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Old 6th April 2012, 11:20 PM   #1
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Default enclosure: is having all sides different lengths beneficial?

hi,

when making a box, is using an asymmetrical design using panels with no matching lengths a good thing/worth the effort?

for example i can make the sides vary in length by 2x18mm, not a whole lot but is it worth while in conjunction with stuff like golden rule dimensions?

next mini question, mixed material boxes. i only have access at present to 6mm baltic birch, meaning if i want 18mm i'd have to stack and glue it. given the 2 camps of enclosure design, heavily damped or high resonance, can i just use 12mm MDF external faces, then the 6mm birch ply on the internal faces (or vice versa). using the stacks like that would also let me use a half rabbet joint without using a router etc which would increase the box strength and reduce the need for bracing?

thanks for your help
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Old 6th April 2012, 11:46 PM   #2
fakeout is offline fakeout  Canada
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I have a different question, do tubular or spherical cabinets sound better? (If you don't mind an additional question.)
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Old 6th April 2012, 11:57 PM   #3
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Originally Posted by fakeout View Post
I have a different question, do tubular or spherical cabinets sound better? (If you don't mind an additional question.)
i asked a similar question in a previous thread, not sure if that helps your answer really, but gladly ask away i'd like to know too.

cross sectional area shapes
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Old 7th April 2012, 01:20 AM   #4
fakeout is offline fakeout  Canada
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Can anyone comment on the sound of PVC pipe speakers? PVC sewer pipe speakers
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Old 9th April 2012, 09:26 AM   #5
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Quote:
Originally Posted by gafhenderson View Post
when making a box, is using an asymmetrical design using panels with no matching lengths a good thing/worth the effort?
Depends on the design goals, and cabinet type / size in question. Asymmetry can be useful, it can also be more trouble than it's worth. Some form of acoustic ratio can be worth having, but differences tend to be more significant with larger enclosures.

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can i just use 12mm MDF external faces, then the 6mm birch ply on the internal faces (or vice versa).
You can, but depends on what you are trying to achieve, your particular design goals, the panel dimensions & bracing employed.

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I have a different question, do tubular or spherical cabinets sound better? (If you don't mind an additional question.)
You need to say what you mean by 'better.' Better than what?

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Can anyone comment on the sound of PVC pipe speakers?
Not really, since this implies that all speaker enclosures made from PVC pipe sound the same, rather than having an output that reflects their alignment and design goals. Generally speaking, you don't want the build material to audably affect the end result.

Last edited by Scottmoose; 9th April 2012 at 09:29 AM.
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Old 9th April 2012, 09:45 AM   #6
dangus is offline dangus  Canada
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It's best to avoid internal dimensions that are even multiples or something. According to "High Performance Loudspeakers", a ratio of 2.3:1.6:1.0 is supposed to "provide minimum excitation of standing-wave modes." Non-parallel sides may be even better.

If the box is well-stuffed, though, standing waves will be much less of a problem.
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Old 9th April 2012, 10:47 AM   #7
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Originally Posted by dangus View Post
It's best to avoid internal dimensions that are even multiples or something. According to "High Performance Loudspeakers", a ratio of 2.3:1.6:1.0 is supposed to "provide minimum excitation of standing-wave modes."
Depends on the box type. This assumes we're discussing enclosures intended to have ~uniform air particle density and no standing waves present -when it comes to enclosures intended to generate / use standing waves, it becomes somewhat more complicated. Either way, larger boxes tend to benefit more from acoustic ratios (there are quite a few) than smaller, especially if the latter are carefully damped, as you mention.

Non parallel walls can be useful; they can also be more trouble than they're worth -as Linkwitz observes (IIRC he was talking about rooms, but that's exactly what a speaker cabinet is), you can end up making life harder for yourself by making resonant frequencies less predictable. YMMV as ever.

Last edited by Scottmoose; 9th April 2012 at 10:49 AM.
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Old 9th April 2012, 01:04 PM   #8
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thanks for the reply Scottmoose.
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Old 9th April 2012, 01:31 PM   #9
pooge is offline pooge  United States
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Quote:
Originally Posted by fakeout View Post
I have a different question, do tubular or spherical cabinets sound better? (If you don't mind an additional question.)
They have inherent structural advantages. There is less surface area per volume enclosed, so for a given volume, there is less surface area vibrating.
Also, the surface can vibrate less because it is inherently stiffer. Pressurization inside tries to stretch the tube into a bigger circle, so a material with even a so-so tensile strength can reduce surface vibration due to internal pressurizations when compared to a large flat panel where material stiffness, thickness, weight, and damping are needed to minimize panel vibrations.

An enclosure, if tubular on the outside with a driver mounted on the side of the tube, can also minimize diffraction. However, depending on the frequency band of the driver, baffle loss may come in to play at lower frequencies, reducing the power output of the driver.

Regarding internal volume, a tubular volume in theory can cancel standing waves at the driver location. There was a paper in AES Journal a couple of decades ago about this, but it was just mathematical, and no actual measurements were made to confirm the theory.
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Old 9th April 2012, 01:49 PM   #10
pooge is offline pooge  United States
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Quote:
Originally Posted by gafhenderson View Post
when making a box, is using an asymmetrical design using panels with no matching lengths a good thing/worth the effort?
Can be. The larger the box, the bigger the panels, and the easier it is for them to vibrate. If they are all the same size, they will vibrate at the same frequency, thus adding their vibrations at that frequency for greater loudness of that vibration. This can be minimized by adequate bracing, dissimilar sized panels, or possibly bracing differently for each panel so they are effectively "sized" differently in their respective open spans. Again, a lot depends on the frequency band of the drivers enclosed. As far as standing waves go, there isn't any if the wavelengths of the driver are so long that standing waves cannot be supported, as in a subwoofer or bass cabinet. The enclosure is equally pressurized. Different sized panels will not matter regarding standing waves. At higher frequencies, enclosure volumes is smaller, wavelengths are shorter, and stuffing can attenuate standing waves more effectively.

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next mini question, mixed material boxes. i only have access at present to 6mm baltic birch, meaning if i want 18mm i'd have to stack and glue it. given the 2 camps of enclosure design, heavily damped or high resonance, can i just use 12mm MDF external faces, then the 6mm birch ply on the internal faces (or vice versa). using the stacks like that would also let me use a half rabbet joint without using a router etc which would increase the box strength and reduce the need for bracing?
Laminating different materials is an excellent way to construct, as the different stiffness and damping properties of each laminate can offset the weaknesses of the other.
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