stuffing

[herndonb]

I've prepaid for a new Ascendant Audio Arsenal 15. This is my first DIY so I'm really excited and am hoping for some really musical results. The Qts is .54 and Qes is .59, with a Vas of 185 liters. I used ajdesigner.com sealed box software and it says I need a huge 9.6 cu ft box. My question is, if that's the correct size and I design good bracing, do I use poly fill stuffing? If so, how much? How do I attach it, spray adhesive? If my design is strong enough can it be unstuffed? Do some just use trial and error?

[Cal Weldon]

Originally posted by herndonb
just use trial and error?

Yes and depending on your XO point, you may not need any. If you wish to decrease the size of your box, sometimes you can stuff it full and fool the woofer into thinking it's the larger box.

[herndonb]

So how does everybody keep their stuffing out of the back of the speaker in down-firing woofer configurations? Some kind of netting? Something that doesn't vibrate audibly? Do you guys just loosly toss the stuffing in the enclouse or do you glue it to the panels? Thanks, great site!!

[Timn8ter]

Make a pillow out of cheesecloth or grill cloth.

[herndonb]

What do you guys use to test your stuffing job on a sealed DIY subwoofer. I'm going to drive my Ascendant Arsenal 15 in a large 9.6 cubic foot box with a Krell KAV-2250 amplifier in bridged configuration. I'm running this full range, but the input to the amp is getting crossed over at the Denon AVR-3806 receiver's subwoofer output at 80 Hz. Is there a good test tone disc or some music CD's that are recommended? Do you test with movies instead, seems like it would be easiest to just play the woofer with all the other speakers disconnected? Maybe something that sweeps from 20-80 Hz or so?

[herndonb]

To cover my 9.6 cu ft sealed box thoroughly enough with poly-fil I used 140 oz (8.75 lbs). Is this too much, or sound about right for a starting point. My priorities are:
1) Sound Quality
2) Sound Quality
3) Smooth in-room response
4) Sound Quality
5) SPL
Anyway just saying SPL is low on my list.
Am I on the right track for a good starting point? This is my first woofer. I'm getting the driver this afternoon!!!

[Volenti]

Originally posted by herndonb
What do you guys use to test your stuffing job on a sealed DIY subwoofer.

You can measure the effects of stuffing with an AC volt meter, test tones and a large value resistor (~1kohm).

Hook up the resistor inline with the driver and measure the voltage across the terminals of the driver while you play the test tones through it, the tone that gives the largest voltage reading is the resonant frequency (you can also do this with the driver suspended in open air, to find it's natural resonant frequency)

Now, typically the difference between a completly bare enclosure and an "idealy" stuffed one is the stuffed one will have a slightly lower resonant frequency (by a couple of hertz) and will have ~half the impedance (at resonance) of the bare enclosure.

Stuffing does 3 things;

1. slight effective volume increase caused by the adiabatic effect of the stuffing material (as evidenced by the resonant frequency drop)

2. signifigant damping action, as seen by the halfing of the drivers impedance at resonance (this can lower the output of the system by up to 3db around the resonant frequency, also diminishes the ability of standing waves to form)

3. direct absorption of higher frequency sound (usefull for reducing motor and other aberrant distortion causing noise in the enclosure).