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Sealed enclosure -- golden ratio?
Sealed enclosure -- golden ratio?
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Old 19th December 2009, 06:56 PM   #21
Charles Darwin is offline Charles Darwin  United Kingdom
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With regards to standing waves: Is a sphere really a good idea?
It does replace the three fundamental standing waves possible in the 'normal' rectangular box shape by one.
Would an egg shape not be better?
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Old 19th December 2009, 07:18 PM   #22
picowallspeaker is offline picowallspeaker  Italy
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standing waves occur when ,inside a box or a room , we have two or more parallel faces ,depending in which fluid they propagate ,in our case air , they cause a peak at certain frequencies . In a tall cabinet is easy to find them ,specially low frequencies . The bad thing is that they interact with the movement of the membrane,also.Or they propagate trough the surfaces.An egg made of iron would be good...
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Old 19th December 2009, 07:43 PM   #23
skeptic43 is offline skeptic43  United States
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Quote:
Originally Posted by Charles Darwin View Post
With regards to standing waves: Is a sphere really a good idea?
It does replace the three fundamental standing waves possible in the 'normal' rectangular box shape by one.
Would an egg shape not be better?
Egg shaped speakers have already been comercialized. However, I can't recall the brand name of the speaker.
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Old 19th December 2009, 08:31 PM   #24
Conrad Hoffman is offline Conrad Hoffman  United States
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IMO, a "near cube" has advantages because the panels will be as small as possible for a given volume. More rigid, higher resonant frequencies. Still, I prefer an irregular box. There have been lots of references to "monkey coffins" in other threads and of the dozen or so speakers I've built (not a huge number I admit), the irregular boxes always had the cleaner sound, particularly the lower midrange. Conventional boxes, including the golden ratio boxes I've built, were never as good. I don't think standing waves and reflections are an issue with a stuffed box, as long as it isn't super shallow, only how the box structure vibrates and radiates. It's not that much harder to cut the panels to slope the front or back. Regardless, materials and bracing, not to mention drivers and design, probably trump shape as far as the final result.

CH
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Old 19th December 2009, 09:16 PM   #25
wintermute is offline wintermute  Australia
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Sealed enclosure -- golden ratio?
I bookmarked this Post by GM ages ago. http://www.diyaudio.com/forums/multi...643#post300643 Worth a look if you want to try some different ratios, which GM says many of which are actually better than the golden ratio when it comes to speakers Though I do find the 1:1.4:2 one to seem a little unlikely (due to one of the dimensions being double the other)....

The way I dealt with the problem myself for my small (5L) enclosures was to use prime numbers for each of the W X H X D dimensions... no chance of any of them being a multiple of any other 151 X 173 X 211 = 5.5L which works out nicely for a target of 5L (using the 10% over rule of thumb).

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Old 19th December 2009, 11:20 PM   #26
planet10 is offline planet10  Canada
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Sealed enclosure -- golden ratio?
Quote:
Originally Posted by gedlee View Post
The way you said it the first time was incorrect.
I don't see that.

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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.
It doesn't take a lot of box resonance to contribute to reducing the downward dynamic range of a loudspeaker. And the research Toole presents shows that the low Q event is more audible despite the peak level being lower.

dave
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Old 19th December 2009, 11:28 PM   #27
planet10 is offline planet10  Canada
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Sealed enclosure -- golden ratio?
Quote:
Originally Posted by skeptic43 View Post
Egg shaped speakers have already been comercialized. However, I can't recall the brand name of the speaker.
Waveform Mach 17 (were made in Canada)

Click the image to open in full size.

dave
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Old 19th December 2009, 11:30 PM   #28
planet10 is offline planet10  Canada
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Sealed enclosure -- golden ratio?
Quote:
Originally Posted by wintermute View Post
Though I do find the 1:1.4:2 one to seem a little unlikely (due to one of the dimensions being double the other)....
Exactly why i suggested one be careful using root(2)

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Old 19th December 2009, 11:36 PM   #29
Joachim Gerhard is offline Joachim Gerhard  Germany
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I tried all kind of shapes and forms and without damping material they all had an impedance "blimp" in the fundamental tone range independent of shape. Some damping material removes that usually. I use only so much that the small wrinkles in the impedance curve disappear. It is best to look at phase because that is more sensitive. Another solution is an internal Helmholz resonator tuned to the problematic frequency.
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Old 19th December 2009, 11:38 PM   #30
planet10 is offline planet10  Canada
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Sealed enclosure -- golden ratio?
Quote:
Originally Posted by Conrad Hoffman View Post
IMO, a "near cube" has advantages because the panels will be as small as possible for a given volume... the irregular boxes always had the cleaner sound, particularly the lower midrange.
Althou a cube contains more volume with less material, that does not necessarily lead to a better panel. One of the cardinal rules of bracing a panel is that the subpanels have a higher aspect ratio than the original. A panel tends to vibrate across its smallest dimension and being smaller is at a higher frequency.

A square panel has 2 reinforcing modes, and for its area the lowest resonant frequency.

A trapezodal panel (or subpanel) is even better (assumming that the "short" dimension is the non-parallel one).

dave
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