I need dimensions for a 4 cubic feet speaker box?

Question

I need dimensions for a 4 cubic feet speaker box?

Answer 1

Excluding more complex design criteria such as diffraction loss, etc., when it comes to the most basic rectangular loudspeaker enclosures one of the preferred design practices is to use the “golden ratio” to derive a set of optimal dimensions.



First, take the desired enclosure volume and convert it into a more precise (‘working’) unit of measurement - in your case inches. 1 cubic foot equals 1728 cubic inches; therefore 4 cubic feet equals 6912 cubic inches.



Next, take the cubed root of the total volume, 6912 cubic inches. The result becomes the basic working dimension of the enclosure. For a 6912 cubic inch enclosure this will be 19.0488 inches.



Now take 19.0488 inches and multiply it by the quantity (-1 + √5) ÷ 2, or 0.6180339887, and you will obtain one of the other ‘optimum’ dimensions, which should be 11.7728 inches for the smallest internal dimension for your enclosure.



Finally, take the initial 19.0488 inch result and multiply it by the quantity (1 + √5) ÷ 2, or 1.6180339887, and you will obtain the remaining optimum dimension, which should be 30.8216 inches for the largest internal dimension for your enclosure.



If you wish to verify the validity of your calculations simply multiply the three results together and you should obtain almost exactly the original enclosure volume. Thus, (11.7728 in.)(19.0488 in.)(30.8216 in.) = 6911.9993 in³ approximately. Again, I have to emphasize that it is very important to remember that all of the dimensions above are INTERNAL enclosure dimensions. Also please note that if you prefer you can safely round each of the derived dimensions to the nearest half-inch (0.50 in) without incurring any detrimental consequences.



Therefore the dimensions that many would consider to be optimum for a simple rectangular loudspeaker enclosure with a total internal (box) volume of 6912 cubic inches would be 12.0 in. × 19.0 in. × 31.0 in., approximately.



One other equally popular loudspeaker enclosure design is the equal depth and width design, to which the “golden ratio” may be partially applied. This will produce internal enclosure dimensions with an approximate internal width and depth of 16.2258 inches and an internal height of 26.2538 inches, which for the sake of convenience may be rounded to 16.0 in. × 16.0 in. × 27.0 in. (Though the dimensions of 16.0 and 27.0 inches are a little further from the golden ratio dimensions than the preceding results above they are still more than adequate to help minimize resonances.) Other than this one exception (including compact subwoofer enclosures,) as a general rule of thumb when designing and constructing full-range loudspeaker enclosures you should attempt to avoid using any set of dimensions where one dimension is an integer multiple of another.



On a final note always be sure to use plenty of bracing (preferably dadoed and glued in place) for any loudspeaker enclosure this size. Doing so will also help increase the effectiveness of any applied mechanical damping materials by raising the resonant frequency of the enclosure. The intent is to always produce as rigid and mechanically inert a loudspeaker enclosure as possible.



Note: assuming you haven’t already done so..., depending on the quantity of acoustical damping material, the amount of bracing that you use, the volume occupied by the drivers, passive crossovers, sub-enclosures, vent ducts, etc., you may need to add a small amount (rarely more than 10%) of additional volume to the overall internal enclosure volume (which hopefully was calculated using the Thiele-Small parameters for any low and low-mid frequency drivers that you’re using,) BEFORE settling on the final enclosure dimensions.



######## RESOURCES ########



Wiki: Golden Ratio

http://en.wikipedia.org/wiki/Golden_rati...



Loudspeaker Design Cookbook

http://www.audioxpress.com/bksprods/prod...



audioXpress (Old Colony) Loudspeaker Reference Books

http://www.audioxpress.com/bksprods/BKSL...



Best way to build your own speaker box?

http://answers.yahoo.com/question/index?...



Beginner speaker building kits?

http://answers.yahoo.com/question/index?...



What is the best enclosure for sub woofer speakers?

http://answers.yahoo.com/question/index?...



Does anyone know of a site that sells good empty home subwoofer enclosures?

http://answers.yahoo.com/question/index?...

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Acousta-Stuff

http://www.partsexpress.com/pe/showdetl....

 

Answer 2

Imagine using a box measuring

in internal dimensions 12" x 12"

x 12".  And then putting 4 boxes

into a larger box. There you'd get

4 cubic feet. So to convert into a

speaker box size, measure 48" x

48" x 48" then divide it by 1,728,

which would give you 64" to work

with.  So therefore, for example,

you could build a box measuring

(internally) 36"H x 16"W x 12"D.