Deciding between direct firing sub & "Down firing" like JL Stealth Box


New member
Username: Endee666

Post Number: 6
Registered: Jan-09
Changing the sub setup in my Audi A6. Deciding between 2 options. Both with an old school Audiobahn Alum10 that I love. Both sealed with the same volume. The only variable is how they will fire into the cabin. I have tried this woofer in several configurations over the years. The most output was vented but I liked the accuracy of sealed better. All of those were rear-firing in the trunk, and my trunk cost me so much output. It sounded great if I folded the seat down, but with it up I lost everything. So I will now be isolating it to the "ski hole" when the arm rest is folded down, firing direct into the cabin.. I now want to isolate it into the cabin & because of work stuff in the trunk, no longer want the woofer exposed to the trunk..

Option 1:
Sealed off with a little space for excursion, firing direct thru the ski hole.

Option 2:
Similar concept to a lot of JL Stealthboxes, firing against a surface like "down firing", and then venting to the cabin via a slot. See pics & links below for the exammples that inspired the thought. I had a JL Stealthbox in my 300ZX TT and loved it. It sounded so much better than the basic 10" that was in it should have. For this option, the vent would fire directly into the cabin thru the ski hole.

Down firing & slot loading are supposed to give better woofer control, less distortion & less woofer mechanical noise than direct firing.

So option 1 or 2? Pros & cons to each? Also, if option 2, how much space is needed in front of the woofer? Some of the JL boxes & other similar installs I have seen only have an inch or so.. Due to the large surround & excursion of the Alum10 (13mm xmax) I would leave a little extra compared to the JL's..

Pics of examples below:

And another showing "down firing" that isn't down, but vertical:

Thanks for the help.

New member
Username: Endee666

Post Number: 7
Registered: Jan-09

Gold Member
Username: Kaerfpl

Spencerport, NY USA

Post Number: 1345
Registered: Jun-06
Are you building or buying the Enclosure?

Silver Member
Username: Joe1234

Post Number: 334
Registered: May-09
The fact that you didn't like the particular 10" sub in the particular box does not mean a thing.

All those HT subwoofer manufacturers that use front loading claim what you have stated, reduced distortion, mechanical noise, etc.

If you liked the results I would never recommend to attempt improvising a design yourself, I don't think that just nearing a sealed box to the backseats near the ski hole will just give the results you expect. (but of course you can try).

Instead buy a ready made solution from JL Audio for your car or a ready made 4th order bandpass specifically designed for the subs you will be using, and remember that if the port is obstructed in any way the enclosure will lose tuning immediately.

Take a look: tml
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