Contemplating Zaph's waveguide TMM - Heresy?

[djsixbillion]

No, this has nothing to do with Klipsch speakers; what I'm wondering is if the Zaphaudio waveguide TMM design might be adaptable to a pair of enclosures I have which will soon be vacant of drivers. These happen to have the same baffle width of about 9", but the thing is that Zaph's design uses two separate enclosures for the top and bottom mid/woofers, both of the same volume (.69 cu. ft.) and tuned to the same frequency (between 46 and 51 hz, depending on listener preference).

My cabs also have two separate enclosures, but the one the top woofer would be in measures ~.5 cu. ft., while the lower enclosure for the ".5" woofer is about 1 cu. ft. Now I'm guessing that in order for the 2.5-way design to work correctly and provide enough baffle step compensation, the 2 woofers must always be tuned to the same frequency. Is this the case? And could I accomplish such a thing by using different-length ports in the .5 and 1 cu. ft. enclosures?

Further heretical question: if the 2 woofers don't need to be tuned equally, could I use a ~46 hz tuning for the lower BSC woofer and maybe use one of these Scan-Speak Variovent things that I happen to have lying around for the top woofer enclosure?

Sorry for the weird questions, and thanks in advance for any help!

[rc white]

A method of getting the same f3 from your drivers can be found here

http://sound.westhost.com/articles/cscaling.htm

rcw

[djsixbillion]

Thanks for the link, I'll have to spend some time studying that info though! So would you say that in general the 2.5-way design always requires the two woofers to be tuned to an equal f3?

[rc white]

The point about the 2.5 way is that it parallels two drivers below a particular frequency too get enough volume displacement for adequate low bass output with out too much strain, if they don't cover the same range then you are defeating the purpose.
rcw

[djsixbillion]

That's what I figured, but I wanted to make sure that my logic wasn't flawed. To your previous post, I haven't had much time to play around with those equations, but is the gist of it that you can't simply tune two enclosures of differing volume to the same Fb by using different length ports?

I put the CA18RNX driver into unibox, and it shows that you can achieve equal tunings of 46hz by using a 10cm port (2" dia.) for the .5 cu. ft. enclosure and a 6.33cm port for the 1 cu. ft. enclosure, with the larger enclosure showing a small peak in the response at the tuning frequency while the smaller one stays mostly flat.

So, to help out a confused engineer, where and how do I apply a correction factor?!

[Nemophyle]

i remember a blog entry on zaph's site some time ago, with measurements to prove the point, saying that the improvement in performance from having two separate enclosures for a double woofer speaker was kind of minor. Unfortunately it's gone, but maybe he may confirm that if he wanders around

So my advice is, make the double enclosure a simple enclosure !

That should not be too hard, and it will simplify tuning in your situation

EDIT : Oh and btw , i read your above post. I'm no expert but i think that may not be a good idea. In fact they wont have the same excursion and power handling , and MOST importantly group delay will be different that means you will have two ports with bass frequencies not coming out at the same time, wich may cause phase cancellations in the bass, so IMHO to avoid.I'm no enginneer so i may be missing something important too

[djsixbillion]

That's a great point about the group delay, hadn't thought of that...

So here's another potentially unconventional question: The tower cabinets I built are actually composed of two physically separate enclosures per side (i.e. one sitting on top of the other). What would be the implications of joining these two together with, say, a piece of 4" PVC between them, such that they could still be slipped apart in the future? Would this "port" between the two separate enclosures contribute a resonant frequency of its own?

Thanks all, this forum is a great place to learn!

[rc white]

coupled boxes

What we are trying to do is to reduce the problem to the two resonator one solved by Thiele and Small.
Two drivers adjusted to the same f3 will go close, two identical drivers in one box closer, but putting a port between two boxes with perhaps dissimilar drivers adds more complexity than is really called for.
If you make an opening in the boxes where they join large enough so they act a a single box rather than two coupled ones then that is preferable.

[Nemophyle]

What we are trying to do is to reduce the problem to the two resonator one solved by Thiele and Small.
Two drivers adjusted to the same f3 will go close, two identical drivers in one box closer, but putting a port between two boxes with perhaps dissimilar drivers adds more complexity than is really called for.
If you make an opening in the boxes where they join large enough so they act a a single box rather than two coupled ones then that is preferable.

Agreed, that's what i was thinking

Basically if you did what you said you would have two drivers tuned in Double bass reflex, wich is a complicated loading method with two tuning frequencies, but the two of them would be tuned differently cause they would have first and second chambers of different volumes.

Shortly, something impossible to theorize , and unlikely to sound good except if you have an anechoic chamber and good measurement equipment to tune that :B

The quite large opening is the best way IMHO.