I meant the glue was squishing out between the inner and outer front baffle.
There isn't enough glue between them on the bottom.
I did use the B&C 10PS26.
It is the inner hole that is to small.
There isn't enough glue between them on the bottom.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I did use the B&C 10PS26.
It is the inner hole that is to small.
Thomas did an interesting experiment and posted the results in a German forum:
http://www.casakustik.de/forum/index.php/topic,309.0.html
He put a sound source (one earpiece of a headphone) in the middle of a box and a mic at the bottom:
The box then is closed:
The first axial mode occured at 567Hz:
Applying an EQ at the same frequency with a reasonably matching Q and gain reduced the peak in the frequency response AND the modes' decay rate:
Best, Markus
http://www.casakustik.de/forum/index.php/topic,309.0.html
He put a sound source (one earpiece of a headphone) in the middle of a box and a mic at the bottom:
An externally hosted image should be here but it was not working when we last tested it.
The box then is closed:
An externally hosted image should be here but it was not working when we last tested it.
The first axial mode occured at 567Hz:
An externally hosted image should be here but it was not working when we last tested it.
Applying an EQ at the same frequency with a reasonably matching Q and gain reduced the peak in the frequency response AND the modes' decay rate:
An externally hosted image should be here but it was not working when we last tested it.
Best, Markus
terry j said:
The thing is that I use the word "importance" while audiophiles use "audible". They are not the same thing. Very small differences in two compoenets can be audible and yet the system can be horrible. I've seen this so many times before. People obsess over small insiginificant "differences" in systems that are just terrible. You have to keep things in perspective. Electronics is not inaudible, its just not significant in comparison with loudspeakers and rooms.
Could my system be audibly "different" with different electronics - of course it could. Would it be better - thats an entirely different question. And even if this "difference" is detectable and shown to be an improvement in some objective way, is it cost effective?
I see people spending huge sums on electronics and minimal amounts on speakers and doing nothing with the room. Is this going to make a good system because the electronics are good? - of course not. The system is no better than its weakest link.
And you must scale "benefit" in this weakest link by the significance of the link. Thus if the electronics is not the weakest link and you improve it then the net improvement is minimal to nonexistant. Change the speakers and make them better and the improvement is huge. The situation between electronics and acoustics is simply not comparable - they are vastly different in terms of cost and complexity and influence to the end result.
My point is that acoustics is vastly more "important" than the electronics even if the electronics is not insignificant.
What was the title of the document that you wanted? E-mail me with the title and I'll send it to you.
I think that's a little hard to tell, but I am not sure thats its obvious. The rate should fall linearly with time in both cases, but since this is a log graph it may look different.
At any rate, as I said, theoretically it should not change. There may be other things going on here as well, such as the source may not be linear, etc. I'd have to be shown how, in theory, a different rate would occur.
At any rate, as I said, theoretically it should not change. There may be other things going on here as well, such as the source may not be linear, etc. I'd have to be shown how, in theory, a different rate would occur.
I am not going to discuss this here - I didn't post it here. The results shown by Markus are incomplete, the experiment was originally made with tone bursts. The experiment is presented
here.
Interesting. So you're saying that the resonance of a single mode is not minimum-phase?
Thomas
here.
gedlee said:
Interesting. So you're saying that the resonance of a single mode is not minimum-phase?
Thomas
Decay rate importance
Hey guys, there's an AES paper about the subject, researched at my uni few years ago. It is called "Perception of Temporal Decay of Low-frequency Room Modes". You can find it here among others: http://www.genelec.fi/tuotetuki/julkaisut/academic-papers/
Excerpt from the abstract
Hey guys, there's an AES paper about the subject, researched at my uni few years ago. It is called "Perception of Temporal Decay of Low-frequency Room Modes". You can find it here among others: http://www.genelec.fi/tuotetuki/julkaisut/academic-papers/
Excerpt from the abstract
mat02ah said:
It would be pointless for me to discuss this on a German forum as I don't speak German well enough.
I'm not sure what minimum phase has to do with this.
The energy loss rate of the mode is constant, how could it be otherwise and the system be linear? Thus no matter how much energy you put in the loss "rate" must be constant. The EQ does nothing more than reduce the energy injected, it can't change the energy lost. To correct what I said before however, I think that the energy loss is exponential, but the exponent is constant independent of anything that you do electronically.
There will be an interaction of the EQ's impulse response with the enclosures impulse response and this can be seen in the data as the varying double peaks.
The "real" situation is incredibly complex because the system is actually quite complex. A good read (essential!?) in this regard is the very last section of Morse's "Vibration and Sound". In it he shows how a mode in steady state will vibrate at the driven frequency even if its not precisely on that frequency, but, and this is the NON-minimum phase part, the decay occurs AT the resonant frequency. For example, lets say we have a mode at 51 Hz and we drive it at 49 Hz. In the steady state the enclosure has 49 Hz in the sound field, but when I turn off this source, the sound field slowly (relative to the decay rate) changes from 49 Hz to 51 Hz. No electronic system can do this and to call this kind of phenomina "minimum phase" is certainly not correct. Acoustics is not electronics and behaves quite differently. Concepts in electronics such as "minimum phase" can often be completely inappropriate in acoustics.
The conclusion of the AES paper indeed seems very logical to me - that we do not perceive the decay rate of LF sound, we perceive the intensity level. So that makes the whole discussion mute as regards what we hear.
Certainly an electrical system, when stimulated by an oscillatory input will oscillate at the input frequency and when the signal is removed it will decay it its natural frequency of the resonant circuit. A simple example would be something like a high Q 2nd order HP filter. Makes no difference if the system is electrical, mechanical, acoustic or thermal. For example a vented woofer system with a B4 HP alignment will have the same response as a sealed box woofer system with an electrical HP filer such that the response net response is also B4 at the same frequency. Such behavior is a result that when an input is applied the system response is the forced response and when the input is removed the system decays in acordance with its natural response from its condition at the time the input was removed.
Also, if we are sensitive to low frequency level and the decay rate is infact the rate of decay of the level of the LF, then how can we not be sensitive to decay rate? Sees logical to me that the decay rate would have something to do with whether we hear BOOOOooommmm or BOom.
Also, if we are sensitive to low frequency level and the decay rate is infact the rate of decay of the level of the LF, then how can we not be sensitive to decay rate? Sees logical to me that the decay rate would have something to do with whether we hear BOOOOooommmm or BOom.
john k..., so is a PEQ able to change the decay rate of a mode?
soongsc, as always I don't understand what you're trying to say. "the response at time "0" is also changed" - of course! We applied an EQ. That's what an EQ does: attenuate the level at or around a certain frequency.
And why do we need to "increase the rate of decay"? We don't want to enforce modal ringing, we want to control it.
soongsc, as always I don't understand what you're trying to say. "the response at time "0" is also changed" - of course! We applied an EQ. That's what an EQ does: attenuate the level at or around a certain frequency.
And why do we need to "increase the rate of decay"? We don't want to enforce modal ringing, we want to control it.
markus76 said:
I dwouldn't say that and if the mode behaves linearly then the decay rate won't changes, as Earl said. However, there is one thing missing here. If you remember my post of a few days ago I presented the equation for in room SPL. It showed that the SPL at ANY frequency is the sum of the contributions from all modes. Now, if the room is excited at a modal frequency then, for sure, that mode contributed the most to the response. However, other modes also contribute. Thus the decay rate is a conglomerate of the decay rates of all the modes. Furthermore, the effects of damping are not necessarily constant and may provide changes in decay rate with time and amplitude. But even with all that taken into account I don't think you should see a significant change in the decay rate.
I don't think the plots you showed are conclusive at all. One reason is that the amplitude of the resonance was not reduced appropriately, IMO. The peak ahs been reduced but the side bands remain at higher amplitude. I think that if the PEQ was adjusted to that it had the same bandwidth as the box resonance and the response was uniformly reduce towards flat you may see what would look like a constant decay.
I always get that wrong.
