OK, you see this is NOT what I thought you were saying. In what you did the area rate-of-change is changing because all wall contours are "rotated". If the entire waveguide is rotated then the rate-of-change does not change.
I understand your results when I understand what you did, but I did not understand your results given what I misunderstood that you did. Hence my question.
Now I design a waveguide for my 1,4" Faital HF1440, so far I'm at ⌀530x230 mm. I try to find a balance between overall smoothness (which I believe is important), controlled directivity and efficiency.
Using the same polar map scale as B&C above:
Using the same polar map scale as B&C above:
Attachments
BTW, I'd love to see the throat impedance of the B&C horn, just to see what "Excellent loading down to 300 Hz" means in practice. Does anyone know how it can look like?
Also, does anyone know whether the data that B&C shows for this horn are a BEM simulation or VACS visualization of measured data?
Also, does anyone know whether the data that B&C shows for this horn are a BEM simulation or VACS visualization of measured data?
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Attached are the throat resistance and reactance of a 425Hz JMLC horn simulated and measured by Kirkup, Kolbrek et al.
The Polar map shows the Measured directivity response of the test horn.
The impedance/reactance peak of the B&C horn should be 125Hz lower.
I believe the polars are based on actual measurements (in anechoic conditions).
From the drawing it's clear the horn opens slowly (expo-like) in the vertical plane, which defines the cutoff freq. in combination with the depth of 46 cm.
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"Excellent loading down to 300 Hz" in PA terms translates into: can be used from roughly 600Hz.
At home (much lower SPL required) the ME464 could be used from 400-500Hz, perhaps even slightly lower.
It's interesting to compare the ME464 to B&C's prototype "Tromba" that was sent to Vance Dickason for his test of the DCX464.
This is also a 300Hz horn, with 80° x 60° coverage angles (23.5” × 17.5” and a depth of 17.5”), but without a diffraction slot.
It actually looks more like a Tractrix horn.
Quote:
"As can be seen, the -3 dB frequency of the DCX464 mounted in the prototype horn was exactly 300 Hz!"
Only the plots of the DCX-464's mid-frequency section are attached.
At home (much lower SPL required) the ME464 could be used from 400-500Hz, perhaps even slightly lower.
It's interesting to compare the ME464 to B&C's prototype "Tromba" that was sent to Vance Dickason for his test of the DCX464.
This is also a 300Hz horn, with 80° x 60° coverage angles (23.5” × 17.5” and a depth of 17.5”), but without a diffraction slot.
It actually looks more like a Tractrix horn.
Quote:
"As can be seen, the -3 dB frequency of the DCX464 mounted in the prototype horn was exactly 300 Hz!"
Only the plots of the DCX-464's mid-frequency section are attached.
Attachments
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It is just not that clear to me. A lot of profiles look like an expo for smaller coverage angles, even if they don't load that well. And once the profile is close to conical (here from about 2/5 of the length), the length of the horn doesn't have virtually any effect on throat impedance anymore. It is big because of the desired controlled dispersion for low enough frequencies, not because of loading. I guess I'll have to simulate it myself - I once did simulate a similar horn and wasn't very impressed but maybe I missed something.
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You can always extend high throat resistance lower in frequency but you pay for that by increased beaming. That's something I don't want to do...
In the overall picture this probably doesn't play a major role anyway.
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Seeing Ro808 measurements presenting both mouth and throat impedance I wonder why both are not presented in one and the same graph? It's a transformer, right? No energy is gained, only lost, but trading can be made between different properties (which?).
And what do the target requirement chart look like?
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And what do the target requirement chart look like?
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Attachments
I live with the view that a horn is possible to descirbe with the electrical equivalent schema of a transformer. For a trafo, there is a impedance of the primary and one for the secondary. I would have though this was the throat and the mouth. I'm probably wrong and just shows how weak my knowledge is in the theory here... someone more well educated will soon correct this I hope.
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Reason why B&C opted for a diffraction slot is coverage.
The Tromba prototype horn starts to beam from the midrange, but it loads the DCX464 extremely well. Actually better than I realized when I first read the test.
At 300Hz the driver is almost 'fully loaded'.
The principle of horn loading reminds me of ultra high RPM race engines with a very small 'power band', or more appropriate in this respect; low RPM marine diesel engines that produce gigantic amounts of torque at very low RPM, just above idle speed.
Here's an example of a classic HONDA 250cc 6 cylinder, that 'comes on cam' at around 00:45.
Ok, back on topic
mark100 uses his DCX from 500Hz, perhaps even slightly higher, in his Synergy horn.
In the conical Synergy horn, the driver operates progressively in reactive mode below 1000Hz, which means the driver isn't properly 'supported' by the horn and may therefore sound strangled and possibly raw when pushed too low.
The throat resistance and reactance of the (AH)425 are probably shown in separate plots for visibility reasons. Each plot shows a comparison of BERIMA, AEBEMA and measured values.
The Tromba prototype horn starts to beam from the midrange, but it loads the DCX464 extremely well. Actually better than I realized when I first read the test.
At 300Hz the driver is almost 'fully loaded'.
The principle of horn loading reminds me of ultra high RPM race engines with a very small 'power band', or more appropriate in this respect; low RPM marine diesel engines that produce gigantic amounts of torque at very low RPM, just above idle speed.
Here's an example of a classic HONDA 250cc 6 cylinder, that 'comes on cam' at around 00:45.
Ok, back on topic
mark100 uses his DCX from 500Hz, perhaps even slightly higher, in his Synergy horn.
In the conical Synergy horn, the driver operates progressively in reactive mode below 1000Hz, which means the driver isn't properly 'supported' by the horn and may therefore sound strangled and possibly raw when pushed too low.
The throat resistance and reactance of the (AH)425 are probably shown in separate plots for visibility reasons. Each plot shows a comparison of BERIMA, AEBEMA and measured values.
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