speaker box assignment

1-W SPL=87dB 2.83-V SPL=90.59dB.

Woofer properties: Goldwood, GS204/4S (290-370) standard one-way driver. Driver parameters: Fs = 138 Hz Qms = 7.19 Vas= 0.991 Liters

Cms= 0.336 mm/N Mms= 3.964 g Rms= 0.478 kg/s Xmax= 1.5mm Xmech= 2.25mm P-dia= 3in Sd= 45.6 sq.cm P-Vd= 0.00684 Liters Qes= 2.2 Re= 3.333 Ohms Le= 0.184 mH Z= 4 ohms BL= 2.282 N/A Pe= 40 watts Qts= 1.69 No= 0.114%

1-W SPL = 82.72 dB 2.83-V Spl = 86 dB

Box parameters: Type" Closed Box Vb= 4.248 Liters QL=20 Fill = Heavy

My assignment is to design two bookshelf / desktop speakers that not only produce quality sound but are visually appealing. Our professor suggests we use ½" or ¾" MDF fiber board because it is dense and good for sound applications. We are allowed to explore other materials if we desire. This assignment is pretty open as far as materials and box design. I'm not asking for someone to do all the work for me with this assignment but rather provide me with some tips or possible places I can find some information about speaker boxes. Anything you can provide me would be most appreciated. Thanks!

Jesse Stein

If this is not the correct newsgroup to post this to if someone could direct me to a more appropriate group I would really appreciate it.

Try the following links.

Some of these links are old but their should be something there that'll get you started.

I've used a program called win ISD to calculate box volumes and dimns that is fairly accurate and is free to be had at their site.

There are better programs but this one gets the job done.

If your going with a woofer as small as 4 inchs 1/2 inch mdf will do though I always use 3/4 or thicker for my projects. The key thing for getting good sound out of such a small driver is to be sure to limit the low pass frequencies to keep response tight.( I wouldn't try and drive anything below 40hz into it, it would most likely cause distortion and will certainly rob it of most of it's efficiency.) Keep the design simple, go with a sealed box, you really won't see much benefit from porting with such a small driver.( You might consider a dual woofer setup wired out of phase if you can get two more of those Goldwood's.(It's called an isobarik or push/pull design and works wonders when used with smaller drivers. Most designs use a simple tube configuration which can be designed for an esthetically pleasing appearance.)

Here are a couple of up-to-date links for software.

The so called woofer is a bit strange. It high resonance is higher than typical full range drivers, and it sensitivity is very low. Both strange. Your going to be using a high crossover frequency, so stuffing requirments are not only for bass response, but also high frequency attenuation. I would use foam and or fiberglass since they have the best attenuation.

greg

I'd always figured that granite enclosures would rule audio-wise - they'd look nice too. All other things being equal, I suspect that the higher the density of the enclosure material, the better the sound quality.

I just salvaged almost 3000 solid bricks from a house scheduled for demolition. I wonder what kind of enclosure 'those' would make.....?

jak

Mebbe but it's not so much the density as the damping. Some of the best enclosures were made of Aerolam damped with bituminous felt. Many modern enclosures are made of synthetic laminates with internal damping layers.

One might check the archives of speaker reviews at

(shameless plug) to see the bench tests of speaker enclosure resonances. Fewer and shorter is better.

Kal

Correct me if I'm wrong, but wouldn't a higher density material cause the damping to improve? (Lead speakers anyone?)

Lead is dense and soft, both of which contribute to its damping properties. The problem with simply saying that a dense material is sufficient is that it leaves out the thickness. A dense but thin wall is harder to damp than a light but thin wall. Same for thick walls. It really depends on the sizes of the walls and where you want to move the resonances.

As a general rule, you can get away with dense, thick, braced panels but that might not be practical (or moveable).

Kal

4+ liters sounds big for a 4" woofer to me. Particle board or plywood (high grade, very fer voids) are good choices.

or depleted uranium : )

Two birds with one stone! Who could ask for anything more?

I'm not sure exactly what you mean by dampening but will have a go at explaining why dampening materials are of benefit in box building. In regards to dampening in box material itself( mdf, plywood, concrete etc...) Yes the more rigid and dense the material the better as it acts to reflect the back waves better resulting is less energy loss and of course lower resonance which only adds coloration/noise. In box stuffing the idea is to add a material such as polyfill which acts as an "acoustic maze" or baffle which has the effect of increasing box volume. There are special materials such as acoustastuff which has the optimum characteristics, they can be had at parts express or any good speaker parts dealer. In the old days we used a material called kimsul, a kind of wool-like material which has been rendered obsolete by better materials

As for box materials, I've seen them made with just about every kind of high density material. I've always favored acoustic plywood.( 10 ply birch or white oak, usually 1-1/4 inch thick. It has the advantage of being a bit denser than regular plywood as it's pressed under greater pressure and with a glue that has stronger adhesion qualities than the water based stuff used in ordinary ply.) The best box I've seen in regards to it's dampening properties was formed out of concrete. Hard to build, heavy as hell and not too attactive in the home setting though. Years back a friend of mine had me help him wire up an isobarik that he'd made using 8 inch concrete drain pipe. About 4 feet tall as I recall using two woofers wired out of phase for push/pull effect. The bass was fairly clean and it had decent efficiency specs but were they heavy! Not too pretty either.(though he did improve their looks with some concrete paint and a bit of gloss laquer.)

I've had occasion to use the mdf especially designed for audio boxes.(can be gotten at most automotive sound shops) It's of a finer construct material and is sealed on the outer surfaces rather than the more coarse, open grain stuff you get at home building supply stores. It's also thicker( 7/8 for what we used) and is easier to apply paints or finishing coats to.

I talked to a fellow online that was attempting to use wonderboard to build a set of boxes, though I never heard how it worked out.

"none" bravely wrote to "All" (05 Nov 05 04:49:02) --- on the heady topic of "Re: speaker box assignment"

no> From: n >

no> I'm not sure exactly what you mean by dampening but will have a go at no> explaining why dampening materials are of benefit in box building. no> In regards to dampening in box material itself( mdf, plywood, concrete no> etc...) Yes the more rigid and dense the material the better as it no> acts to reflect the back waves better resulting is less energy loss no> and of course lower resonance which only adds coloration/noise. no> In box stuffing the idea is to add a material such as polyfill which no> acts as an "acoustic maze" or baffle which has the effect of no> increasing box volume. There are special materials such as no> acoustastuff which has the optimum characteristics, they can be had at no> parts express or any good speaker parts dealer. no> In the old days we used a material called kimsul, a kind of wool-like no> material which has been rendered obsolete by better materials

no> As for box materials, I've seen them made with just about every kind no> of high density material. no> I've always favored acoustic plywood.( 10 ply birch or white oak, no> usually 1-1/4 inch thick. It has the advantage of being a bit denser no> than regular plywood as it's pressed under greater pressure and with a no> glue that has stronger adhesion qualities than the water based stuff no> used in ordinary ply.) no> The best box I've seen in regards to it's dampening properties was no> formed out of concrete. Hard to build, heavy as hell and not too no> attactive in the home setting though. no> Years back a friend of mine had me help him wire up an isobarik that no> he'd made using 8 inch concrete drain pipe. About 4 feet tall as I no> recall using two woofers wired out of phase for push/pull effect. no> The bass was fairly clean and it had decent efficiency specs but were no> they heavy! Not too pretty either.(though he did improve their looks no> with some concrete paint and a bit of gloss laquer.)

no> I've had occasion to use the mdf especially designed for audio no> boxes.(can be gotten at most automotive sound shops) no> It's of a finer construct material and is sealed on the outer surfaces no> rather than the more coarse, open grain stuff you get at home building no> supply stores. It's also thicker( 7/8 for what we used) and is easier no> to apply paints or finishing coats to.

no> I talked to a fellow online that was attempting to use wonderboard to no> build a set of boxes, though I never heard how it worked out.

Speaking of experimenting, how about making an enclosure out of a semi-rigid shell perhaps 1/4" thick (aluminium alloy?) but lined on the inside with sonopan glued to its inner surface? It would lose some efficiency but it could then be much lighter weight. I've seen a similar sandwich construction used in quieting ventilation baffles for mainframe computers so it isn't a new idea.

A*s*i*m*o*v

... A stereo system is the altar to the god of music.

That's similar to Aerolam/bitumen idea except that the Aerolam is lighter but stiffer for any given thickness and its lightness makes the damping layer work more effectively.

Kal