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Old 13th September 2001, 08:04 PM   #1
Vivek is offline Vivek  India
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Hi guys,
How does one calculate enclosure dimensions for a speaker box? Is there any ratio involved?
Thanks for any help.
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Old 13th September 2001, 09:57 PM   #2
Super is offline Super  United States
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Yes, the volume of a box is one of the most important factors in designing a speaker, especially in relevance to bass. The actual dimensions arent as important though, considering there are many shapes of enclosure types. Rather, its the volume inside the enclosure that makes the greatest difference. The TS parameters of the driver are what can help you determine what box dimensions to use, and there are many fine examples of enclosure design software. What kind of speaker are you looking to build?

By the way, I'm sure someone will go into mention about the golden ration a little later
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Old 14th September 2001, 08:49 AM   #3
Vivek is offline Vivek  India
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Hi,
I have designed bookshelf speakers with WxHxD=23.25x37.62x14.37 (all in cms). I want to have more depth and less width and height. Now, can I just make arbitrary changes in the box or is there a procedure in doing so?
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Old 14th September 2001, 08:11 PM   #4
Super is offline Super  United States
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Sure, you can make the speakers deeper and shorter. When adding to the depth, make sure to reduce the size of your other dimensions accordingly. Find the volume of your current calculations, and just make sure that any changes you make multiply out to the same volume. If you have a certain depth in mind, choose either the width or height you want as well, and plug in x for the other variable. Set the whole equation equal to your volume, and you'll have the dimension for your other side. For example

If you want your height to be 20 cm, and your depth to be 60 cm with a volume of 48000 cm^3, your equation would be
20 * 60 * X = 48000, which would give you a width of 40 cm to meet the necessary volume.

As long as your internal volume stays the same, you should have no problem. Just make sure to compensate for any added bracing, the volume the drivers occupy, and for extremeists, any stuffing or lining you use. Also make sure that if the enclosure is ported, that the port length doesnt exceed the internal dimensions of the box. Good luck!

Bryan



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Old 14th September 2001, 10:25 PM   #5
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There are many people who advise the use of the "Golden Ratio" for speaker cabinets. This is supposed to attenuate standing waves inside the cabinet. It only matters when the enclosure becomes larger than the shortest wavelength of the enclosed driver. From the dimensions given, your bookshelf speakers appear to have been built with the "Golden Ratio" in mind.

The "Golden Ratio" has the dimensions being x, 0.707x and 1.414x. A cabinet that measures 7" x 10" x 14" is an example of this. NOTE: It doesn't matter which of the numbers is height, width or depth.

Good luck.
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Old 15th September 2001, 11:42 AM   #6
Vivek is offline Vivek  India
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So I can switch box width, height or depth, but the measurements have to remain the same, Right?
Thanks guys.
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Old 15th September 2001, 02:03 PM   #7
Super is offline Super  United States
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They don't necessarily have to remain the same, but they are fine as they are. Minor changes to dimensions can be made, as long as the internal volume is the same. But other than that, you are correct in assuming that you can switch your height, width, or depth for any of the measurements you calculated.
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Old 15th September 2001, 11:17 PM   #8
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An alternative is simply to make the walls of the cabinet non-parallel. That's why you see so many speakers that are pyramidal in shape--there are no internal standing waves to worry about. Takes care of numerous problems at once, although the woodworking is somewhat more complicated.

Grey
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Old 15th September 2001, 11:32 PM   #9
Simon is offline Simon  England
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..... Thoth

Sorry, I think you've made a mistake there...

x, 0.707x and 1.414x doesn't look like a golden ratio.
Mode orders B & C are multiples - this would give you bad standing waves.

There are many 'golden ratios' - some obviously more practical than others.

x, 1.6x, 2.3x is a good one.

Interestingly these golden ratios make good listening room proportions too (for obvious reasons).

Simon
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Old 16th September 2001, 05:07 AM   #10
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Quote:
Originally posted by Simon
Thoth

Sorry, I think you've made a mistake there.

There are many 'golden ratios' - some obviously more practical than others.

x, 1.6x, 2.3x is a good one.

Interestingly these golden ratios make good listening room proportions too (for obvious reasons).
Simon,

You're right. I remembered the WRONG golden ratio. There are several RIGHT golden ratios, some of which are based on the Fibonacci series. Sorry, my mistake.

I checked my archives, and found the following possibilities, all of which should work fairly well for speaker enclosures:

x, 1.14x, 1.39x
x, 1.26x, 1.59x
x, 1.28x, 1.54x
x, 1.60x, 2.33x
x, 1.62x, 2.62x

If there are multiple sealed compartments within the enclosure, this applies to those compartments, individually. The goal for using enclosures with the golden ratio is that a frequency that will resonate in one direction is unlikely to resonate in another direction (no standing waves). Obviously, as the frequency gets higher, this becomes less likely to be true. On the other hand, as the frequency gets higher, there is less likelyhood that the driver for that frequency will use the enclosure as a resonant chamber, and a greater likelyhood that the speaker stuffing will absorb that frequency.

Grey is also right that sloped sides make this unnecessary. What he didn't say is that the speakers require better woodsorking tools and skills. Also, for many of us, these enclosures would have a lower SAF (Spouse Acceptance Factor).
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