Golden ratios and standing waves

[Vikash]

Based on the consensus that: enclosures dimensions should optimally be derived using golden ratios to reduce standing wave effects, I have a question...

My enclosure volume is approx. 98l which I'm building into 244x418x962mm enclosure.

Using W=v/f, I caluclate standing waves at:
1393 Hz
813 Hz
353 Hz

If a golden ratio is used to derive box size: 280x467x747mm, then standing waves exist at:
1214 Hz
728 Hz
455 Hz

The offending frequencies are very close and I see no reason to closely adhere to the golden ratios? ( or have I missed something )

I was going to asymmetrically fill three walls with fiberglass to compensate.

Any comments?

[sfdoddsy]

Sorry to be a cynic, but what consensus? I find the Golden Ratio/Fibonacci etc interesting as an example of coincidental math, but some of the effects ascribed to it by Cardas and others just strike me as voodoo for impressionable audioholics.

Still, it can't hurt.

Cheers

Steve

[ALW]

http://www.acoustica.org.uk

Click on 'speaker positioning' and locate the Excel Spreadsheet, it may help analyse the issues.

Andy.

[Circlotron]

My opinion is that the golden ratio is of better use for the external dimensions of the box so that it looks "right".

but some of the effects ascribed to it by Cardas and others just strike me as voodoo for impressionable audioholics.

Fibonacci numbers are really great but I don't think it applies universally. I'm surprised that the revered *Magic Power Cords* are not in fact 1.6180339.... metres long.

[Vikash]

Just had a look at that spreadsheet. Looks like what I caluclated are actually second order harmonics, the fundamental freq's being half my calculations. How does each harmonic affect the sound - to what degree in amplitude?

At the moment, I think that all rectangular enclosures suffer more or less equally (irrespective of whether the dimensions are golden ratiofied)- and that the important thing is to make sure each dimension is (assuming all parallel walls) different - to avoid adding to another standing wave. Agree?

Edit:
By looking at the harmonics (occuring at each doubling of the fundamental) I've just realised that you need to avoid enclosure dimensions that are multiples of others, as the harmonics will re-inforce each other. I think I may have just justified the reasoning for golden ratios

[Christopher]

Excuse my ignorance, I'm still in the early stages of learning this stuff, but I've been wondering for a while; Doesn't using non parallel sides in an enclosure pretty much deal completely with this problem? I'm sure it's just not that simple, or else you would see no rectangular boxes and yet they abound.

Chris

[mcp]

Originally posted by Vikash
I've just realised that you need to avoid enclosure dimensions that are multiples of others, as the harmonics will re-inforce each other.

And it's the internal dimensions that's important.

[SY]

Originally posted by sfdoddsy
Sorry to be a cynic, but what consensus? I find the Golden Ratio/Fibonacci etc interesting as an example of coincidental math, but some of the effects ascribed to it by Cardas and others just strike me as voodoo for impressionable audioholics.

Steve, you've apparently had my house bugged.

Doesn't using non parallel sides in an enclosure pretty much deal completely with this problem?

No. It just means that the eigentones will not follow the same pattern as a rectangular box. A sphere doesn't have parallel sides, but it resonates quite nicely. Boxless is still the best (and can be pulled off easily, since you CAN box drivers which are reproducing wavelengths large compared to box dimensions without fear of standing waves). Second best is a box with adequate damping and designed with minimizing reflections back through the cone(s) in mind.

[Vikash]

mcp, here's are the standing wave modes for my current design. I see issues with (for example) the 3rd harmonic (height) and the fundamental (width) re-inforcing each other. Are these the problems you were seeing?

It seems clear to me now that using the golden ratios in my design would have resulted in much less overlap of standing waves harmonics. I'm convined of this reasoning now, though I have no idea how much affect this has

using non parallel sides in an enclosure pretty much deal completely with this problem?

My understanding of non-parallell walls is that you're creating/dispersing the standing waves over a wider frequency range, and in doing so the combined mode is of a lesser amplitude.

[mcp]

I see issues with (for example) the 3rd harmonic (height) and the fundamental (width) re-inforcing each other. Are these the problems you were seeing?