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Hi,If the throat transition (the section from the exit of the compression driver to the first part of the horn) is not completely smooth, then where in the frequency band will it affect the sound most - and how?
Thanks!
All the best
Peter
Follow Ups:
PeterYour question is impossible to answer given the extremely broad premise: no driver spec'd; no horn spec'd; size/shape of said discontinuity not spec'd etc. Something like this is best left to Cowboy Enginering: i.e. try it and see what happens (assuming that you can measure and record the results consistantly). Not enough information provided.
Paul
Hi Poul,Sorry about being non-specific and thanks for responding anyway:-)
To be more specific:
I use a pair of 200 Hz exponentially flared rectangular horns (about 30" wide and 15" high at the mouth). These are loaded with 2" BMS 4592 ND "coax" drivers from 266 Hz and up (active high-pass with 12 dB/octave).In the mid/high horns the first 3/4 of an inch (the "adapter")is not flared at all, but resembles a "tube" (I hope it is possible to visualize my description!). After that, the circular entry is slowly (over a distance of app. 2 inches) converted to the rectangular form of the exponential horn. This transition piece is fairly smooth, but not perfect.
In many respects this combo sounds good. However, I still hear some harshness in the treble (s-sounds in voices are too prominent), and it is not a level issue in the treble in general. Although Bill Woods kindly made a passive crossover for me that reduced this problem and certainly is a lot better than the standard BMS filter, I still think it is problematic.
It may have to do with the driver construction in itself (the tweeter section of the BMS coax is not horn loaded in the first part of the driver), but I also wonder whether the non-optimal throat construction may add to the harshness in the 6-9 kHz region. Do you think this might be the case?
Thanks!
Regards
Peter
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
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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