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Old 22nd September 2013, 11:58 AM   #491
pos is offline pos  Europe
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Not sure what you mean?
Max deviation is denoted in dB
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Old 22nd September 2013, 12:40 PM   #492
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by pos View Post
Not sure what you mean?
Max deviation is denoted in dB
Yes, but it is denoted in 0.1 dB, if I'm not mistaken couldn't that be written as -20 dB?
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Old 22nd September 2013, 01:48 PM   #493
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0.1 as a ratio (not dB), ie 10%, can be written -20dB when dealing with distortion figures.
But here it is 0.1dB, so applying this relation would give a percentage of accuracy: "lowest accuracy 99% at XX Hz" or something.
Would that be more meaningful?
You would have to count nines instead of zeros

Anyway, this indication was only useful when no target/result curve was shown (priori to version 0.8) and should probably go away now as close inspection of the curves gives more valuable information.
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Old 22nd September 2013, 02:23 PM   #494
OllBoll is offline OllBoll  Sweden
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Ah, ok =)

It can't hurt to leave it there, a numerical proof that the ripple is small enough is nice to have. If you have to analyze then you might always have missed something somewhere =)

Question about the windowing functions, do they affect the optimizer or is it just for us to see the result? Or in other words, is the goal to find the windowing function which after optimization makes the ripple as small as possible or find the one where it is as large as possible?
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Old 22nd September 2013, 07:24 PM   #495
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Optimization is done on the result, after centering and windowing, so it takes everything into account.
You should choose the windowing that gives you the best result curves (for your criteria) after optimization, or even defeat optimization if it makes thing worse.

As a basic rule of thumb, phase-only correction will call for a rectangular windowing (or complex if "int" centering has to be used, but this is generally a bad idea), whereas corrections implying a LP or HP filter will generally work better with a blackman or nuttal windowing. For moderate amplitude corrections but high Q, rectangular, hamming or hann can be tried...

By the way OllBall, how did you current-drive project for the nc400 turn out?
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Old 22nd September 2013, 07:42 PM   #496
OllBoll is offline OllBoll  Sweden
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Ah,

In my test of phase correction of 30 hz LR2, 100 hz LR4 and 200 hz LR4 with 2048-4096 taps @ 16384-65536 FFT length the hann window produced results with less than 10% as much amplitude ripple as with the rectangular.

And that project was abandoned =)

I built an F2J with ~ 800 ohm output impedance and tested on my speakers and it had a 20-30 dB reduction in odd order distortion except around the resonance of the driver. Putting a resistor in series with the NCore reduced odd distortion somewhat but not even close to the true current source F2J. Wrapping a feedback loop doesn't work either because the open loop is too low on the NCore and putting a such large series resistor isn't feasible either.

Fast forward to this new speaker project I made new distortion measurements but instead of a cheap monacor driver I used an AE TD6M with a high quality motor and on that one there was no significant distortion difference between the F2J and the NCore on odd order distortion. So while it does all the difference on drivers without shorting rings and such it doesn't affect as much if the driver has all that.

In the end I've decided to go active and use Hypex UcD for bass up to 200 hz and then small and inefficient amps above since I found the NCore to sound a bit too bright and not as relaxed as my Aleph J in the treble. I'm even planning to sell the NCores since I already have two PSC2.400d for the sub+woofer channels and the audio difference between the NCore and UcD shoulnd't be significant at those frequencies... and it would save space and money =)
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Old 22nd September 2013, 10:38 PM   #497
Pano is offline Pano  United States
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Hey Pos. I'm trying to figure out how to use the crossover function to hit a desired target. Been searching the thread, but can't seem to find it.

For Example: I want a 4th order Linkwitz-Riley acoustic response at 650Hz. I import the measurement of the raw driver into rephase and see it there. Is there a way to now see the 4th order L-R target I want to achieve? I can see the results of what the built in filters will do to the response, but I can't tell if that matches the target I want. I need a guideline to compare. I've been able to import a target, but can't see it and my measured response at the same time.

Am I missing something? Is there a way to see if your imported and filtered response matches a chosen target? Thanks!
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Old 22nd September 2013, 11:16 PM   #498
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Quote:
Originally Posted by OllBoll View Post
Ah,

In my test of phase correction of 30 hz LR2, 100 hz LR4 and 200 hz LR4 with 2048-4096 taps @ 16384-65536 FFT length the hann window produced results with less than 10% as much amplitude ripple as with the rectangular.
I tried your configuration and indeed rectangular is not giving the best amplitude matching there. Nuttall seems to give even better results than hann in that particular case. But if you look at the phase you will see that that the rectangular windows gives a better match, which seems to preclude the optimizer to get a good matching for the amplitude.
It is all trial and error

Quote:
So while it does all the difference on drivers without shorting rings and such it doesn't affect as much if the driver has all that.
yes that is what I found when comparing the effect of a series resistor between a JBL 2020H (modern motor with shorting rings) and a TAD TM1201 (no shorting ring... but what a cone!).
I had hoped someone would have find a way to turn the ncore into a current source as Bruno told us it was possible...
Why so few current drive amplifier on the market?...
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Old 22nd September 2013, 11:23 PM   #499
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Quote:
Originally Posted by Pano View Post
Hey Pos. I'm trying to figure out how to use the crossover function to hit a desired target. Been searching the thread, but can't seem to find it.

For Example: I want a 4th order Linkwitz-Riley acoustic response at 650Hz. I import the measurement of the raw driver into rephase and see it there. Is there a way to now see the 4th order L-R target I want to achieve? I can see the results of what the built in filters will do to the response, but I can't tell if that matches the target I want. I need a guideline to compare. I've been able to import a target, but can't see it and my measured response at the same time.

Am I missing something? Is there a way to see if your imported and filtered response matches a chosen target? Thanks!
Hi Pano,

There are no target curve as for now. The plan was to use the "capture" functionality to do that, but it is not there yet.

Anyhow, the easiest solution to get any acoustical filter you want is to EQ your drivers for flat (amplitude and phase) using any amount of EQ you need (watch your noise floor though), and then apply your filter(s).
That way you can try different filters slopes and types without having to redo all your EQing.
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Old 23rd September 2013, 10:57 PM   #500
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Merci Pos. I was trying doing some of that last night. It seems to work pretty well. Also working with the active filter section of the Passive Crossover Designer (PCD) and transferring those setting to rephase, then a little tweaking.

Generally I've been doing this.
  1. Import measurement.
  2. Correct for high pass phase
  3. Correct amplitude (overall, then low, mid, high)
  4. Fine tune phase. (overall, then low, mid high)
  5. Export impulse

I'll let you know how it goes from here.
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