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Multi-Way Conventional loudspeakers with crossovers

can sb explain how this horn works
can sb explain how this horn works
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Old 18th April 2019, 10:32 AM   #1
apolinary is offline apolinary  Poland
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Default can sb explain how this horn works

Hi guys,
I thought I understood the basics of CD horns but there's something I clearly don't understand.
The rule of thumb is: if you want to cover lower frequencies you need a bigger horn. For example: Faital LTH102 in theory is good down to 1kHz and is 17cm deep. Faital LTH142 is good down to 800Hz and is 23 cm deep (and wider comparing to the former).
And now we have this: Beyma TD/385
HORN TD/385
It's quite small and only 12 cm deep. Still cut-off FQ is 800Hz an if you look at the response curve of CD14Fe coupled with that horn you would find it quite impressive:
SPEAKER DRIVER CD14Fe 8 OH
So it is small and shallow and seem to work. Are there any downsides? Or maybe even some advantages (less horn colouration?)
What am I missing?
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Old 18th April 2019, 10:58 AM   #2
frangus is offline frangus  Australia
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It is the geometry of the flare that sets the cutoff along with the size
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Old 18th April 2019, 11:48 AM   #3
oohms is offline oohms  Australia
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Cutoff frequency isn't the same as recommended crossover frequency.. I wouldn't want to use it below 1.6khz based on the data
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Old 18th April 2019, 12:04 PM   #4
AllenB is offline AllenB  Australia
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When you say CD, do you mean compression driver, or constant directivity.
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Old 18th April 2019, 12:15 PM   #5
apolinary is offline apolinary  Poland
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What I meant was compression driver.
Cutoff fq: I was quite suprised as well. But those Beyma guys (for some reason) desided to measure and recommend the above-mentioned driver coupled with the very horn. And the driver recommended crossover frequency is 800Hz...
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Old 18th April 2019, 12:33 PM   #6
AllenB is offline AllenB  Australia
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You are comparing horn lengths, which may not be helpful. The length can change depending on where you choose to start and to end the horn. Then there are different types of horn.

Perhaps you could get a copy of hornresp.exe and design a few to get a feel of what sets the cutoff. Also watch the directivity (beamwidth) to see how they differ in other ways.
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Old 18th April 2019, 02:51 PM   #7
phivates is offline phivates  United States
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We need to make up a new abbreviation for one of the CDs. CDr? CDh/wg??
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Old 18th April 2019, 03:08 PM   #8
lowmass is offline lowmass  United States
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when a "smaller" horn seems to go as low as a "larger" horn, isnt it just diffraction at horn exit that's lifting response?
And if so then not really the same directive control?
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Old 19th April 2019, 12:28 AM   #9
AllenB is offline AllenB  Australia
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Possibly. The throat still exists to load the driver over some range. The shortened mouth may result in overall axial resonance at lower frequencies with features particularly at standing wave dimensions. The directivity may suffer from narrowing or widening within a certain range.
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Old 19th April 2019, 01:45 AM   #10
cspieker is offline cspieker  United States
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Correct me someone if I'm mistaken, but horn length is not necessarily related to cutoff frequency. Take a Tractrix and an OS wg of the same mouth size, the OS will provide slightly lower cutoff frequency even though it is much shorter. The tradeoff is that the flare rate is greater at the throat end in the OS. Hence it will have broader dispersion in the high frequencies and resulting lower efficiency. Likewise the higher flare at the mouth of the Tractrix will spread the lower frequencies more and hence compromise low frequency efficiency and apparent cutoff. To simplify, it's not about length, but about the flare angle at the point in the horn which is loading that particular frequency. High frequencies loaded at throat, low frequencies loaded at mouth.
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