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Old 26th December 2012, 11:40 AM   #61
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By the way John, I have a question I wanted to ask you for some time, and this is the perfect opportunity: is a BR (Helmotz resonator) a [minimum] phase thing? Or is there something special about the ringing?
BR is just a minimum phase thing. Ringing is typical of a 4th order HP alignment. Nothing special.

The Four Audio stuff seems way over priced. Sort of like the DQEX. It seems to be aimed at the typical audiophile who has more money than brains. I think a lot of audiophiles don't realize that dsp is more computer science and mathematics than audio once you are between the A/D and D/A converters. I certainly no expert here but good algorithms for FFt convolution aren't exactly a mystery.
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Old 26th December 2012, 11:45 AM   #62
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By the way John, I have a question I wanted to ask you for some time, and this is the perfect opportunity: is a BR (Helmotz resonator) a phase linear thing? Or is there something special about the ringing?
pos, Yes. A Bass Reflex (including the double ported & KEF versions) are all Minimum Phase.

It's very difficult NOT to have a minimum phase speaker at LF though some back & front loaded horns try very hard.

Practically all the phase-distortion in a speaker is from evil xovers & drive unit (mis)alignment.

John K.., I'm impressed by your Dipole speakers having dabbled with them in the previous millenium.
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Old 26th December 2012, 11:57 AM   #63
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Thierry, do you know of any plugin that does direct convolution?
I have played with SIR but found some annoying artifacts... (on specific test signals)
If the PC is powerful enough it looks like direct convolution is the way to go. I have no idea how much power it would require though...
i've read this thread,direct FIR core i7

a nuclear factory !
a powerfull graphic card should be implemented to run 8 convolutions of 8000 taps...

for HTPC or PC HIFI,fft convolution allows passive heatsink and modest processor.no fan noise
i've checked THD an IMD with convolutions in the loop,it's ok too,nothing to notice.

why direct convolution could be a better way ?
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Old 26th December 2012, 02:25 PM   #64
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Quote:
Originally Posted by john k... View Post
BR is just a minimum phase thing. Ringing is typical of a 4th order HP alignment. Nothing special.
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Originally Posted by kgrlee View Post
pos, Yes. A Bass Reflex (including the double ported & KEF versions) are all Minimum Phase.
Thanks!
So if phase can be corrected there is no downside for using a BR!
I am thinking about a BR for my lowbass driver (TAD TM1201) which is seriously excursion-limited (distortion skyrocket right under 400Hz). A passive radiator would even suppress the problem of the hi mids leaking through the vent...
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Old 26th December 2012, 02:27 PM   #65
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John K.., I'm impressed by your Dipole speakers having dabbled with them in the previous millenium.
You should build a pair of my newNote II RS speakers. Relatively inexpensive and very, very good.


Also regarding the comment about direct convolution. There is no difference between direct and FFt convolution, if the algorithms are correctly implemented, other than the reduction in latency which is a big deal if you are trying to sync with video.
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Old 26th December 2012, 02:29 PM   #66
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Originally Posted by john k... View Post
The Four Audio stuff seems way over priced. Sort of like the DQEX. It seems to be aimed at the typical audiophile who has more money than brains. I think a lot of audiophiles don't realize that dsp is more computer science and mathematics than audio once you are between the A/D and D/A converters. I certainly no expert here but good algorithms for FFt convolution aren't exactly a mystery.
It was made in 2007. I think it is not aimed at the end user, but for professional integrator and speaker builder (thus the price of the software).
I think it was used in some H&K/Neumann products.
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Old 26th December 2012, 02:43 PM   #67
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So if phase can be corrected there is no downside for using a BR!
That's a bit of a stretch . . . life is not so simple . . .
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Old 26th December 2012, 02:51 PM   #68
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What are you thinking of?

If the phase is corrected (which is one of the purposes of the tool presented in this thread) and the amplitude slope can be taken into account (especially for a lowbass driver that will cross to a sub...) then the only possible downsides I see are:
- sound leaking through the port, that can be suppressed using a PR
- cannot fill the whole encolure with damping material, so the of shape of the box might be more critical to avoid standing waves
- need to add another HP filter (linear phase) to prevent excursion problems under resonance, so final target slope will likely be around 48dB/oct
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Old 26th December 2012, 03:09 PM   #69
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Originally Posted by pos View Post
What are you thinking of?

If the phase is corrected (which is one of the purposes of the tool presented in this thread) and the amplitude slope can be taken into account (especially for a lowbass driver that will cross to a sub...) then the only possible downsides I see are:
- sound leaking through the port, that can be suppressed using a PR
- cannot fill the whole encolure with damping material, so the of shape of the box might be more critical to avoid standing waves
- need to add another HP filter (linear phase) to prevent excursion problems under resonance, so final target slope will likely be around 48dB/oct
Provided the cut off is below any frequency to be reproduced. If there is content below the cut off point it will introduce preringing. A ported system with 25Hz cutr off should be pretty good.
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Old 26th December 2012, 03:14 PM   #70
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What do you mean John?
Lets say I am aiming to go down to 200Hz and tune the vent at 200Hz, add EQ and filters to end up with a LR48 @ 200Hz (and subsequently correct its phase). Where would the preringing come from?
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