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#41
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Non-modal peaks and nulls - here's the proof!
Don,
This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. --Ethan |
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#42
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. Place two speakers a given distance apart, playing the same tone, even suspended in space, and you will hear this. The big difference between these comb filtered effects and standing waves is that there is no resonance involved, there is no build-up and no finite collapse time. As I said, a completely different phenomenon. As for standing waves unrelated to the room's dimension - well, yes and no. The wave will be at its most powerful at exact half wave multiples., when the forward and back waves arrive in perfect phase. But standing waves at other frequencies will be of a reduced amplitude, in cos squared relation between two nodal frequencies. It looks almost like a resonance with a finite Q, but of course it isn't. d _____________________________ http://www.pearce.uk.com |
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#43
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. Place two speakers a given distance apart, playing the same tone, even suspended in space, and you will hear this. The big difference between these comb filtered effects and standing waves is that there is no resonance involved, there is no build-up and no finite collapse time. As I said, a completely different phenomenon. As for standing waves unrelated to the room's dimension - well, yes and no. The wave will be at its most powerful at exact half wave multiples., when the forward and back waves arrive in perfect phase. But standing waves at other frequencies will be of a reduced amplitude, in cos squared relation between two nodal frequencies. It looks almost like a resonance with a finite Q, but of course it isn't. d _____________________________ http://www.pearce.uk.com |
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#44
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. Place two speakers a given distance apart, playing the same tone, even suspended in space, and you will hear this. The big difference between these comb filtered effects and standing waves is that there is no resonance involved, there is no build-up and no finite collapse time. As I said, a completely different phenomenon. As for standing waves unrelated to the room's dimension - well, yes and no. The wave will be at its most powerful at exact half wave multiples., when the forward and back waves arrive in perfect phase. But standing waves at other frequencies will be of a reduced amplitude, in cos squared relation between two nodal frequencies. It looks almost like a resonance with a finite Q, but of course it isn't. d _____________________________ http://www.pearce.uk.com |
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#45
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. Place two speakers a given distance apart, playing the same tone, even suspended in space, and you will hear this. The big difference between these comb filtered effects and standing waves is that there is no resonance involved, there is no build-up and no finite collapse time. As I said, a completely different phenomenon. As for standing waves unrelated to the room's dimension - well, yes and no. The wave will be at its most powerful at exact half wave multiples., when the forward and back waves arrive in perfect phase. But standing waves at other frequencies will be of a reduced amplitude, in cos squared relation between two nodal frequencies. It looks almost like a resonance with a finite Q, but of course it isn't. d _____________________________ http://www.pearce.uk.com |
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#47
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Non-modal peaks and nulls - here's the proof!
On 19 Jan 2004 07:00:14 -0800, (Thomas A)
wrote: Don Pearce wrote in message . .. On Sun, 18 Jan 2004 14:25:08 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d Agree. A speaker located against a wall will show comb filtering effects due to direct and reflected sound, which have nothing to do with standing waves. Indeed, playing with LSPCad will handily demonstrate exactly this effect. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#48
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Non-modal peaks and nulls - here's the proof!
On 19 Jan 2004 07:00:14 -0800, (Thomas A)
wrote: Don Pearce wrote in message . .. On Sun, 18 Jan 2004 14:25:08 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d Agree. A speaker located against a wall will show comb filtering effects due to direct and reflected sound, which have nothing to do with standing waves. Indeed, playing with LSPCad will handily demonstrate exactly this effect. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#49
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Non-modal peaks and nulls - here's the proof!
On 19 Jan 2004 07:00:14 -0800, (Thomas A)
wrote: Don Pearce wrote in message . .. On Sun, 18 Jan 2004 14:25:08 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d Agree. A speaker located against a wall will show comb filtering effects due to direct and reflected sound, which have nothing to do with standing waves. Indeed, playing with LSPCad will handily demonstrate exactly this effect. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#50
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:26:47 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Stewart, why use a single microphone As Arny said, the point was to prove the existance of 1/4 wavelength nulls, not assess their audibility. And as has been pointed out, they have nothing to do with standing waves. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#51
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:26:47 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Stewart, why use a single microphone As Arny said, the point was to prove the existance of 1/4 wavelength nulls, not assess their audibility. And as has been pointed out, they have nothing to do with standing waves. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#52
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:26:47 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Stewart, why use a single microphone As Arny said, the point was to prove the existance of 1/4 wavelength nulls, not assess their audibility. And as has been pointed out, they have nothing to do with standing waves. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#53
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 11:26:47 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: Stewart, why use a single microphone As Arny said, the point was to prove the existance of 1/4 wavelength nulls, not assess their audibility. And as has been pointed out, they have nothing to do with standing waves. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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#54
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce
wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d _____________________________ http://www.pearce.uk.com |
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#55
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce
wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d _____________________________ http://www.pearce.uk.com |
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#56
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce
wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d _____________________________ http://www.pearce.uk.com |
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#57
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce
wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Do the test again with every wall padded except one - or even do it outside on a flat concrete surface so there can be no other reflections, and you will still find this effect works. d _____________________________ http://www.pearce.uk.com |
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#58
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 19:03:52 GMT, ow
(Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. d _____________________________ http://www.pearce.uk.com |
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#59
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 19:03:52 GMT, ow
(Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. d _____________________________ http://www.pearce.uk.com |
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#60
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 19:03:52 GMT, ow
(Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. d _____________________________ http://www.pearce.uk.com |
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#61
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Non-modal peaks and nulls - here's the proof!
On Mon, 19 Jan 2004 19:03:52 GMT, ow
(Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. d _____________________________ http://www.pearce.uk.com |
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#62
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Non-modal peaks and nulls - here's the proof!
"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan Even though I don't have a definite opinion or understanding of this yet, I have one small warning flag to raise here. The room modes are fairly easy to calculate for the normal, empty straight-angle room. You put in a lot of effort to fix such a room, as I saw in the film, and appreciate the effort you went through. But if the dimensions of the room is not EXACTLY as what you feed the model or if a corner is cut in the actual room, the actual mode frequencies will shift slightly. There were, as I understand some small deviations from the "straight angled, empty" room, like the ceiling, and the fact that there were three persons and some equipment inside the room. There is a risk that the frequencies you measure at are actually mode frequencies. I am not saying that they were, only that there is a risk. I would be very interested in seing frequency sweeps recorded at the points of the zeroes (and possibly some other locations). Maybe this could shed some light on what the ACTUAL modes frequencies are. I have software for this if you are interested. |
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#63
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Non-modal peaks and nulls - here's the proof!
"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan Even though I don't have a definite opinion or understanding of this yet, I have one small warning flag to raise here. The room modes are fairly easy to calculate for the normal, empty straight-angle room. You put in a lot of effort to fix such a room, as I saw in the film, and appreciate the effort you went through. But if the dimensions of the room is not EXACTLY as what you feed the model or if a corner is cut in the actual room, the actual mode frequencies will shift slightly. There were, as I understand some small deviations from the "straight angled, empty" room, like the ceiling, and the fact that there were three persons and some equipment inside the room. There is a risk that the frequencies you measure at are actually mode frequencies. I am not saying that they were, only that there is a risk. I would be very interested in seing frequency sweeps recorded at the points of the zeroes (and possibly some other locations). Maybe this could shed some light on what the ACTUAL modes frequencies are. I have software for this if you are interested. |
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#64
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Non-modal peaks and nulls - here's the proof!
"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan Even though I don't have a definite opinion or understanding of this yet, I have one small warning flag to raise here. The room modes are fairly easy to calculate for the normal, empty straight-angle room. You put in a lot of effort to fix such a room, as I saw in the film, and appreciate the effort you went through. But if the dimensions of the room is not EXACTLY as what you feed the model or if a corner is cut in the actual room, the actual mode frequencies will shift slightly. There were, as I understand some small deviations from the "straight angled, empty" room, like the ceiling, and the fact that there were three persons and some equipment inside the room. There is a risk that the frequencies you measure at are actually mode frequencies. I am not saying that they were, only that there is a risk. I would be very interested in seing frequency sweeps recorded at the points of the zeroes (and possibly some other locations). Maybe this could shed some light on what the ACTUAL modes frequencies are. I have software for this if you are interested. |
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#65
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Non-modal peaks and nulls - here's the proof!
"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Folks, Over the past year in various audio newsgroups I've explained that peaks and severe nulls occur in all rooms at nearly all frequencies. Many people have argued that nulls can't exist at non-modal frequencies, or disputed that non-modal nulls exist one quarter wavelength away from a room's boundaries. Others have argued that low frequency nulls cannot occupy a very small physical space because the wavelengths are so long. I just posted a video on my web site that proves all of these phenomena beyond all reasonable doubt. Go to www.realtraps.com/videos.htm and you'll find links for this video in several popular media formats. Although the video is decidedly home made, the content is presented clearly and accurately. It was shot all in one take, with no substantive editing, to document exactly what occurred. The video is self-explanatory, so all I'll add is to watch carefully the VU meter and microphone movement because our friend with the camcorder panned around a little too much. But if you watch closely you'll clearly see the VU meter dip by large amounts as the mike is moved into and out of the null zones. Also note that each major meter division is a 9 dB increment, so the seemingly small deflections actually represent 15 dB and greater null depths. For reference, the script and other test details are also linked from that page. Comments and questions are most welcome. --Ethan Even though I don't have a definite opinion or understanding of this yet, I have one small warning flag to raise here. The room modes are fairly easy to calculate for the normal, empty straight-angle room. You put in a lot of effort to fix such a room, as I saw in the film, and appreciate the effort you went through. But if the dimensions of the room is not EXACTLY as what you feed the model or if a corner is cut in the actual room, the actual mode frequencies will shift slightly. There were, as I understand some small deviations from the "straight angled, empty" room, like the ceiling, and the fact that there were three persons and some equipment inside the room. There is a risk that the frequencies you measure at are actually mode frequencies. I am not saying that they were, only that there is a risk. I would be very interested in seing frequency sweeps recorded at the points of the zeroes (and possibly some other locations). Maybe this could shed some light on what the ACTUAL modes frequencies are. I have software for this if you are interested. |
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Non-modal peaks and nulls - here's the proof!
Don Pearce writes:
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. And they'd be wrong. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. And this is most definitely BULL****. The waves Ethan is describing are precisely "standing waves." Go look it up in a physics book. -- % Randy Yates % "My Shangri-la has gone away, fading like %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" %%% 919-577-9882 % %%%% % 'Shangri-La', *A New World Record*, ELO |
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Non-modal peaks and nulls - here's the proof!
Don Pearce writes:
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. And they'd be wrong. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. And this is most definitely BULL****. The waves Ethan is describing are precisely "standing waves." Go look it up in a physics book. -- % Randy Yates % "My Shangri-la has gone away, fading like %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" %%% 919-577-9882 % %%%% % 'Shangri-La', *A New World Record*, ELO |
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Non-modal peaks and nulls - here's the proof!
Don Pearce writes:
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. And they'd be wrong. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. And this is most definitely BULL****. The waves Ethan is describing are precisely "standing waves." Go look it up in a physics book. -- % Randy Yates % "My Shangri-la has gone away, fading like %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" %%% 919-577-9882 % %%%% % 'Shangri-La', *A New World Record*, ELO |
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Non-modal peaks and nulls - here's the proof!
Don Pearce writes:
On Mon, 19 Jan 2004 11:31:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: Don, This is what I would expect at any frequency ... this has nothing to do with room modes or standing waves. Yes, exactly. This is the precise point I have made repeatedly dozens upon dozens of times here and in many other audio newsgroups. But nobody believed me, so I made the video to prove the point. I will mention that standing waves are standing still whether or not they relate to a room's dimensions. As long as a "forcing" tone is present the waves will stabilize into a static pattern. But I accept that many people reserve the term "standing wave" for modal frequencies only. And they'd be wrong. --Ethan OK - I see he problem - one of terminology. What is going on here is most definitely NOT a standing wave phenomenon, but a free wave one. And this is most definitely BULL****. The waves Ethan is describing are precisely "standing waves." Go look it up in a physics book. -- % Randy Yates % "My Shangri-la has gone away, fading like %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" %%% 919-577-9882 % %%%% % 'Shangri-La', *A New World Record*, ELO |
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Non-modal peaks and nulls - here's the proof!
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Non-modal peaks and nulls - here's the proof!
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Non-modal peaks and nulls - here's the proof!
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Non-modal peaks and nulls - here's the proof!
On Tue, 20 Jan 2004 01:39:40 GMT, Randy Yates wrote:
(Goofball_star_dot_etal) writes: Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Apart from the "at the same speed" qualification, which is redundant (energy at a specific frequency and a specific medium will travel at the same speed), you're absolutely right. I was not sure what would happen if there was a wind blowing, err, through the wall :-) |
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Non-modal peaks and nulls - here's the proof!
On Tue, 20 Jan 2004 01:39:40 GMT, Randy Yates wrote:
(Goofball_star_dot_etal) writes: Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Apart from the "at the same speed" qualification, which is redundant (energy at a specific frequency and a specific medium will travel at the same speed), you're absolutely right. I was not sure what would happen if there was a wind blowing, err, through the wall :-) |
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Non-modal peaks and nulls - here's the proof!
On Tue, 20 Jan 2004 01:39:40 GMT, Randy Yates wrote:
(Goofball_star_dot_etal) writes: Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Apart from the "at the same speed" qualification, which is redundant (energy at a specific frequency and a specific medium will travel at the same speed), you're absolutely right. I was not sure what would happen if there was a wind blowing, err, through the wall :-) |
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Non-modal peaks and nulls - here's the proof!
On Tue, 20 Jan 2004 01:39:40 GMT, Randy Yates wrote:
(Goofball_star_dot_etal) writes: Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. Apart from the "at the same speed" qualification, which is redundant (energy at a specific frequency and a specific medium will travel at the same speed), you're absolutely right. I was not sure what would happen if there was a wind blowing, err, through the wall :-) |
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Non-modal peaks and nulls - here's the proof!
"Don Pearce" wrote in message
On Mon, 19 Jan 2004 20:08:16 GMT, ow (Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 19:19:51 +0000, Don Pearce wrote: On Mon, 19 Jan 2004 19:03:52 GMT, ow (Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. I'm just sitting here mostly lurking, watching people argue over the meanings of words. It seems quite clear that something bad is happening in rooms and something might be done about it. How long does this haggling over words go on before someone actually says something about improving sound quality? |
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Non-modal peaks and nulls - here's the proof!
"Don Pearce" wrote in message
On Mon, 19 Jan 2004 20:08:16 GMT, ow (Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 19:19:51 +0000, Don Pearce wrote: On Mon, 19 Jan 2004 19:03:52 GMT, ow (Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. I'm just sitting here mostly lurking, watching people argue over the meanings of words. It seems quite clear that something bad is happening in rooms and something might be done about it. How long does this haggling over words go on before someone actually says something about improving sound quality? |
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Non-modal peaks and nulls - here's the proof!
"Don Pearce" wrote in message
On Mon, 19 Jan 2004 20:08:16 GMT, ow (Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 19:19:51 +0000, Don Pearce wrote: On Mon, 19 Jan 2004 19:03:52 GMT, ow (Goofball_star_dot_etal) wrote: On Mon, 19 Jan 2004 09:30:22 +0000, Don Pearce wrote: This is what I would expect at any frequency, and looks a lot like normal comb filtering - the signal arrives at the microphone via two paths, one direct and one reflected. For some positions there is reinforcement and for others cancellation. But this has nothing to do with room modes or standing waves. It is a purely travelling wave phenomenon. Ahem, I thought a standing wave *was* traveling waves (or components thereof) of the same frequency travelling in opposite directions at the same speed. In a standing wave there is no net transfer of energy along the direction of "travel" of the wave. The energy remains constrained between two boundaries. This is why they build up; they can be pumped - and also why they don't die the instant the stimulus is removed. In fact, standing waves make it impossible to measure the reverberation time of a room at very low frequencies - the wave collapses when it will, and the time taken is generally longer than the T60 of the room. Travelling waves possess none of these qualities, and must be handled, both analytically and practically, quite differently. I'm just sitting here mostly lurking, watching people argue over the meanings of words. It seems quite clear that something bad is happening in rooms and something might be done about it. How long does this haggling over words go on before someone actually says something about improving sound quality? |
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