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In Reply to: Re: Basshorn impedance posted by DMoore on January 30, 2007 at 18:55:05:
I think we might be talking about two slightly different things here. A pure horn, or at least what I and some others might define as a "pure horn", is one that has a basic flare driven by a diaphragm. It's a simple device, with characteristics determined by its properties. One of those characteritics is bandwidth, another is impedance, another still is efficiency, and so on.There are other acoustic devices besides horns that can be employed to modify the horn's characteristics somewhat. Resonators (be they Helmholtz chambers or standing wave reflectors) can be employed to cancel modes formed by the main horn. The rear chamber can be tuned in a similar fashion. Likewise, electrical devices can also be employed, things like notch filters, compensation networks, and so on. These acoustic and electrical filters can be used to extend bandwidth, reduce impedance peaks and smooth response.
Follow Ups:
Not to me, I've been talking about the same thing all along; short horns can be designed that do not display reactance problems, however, I previously agreed that the general 1/4 wavelength long pathway "rule" was appropriate for single flare-rate horns.Is that why you guys have been arguing with me? I was beginning to wonder what that was all about...
My opinion is single-flare rate bass horns cannot compete with multi-flare ones on a performance level (and all that entails) given the constraints of footprint size, bandwidth, nominal Fc, and overall cabinet volume.
Well, no, I'm not talking about flare rate. I'm talking about additional devices, such as Helmholtz resonators, standing wave reflectors, etc. When those things are incorporated, they change the landscape a bit. One cannot make an undersized horn without associated impedance peaks, but by adding additional devices, one can counter the impedance peaks. It's the added resonators that do the trick.
But I'm not necessarily talking about "undersized" horns, actually SHORT PATHWAY horns, in particular BUT I should add that I'm refering to1/8th space horns, too, as in the case of the Jubilee. Correct mouth size for the Fc, large throat area = short pathway, well under 1/4 Fc wavelength down to around a meter in length.In such a case, annulled drivers and multiple flare rates can get you where you want to go, and in a wideband manner, too.
We've all seen Olson's seminal work regarding foreshortened horns in "Acoustic Engineering", etc., I'd point out that he noted that changing the throat size had much less effect than changing the mouth size, for instance, on the overall reactance. But then those examples were single flare-rate horns and were not annulled considering the "new" larger throat size (changes as a lessening of acoustic resistance), either, which would likely have an potentially exploitable effect.
But i'm not entirely convinced klipsch's stuff can be classified as a horn. Multiple flare rate seems to be a gross understatement and the mouth on the lf section of the jubilee sure seems to bear that out. The lascala, is even weirder.
If Sd exceeds throat area and mouth area exceeds throat area it is a horn. How far down it operates in horn mode is another question, but PK answered that one as well.
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