| phishead8 |
I was wondering about our ear's ability to discern phase correctly.
My first problem was with the large variations in frequencies that our magic ears can hear. A large range in frequencies neccessitates a large range in wavelengths.
Here are some numbers:
Speed of sound in air = 343m/s
Freq range = ~20-20000hz
Wavelength range = ~16m - 1.6cm
This means that if you move your listening chair a mere .8 cm forward, you've completely changed the phase of the 20khz frequencies compared to the 20hz. I know this is being picky, but this makes me question our ability to hear phase differences at all. If such a small motions of our head can make large differences in the phase of the sound we are hearing, when does it start to matter? I've never noticed a difference between leaning forward or leaning backward while listening to music, a difference of about 20 cm. This 20 cm changes the phase of 850hz by 180 degrees, while changing 1700hz by 360 degrees. You'd imagine that such a change would be noticable.
Any absolute polaritists want to speak out?
-Dan |
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| Bill Fitzpatrick |
phish
This is probably one of the best questions I've read here on the forums. Very, very perceptive of you to ask it.
It's now been 6 hours since you posted it and no one has tackled it.
Before I answer it for you I'm going to hang back and see if anyone has a go at it. |
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| Keld |
OK I'll have a go on it
First of all the most important: whatever the frequence sound travels at the same speed. If you lean your head forward the hi and low have the the same phase diff as it will have when the sound reach the place where your head was supposed to be (uppright position) some millisec later.
do you understand ??
so the sound is the same in a relative way but you're older, shorter of breath and one soundwave closer to death:D
Keld |
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| pinkmouse |
| quote: | so the sound is the same in a relative way but you're older, shorter of breath and one soundwave closer to death /[quote]
Too true :) :) :)
When I did my degree in psychology in the early 80s I was very interested in psychoaccoustics, and read many a paper on the subject. None, repeat, None, showed any proof that absolute phase is perceived by the human ear, phase differences between the two ears are only used for the localisation of sound in space, and that mostly only in two dimensions, as the human ear is geared not to notice up and down, only left and right, and peceptual cues are used to differentiate height, ie bird song is up and scratching sounds are usually on the floor, showing you have a mice infestation!
[quote]If you lean your head forward the hi and low have the the same phase diff as it will have when the sound reach the place where your head was supposed to be (uppright position) some millisec later. |
Sorry Keld, but phis is correct, phase does change between positions, proportionately by the difference in frequency between the two wavelengths, this is one of the perceptual mechanisms the human brain uses to locate a sound source.
Now normally at this point I would duck and cover, but hopefully with the new regime in place, all I will get is constructive critique :) |
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| Lisandro_P |
Rod Elliot had a good series of articles about phase relationships and their audibilty. Basically, our ears care for harmonic content only, and not their components phasing, so we can only hear changes in phase when they create interference effects f.ex. (cancellations and such).
Having said that, i LIKE to have the minimum phase shift necesary on my audio circuits, even if all that is ruined by the internal crossover of my speakers. Such is life. |
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| Bill Fitzpatrick |
Come on you guys. Let's get back to the original question.
Or, Is this another post that goes off on a tangents?
The answer has nothing to do with phase, phase relationships, absolute phase, frequency, the speed of sound, psychoacoustics, wavelengths or localization.
Again, phish, I must say this is a most excellent question and I really hope it will get people to think. |
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| planet10 |
When the hunter-gatherer came down from the trees he was always on the move. It was very important for him to know whether the thing he was hearing was moving or if he was moving and the thing was fixed in place.
You are moving, the speakers are fixed, the ear-brain knows how to deal with things when you move your head. Now if you clamped your head and had someone move the speakers...
dave |
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| Lisandro_P |
You knew my answer :D I don't beleive in phase audibility, so *I* don't care. Yet, i like to keep my signals as "in-phase" as posible.
As for moving the speakers, its the same deal. Your brain will make it sound like the music is moving, but it will STILL be audible as music. It might change (doppler effect, frequency response change because of room, etc) but that'd be in no way related to the phasing of the harmonic content. |
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| phase_accurate |
Hi phishead8
This is indeed a good question you asked.
The main fact is that our hearing system doesn't use phase to determine the direction of a sound source. It mainly uses the TIME DELAY between the ears to do so (I.e some other effects are also used but to a lesser extent).
Because of this, it doesen't matter that much from a first view, if you move your head back and forth while listening.
Our hearing system is performing a temporal correlation process on the lows and highs of the signals it receives. The more they correlate the more exact we can localize the source of an acoustic event.
According to John Watkinson our hearing system is able to distinguish inter earal time-differences of about 16 microseconds !
The signal localisation is performed on transients because with a steady state signal you don't have any unique time relationship between the left and the right ear anymore. If you'd use phase to detect direction by using only two receivers (in our case our ears) then the result would always be ambiguous.
Just try to to localise a sound source with sinusoidal character and steady level in a reverberant room and then try to localise somebody who is speaking in the same location. Guess which one you can do more easily ?
But there IS a relationship between phase and time as you have already noticed.
If your reproduction system has too much phase DISTORTION (i.e. the phase isnt't shifted proportional to frequency anymore) it will disturb the temporal alignment of lower- and higher frequency contents of transients (and music contains a lot of it -- at least I don't listen to steady sinusoidals but I don't know anybody else's taste so far).
To say it once again: detection of phase doesn't give you an exact direction of an acoustic event but phase distortion in a reproduction system would blurr the localization of sound sources.
This is one reason why some people prefer to listen to single broadband drivers: The absence of a crossover and the single source caracter introduce less phase distortion and give better imaging.
There was a good series of articles in Electronics World and Wireless World on that subject, written by John Watkinson. You can find some info in short form on this subject (amongst other stuff) written by him also under:
http://www.celticaudio.co.uk/technical2.htm
If I was unclear in any way don't be afraid to ask.
Anybody who disagress is also invited to shoot at me (In the end life would be boring if everybody always agrees to everybody).
Regards
Charles |
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| Circlotron |
I think it was the late Neville Williams in Electronics Australia magazine who was discussing the left to right phase difference of early (then new) CD players that because of cost, only had one D/A converter. Apparently it was rapidly switched back and forth between the two channels and as a result one channel always ran slightly behind the other. The remedy he sugested was to "collectively move your [heads] to the left about an eigth of an inch!" Sounds about right for 1/44,000 of a second phase difference.
Also, once while messing around with a dc/dc converter using ferrite potcores that ran at about 3.5 kHz and as a result made quite a piercing squeal, I noticed that if I moved my head slightly it made quite a difference to the perceived loudness of the sound. If I moved around the room there were very noticeable live and dead spots. The converter ran with a square wave and so the resulting sound from the ferrite core magnetostriction would have had lots of harmonics that would have added and subtracted as the listening position was changed.
GP. |
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| DocP |
Yea, interesting topic indeed. But Bill Fitz is correct, people are going off on tangents.
What Phish has brought up has nothing to do with interaural phase or time differences, so even though what Phase_accurate writes is interesting and mostly correct, it isn't relevant. If phish wrote about moving his head from side to side, or even rotating it, then interaural thingies would be significant but for axial translation, it ain't.
What is relevant is whether the human hearing system is sensitive to absolute phase and there is no significant evidence to suggest that it is. Even relative phase differences between signals are extremely difficult to perceive, particularly when there is a large frequency difference between the two signals. As for phase distortion, this is usually perceived in terms of "sound quality", rather than some tangible specific quantity although it is reasonable to say that it may well result in a smearing of the sound image (increased localisation blur, something entire books have been written about).
DocP
As a pedantic footnote, the nominal range of human hearing is 20 Hz to 20 kHz. In reality for a healthy adult very few individuals would be able to hear anything above about 16 kHz which isn't as bad as it sounds because there is virtually no musical content above that anyway. |
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| phase_accurate |
Hi DocP
Maybe I was a bit unclear with my statements (English isn't my mothertongue).
What I wanted to say is that phase alone doesn't matter at all.
Even the different phase lag for different frequencies for a given distance and the subsequent different change in degrees for the same change of way doesn't matter, as long as the alignment in time fo rlow and high frequencies stays the same.
Moving back a little would have the same effect as pushing the start button on the CD player a little later and vice versa (I deliberately omitted room interactions for simplicity, but thats what Circlotron experienced during his converter adventure ).
Regards
Charles |
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| sam9 |
If human hearing was really as sensitive as audiophiles believe (including me in moments of weakness and irrational aberition), I doubt we could make sense of a damn thing we hear. It's pretty clear that the brain performs extensive but very useful "signal processing" to both visual and audiatory inputs. If anyone tried to market devices that do anything comparable he'd be cursed for massively corrupting the sanctity of the signal path -- his very name would be reviled - in comparrison Bose would be among the saints.
Doubtless all this processing is not directed toward not to aesthetic ends but rather toward snagging the next meal and avoiding becomeing some other creatures meal. |
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| MRehorst |
| quote: | Originally posted by Keld
OK I'll have a go on it
First of all the most important: whatever the frequence sound travels at the same speed. If you lean your head forward the hi and low have the the same phase diff as it will have when the sound reach the place where your head was supposed to be (uppright position) some millisec later.
do you understand ??
Keld |
Not quite. The wavelength of high frequency signals is much shorter, so you do not shift the phase of all by the same amount.
Move a couple cm and you have completely inverted the phase of a high freq signal while you have barely moved the phase of a low freq signal at all.
This sort of effect is why moving speakers a small amount has a major effect on the sound at any location in the room. When you add in the effect of multipath you quickly see how silly it is to tweak power cords for the microscopic (if any) effect you will get rather than moving your speakers an inch or two which, in most rooms, will have a big effect.
From what I have read (mostly just subjective tests of phase reversal, and we all know how valid subjective "tests" are), those who claim to hear a difference usually claim to hear it in things like bass drums which will typically have very long wavelengths. It may be that it sounds different, but who can say which is correct, and on which recordings? Yet another angels dancing on pin heads issue...
MR |
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| Bill Fitzpatrick |
Further tangents.
I repeat:
<blockquote>
The answer has NOTHING to do with phase, phase relationships, absolute phase, frequency, the speed of sound, psychoacoustics, wavelengths or localization.
</blockquote>
Anyone who has looked at music on a scope knows the answer - even if they don't know they know it.
Eventually, someone is going to nail this. |
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| phishead8 |
Thanks for the replies.
It is always nice to come back to a seemingly unanswered question to find 12 replies.
phase_accurate, I am not convinced that the phase has any effect on localization. (I am not talking about the phase difference between the speakers) When I had my ESLs up and running I would be able to have a very well defined sound stage. This sound stage did not disappear as my head was leaning forward or backward. It was even obvious if I was standing behind my chair. As long as I stayed in the beams of the ESLs I could localize the sound to a pinpoint.
The fact is that the phases of the different frequencies vary greatly from each of the listening positions that I mentioned, and I didn't notice a single difference.
My question, by the way, is neglecting acoustical effects from rooms, as they are as different as people's musical tastes.
-Dan |
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| Bill Fitzpatrick |
| quote: | Originally posted by phishead8
The fact is that the phases of the different frequencies vary greatly from each of the listening positions that I mentioned
<i>No, they don't!</i>
and I didn't notice a single difference.
<i>You shouldn't</i>
My question, by the way, is neglecting acoustical effects from rooms, as they are as different as people's musical tastes.
<i>assumed</i>
-Dan |
And of course you question remains unanswered. |
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| phishead8 |
So spit it out, Bill.
Why doesn't a displacement in distance change phase from the different frequencies? Any explanation?
-Dan |
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| jteef |
Consider the impulse response.
And while you're doing that, i'll be over here looking through your stuff.
jt |
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| phishead8 |
Jteef,
Impulses are merely made up of infinitely many sinusoidal waves. They effectively happen at all frequencies. Simple Fourier analysis. So, I merely apply the same techniques as above. The frequencies all start from the speaker in phase, but by the time that they reach my ears some of those frequencies are in phase, some are completely out of phase, depending on the exact distance from speaker to ear. It still sounds like an impulse to me, however. Nice try.
-Dan |
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| jteef |
apparently you aren't as much of a fan of Jack Handey as I...
I wish i had the tools to run some experiments to verify or disprove my own hypothesis' so that i might answer your real question though...
jt |
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| planet10 |
| quote: | Originally posted by phishead8
Impulses are merely made up of infinitely many sinusoidal waves. They effectively happen at all frequencies. Simple Fourier analysis. So, I merely apply the same techniques as above. |
Another's take on this whole Fourier analysis (a theory i am well versed in and often mis-applied):
A conversation with Mr. Fourier
dave |
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| phishead8 |
Jteef,
What is your hypothesis? Maybe a gedanken experiment is enough to see it through. Or maybe someone else has some experience with it.
-Dan |
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| pinkmouse |
| quote: | | And of course you question remains unanswered. |
Bill, you seem to think we are not answering phishead's question...
He seems quite happy with the answers he is getting, so perhaps you could use your superior brainpower and experience to tell us what question he is really asking, or maybe even post something constructive for a change in this thread and give us your well thought out answer. |
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| MRehorst |
If you put simple sinewaves into your system and listen as you move your head a couple inches, you will be amazed at how the volume of any particular frequency bounces up and down depending on where you put your head. With very high frequency tones, moving your head as little as an inch will allow you to locate peaks and nulls that are a function of multipath (reflections from room boundaries and the direct signal from the driver) and loudspeaker output phase.
Is this audible in music which almost always consists of much more complex waves than simple sines? Sure it is- this is the sort of thing that makes up the in-room frequency response of a speaker. Does it matter?
MR |
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| Bill Fitzpatrick |
pinkmouse:
Didn't you read the new rules? You're supposed to be nice and make an effort not to be sarcastic.
Here is the original question:
<blockquote>
If you move your listening chair a mere .8 cm forward, you've completely changed the phase of the 20khz frequencies compared to the 20hz. I know this is being picky, but this makes me question our ability to hear phase differences at all. If such a small motions of our head can make large differences in the phase of the sound we are hearing, when does it start to matter? I've never noticed a difference between leaning forward or leaning backward while listening to music, a difference of about 20 cm. This 20 cm changes the phase of 850hz by 180 degrees, while changing 1700hz by 360 degrees. You'd imagine that such a change would be noticable.
</blockquote>
This discussion has gotten off track.
Can anyone imagine a 100msec block of music in the form of acoustic energy coming toward you? Can anyone picture the waveform? Does anyone know what is happening at a given point in space in any given instant in time? Hasn't anyone looked at music on an oscilloscope?
These forums are not just about answering questions. Those who come to an understanding because they have participated in a thinking process are much better off than those who are simply told.
The phrasing of the original question notwithstanding, the answer does not involve the terms frequency or phase.
If necessary, I will draw and post a series of diagrams. I don't think that will be needed though. Someone will come forward. Who knows, they may be lurking in the background reading this thread but not posting.
On the other hand, I may have finally gone off the deep end. These forums do take their toll. |
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| roddyama |
OK Phis, Bill,
How about this.
Consider a sound source in an open field, and your sitting on your couch listening to this sound source.
First it doesn't matter how simple or complex the sound being generated is. It will create pressure variations in the air that will travel (in all directions, but) toward you, the listener.
Second, as the sound is being generated, it will leave the sound source at the speed of sound. This speed of propogation will not change in mid journey on it way to your ear. And certianly, different frequencies will not travel at different speeds. All sound will travel at the same speed indiscriminate of frequency or phase.
So the sequence at which the "sound waves" leaves the sound source is the same sequence when it reaches your ear. There is no change of sequence (one pressure wave to the next) no matter how close or how far you move from the source.
You would have be moving your head pretty fast to get doppler distortion, so that out of the argument. If you talk about a reverberent sound field, like a room, all bets are off on what you'll hear. If you solve that one, write a paper about it.
That leaves us with, there is no perceptible difference in moving your head a small distance in relation to the sound source because in fact, there is no difference (except for the very small change in SPL).
Well Bill, how'd I do?:p
Rodd Yamas***a |
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| Bill Fitzpatrick |
You should get a couple of points, save for . .
<blockquote>
So the sequence at which the "sound waves" leaves the sound source is the same sequence when it reaches your ear.
</blockquote>
There are no sound waves (plural). This is at the heart of the problem. There is only ONE. I keep getting the idea that people think that there are a multiplicity of waves, each independent from the others. Not so. The sound issued by the speaker is a "composite". It is a SINGLE wave whose only relevant (to this discussion) attribute is that it varies in pressure over time. The relationship of the frequencies (and their relative phases) which make up this composite are already SET the instant that the sound leaves the speaker. At this point the entire concept of phase no longer applies - it disappears from the equation leaving only amplitude and time. Phase is an intermediate player who often gets benched. By moving forward or backwards you are only changing WHEN you hear the pressure change at your ear - you are not changing any relationships between the constituent parts of the wave because they cannot be changed. They cannot be changed because they no longer exist. But, sadly, they can be revived and phase will rear its ugly head again. So remember, whenever you meet phase on the street you need to say, "get outta my phase."
Now, of course, someone is going to say, "But, wait, my tweeter is tweeting and my woofer is woofing. Surely they are issuing separate waves."
So they are. |
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| phase_accurate |
Bill Fitzpatrick wrote:| quote: | | By moving forward or backwards you are only changing WHEN you hear the pressure change at your ear - you are not changing any relationships between the constituent parts of the wave because they cannot be changed. |
Isn't this the same as I also said within my last post (the thing about starting the CD player a little later or earlier)?
:confused:
I also repeatedly said that phase alone doesn't matter at all. But phase DISTORTION will cause signal distortion (i.e. linear distortion). Maybe it was a mistake not to mention that these form of distortion is introduced by electronics (to the least extent) and by loudspeakers (the main culprit) but never by changing distance to a sound source - because it just changes a frequency-independant delay which leaves waveshapes as they are.
Regards
Charles |
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| DocP |
Good stuff Bill.
Of course when you have real speakers with multiple drivers in a real room with diffractions, reflections, standing waves, etc. all bets are off.
I think the confusion may come from a misunderstanding of Fourier Theory. Lots of people seem to have got the idea that all sound waves are made from sinusoidal signals added together. The misunderstanding is that this is just a mathematical tool to help to understand and analyse what is going on. It's not the real worlds.
As Bill pointed out, an impusle from a loudspeaker travels round the room as an impulse. In a real room it will hit floors, walls and objects, each of which will absorbe part of the energy and bounce the rest back again. In this real world, each object will have a non uniform frequency response and will therefore change that impulse a little bit before sending it back into the room. So, if you have a room, for example, that has walls that perfectly reflect 1 kHz but have a good coefficient of absorbtion for all other frequencies, then, every time you play an impulse (or any other complex signal) from your loudspeaker, you will get really irritating standing waves at 1 kHz, providing that the original signal contained a 1 kHz component.
"But DocP, you just said that splitting a signal into its component sinusoids was just a mathematical trick ?" Confusing the real world, isn't it !!!
In practice exactly this sort of thing happens quite often with low frequencies where a room will "boom" at a given bass frequency. Often the solution can be found by changing the location of the speakers and the listening position (easier than changing where the walls are located). This doesn't stop standing waves existing, but it can alter the phase and amplitude just enough to make all the difference. Interestingly, the human hearing system is remarkably good at ignoring what the room is doing to a given signal, within limits. But I've gone off on a rant about room acoustics....
Going back to the phase bit, this is the reason for time aligning the drivers and the popularity of electrostatic drivers, Kef's Uni-Q or full bandwidth drivers. They do all the time alignment for you and you don't end up with the low frequency bit arriving slightly after the high frequency bit which confuses the hell out of the hearing system. Similarly diffraction from sharp edges of the loudspeaker box can add another bit of the impulse to the overall sound, resulting in smearing of the image. |
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| pinkmouse |
Sorry Bill, I just thought you were getting a bit gro....my fault
| quote: | | this is the reason for time aligning the drivers and the popularity of electrostatic drivers, Kef's Uni-Q or full bandwidth drivers. |
.
Yes, totally correct, but to agree with Bill, all you are hearing is still one modulated compression wave, once the sound leaves the speakers, and distance from that source is irrelevant.
| quote: | | Second, as the sound is being generated, it will leave the sound source at the speed of sound. This speed of propogation will not change in mid journey on it way to your ear. And certainly, different frequencies will not travel at different speeds. All sound will travel at the same speed indiscriminate of frequency or phase. |
Yes also true in a perfect world, but in the real world there are many complications, to give one example, on a sunny morning at an outdoor festival the relative humidity close to the ground is high, due to evaporation of night time dew. This difference in humidity causes sound to curve down towards the ground, as the speed of propagation of a sound wave is slowed by the denser air, ( just think of light, a prism, and the resulting rainbow). |
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| roddyama |
Hi Pinkmouse,
You were doing fine up to this point.| quote: | | (just think of light, a prism, and the resulting rainbow) |
This statement implies that different frequencies are affected to different degrees by temperature or humidity changes. This is not true. As the wave propagates through the changing conditions, its speed changes creating a dispertion or focusing effect. It is frequency independent.
Rodd Yamas***a |
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| phishead8 |
After reading your posts I will sit and think a little bit about it.
I am not entirely convinced that splitting the signal into its original frequencies is a bad idea. Fourier isn't just a mathematical tool, it is how our ears perceive the sound. Our choclea are filled with hairs of different lengths. Each hair is tuned to a specific frequency and picks up only one frequency at a time.
Thanks for the dialogue, folks. I find that this is the best way to sift through the heaps of **** that I've managed to acrue.
-Dan |
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| Bill Fitzpatrick |
| quote: | Originally posted by phishead8
I am not entirely convinced that splitting the signal into its original frequencies is a bad idea.
-Dan |
Am curious as to what you mean by this. |
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| phishead8 |
That was poorly worded. I meant "constituent frequencies." In other words, to use Fourier.
-Dan |
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| Bill Fitzpatrick |
| Must be my day to be stupid. I still don't understand. What is this relating to? |
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| nania |
| Unfortunately, I found this thread to late to impress Bill with my grasp upon this topic. Richard Vandersteen designed his speaker line around this very issue. According to the subjective tests on a "standard listener", he discovered that phase misalignment is indeed audable and results from recreating a sound from speaker drivers of different frequencies on the same plane. In nature, a soundwave carrying different frequencies and amplitudes is generated from the source point(s) and transmitted omnidirectionally. Our hearing has evolved to locate the source(s) of the sound by processing the time delays of the reflected wave(s) to identify its location within a space. Vandersteens solution was to stagger the speaker drivers so as to time their arrival more accurately within a listening space. Since low frequency waves travel more slowly, the lower frequency drivers are placed closer to the listening position than the higher frequency drivers. Unfortunately, his speakers are not to create the enormous soundstages that his competitors can achieve. Whether this is the fault of his speaker or of the way we record sound is still up for debate. Vnadersteen addressed this issue with the cabinet design, some have addressed it in the crossover. The so called "time aligned crossovers" that you have heard about try to time/phase align the different drivers electronically. |
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| nania |
edit
...this thread too late to impress Bill...
edit
...Unfortunately, his speakers are not able to create... |
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| Bill Fitzpatrick |
nania:
The speed of sound is NOT related to frequency. Midrange drivers and then tweeters are set back in an attempt to put the <font color="#ff0000">acoustic centers</font> (read voice coils here but only as a discussional reference) of all the drivers on the same plane. This is what time alignment is about. This works to <i>some</i> degree but as Richard Heyser pointed out decades ago in one of his great <u>Audio Engineering Society</u> papers, the acoustic center of a given driver varies with frequency.
Anyway, your post, however important it might be, has nothing to do with the original question of this thread which, I believe has been answered.
I don't know if everyone is happy with the answer but it's correct nonetheless. If anyone thinks my answer is in error, let me know - I'll be happy to continue the discussion. |
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| nania |
Bill Fitzpatrick| quote: | | The speed of sound is NOT related to frequency. |
It isn't when it occurs in nature because the wave is created from the point(s) of origin omnidirectionally in a natural space but it definitely is related to frequency when it is recreated by speaker drivers. There are spatial differences in the point of the source sound as opposed to the speaker recreation of the sound which do relate it to frequency. |
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| Bill Fitzpatrick |
Well, you could do a lot better in explaining what on earth you are talking about.
<i>Nevertheless, the speed of sound is constant for all frequencies regardless of the origin of the sound.</i>
If you want to believe otherwise, that's your business but I would like to point out that hanging on to erroneous beliefs will do you no good in the long run.
Personally, I think you should be asking questions rather than answering them. |
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| nania |
| Well, I seemed to have gotten under your skin. For that I am sorry because we do agree that the speed of sound in nature is not frequency dependent. What I am trying to say is that the speed of sound is related to frequency when reproduced in an audio system. One of the reasons Linkweitz developed his dipole speakers was an attempt to deal with the omnidirectionality of sound and to get around the spatial limitations of reproducing sound within a foreign environment. Speakers introduce their own frequency distortions so you cannot say that the speed of sound created through them is not related to frequency. Neither can you remove the amplifier and its power component representation of those frequencies as being unrelated to the speed of sound. If it were unrelated, a fast amp or speaker would not be an understood adjective to audiophiles |
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| nania |
| If I have not explained myself properly, please tell me where you believe my beliefs are erroneous? |
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| planet10 |
nania,
you have me confused... the speed of sound is different at different frequencies if reproduced by a speaker, but not in nature? Strange, very strange. Scotty, beam me up, i think i'm on the wrong planet.
dave |
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| Bill Fitzpatrick |
Only gro got under my skin and only because he's a nut bag.
I really can't be of further help to you until you get rid of the notion that the speed of sound varies with frequency.
The source of the sound is not relevant. Whether it's an owl hooting, a wine glass clinking, your lover whispering sweet nothings in your ear or a speaker system speaking does not matter a single iota.
When you come to terms with this basic fundamental truth we can go on. Sorry to be the bearer of bad tidings but you don't know as much as you think you do. |
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| nania |
| Okay, I see the source of the confusion. If we accept the speaker as the originating source of the sound, then all the constituent frequencies within the waves created by the speaker travel at the same speed. The point that I evidently failed to bring across is that the recorded sound has speed differences to the original and they are frequency related. This ties into the Nania Audio Power Theory which I have recently edited and restated. |
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| AudioFreak |
| The recording media has nothing to do with the resultant speed of sound sorry nania; The recording process records frequency and amplitude not the speed of sound. It can vary the frequency and the time domain relationship between the various frequencies but once the electrical wave is tranformed into sound at the speaker, all sound travels at the same speed so this arguement is void. |
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| nania |
| It's not the recording media, its the recorded representation . There is a distinction so don't be so quick to apologize for me. |
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| AudioFreak |
| Nor does the recorded representation have any effect on the resultant speed of sound... |
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| nania |
AudioFreak
When you compare the original to the recorded representation through a speaker, I believe there is a soundspeed differential that is frequency related and furthermore, I believe it also causes soundspace degradation. |
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| AudioFreak |
| There are frequency dependant phase / time domain and amplitude differences. However, all sounds travels at the speed of sound regardless of the frequency or how it was created. Furthermore, the speed of sound is determined by the temperature, humidity, air density and so on. Therefore, any differential in the speed of sound relative to the original can be attributed to the environmental conditions but for the sake of repeating myself one more time, all the frequencies still travel at the speed of sound ... it's just that the specific speed of sound is variable. |
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| Peter Daniel |
Sound waves cannot travel through a vacuum and need some type of matter as a carrier. Their speed is affected by the density of the substance through which they pass, as well by its temperature. In air the speed of sound is 343m/s and in water it's 1,469m/s, while in steel it's 5,121m/s.
Frequency is the number of complete waves (or oscillations) that occur over a given time period. Frequency is measured in cycles per second.;) For example, if 10 wave crests pass a point in 1 second, the frequency would be 10 cycles per second. Frequency is not dependant on a matter in which it occurs because it is only a describtion of a pattern.
The frequency, wavelength and velocity of waves are all interrelated, and these relationships can be expressed by equation:
v = l x f
where v is the wave velocity measured in meters per second, l is the wavelength measured in meters, and f is the frequency of the wave in cycles per second.
From that short physics lesson we can conclude that we could not talk about frequncies if they would have different speed in a particular matter.;) |
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| cocolino |
Though I believe Bill and phase_accurate gave excellent response to the initial question of phishead, I feel there is still a lot of confusion about phase, time etc. and therefore I try to add something which might (hopefully) contribute to better understanding of what has been said so far (or maybe at least one or the other part of it).
I think the hole issue of misunderstanding about the term phase mostly comes from being applied in the wrong context.
Phase applies to steady periodic signals only, which are related in that way to each other (or themselves) in respect of their max. peak amplitude (respectively zero crossing) in relation to their wavelength.
Phase relationships do only apply correctly and senseful to different periodic and steady signals being of or containing the same frequency. For example think about phase response of an amplifier or a speaker or whatever. What is to be compared? The phase versus frequency of the input signal in relation to the output - but of the same frequency at a time.
Phase is interesting until that point where two or more steady state signals containing the same frequency are going to be mixed together and they form a new signal. The mixing may happen electronically (summing amplifier) as well acoustically (multiway speaker).
Also what concerns the amplitude of the created "composite" wave, phase does only matter for signals containing the same frequency. Regarding amplitude, while summing a 1V/100Hz sinus with another sinus 1V/10kHz phase obviously does not matter at all.
After the mixing process there is no thuch thing as relative phase anymore because it is only one signal now and we should refer to time, respectively (group) delay and amplitude instead (guess that`s what Bill have meant with his oscilloscope hint - on a scope there is only time and amplitude).
For music which is a row of unsteady, nonperiodic pulses (unless that techno stuff which to a great extend is steady, periodic and boring exclusively.. hehe..) of mixed signals, the same apply - there is only time and amplitude -
and the term phase is already integrated in the terms time and amplitude. |
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| roddyama |
Christoph,
You used that "phase" word a lot.
You're a "Big Man" now, just wait 'till Bill gets back.:eek:
Keep Smiling:D ,
Rodd Yamas***a |
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| cocolino |
:( :( :) ;)
Rodd,
I didnīt intend to answer THE question because Bill already did it and I think he is right about what he said. Indeed I have to admit that his answer made me a lot (the hole last night) of thinking again about this things. Refreshing and over- or rethinking all that stuff what once was assumed to has been understood already by oneself, isn`t a bad thing.
I think he didn`t come out with his answer because that is what he wanted - to think about it - and all that stuff isn`t so easy to understand as it may appear at the first glance - at least not for me because I`m a little slow in matters of comprehension.
Tough the word phase appears quite often, I can see nothing what is in contrary to what Bill said .
But as per one of our great Bavarian philosophers always used to say:
"let`s looking and we`ll see" (Franz Beckenbauer):D |
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