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Old 13th June 2008, 06:37 AM   #3941
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Default Directivity


Here's the measured directivity of a Le Cleac'h 320 Hz horn (top graph), courtesy of the author. The directivity pattern looks very much like a 1.4" to 2" direct-radiator dome-midrange.
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Old 13th June 2008, 06:40 AM   #3942
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Default Plane Wave Tube Measurements


Here's Bjorn Kolbrek's measurements of his Altec 288B in a plane wave tube - the reason for not wanting to cross over above 7 Khz should be evident.
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Old 13th June 2008, 07:03 AM   #3943
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Default Simulations


Here is Bjorn Kolbrek's simulation of the radiation impedance of a 420 Hz Le Cleac'h horn with a T = 0.707 and profile optimized for an Altec 288. The green curve on the right is the power factor, or the power admitted into the horn. The red curve on the left is the reflection coefficient, the power reflected back towards the diaphragm. I see this as similar to a VSWR curve for an antenna, showing the transmitted power versus power reflected back to the transmitter.

Now, it is a simulation, and I treat all simulations with a degree of skepticism. But still, it is interesting to look at, and other simulations by Bjorn Kolbrek showed strong reflections when the throat flare of the horn did not match the internal flare of the 288 driver (which is 8 degrees). Very slight mismatches between the compression driver and the throat flare of the horn create surprisingly large ripples in the 500 Hz to 3 kHz response region.
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Old 13th June 2008, 07:27 AM   #3944
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Default Comment


The reasons for choosing a compression driver & horn bandwidth of 700~850 Hz to 5~7 kHz should be evident. Performance is very high within the bandwidth, but declines rapidly outside of it, which is normal for horns. What little I do know about horns is they do not respond to attempts to "stretch" their bandwidth.

Fortunately, neither the midbass driver nor the ribbon should be greatly stressed by this choice of crossover points. Both drivers should have acceptable performance an octave beyond the nominal crossover points, and the mid-high performance of the midbass driver, along with overall sonics, will be a determining factor in its selection.
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Old 13th June 2008, 07:54 AM   #3945
mige0 is offline mige0  Austria
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Default Re: Good Articles

Quote:
Originally posted by Lynn Olson


As for the continued interest in big midranges - well, the answer is simple: Dynamics! I've been listening to pairs of 5.5" drivers for fifteen years now, and it's time for a change. A small midrange just doesn't sound like a large one, regardless of efficiency. I guess the word I'm reaching for is "presence" - a piano sounds more like a real piano, and less like a hifi trying to imitate a piano. More palpable, more "in-the-room", more real.


Lynn, having also worked with large PA horns, my findings are slightly different from yours.
I agree that there might be some brute force sensation coming along with that beasts but I trace down the underlying aspects differently.

- the effortless presentation I assume to be a side effect of low thermal transients = BIG voice coils.
- the sensation of "bigness" I assume to be the same like from line arrays = the room angle covered by the source.
- going up "endlessly" in SPL is just that it usually is like that (at listening room distances) due to high efficiency and usually extend excursion designs.
- some of the "lifelike clarity" I assume to be due to low Doppler IM with large radiating areas

Put one or two 15" besides your Ariel and cross at around 300-500Hz – I'll bet, you'll experience the sensation you are heading for (within the limits of the Ariel drivers).



Greetings
Michael
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Old 13th June 2008, 08:29 AM   #3946
jamikl is offline jamikl  Australia
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I have been around long enough to have read articles in the old
Wireless world etc about horn design. A lot of what was written then is much derided now but a golden rule I understood from what I read was that no horn should handle more than 3 to 31/2 octaves, probably less at low frequencies. From what has been shown lately theu seem to have at least got that part right.
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Old 13th June 2008, 11:54 AM   #3947
Jmmlc is offline Jmmlc  France
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Hello,

Quote:

... no horn should handle more than 3 to 3.5 octaves...
We have to take care about such "universally admitted sentence" which comes from a time that gave us a lot of empirical formulas... and a lot of bad horns.

Could someone explains to us why a horn could not be used to reproduce an interval of frequency larger than 3 octaves...

Best regards from Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally posted by jamikl
I have been around long enough to have read articles in the old
Wireless world etc about horn design. A lot of what was written then is much derided now but a golden rule I understood from what I read was that no horn should handle more than 3 to 31/2 octaves, probably less at low frequencies. From what has been shown lately theu seem to have at least got that part right.
jamikl
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Old 13th June 2008, 03:23 PM   #3948
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Quote:
Originally posted by Jmmlc
Hello,



We have to take care about such "universally admitted sentence" which comes from a time that gave us a lot of empirical formulas... and a lot of bad horns.

Could someone explains to us why a horn could not be used to reproduce an interval of frequency larger than 3 octaves...

Best regards from Paris, France

Jean-Michel Le Cléac'h

Not to be a jerk but that's a silly question coming from you. You should know that all horn/drivers are different as well as what is expected of them. For example I could not live with this horn Lynn is using beyond 2K (a little over an octave) looking at the graph of it's narrowing directivity- it would need a treble unit because I expect better dispersion - (should I now call his horn a bad horn? No, it seem to be what he wants)Also look at the response of the Altec 288 beyond 6K - the treble is missing. In any horn it would only be good out to around 6K

Another example would be a bass horn where the driver won't do 3 or more octaves. There are unlimited examples of horns that work well (as designed) over less then 3 octaves
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Old 13th June 2008, 04:16 PM   #3949
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"Here's the measured directivity of a Le Cleac'h 320 Hz horn (top graph), courtesy of the author. The directivity pattern looks very much like a 1.4" to 2" direct-radiator dome-midrange."

Hello Lynn

With twice the DI number for the horn. The included angle 6 db point is twice the horns for a 2 in driver. At 10K you are looking at 80 degrees for the driver and less than 40 degrees for the horn.

Rob
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Old 13th June 2008, 04:51 PM   #3950
Jmmlc is offline Jmmlc  France
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Hello,

There is no silly questions only silly ******s. ;-)

From an historical point of view, to my knowledge, the increasing directivity of horns were never used as an argument to the "3 octave question"...

Most often the upper limit of the power response is one of the arguments.

If we use the empirical (again) formula for the lower frequency limit Fl and for the upper frequency limit Fh (see JBL technical paper http://www.petoindominique.fr/pdf/JB...-frequency.pdf )

Fl = Fs . Qts / 2 and Fh = 2 . Fs / Qts

Generally compression drivers are used above the resonance frequency of the (loaded) loudspeaker Fs with horns having quite the same cut off frequency: Fc ~= Fs . (well if you use an Altec 802 it can be different due to high Fs...). This means that for a horn loaded compression driver we have to consider as the bandwith the frequency interval between Fs and Fs/(2 . Qts).

A rapid calulation will indicate that Fh = 8. Fs (3 octave bandwith) for Qts = 0.25. I let you know if this is relevant in your case...

This is for the power response. Power response is very important when you have to design folded bass horns by example (see Marshall leach and others).

But is it important for straight horns? Your own taste can lead you to reply YES if you prefer the horn or the waveguide to have a response similar in shape to the power response. My own answer will be NO , I don't want my driver + horn equalized and my preference for music recorded in phase stereophony lead me to listen alone at the sweet spot on my main system so I don't care so much about the off axis response (if the reverberated field is OK to those ears).

To my knowledge there is no compression driver for which the upper limit of the power response as mesured on planar wave tube is over 4kHz or such. Does this means that the compression driver cannot reproduce 18kHz? No, see on axis response for an unaqualized TAD TD2001 driver on a Le Cléac'h horn as a good example.

Have a good week-end.

Best regards from Paris, France

Jean-Michel Le Cléac'h





Quote:
Originally posted by Magnetar


Not to be a jerk but that's a silly question coming from you. You should know that all horn/drivers are different as well as what is expected of them. For example I could not live with this horn Lynn is using beyond 2K (a little over an octave) looking at the graph of it's narrowing directivity- it would need a treble unit because I expect better dispersion - (should I now call his horn a bad horn? No, it seem to be what he wants)Also look at the response of the Altec 288 beyond 6K - the treble is missing. In any horn it would only be good out to around 6K

Another example would be a bass horn where the driver won't do 3 or more octaves. There are unlimited examples of horns that work well (as designed) over less then 3 octaves
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