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Old 5th December 2012, 12:32 AM   #21
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Theres no advantage in using irrational numbers. You can use normal numbers like 3,5 and 7.
2 x an odd number is even, you just push potential issues up an octave (giving a better cahnce of killing it with damping)

And if you are getting multipliers of 5 or 7 you now have a quarter-wave line (if it was a BR) or 1/2 wl (if sealed)

2 x an irrational number is still irrational.

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Old 5th December 2012, 12:47 AM   #22
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My understanding is that the golden ratio is one of several ratios for internal dimensions of a speaker cabinet that is such that the harmonics of each dimensions resonant frequency don't double up with the harmonics of resonant frequencies produced by the other dimensions of the box. I think 1.41 was another good one. I did the calculations back in the 1980's for several ratios. You divide the distance between the two parallel walls into the speed of sound (1128ft/sec) to get the fundamental resonant frequency, and then add this fundamental frequency to itself over and over to get the harmonics (integral multiples). If the fundamental resonance was 500HZ for example, you'd have resonant harmonics at 500, 1k, 1.5k, 2k, 2.5K and so on, until any kind of damping material starts to absorb the sound energy, at which point the amplitude of the resonances will roll off. Gluing 1/4 inch thick (or more) upholstery padding to the inside walls of the enclosure (or equivalent) is perhaps the most important thing you can do though. Especially in any corners. I glue this padding to the front outside of the enclosure as well to minimize cabinet radiation and edge diffraction. Foam rubber works real well too.

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Old 5th December 2012, 01:41 AM   #23
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to completely kill a standing wave you need to pass it thru at least a 1/4 wl of damping.

dave
So in a subwoofer, how are you ever going to fit in that amount of damping? You cant and therefore you will never kill the standing wave.
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Old 5th December 2012, 01:44 AM   #24
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Quote:
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2 x an odd number is even, you just push potential issues up an octave (giving a better cahnce of killing it with damping)

And if you are getting multipliers of 5 or 7 you now have a quarter-wave line (if it was a BR) or 1/2 wl (if sealed)

2 x an irrational number is still irrational.

dave
in practice its never going to be irrational though is it? It will always be rational and finite.
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Old 5th December 2012, 01:51 AM   #25
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So in a subwoofer, how are you ever going to fit in that amount of damping? You cant and therefore you will never kill the standing wave.
Typically in a subwoofer none of the dimensions are long enuff to support a standing wave. You do instead have the issue of ballooning.

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Old 5th December 2012, 01:54 AM   #26
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Typically in a subwoofer none of the dimensions are long enuff to support a standing wave. You do instead have the issue of ballooning.

dave
wouldnt the rear wave still pass through the woofer if its undamped?
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Old 5th December 2012, 01:55 AM   #27
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in practice its never going to be irrational though is it? It will always be rational and finite.
Actually since the actual dimension is only close to what you intend to cut, and there are infinitely more Irrational numbers than Rational numbers, statistically you are more likely to have an irrational dimension/ratio -- no matter what the units.

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Old 5th December 2012, 01:58 AM   #28
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wouldnt the rear wave still pass through the woofer if its undamped?
That happens irregardless. Damping will take some energy out of the back wave (a vent of any sort will to), but you are not dealing with standing waves.

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Old 5th December 2012, 02:01 AM   #29
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is that possible though considering that there are not infinitely many atoms that make up mdf so it will never be an irrational length. What do you mean there are infinitely many more? You will have to explain that in more detail.
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Old 5th December 2012, 02:08 AM   #30
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Those atoms can be in an infinite possible places so that there are a finite number of them makes no difference.

The practical minimum unit of concern is a function of the highest frequency the device will reproduce.

And i'd never use MDF for a woofer enclosure.

As far as the concept of an infinity of infinities, you'd have to see the proof to realize the reality of that. Beyond the scope of the forum. Rudy Rucker has both a text book & a science fiction (White Light) book that try to get the idea across.

Integers & Rational numbers belong to Aleph nought, irrational numbers (& Reals) are part of aleph 1.

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