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Old 18th June 2021, 01:36 PM   #21
newvirus2008 is offline newvirus2008  India
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Dear Multitask,

That's the horn from the JRX125/225, a modern version of the 2370 you could say. At 12"x6.375"x5.75", that horn is usually crossed as high as 2kHz. There are a lot of people who have modified JRX cabs with the Selenium D220Ti, but I don't think they changed the crossover frequency. But I guess, you chose 1.3kHz for matching directivity with the 12" woofer beneath.

However, the horns in consideration here are cinema horns that are as wide as the LF baffle itself (see post#8) and 12-14" deep, which is at more than twice as deep as the JRX. With such dimensions, these could properly load a compression driver to much lower frequencies (~700Hz or so).

Regards.

I'm sure at least a few on the forum use/have used these cinema horns and could confirm these points for the OP.
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Old 18th June 2021, 01:57 PM   #22
AllenB is offline AllenB  Australia
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The waveguide width and depth isn't really going affect loading, at least not by frequency.. all else being equal.
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Old 18th June 2021, 03:26 PM   #23
newvirus2008 is offline newvirus2008  India
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As far as I've read, not only the higher depth but higher width and/or height contribute to larger mouth area that has a direct influence on the lower frequency capabilities. I suggest you check post #22 again.
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Old 18th June 2021, 11:41 PM   #24
AllenB is offline AllenB  Australia
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Yes but which low frequency capabilities, is it loading or something else?
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Old 19th June 2021, 06:52 AM   #25
newvirus2008 is offline newvirus2008  India
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My point was that a long, deep horn (vs. short one) essentially implies a slower flare rate, making the horn more suitable for LF reproduction.

And the longer (deeper) it gets, the earlier (in frequency) its acoustic resistance (real part) rises to useful values, once again, implying an improved LF reproduction.
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Old 19th June 2021, 07:06 AM   #26
AllenB is offline AllenB  Australia
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Fair enough for certain horns. The counterpoint is that this is not necessarily so with waveguides.
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Old 19th June 2021, 08:18 AM   #27
newvirus2008 is offline newvirus2008  India
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Oh, so "horn vs waveguide" ? Technically speaking, anything that resembles a "pipe" will be able to load the driver!

In my opinion, both the JBL Screenarray (vertically asymmetric) and Progressive Transition (PT) waveguides are simply bleedovers between diffraction type horns and standard ones. There are other threads here where people show how to obtain such profiles (and results), from standard ones, and the term "waveguide" simply appears to be a horn that places large amount of importance on dispersion.

I agree with that there's no point in trying to define a cutoff frequency for a waveguide, like with an exponential horn etc. However, a physical dimension like length/depth is a "very" fundamental aspect that no waveguide/horn/anything else can violate. Besides, if you ask me, I would only say that waveguides and horns may have differing dispersion, but both match acoustic impedance to the airload in front of their mouth area and larger dimensions (mouth area) do that to lower frequencies.

Last edited by newvirus2008; 19th June 2021 at 08:35 AM.
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Old 19th June 2021, 08:58 AM   #28
AllenB is offline AllenB  Australia
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You mention waveguides with pinched throats, but recall that I said "all else being equal" so try comparing waveguides with similar throats and angles but different lengths and mouth sizes.

Why is it that loading is so important?
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Old 19th June 2021, 09:25 AM   #29
newvirus2008 is offline newvirus2008  India
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Quote:
Try comparing waveguides with similar throats and angles but different lengths and mouth sizes...
Well, you're talking scaling, and scaling does cause the frequency axis to scale inversely as well .. (I had asked that question to which Mr. McBean answered yes, pointing to the resize option within Hornresp).

Quote:
Why is it that loading is so important?
I'm surprised you're asking that! With no real part in its impedance to load, how could you expect the horn/waveguide to put out any real acoustic power into the air? Well, attached is the manufacturer's take on terminology for the Screenarrays.

Untitled-1.jpg

Last edited by newvirus2008; 19th June 2021 at 09:27 AM.
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Old 19th June 2021, 10:49 AM   #30
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by newvirus2008 View Post
Hornresp
For both questions.
Attached Images
File Type: png hr.png (115.0 KB, 94 views)
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