First, many thanks to Coppertone for steering me towards the amp and sub for this project.
So I set out to install a subwoofer unit that takes up NO additional space in the car. The install is to augment the OEM head unit and speakers.
The install was a birthday present for my daughter who drives the 2007 Outback.
Have ended up with is a common solution for at least the OB and Legacy platforms, that spans multiple generations. Whoo!
There are two options that I focused in on; under seat sub and wheel well sub. Had initially been leaning towards under seat subs from Kicker, sound ordinance and kenwood.
The limitation here, of course with this setup is enclosure volume. The under seat amplified sub system is essentially pushing a small sub with no lower frequency gain contribution from an enclosure. Pouring through the many threads, there was a possible height issue for the kicker (number one pick). Although a lesser problem on the 5th gen, the undeseat subs installed in the 2007 OB would be kicked by a passenger in the rear seat. Typically for an adult in the rear seat, the front seat must be moved forward to gain leg room.
I stumbled upon this cool amplified sub at Crutchfield.
Had to use Google to translate a bunch of German posts, but the reviews were really good. Thing is built like a Panzer. Since there is ft3 volume to this enclosure, the specs on this sub reach down to 20hz. The problem here is that the height of this is under 7". This means that the spare tire needs to be removed. Thus for this effort, the Blaupunkt is a non starter. There are many DYI posts that create a fiberglass enclosure using the trunk to create the mold. Again, can't use the spare tire with these concepts.
The simple aha moment for this project came when thinking about the fiberglass enclosures and wondering why it was needed since essentially just a cover is needed; the wheel well is the enclosure, duh. Did a rough measurements. The volume is alittle bigger than 25" x 25" x 3.5" or a volume of at least 1.3 cubic feet - not too shabby. Adding the rough volume withing the spare rim (less where it mounts on the hub) is roughly another 0.67 ft3 so crap, the total volume with the spare tire is 1.9 ft3. In reality, it's got to be a little over 2.0 ft3. The difference is volume is simple; keep the spare tire foam insert in the tire (that has the jack and tire iron ...) for a volume of 1.3 cubic feet, or remove it for 2.0 ft3.
This drove the selection to a shallow mount woofer and compact amp.
Calling Coppertone, calling Coppertone ..... Yes, I contacted Coppertone to see what electronics he had in his arsenal of new or slightly used cache of audio electronics. Well, as it turns out, we settled in on two components to get the job done:
Massive Audio Nano BiT BX2 Class D dual channel Amp. OMG this thing is small (6.3" x 5.0" x 1.6") For this application, bringing the amp for a singe sub puts out 480 watts RMS. This BLOWS away the under seat offerings @ 150 Watts RMS or three times the power out.
The BX2 has all of the standard offerings - RCA inputs, hi-level (speaker) inputs, remote power on, auto turn-on from hi-level inputs, fused an thermal protection, adjustable low pass filter, bass boost, And it's a class D amp with circuit cards meeting Mil-Specs.
Coppertone paired the BX2 amp with a Kenwood Excelon KFC-XW1200F. http://www.crutchfield.com/p_113XW12...0F.html?tp=111
This sub an efficient shallow mount woofer. Up to 350 Watts RMS (1400W peak), sensitivity 91dB, 30-700 Hz response, minimum enclosure volume of 0.8 cubic feet.
The sub would be mounted underneath a 30" x 27" plywood rectangle. The 07 Outback was the restriction for the size (Attachment 1) Also cut out a bottom piece ( that can rest on the tire.) The pieces two are connected by 1/4" carriage bolts. (Attachment 2) The bottom piece rests on the tire. Currently, I have removed the bottom piece until the open diameter is increased from 12" to the 18" diameter of the spare tire rim.
The next two attachments are fitted in the 07 OB and in the 2010 LGT. It may not be visible in the pic but the 2010 wheel well is slightly wider and there is a small gap (less than 1/2" gap on the sides. Note1: Used 1/2" plywood to leave about a 3/8" gap between the top of the plywood to the OEM carpeted wheel well access cover. The gap leaves enough room to support a noise dampening layer under the carpet.
Finally, purchased some speaker grille material to stretch over the top of the wood and staple underneath.
Took the electronic to a local shop to run the power wire and hook up the electronics. The fifth attachment shows the sub, amp and line leveler. There are inline fuses at the battery for power and for the +12v remote turn on signal. The reasoning to mount it all together is portability. The shop used a Molex connector (attachment 6) laying around to disconnect audio and power lines from a single harness. Install a harness in the LGT and this sub moves from one car to another in minutes.
All I can say is this sub rocks. It has transformed the OEM system above expectations. There is some really good extension down low. I don't have a meter to check it out, but maybe there is an Android app that can show the shape of the freq spectrum
What is left .... vibration and noise isolation. Great link: http://www.sounddeadenershowdown.com/
Vibration isolation. Upon research, vibration isolation seems to be quite an emotional topic. There are many companies out there. The only critical thing to remember is to NOT get a product with asphalt filler. Butyl rubber dampening layer. What is important here is to get as much rubber as possible wit little to no filler. It is the rubber particles that convert vibration to heat. Another important attribute is the containing layer. This layer is typically made of aluminum 4mm or greater. Vibration itself is dampened in corners. 25-33% of a flat area. Many go wild and with 100% coverage, but that's just not needed.
Picked up some Murdermat MDK as a balance of specs and cost. (Attachment 7) 79mm butyl rubber (99.9%) dampening layer, 8mm T6061 high grade aluminum constraint layer, and an added bonus thin clear vinyl layer to reduce cut fingers. Of course it remains too cold outside (no garage) to install. I bought enough for both cars, but the focus will be on the LGT for vibration isolation of the TBE.
Noise isolation. OK, so vibration isolation alone is not the full solution. A barrier layer is essential to block the noise from outside (and keep the desired nose inside with out frequency summing or cancellation from outside noise sources. Mass loaded vinyl (1lb/ft2) with a closed foam separation layer does the trick. Crap, the stuff for the auto industry seems expensive. I took a different tactic and looked into what is used in buildings and home theaters. I whittled it down between two companies and found a carpet underlayment with the foam separation adhered to the MLV. This stuff can be ordered by the foot with a 4.5' width. I picked up 8' of it (Attachment 8). May be able to cut this out today. Again, the LGT is simpler than the 07 OB to install.
Will focus on the trunk first, then may look into vibration isolation on the doors. Did not want to go too crazy. I have a sound meter and will take some before/after averages of level changes.