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Old 2nd January 2013, 02:48 PM   #191
Pano is offline Pano  United States
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Quote:
Originally Posted by bohdan1232000 View Post
This may be helpful to you.
http://www.bodziosoftware.com.au/
Thanks Bohdan, I've given it a quick look, will do some further reading, including the material you've linked to in the PDF.
Before I study it, tho, I'll give my impressions of what I heard.
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Old 2nd January 2013, 02:49 PM   #192
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Originally Posted by Barleywater View Post
Hi John,

In above, what is spectrum of reference? And what are driver diameters, what is vertical spacing of acoustic centers, and what is crossover frequency?

Edit:
Sorry, see fine print: 2kHz, but spacing?

And, on axis response should return reference for linear phase conditions, but doesn't, indicating error in level matching. Almost looks like polarity reversal.
Everything is correct. No reversed polarity. Vertical spacing is about 4.5". level matching is not relevant since the reference trace is the input electrical signal and the lower traces are the measured acoustic output of the speaker. All that matters is the comparison of the shape.
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Old 2nd January 2013, 03:45 PM   #193
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Default What I heard (I think)

Yesterday I did some 1st of the Year listening test to phase correction via convolved impulse. See Post # 165
This involved ONLY phase correction, not amplitude - that's the fun and interesting part of the experiment that rePhase and software like it allows. The only correction in the convolution was to flatten the phase rotation normally caused by the high pass filter that is a bass reflex box. In this case the high pass filter is circa 37Hz, 4th order. Using an impulse generated in rePhase, I was able to eliminate this phase shift without changing amplitude.

For the first tests I listened only to the Altec 416-8A woofers in their bass reflex bass (Altec 828 with modified ports). A 6dB shelving filter was used to lower response above ~250Hz, where the front horn loading of the Altec cabinet gives a boost. The result is fairly flat over 2 decades, 37Hz to 3.7Khz. Even if a speaker is flat from 37Hz to 3.7Khz, it doesn't sound great. But it's OK on a lot of material.

Take these listening reports with a "grain of salt", as we say in English, because they were not blind tests. I don't yet have a way to do ABX from the listening position with my rig (headphones, yes). I'll try to set this up and do proper ABX testing.

What I heard (I think). A difference.
For the first few tracks, I didn't like flattened phase. It sounded looser and not as natural as the normal phase of the BR box. The normal (not flat) phase seemed to give a tighter, cleaner bass. It seemed more focused than the flattened phase. I.E. slightly, subtlety, different, but not an improvement. The flattened phase seemed slightly less focused, more diffused, looser.

Then I started to notice the mids sounded different, not as prominent or edgy. You might not think that a bandwidth limited to just under 4K could sound edgy, but it did and was a bit annoying. With the phase flattened at the bottom, the mids tended to shift backward, away from me and were easier to listen to for long periods. The midrange was the area where there seemed to be the biggest change. Bass did seem wider and more stereophonic, too. On some symphonic pieces, bass notes that wrapped all the way around my head with unaltered phase went distinctly only as far as left and right ears with the flattened phase. Odd!

Another odd effect was that even tho the bass seemed wider and more stereophonic with the flattened phase, bass instruments were easier to locate - more stable - and easier to follow in the musical line.

Going back to the full system - lows, mids, highs and crossovers - revealed pretty much the same effects, sometimes more pronounced. With the flattened phase, some midrange sounds - like voices, strings, etc. - tended to move back into the space. The whole space became deeper and wider and ambient clues of the recording space were more obvious. I was also able to listen louder than before. At some point I just left the convolver in and enjoyed the music. I stayed up listening until 3AM, it was so much fun hearing the better soundstage and depth. The low bass still seemed looser with flattened phase, but everything else seemed better focused and open at the same time.

That all seems pretty remarkable and rather hard to believe from a simple phase flattening at the low end of the frequency range. I'll continue to listen to find out if it's all just my imagination.
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Old 2nd January 2013, 04:22 PM   #194
Elias is offline Elias  Finland
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Quote:
Originally Posted by Pano View Post
What I heard (I think). A difference.
Can it be Griesinger was right with his
"The phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz" ?

"The phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz"


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Old 2nd January 2013, 07:52 PM   #195
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Hi Pano and all!

There has been a lot of activity on that thread lately, I will have to catch all that up

Great to read your interesting results.
So far, people using rePhase have mainly reported audible gains on the subwoofer crossover (~100Hz), with bass that seems more laid back at first, but with better "impact". This seems logical as the bass is more in phase with the rest of the spectrum, so it is less audible (some sort of masking effect) but happens at the same time as the parts of the spectrum that account for the impact feeling...

So far you only tested linearization on the BR?
What is you crossover frequency with the horn?

Last edited by pos; 2nd January 2013 at 08:00 PM.
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Old 2nd January 2013, 08:06 PM   #196
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Skimming through Griesinger's deck I don't see anything I disagree with but I think we're mostly just talking about subjective differences in how people organize their thoughts around what they're hearing. When I went through the same correction exercise as Pano years ago what I heard was an immediate and obvious improvement in bass tightness when the port phase was corrected and more natural rendition of instruments' tone when the crossover was corrected. I wouldn't call any of the corrections a huge difference---the higher end of hi fi is mostly about accumulating small, incremental improvements, after all---but it's interesting to see the extent of individual variation which can underly a subjective preference for better measured performance.
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Old 2nd January 2013, 08:24 PM   #197
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Pos. Crossover to horn is 650Hz, 4th order L-R (acoustical). But I don't see the phase shift there. Maybe because of the way I've offset the horns. Tweeter phase is still funky, it's hard to get it just right up around 6-5Khz.
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Old 2nd January 2013, 10:14 PM   #198
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Could I ask which of you are able to switch between filters in real time, while listening?
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Old 2nd January 2013, 10:15 PM   #199
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I can, tho I'm off to the side of the "sweet spot" by a good bit.
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Old 2nd January 2013, 10:35 PM   #200
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Quote:
Originally Posted by Pano View Post
The only correction in the convolution was to flatten the phase rotation normally caused by the high pass filter that is a bass reflex box. In this case the high pass filter is circa 37Hz, 4th order. Using an impulse generated in rePhase, I was able to eliminate this phase shift without changing amplitude.
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?
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