Shape of the loudspeaker box

[r_s_dhar]

Hello all,

text books say that the shape of the loudspeaker box should follow a golden rule in terms of dimensions. The nearest convenient ratio of this dimension would be 4:3:2 (I think!). does anybody know how those beautiful floor-standing tower models violate this rule and still get away with it, acoustics wise? As I understand it, towers are a sort of square pipe and may develop self-resonance at certain frequencies. Am I right?

[SimontY]

Hi,

You're slightly off with the 'convenient' dimensions I'm afraid. The idea is that multiples of the same dimension don't occur. 4:3:2 clearly won't be any good, as 2x2=4!

With each dimension there is the frequency the standing wave will occur at, then every multiple of that frequency will exist too, at least until they are broken up or absorbed by other materials in the box. These are called f2, f3, etc.

The idea with these golden ratios is there will be the smallest possible buildup of peaks, hence ideal numbers that dont divide into one another. It is exactly the same problem with room modes, except these are almost impossible to cure! Eg. a room could have the same width and height, and be twice as long - this will produce peaks at the same bass frequencies from all 3 dimensions, and sound awful!

Hope this helps!

btw, I doubt many cheaper commercial speakers follow any particlular golden rules, they probably go for looks first...

-Simon

[Ken L]

Originally posted by r_s_dhar
,...text books say that the shape of the loudspeaker box should follow a golden rule..

Golden ratio is 1x1.618x1.618

Sooo a speaker that has the dimensions 10x16x26 in any combination would conform to golden ratio formula.

The golden ratio is no _magical ratio_ that has special properties. However, it is a convenient and easy method for getting good proportions in order to prevent problems with waves.

10 plus 16.18 give the third number 26.18, and so on in a Fibonacci series.

If you search on the internet you are bound to find that these ratios and formulas have certain cosmic and mystical properties, can make you healthy, wealthy and wise in addition to leading a charmed life.

In the event that you believe that in fact there is mystery and magic at work here, there's some low-country swamp land I would love to see if you are interested in buying

_big grin_

regards

Ken L

[Ron E]

Golden ratio doesn't matter that much.

10+ times more effective than dimension ratios or nonparallel walls or whatever geometric solution someone might brag about is damping material.

All boxes have self resonance, not just towers. Damping material minimizes this.

[Bull]

Or you could build speaker boxes trapzoidal shape [curved sides smaller back and bigger front.

[wintermute]

A quote from David B Weems "Designing, Building and Testing your own speaker system 4th ed": P27.

Placing the driver at a point which is 1/5th the distance from the top of the pipe suppresses the 5th harmonic, a major cause of resonance in closed pipes

The pipe in this case being a tall skinny speaker box. The other thing you might find is that the box is partitioned and the bottom half is nothing more than a stand.

Regards,

Tony.