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Multi-Way Conventional loudspeakers with crossovers

Stuffing the box. How much?
Stuffing the box. How much?
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Old 29th May 2006, 08:59 PM   #1
Pano is offline Pano  United States
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Stuffing the box. How much?
Default Stuffing the box. How much?

Here is another Stuffing thread for you.

How much and how?

I've been reading all I can find here and throughout the web on box stuffing. There is a surprising lack of information. "Stuff to Taste" seems to be the common advice. O.K.....

No charts, no guidelines, measurements, formulas, etc. That seems odd considering how much math and measurements are used in other areas of speaker building.

Many builders use polyfill - and say that over-stuffing makes a speaker sound "DULL". Does that mean it kills the midrange? No one ever seems to give a guideline for how much, or what type. Only Martin J. King seems to point to about 1/2 pound of fill per cubic foot of box.

In the past I have always followed well thought out and tested designs that told me what to use and how much (generally wool felt). But where does one start on his own design?
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Old 29th May 2006, 09:12 PM   #2
Cal Weldon is offline Cal Weldon  Canada
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Stuffing the box. How much?
There really isn't anything in stone here. It is to taste and it really can't have a formula. It's like asking a stranger how much salt you should put on your food.

So without getting technical...

Depending on the size of the box, the affect is often that as you increase the amount of stuffing, it will reduce the boominess and seem to tighten the bass a little. On the other side of the coin, that also sounds like having the life sucked out of them to some people. The way I do it is to start with a small amount, say three sides covered at about 1" to 2", close 'er up and have a listen. If it sounds boomy, double the amount and listen again. A lot can depend on where you are listening so do your testing where you will have the speakers.

It won't affect the really low bass, only midbass and up.
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Old 30th May 2006, 01:06 AM   #3
lndm is offline lndm  Australia
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In the past I have stuffed boxes heavily trying to fix problems which were actually elsewhere. I find the maximum amount of stuffing needed to attend to reflections/standing waves is not that much. If you need to shove it in, it's probably too much. Adjusting the bass driver's fundamental resonance damping is an independent issue, but I feel too much stuffing does seem to make the sound less lively and I try to avoid it.

This applies mainly to closed boxes. If you are building a reflex enclosure, you really want to use the minimum amount reasonably possible. For a transmission line, there is probably an ideal amount, that can be calculated. For horns, I like to remove the damping material as much as possible, and use equalisation if needed.

BTW, I like to use fibreglass batts, but they are not without problems.
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Old 30th May 2006, 08:02 PM   #4
Pano is offline Pano  United States
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Stuffing the box. How much?
Thanks for the answers.

I'm working on a bass reflex design now. Will pull all the stuffing and see how it sounds. It's the reflections and standing waves that scare me.

I think it's surprising that stuffing formulas do not abound. We have so much else calculated in speaker design, box tuning, baffle step, T/S parameters, crossovers. Why not stuffing?

As Cal said, it's a bit like asking how much salt to put in your food. My problem is that at least a recipe will give me a starting point for the amount of salt. But I can't find that for box stuffing. Maybe I'm not looking in the right places.
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Old 30th May 2006, 11:14 PM   #5
lndm is offline lndm  Australia
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A starting point for a bass reflex enclosure might be to put a 2cm thick panel of damping material on each wall for a small enclosure. A 5cm panel will do for a large enclosure.

These are not necessarily ideal for standing waves. What you will be trying to do is keep the main volume of the enclosure clear so that the 'reflex' works. One old trick that has been suggested is to suspend the material a little away from the walls. You might even try stuffing the middle of the box with something really light.

When I build a reflex system, I find it necessary to experiment with types of damping material to get the best from the small amount I use.
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Old 31st May 2006, 06:50 AM   #6
Pano is offline Pano  United States
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Stuffing the box. How much?
Thanks Indm,
I pulled almost all the stuffing out of the boxes and got a LOT more mid-bass. Maybe too much, but at least it was a move in the right direction.

I had forgotten about the damping curtain, might be worth a try. Starting to feel like going back to the old tried and true wool felt around the inside - no stuffing. Or maybe carpet.

BTW, box is 2.75 cu. ft. tuned high - about 60Hz. Padding was about 2" (5cm) thick on bottom, back and one side only. So not very full.
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Old 31st May 2006, 07:20 AM   #7
Virtalahde is offline Virtalahde  Finland
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So, how does stuff used for acoustic treatment work for cabinet damping? Rockwool for example. A 50mm rigid rockwool panel absorbs insane amounts of bass energy, even more at higher frequencies. This stuff comes here in 25mm panels, too..
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Old 7th June 2006, 09:46 AM   #8
frostbiter is offline frostbiter  Australia
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Man I wish I had of read this about 2 months ago.

The only guide I found to speaker stuffing was by someone who reccomended lots. So I followed suit and have been complaining of how my DIY speakers sound so dull.

After reading this and removing all and only using a lining of fibreglass roof insulation, the same speakers now sound so much more lively.

They may need a little more, but the midrange which was completely dull is now far more dynamic giving the speakers far more depth than I thought they ever would.

I was considering replacing the drivers with more expensive ones, so I am so glad I read this.

Cheers
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Old 7th June 2006, 12:17 PM   #9
Pano is offline Pano  United States
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Stuffing the box. How much?
Quote:
Originally posted by frostbiter
After reading this and removing all and only using a lining of fibreglass roof insulation, the same speakers now sound so much more lively.
It is surprising how much a change in the amount and/or type of stuffing can change the sound. As you've just found.

What is just as surprising is how little published research and math there is on the subject. So many other aspects of speaker design are quantified and formulated, why not stuffing?
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Old 7th June 2006, 03:48 PM   #10
Cal Weldon is offline Cal Weldon  Canada
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Stuffing the box. How much?
In my email, I forgot to mention egg cartons, the cardboard type. If you layer those with the carpet, I wonder what might happen.
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