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6th October 2008, 08:05 AM  #81  
R.I.P.
Join Date: Oct 2005

Hello Soongsc,
If the input parameters are well known then Hornresp is pretty accurate to simulate axisymetrical horns. Calculation of the acoustical impedance presented by the horn at its throat to the driver is the main purpose of such software as the other curves like response, phase, etc need the knowledge of the acoustical impedance. We can see how accurate is Hornresp in looking at the comparison between measured and predicted acoustical impedance. (Unfortunately acoustical impedance is pretty hard to measure without a well equipped laboratory ) David McBean gave few example of comparison between measured acoustical impedance curves and predicted. See:                                       for an exponential horn . . . . . measurements http://www.diyaudio.com/forums/attac...amp=1212155433 . . . . .as predicted by Hornresp http://www.diyaudio.com/forums/attac...amp=1212155580                                       for a tractrix horn . . . . . measurements http://www.diyaudio.com/forums/attac...amp=1212155510 . . . . . as predicted by Hornresp http://www.diyaudio.com/forums/attac...amp=1212155659                                       Generally when designing a horn we want the resistive part of the acoustical impedance the most constant. Electrical impedance is another animal and as the horn influences the electrical impedance of the driver near its acoustical cutoff frequency but don't modify the electrical impedance at high frequency, I guess that it is quasi impossibe to design a horn to obtain a constant electrical impedance. Most probably a series of tuned pipes of various length may be more adapted to reach such goal. Best regards from Paris, France JeanMichel Le Cléac'h Quote:


6th October 2008, 08:22 AM  #82  
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Join Date: Oct 2005

Hello,
The knowledge of the acoustical impedance of the horn should be the basis to the choice of Fc. We want the horn to have the most resistive impedance inside the desired interval of frequency to reproduce. As it is very difficult for an hobbyist to measure the 2 parts of the acoustical impedance (acoustical resistance and acoustical reactance) I prefer myself to choose Fc after the study of the group delay curve of the horn (mounted on a driver able to reproduce the desireable range of frequency). I obtain the group delay curve by derivation of the phase curve which one, in parallel to the response curve, is obtained by my own Matlab routine that is based on Discrete Fourier Transform (DFT) and not FFT (with DFT you can place the origin of time at the arrival of the pulse so then it is far more easy to unwrap the phase than with FFT). I express the group delay in equivalent distance travelled at the speed of sound (c = 341 to 344 m/s). For my own use I only use horns above frequency for which the group delay is less than 8 centimeters. Doing this I am sure that the harmonics and fundamental keep their initial phase relations at best in the reproduced range of frequency. With Le Cleac'h horns this leads to use a high pass crossover at 2.5 to 3 times the cutoff frequency of the horn. Best regards from Paris, France JeanMichel Le Cléac'h Quote:


6th October 2008, 08:39 AM  #83 
diyAudio Member

Could you show us some sample group delay plots from real horns? I'm very interested.
I use equalization to flatten group delay down to the cutoff frequency but I can't currently measure it, I can only estimate it indirectly.
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6th October 2008, 10:33 AM  #84  
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Join Date: Oct 2005

Hello Eva,
You'll find in attached file, group delay curves for one of my TAD TD2001 on a Le Cléac'h horn (Fc = 320Hz). (group delay on this graph is expressed, as I am accustomed to, in equivalent distance travelled at the speed of sound, so it is given in meters). There is 3 curves to show the influence of a series resistor. (a large series resistor or better a current source fills the famous hole at 1600Hz on the TD2001curves, the origin of which is explained in Kinoshita's paper in JAES and this as also its infleunce on the group delay curve in the interval 1300Hz 2000Hz.) Best regards from Paris, France JeanMichel Le Cléac'h Quote:


19th February 2009, 03:21 AM  #85 
diyAudio Member
Join Date: Dec 2004
Location: Dallas, Texas

Moving away from cut off frequency.
I just found this thread and wanted to thank the participants, especially JMMLC. When I was implementing the crossovers I found that moving away from the cut off of the upper horn, 250hz, had decided sonic benefits although it seemed a waste to have a larger horn than was being used. After JMMLC post on this here in this thread I can understand much better why I heard what I heard. When I design crossovers I measure and listen, measure and listen, the ear always finds things the measurements do not. This information has just saved me a lot of effort as I was about to try a smaller horn. Instead, it seems that a similar frequency elliptical horn would be a better choice. Many Thanks.

19th February 2009, 01:41 PM  #86 
diyAudio Member
Join Date: Nov 2003
Location: California

If you hear things you aren't measuring, you aren't taking the right measurements. This effect is easy to measure. JeanMichel has just shown it in the previous post as group delay. I've measured something similar as stored energy similarly to how Linkwitz does. See: http://ldsg.snippets.org/HORNS/storede.html

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