Multiple driver enclosure calculation adjustment?

[drmcclainphd]

I'm working on a closed design 4x12 guitar cabinet. I know the recommended volume per driver. To calculate the volume of the 4x12, should I simply multiply the per-driver volume by 4, or should I make an adjustment for factors such as large enclosure dimensions (ie. absorption).

[Chris Roemer]

Re: Multiple driver enclosure calculation adjustment?

You got it!

[Paul O]

Re: Multiple driver enclosure calculation adjustment?

Yes use the recommended driver volume as a starting point but don't worry about being exact it has little effect on sealed response as long as it's not grossly over/undersized. Adjust the size and shape of the enclosure to complement the head it will be paired with.

[drmcclainphd]

Re: Multiple driver enclosure calculation adjustment?

Yes use the recommended driver volume as a starting point but don't worry about being exact it has little effect on sealed response as long as it's not grossly over/undersized. Adjust the size and shape of the enclosure to complement the head it will be paired with.

A wise idea, one I use often, including putting rails atop to keep the head from slipping if I pull.

That said, I've read that a recommended dimension ratio to minimize resonance to be
0.618 : 1 : 1.618. Weird shape for a cab. Worth doing?

[Chris Roemer]

Re: Multiple driver enclosure calculation adjustment?

Maybe you want those resonances for guitar? If not, stuffing the enclosure with something like fiberglass will be at least as effective as following the "golden rule" dimension ratios.

[xaosbass]

Re: Multiple driver enclosure calculation adjustment?

A wise idea, one I use often, including putting rails atop to keep the head from slipping if I pull.

That said, I've read that a recommended dimension ratio to minimize resonance to be
0.618 : 1 : 1.618. Weird shape for a cab. Worth doing?

maybe try 0.7937: 1 : 1.2599 instead.

[drmcclainphd]

Re: Multiple driver enclosure calculation adjustment?

maybe try 0.7937: 1 : 1.2599 instead.

I'm familiar with 1/3 octave (r = 1 / curt 2) for frequency decomp work, using fast Fourier transfer for spectral analysis. It was commonly used for EEG analysis before we started using continuous waveform analysis for time/frequency plots. I hadn't seen it before for acoustics so I did some digging. The 1.2599 is a major third, and that didn't seem a likely candidate for reducing resonance. But the .7937 is a minor sixth, not very conducive to resonance. And, the interval between them is also a minor sixth, so there's two potential resonances which aren't very good at it, battling across an octave and among constructive and destructive interference, with the result of smearing out what little resonance does occur. A very interesting excursion, thank you.

Unfortunately the 1/3 octave ratio makes the cabs come out even more cubical than the golden ratio, and to fit four 12" drivers makes the face come out around 24 x 30 with a depth of 20. For other uses this might be a good idea, but I also have to contend with the eventual size and shape, and how well I can pack more things into the small space of a mini-van. The more rectangular phi ratio just seems a little more practical. Even though larger overall, it's a bit less cubical and easier to fit.

BTW, if I'm not mistaken, the phi (golden) ratio vs. the 1/3 octave ratio are numbers 5 and 8 on the Fibonacci series, respectively. This might lead to ratios that are even less likely to produce resonance peaks, and still have similar self-suppressing characteristics. A very, as we used to say, groovy concept. Thanks again.