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Sealed enclosure -- golden ratio?
Sealed enclosure -- golden ratio?
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Old 19th December 2009, 07:16 AM   #11
planet10 is online now planet10  Canada
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Sealed enclosure -- golden ratio?
Floyd's work only supplemented my supposition that a high Q resonance is better by providing research that shows a high Q resonance is less audible.

My reasoning for such a Q has to do with the energy available to excite a resonance and the distribution of energy in music.

This ties in with my box building philosophy of pushing panel resonances up as high as feasible. If one has a resonance and it is high Q then sustained energy in a very narrow bandwidth is required to excite the resonance.

In the unlikely situation where the resonance is excited, Floyd's research shows that it will be less audible than (with more available energy to excite) low Q resonance.

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Old 19th December 2009, 08:45 AM   #12
gedlee is offline gedlee  United States
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Quote:
Originally Posted by planet10 View Post
Floyd's work only supplemented my supposition that a high Q resonance is better by providing research that shows a high Q resonance is less audible.

My reasoning for such a Q has to do with the energy available to excite a resonance and the distribution of energy in music.

This ties in with my box building philosophy of pushing panel resonances up as high as feasible. If one has a resonance and it is high Q then sustained energy in a very narrow bandwidth is required to excite the resonance.

In the unlikely situation where the resonance is excited, Floyd's research shows that it will be less audible than (with more available energy to excite) low Q resonance.

dave
Floyds work applied to acoustic radiated resonance, not box resonances. My reasoning goes as follows: If the resonance is high Q then there is a stronger likelihood of its rising above the background of "noise" in the sense of all the other types of aberations going on such as diffraction, other resonances, etc. and let's not forget the signal itself. Floyds work assumed that the resonances were such that they rose above the basline of the signal and his study went from there. If the level of the resonances never reach the baseline of the signal such that they add significantly to the output then his conclusions don't apply.

Pushing box resonances as high as possible is logical, I do the same myself, but the statement "If one has a resonance and it is high Q then sustained energy in a very narrow bandwidth is required to excite the resonance." is not correct. A high Q resonance takes less energy to excite than a low Q one - bandwidth is not relavent if we are talking about musical types of signals which are very impulsive and contain broadband excitation. Bandwidth would be relavent for steady state excitation. And High Q resonances ring longer - the ear masks less in time than it does in frequency.

Finally, Floyds results implied that the area under the resonance was what mattered, so yes, a narrow Q resonance at the same level as a broad one would be less audible. But thats not what happens with a high Q - its generally higher but narrower.

In the end its a guess either way since there are no direct studies to quantify this either way. But applying Floyds conclusions to the situation is a misnomer IMO.
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Old 19th December 2009, 10:10 AM   #13
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Sealed enclosure -- golden ratio?
Earl,

You are saying the same things as i am and coming to different conclusions. Since the resonance needs energy at its frequency the bandwidth is important, because the likelihood of music supplying the necessary energy is low. A low Q resonance can accept energy over a larger bandwidth. To figure which one requires more energy to excite you'd actually have to measure the area under the curve.

If a box resonance does not produce acoustic radiation then i don't see it as a problem. This makes you 1st argument moot.

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Old 19th December 2009, 10:35 AM   #14
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Earl,

You are saying the same things as i am and coming to different conclusions. Since the resonance needs energy at its frequency the bandwidth is important, because the likelihood of music supplying the necessary energy is low. A low Q resonance can accept energy over a larger bandwidth. To figure which one requires more energy to excite you'd actually have to measure the area under the curve.

If a box resonance does not produce acoustic radiation then i don't see it as a problem. This makes you 1st argument moot.

dave
Dave

We weren't saying the same things at all. The way you said it the first time was incorrect. You are now correct to say that it is the integral of the resonance times the excitation, but that is NOT at all what you said the first time. Its quite a bit different. Because the high Q resonance has such a large value at resonance it can easily equal the low energy level of the low Q excitation.

And your last point is meaningless because a box resonance ALWAYS produces radiation - its the level that is important. And thats exactly my point! If the level is low enough so as to not contribute significantly to the sound from the main driver then it doesn't mater, just as you say, BUT, the higher Q resonance IS MORE LIKELY to do that than the low Q one, not less.
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Old 19th December 2009, 11:11 AM   #15
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Sealed enclosure -- golden ratio?
hehe It's funny that I think that the golden ratio dimention boxes are ugly (I know that things in the golden ratio are supposed to be pleasing) I have a pair of golden ratio 70L boxes and frankly they look very "boxy" They are old school and have a wide baffle and shallow depth. I'm going to rebuild them sometime, I might stray from the golden ratio when I do but I will certainly be making the narrower dimention the baffle. I personally think having a narrow deep speaker looks much nicer than a wide shallow one.. also appears to take up less space

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Old 19th December 2009, 01:10 PM   #16
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I simply tried to answer the OP's question. GM box geometry is a good starting point for a noob building his first cabinet. It may be old school but is effective. Is it maximally effective? Maybe not, but alternative box shapes come with their own problems to solve.
Like most things associated with speakers building, there's no perfect way. Just a whole host of compromises.

Gedlee's cube comes with damping challenges and sloping front boxes can be a challange to build. Unless, of course, you are an accomplished carpenter. BTW, a sphere is the smallest shape for a given volume and structurally superior to a cube. About 20% lower surface area, but obviously, more difficult to build.

Last edited by skeptic43; 19th December 2009 at 01:13 PM.
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Old 19th December 2009, 01:42 PM   #17
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Gedlee's cube comes with damping challenges and sloping front boxes can be a challange to build. Unless, of course, you are an accomplished carpenter. BTW, a sphere is the smallest shape for a given volume and structurally superior to a cube. About 20% lower surface area, but obviously, more difficult to build.
I didn't say cube - please don't misquote me. And what exactly are the "damping challenges"? The box aspect ratio is not a factor in that.

And please, the lecture on the sphere! That's real practical to build and the volume to surface area rather is rather elementary. I excluded it for the obvious reasons.
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Old 19th December 2009, 02:00 PM   #18
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So, what's more important than box shape is the box materials ability to reflect sound?

(In simple terms)?

Concrete would be better than plywood for example?


If that's the case, you would think what's really important is the quality of the deadening material inside the enclosure?

Like a sound foam instead of "pillow stuffing"?
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Old 19th December 2009, 02:01 PM   #19
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And bracing too because any vibrating surface would create standing waves as well.

?
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Old 19th December 2009, 03:14 PM   #20
skeptic43 is offline skeptic43  United States
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Originally Posted by gedlee View Post
I didn't say cube - please don't misquote me. And what exactly are the "damping challenges"? The box aspect ratio is not a factor in that.

And please, the lecture on the sphere! That's real practical to build and the volume to surface area rather is rather elementary. I excluded it for the obvious reasons.
"nearly cube" might as well be a cube. Sorry for not precisely quoting you. The damping challenges are finding the right type and amount to accomplish the task. Could be a challenge for a noob.

Here's an exact quote from your prior post:
"The cube has the greatest internal volume with the least surface area." - wrong as a general statement which could mislead a noob. Hence the lecture.

Look, many here have gotten off on what I believe is a tangent other than what the OP asked for.
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