I run a kind of Jean-Michel Le Cléac'h horn in my home system, and had one in my studio.
II write "kind-a", because it was done before the Cléac'h publication, calculated on spherical waves too with the same principle, and look the same.
Well i was astonished, at this time, till now, by how realistic and natural was the reproduction as well as analytic, detailed and dynamic, with a perfect localization, no directivity problems etc.
Never the slightest trace of those Donald duck sounds of all the previous horns i knew (numerous).
One thing i would like to understand, as i was questioned about.
Compression horns drivers suffer from a generic problem of distortion due to non linearity of the air with pressure.
I'm unable to feel any distortion in my horns, both with JBL BL 2426J 1" driver, used from 700 to 20 000 in one set, and 1500 to 20 000 in the other, even at high level.
Any explanation ?
II write "kind-a", because it was done before the Cléac'h publication, calculated on spherical waves too with the same principle, and look the same.
Well i was astonished, at this time, till now, by how realistic and natural was the reproduction as well as analytic, detailed and dynamic, with a perfect localization, no directivity problems etc.
Never the slightest trace of those Donald duck sounds of all the previous horns i knew (numerous).
One thing i would like to understand, as i was questioned about.
Compression horns drivers suffer from a generic problem of distortion due to non linearity of the air with pressure.
I'm unable to feel any distortion in my horns, both with JBL BL 2426J 1" driver, used from 700 to 20 000 in one set, and 1500 to 20 000 in the other, even at high level.
Any explanation ?
Hello Esperado,
The distortion due to air non linearity is mainly 2nd order distortion (H2) and this is due that compression of a given volume of air is not the symetric of dilation of the same volume of air.
For some reading :
http://www.arcavia.com/kyle/Equations/Distortion.html
Then the H2 distortion of air becomes large at very large values of the SPL (>120dB). For sure such high pressure can be found at the throat of a horn but mainly in PA application. For hifi purpose that effect is not audible (H2 distortion can be eventually perceived by traine ears when it becomes larger than 5%).
The high distortion of horns is also an unfair argument used by an anti-horn lobby. Even they compare measurement done at 2.83V (or 1W) on a "normal" loudspeaker and a compression driver mounted on a horn. They always forget to mention that with 2,83V the fist one may deliver an SPL level 10dB to 20dB lower than the second...
Best regards from Paris, France
Jean-Michel Le Cléac'h
Jean-Michel,
While I agree the distortion in a good horn/driver can be less than a cone tweeter, the levels even in home at the throat/diaphragm can be far above 120 dB.
I did an outdoor test on a very narrow dispersion Maltese conical horn using a B&C DE82TN 1.4” exit 3” diaphragm driver crossed at 1250 Hz, horn facing skyward, 5 feet above ground, mounted on a 41” x 26.5” baffle.
The 13 x 13 degree horn angle results in an on axis sensitivity around 6 dB more than most typical 90 degree horns, the 2 meter results would be similar to one meter results on some horns.
Pink noise signal, approximately 2 watt average level.
110 dBA response 2 meters
115.2 dBA 1meter +5.2 dB
119.7 dBA .5 meter 19.5” +4.5 dB (“horn bubble” effect)
126.3 dBA at horn mouth +6.6 dB (26” from throat screen)
131.7 dBA 13” from screen +5.4 dB
136.8 dBA 6.5” from screen +5.1 dB
141.0 dBA 3.25” from screen +4.2 dB
143.7 dBA at screen +2.7 dB (144+ impulse, flat)
The inverse distance reduction was fairly consistent until the last halving of distance.
The distance from the screen to diaphragm is an additional 2 inches, the SPL level at the diaphragm probably was in excess of 145 dB when levels of 110 dB at 2 meters were hit.
Live snare hits, cymbal crashes, brass and reeds peaks can easily hit 110 dB at 2 meters, so can horn/drivers, but throat distortion can be fairly high at those levels.
If 2 meter levels were reduced to only 85 dB peak, the SPL at the diaphragm would be 120 dB , 126 dB on a typical 90 degree horn.
Although air non-linearity throat distortion is not a problem at the under 1 watt levels usually delivered in a home situation, at the rated power level of most modern compression drivers distortion can easily rise to double digits as I found in this series of evaluations:
http://www.diyaudio.com/forums/multi-way/212240-high-frequency-compression-driver-evaluation.html
Art Welter
Smile & merci mille fois, jean-michel.
All you wrote i knew.
I was wondering if the horn could have a noticeable influence in the amount of distortion, mainly in the first centimeters.
Too if the drivers are optimized to reduce this distortion (volume of the back chamber).
Can-t we imagine to use a foam to make the compression of air adiabatic, between the membrane and the "piece de phase" (Throat ?) ?
Is there somewhere comparative measurements of real distortions between a good traditional cone in free air and a good driver at various levels and frequencies ? I made those decades ago, when i was working on my system, but lost the sheets...
I used to leave 1 octave free, down the transition filter frequency, and high slope, as distortion is a factor of it, too.
Thanks a lot.
Hello Esperado,
Apart the air non linearity at throat that a horn provides due to a large ratio mouth area / throat area, I don't think a horn can bring distortion by itself.
Bad horns and noticeably the ones based on diffraction (waveguides...) may eventually redistribute the distortion components appearing at the throat in more or less discrete directions. BTW the same effect is desired in ultrasonic devices fro which we want them to deliver a thin ultrasonic beams...
It make me smiling when I see people asking for the distortion curve of a horn considered by itself. There is not such. But the way a horn loads more or less resistively and actively a loudspeaker can for sure leads to differences in distortion curves (on the same driver).
As an example, see the measurement I have done at ETF2010
(Measurements performed on 16 horns ... http://forums.melaudia.net/attachment.php?aid=1760 )
from which I extract the measurement of a TAD TD2001 on 2 different horns :
- Le Dauphin sectoral horn
- J321 Le CLéac'h horn.
see how the H2 curves are similar, noticeably around 1kHz. For the J321 measurement, reduced H2 at HF and other H3, H4, H5... components are mostly due that for the measurement performed on my J321 I used (as I always do with a TAD TD2001) a series resistor (30ohms) which one provides a reduction of distortion of the compression driver due to a better "current drive" (see Hawksford paper : http://www.essex.ac.uk/csee/researc...J12 Distortion reduction MC current drive.pdf )
Best regards from Paris, France
Jean-Michel Le Cléac'h
Apart the air non linearity at throat that a horn provides due to a large ratio mouth area / throat area, I don't think a horn can bring distortion by itself.
Bad horns and noticeably the ones based on diffraction (waveguides...) may eventually redistribute the distortion components appearing at the throat in more or less discrete directions. BTW the same effect is desired in ultrasonic devices fro which we want them to deliver a thin ultrasonic beams...
It make me smiling when I see people asking for the distortion curve of a horn considered by itself. There is not such. But the way a horn loads more or less resistively and actively a loudspeaker can for sure leads to differences in distortion curves (on the same driver).
As an example, see the measurement I have done at ETF2010
(Measurements performed on 16 horns ... http://forums.melaudia.net/attachment.php?aid=1760 )
from which I extract the measurement of a TAD TD2001 on 2 different horns :
- Le Dauphin sectoral horn
- J321 Le CLéac'h horn.
see how the H2 curves are similar, noticeably around 1kHz. For the J321 measurement, reduced H2 at HF and other H3, H4, H5... components are mostly due that for the measurement performed on my J321 I used (as I always do with a TAD TD2001) a series resistor (30ohms) which one provides a reduction of distortion of the compression driver due to a better "current drive" (see Hawksford paper : http://www.essex.ac.uk/csee/researc...J12 Distortion reduction MC current drive.pdf )
Best regards from Paris, France
Jean-Michel Le Cléac'h
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Thanks a lot, Jean Michel, for this very informative and documented response, in a perfect scientific spirit.
People like you, with such a generosity, such a passion, such a knowledge and such an objectivity are rare and precious as diamonds.
I wonder, looking at those curves, where , most of the time, the distortion increase with frequency, if this is due to the membrane fractioning or the air non-linearity ?
Because i suppose that, like in a cone, for the same level, excursion is supposed to decrease with frequency, so the air compression ?
I suppose that, because the decrease of distortion when driver is feed across a resistance : mean less electric damping, mean less fractioning ?
Best regards from sud ouest, France, under the rain.
Agree, Art.
Congratulation and thanks for your huge work of evaluation.
Your idea of virtual basses is amazing, and opens a field of reflexion for me...
I am asking myself a lot of questions, since decades, about this distortion subject.
One of them is how are we aware of 0.1% distortion in amps, while we can afford, and even enjoy, so much from acoustic transducers.
MAy-be it would be better to evaluate IM and TIM more than HD ?
As far i'm concerned (i used to manage a big PA system with JBLs horns decades ago) and use horns at home in my high end system, i tend to prefer horns for home, while the distortions of them in PA was sometimes problematic, mostly in free air. (while we used arrays of horns).
I wonder why drivers manufacturers do not care to try to equalize front and back pressure at their membranes, using some kind of throat to charge the back of it.
All in one, regarding several aspects, control of directivity, damping of transients, emission surface, membranes fractioning -> frequency range etc...good horns present so much benefits...
Hello,
In compression driver there is 3 mains sources of high frequency distortion :
1) dome breakups : this lead generally to peaks and holes visible in the response curve and also in the H2, H3... curves.
For 2 inches compression drivers having aluminum diaphragms the breakup occurs above 7000hz, for titanium diaphragms above 4000hz and for beryllium above 15kHz.
2) back FEM in the coil due to flux modulation in the magnetic assembly. That's why good compression drivers (and loudpeakers) possess a shorting ring. (Also when it is possible to use current drive, this effect is drastically reduced).
3) non linearity of the air at throat. Beranek (even if it a bit schematized) said that for a given intensity harmonic distortion doubles with each doubling of driving frequency (this should lead to a +6dB/octave of the H2 curve).
Best regards from Paris, France
Jean-Michel Le Cléac'h
In compression driver there is 3 mains sources of high frequency distortion :
1) dome breakups : this lead generally to peaks and holes visible in the response curve and also in the H2, H3... curves.
For 2 inches compression drivers having aluminum diaphragms the breakup occurs above 7000hz, for titanium diaphragms above 4000hz and for beryllium above 15kHz.
2) back FEM in the coil due to flux modulation in the magnetic assembly. That's why good compression drivers (and loudpeakers) possess a shorting ring. (Also when it is possible to use current drive, this effect is drastically reduced).
3) non linearity of the air at throat. Beranek (even if it a bit schematized) said that for a given intensity harmonic distortion doubles with each doubling of driving frequency (this should lead to a +6dB/octave of the H2 curve).
Best regards from Paris, France
Jean-Michel Le Cléac'h
At what point? Or above what frequency? That should be easy enough to measure.
And impedance curves, as for cones loudspeakers...
And double each 6db increase of acoustic level (square root of the acoustic pressure)
Jean-Michel,
In Beranek's book “Acoustics”, he describes the nonlinear distortion mechanism:
"If the horn were simply a long cylindrical pipe, the distortion would increase the farther the wave progressed..."
Doubling the distance would double second harmonic distortion in a pipe.
The nonlinear distortion increases linearly with distance traveled in the tube, or the length of the horn.
"in the case of an exponential horn, the amplitude of the fundamental decreases as the wave travels away from the throat, so that the second-harmonic distortion does not increase linearly with distance."
In a long, narrow horn, while SPL is falling at roughly the inverse distance law, the nonlinear (air) distortion increases with distance.
It appears in the horns you tested, those that had long narrow sections had the highest distortion.
It seems your tests support Beranek's view quite well.
Art
Hello Art,
I don't advocate that Beranek is wrong on that.
What I see is that with horns when the acoustic level rises, it is H2 which is produced.
With electrodynamic loudspeakers when the acoustic level rises, and when the coil begins to move in a non linear zone of the magnetic field, it is H3, and high order distortion component which are produced.
Also at the level distortion at the throat of horns becomes to be large, we have also to consider the distortion of our ear. Objectivists will surely smile...
Considering the way our ear distorts, ones explained that it is a reason why monotriode amplifiers and why horns produce an euphonic distortion at large output level... I'll not develope here, all of you know that.
Best regards from Paris, France
Jean-Michel Le Cléac'h
I don't advocate that Beranek is wrong on that.
What I see is that with horns when the acoustic level rises, it is H2 which is produced.
With electrodynamic loudspeakers when the acoustic level rises, and when the coil begins to move in a non linear zone of the magnetic field, it is H3, and high order distortion component which are produced.
Also at the level distortion at the throat of horns becomes to be large, we have also to consider the distortion of our ear. Objectivists will surely smile...
Considering the way our ear distorts, ones explained that it is a reason why monotriode amplifiers and why horns produce an euphonic distortion at large output level... I'll not develope here, all of you know that.
Best regards from Paris, France
Jean-Michel Le Cléac'h
I smile... because it is obvious.
After all, our ears are horns, and not symmetrical at each side of our membrane (tympan)...
Levels of harmonics is one of the way our brain make interpretation of the original level of a known source and his distance.. We use that, during mixs...
I believe that, in audio, H.D. (when not too high) is not so important. It changes slightly the texture of an instrument in a natural way. H2 gives warm, H3 presence. I worry more about awful IM and TIM.
Well, this distortion question interest-me on a subjective point of view too. In my system, at high level, there is distortion due to my driver/horn. I notice them at such a level that my brain interpret them as a product of my own ears. It don't bores-me. It gives-me the feeling that my system is louder than the measure would show.
While i always found that cones produced some kind of sound unnatural at those levels... go figure...
We often use horns to PA. There, distortion is a problem. In big halls, at some distance, distortion is so high , and acoustic level so low that this distortion seems awful. While, near the stage, very high level, it sounds ok, because the distortion is near the one of our ears.
Are horns better for home, and arrays of cones for big PA ? I believe that, at the end.
I'm using TAD 2002 in a A-480 horn. I'm a bit puzzled about how thin the wooden horns are normally made. When I had a couple friends pressing on and damping a resonance in the wood it sounded quite a bit better. If you tap with one finger tips you can hear a distinct tone and when you have once heard the absence of that tone in the music it's quite easy to hear that tone most often. I will also try to round of the upper edge by having a bit rounded while I will try to either press on the horn by "something" or applied some sort of rubber damping. The wood structure is too nice to glue something on. Have anyone any experience of damping freestanding wood horn?
/Harry
/Harry
I am in need of some adivce. I am trying to build a DIY profile to use in a speaker similar to the JBL k2. I have looked at the Iwata profile over a biradial, as it seem to offer better performance. I am trying to decide what profile to use, its location(vertical or horizontal dispersion), and idea of expected response. I downloaded one of you excel sheets, JMLc, from earlier in the thread and have a profile created. My assuption is that this prfile should be use for the horizontal plane(as the platter), but unsure what to do in the vertical plane. Trying to avoid straight sided biaradial. How do I go about making these decisions?
Yes, and you gave yourself the response. You have to chose between look and sound quality. If you need to dump them, you need to glue or stick material on it.
It can be more thickness of the same wood, and can be nice looking as well, but lot of work.