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Multi-Way Conventional loudspeakers with crossovers

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Old 12th July 2007, 10:27 PM   #11
OzMikeH is offline OzMikeH  Australia
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Just consider: If you spent that much money on building a pair if speakers the rough textures would NOT be an accident or sloppiness. It's definitely there for a purpose.
Note how the texture gets rougher for the lower frequency drivers.
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Old 13th July 2007, 12:40 AM   #12
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Hmmm, I like the gist of what John Watkinson says in that article, but he seems to avoid details about the Heisenberg Inequality (re: time and frequency accuracy being mutually exclusive).

A simple experiment that anyone can do with a music keyboard and/or software is to play two closely spaced sinusoidal tones, and vary the frequency of one of them to observe some effects based on one's own hearing.

What I've typically found is that a tremelo effect can be heard up to a difference of F1 - F2 = approximately 20Hz. Above that, the sound of 2 dissonant frequencies starts to dominate over the AM effect.

Contrary to what Watkinson appeared to be saying about the importance of reproducing transients with high accuracy, experimental results suggest that their importance starts to diminish substantially below around 25ms ( 1/ (20Hz times 2 peaks per cycle)). The thing is that 25ms is a huge amount of time compared to the <1ms accuracy that's often suggested for so called "phase accurate" crossovers.
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Old 13th July 2007, 12:49 AM   #13
SY is offline SY  United States
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Pedant alert- the time/frequency trade-off is not the Heisenberg relationship. It's a classical uncertainty, well-known a hundred years earlier. It is, though, an effective way of illustrating the general concept.
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Old 13th July 2007, 01:18 AM   #14
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Quote:
Originally posted by SY
It's a classical uncertainty, well-known a hundred years earlier.
One would hope so! Most of these things are very easy to visualize and figure out intuitively. Lack of mathematical rigor only seems to become a problem when people don't intuitively understand the underlying processes, so they demand proofs or experimental results.
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Old 13th July 2007, 06:24 AM   #15
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Having read many articles written by John W I know for sure that he is aware of the time/frequency trade-off.

I don't understand what a phase-accurate crossover has to do with the beat between two frequencies.

But I am convinced that timing errors in the area of 1ms or even larger are too much if one takes into consideration how our hearing detects direction.

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Old 13th July 2007, 06:41 AM   #16
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Quote:
Originally posted by phase_accurate
I don't understand what a phase-accurate crossover has to do with the beat between two frequencies.

But I am convinced that timing errors in the area of 1ms or even larger are too much if one takes into consideration how our hearing detects direction.

Regards

Charles
Well if the line starts to get blurred below 25ms and instead of hearing one pulsating tone we start hearing 2 continuous tones, then why worry about delays that are 25 times smaller?

It seems a bit like insisting on a 2,000Hz refresh rate on a CRT monitor, because it might be possible to see a little bit of flicker at 85Hz. It doesn't make sense.

I understand that human ears can distinguish small phase differences at several kHz, but I'm not sure how that's meant to translate to timing differences, which may vary from a few degrees to several thousand degrees depending on frequency.
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Old 13th July 2007, 07:25 AM   #17
ScottG is offline ScottG  United States
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SL still has the paper (along with others) here:

http://www.linkwitzlab.com/links.htm




Quote:
Originally posted by CeramicMan


Well if the line starts to get blurred below 25ms and instead of hearing one pulsating tone we start hearing 2 continuous tones, then why worry about delays that are 25 times smaller?

It seems a bit like insisting on a 2,000Hz refresh rate on a CRT monitor, because it might be possible to see a little bit of flicker at 85Hz. It doesn't make sense.

I understand that human ears can distinguish small phase differences at several kHz, but I'm not sure how that's meant to translate to timing differences, which may vary from a few degrees to several thousand degrees depending on frequency.
In particular, see this link:

http://www.aip.org/pt/nov99/locsound.html
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Old 13th July 2007, 07:42 AM   #18
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Quote:
Well if the line starts to get blurred below 25ms and instead of hearing one pulsating tone we start hearing 2 continuous tones, then why worry about delays that are 25 times smaller?
I think you definitely look at it the wrong way around: The blurred picture is definitely the pulsating tone and the clear one is the 2 continuous tones !

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Charles
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Old 13th July 2007, 09:09 AM   #19
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Lol, you know what I mean! There's no 'right' or 'wrong' regarding those mutually exclusive properties. Hearing two continuous tones could equally be described as an inability to resolve pulses above a certain repetition rate

Besides, I think we're talking about two different effects here. I agree that localization of sounds in the 500Hz~5kHz range demonstrates an ability to work out phase differences in the order of microseconds. It could be as simple as neurons firing from opposite sides of the head and combining near the middle, where slight lateral offsets enable a natural learning process where the brain literally maps the sounds and recognizes familiar patterns.

But I don't see how that's relevant to crossovers as John Watkinson suggested. By definition, low-pass filters reduce the timing accuracy at which transients can be determined. Lobing effects are well known and phase rotation merely changes the angles at which they occur - usually it's in the vertical axis anyway.

IMO the important point is that each ear gets equal treatment, so the loudspeakers have to have very similar performance on both sides.
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Old 13th July 2007, 09:42 AM   #20
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But I don't see how that's relevant to crossovers as John Watkinson suggested. By definition, low-pass filters reduce the timing accuracy at which transients can be determined. Lobing effects are well known and phase rotation merely changes the angles at which they occur - usually it's in the vertical axis anyway.
I have to basically agree that treating both ears (or the signals for both ears) the same way should theoretically be sufficient.

But time-smear (due to allpass crossovers) would change the perceived SIZE of a virtual sond-source. Apart from that: Why do we accept speakers whose output is a mere caricature of its input signal ?

Regards

Charles
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