Jwebb335xi

Thanks for the comments Subterfuse. In your case, you've completely sealed off your trunk, haven't you? So, if I did a decidedly lower priced, but similar concept, would I lose my ability to fold down rear seats? I wonder if it's reasonable to build a "half" wall that's easily removed.. Is that crazy?

When I talked with the local shop, they just wanted to put a JL Audio powered box in the trunk and call it good enough, but for a car that I plan to keep long-term, I'd rather have something slick. OlyS6 over on Audizine has a gr8 looking set-up, but his installer is halfway across the country!

Jwebb335xi

I crawled into my trunk over lunch today.. The opening for that 10" sub is a touch over 9". It seems as though I could place two 10 1/2 squares on either side of the metal deck with a hole large enough to support an 8" sub, and keep everything relatively ridged... I've been told I might get front and back waves hitting each other. I'm not sure if that starts a tornado in the back seat, but I'm told it plays havoc with the sound..

Why can't this be easy.

subterFUSE

Yes, my rear seats are now sealed off from the cabin. However, in my car we made the baffle wall removable with 10 screws. But I have never once needed my seat pass thru in all the years I've had the car this way.

No, a half baffle wall is not going to perform well at all. The whole concept of a "infinite baffle" subwoofer is that the front wave and the rear wave of the subwoofer are isolated from each other. In a car, a baffle wall needs to seal off the airspace in the trunk from the airspace inside the car. Any gaps will allow rear wave bleed-though and will result in cancellations. A sealed box enclosure would be preferred to a half baffle, as the box itself is what isolates the rear wave from the front wave. There might still be issues with box placement and reflections interacting with the primary waves, but those can be addressed mostly by moving the box around and experimenting. Generally speaking, a subwoofer will sound best when installed as far back in the car as possible, up against the trunk lid, if possible. But every car is different. The IB wall I have in my car is a fantastic solution, and the car has done very well in national competition.

subterFUSE

Front and back wave interactions will cause boosts and cancellations in the bass, depending on the size of the car, the location of the sub, and the frequencies being played.
Some of the music will be bloated and boomy, and then some of the music will get cancelled out and silenced.

Different frequencies of sound have different wavelengths. The deeper the sound, the larger the wavelength. When the sub plays sound, the primary wave will go directly to your ears. But the sound will also go in every other direction, and it will reflect off the frame of the car and come back at you.
When the reflections come back at the listener and then combine with the primary sound, the 2 waves will either add to each other, or cancel each other. It all depends on the phase relationships of the waves. Waves that are in phase will reinforce each other. Waves that are out of phase will cancel each other.

All rooms have this problem, but cars are especially bad because the confined space is so small and the reflections are so strong.

Jwebb335xi

My brain hurts! Do you think that a simple sealed box is likely to preform better than a properly done shelf mount. I'd prefer the later over the long-term despite it likely costing more $$$. That said, if implementation is tough and it's more money, I may be better off going the quick/easy route.

subterFUSE

Most likely, yes. The sealed box will sound better.

A properly designed rear shelf subwoofer install would still require a baffle wall sealing off the rear seat pass-thru just like my car. Like I said, an infinite baffle subwoofer needs to isolate the front wave from the rear wave of the sub. In a car this means the trunk has to be sealed off from the cabin.
Doesn't matter if the sub is in the rear deck, or in the baffle wall firing through the seats. The trunk has to be a sealed airspace separate from the cabin of the car, if you want it done correctly.

Truthfully, an infinite baffle in a car would mean a subwoofer installed in the tire well, with the bottom of the tire well cut out so that the rear of the subwoofer is vented to the outside of the car.
The proper terminology for what I have is a "trunk baffle."

Jwebb335xi

Thanks for all the comments; I'm finally at a point where I understand what I want and what's likely to work best are two different things. So, I think I may go with a powered 10" unit by JL Audio, and have it done such that it can be disconnected, but leave the stock sub intact for those times when I pull out the JL entirely.

Would you see any problems having a competent shop do an install that way? I believe they'd tap the Speaker input to the stock sub, and send that to the JL, also ground, power and fuse the JL properly, which I understand is necessary to protect the car!

Vodka G

Yeah that's a LOT easier way to do it :-)

DanfZX14

Properly done you will be happy with the results. Just be sure to vet the shop out before hand and you won't be disappointed.

cccjrsbox

Just did this project, pretty disappointed in the results. Might be the amp/speaker combo I picked. Went with:

Sony XM-GS100: Here
Alpine SWT-10S4 10" Woofer:
It does add more bass, but not very loud at low to mid volumes. If I really crank it, it gets louder but rattles galore. Good news is that the sub control in MMI does work, and the amp works great without a signal wire (using auto detect).

Now thinking about either adding dynamite and trying to track down the rattles - or - pulling the speaker and putting it into a box behind the rear seats. Debating on a sealed vs. ported box, these are the contenders:

Ported Box: Non-Ported Box:
Would appreciate it if anyone has any suggestions here.

Car is a 2014 A6 Premium Plus (non-Bose, non-B&O).

Thanks!