salas said:
Hi Salas,
I think that depends on preferences. What I do believe is that above 150 Hz or so constant directivity is desirable, be it dipole, cardioid or omni. At that point it becomes very dependent on the room and preferences. But as I develop the ICTA I may move away from a cardioid type woofer though I expect to keep the mids and top end cardioid. On the other hand, there is nothing wrong with taking the NaO II approach where the choice of cardioid or sealed box is in the hands of the listener.
Earl,
I checked the top plot on the right (number 3) against SE's FEM. The good news is that the agreement is pretty good. The bad news is that what I posted isn't the correct result. I must have mixed up some files or something. I'll have to recheck all the plots, again.
john k... said:
Hi Salas,
Earl,
I checked the top plot on the right (number 3) against SE's FEM. The good news is that the agreement is pretty good. The bad news is that what I posted isn't the correct result. I must have mixed up some files or something. I'll have to recheck all the plots, again.
Then it was four versus six that I question. Some of our differences may come from damping. I prefer to use larger values than you are using because, to me, thats more realistic. In a real room there is more damping from the entire structure moving than you will ever get from wall treatments. Putting a value of impedance on the walls thus yields a vvalue far below my expectation.
You can find my raw data for the subwoofer study here. http://www.gedlee.com/archive.htm
Hi Jon,
Posts 3546 to 3551 inclusive. I'll see if this works;-
http://www.diyaudio.com/forums/showthread.php?postid=1506272#post1506272
Cheers .... Graham
Posts 3546 to 3551 inclusive. I'll see if this works;-
http://www.diyaudio.com/forums/showthread.php?postid=1506272#post1506272
Cheers .... Graham
Graham Maynard said:
If you are implying that the comments made by Lynn regarding minimum phase somehow apply to a cardioid made form an eqed Dipole +monopole you are mistaken. It will be minimum phase.
Earl,
I noticed that you were counting figures differently after I posted. All the figures agree pretty well with SE. You comment about damping is possiblity. I don't know exactly what SE uses as wall damping (admittance) models. It may be purely resistive or could include reactive components as well (but I don't think so). The user can select wall characteristics based onSoft and comfortable, mediud absorption, hard finish, steel panels. Obviously these are supposed to be "user friendly" terms.
Another issue to remember is that the model I am using, as you noted, is really only 1st order accurate applicable for small admittance. It is probably being pushed pretty hard at the beta values I am using. But the predicted behavior is still pretty reasonable, particualrly in regard to looking at differences between sources. I would not exect full FEM simulations to suddenly indicate that dipole behave totally differently than the simple model predicts.
John
As I said, how the damping is handled will make a big difference. It was a major portion of my thesis. I would suggest you look at the older Morse "Vibration and Sound" because in it he derives the exact expressions that I used. I find that discussion clearer than Morse and Ingard (in fact I find the entire earlier book clearer). I got mine used (first edition) from Amazon for less that the new paperbacks cost from ASA.
As I said, how the damping is handled will make a big difference. It was a major portion of my thesis. I would suggest you look at the older Morse "Vibration and Sound" because in it he derives the exact expressions that I used. I find that discussion clearer than Morse and Ingard (in fact I find the entire earlier book clearer). I got mine used (first edition) from Amazon for less that the new paperbacks cost from ASA.
Above, John K wrote;-
>> "If you are implying that the comments made by Lynn regarding minimum phase somehow apply to a cardioid made form an eqed Dipole +monopole you are mistaken. It will be minimum phase." <<
( You know John - this snide remark is ridiculous ! )
I wrote;-
>> " Comments made here by Lynn Olson would also relate to EQed dipole+monopole 'systems' generated cardioid bass."" <<
because I thought Lynn's comments were relevent as he was pointing out aspects related to responses in TIME, not just amplitude and phase etc., for responses in time are also crucially relevent to cardioid response generation, and time aspects are not covered by many amplitude or phase versus frequency plots shown in this thread. Such standard frequency responses were also raised by Lynn in relation to waveform coherence !
I should not be expected to have to explain my thoughts to satisfy anyone's 'imaginings' about what I did not write about, nor think about !
Watch out - the *thought* police are about !
Cheers ...... Graham.
>> "If you are implying that the comments made by Lynn regarding minimum phase somehow apply to a cardioid made form an eqed Dipole +monopole you are mistaken. It will be minimum phase." <<
( You know John - this snide remark is ridiculous ! )
I wrote;-
>> " Comments made here by Lynn Olson would also relate to EQed dipole+monopole 'systems' generated cardioid bass."" <<
because I thought Lynn's comments were relevent as he was pointing out aspects related to responses in TIME, not just amplitude and phase etc., for responses in time are also crucially relevent to cardioid response generation, and time aspects are not covered by many amplitude or phase versus frequency plots shown in this thread. Such standard frequency responses were also raised by Lynn in relation to waveform coherence !
I should not be expected to have to explain my thoughts to satisfy anyone's 'imaginings' about what I did not write about, nor think about !
Watch out - the *thought* police are about !
Cheers ...... Graham.
Etienne88 said:
Given the masking effects in a real room with typical stereo speakers I would expect the audibility to be well above B-L thresholds. Unless you have access to quality data that shows otherwise, there is not much to dispute, is there?
The truth is subjective, isn't it?
Strongly disagree in this case. However, I am not interested in getting involved in a philosophical discussion.
I fear I do not speak French, but something seems to be lost in the translation. Your translation: ".... implies that the phase distortion is not audible" seems to suggest that he agrees. Can you please provide a reference with some measured data?
Earl, if you are out there I have a question for you. In general can the in room response at low frequency, for arbitrary source and listening positions, be decomposed into a minimum phase compnent plus a linear phase component? That is, can it be reduced to minimum phase by removal of a time delay? I know this is possible in some cases but does it apply in general?
john k... said:
John, I have never viewed the problem in that light before so I am not sure. I do know that the concept of "minimum phase" is one that is derived for electrical circuits and one dimension problems, but in general such features of a system won't hold in three dimensional acoustic fields. In the geometical or statistical region of acoustics the direct field can obey such principles since there is no multi-path etc. and it is basically a one dimensional problem. The reverberation or steady state field would most definately not obey any minimum phase criteria. I have never been convinced that the free field sound radiation problem in 3 dimensions is minimum phase at all. In fact I believe that it isn't. The amplitude, phase and time of arrival of a wavefront can all change independently with angle about a complex source.
At LF in a room, it is kind of ridiculous to talk about a direct field since the time of propagation to a wall is on the same order as the period. Thus a single period cannot even have passed before there is multipath. How could such a situation be minimum phase except by coincidence.
John,
The way I see it, any linear system can be decomposed into a minimum-phase system and an all-pass system, including room acoustics for a particular speaker placement. Sometimes that all-pass component happens to be linear phase (i.e. constant delay), but I doubt that is the case here. You could extract the minimum-phase component from a long windowed FR measurement and divide it out to get the all-pass component. I bet its phase would be all over the place, but I haven't actually tried.
The way I see it, any linear system can be decomposed into a minimum-phase system and an all-pass system, including room acoustics for a particular speaker placement. Sometimes that all-pass component happens to be linear phase (i.e. constant delay), but I doubt that is the case here. You could extract the minimum-phase component from a long windowed FR measurement and divide it out to get the all-pass component. I bet its phase would be all over the place, but I haven't actually tried.
Kilentra said:
Yes, of course this would be true - that you could seperate the two parts. I was thinking more along the lines of would the resulting seperation have any meaning as it does in the one dimensional case.
A long time window would basically be a steady state measurement - what meaning does "delay" have in such a context.
You could seperate a nonlinear system into minimum phase and all-pass components, but what would it mean?
I understand that all systems can be decomposed into and MP plus an all pass. That's text book stuff. I also know that the in room response can be MP plus delay in some cases. What I need to figure out is if at low frequency (modal range) it is MP plus delay always. At higher frequency, well above the modal region, it can definately deviate from MP depending on the relative strength of the direct and reflected sound.
I also know that the in room response can be MP plus delay in some cases. What I need to figure out is if at low frequency (modal range) it is MP plus delay always. At higher frequency, well above the modal region, it can definately deviate from MP depending on the relative strength of the direct and reflected sound.
john k... said:I understand that all systems can be decomposed into and MP plus an all pass. That's text book stuff.
John if what you are asking is when seperated, is the non-MP part a pure delay independent of frequency? How could it be? And of course if you seperate off the MP part there will be a pure all-pass part and by taking the derivative of this phase you will get a delay, but in all liklihood it will be a complex function of frequency. What meaning could you subscribe to this?
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