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Old 17th November 2006, 07:04 AM   #1
brianon is offline brianon  United States
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Default Loudspeaker Stuffing Theory ?

Hi All....

Anyone have pointers to sites that really deal with loudspeaker stuffing theory?

Or can anyone offer their own observations, advice on loudspeaker stuffing? I'm not looking for "the best stuffing"-- more later :- )

Actually looking for how to design better loudspeaker stuffing based on the Theory behind loudspeaker stuffing.

OK... now time to ask... the best stuffing... lambswool, polyester, fiberglass. All work well in certain applications. Are there companies that make stuffing engineered for loudspeakers? I am aware of companies like Black Hole, etc that make sound absorbant coatings. What about stuffing? Any companies "out there" that have engineered products designed specifically for loudspeaker stuffing?

Conclusion... really looking for information one can provide or pointers to websites regarding the "Theory" of loudspeaker stuffing. The best I found was this:

The compressibility of air inside a loudspeaker enclosure can be increased if the enclosure can be made isothermal. Stuffing fibrous material into an enclosure tends to make it isothermal since the material acts as a heat sink. In order to evaluate the effectiveness of filling material in loudspeaker enclosures, the thermal time response of fibrous materials is calculated. The time response is found to depend on the density of the material and the radius of the fibers.

In standard english, stuffing partially absorbs the internal soundwave energy and converts it into heat and that Density and Fiber Size are the variables.

So if anyone can offer information on their own, or, pointers to websites that detail this further, I would appreciate it.

Stuffing is an area that needs additional research because:

Stuffing has the important effect of reducing internal reflections, to reduce standing waves and comb filtering. lining the walls of a vented enclosure to reduce internal reflections, or filling a transmission line to absorb the back wave, highly absorptive wool or fiberglass results in a sealed system. They will provide more reflection absorption than polyester, but the latter is quite good in this regard in the critical midrange. In a sealed system you don't want absorption at lower frequencies anyway; you want damping and isothermal conversion.

So theory is important. Any advice, pointers, etc will be truly appreciated.

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Old 17th November 2006, 08:46 AM   #2
Pano is offline Pano  United States
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Good luck! About all I ever read or hear is "Stuff to taste." Hmmm... The TL guys do calculate, then tune by ear.

Stuffing seems to be the "Final Frontier" of speaker buiding.
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Old 17th November 2006, 09:19 AM   #3
sreten is offline sreten  United Kingdom
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You need to be able to measure impedance.

As you stuff Fbox lowers. Overstuff Fbox rises. Optimum stuffing = Fbox min.

Not that popular any more as it does not allow the use of ports.

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Old 17th November 2006, 12:42 PM   #4
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Old 17th November 2006, 01:04 PM   #5
DorinD is offline DorinD  Romania
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Red it on this Forum:

"From Altec - 1974
The normal method to check speaker damping is simple, but is easiest if you start out with too little fiberglass. We recommend the battery test method to check for damping. Attach a short length of speaker wire to the loudspeaker terminals in the normal manner, and bring the loose end around front – where you can easily listen to the loudspeaker sound while testing. Hold one of the speaker leads to either end of a standard 1.5 volt flashlight battery. Then touch the second lead to the other end of the battery and release. A properly damped loudspeaker will reproduce a clean “click” as contact is made and released.

The underdamped speaker will reproduce the battery contact as a “whomp” sound. Fiberglass may be added in a loose manner to the enclosure until the proper “click” is obtained, and then stapled into place according to above practices relating to the specific type of enclosure.

The overdamped speaker is more difficult to observe. It is a matter of degrees that becomes familiar with one or two experiments. Thus, the recommendation to start tests with too little, build up, and then go back down as required."
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Old 17th November 2006, 04:44 PM   #6
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I've got some long fibre wool(teased out) just behind the midrange driver on my TL's, I also added some just inside the port, but thought it muddied the bass so took it out. (the speaker is also lined on one side with eggcrate acoustic foam.)

Have looked at tons of different designs, normal ported speakers
most people seem to completely fill with all different types of filler.
But I haven't actually seen any advice on what is best - they all seem to be a bit of an experiment...
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Old 17th November 2006, 07:09 PM   #7
Pano is offline Pano  United States
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Originally posted by DorinD
From Altec - 1974
I think I may have posted that. -- Read it, anyway.

That is the most exact advice I've read about speaker stuffing. And of coure they are talking about bass reflex cabinets.

Stuffing sure can cahnge the sound of a bass reflex box.
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Old 18th November 2006, 05:48 PM   #8
Ron E is offline Ron E  United States
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The only online information clearly presented is the PhD Thesis of Gavin Putland.

The Loudspeaker disign Cookbook has a series of empirical tests with different stuffing materials, but it doesn't give the T/S of the woofer so it is of limited usefulness.

There are articles in the JAES, notably one by Leach in the late 80's.
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