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Old 2nd January 2013, 10:59 PM   #201
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Theoretically is the result of this experiment the same phase and transient performance as a sealed speaker?
*
yes,and more than a perfect Linkwitz transform with FIR EQ
i'm able too to bypass convolver plugin during listening
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Old 3rd January 2013, 01:17 AM   #202
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Actually, it's not the same. An acoustic suspension has a second order highpass so, if you wanted to emulate that phase response in a ported speaker, you'd apply an LR2 correction to the port rather than an LR4. The magnitude slope is also different, though that'll largely be masked by the room acoustics.

As to CopperTop's question, all my XO and EQ is easy to ABX in real time.
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Old 3rd January 2013, 05:02 AM   #203
tomtom is offline tomtom  Slovakia
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Hi Guys.

I have stupid question. How you actually reliable measure phase. Do you trust HOLM? In my case sweep length affect phase in quite radical way. The shortest sweep the flattest phase i get /almost flat/. The long sweep measure several rotation. I like to correct phase with rephase - but without reliable measurement... My setup is PCI sound card to DCX playback and Mobilepre USB to measure

Thanks for you comment
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Old 3rd January 2013, 08:24 AM   #204
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Quote:
Originally Posted by CopperTop View Post
Forgive a couple of naive questions from someone who is considering having a go at building (or at least 'converting') some sealed speakers...

Theoretically is the result of this experiment the same phase and transient performance as a sealed speaker?

Is the port/DSP combination therefore an unalloyed win-win, that renders active sealed speakers a bit of a waste of space?
John K and Kgrlee confirmed that a BR is a minimal phase thing, so it can be corrected without problem.
In rePhase you can use the "box" corrections in the linearization tab to achieve this.

If you manage to stick the port size you want in your box (with low noise...), limit the excursion down low (using an additional subsonic filter that you can also linearize in rePhase) and stick enough dampening material in the box without restricting air flow, then there should be no drawback in using a ported enclosure vs a sealed one.

I am planning to use a ported enclosure for my midbass driver, with a 200Hz tuning and additional filters and EQ to get a LR 48dB/oct HP filter and subsequently linearize it as such.

Here is a WinISD simulation with a JBL 2123H in a sealed box in yellow (+ heavy Linkwitz transform and LR 48dB/oct HP filter) and various ported boxes of different size and 200 tunning (+ filtering and various EQ to get the same LR 48dB/oct magnitude and phase), and the resulting excursion at 300W, as well as the power seen by the driver.
Attached Images
File Type: png 2123H midbass.PNG (47.0 KB, 218 views)

Last edited by pos; 3rd January 2013 at 08:30 AM.
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Old 3rd January 2013, 10:12 AM   #205
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Quote:
Originally Posted by tomtom View Post
Hi Guys.

I have stupid question. How you actually reliable measure phase. Do you trust HOLM? In my case sweep length affect phase in quite radical way. The shortest sweep the flattest phase i get /almost flat/. The long sweep measure several rotation. I like to correct phase with rephase - but without reliable measurement... My setup is PCI sound card to DCX playback and Mobilepre USB to measure

Thanks for you comment
Reflexions in a typicall room will of course make phase measurement at low frequency doubtful, but gating is not necessary either as only the low frequenbcy will be affected (contrary to magnitude measurements).
You can use the realtime gating marker (on the impulse and on the frequency curves) to see where the first reflexions occure though, and consider the frequency lower than that point with a grain of salt...

If you can "see" your theoritical crossover point on your measurement (eg 180 phase rotation at LR4 crossover point) then you know you are on the right track.
If you don't, first check the polarityn, and then the impulse offset.
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Old 3rd January 2013, 11:28 AM   #206
tomtom is offline tomtom  Slovakia
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Thanks but do sweep lenght affect phase measurement in your setup (holm) so its general problem or its just my setup. Thank you very much for confirm.
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Old 3rd January 2013, 11:38 AM   #207
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there's an option in holm
use centering impulse,peak at t=0

Click the image to open in full size.
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Old 3rd January 2013, 11:53 AM   #208
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Originally Posted by tomtom View Post
Thanks but do sweep lenght affect phase measurement in your setup (holm) so its general problem or its just my setup. Thank you very much for confirm.
The longer the measurement signal the more resolution you get in the low frequency.
2^16 should give good results. I have add some strange problems with the 2^14 setting (looks like a bug).
(of course you can also change the length of the sweep by changing the start frequency, but I assume this is not what you are talking about).
I usually use MLS for these measurements, as I have not found any advantage for the sweep (no need for THD or high noise rejection here) and it is easier to the ear...
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Old 3rd January 2013, 11:56 AM   #209
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Originally Posted by thierry38efd View Post
there's an option in holm
use centering impulse,peak at t=0
Once the polarity is rigth this will work but will hide any LP filter up high.
This is usually what you want when measuring a fullrange loudspeaker or a tweeter (no need to vizualise nor to correct the LP in this case) but can be dangerous when measuring a woofer for example, as it will mask the phase shift of the LP and make it impossible to properly align with the upper driver.
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Old 3rd January 2013, 01:08 PM   #210
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ok
i believe it was to correct only bass enclosure
adjust the offset to get the 0 crossover and bassreflex phase

here's an old capture
35 Hz bass reflex
120 Hz active crossover
3000 Hz passive crossover

Click the image to open in full size.
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