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In Reply to: Re: What are the consequences of a non-optimal throat transition in a horn? posted by PK on March 19, 2007 at 23:54:12:
PeterFrom the pics of the BMS 4592ND I found on the web, it's difficult to figure out how they made the transition from the tweeter to the 2" midrange diaphram. There does'nt seen like there is enough room to bring this off in a 2" driver. A discontinuity in this area would be a cause for concern and could be the cause of the sibilance you note. If you could identify the center of the resonance with a test microphone, you might try tuning it out with a passive filter (zobel), however if it's a complex series of peaks and dips, this approach would have limited sucess. You don't mention if the horn is one of the BMS horns for this driver or one you have constructed. You might try smoothing out discontinuities in the horn with modeling clay. One of the disadvantages of the exponential horn in the midrange is it's abrupt termination at the mouth. You could try smoothing this out. Someone posted some experiments on the Lansing Heritage Forum where they attached some rolled up towels around the mouth of a conical horn, which improved the response. Do a search for the post "Factors Affecting Sonic Quality of Mid & HF Horns & Waveguides" over there.
Hope this helps.
Paul
Follow Ups:
Hi Paul,Thanks a lot for taking the time to answer!
In the filter RCA-fan simulated for me, there is actually a notch filter to dampen a peak around 6 kHz of the tweeter, and this clearly helped, although it did not remove the sibilance all together.
I have also tried the "towel approach" at the mouth, but this did not make any difference as far as I can tell.
I can maybe smooth out the transition to some extent, but I can not get rid of the "tube" section of the horn. So now I wonder whether I should try a different horn in which the throat is better constructed and see whether this brings better results. (There is a large 200 Hz German horn [Jabo KH-72] of the salad-bowl type that isn't too expensive, that I would really like to try.)
Once again thanks for your time!
Regards
Peter
Hi again PeterSeeing as you already have a notch filter, adding another may not be a practical solution, and you are already in good hands with RCA Fan's help to begin with. Before you order another horn try an Edgar gap. The driver you have is bolted to the horn allowing you to add some spacers between the driver exit flange and the flange where horn throat begins. Try adding a gap with some spacers here, say about 1/4" to start, and fill the gap with some Scotchbrite scouring pad material. You can play around with the thickness of the gap and the thickness and density of the Scotchbrite which comes in different degrees of courseness like steel wool. This was discovered by Dr, Edgar and used to tame a peak in a horn loaded cone driver in one of his Speaker Builder articles. It's a low budget way to tame a peaky compression driver too. You may lose a few dB of output with this controlled leak at the throat, but it may also be able to tone down the sibilance. And you can always recycle the Scotchbrite to it's intended duties if it does'nt work.
Good luck!
Paul
Hi Paul,Thanks a lot for the suggestion - and for taking the time to repond in the first place. I really appreciate it!
Regards
Peter
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