Multiple Small Subs - Geddes Approach

dlr said:


I understand your position on the acoustics in the reverberant room environment, but I don't understand dismissing it in this manner. Without MP in acoustics to some extent, CAD software could not work as it does. It is true that considering specific individual axes does not provide the full story, but I would be hard pressed to find a way to do what I do if acoustics were not MP in certain aspects. Were acoustics completely non-MP in all aspects, I could agree with you. I see "ill applied" as being in the context in which you focus, not all aspects.

Dave


That there are aspects for which it is applicable I do not deny, but that it is generally applicable I do deny. I have consistantly pointed out aspects of acoustics where it does not apply and hence, to me, failure of one situation means failure in the general sense. In physics a law must ALWAYS be correct to be a law, not correct "some of the time".

"Without MP in acoustics to some extent, CAD software could not work as it does. "

But it would still work. I have done CAD software and never used the concept of minimum phase at all, it works fine. I will repeat again, for the umpteenth time, you will not find the notion of minimum phase used in any text in acoustics. That it can be applied in SOME circumstances is, to me, completely beside the point.
 
gedlee said:
I have done CAD software and never used the concept of minimum phase at all, it works fine. I will repeat again, for the umpteenth time, you will not find the notion of minimum phase used in any text in acoustics. That it can be applied in SOME circumstances is, to me, completely beside the point.

I have followed your references to your software and I recognize the absence of MP in them. However, I am unaware of any commercial software that does not rely upon MP to some degree. Are you aware of any commercial software that provides similar functions, yet does not rely upon MP? Your software is not commercially available to the public if I'm not mistaken.

Dave
 
markus76 said:


Aha...and in which exact cases non-minimum phase aspects are not significant enough and which cases don't allow for non-minimum phase aspects? Please provide a listing.

Thanks, Markus
It's amazing I'm not on ya'alls ignor list. For one, we all know that baffle edges will cause diffraction waves. If this is significant enough, you will see very consistent range of ripples in the SPL. This is not significant in the case of XO design, and most possible you won't move the speakers around in the room due to this. So this would be considered "not significant". However, if you consider the audibility of the diffraction wave such that it will effect your baffle design, then it becomes "significant". Lot's of things everyone already know, but probably nor many think in terms of minimum phase or not. Minimum phase is a theoretical model that in most cases provides good enough results to predict what you will get in the electronics or mechanical world. The question is, when you get different measurements when you measure at different points, do you consider this non-minimum phase, a different system, or is the difference such that it can be ignored such that you still feel it fits the minimum phase model close enough.:D

Sorry, but I have not found a way to conclude all this into a simple list.:D Maybe by the time I'm 80...
 
pjpoes said:
This may be a completely unimportant issue, but what about group delay. I know that group delay at low frequencies is generally a really small to non-existant issue because of the wavelengths, but it's my understanding that group delay audibility thresholds vary with frequency. How much group delay is audible at 100hz, 80 hz, 150hz, etc. Highpass filters add group delay, and the steep the filter the more delay. If you added a 4th order L-R at 100hz the group delay at 100hz would go from around 1ms with no filter (clearly inaudible) to 6-7ms. It seems that some research on group delay indicated that between 1 and 2 cycles is just audible. At 100hz, 6ms isn't a full cycle, but it's getting close. Does this become an issue? EQ add's group delay, if you eq the mains above 100hz, could the amount it adds be enough to be audible?

Studies has shown that GD around/below 1/F is free from audible effects. A safety margin would be 0.8/F since at the 100-250hz range the ear is most sensitive to groupdelay.


In order to avoid excessive GD with a sub/sat combo it seems important to have decent extension from the sub as a narrow bandwith sub crossed to a high order highpassed main will possibly result in problems.

An EQ turn the phase but a non-flat speaker has phase distortion as well and if you get the frequency response right, phase will follow. Both speakers (sans the crossovers in most cases) and analog EQ's are MP.


/Peter
 
gedlee said:


...

But it would still work. I have done CAD software and never used the concept of minimum phase at all, it works fine. I will repeat again, for the umpteenth time, you will not find the notion of minimum phase used in any text in acoustics. That it can be applied in SOME circumstances is, to me, completely beside the point.
I take it that you feel time alignment is not important?
 
dlr said:


I have followed your references to your software and I recognize the absence of MP in them. However, I am unaware of any commercial software that does not rely upon MP to some degree. Are you aware of any commercial software that provides similar functions, yet does not rely upon MP? Your software is not commercially available to the public if I'm not mistaken.

Dave


My software is and has been commercially available, although now it is free, so I suppose that's not commercial anymore. I am not an authourity on what software exists or how it is implimemented. But let me ask, just what is it that MP makes easier or is required in "CAD" software? (By CAD I was assuming that you mean array and speaker predictions in rooms. Otherwise I don;t understand.)

Quite honestly though, I am just not that interested in a continued MP discussion. It's just not that important to me. If it makes your life easier then fine use it. I just do everything complex in all cases and if its MP or not is of no matter. The concept does allow some simplifications for EQ discussions, but only in as much as we are talking about single points and not sound fields.
 
soongsc said:

I take it that you feel time alignment is not important?

Soongsc

Sorry you are taking such heat, but you are well known for speaking about things with an air of authority that is apparently unjustified. Questioning might be a better tact in your situation that making such bold statements.

Time alignment is important in that it has a major effect on the polar pattern at the crossover. One finds that obtaining a good polar response at crossover necessitates a near time alignment of the drivers to come out right. But the need is for a good polar response and not for some belief that phase matching or phase itself is an audible characteristic. What is audible is the poor polar response that one gets when the two drivers do not have the minimum time differential between their signals.
 
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Joined 2009
gedlee said:

Well you are both wrong. Morse is one of the formost Physicists of the 20th century and doesn't get things like this wrong. Read it in his book - Morse, P.M., "Vibration and Sound" - last page of the book pg. 429 Do a "further analysis" if you dare! If you have the capability to do that! Show its wrong or recind your comments!


Sorry Earl,

The context is lost a bit now. I've got a degree in high energy physics. So people once ment that i've got some capabilities. Thats for the record only.

Your claim was:
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.

I think using the term "AT frequency" provoces a missconception. Switching the power source off is the same as driving the system with an anti-signal. This anti signal will not consist of one special frequency but of a broader spectrum. The system will -linearly- react to all that new stuff on its input. It is not easy explained to common people, but I think You're educated enough to check out things.

Regarding these basics all systems called resonators do the same. That is the use in models, abstracions etc.

Again. If we talk about a single certain -frequency- then by pure logic (math) we talk about steady state. No temporal development. If we talk about -time-, temporal development of systems states we should use the term -spectrum. Would have been doing so many anger could have been avoided in the past.

As a first example lets get te misleading term "decay on resonance frequency" right. If the systems energy decays, it will show a spectral distribution around its defined resonance frequency. The width of that distribution is determined by the "Q".

Terms like "minimum phase" etc have to do with the transfer function of a system. These characteristics can not be derived from the basic mechanical or electric model as being a resonator. The transfer component is missing in the first place.

Thank You
 
gedlee said:


Soongsc

Sorry you are taking such heat, but you are well known for speaking about things with an air of authority that is apparently unjustified. Questioning might be a better tact in your situation that making such bold statements.

Time alignment is important in that it has a major effect on the polar pattern at the crossover. One finds that obtaining a good polar response at crossover necessitates a near time alignment of the drivers to come out right. But the need is for a good polar response and not for some belief that phase matching or phase itself is an audible characteristic. What is audible is the poor polar response that one gets when the two drivers do not have the minimum time differential between their signals.
I understand your point concerning time alignment.

I don't mind taking heat. Most people don't have the knowledge to prove me wrong, thus the conflict. I think any new point of view will face this kind of rejection. The ultimate decision is made by customers, optinions of which I always spend time to try to understand rather than reject. I do communicate with audiophiles, and in many cases, they find similar trends that I predict. Some of which are related with horns/guides.

Anyway, anyone with an open mind will learn faster and have more fun than those that don't. I think we will be making some news a few months from now.
 
Your analysis is lost on me - sorry. I don't follow it at all. And some phrases are not even sentences like:

"As a first example lets get te misleading term "decay on resonance frequency" right. "

I never used the phrase "decay on resonance frequency" so I have no idea what the quotes mean. The rest of the discussion is just as illusive. If you want to have an intelligent discussion about the math thats fine, but you at least need to write in complete sentences and in a comprehensive manner.
 
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gedlee said:
Your analysis is lost on me - sorry. I don't follow it at all. And some phrases are not even sentences like:

"As a first example lets get te misleading term "decay on resonance frequency" right. "

I never used the phrase "decay on resonance frequency" so I have no idea what the quotes mean. The rest of the discussion is just as illusive. If you want to have an intelligent discussion about the math thats fine, but you at least need to write in complete sentences and in a comprehensive manner.


Earl,

You wrote:

"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."

Sorry for being insistently. What You wrote above is in no way supported by contemporary knowledge (remember my degree in physics?). Neither is the maths of mechanical systems in any way different from that of electronic systems in this scope. Nor does the decay mechanism drift from one frequency to an other. Neither abrupt nor gardually. If so it could never be called linear, that simple.

Again, there is no relation to any phase, especially no so called minimum phase.

You have to admit a misstake. Anybody is prone to such anytime, nearly. So, as You are a native speaker please forgive my incomplete whackey so called sentences. I'll try to live up to Your expectations. I wish You would live up to mine.

thanks a lot
 
xpert said:



Earl,

You wrote:

"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."

Sorry for being insistently. What You wrote above is in no way supported by contemporary knowledge (remember my degree in physics?). Neither is the maths of mechanical systems in any way different from that of electronic systems in this scope. Nor does the decay mechanism drift from one frequency to an other. Neither abrupt nor gardually. If so it could never be called linear, that simple.

Again, there is no relation to any phase, especially no so called minimum phase.

You have to admit a misstake. Anybody is prone to such anytime, nearly. So, as You are a native speaker please forgive my incomplete whackey so called sentences. I'll try to live up to Your expectations. I wish You would live up to mine.

thanks a lot


Lets forget about the minimum phase comment, thats a whole other can of worms.

If you dod not recall I too have a PhD in Physics, in Theoretical Physics to be precise, and my math skills are not rudimentary.

I stand by my statements as correct as shown by Morse in said text and they are not wrong simply because YOU say that they are wrong. The burdon of proof is on you since I have attached my proof from the work that I described.