Don't forget to make sure the amplitude response over 20 - 20k Hz is matched to better than 0.1dB for the two impulse responses.
you're right,i've been traped several times.
that may leads to wrong conclusion.
with jriver,send a sine at 1 or 2 kHz,check the level and adjust with/without convolution.(with yours ears)
once adjusted,try with musical file.
vsthost allows more flexible adjustemnt in this way but level must be matched perfectly.
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An impulse response is complete characterization of system, the IR doesn’t have a pre-impulse; this is confusing a causal source of information with the transmission of information. IR of transmission system describes what will happen to information that is being transmitted through the system via convolution.
As old fashioned speaker designer, self interested prejudice against tools that flatten the playing field is understandable, but is not an excuse for calling time domain behavior of linear phase filters with frequency dependent amplitude evil.
You see the sense with anti-aliasing filters. See the rest of it.
Hi Pano,
This may be helpful to you.
http://www.bodziosoftware.com.au/Attributes_Of_Linear_Phase_Loudspeakers.pdf
Best Regards,
Bohdan
example of 3 impulses responses
a acausal one,centered at t=0,and two causal shift in time.
phase resulting,note the linear X axe.
a acausal one,centered at t=0,and two causal shift in time.
An externally hosted image should be here but it was not working when we last tested it.
phase resulting,note the linear X axe.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I think what is being referred to is the effect of summing of axis. At linear phase filter has pre-ringing. But the sum of a HP and LP, at the design point, sums to a perfect impulse. As you move off axis the times of flight for the woofer and tweeter become different and the sum is not longer a perfect impulse. This reveals the pre-ringing, typically in the tweeter's impulse.
Here is an example of the effect of moving off axis for a linear phase LR4 type crossover and a normal. causal LR4 crossover. I've posted this figure many time in the past.
The upper trace in each plot if the input or reference impulse. The lower trace is the measured impulse at the positions indicated. The upper set of plots is for the linear phase system, the lower set for the normal LR4. What you see, particularly in the 15 degree vertical plot, is the development of the pre-response of the linear phase crossover. Of course, it can be argued that with a normal crossover the tweeter response always leads the woofer.
An externally hosted image should be here but it was not working when we last tested it.
The upper trace in each plot if the input or reference impulse. The lower trace is the measured impulse at the positions indicated. The upper set of plots is for the linear phase system, the lower set for the normal LR4. What you see, particularly in the 15 degree vertical plot, is the development of the pre-response of the linear phase crossover. Of course, it can be argued that with a normal crossover the tweeter response always leads the woofer.
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.
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.
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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.
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.
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.
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.
Can it be Griesinger was right with his
"The phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz" ?
http://www.diyaudio.com/forums/multi-way/223714-phase-coherence-harmonics-vocal-formant-range-630hz-4000hz.html
- Elias
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?
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?
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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.
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?