Curved sided speaker enclosures, why? - diyAudio
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Old 20th January 2009, 08:34 PM   #1
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Default Curved sided speaker enclosures, why?

Some people are building curved enclosures (like the one in this picture) rather than the usual coffin shape. There must be a good technical reason for doing this and I am wondering if someone out there could explain.

I'm going to build a couple of three-way speaker enclosures and would make them curved if it's worth all the effort.
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Old 20th January 2009, 08:50 PM   #2
HK26147 is offline HK26147  United States
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In your posted example: because internally there are less parallel walls to cause standing waves
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Old 20th January 2009, 10:29 PM   #3
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Visually curved shapes reduce the appears of size. While acoustics plays a role in curved cabinets, I believe the primary one is appearance. It looks more visually appealing, and has the effect of reducing the visual presence a speaker has in a room. My brother, who works as a communications designer, told me that while at Syracuse University, they spent multiple weeks just on the subject of how the eye wraps around various shapes, and how best to design things for certain visual impacts, or in this case, lack of visual impact.
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Old 20th January 2009, 10:36 PM   #4
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The stiffness of curved walls may be higher than that of straight walls.

I don't believe in the standing wave theory, but it's moot IMO since most people stuff their enclosures.
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Old 20th January 2009, 11:03 PM   #5
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I'm a little bemused as why you don't beleive the standing wave theory. Surely there has been enough scientific research into this. The sphere being the perfect shape for a loudspeaker.
Curved loudspeaker cabinets have been hard and expensive to make. Now with the improved technology the enclousures can be manufactured at a very resonable price.
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Old 21st January 2009, 02:57 AM   #6
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Unfortunately the curved sided "reduced standing waves" isn't really correct... you do get a change vs. parallel wall boxes, but you don't get a significant reduction in total. Besides the real problem isn't "standing waves" as much as it is simple reflected energy. At LF the shape of the box has almost no effect. As you go higher in freq the shape starts to have an effect, but if you've got no absorption on the inner walls, then the level of internal reflected energy is so high that I'd not worry much about "standing waves" at all...

One can compare the internal effect of "shape" with the external effect of shape vs. freq response... except (again) most external surfaces can not be made absorptive, whereas internal surfaces can. And the problems are related to freq vs. dimensions, where higher freqs can be absorbed or attenuated, and lower freqs don't care about the smaller dimensions vs. freq...

I vote for the aesthetic design being the driving force, and that CNC routers make the more complex box shapes feasible from an economic and production point of view.

Fwiw, I don't subscribe to the "egg" or "sphere" is best school of thought when we're talking about interal reflections or resonances... for the external shape, there is clearly a difference, especially as the size of the egg/sphere goes up WRT frequency.

Just my opinion... ymmv.

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Old 21st January 2009, 04:52 AM   #7
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Quote:
Originally posted by delphiplasma
I'm a little bemused as why you don't beleive the standing wave theory. Surely there has been enough scientific research into this. The sphere being the perfect shape for a loudspeaker.
Curved loudspeaker cabinets have been hard and expensive to make. Now with the improved technology the enclousures can be manufactured at a very resonable price.
Er, what exactly are you trying to say?
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Old 21st January 2009, 05:51 AM   #8
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Quote:
Originally posted by delphiplasma
I'm a little bemused as why you don't beleive the standing wave theory. Surely there has been enough scientific research into this. The sphere being the perfect shape for a loudspeaker.
Curved loudspeaker cabinets have been hard and expensive to make. Now with the improved technology the enclousures can be manufactured at a very resonable price.
Let's start here... the difference between a good speaker and a really good speaker is what it does WAY down (for the sake of a number, to quote Bill Perkins, 40 dB down (from the average signal)).

Curved (and slanted or pyrimidal) boxes 1st started in the high end, and it was primamrily for the sonic benefits.

They do reduce the standing waves by creating non-parallel walls. (a slant is probably better than a curve in this respect, but only marginally). Instead of only having the potential for a single high Q resonance, you end up with a much lower Q wider bandwidth resonance problem. This is much less obvious sonically, if excited. To be excited the driver needs o be emitting sound at frequencies that could excite the resonance.

That brings us to reason number 2... a curved wall is -- all things equal -- stiffer than a flat panel (much stiffer in most cases), so it resonates at a higher frequency so is much less likely to get excited (especially if the driver's bandpass does not extend up that high). As an example lets consider the big B&W 800 Nautilus series... the bass drivers are not going high enuff to exite side-to-side standing waves so the sides are all about stiffness (from an engineering POV*). You'll note that these boxes also have non-parallel top & bottom where the woofer might get high enuff to excite a standing wave. An interesting consequence of the curved sides is that it is generally easier to make them with multiple layers of thing plywood, which further stiffens things.

(and this takes us to 3, aesthetics... that these are generally more pleasing than a rectangular money coffin is what got then past the cost accountants.

Once the high end exposed the concept to the general public, we find that the price point keeps coming doen, and in a lot of cases it is purely the looks doing it... a curve created with a kerf for instance throws away alot of the stiffness advantages. But not always... look at the PE boxes... they have rectangular ones that jut aren't very good (they need lots of added bracing). To get the new cury ones, the sides are made of 6 lyers of 1/8" MDF (ie MDF plywood) and the walls are dramatically stiffer. These are quite reasonable boxes -- i'd replace the baffles with ones made of ply, but the target audience is unluckly to have the facilities to do that. The MDF is on the soft ide and it is fairly easy to damage them.

dave
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Old 21st January 2009, 06:50 AM   #9
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If done well, curved designs are stiffer than flat-walled ones. The diffraction properties of their surfaces are different as well.

To quote a famous audio guru: "No one builds pressure vessels and submarines with flat walls - so why should a speaker be built with flat walls ?"

To be honest: I also build my speakers with flat walls for two reasons:

- simplicity
- lazyness

Regards

Charles
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Old 21st January 2009, 07:24 AM   #10
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Quote:
Originally posted by delphiplasma
The sphere being the perfect shape for a loudspeaker.
For the outside of a loudspeaker (actually the shape used in the B&W Nautilus 801 is better). For the inside of a loudspeaker it is worst.

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