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Subwoofers Why a cube shape?


GWklipsch

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I wonder if a few of you who know about subwoofers could discus why they are often built with a cube shape. I ask this because after reading a few books on speaker building

they all seem to agree that a cube is the worst shape to build a speaker.My guess is that it has something to do with getting more low end output with less power. I would really like to understand this better.George

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My thoughts,

The cube is a bad shape for the listening room because of the sharp resonance at one particular frequency. But in a sub box this would seem to be an advantage. It would amount to a strong controlled resonance which would complement the sub's woofer.

That's my take on this subject. I do realize that there is a lot going on between the driver, it's box, and it's operating room. A lot more than this simple explanation. It is about getting more output as well as providing good control.

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John P

St Paul, MN

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I understand the idea of a box, of course with corners would seem very wrong for a sub woofer enclosure. I always felt that a tubular ported design seem very natural. But as physics plays all parts of the critical and theoretical design process such as porting or not, fold cavities and space and volume design practices all come into play. Terminology such as "orders" by design as far structure and crossover configurations etc. I have read books and attended classes on speaker design and still I have reservation. I have experimented using CAD programs and design software and still it comes down to bang for the buck. What works best for the total cost of getting the product to market and having the end users ecstatic about the product?

Kurt

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A lot of subwoofers (SVS, Hsu, Gallo) don't use cubes, they use cylinders or spheres.

I think it comes down to fact that if you're a speaker manufacturer, and you've got tooling to build other cabinets, it's cheaper and easier to build a square box than some other shape. Also, square boxes look more "normal" which helps with acceptance by other family members.

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I think Stig has the answer. It is more a question of why a cube is not used elsewhere.

In other direct radiator speakers, i.e. where the bass cabinet and driver are used up to, say 600 to 2000 Hz, we want to make sure that the internal dimensions of the box H, W, D are different.

To some extent, the inside of the box will form a resonant tube (closed on each end) with a length equal to the H, W, and D. (This is a simplied explanation.) The worst case would be if all three dimensions are equal to effectively form three "tubes" of identical length.

With a sub though, there is little or no high frequency power being provided by the driver. Therefore, the relative dimensions don't make a difference, as long as they're a small fraction of a wavelength. Even if there is a potential for resonance, it is not excited. As pointed out above, the wavelengths fed to sub are just too long.

There is something to be said for avoiding long panels in the sub. The cube shape avoids this.

Of course, if you are designing a ported sub, you may wind us using a long pipe. So then you need a longer container in which to fit it, or will have to fold the pipe.

That is my read.

Gil

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Well, first of all my M&K isn't an exact cube, but what do you propose is better? A Tube? a sphere? a pyramid? The tube is probably the best of the three(maybe over all) but integrating an amp in could be tricky, and a large portion of subs are powered now-a-days. Aesthetics plays a part as well as the fact that multiple drivers and large amps are easily fit into a "cube" configuration. It's not something your kids knock over either. Plain and simple - They are practical but not necessarily the sole best. It depends on what one wants to achieve...

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