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4th May 2009, 02:47 PM  #1101  
diyAudio Member
Join Date: Dec 2004
Location: Novi, Michigan

Quote:
I would like to ask that we get off of this discussion of mathematical details to the main topic, since none of this is constructive. 

4th May 2009, 03:04 PM  #1102  
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Join Date: Apr 2009

Quote:
Won't You please admit an error regarding frequency shift with decay ? Is that the insult You mention? You Yourself asked for a discussion as cited above. I never ever claimed "superior knowledge". It's a trival rethoric figure with wich You try to insult me by irony. Thank You. In the end the topic is done, isn't it? On phase distortion I suggest the following  free  reading: http://www.genelecht.com/documents/...ns/IOARP21.pdf Thank You 

4th May 2009, 03:42 PM  #1103  
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Join Date: Dec 2004
Location: Novi, Michigan

Quote:
I do not admit to any errors. I thought that I made that clear. There IS a frequency shift in a decay, thats clear. What you seem to be saying (and its never been clear to me) is that I am in error because the decay is not at a "pure tone" but occurs over a spectrum. That is correct, (everything is a spectrum!) but does not change the fact that the pure tone of excitation disappears and what appears in its place is a "spectrum" which has peaks at the resonance frequencies the widths and heights of which depend on the damping and the relationship between these frequencies and the driven frequency. This is what I said and this is what happens. 

4th May 2009, 03:57 PM  #1104  
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Join Date: Apr 2009

Quote:
I gave it up earlier. If You don't see that very mistake yet I'm not Jesus to make You see by wonder. You ever gave additional input, e/g the homogenious DifEq. You DO know that the non trivial solution is a spectrum, and that this spectrum is temporally constant irregardless of its starting state, isn't it? No shift! Otherwise it was non linear ... I never tried to insult You. I simply do not take it personally. To end it up, I really appreciate Your algorithm on optimizing in room bass response. An algorithm is defined as a correct methodology that end with a propper result. Why should I long for more? The yield is mostly equivalent to optimum, so what? But as You knock on peoples heads quite often when they babble audiophile BS, I felt free to gave in the first time a very friendly hint. Regarding some misleading wording. Don't take it to serious, ain't worth it. so long a more recent publication on the related side topic http://www.genelecht.com/documents/...aes116th_2.pdf 

4th May 2009, 07:35 PM  #1105 
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Join Date: Dec 2004
Location: Novi, Michigan

I don't think that the Genelec papers tell us anything that is surprising or new, their results are to be expected from simple psychoacoustics, but its good to see people doing real work in the area.

4th May 2009, 08:46 PM  #1106  
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Join Date: Dec 2006

Quote:
Let's consider a second order system underdamped ( typical of acoustical systems) When the force function is switched off, what remains is of course the transient. In this case, it is easy to calculate analytically and any text book will show that this transient is a exponentially decaying sinusoid depending only on the system and the initial conditions and not on the force function except for the initial amplitude which depends on the value of the force function when it is switched off. This decaying sinusoid is not a pure tone from a spectrum point of view of course but the decaying sinusoid is at a fixed frequency not related to the force function frequency. This fixed frequency in not the natural frequency of the underdamped system but is the natural frequency times a coefficient depending on the damping ratio z of the system. This coefficient is sqrt ( 1z²). Therefore if the system has a very low damping ( z<<1), this frequency is very close to the natural one. If the system is close to critically damped ( z=1), then the decaying sinusoid will be at very low frequency with respect to the natural frequency of the system. JPV 

5th May 2009, 12:16 AM  #1107  
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Join Date: Dec 2004
Location: Novi, Michigan

Quote:
I agree completely but left off the part about the shift in natural frequency because of damping (this is usually a small effect for acoustic room modes, not so for mechanical systems). The point is that the decay is not at the excitation frequency but at the "resonances" which in room acoustics are the damped modes. In acoustics the difference in natural frequency and the damped frequency are never considered because the modal frequency needs to include the boundary conditions which will always include the damping since all damping in room acoustics occurs at the boundary. Short of this subtle difference I agree completely. 

5th May 2009, 07:07 AM  #1108  
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Join Date: Dec 2006

Quote:
But at low frequencies in small rooms, the acoustical system is more like a lumped parameter one and there, don't you think that this damped resonance frequency effect is existing? JPV 

5th May 2009, 10:31 AM  #1109 
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Join Date: Aug 2004
Location: US

Five days of "quién es más macho".
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John k.... Music and Design NaO dsp Dipole Loudspeakers. 
5th May 2009, 11:11 AM  #1110  
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Join Date: Dec 2006

Quote:
But I asked this question because at low frequencies in small rooms it is said that there is nearly no damping. Therefore introduction of a little bit of damping could ( if what I thought is right about a more mechanical system at low frequencies) decrease the decay but also decrease the damping frequency of the transient and shift it to less audible. This must have been experimented I suppose. It is a reason more to try to damp the listening room at low frequencies. Because this is also the living room, the question is if any small trial there will be worthwhile. This is in fact my real question. JPV 

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