P-N configuration. To ensure you don't get this wrong and damage the drivers, make sure that when you bolt them together they are aligned to allow the wiring not to have to cross. To mount the drivers first run a circle of the gasket on each side of the board around the hole. I decided to use the plastic ring since the drivers' rim could use the additional support. The 4 #10x32 machine screws should be threaded through a sandwich of flange, ring, gasket, wood, gasket, ring, and flange. I used #10 locking nuts to ensure the connection will remain tight.

      There are several approaches one can take to the speaker terminals. I could have simply used a pigtail arrangement, but I wanted to be able to remove the speaker without having to remove the wire-run to the amplifier. I chose the sheathed banana style as it allows a quality soldered connection and there is no chance of the connectors shorting together or falling out. The internal wiring as seen in the picture is very short and can be 12 - 16ga. I recommend all connections be soldered. As the driver terminals are small and vertical clearance is tight I recommend using a continuous run for each wire and for the vented driver that needs to support two wires, strip away a section of insulation and insert the terminal through the center of the strands and solder on both sides. Below is a picture of the wiring from the top.

      Subwoofer Wiring - Top View

      Note that you need to drill a hole for the wires from the the bottom driver and that the hole is sealed with caulking as are the terminals. Also I recommend that you apply heat shrink to connections as it will prevent shorting and provide a more stable connection.

      More to come (including a complete parts list) ...
      Last edited by mark-sf; 02-13-2020 at 11:29 PM.
      2011.5 XC60 3.2L Flamenco Red/Anthracite Black, Premium, Multimedia, Convenience, BLIS, Xenon + Custom Subwoofer

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    3. #2
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      Outstanding work, we're all following, thanks for the updates
      2018 XC60 T5 Momentum AWD/Osmium Grey Metallic/Charcoal Leather/B&W Audio/ACC-PA2 (OSD)
      2011.5 XC60 3.2 AWD/Saville Grey Metallic/Anthracite Black Leather/Premium/Climate/BLIS/Rear Cam/

    4. #3
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      Awesome!

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    6. #4
      Junior Member Star4ever's Avatar
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      Very nice job... methodical engineering type approach.
      So how does it sound?
      Have you met your goals?
      Having done this now... what if anything would you have changed or improved upon?
      2011.5 XC60 T6 - Xenons - BLISS - PCC - Convenience - Climate - Nordic Oak Stack - Ice White w Rear Skid and Side Scuff Plates, Mud Flaps, Sill Plates, R-Design Pedals
      MY XC60 T6's FUEL USAGE ->http://www.fuelly.com/driver/2011xc60t6/xc60

    7. #5
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      Thanks for the kind words everyone. As to your questions Star4ever, my evaluation is in Part IV. We still have the power amp and installation parts first. To give you a hint, my fellow commuters must think I am wierd to be sitting in trafic with a . As to some of the items I would do different, I have incorporated those in these instructions. For example, I used four lengths of wire instead of the two I recommended for the internal wiring.
      2011.5 XC60 3.2L Flamenco Red/Anthracite Black, Premium, Multimedia, Convenience, BLIS, Xenon + Custom Subwoofer

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      Part II - Providing the Power

      I spent quite some time deciding on the power amp for this project. This is because multiple factors needed to be considered. Besides the obvious ones dictated by the drivers selected and the enclosure design, there were what level of current could the car comfortably provide and environmental factors relating to mounting wiring and cooling. As this design uses two 4 ohm speakers in parallel the amplifier would need to be able to drive a 2 ohm load. In my opinion this was not sufficient as dynamic drivers are never a fixed load or more accurately have a fixed impedance especially around their resonance. I therefore decided that I wanted an amp that was unconditionally stable into 1 ohm. Then came the issue of power or watts. Forget those peak power claims and focus on continuous power across its rated bandwidth. Since the enclosure design was going to provide at least 6db of bass gain, the WinISD program predicted that I would get 100+ db for 150W power input in free space. When placed in a small enclosed space as a car, I could expect to be able to easily achieve 105db which was more than enough low energy for my ears. It turns out that 150W can be comfortably delivered by a number of amps when powered by a 30A circuit. Why 30A? Volvo's OEM subwoofer comes with its own power amp that is fused for 30A. This told me that the alternator could comfortably handle this level of extra current. But which power amp to choose?

      Obviously, there an quite a few quality amps that could deliver 150W from a 30A line. Most of these amps incorporate digital/switching technology either in their power supply and/or amp sections. Before deciding I first wanted to figure out how I was going to install it as that would constrain its sizing, cooling and amplifier technology. I got a copy of the Volvo Electrical Wiring Diagram (EWD) and carefully reviewed it. Most after-market installs call for running a dedicated heavy gauge line straight to the positive battery clamp and away from any signal wires. After looking at how dense the engine compartment was and how inaccessible the firewall was, I decided to see if there was an alternative to tearing apart portions of my brand new car. Most car amps require a dedicated 4-8ga. run to support their high power ratings of 300-1000W. I did not need that much and it turned out that I got lucky. The XC60 has 3 electrical distribution blocks (engine, dash, and cargo). While the main 5 channel power amp is powered by the dash block, the OEM subwoofer was designed to be powered by the cargo one. Now it turns out that for the U.S. models this power wire is not there, but there is one for the trailer hitch option that is rated for 40A. Additionally, and as importantly there are factory grounding studs in both the left and right rear corners of the cargo bed that would provide the necessary short path to ground for noise immunity.

      Using this power point had one down side and that was that the power line was run in the wiring harness with other signal wires (though not audio ones which are optical). To be conservative I narrowed down my search to efficient non-digital amplifiers and found that Rockford Fosgate had recently released their PBR300X1 that used a modern evolution of a Class G design to delivery digital efficiency without the high frequency, high current switching issues. This is a company that I have a lot of respect for and though no longer run by Jim Fosgate (who I knew back in his circle surround days), it maintains engineering excellence especially in the car audio market. As an added benefit, the amp is exceptionally small and runs very cool requiring only 30A to reach 300W into 1 ohm and 150W into 2 ohms. Now, I am sure other amps will work and many of you have your own preference. I did check out both the JL Audio G1300 and Soundstream REF1.500 which both are Class G. I decided not to go with either mostly due to size and from my Fosgate experience but believe they are valid choices.

      It turned out that there was one downside to selecting the PBR300X1 that I did not discover until I received it. It advertises that it will automatically turn-on when using the high-level inputs and this is true IF the source power amp provides a super-imposed 6v DC offset on one of the channels. Not having experience with this method, I talked to Fosgate about this and apparently many OEM units control remote devices this way, for example to allow segregation of phone and guidance from music. I am not a fan of this as it can damage loudspeakers if one is not careful to always block the DC. It was not turning on for me because Volvo does not use this method which I confirmed by checking each channel with my multimeter. I then began researching the EWD and checking for switched 12v power in the cargo area. I could only find one switched line which was to the Parking Assist Module(PAM) for the rear camera. Unfortunately, it was not accessible without removing a good portion of the cargo area interior. Therefore, I got a signal triggered Remote 12v unit, N-902 ($19 from Navone Engineering). to sense the output from the Volvo amp and turn on the Fosgate. Works great. As an aside, what I did discover was that almost all of the XC60's electronics have 12 volts live even when the ignition is off apparently depending on a control signal to power each module on. This may be why early XC60 owners were having dead battery problems that were fixed with software updates.

      Before moving to the actual installation in the next part, below is the parts list for this project and sources where specific:

      PARTS LIST


      Part III - The Installation to follow...
      Last edited by mark-sf; 02-18-2020 at 11:15 PM.
      2011.5 XC60 3.2L Flamenco Red/Anthracite Black, Premium, Multimedia, Convenience, BLIS, Xenon + Custom Subwoofer

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      Part III - The Installation

      Now that we have all the pieces, its time to perform the installation. First up is the wiring of the amplifier inputs. Since the XC60 has all line-level audio in optical digital and not accessible, I had to tap off the LF and RF speaker outputs of the OEM amp under the passenger seat. Instead of splicing the wires in a vulnerable position, I decided to research whether a wiring harness was available. Off course it wasn't as the XC60 is so new. Also the new Premium amps use a 16pin connector instead of the older 14pin one so older harnesses would not work. I widened my search and found a harness for a Parrot Bluetooth system from a distributor in the UK that used the 16pin connector. It was quickly shipped and though it had far more wire and connectors than I needed I was able to create a plug-in solution by splicing only the harness wires as shown below:


      Amplifier Wiring Harness

      The wires of interest are the Solid White, White w/ Black stripe, Solid Gray, Gray w/ Black Stripe which are on the right in the 1st and 3rd columns if viewed from the connector rear. The wiring diagram for the amp:


      OEM Amp Wiring Diagram

      For the audio run I used a 4 conductor Mogami cable that I already had. This run does not need to be heavy gauge as it is only a voltage source. 18-22ga is fine. However if it is one cable it is easier to run. The route I chose was to go under the floor door trim strip and through the bottom outside of the rear passenger seat. Using a fish tape or stiff wire to initially go into the cargo are makes it very easy. The wire will end up under the right hand insulation which became a straight shot to my amp location.

      Speaking of the amp location, with it being so small there were a number of choices. Before deciding on the location I ran it connected to the woofer just resting on the cargo bed and the amp next to the spare tire to see how much air circulation it needed. Even at sustained heavy bass levels it stayed cool. Therefore, I decided to tuck it into the right rear area that was adjacent to the ground stud. Below is a picture of it. Note that the level adjustments are easily accessible. There is also a rear stud that the amp flange will slide over.


      Amplifier Mounted in Right Rear

      With the ground right there I was left with routing a power wire from the left rear distribution block to the amp.This is easily fished by hand under the cargo door sill and up to the panel. I had a 10-12 ga. wire tap connector that I used to connect the 30A fuse holder leads to the Trailer Hitch power line. Below is a picture of the connection to the rear. This fuse block simply unclips from it holder.


      Power Connection from Cargo Fuse Block

      Next came the remote trigger module that I spliced in where I connected the input signal wires. This tiny 2" square box can be hidden away next to the amp. Finally it was time for the speaker wires. I had some Monster Cable lying around but any 12-14ga. will work fine. As with the signal wires the amp came with pre-wired molex connectors that you then splice with your speaker wire. Terminating the speaker ends is the trickiest part as it is not obvious how the connectors separate. There are small notches that hold the outer sheath that need to be sprung for it to be pulled down exposing the inner plug. The wire is inserted through the sheath making a 90 deg. turn into the side hole and soldered. The sheath can then be locked back up. The speaker wire can now routed under the insulation and under the black plastic wiring harness channel to get to the front of the speaker.

      Finally, its time for the speaker mounting. I spent some time musing over the best least destructive technique. The first problem was studs for the OEM subwoofer. Initially, I was going to cut them off, but once I found that when the woofer was in, that they would not fully penetrate the bottom panel, I decided to use them as key pins. Using a 24.5" x 11" cardboard template I captured the pattern and transferred it to the bottom of the sub. Then I drilled 5/16" deep holes to precisely align the sub. I noted that there were two rear seat vertical brackets that the sub front would rest against. The right side already had a hole where an angle bracket could be attached. I simply drilled my one and only hole in the same position on the left one. Below is a picture of the sub front attachment using machine screws and locking nuts.


      Front Subwoofer attachment and wiring

      For the rear of the sub, I did something different as I really didn't want to drill holes into the bed. I have used these interlocking nylon strips in the past and have found them quite effective. The only issue is being careful to select a clear spot on the rear panel for the corner brackets where its screws will not interfere with the ones up from the bottom plate. Once secured this way I could not budge the box and remember it will also have the weight of the cargo floor on it as well. Those less concerned about a few holes can use screws instead. Below is a picture of the rear of the mounted sub.


      Rear Subwoofer attachment

      Unfortunately, I was not quite done and two initially daunting tasks remained. First there was the problem with the rear cargo panel's strut coming into contact with the top of the sub. For the Volvo sub this was not a problem as the box does not come up as high. Given the depth of my drivers, my height was not flexible. Out came my rotary cutting tool (Dremel or Dewalt is fine) with a cutting disk. You don't need to cut all the way to the facing as the edges are easily sanded. In fact I do not recommend that you sand to flush as it will expose the corrugated insides of the panel. Simply sand and test fit, etc.

      The last problem was the molded insert. One can of course simply discard it but I liked its utility and how if cut precisely it would finish off the installation. I tried several techniques but the best one was to first on the topside precisely position that cardboard template used for the bottom. This should give you about 3/4" of the rear cross piece that you can keep for structural stability. Take 2" masking or painters tape and run it across the front and rear edges sticking it to the insert not the cardboard. Then do the same for the sides but have it wrap around to extend a few inches on the underside. Now drill a 1/4" holes, at each corner. You will note that the spare tire edge will be cut across the downslope. Now turn the insert over and continue the side lines with the tape till you reach the holes on each side. At this point you can cut the insert with a heavy duty razor blade knife. I found the tall blade helps keep the line straight even though you are cutting freehand. You can clean up the edges or adjust the size with coarse sandpaper. Below is the completed installation.


      Completed Subwoofer Installation

      If any of you are going on the No. Cal. GGVOA Skaggs Spring run tomorrow, I will be there and you can have a listen.

      Part IV: Tuning and Evaluation to follow...
      Last edited by mark-sf; 02-13-2020 at 11:42 PM.
      2011.5 XC60 3.2L Flamenco Red/Anthracite Black, Premium, Multimedia, Convenience, BLIS, Xenon + Custom Subwoofer

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      Part IV: Tuning and Evaluation

      We have now come to the final part of this journey. I have combined tuning and evaluation together as the way I approach tuning requires among straight measurements, leaving with the system in various states of tune for my ears to adjust before picking the final settings. This process has not yet been completed but I can report on results to date as well as my overall evaluation.

      Let's start with the evaluation and I will integrate tuning where appropriate, Going back to my original requirements in reverse order:

      6. Be within my capabilities to implement - After completing everything none of the tasks were altered, because they were too difficult. While I could have spent more time finishing the enclosure, It is after all hidden and even with the cargo top raised only the top inch is visible. The paint was several coats of Rustoleum Textured Galaxy Metallic that matches the insert very well. While this project took time if you can cut a straight line with a saw and knife and solder wires, it is straight forward.

      5. Have the driver(s) protected from physical damage through normal use. As the drivers are entirely enclosed yet accessible and the sub is below the cargo panel, this requirement was obviously met.

      4. Make no irreversible changes or modifications to the car. If you have been reading closely, there were three modifications made. Obviously the cargo panel had a strut removed and the molded insert was cut out. However, both of these are replaceable parts should that be necessary in the future. The only irreversible change was the 3/8" hole in the rear seat mount. I could have avoided this one through use of a bigger corner bracket, but as this hole is aligned with the other mount's hole, I am not suffering this one modification.

      3. Lose no significant cargo space. Technically, I lost some tray space in the insert but I don't classify that as cargo space. Being able to hide it completely under the cargo panel while using the design and drivers I wanted makes me very happy. We need every square foot of that space for our trips.

      2. Stay comfortably within the XC60's alternator/battery capabilities. This was the requirement I was most worried about as it had unknowns that I had no direct control over. Up front I was concerned because of reports of battery drainage issues, and while I don't have every option, I have most of the power demanding ones. Only time will tell but given that the LED that displays when the amp switches to its higher voltage mode almost never lights, and when it does it only briefly flashes, I am confident that I am not drawing anywhere near even 20A for sustained periods. Thus there should be no out-of-spec stress placed upon the alternator.

      1. Extend seamlessly the existing system's response to the mid-30Hz range at low distortion and comparable dynamic capability.
      This is the portion most of you have been waiting for and the one where I will have the most to say. Note that the requirement contains both objective and subjective requirements. Let's get the former out of the way first as they are the easiest. Computer modeling of the design predicted a -3 db down low frequency of between 35 and 36Hz. I measured ~36Hz when mounted in place. Now some may view this as too high a cut-off especially when compared to high-end home theater subwoofers. Though, the head unit is capable of playing back DVD movies in DD5.1, I have no desire to watch movies in my car. The .1 LFE channel will produce sound effects below 30 Hz but these are not music. Even in the home, if you have a stereo music system that produces good clean bass down to this range you would be very pleased with the bottom end. I should also mention that while down in level I did hear non-doubled 32Hz frequencies from the system.

      The low distortion requirement is a bit tough to measure without more expensive equipment than I have. Fortunately, the ear is not very sensitive to low frequency distortion in a sub with a low pass filter. This design has two inherent advantages in this area. As a 4th Order Bandpass design it has an steep acoustic rolloff on both sides of its bandwidth. Also the isobaric alignment provides distortion cancelation as both drivers are moving in opposite directions relative to the signal. I did a frequency sweep test which would audibly reveal distortion caused by spider/surround issues, doubling, bottoming or artifacts such as air leaks, buzzing panels, etc. None of these were detected in the sub; however, I did find a number of spots in the car that I could get to buzz and rattle. I will take car of these if they do so with music.

      The seamless integration requirement is both objective and subjective. If the factory system was nominally flat one would usually incorporate both a high and low pass filter to integrate the sub. This was not the case with the XC60 as I was already rolling off the bottom end with the 60Hz EQ control in order to get reasonable mid to upper bass response. This produced an asymmetrical arrangement as changing the "high pass" rolloff (EQ) also affects the signal the sub gets. This can easily produce a "chasing your tail" attempt at optimization. So what I did was to select a number of frequencies that produced fairly uniform sound level in various positions as my markers and then using a combination of the 60Hz EQ, Sub Gain, and Low Pass Cutoff control leveled my markers at about 80 db. I then started listening to my reference CDs for evaluating bass for the final tweaks. I am not finished with this process but currently am pleased with 60EQ: -8; 200EQ: +2; Sub Gain: Just past 1, Sub LPCutoff: 150Hz. If the 150 sounds high, you should remember that there is a built-in acoustical rolloff at 70Hz. Subjectively, at this point the system sounds very well integrated. You do not hear the typical car hump in the 80-120Hz region that causes boominess. For each of my CDs which span genres of Classical, Rock, Jazz, World, New Age, Country, etc, what first strikes you is that you know exactly which type of instrument is creating the bass notes and the bass does not interfere with the audibility of the other instruments or vocals. As there are no cabinet resonances and this is a close to critically damped design there is no bass overhang that would obscure the bass note decay. This allows you to clearly differentiate for example not only the type of drum but whether it is hit with a stick or mallet. Can this system be better integrated or equalized? The answer is yes but what issues I am now hearing are in the upper bass and upper midrange which are only apparent on certain pieces and I expect would take a DSP-based EQ unit to smooth out.

      Finally, there is the comparable dynamic capability requirement to report, and this too is both objective and subjective. Obviously, one can measure the peak output at various frequencies. Not being able to observe the drivers in motion I was conservative in running up the volume as I knew from my amp gain setting that I would likely run out of driver excursion before clipping the amp. I ran the system up to 105db with the only strain being to my ears. While obviously not a competitive SPL level, it is one which more than hour of exposure will cause hearing loss. Quite sufficient objectively.

      To report on my subjective evaluation of the dynamics I need to first explain some characteristic differences in designs in this area. Dynamics of course does not simply mean how loud but also how soft. Many arrangements score bass lines that are soft and subtle but no less important. These bass lines can give weight to a rhythm or convey a mood. Soft bass reproduction can be a problem for large driver in sealed boxes as to get the driver moving the signal not only needs to overcome the mass of the cone but the damping factor of the enclosure. This is an even greater problem for designs that run the driver below its resonance by mounting it in a very small enclosure as is typically done in car subs. This is because they must work against their suspensions as well. To provide a car analogy, you may have all the suspension travel in the world but if you hit a series of ruts at a speed above the resonance of your suspension, you will feel every one as if you did not have a suspension. These systems typically in my experience exhibit an on/off characteristic much like hitting turboboost. with enough power and piston area, they go very loud but disappear once the bass gets soft. Now one can argue that a car environment is so noisy that one can't hear soft or subtle anything but the ear is quite discriminating and can filter out a surprising level of background noise.

      Now having explained what is not a good design for subtle bass, how does this design and implementation stack up. First, the drivers have a very lightweight aluminum cone. They are driven in push-pull mode which applies double the force to the cones for a given signal level. Therefore instead of using the additional driver to move more air, it is used to lower the system resonance (emulating a bigger box) and provides better acceleration. The net result is an ability to reproduce bass that one may not have known was there. When I was evaluating the XC60 vs. the RC350, I found that given the stock tires the XC60 was quieter on the freeways due to less intrusive road noise. Thus with everything closed and blower on low or off, I can get very good dynamic range and I don't feel the need to turn up the volume in order to hear the bass.

      In summary, the result was better than I expected. I had anticipated that I would probably have to add a DSP-EQ unit for reasonable integration and the impact of having the port firing into the cavity behind the rear seats was unknown. Neither of these proved to be issues. As to what I would do different if I did it again, so far outside of the few changes that I already have incorporated in these instructions, there is nothing that I would change. Quite frankly this is the best quality, totally hidden, car sub I have heard. Now I do believe the overall system could be improved by adding a DSP and 5-channel power amp in addition to this sub and its amplifier, but for my money (even with my champagne audio tastes) this is well down the road of diminishing returns. For a bit over $300 and labor there is not a better audio enhancement that you can make to the XC60.

      Hope you found this journey interesting and informative. Please feel free to respond with questions or comments. I would prefer they be posted here instead of by private message, so others can benefit from the exchange. Hope some of you give it a try. Please let us know if you do.
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    11. #9
      Junior Member dmcj's Avatar
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      Excellent work and great write-up!!

      I have a 2012 XC60 R-Design on OSD orded and expect to have it home in Denver later this year. Your excellent work will be my first upgrade project.

      Thanks again for such a well thought out project (written, visual, parts list w/links, and instructions). A DIY grand slam!!

      Thanks again.

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      Quote Originally Posted by dmcj View Post
      Excellent work and great write-up!!

      I have a 2012 XC60 R-Design on OSD orded and expect to have it home in Denver later this year. Your excellent work will be my first upgrade project.

      Thanks again for such a well thought out project (written, visual, parts list w/links, and instructions). A DIY grand slam!!

      Thanks again.
      Your welcome and congratulations on your selection. Which color combination are you going with? Once you get it don't hesitate to ask about anything regarding the construction or installation of the sub.
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      I seem to be having a problem downloading the constuction diagram. Could you post another link?

    14. #12
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      Quote Originally Posted by Mephisto View Post
      I seem to be having a problem downloading the constuction diagram. Could you post another link?
      I just tried the link and it works for me. Here is the URLs: https://i.imgur.com/he3z70r.png?1 and https://i.imgur.com/KDR0LUB.png?1 which you can copy and paste. Are you also having a problem with the Wiring Diagram link as it is hosted the same way? If this doesn't work PM me with your email and I will send it to you.
      Last edited by mark-sf; 04-26-2020 at 08:07 PM.
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    15. #13
      Junior Member dmcj's Avatar
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      Quote Originally Posted by mark-sf View Post
      Your welcome and congratulations on your selection. Which color combination are you going with? Once you get it don't hesitate to ask about anything regarding the construction or installation of the sub.
      I ordered the Black Sapphire Metallic XC60 R-Design with Off Black/Beige Inserts.

      Loking forward to tagging with you later on the sub-woofer install.

      Thanks again.

    16. #14
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      Really like your end result, glad everything worked out well for you.

      I wish I had the time to do mine all myself, but I'm taking it to a very reputable install shop instead. Hopefully their install comes out just as clean as yours.

      edit: deleted what I typed, just realized that since mine is a R-Design, it won't have that optional tow hitch power harness. Oh well, guess I'm going to have to have the install shop run the power wire up to the battery.
      Last edited by superbike81; 06-25-2011 at 03:50 AM.

    17. #15
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      Oh, and could you please tell me exactly which wires are the front left and front right pos/neg? Maybe just colors or however else they are labeled. Thanks!

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      Quote Originally Posted by superbike81 View Post
      Really like your end result, glad everything worked out well for you.

      I wish I had the time to do mine all myself, but I'm taking it to a very reputable install shop instead. Hopefully their install comes out just as clean as yours.

      edit: deleted what I typed, just realized that since mine is a R-Design, it won't have that optional tow hitch power harness. Oh well, guess I'm going to have to have the install shop run the power wire up to the battery.
      Thanks for the compliment. You didn't need to edit your post as your R is going to have this circuit according to the EWD. It is not a separate harness as the power lines also service the parking brake modules, tail lights, etc. For those that did not see the original question, superbike81 asked abut whether the existing wiring could provide the 600W average power that was the Alpine T12 driver's maximum rating. This type of answer cannot generally be given without knowing the efficiency of both the planned amp's power supply and output stage as well as whether the amp normally runs in bridged mode. Unfortunately both figures are rarely provided and all one can really evalulate with is what are the fuse specifications or the 12V power requirement's of the amp. I would not be comfortable with using an amp that required more than 30A max or was fused at 40A on that line. If the amp has two fuses their values need to be added together. It is highly unlikely that you will find a 600W Average RMS amp into 4 ohms that will be this efficient. This does not take into account that such an amp if it were available is likely to be a powerline noise source which is not recommended to run in existing wiring bundles.

      I would however caution on specifying a subwoofer amp that could provide more power than a woofer can safely handle for the following reasons. Woofers fail for two reasons assuming no factory defects. The first is that the voltage is so high as to cause them to hyper-extend their suspension and this displaces the voice coil. If an amplifier cannot do this because the required input would cause it to clip, then the driver will not be at risk for this type of failure. A legitimate follow-up question would be "Isn't it always advisable to size a power amp so that it will never clip into a speaker?" If one is talking about a full range speaker, this is true as when an amp clips it dumps a large distortion signal into the midrange and tweeter whose power handing is never as high as the woofer's and this is the principal cause of tweeter failures. However, in this case there is no midrange or tweeter connected to the amp. Your ears will hear distortion but the woofer will not be at risk of hyper-extension. The other failure mode is driving a woofer for an extended time beyond its AverageRMS levels. This causes the voicecoil to overheat and either short or open. It can also cause the voicecoil former to deform freezing the cone.

      Since this sub is being added to an existing system which has both a peak and average max output already defined and you presumably also have a max average and peak SPL that you desire to achieve, this is where I would start. There is nothing to be gained by over-specifying the power requirements necessary to either satisfy your SPL or balance with the existing system. With the Alpine T12 driver and a sealed enclosure of .6 cu.ft. you will be -3db at 45Hz and about -8db at 35Hz. Therefore to achieve comparable response to the rest of your range, you need to boost the signal in the mid-30s by about 6db which requires 4x the power. For example, if your finished system is able to generate 100db SPL at 60Hz with 100W then you will need 400W to get that level in the mid-30's.

      None of the above takes into account the response in the enclosed space of your XC60 nor the way the driver couples with it. I believe you are planning on using the spare tire well for a custom fiberglass enclosure. Whether the driver is firing into an unmodified cargo floor panel or one that has been cut out will significantly impact the performance especially if the enclosure is extended to bring the driver close to the panel. If you provide updated details of you or your installer's plan and to range and SPL requirements I could perhaps provide more specific advice.
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      Quote Originally Posted by superbike81 View Post
      Oh, and could you please tell me exactly which wires are the front left and front right pos/neg? Maybe just colors or however else they are labeled. Thanks!
      Sure, as follows:

      LF- Pin 1
      LF+ Pin 9
      RF- Pin 3
      RF+ Pin 11
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      Thank you for the information.

      The amp I have is the Alpine PDX-M6 which is rated at 600rms at 4ohms which exactly matches the subwoofer's specs which is the whole reason I bought it. Taking into account what you said about the efficiency and power requirements, I think I will stick with this amp and have it wired up to the battery. I have been looking quite a bit lately into different mounting options for the subwoofer. As I have been researching more and more about having a subwoofer covered by something and how it changes the sound characteristics I have been looking into other options, I don't want to cut the cargo floor.

      I'm going to have to sit down with my installer in a couple weeks when my car is all registered and delivered and see if they have some ideas. The guys I am going to be working with have done some incredible magazine quality custom installs so hopefully they can give me some more input.

    21. #19
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      Nice install.

      Yeah, Jim Fosgate is quite the man. I found out recently he lives pretty close to me apparently (in Utah). Allegedly he also created the first car amplifier.

      Curious, what other amplifiers did you look at? I think a PPI Art or Power series would have done really well with your setup. The sound is stunning. I'm assuming you didn't use them, however, as the PPI power and arts use an AB design which draws more current?

      And I have to ask, even though it's slightly off topic: what do you have as your home audio system?
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    22. #20
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      Quote Originally Posted by superbike81 View Post
      Thank you for the information.

      The amp I have is the Alpine PDX-M6 which is rated at 600rms at 4ohms which exactly matches the subwoofer's specs which is the whole reason I bought it. Taking into account what you said about the efficiency and power requirements, I think I will stick with this amp and have it wired up to the battery. I have been looking quite a bit lately into different mounting options for the subwoofer. As I have been researching more and more about having a subwoofer covered by something and how it changes the sound characteristics I have been looking into other options, I don't want to cut the cargo floor.

      I'm going to have to sit down with my installer in a couple weeks when my car is all registered and delivered and see if they have some ideas. The guys I am going to be working with have done some incredible magazine quality custom installs so hopefully they can give me some more input.
      Since you are going with an experienced installer who most likely will have no hesitation about removing interior pieces, you should look into the space under the rear seat which looks to have room to custom fit an enclosure and woofer of that size. This is one area we suffer due to the fact that so few XC60's are sold to establish prior experience.
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    23. #21
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      Quote Originally Posted by Jexx View Post
      Nice install.

      Yeah, Jim Fosgate is quite the man. I found out recently he lives pretty close to me apparently (in Utah). Allegedly he also created the first car amplifier.

      Curious, what other amplifiers did you look at? I think a PPI Art or Power series would have done really well with your setup. The sound is stunning. I'm assuming you didn't use them, however, as the PPI power and arts use an AB design which draws more current?

      And I have to ask, even though it's slightly off topic: what do you have as your home audio system?
      Thanks! I really enjoyed the project. Most PPI amps use a Pulse Width Modulation (PWM) power supply to achieve improved efficiency that allows them to use a conventional AB output stage. This type of supply can also generate noise in the power lines unless care is taken as to their routing and guage. As to which design draws more current, it can't be determined without benching them since they are significantly different designs. Even when comparing two Class AB amps, one may run in Class A to a higher power level than the other thereby drawing more average current. I have heard very good things about PPI amps but have no direct experience with them. Also, remember I am only amplifying between 30 and 80Hz and driving a very easy load making the amp's absolute sound quality across the entire spectrum not as critical.

      As to my home system, since you asked, I have a pair of Dunlavy SC-III.a's in the front with a SC-1a/v as my center and Anthem amps and tuner/processor. Primary sources are an Oppo BDP-80SE, Mac Mini, and for records a B&O 4400 mated to a Supex SDX2000 plus Sumiko PhonoAmp (both of which were my designs from the 1980's).
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    24. #22
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      Interesting. I didn't think about under the rear seat. I will look into that more closely next week when my car arrives at the dealer.

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      Quote Originally Posted by superbike81 View Post
      Interesting. I didn't think about under the rear seat. I will look into that more closely next week when my car arrives at the dealer.
      BTW, you also may want to point your installer to the Front Camera option installation doc here. If you take a look at steps 67, 88. and 89 you'll see that there is a pre-existing feedthru into the engine compartment that he may want to use for the dedicated amp power line.
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      Followup: Tuning and Installation Updates

      I have been living with this configuration now for several weeks, experimenting with the combination of EQ/Tone settings offered. I was hearing some unexpected effects to the EQ controls which seemed to indicate that they were not implemented as conventional 5-band EQ with a preset Q (frequency width) for each frequency. I decided to perform some impulse frequency response tests on the system without the sub to examine the effect of the various controls. What I found is surprising and may be helpful to those trying to balance their systems.

      All the tests were performed with the mic place in the drivers seat at ear level with Dolby Off and Fader full Forward. The graphs are representative of several mic positions and was replicated using the right channel. Please note the focus should not be on the flatness but the differences between the curves. Given the driver locations, angle and irregularity of the interior, from my experience it is more important to go for overall balance and not worry about narrow peaks and valleys.

      First, I measured the left channel with every control in its Flat or 0 position except the Fader was full Forward. Sound was only sent to the Left channel. I then ran the same test with the 60Hz control at full -10 and finally Bass at full -10. The following is a graph of the three responses overlaid.


      Flat Response (Black) versus [email protected] (Red) versus [email protected] (Green)

      Obvious the Bass and 60Hz control are the same and the 60Hz cannot be used like you would as an equalizer. It also validates why prior to installing the sub, setting 60Hz to -7 reduced bass boom across the board. There is however an upside as one can use these controls together when using a subwoofer to apply a high pass filter to the door speakers. The following is a graph of Flat response versus both the 60 EQ and Bass control at -10.


      Flat Response (Black) versus [email protected] plus [email protected] (Purple)

      I am experimenting with using this combination to further reduce the sub-100Hz energy going to the doors instead of adding a high-pass filter on the amp outputs. While the low end had been much improved there was still too much bass in the doors after extended listening causing vibrations and mid-range harshness at higher levels. To bring the low end back up in level, I have increased the input gain on the sub amp to the 5-7 range which has cleared this up. I'll need to listen for a while before confirming the final setting.

      At this point I have not decided on the final setting of the 200 and 1K controls as they too are quite broad in their action. Below are their curves:


      Flat Response (Black) versus [email protected] (Yellow)


      Flat Response (Black) versus [email protected] (Blue)

      Finally, I have two installation updates. First, I added screws to the port flange as after the vibrations of sound and driving, I began to detect a buzz on frequency sweeps. This should not be considered optional as I initially proposed due to the length of the port tube and the torque that can be generated. I used 4 countersunk #6x3/4" black wood screws which cleared it up. Finally, I noticed some rubbing of the cabinet finish between sub top and the bottom of the cargo floor as these are both hard surfaces and are in contact. I applied some of the leftover 1/2" gasket to the bottom of the cargo floor cushioning the sub contact area.
      Last edited by mark-sf; 02-13-2020 at 11:48 PM.
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      So much reading, looks like a very cool install, is there any chance that the 8" SWS would have worked as well or couldn't you get the depth/volume needed. I have two of their 8" woofers and they are quite a nice little woofer but sadly (like yours) are only an aluminised plastic cone, the dustcap however is aluminium.

      Also as your amp is a class G amp it would struggle to draw 20amps even if you only had 12V at the battery, I am not a fan of Scotch Locks anywhere but to power an amp with it is just crazy. I would strip some of the wire and solder the wire to it or remove the terminal from the plug and find a spade terminal that fit into it and heatshrink it all together. If you turn your system up do you know if the Scotch Lock gets warm? I would love to know if you get any voltage drop through it.

      Also do you have any screen shots from WinISD for the box design/output? I would love to see the freq response from those beastly little drivers.


      Top quality stealth install, well done!

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      Bingo! You win the prize! I have been waiting for someone to comment on my power connection. When I initially installed I did not have a female spade large enough but had these 10-12ga scotchlocks. Since I was not sure that I would end up using this block as a power distribution point, they would allow me to not have to splice the wire. As it turns out I have left this connection as I measured zero resistence (<.05ohm meter resolution or voltage drop even under heavy load no heat i measured this not to evaluate the connector but because was concerned about overall current capability of distribution point.>
      Now why does this connector work and is not crazy? This connector is rated at 600V and has a .8mm thick compression slot that creates a reasonably large contact cross section especially with the stranded 10-12ga wire it is rated for and that I am using. Take a look at the conductor cross section of the 30A fuse used. It is significantly smaller and in series. It will open long before the connector will be damaged. Having blown the fuse once (not through amp use) I can attest to that.

      As to you other questions and comments. First I do not understand your comment about the cone material. It is sufficiently light an stiff as it is only driven at low frequencies so there is no concern about cone breakup. Please explain.

      To your question regarding using the SWS-8x drivers. This may be possible within the height limitations of the space and how much space you actually measure is reequired to mount the drivers face-to-face. Give the driver specs, you will need to acommodate at least 3/4" more depth. Now, you can rabbit out the mounting holes in the 3/4" MDF to bring the drivers closer together. You may be able to gain as much as 1/2" there. I specified the overall height to be 5-7/8" but mine is actually 6" (though it meant taking the cargo strut all the way down to be flush). I would not recommend reducing the top and bottom pieces from 1/2" to 3/8" but you could rout out some material directly behind the woofers which would give you another 1/8/-1/4" total for both. FInally, and most radically, if you have the cargo mat, you can cut out a piece of the cargo floor to allow the sub cabinet to be flush with the top instead of the bottom. This would give you another aproximately 3/8".
      One more thing is that you would have to re-do the volume calculations as the SWS-8x drivers have different parameters.

      Therefore, it is doable to use your 8's, but I would compare the additional work and issues with selling them and getting a pair of SWS-6.5's. I can say that everyone who has heard mine, see no need for more output capability. I will post a screenshot of the WinISD expected performance this evening.

      Thanks for your comments.
      Last edited by mark-sf; 04-26-2020 at 08:19 PM.
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    29. #27
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      Quote Originally Posted by mark-sf View Post
      Now why does this connector work and is not crazy? This connector is rated at 600V and has a .8mm thick compression slot that creates a reasonably large contact cross section especially with the stranded 10-12ga wire it is rated for and that I am using. Take a look at the conductor cross section of the 30A fuse used. It is significantly smaller and in series. It will open long before the connector will be damaged. Having blown the fuse once (not through amp use) I can attest to that.

      As to you other questions and comments. First I do not understand your comment about the cone material. It is sufficiently light an stiff as it is only driven at low frequencies so there is no concern about cone breakup. Please explain.

      Thanks for your comments.
      Sorry I just hate those connectors, I guess they aren't too bad to use inside a car but they still create a weak spot in the wire as they tend to slice a few strands of copper as the blade(?) goes through. I see them as the equivalent of hanging your exhaust with a piece of wire, sure it works but it doesn't mean is good in the long term.

      As to the cone question I was just stating that the cone is made of plastic not Aluminium as you stated, the sneaky marketing people make it sound like it is made from aluminium but it just a thin layer on the speaker cone. For the price of the Earthquake drivers a plastic cone is all that can be expected and they do sound great for a small speaker.

      I don't actually have an XC60 I was just wondering about woofer sizing and what may possibly fit as more cone area is always a good thing, that is if you can make an enclosure to suit.
      I currently have a 10" woofer and wish I could fit a 12 but loosing more trunk space in an already tight S60 is not an option so I have to make do with what I have.

      Now i really want to build an isobarik 4th order box just to see how they sound and how it effects power handling. I know you lose 3dB of efficiency as soon as you go to an Isobarik configuration but you end up with the same cone area and two motors, so it should sound quite punchy I'd imagine.

      My home theatre sub is a Dyn MW 180 ina 4th order BP box and I love it, it plays much louder than I was expecting.

    30. #28
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      We will just have to agree to disagree as I have used the connectors for years and as long as they are sized correctly, have not had any long term issues. As to the cone, whether it is pure aluminum or a composite my comment was regarding its desirable low mass. The -3db disadvantage associated with Isobaric configurations you point out is correct, but is balanced by the reduction in enclosure to half the volume in order to hit the same low frequency cut off without equalization. As you also will see in the graph below that -3db is also more than offset by using the vented bandpass configuration's gain.

      Last edited by mark-sf; 02-13-2020 at 11:49 PM.
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      Thanks for the pic, I was wondering what frequency range it would play effectively, I might have to enter the values for the SWS 8 to see how it compares just satisfy my curiosity.

      On a different note because of my poor speaker/amp selection my lights dim like crazy on bass hits so I now have to inspect and clean all earth points in the engine bay and run some larger wire from the alternator to the starter to see if that helps my situaltion.
      There is a lot to be said for a modest SQ install such as yours, mine has been headache after headache, I now have to work how to get my headliner out as my roof beams vibrate even with the stereo switched off, the sub has shaken them all loose along with the tailgate outer trim panel.

    32. #30
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      Quote Originally Posted by Volvofool View Post
      On a different note because of my poor speaker/amp selection my lights dim like crazy on bass hits so I now have to inspect and clean all earth points in the engine bay and run some larger wire from the alternator to the starter to see if that helps my situaltion.
      There is a lot to be said for a modest SQ install such as yours, mine has been headache after headache, I now have to work how to get my headliner out as my roof beams vibrate even with the stereo switched off, the sub has shaken them all loose along with the tailgate outer trim panel.
      Sorry to hear that. Have you tried adding a 1-2 farad capacitor to stiffen your voltage? Outside of a higher output alternator or second battery, it has been effective in my experience solving this type of issue. Generally the alternator wire gauge is over-specified for the alternator output and unless you have a high level of corrosion augmenting the capacitance provided by the battery would be a more effective long term solution.
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    33. #31
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      Quote Originally Posted by Volvofool View Post
      Thanks for the pic, I was wondering what frequency range it would play effectively, I might have to enter the values for the SWS 8 to see how it compares just satisfy my curiosity.

      On a different note because of my poor speaker/amp selection my lights dim like crazy on bass hits so I now have to inspect and clean all earth points in the engine bay and run some larger wire from the alternator to the starter to see if that helps my situaltion.
      There is a lot to be said for a modest SQ install such as yours, mine has been headache after headache, I now have to work how to get my headliner out as my roof beams vibrate even with the stereo switched off, the sub has shaken them all loose along with the tailgate outer trim panel.
      Out of curiosity, how many watts are you running exactly?
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    34. #32
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      Quote Originally Posted by superbike81 View Post
      Out of curiosity, how many watts are you running exactly?
      A bit over 1000WRMS with A/B class amps so current draw is about 140 or so amps, I cleaned the earth terminals up and ran an extra eart wire as shown in my build thread- noob build
      Excuse my lack of effort in my thread, I really didn't think people would care about Win ISD screen shots etc, obviously I was wrong.

    35. #33
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      Jan 2011
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      Japan and Seattle
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      Oh ok, well that has me a little less worried, as I'll only be running 600rms from an Alpine PDX-M6.

      After talking with my installer more, he's convinced me to go ahead and go with the Alpine SWR-T12 flat subwoofer I already have. I described the install I saw that didn't impress me as far as SQ goes and he is confident he can get me set up with an install that will please me.

      I pick up the car in a couple days, and then the install will commence in a couple weeks.
      2011.5 XC60 T6 R-Design
      2006 Ferrari F430 Spider

    36. #34
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      Spangdahlem AB, Germany
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      Quote Originally Posted by superbike81 View Post
      Oh ok, well that has me a little less worried, as I'll only be running 600rms from an Alpine PDX-M6.

      After talking with my installer more, he's convinced me to go ahead and go with the Alpine SWR-T12 flat subwoofer I already have. I described the install I saw that didn't impress me as far as SQ goes and he is confident he can get me set up with an install that will please me.

      I pick up the car in a couple days, and then the install will commence in a couple weeks.
      Post pics. I am curious how you are going to get a stealth 12" in the XC60.

    37. #35
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      Japan and Seattle
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      Quote Originally Posted by Mephisto View Post
      Post pics. I am curious how you are going to get a stealth 12" in the XC60.
      By eliminating the spare tire. I don't see it being terribly useful anyways, as I have free towing and am almost always in the city. If I am going to go on a longer trip, I'll throw the spare and tools in the back. Install should be done by the first week of Sept. Not going to post much more here, don't want to take Mark's thread any more off topic.
      2011.5 XC60 T6 R-Design
      2006 Ferrari F430 Spider

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