hans14914

This will be my 928th post, so figured I would share a project with you guys that I have been working on since this past fall.

After speaking with many 928 owners who are both disappointed in the factory stereo, and also frustrated with the available options, I decided to take a look and see if it is possible to make a true stealth 928 subwoofer enclosure and "amp rack."

Coming from a strong audio hobbyist background, I wanted a sealed enclosure with good, clean, deep bass response. 12" drivers are generally best suited for these tasks, as they have the requisite displacement to get low, and also still small enough to fit in most installs. The search was on to find the ideal driver for the 928. After lots of research, I settled on the best driver currently available for a 928 like predicament - the Stereo Integrity SI BM MKIII. Sine early last year, I have been in touch with the owner of SI and the creator of the MKIII. Specs can be found on the SI website, but I can tell you that it plays below 20hz in a .5cuft sealed enclosure, which is just about all you need to know.

The next challenge was where do you hide a subwoofer amp in a 928 - not an easy task. Furthermore, if you find a location, it will be occupying the same space someone would likely want to use for their primary amplifier (if you are going to install an aftermarket sub, it is likely the in-headunit amplifier wont be enough to keep up). So I made the early decision that whatever amp I wanted to use, it would have to have a similar footprint as an equally capable 5-channel amplifier, giving future flexibility. After digging around, I found that the Kenwood was planning on releasing a 5-channel amp in its Reference Fit line with an identical footprint to both its 4-channel and mono amplifier. So armed with my decision of subwoofer and amplifier package, I started the CAD modeling process. Shortly after getting everything drawn in CAD, I double checked all the other available small format 5-channel amps, and found that I guessed correct on the first try, and that the Kenwood is the only amp that would fit.

Once the CAD models were made, it was apparent that only a fiberglass enclosure would work for the subwoofer. MDF or any other "construction" type materials would add too much thickness and the project wouldnt be possible. So i started by CNC cutting several forms to make the fiberglass mold. After 3 attempts, I finally had a mold that fit. I then realized that mounting the enclosure to the board would be difficult and potentially yield a poor seal.... so I went back and had a 3-piece fiberglass mold made, which creates a sealed part for the sub to fit into. This entire sealed part is then bolted to the mounting board, eliminating any possible leaks, and creating a much easier assembly method.

The final result is a CNC cut top plate of marine-grade HDPE (will never warp, mold, expand... etc, it has UV stability agents and is chemical and water resistant). The fiberglass enclosure weighs in at around 8lbs and is strong enough to stand on (probably strong enough to use a jackstand, but I didnt test this theory). The amp is mounted using rubber isolation bushing, and is actively cooled by a 90mm fan (I beleive I will increase this to a 120mm fan in the next part, as well as increase the size of the intake ducts).

What makes all this noteworthy, is that it fits in the location of the factory spare tire. The only necessary modifications is to remove the carpet backing from the cargo mat so the fan can breath and the sub can play through the Sliverknit (additional perforation of the Sliverknit with a sharp awl or pick also improves sound and air transmission without cosmetically altering the carpet).

Here are some pictures of the unit test fitted in a 1989 model:











And here are some pictures of the part and mold:































This is the first part from the final version of the mold. There are unfinished edges an also part-release which make the enclosure look a little sloppier than it really is. We didnt want to completely finish out the enclosure until after the final test fit. The finished versions will have a the seams full ground, and a texturized coating on them to improve sound dampening and also resist scratching.

Thanks,
Hans

hacker-pschorr

Very nice!!!

When can I order one of those?

Jadz928

Holy Jeebus!

Thats really awesome!!

Speedtoys

Me Too! (c)AOL

Ninespub

Hans, that looks great. You never cease to amaze me. Obviously you have a lot of time on your hands (that's a good thing) or some of the 928 upgrades you're involved in would never happen. BTW, PM me if you're still interested in a strosek nose.

cpayne

Wow very nice! Great work!

jpNcos

Very nice.
So is the box volume .5 cubic feet?

Speedtoys

I was wondering about that as well...gotta get the right driver for the volume...it aint much.

tmpusfugit

Nice work!

Randy V

Very nice indeed.

I have installed a 10" sub and amp. Rob Rositto (recently passed) manufactured the sub enclosure and the amp panel.

I need to take pics and post.

hacker-pschorr

Plenty of subs out there will sound fine with .5' of space in a 928.

I had two 12" PPI Comp subs in my 944S, each had about .46 and sounded great.

Speedtoys

I wasnt saying they dont exist..but as noted in the OP...gotta pay attention to it.

Ducman82

wow! great job man! id be down for one! :-)

hans14914

Thanks for the kind words. Technically, the volume is a bit more than 0.5cuft. I wanted to get the enclosure as large as possible for use with other subwoofers. I am not really aware of any other 12's that will play properly in this size enclosure, but there are several 10" drivers which can. The total volume is approximately 0.62cuft. I want to remeasure this number, as there were some changes since the last time I measured the internal volume (at which time it was approximately 0.67). I am currently installing a piece of foam in one of the "horns" which reduced the volume to the nominal 0.5 required for optimal performance.

Using a 10" driver in this style enclosure is very easy, and can always be re-trimmed for the 12" part instead. I like the Dayton 10" driver for this application, it is about half the price of the 12" I am using, and performs very well for it size:

http://www.parts-express.com/pe/show...number=295-134

There is currently a very limited amount of the 12" SI BM MKIII drivers available. A new production run is not scheduled till spring.

When these are officially available, they will be offered on Rennlist through a paid sponsor. Until then, I want to stick to the rules and not discuss pricing/availability but any other questions feel free to ask.

Thanks,
Hans

Mike B

Very nice...when might this enclosure be available?

EDIT: Thanks...