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Old 24th May 2012, 04:46 PM   #81
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I have another difficulty with high rolloff on my tweeter horn. It starts to drop about 12Khz, and slowly falls about 6 db at 20Khz.

I know it's the horn, not the CD, and I have plenty of excess CD efficiency to play with, on the order of 10+ db.

I understand there is a way to EQ this in the crossover to give a rise at 20Khz. How is that possible, and how do I avoid something that might lead to other problems?
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Old 24th May 2012, 05:43 PM   #82
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This guy seems to know what he is talking about. EQ circuit on page 414 of the AES paper.

Improvements in Monitor Loudspeaker Systems

D. Smith

Last edited by speaker dave; 24th May 2012 at 05:56 PM.
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Old 24th May 2012, 06:35 PM   #83
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Awesome! - and in a 7 year old thread too!

Thanks Mr. Smith!

Last edited by LafeEric; 24th May 2012 at 06:50 PM.
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Old 24th May 2012, 07:40 PM   #84
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I think this became the standard approach to passive EQ of CD horns. I had experimented with a first order bypass but the loss at 15kHz was too much and I couldn't get flat HF response. There is always lots of mid band sensitivity, so the 2 resistor pad drops that to a reasonable level (leaving a bit of excess for the variable L-pad range). The second order resonant circuit shunts the top frequencies around it.

If I recall correctly it took some playing so that the HF pot and MF L-pad had minimal interaction.

Good luck,
David
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Old 24th May 2012, 08:12 PM   #85
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Thanks again! Yes, that sounds like exactly what I am looking for.

My test cab is nearly together, so I should start experimenting soon.

Last edited by LafeEric; 24th May 2012 at 08:16 PM.
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Old 6th June 2012, 11:55 AM   #86
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Didnt we get completely of the track, and also loose our threat starter on the way?

It could have been very interesting to follow the intended test project.


Best regards
Arthur.
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Old 6th June 2012, 12:01 PM   #87
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i agree , let the man build the speakers and post mesurements then will see what happens
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Old 6th June 2012, 03:03 PM   #88
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Quote:
Originally Posted by speaker dave View Post
....but errors of less than a foot or a mSec in time are generally not heard except with some specialized test tones.....

David S.
I haven't read the entire thread yet, but anybody who has used an active system with time correction will tell you that statement is completely false.

.1 ms is quite easy to hear when fine tuning, in my experience.
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Old 6th June 2012, 03:07 PM   #89
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Quote:
Originally Posted by tvrgeek View Post
Phase is totally disregarded through the entire recording process.
I'm not a sound engineer, but from reading around, it seems that phase most certainly is a concern in recording.
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Old 6th June 2012, 03:41 PM   #90
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Quote:
Originally Posted by turbodawg View Post
I haven't read the entire thread yet, but anybody who has used an active system with time correction will tell you that statement is completely false.

.1 ms is quite easy to hear when fine tuning, in my experience.
You have to separate frequency response errors from all-pass errors. If you have an electronic crossover and create a system with perfect response at some exact delay between woofer and tweeter then advancing one unit or the other in small steps would likely be audible. This is not due to the phase or time error, but due to the large frequency response error that would be introduced.

If, on the other hand, you adjust an all-pass network (flat response but no frequency response error) then errors below 1ms are hard to hear on test signals and usually inaudible on music.

Perhaps you should read the entire thread. Better yet, the published papers on the subject.

David S.
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