Beyond the Ariel

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#5,801
Hi Earl,

Yes, I follow. But isn't a MP system dispersive if the amplitude isn't flat, DC to light (theoretically)? For example, a simple electrical HP or LP filter is MP but has non constant GD, thus it is dispersive, no? Anything that doesn't have linear phase vs. frequency is dispersive, no? I.e. the effective propogation velocity is frequency dependent.
 
#5,802
Yes, but isn't "dispersive" more general. One could have a dispersive medium that was perfectly flat.

I think that all filters are dispersive, yes, but they can also be MP, meaning that there is a very tight relationship between the group delay and the frequency response. Dispersive could also be non MP. I guess what you saying is that dispersive is not the right term, and that is probably correct. Non MP group delay, or what I believe is called "excess group delay" is the culprit.

At any rate, I think that its clear that it isn't so easy to sort these things out.
 
#5,803
Allow me to throw into the discussion Bjørn Kolbrek's excellent summary about horns / wave guides.

Many thanks Bjørn, for writing such papers!
:spin:

In part 2 some basic distortionn principles are discussed in a way as easy to understand as the subject allowes (also giving the scientifically explanation on "absolute phase" detection some of us are sensitive for):

part 1:
http://www.audioxpress.com/magsdirx/ax/addenda/media/kolbrek2884.pdf

part2:
http://www.audioxpress.com/magsdirx/ax/addenda/media/kolbrek2885.pdf


With respect to the double horn approach it may be interesting that part of the distortion mentioned should be cancelled due to its symmetric front-rear loading / radiation - not sure that impacts this may have on HOM at the moment

Michael
 
#5,804
tiki said:

Well, "Hier liegt der Hase im Pfeffer", as the Germans say. Because the AMT driving (Lorentz) force is directed orthogonal to the SPL, the SPL reaction force operates against the mechanical stiffnes of the folded foil only which cannot be evenly distributed across the whole AMT surface.

Cheers, Timo
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Hi Timo, what you are referring to is what kept me off trying AMT for a (too) long time - besides the prices (ESS, Mundorf, Beyma) that are a plain rip off IMO.

But once you have listened to AMT this reservations are gone (and with double horn the "goose pimple factor" is even substantially raised - I can tell you) – also distortion measurements of standard AMT implemetations show exceptional results.

If Earl could outline a practicable method to measure HOM - I'd possibly would try to provode own results of the double horn approach to compare whith his OS wave guide - given he would agree and provides his measurements as well.


Michael
 
#5,805
gedlee said:

At any rate, I think that its clear that it isn't so easy to sort these things out.
Click to expand...


As all these effects from mouth and contour reflections and higher order modes (due to wall reflection like in opical fibers) should show up in the impedance curve in odrer to do non-linear modulation - possibly a standardised processing of the mere electric impedance measurement would possibly make a good starting point?

To me it seems that it is highly a matter of interpretation / definition of - and distinction between - different distortion types - no ?

Michael
 
#5,806
gedlee said:
Yes, but isn't "dispersive" more general. One could have a dispersive medium that was perfectly flat.
Click to expand...

Yes, as I said, anything that does not have a linear phase vs frequency is dispersive. A little OT here, but a good example is a typical 2-way speaker. In the crossover region the response sums flat (at least on axis) but, unless the crossover is of the transient perfect type, the crossover introduces dispersion. That is one reason why I have always been interested in TP crossovers. So then one gets into the argument of how much of this crossover induced dispersion is audible. One school says we can't hear it at all in a typical loudspeaker. Another says it's audible at low frequency, yet another says it's audible at higher frequency. Others argue that it depends on the transient nature of the source material. My argument has always been that if you can eliminate it, at least in the direct sound, without detrimental effects of the off axis and reflected sound, then why not eliminate it?
 
#5,808
mige0 said:

possibly a standardised processing of the mere electric impedance measurement would possibly make a good starting point?
Click to expand...


I made a device to get a relative measure of the diffraction using the impedance curve.

This is on my site in "Mesure de la diffraction d'un pavillon" which means "Measure of horn diffraction", I know it's in french but with an automatic translator, i hope it's much easier to understand:

http://translate.google.com/transla...illon.html&sl=fr&tl=en&history_state0=&swap=1

With some adjustment you can use a microphone for a no relative measure, but the version in my site is really, realy simple to implement.
 
#5,809
mige0 said:
Allow me to throw into the discussion Bjørn Kolbrek's excellent summary about horns / wave guides.

Michael
Click to expand...

Michael

Please also mention my paper disputing much of Kolbrek's paper.


john k... said:
My argument has always been that if you can eliminate it, at least in the direct sound, without detrimental effects of the off axis and reflected sound, then why not eliminate it?
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John, I completely agree and I often do things like this. But the usual case is that there are tradeoffs and the "without detrimental effects" clause takes effect.

When I started my Summa designs, I did not have much data on the audibility of diffraction, but it was easy enough in the early designs to minimize it - so I just did it. Now I see that this was the right thing to do, but that is, quite honestly, just hindsight and the data that I know have was an attempt to explain the good subjective results that I got. I then went on to minimize all of the nearfield diffraction in my room as well as in the speakers themselves. This too was a pronounced effect.
 
#5,816
gedlee said:


I agree that the impedance curve is very sensitive to many things, but I don't believe that you will see diffraction in an impedance curve. Reflections, yes, but not diffraction.
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You right, I measure the reflexion.
But the difraction is the result of interference of wave; interference from the reflexion, and less there are reflections, the less there will diffractions.
Ultimately it's the same, i measure the cause of the horn diffraction.
 
#5,818
thend said:


You right, I measure the reflexion.
But the difraction is the result of interference of wave; interference from the reflexion, and less there are reflections, the less there will diffractions.
Ultimately it's the same, i measure the cause of the horn diffraction.
Click to expand...


Sorry to disagree, but reflections and diffraction ARE NOT the same thing. They can be related to each other, such as a diffraction can cause a reflection, but don;t have to be. IF there is a reflection you can be pretty sure that there is also diffraction, but the converse is NOT true - if there is no reflection DOES NOT MEAN that there is no diffraction.
 
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