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Old 2nd February 2014, 03:24 PM   #11
fpitas is offline fpitas  United States
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Quote:
Originally Posted by Defo View Post
Thanks for the inputs everyone!

My hope was that I could use one single woofer section for both horns, as it would raise WAF quite a bit compared to my current system. But I see that I will face location and CTC spacing issues, as well as beaming issues, so I reckon it won't be a good idea.

fpitas:
The Faital Pro HF204 does'nt seem to have much breakup issues with its Ketone Polymer diagphram, compared to traditional metal diagphram drivers.
Well, you'll find out how it sounds. I'm sure it is better than most metal diaphragms in that regard, especially titanium.
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Old 2nd February 2014, 04:30 PM   #12
DougL is offline DougL  United States
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You didn't specify what the horn was(or I missed it), but based on the drawing it was not Conical.
Typically you want to cross about an octave above cutoff to avoid group delay issues, which can further complicate crossover design. So we are looking at a 250 Hz to 300 Hz cutoff horn, rather than a 400 Hz.

Rule of thumb is that you start to have problems with the frequency response when the throat becomes more than 1 wavelength. For a 2" Compression driver, that's a bit over 6K. Another reason to have a backup plan to have a tweeter crossed at between 4k Hz and 8k Hz. Because of the wavelengths, not an easy crossover point.

Good luck with your build.

Doug
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Old 2nd February 2014, 05:45 PM   #13
Defo is offline Defo  Norway
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Originally Posted by DougL View Post
You didn't specify what the horn was(or I missed it), but based on the drawing it was not Conical.
Typically you want to cross about an octave above cutoff to avoid group delay issues, which can further complicate crossover design. So we are looking at a 250 Hz to 300 Hz cutoff horn, rather than a 400 Hz.
The horn profile is spherical. Having a horn cutoff an octave below crossover frequency is indeed good practice. But I reckon that this will be more or less a non-issue when dealing with such high order digital crossover slopes (48 db/octave), that I can get away with a 400hz cf horn without too much trouble.

Quote:
Originally Posted by DougL View Post
Rule of thumb is that you start to have problems with the frequency response when the throat becomes more than 1 wavelength. For a 2" Compression driver, that's a bit over 6K. Another reason to have a backup plan to have a tweeter crossed at between 4k Hz and 8k Hz. Because of the wavelengths, not an easy crossover point.
Problems with frequency response in which way? I know a CD horn will stop loading the driver when you reach about 6khz for a 2" driver, but not a traditional spherical/tractrix/JMCL horn which start to beam instead.
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Old 2nd February 2014, 06:58 PM   #14
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Having just measured a ~380Hz LeCleac'h horn crossed over to a sealed 15" at 500Hz, I'd say:
- use a 15", not a 10". Your woofer should be about the same size as the horn to get a smooth directivity through the crossover. In my case horizontal directivity is very smooth through the crossover. Vertical definitely has an issue at crossover due to the vertical separation, but other than that it's a good match.
- put the woofer directly below the horn and as close as possible, otherwise your horizontal and vertical polar response will get destroyed.
- it looks like playing with delay will let me smooth out the vertical polar response a bit while still being able to correct on axis, but I have only simulated this so far.
- you might well need a super tweeter - I am using a 1.5" exit driver, a JBL 2435, and the combination of it and the horn dies at 10k. It is noticeably lacking in highs. It both rolls off more than I want to equalize for and the polar pattern gets very narrow. To be clear, the LeCleac'h horn has a polar pattern that continually narrows as frequency rises in a very smooth way which is fine. But at 10k, the polar pattern suddenly narrows even further and then gets a bit chaotic at higher frequencies.
- crossing at 500hz is really pushing the horn. You probably won't damage the driver (I'm not worried about it in my case), but you'll be pushing it right to the bottom end of its passband. You'll have to add eq to get it to match a target roll off. Just dropping in a text book crossover will not work that well since the horn's response will not be flat there. I plan on switching woofers soon to something where I can cross over higher to use the horn in a more optimal range.
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Old 2nd February 2014, 07:53 PM   #15
DougL is offline DougL  United States
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Problems with frequency response in which way? I know a CD horn will stop loading the driver when you reach about 6khz for a 2" driver, but not a traditional spherical/tractrix/JMCL horn which start to beam instead.
My understanding is that you will get constructive and destructive resonances as well as beaming. May not be a big issue. Just be aware.
Quote:
The horn profile is spherical. Having a horn cutoff an octave below crossover frequency is indeed good practice. But I reckon that this will be more or less a non-issue when dealing with such high order digital crossover slopes (48 db/octave), that I can get away with a 400hz cf horn without too much trouble.
Everything is a compromise. The high order slops should help.

Let us know how you like it.

Doug
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Old 3rd February 2014, 09:25 AM   #16
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Quote:
Originally Posted by Defo View Post
The horn profile is spherical. Having a horn cutoff an octave below crossover frequency is indeed good practice. But I reckon that this will be more or less a non-issue when dealing with such high order digital crossover slopes (48 db/octave), that I can get away with a 400hz cf horn without too much trouble.


Problems with frequency response in which way? I know a CD horn will stop loading the driver when you reach about 6khz for a 2" driver, but not a traditional spherical/tractrix/JMCL horn which start to beam instead.
Can you share what you base this on Defo? The Tractrixes and JMLC's with large format drivers I've seen all start to showing destructive intereference around 8-10kHz. The wavelengths are smaller than the exit of the compression driver at this point so they don't couple to the horn smoothly anymore.

Have a back-up tweeter horn/ super tweeter ready. People have been batling this for decades. I've not heard of many that prefer to run a large format all the way up instead of using a supertweeter.

If you absolutely want to go two-way, a 1" crossed to a 10/12" at 12-1500hz is IMO a better idea.

High order slopes have more ringing in the time domain and protect the driver less just above the XO frequency. This will highlight any problems in the low end of the horn/driver combination.

Why a 10" at 500hz? A 15 will be a better match in terms of dispersion and also dynamic headroom and LF extension.
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Old 3rd February 2014, 06:16 PM   #17
Defo is offline Defo  Norway
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Originally Posted by FredrikC View Post
Can you share what you base this on Defo? The Tractrixes and JMLC's with large format drivers I've seen all start to showing destructive intereference around 8-10kHz. The wavelengths are smaller than the exit of the compression driver at this point so they don't couple to the horn smoothly anymore.
I was under the impression that when the wavelenghts are smaller then the horn throat, then frequency response will simply drop due the horn no longer being able to load frequencies beyond that point, and that destructive interference is more tied to horn lenght and it's expansion rate.

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Why a 10" at 500hz? A 15 will be a better match in terms of dispersion and also dynamic headroom and LF extension.
The keyword here is WAF Also, it's my experience that large woofers are harder to integrate into smaller rooms, which is the case for me.
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Old 3rd February 2014, 06:23 PM   #18
tinitus is offline tinitus  Europe
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are these steep 48db xo slopes good ?
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Old 3rd February 2014, 07:09 PM   #19
GM is offline GM  United States
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High slope order primer: Linkwitz-Riley Crossovers: A Primer

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Old 3rd February 2014, 07:17 PM   #20
GM is offline GM  United States
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Originally Posted by Defo View Post
it's my experience that large woofers are harder to integrate into smaller rooms
I assume you mean WRT WAF since larger drivers are sometimes required in smaller rooms: Questions about speakers in small room

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