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In Reply to: RE: WE11 long throat ideas posted by pix on February 01, 2017 at 22:45:35
What is the length of the horns in the picture, and the mouth diameter or radius? Is the Radian 750Pb a 2 inch driver? Some of the other posters also seemed confused about this too, and a web search did not provide any info from the Radian catalog that came up. Are you attempting to couple a 2 inch horn mouth to an existing 2 inch driver? Or are you attempting to couple a 2 inch horn mouth to a 2 inch driver with a smaller horn mouth adapter? There have been adaptors like this available to couple a smaller compression driver to a 2 inch horn mouth (I have some JBL examples) but it's to hard to generalize about whether this would be an improvement, it all depends on the driver and the horns in question. Do you have a way to measure this experiment? You can download Room Eq Wizard for free (REW for both PC and Mac) and with this and a decent test microphone you can evaluate the results.
I have written some clearifications in Mr steadys post.
My first goal was to eliminate the exit angle missmatch between a 10.4 degree driver exit to a 4 degree horn throat (both 2" in diameter)
I figure I could do this by extending the horn curvature 107 mm in length, and letting the horn pass the driver exit, going inside the driver.
Secondly I figure, why sattle with an 107 mm extension?
Would it be of any gain indreasing this to (lets say 200-300mm) in terms of distorsion of cutoff?
The horns are 200 Hz cutoff tractrix (approx 600 i length and diamter). The horn throat are 2"
The Radian 750Pb is a 2" exit driver with 10.4 degree exit angle (about 1" Deep). It has a 3" voice coil
I am currently using a single serial cap making a very shallow x-over point at 350Hz. This was chosen by hearing rather than measuring. I have tryed several passive and active x-over configurations, but also digital (MiniDSP) -variants. But simple filters sounds best in my ears.
A horn is most efficient when the horn length is equal to 1/2 of the wavelength at the lowest target frequency. If the horns pictured here are 600 mm (23 5/8") in length they would fall short of being 200 Hz midrange horns:
13,500/200=67.5/2=33.75", which would be the ideal length for a midrange horn with a low frequency target of 200 Hz.
As a 350 Hz horn it should work as the half wave dimension for 350 Hz is 19.28" which is quite close to the 600mm (23 5/8") length.
Making the horn throat smaller than the 2" driver exit (if I understand your intension) would have the effect of making the volume of the air chamber in front of the driver diaphragm larger, which would have the effect of rolling off some of the high frequencies at some point, and this may be constructive or it may not. This is to say it could be useful rolling off a high frequency peak in the response, or it could just put a dip in the response which may not be useful.
A frequency response test graph would reveal if there is a peak in the response of this horn and driver combination that techniques like this could be used to tune out, but it's difficult to generalize if something like you are proposing would be an improvement or not. Tuning something like this "by ear"can be problematic as you can wind up with something that sounds good with one particular favorite recording, but worse with other types of music, and I've been there and done that.
So this all comes down to Cowboy Engineering: try it and see what happens.
BTW I would avoid a curved adaptor in a midrange horn, as this would assume that the wave front can maintain the same speed between the longer outside radius and shorter inside radius. Also a first order crossover is a good match for a horn where the bass end typically will roll off naturally at a quite steep angle.
I hope all this helps
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