JL Audio 13w7 project...stuffing for Q

[kramskoi]

Since my Tumult has been reduced to music only, i'm looking to a 13w7 to use as the main theater sub. I plan to run them both together (with the tumult at a lower level) while watching DVD's.

My only concern is that the enclosure will have to be somewhat larger than my current one, which is about 3.5 cu.ft. internal. The 13w7, at 6 cu. ft. internal (22.75 x 22.75 x 21.125), models virtually the same in response and output at 20 Hz as the Tumult does. A 24" cube (8 cu. ft.) is about the largest i'm willing to build, hence the Q problem.

The Tumult box has a Q of around .65 and sounds quite nice but for the 13w7 i'm looking to get down between .57 and .6 damping.

I used 1" foam lining and polyfill from wal-mart for the Tumult box and i'm wondering how much i will need to drop the Q from .65 to .57 for the JL box.
Thanks all. :T

[ThomasW]

Sorry I read this last noc and it got lost in the shuffle before I posted a reply....

It's not something that can accurately be modeled. The only way to accurately determine is to measure as you add-in the material.

power amp
test tone generator
DMM (True RMS is best)
high power 20 ohm resistor (this isn't etched in stone so anything close is fine)

Resistor goes in series with the (+) input on the sub and the leads of the meter are attached to the terminals of the sub

Set the power output from the amp so you get a reading of 1.5VAC on the meter with a frequency of say 50Hz

As you run lower and lower test tones the you'll see a voltage trough followed by a peak and another trough in the voltage. The peak is the tuning frequency of the box.

Depending on the driver, the box size and the amount of damping you may not be able to hit your targeted "Q" exactly, but you can optimize the box tuning by doing the following.

As you add stuffing, the frequency where the voltage peaks (actually this is the impedance peak of the box) will go lower in frequency. At the point where you've added more stuffing and the peak occurs at a higher frequency instead of a lower one, remove the last amount added.

This is the optimal tuning for your box....

[kramskoi]

Sorry I read this last noc and it got lost in the shuffle before I posted a reply....

It's not something that can accurately be modeled. The only way to accurately determine is to measure as you add-in the material.

power amp
test tone generator
DMM (True RMS is best)
high power 20 ohm resistor (this isn't etched in stone so anything close is fine)

Resistor goes in series with the (+) input on the sub and the leads of the meter are attached to the terminals of the sub

Set the power output from the amp so you get a reading of 1.5VAC on the meter with a frequency of say 50Hz

As you run lower and lower test tones the you'll see a voltage trough followed by a peak and another trough in the voltage. The peak is the tuning frequency of the box.

Depending on the driver, the box size and the amount of damping you may not be able to hit your targeted "Q" exactly, but you can optimize the box tuning by doing the following.

As you add stuffing, the frequency where the voltage peaks (actually this is the impedance peak of the box) will go lower in frequency. At the point where you've added more stuffing and the peak occurs at a higher frequency instead of a lower one, remove the last amount added.

This is the optimal tuning for your box....

Thanks Thomas...appreciated :T