Michael Benno

Nothing all that new here, I know few 928 people have previously installed this Bose subwooder from the Nissan Murano / Mazda 6 / Acura RKX. But I wanted to share the installation details, driver specifications for amp compatibility, and overall impressions. Special thanks to @Shawn Stanford who seems to be the first list member to post on this solution and what the inspiration for my project.

While I am not an audiophile, I have come to appreciate the high quality sound from modern cars. I know from experience that adding a subwoofer can do a lot to help make any old audio system sound better. On my previous 1988 928 S4 5spd (sold), I tried lots of different things to try and improve the sound quality. I started with a nice head unit, better speakers, more powerful amp, and sound proofing. But the thing that made the biggest impact was adding an inexpensive compact sub woofer. This was a great addition and really helped fill out sound in the car. While the improvements to the sound were nice, I felt my installation was a little too rough looking:



So as I considered adding a sub to my 1992 GTS, I wanted something that looked a little more factory or at least professional looking. I considered making a custom box but felt that any custom box would be a major engineering and construction exercise and though I would look into pre-fabed options and other OEM options that would fit inside of the factory spare wheel 16″ for pre GTS cars and 17″ for GTS models.


The Bose sub seemed to be a really good option for me and inexpensive enough to experiment with. Please note there are endless versions of these Bose subs some come with amps built in and some come with two speakers. The one I ended up with has a single driver with two voice coils and not build in amp. I quick search on eBay yielded several options, I purchased this one for $60 including shipping. Here are some detailed images
Below you can see a test fit in the GTS with the 17″ space saver spare. The sub box sits a little proud of the spare, but it is still level with with the rear deck. I decided to leave out the foam insulation and plastic cover that would normally sit between the carpet and the spare since the sub box sits proud an d would provide the necessary support for items in the trunk. The omission of those materials should also help with sound transmission.


Securing the sub was a simple task of using a longer bolt that secures both the sub and the tire to the chassis through the anchor nut used to secure the spare. In this case a 150mm bolt worked well. Because the anchor nut is offset from the center of the spare you will need to shift the sub so you can align the bolt. It almost does not align but I was able to get it threaded and properly secured.

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Wiring the sub was a bit more complicated and required some research and math! I think this is an important time to disclose I dont know much about audio connections or design so please let me know if I got this wrong some how. In order to install sub, I needed to know the specifications on the driver speaker, which means I needed to disassemble it.


I was able to find some specifications on the driver. It is a Dual Voice Coil driver, rated at 2-ohms/45-watt RMS for each voice coil. This is an un powered sub box, but this sub is often configured to optionally have a Bose amp built in (see the extra cavity in the box). I tested the resistance of each voice coil and confirmed the 2-ohm resistance. The two voice coil is currently wired in parallel.






So now that I had the specs of the driver, I needed to determine what amp I need to drive it depending on how I wanted to connect it. I wont go into detail because everyone will be different. But I decided to wire it in parallel which meant I needed to drive each voice coil with 40-50 watts with 2-ohms each which roughly matched the 2 channels that I had available on my amp.

In the GTS there were two of these Alpine amps. its small simple amp with not much functionality. But it does serve both 2 and 4 ohm output and it’s bridgeable if needed. The previous owner installed this such that the door speakers; the large woofers; rear mid/tweeters are all driven on 2 channels for each set (6 channels total). Which meant I had 2 unused channels at 45-watts each which was perfect for this sub.



I found the above guide on wiring the sub and this helped confirm my decision to wire it in parallel using two channels on the amp.


As a reminder, I am using the Blaupunkt Bremen SQR 46 DAB head unit which has a separate sub channel output and a digital sound processor to limit the FREQUENCY (settings: 80/120/160 Hz) and GAIN (settings: 0 to +7). Which means I can have some really nice control over the sub from the head unit.



Testing and tuning
Once I had it all wired up and tested, I spent some time fussing with the gain settings on the amps until it felt right for most of the music I listen to. I can tell you that with this amp, I can turn the gain up to maximum without distortion. However I do get some white noise as max gain and no volume, so I dialed back the gain a little to prevent the white noise. I then tuned the cross-over frequency with head unit. I found the middle setting of 120hz to be a good compromise between the hard punch of a sub woofer and the medium bass reverb that seems to be lacking in the OEM speakers in the 928. The head unit gain control will need to vary based on the music but I found a seeing of 2 or 3 to be fine for most pop music.

Final Results
I could not be happier! The base sound quality is more than enough for my ears and does not diminish while driving on highways and noisy road surfaces. It's a very noticeable upgrade to the sound system. Not sure I need much more at this point. I feel this Bose sub is offering just as good, if not better than the compact sub I had installed in my 1988 S4. So at $60 vs $275 way better boom for my buck!

I would definitively recommend this as an easy upgrade for folks wanting a step 1 upgrade. I think if you dont have a dedicated sub output on your head unit you are definitively going to need a dedicated sub amp with some bass management control (eg base boost, DSP, or low pass filters). Most amps for subs have this.

PS, I am using the stock Blaupunkt 10-speaker system in this car with factory wiring. Only Amp and head unit has changed

hacker-pschorr

Nice write-up. This is one mod on my shortlist for two of our 928's.

jheis

Why would anyone put anything Bose in a Porsche...?

The Forgotten On

Right? It should be A/D/S only

LKI

Why don't you ask Porsche?
https://automotive.bose.com/vehicles/porsche/taycan

jheis

While I despise Bose for it's over priced crap components and artificial sound "colorization," they have been very successful at catering to the lowest common denominator.
Ever wonder why Bose has "stand alone" kiosks - it's so you can't do a real "side to side" comparison with the competition.
Porsche's affiliation with Bose is most likely a marketing decision - driven by of a perceived need to produce a certain sound - Bose is very good at covering up acoustic deficiencies.

LKI

Wake me when we're back on topic.

gazfish

A grenade on your second post?

bw1999

Thanks for this post. To add a different option, I purchased the Blaupunkt Bremen from FVD:
https://www.fvd.net/us-en/FVD6459110...ro-design.html

I removed the aftermarket amplifier someone installed as the bremen puts out enough to not need it (according to Crutchfield).

I then installed this subwoofer instead of the Bazooka sub that was there.
https://smile.amazon.com/Kenwood-KSC...7015495&sr=8-1

It fits inside the wheel with spare installed.

19psi

You don't have to go with Bose. When you order your next new Porsche, you can always opt for the Burmester. Should only set you back an additional $7,000.00 over the Bose.

Bales

Wondering, were both the Alpine 445u amps installed in the same place as the original 928 amp? Looks like they might just squeeze in side by side. If so is it ok heat wise?

I have just installed SQR46 head and have picked up the same bose sub from a local wreckers yard. Now just need to find the right amp/amps but want to fit them into the original location.

Michael Benno

those little amps don’t produce much heat at all and are never very warm to touch. Yes both fit nicely under the cover. You will need some flat stock aluminum to mount the amps into and then mount to the factory points.

these amps are cheap and don’t have any nice features but the system sounds great. I get some more pics of the install for you when I get home from vacation.

Shawn Stanford

I'm working on upgrading the sound in my '84 by replacing the stock Blaupunkt amp with a modern 5-channel amp that can drive a Nissan spare tire sub. I measured the available space and I'm going with the "Soundstream PN5.640D Picasso Nano 640 W 5-Channel Class D Digital Car Audio Amplifier". It's 5"x1.5"x10", which will fit into the existing cover. I'm also going to try to do this without cutting any wires from the factory install, so I've ordered some female 2-pin DIN speaker plugs to go from the new amp to the factory speaker harness.

Bales

Thanks Michael, a pic would be great when you have time.

Shawn, could love to see this option and how well it fits. Cost wise I can get that amp here ~NZD450, which is better value than buying 2 of the 445u. The spec I can see online claims 1 3/4 inches high so I was worried about height fit. Also, it from the spec is seems if you want you main speakers at 4 ohms you can't have the sub a 2 ohms. Mine is the 2 ohm sub, maybe yours is a different model?

saxonite

Great write up. This has never crossed my mind to do in my '81 928. My RSX is gutted for track use and the sub has been sitting in the garage for years collecting dust.