Hi all, I’m looking for a pair of these JBL 8” x 8” horns. I can’t find them on line. They are PT-D95HF. jbl pro parts # 364700-001
I can't see how those "beaks" aren't a source of diffraction..........................
But to be fair, the newest horns (M2) are the same way.........................
But to be fair, the newest horns (M2) are the same way.........................
If you look at the measurements you can see they create a compression chamber of sorts, turning a 4th order BP into a quasi- 6th order with a multiple channel flared 'vent', so nothing to really diffract.
just weird to me, compared to a tractrix, OS, or round spherical horn profiles .......
https://www.diyaudio.com/community/threads/jbl-m2-for-the-poors.247050/page-25
post 499
"The M2 has these weird 'beaks' on the side. Why is this?
As the axidriver sim demonstrates, the high frequencies on a disc shaped wavefront are like a LASER above 10khz. (This assumes a disc that's 3.8cm in diameter; 9khz is 3.8cm long.)
So the only way to WIDEN the beamwidth above 10khz is to NARROW the throat. And JBL isn't stupid, note that their new speakers have a throat that's 3/4" wide. This isn't accidental, this is to widen the beamwidth above 10khz.
But in the M2, we CAN'T narrow the throat, because the D2 2430K compression driver plays down to 700Hz. If you try to cram 700Hz through a 1" throat, it's going to sound like garbage. (700Hz is almost half a meter long!)
So what do you do?
You create a throat that's an inch in diameter on one axis, and 3" in diameter on another axis. On the X and Y axis, it behaves like a waveguide with a 1" throat. On the orthogonals, it behaves like a waveguide with a 3" throat."
post 500
"JBL M2 waveguide. Same diffraction slot, now in 3D. The idea is to "have your cake and eat it too". The low frequency loading of diffraction horn, without the resonances that are generated in a conventional diffraction slot. Pipes are very resonant and a diffraction slot is a pipe. The JBL slot, with it's varied geometry, reduces the resonances. A clever design. (Keep in mind, a plain ol' OS waveguide works pretty darn good. The JBL style is required because they're covering such a wide bandwidth with a single driver.)"
https://www.diyaudio.com/community/threads/jbl-m2-for-the-poors.247050/page-25
post 499
"The M2 has these weird 'beaks' on the side. Why is this?
As the axidriver sim demonstrates, the high frequencies on a disc shaped wavefront are like a LASER above 10khz. (This assumes a disc that's 3.8cm in diameter; 9khz is 3.8cm long.)
So the only way to WIDEN the beamwidth above 10khz is to NARROW the throat. And JBL isn't stupid, note that their new speakers have a throat that's 3/4" wide. This isn't accidental, this is to widen the beamwidth above 10khz.
But in the M2, we CAN'T narrow the throat, because the D2 2430K compression driver plays down to 700Hz. If you try to cram 700Hz through a 1" throat, it's going to sound like garbage. (700Hz is almost half a meter long!)
So what do you do?
You create a throat that's an inch in diameter on one axis, and 3" in diameter on another axis. On the X and Y axis, it behaves like a waveguide with a 1" throat. On the orthogonals, it behaves like a waveguide with a 3" throat."
post 500
"JBL M2 waveguide. Same diffraction slot, now in 3D. The idea is to "have your cake and eat it too". The low frequency loading of diffraction horn, without the resonances that are generated in a conventional diffraction slot. Pipes are very resonant and a diffraction slot is a pipe. The JBL slot, with it's varied geometry, reduces the resonances. A clever design. (Keep in mind, a plain ol' OS waveguide works pretty darn good. The JBL style is required because they're covering such a wide bandwidth with a single driver.)"
Last edited:
Thanks! Works for me 😉; falls right in line with my physical description.
https://www.diyaudio.com/community/threads/beaks.350634/
post #7
"I think what's going on, is that the more 'pronounced' the "beaks" are, the more the output is focused onto the horizontal and the vertical axis.
Basically the "X" shape "robs" output from the diagonal and focuses it onto the horizontal and the vertical axis.
But I'm stunned by how much more output it generates. I would expect an extra decibel or two, but ten decibels is astounding."
post #20
From the designer, Charles Sprinkle:
“The second thing we did was use a
blending geometry—there are no straight
lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an
infinite number of reflections, and the net
effect is that it smears the reflections coming
back down the horn and negates them.
post #21
"This one was really bugging me, because there's just NO way that something as subtle as adding some 'beaks' to a waveguide is going to deliver a gain of 10dB.
I think it's caused by a combination of things.......... The waveguide with the prominent beaks has a diffraction slot at the throat that isn't expanding as fast. Because of this, it's exacerbating the amplitude of the peak at 1500Hz."
post #7
"I think what's going on, is that the more 'pronounced' the "beaks" are, the more the output is focused onto the horizontal and the vertical axis.
Basically the "X" shape "robs" output from the diagonal and focuses it onto the horizontal and the vertical axis.
But I'm stunned by how much more output it generates. I would expect an extra decibel or two, but ten decibels is astounding."
post #20
From the designer, Charles Sprinkle:
“The second thing we did was use a
blending geometry—there are no straight
lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an
infinite number of reflections, and the net
effect is that it smears the reflections coming
back down the horn and negates them.
post #21
"This one was really bugging me, because there's just NO way that something as subtle as adding some 'beaks' to a waveguide is going to deliver a gain of 10dB.
I think it's caused by a combination of things.......... The waveguide with the prominent beaks has a diffraction slot at the throat that isn't expanding as fast. Because of this, it's exacerbating the amplitude of the peak at 1500Hz."
Post #21 "Good News! I think I solved the mystery.
This one was really bugging me, because there's just NO way that something as subtle as adding some 'beaks' to a waveguide is going to deliver a gain of 10dB."
And post #24
"Thanks for re-running the tests!
So it now appears that the longer, slower expanding prominent beak horn adds as much as 4dB in the lower range while loosing a similar amount in the upper range."