# Some notes on coupe Bose system (fitment, specs, dimensions)



## ttwsm (Feb 27, 2011)

_Updated with ProDemand wiring diagram (2016-08-06)._
_Updated with SPL curve for one test where Bose equalization may have been inactive (2016-07-12)._
_Updated with note and link about high-frequency issues with SPL response curves (2016-07-07)._
_Updated with SPL response curves and some more pictures (2016-07-04)._

Just completed an overhaul of my audio system. Wanted to share some things regarding fitment that I thought might be useful, and also a couple things I found interesting.

*Wiring Diagram*

A helpful tech at a local install shop shared the wiring diagram from their internal system. I've scanned it to a PDF.

*Bose amp dimensions & cavity space*

The Bose amp resides in the space below the right rear speaker. It is 25 cm or 9 7/8 in. long, 15 cm or 5 7/8 in. wide, and 5.4 cm or 2 1/8 in. tall. 




























An amp that fits within these dimensions will of course fit. However, there is more space in the cavity, and larger amps will also fit. With the factory bracket in place, the outside edge of the cavity ends almost exactly two inches past the top left corner screw. Across the bottom two screws, the outside edge is about 4.75" past the bottom left corner screw.



















I cut a piece of poly, and drilled four holes to fit onto the same screws that hold the Bose amp to the mounting bracket. A piece that starts as a 10" x 10" square, with the left side cut down so that it's 7" across the top (still 10" across the bottom and 10" high), can be attached to the bracket in place of the Bose amp. If you align it so it's flush with where the interior edge of the Bose amp would be (set amp on top of plastic, mark holes, and drill), when placed on the bracket, it will show the outline of what will fit in the cavity.



















I trimmed the top right corner just a bit to make it easier to fit into place. I also cut an edge on the bottom left and in the middle of the back for future use running cables around behind the amp. I then mounted the amp onto the poly, mounted the poly onto the bracket, and the whole thing fit very nicely into the cavity.



















I hope that's useful. The Alpine F300 amp fits very nicely in the space. I believe there may be a fair amount of additional height in the cavity (i.e. a thicker amp would fit). I was not able to measure this, however.

*Bose tweeter*

The Bose system is known to use 2-ohm speakers. Having seen some old Bose home speakers, I assumed that the tweeters would be small paper cones. To my surprise, the system uses 4-ohm soft domes. If one were replacing the speakers in the Bose system, it might be possible to replace only the in-door 6.5 inch driver and retain this tweeter.



















The crossover is a 50 V 4.7 microfarad electrolytic capacitor. It is soldered into the speaker wires in the door that go to the tweeter (under some heatshrink). I have put small film capacitors (like roughly 0.3 microfarad) in parallel with electrolytics in the past (home speaker application), and observed a noticeable improvement in the clarity of really high frequencies at higher volumes. The same trick might work here, although I haven't heard the distortion that I heard in the old Infinity bookshelf speakers that responded so well to that trick.

*Bose midrange driver (door panels)*

The midrange driver is a 6.5 inch, 2-ohm paper cone woofer. It is secured from behind by a plastic ring that sits on four screw posts. When fitting a replacement, a critical dimension is the thickness of the outermost ring of the speaker. There is very little extra height on the screw posts. My Focal 165 AS drivers were just barely thin enough to work. The screw posts, with a lot of torque, were about 80% of the way through the nuts. According to the Focal drawings, the outer rim is 6.8 mm thick. I would not want to try a speaker with an outer face any thicker than that. Plan on extra work to mount the a driver with a thicker outer face.










I didn't realize that my only picture of a diameter measurement was so blurry - it's a standard 6.5" / 165mm diameter basket.










*Bose woofer (rear side panels)*

The woofer is also a 6.5 inch, 2-ohm paper cone woofer. Its surround appears to support higher excursion, and it has foam gaskets on the front and rear. It seats into a plastic adaptor, which in turn attaches to the metal side panel. This is a true 6.5" / 165 mm driver. A 6.75" driver may require some modification (i.e. new holes) in order to secure it to the plastic adaptor, even though it physically fits.



















It appears that a moderately deeper woofer might physically fit into the opening. I measured about 3 3/16" distance from the adaptor face back into the back of the opening. 










Also, the plastic adaptor converts the round speaker opening to a nearly square one. This means that, especially near the centers of the four sides, the interior slopes toward the center very quickly. This means that some drivers may fail to fit due to the _angle_ behind the outer front face. For example, the Earthquake Sound SWS 6.5" shallow-mount woofer fits every dimension - diameter is right, depth is sufficiently shallow - but will _not_ fit into the plastic adaptor - the metal basket goes straight back for about a quarter of an inch behind the front face. 

*Radio Coding*

When I used VCDS to change the radio coding after installing my aftermarket speakers, amp, and sub, I used a reference found on the Wak TT web site. However, my stereo had an unusual code in it: 00302. This should mean equalization for an A8 (second digit set to 0 instead of 4). I did not change it. Has anyone else seen this? I wonder whether the codes on that site are correct. Note that Ross-Tech also has radio codes, presented in a slightly different format.

_The equalization curves specified by the radio coding appear to exist in the amp itself, *not* the head unit._ Changing the radio code to a different vehicle makes no change in the equalization applied to the output if the Bose amp has been replaced by an aftermarket unit. To retain the built-in TT-specific equalization (and any time correction, if present) used by the Bose system, one must keep the Bose amp and use speaker-level outputs to feed an aftermarket amplifier.

*System SPL Measurements*

I used Room EQ Wizard with a calibrated Dayton Audio UMM-6 microphone to measure system response. I placed the microphone between the headrest and seatback of the passenger seat, sticking forward about six inches from the front of the seatback. Below are averages of five sweeps taken with the windows open, and another five with the windows closed. _Update:_ I have learned that FM signals are cut off above 15 kHz, so the high end of the response curves below is meaningless.










Close-up of the low frequency end of the audible spectrum:










Measurements were very consistent between runs. Any individual measurement would basically fall on top of the averages shown above. HOWEVER I do have one run where I _believe_ the equalization was inactive. Here's the low-frequency spectrum comparison:










Anyway, I hope this is useful when planning an audio upgrade from the Bose system in the coupe.


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## chrisc351 (Feb 17, 2011)

You wanna create a DIY Wade? I have a sub already mounted in my car, and an amp laying around somewhere that just needs to be hooked up. I might as well make the sub actually do something :screwy:


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## ttwsm (Feb 27, 2011)

I think I finished my audio project, hardware-wise at least, today. I want to take some measurements, and then will put all the "audio build" stuff into a separate thread... I do plan on adding a bit more info to this one, though - dimensions for the two different 6.5" drivers, and SPL measurements for the factory system. Maybe this afternoon or tomorrow on that stuff? 

You DEFINITELY need to put that sub to good use!


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## ttwsm (Feb 27, 2011)

Updated with SPL measurement data, more pictures, and more notes about radio coding.


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## ttwsm (Feb 27, 2011)

Updated with ProDemand wiring diagram.


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## goofydug (Feb 5, 2004)

Bump from the dead. Thank you for this great information!


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## ttwsm (Feb 27, 2011)

You’re welcome - thanks for the note - hope you install something awesome!


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