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In Reply to: RE: Some horn speaker technical questions... posted by Enophile on August 21, 2007 at 09:17:44
1. The dimples in the B&W port are intended to minimize turbulence at high airflow speeds, which is a different problem from what a horn design has to deal with. Possibly a compression driver at high sound pressure levels could generate turbulence in the throat of a horn, but I don't think that's likely to be an issue at any sane in-home listening level.
My understanding is that, as a general principle, the fewer and less abrupt the discontinuitites along the horn surface, the better. Now this might not apply to dimpling; I just don't know. My guess is that the audible benefits of dimpling would be minimal at best.
2. The material that the horn surface is made of doesn't matter a whole lot as long as it is smooth, hard and non-resonant. Aluminum-skinned Dynamat applied to the backside is what I use to damp fiberglass, metal, or plastic horns.
3. My recollection is that the edge of the La Scala's midrange and tweeter horn has an abrupt corner, in which case I don't think rounding it into the baffle will make a whole lot of difference - but it wouldn't hurt either. In my opinion the throat and the mouth should avoid abrupt transitions, and most horns have 'em in both places (diffraction slot in the throat, and sharp [instead of large-radius rounded] lips).
4. It is my understanding that sharp bends in the bass horn pathway reduce amount of midrange energy that emerges from the mouth of the bass horn, so it's possible that rounding those corners could have a detrimental effect on the frequency response.
Duke
Follow Ups:
"It is my understanding that sharp bends in the bass horn pathway reduce amount of midrange energy that emerges from the mouth of the bass horn, so it's possible that rounding those corners could have a detrimental effect on the frequency response."
Up to about 200 Hz or so the shape of the bends/reflectors doesn't matter all that much, or for that matter even whether there are reflectors. Above 200 Hz or so reflectors are necessary mostly to prevent 1/4 wavelength distances between parallel surfaces in the pathway. Above 600 Hz or so both rounded bends and rounded reflectors give the best results. I've seen rounded pathways used in basshorns, but it's an unecessary complication.
So whats better anyway_
It depends on the driver and all over topology, of course. I've built folded midbass horns loaded with ten inch woofers with 100Hz-3kHz passbands. How high you can go isn't limited by the bending of the horn as much as by the low-pass function of the horn.
So Bill as you said:
"How high you can go isn't limited by the bending of the horn as much as by the low-pass function of the horn"
Then what determines the low pass function of horns? How can you get a horn to pass more HF? How do rounded reflectors compare to bending of horns?
"Then what determines the low pass function of horns?"
A variety of factors, starting with the size of the throat chamber, thence moving to the cross-section of the throat, culminating with the area of the mouth, with a few other factors in between. Mouth area doesn't affect the high frequency limit per se, but the mouth dimensions do affect dispersion, which de facto amounts to the same thing. Axial response is of little value without useable dispersion.
I was asking myself this question after seeing a cross sectional picture of one of the Fostex DIY kits, too.
Your reply is much appreciated.
Thanks. I was hoping you'd post.
Duke
You had the rest of it pretty well covered. But he didn't ask about the orientation of the diffraction horns, which should be vertical. Odd that PK made that one concession to form over function.
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