What type of fiberglass insulation for stuffing?

[just a guy]

But since none of these materials absorb much at low frequencies, what is their action inside a sub?

It's ironic that you recommend leaky sealed boxes for every application regardless of target goals and yet you don't know how these devices work despite the fact that I've told you countless times over the years how they work. I've mentioned how stuffing works at least a couple of times in this thread alone, and at least a dozen times in the church organ thread. But let's do it again anyway.

Stuffing in a box flattens out the impedance peaks to some extent, the more stuffing you use the lower the impedance peaks get. It doesn't take a lot of stuffing to see the effect. At high frequencies this will result in a smoothing of high frequency ripple, regardless of box type.

In sealed boxes, flattening the box impedance peak will eliminate some of the spl near the impedance peak frequency and will add some spl below this frequency, resulting in a lower box q.

In resonant boxes, impedance peaks are still flattened but which impedance peaks are flattened depends very much on where the stuffing is placed in the box. Even if you don't believe in sims it's not hard to imagine that a small handful of stuffing placed right in the port (blocking the port) will aggressively attack the fundamental resonance. But the same small handful placed inside the box well away from the port will have little or no effect on the fundamental but can be effective in eliminating the higher frequency ripple.

Here's the data-bass stuffing article again, but there are countless measurements available that show the same thing if you do a quick search. Data-Bass

I'm also puzzled just why learned people say there's a Goldilocks optimum amount of stuffing which sounds to me kind of on the light side? I've seen the recommendation but not grasped the rationale; you can fill the whole box using just a few ounces of Pink and it would still be taking barely a few cubic inches of volume and barely absorb much if put on the wall.

(BTW, I hoard true-felt rug underlayer and Tectum, two favourite materials that are more effective at low frequencies.)

Ben

I'm not aware of any "optimum amount of stuffing" or anyone who says there is. For a subwoofer, if you have high frequency ripple or if you want to lower the q of a sealed box then stuffing is necessary, how much depends on how much you need to accomplish these things. But if there's no higher frequency ripple and the box q is already the q you want there is no need whatsoever for stuffing.

Also on a side note, sealed box speakers have no "whomp up" at fs as you previously said unless the driver q is extremely high. .7 qts will give a max flat response if the box is big enough, it's not until you get to well above .7 qts in a large box that you will get a spike at (or just above) fs. And even if the the driver qts is very high, if the box isn't big enough this spike won't appear at fs, it will be much higher in frequency than fs. So the leaky sealed boxes you constantly recommend won't provide the frequency response that you advocate here in this thread without a lot of eq. The type of box that WILL give this type of response in room is a max flat ported box, flat in 2 pi but with a room gain boost it gives the boosted low frequencies that you say you like.

Since you recommend leaky sealed boxes for every application regardless of user goals you should learn how they work.

 

[iScream]

I started a build thread if anyone is interested.

http://www.diyaudio.com/forums/multi-way/287645-my-attempt-4-way-digital-active.html

-Chris

 

[Kravchenko_Audio]

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