Dear wxa666,
I am not a "shill" or spokesperson for Dr. Geddes. In fact I do not actually agree with some things he espouses.
The EV horn you suggested is of the "Manta Ray" style developed by Altec many years ago. It has known issues and problems. Not just my idea or opinion. I have heard quite a number of them. Pretty good for PA, but even the PA/SR people have dumped them in favor of other designs now.
Not sure where the "ribs" are in the EV horn you mentioned. I can't see them in the pix I saw.
I don't care if there are HOM present or not. In my experience that style of horn does not sound very good. The design uses diffraction to obtain the polar response. Dr. Geddes design specifically does not use diffraction as a means of obtaining the desired polar response - to the extent that a horn can minimize diffraction. THAT is one of the major points of his design breakthrough.
Like it or not, he has a breakthrough in "horn" (ok, waveguide) design here.
If you like intentional diffraction in your horn, fine. There are many horn designs with diffraction lenses, and the like. No problem.
I'd prefer to avoid that sort of thing in the main.
Ymmv.
Now back to our regularly scheduled programming...
_-_-bear
I am not a "shill" or spokesperson for Dr. Geddes. In fact I do not actually agree with some things he espouses.
The EV horn you suggested is of the "Manta Ray" style developed by Altec many years ago. It has known issues and problems. Not just my idea or opinion. I have heard quite a number of them. Pretty good for PA, but even the PA/SR people have dumped them in favor of other designs now.
Not sure where the "ribs" are in the EV horn you mentioned. I can't see them in the pix I saw.
I don't care if there are HOM present or not. In my experience that style of horn does not sound very good. The design uses diffraction to obtain the polar response. Dr. Geddes design specifically does not use diffraction as a means of obtaining the desired polar response - to the extent that a horn can minimize diffraction. THAT is one of the major points of his design breakthrough.
Like it or not, he has a breakthrough in "horn" (ok, waveguide) design here.
If you like intentional diffraction in your horn, fine. There are many horn designs with diffraction lenses, and the like. No problem.
I'd prefer to avoid that sort of thing in the main.
Ymmv.
Now back to our regularly scheduled programming...
_-_-bear
bear said:
My explanation was insufficiant then, sorry.
bear said:
Not exactly.
bear said:
Not exactly. But it is what he all so often tries to convince people of.
bear said:
Like it or not, he has a breakthrough in "horn" (ok, waveguide) design here.
If you like intentional diffraction in your horn, fine. There are many horn designs with diffraction lenses, and the like. No problem.
I'd prefer to avoid that sort of thing in the main.
Ymmv.
Now back to our regularly scheduled programming...
_-_-bear
If I didn't knew the Geddes claims I couldn't even understand a word of Yours. The OEM invented a problem to what he tries to sell You a solution. The solution is the absence of the problem "by design". The contenders lack the problem because it even can not be defined.
The former is what You are in with "HOM". It is absolutely the same marygoround as with cables, interconnects and the like. There is something technical that sounds georgious but can not be measured. For instance Bybee: Quantum Mechanics, electrons. But - it is not related to an every day product in an every day environment. HOM seems to be a new mantra to the DIYer. Accidentially it sounds like "OM", a buddistic mantra ever since. And HOM is the name of a corporation that sells underwear for males in Europe. Hom is frensh for "man".
Btw: it can be proved that OS waveguides show HOM. Because they are terminated at the mouth. You could read that in one of Geddes' papers.
I'm trough with it.
edit: Could anyone here calculate diffraction at a slot with pencil and paper? Or develop the concept from first principles? Have fun!
It seems that if we associate the pressure distribution and put them into perspective with the wave length and room dimension, for it to represent a 15KHz scenario, the wave guide would be very small. So I question how realistic the CARA simulation can be applied to wave guides.mige0 said:
It's surprising what a bit of wine and some detachment can do for a fella.
Not to denigrate some of the very useful things said in the umpty-dozen posts preceding this, I do believe the subject of this thread - how to measures HOMs (higher order modes) - is not what is needed by DIY speaker builders.
What is needed is a means of measuring linear distortion at the receiver, whatever be its cause.
If indeed, the speaker is producing linear distortion, then the DIYer can set about chasing down the cause which will be one or a combination of resonance, diffraction, reflection or, yes, higher order modes.
I think a thread about measuring linear distortion might be useful.
Not to denigrate some of the very useful things said in the umpty-dozen posts preceding this, I do believe the subject of this thread - how to measures HOMs (higher order modes) - is not what is needed by DIY speaker builders.
What is needed is a means of measuring linear distortion at the receiver, whatever be its cause.
If indeed, the speaker is producing linear distortion, then the DIYer can set about chasing down the cause which will be one or a combination of resonance, diffraction, reflection or, yes, higher order modes.
I think a thread about measuring linear distortion might be useful.
Hello,
Well, if we think CARA can do the analysis what is does in a room of a size of 5m in the freq range 20Hz-20kHz we can calculate a relativity coefficient = dimension/wavelength and in case of the 5m room it will be within [0.3...300]. Then take a smaller dimension structure say 20cm and simulate in the freq range of 1kHz-20kHz then relativity coefficient is [0.6...12] which falls inside the first range and thus it would be feasible to say CARA can simulate the same phenomenas as it does for a room.
- Elias
Well, if we think CARA can do the analysis what is does in a room of a size of 5m in the freq range 20Hz-20kHz we can calculate a relativity coefficient = dimension/wavelength and in case of the 5m room it will be within [0.3...300]. Then take a smaller dimension structure say 20cm and simulate in the freq range of 1kHz-20kHz then relativity coefficient is [0.6...12] which falls inside the first range and thus it would be feasible to say CARA can simulate the same phenomenas as it does for a room.
- Elias
soongsc said:
Elias said:
soongsc said:
I was continuing a discussion with Michael about a particular scenario he showed.
Soongsc, the answer of Elias is the key.
Whether waveguide or room – it’s a simple matter of “zoom factor” meaning you can scale it linearly.
Sure – there are many shortcomings using CARA for what I did. But I haven’t recommended CARA as to be *the* software for wave guide calculation – did I ?
What CARA – and the “bunch of pretty pictures” was intended and are good for is to have an intuitively understandable picture for the mechanisms at work.
It’s the old discussion of how precise has an analogy to be to merely show the *quality* of what’s going on.
There is no question about that BEM can calculate precise results, whereas CARA cant in this context – but on the other hand CARA seems to capture a specific behavior related to the diffraction> reflection > delay > interference complex not showing up in your BEM simus – no clue why.
I think I have outlined this very clear from the very beginning – so please don’t feel offended - it wasn't meant as an attac towars your excellent work but rather as an additional explanation.
That my “bunch of pretty pictures” are valid within its (minor) restrictions, there’s no doubt IMO. Measurements clearly support my point of view – no?
Michael
I am not offended in any way. I look at the room modes you ran, if I scale the room size to a wave guide size, the room mode would relate to a frequency much lower than our measurements. If we scale the room mode to the frequncy, the wave guide would probably be the size about half wave length of 15KHz.mige0 said:
wxa666 said:
I was not aware that I made "claims"...???
Friend, you appear to be both angry and confused.
Why you would be angry with me is unclear.
You are confused, because I am not Dr. Geddes, but you want to make me responsible for what he says?
No.
I am not a follower, nor part of a herd of animals. I do not care about HOM one way or the other, UNLESS it is useful.
THIS is the thread about MEASURING them/it.
If you do not want to talk about that, then you are in the wrong thread. Eh?
The mouth reflection is not the HOM that Dr. Geddes is addressing. You know that if you read what he wrote and what has been said about them.
Calculate a diffraction slot? Sure, but why? Why do you feel that
is important to this discussion? Perhaps you would like to post the math you think is going to show something important?
It seems that you simply do not like to be told that the horns that you prefer are a design that uses deliberate diffraction to create the bandwidth and polar response that it does? But that is the truth. They may sound fine anyway.
And, you still have yet to explain your "rib" reference?
Although it has nothing to do with the topic of this thread.
What is your point here??
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