This is precisely the kind of folly we should not fall for. Just because you can see it, measure it, does not mean it is audible. If you move around the mic in The Edge, you will get different responses. How does it become a resonance then?
This is somewhat similar to THD. It has been shown to not correlate with perception, at least at low to moderate levels.
Maybe I will, but it reminded me of this:
The example deals with a single point source, not an infinite collection of point sources on a baffle that is not much larger than the source.
I don't understand what resonances have to do with diffraction. They are two separate things.
Actually the multi-source component of diffraction generates a resonance effect.
Really though at any reasonable distance you look to the freq. response plot (over a reasonable polar "window").
IF there is a peak in response due to diffraction and it isn't being shelved or notched, then it's a design flaw. Narrow bandwidth dips generated by diffraction from one driver are largely irrelevant perceptually unless they on top of the crossover freq. and aren't being effectively accounted for by the other driver.
The drivers are both from Dayton: the ND28F tweeter and a RS100 midwoofer. The crossover is 2.1 khz LR4. The RS100 has a funny peek around 2k, but I'm not sure about the widening of the dispersion around 3k. I haven't really looked into it. This build was a proof of concept for me. The concept works
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Classic Olson - he was know to just draw in the data curves. I suspect the diffraction data is done this same way. Good guesses, maybe, but actual measurements, highly unlikely.
More is the pity, I'd say. A couple of month ago I was in Vegas for the NAB trade show. Lots and lots of studio monitors there. The last day a stumbled across the Focal (JMLAbs) booth. I didn't knwo thaty made studio monitors.
Of course I had to sit down for listen to the the 5.1 system. Wow! So good, so right. Superb tonal balance, no subjective distortion, wide, deep & solid imaging. It all seemed so well balanced with no obvious defects that is was a real pleasure to hear.
If I were building a mixing/mastering suite, or even a nice home theater, the Focal monitors would be very high on my list.
Resonances are what he hear as aberrations in the FR. Resonances are not good. A resonance is audible only if you can see it in all the curves: on-axis, listening window, early reflections, power response. If it starts to disappear in the listening window or power response, it is likely that you will not hear it. I'm sure you know this already.
A response with diffraction changes from one point to another because the delay associated with the reflected sound changes. Hence, the listening window is not affected much because all the combs will combine to produce a smooth response, i.e., you cannot see it as a resonance. And hence, you may not be able to hear it.
-you can see it in the Olsen grouping on the shapes and their diffraction alteration (..modulation of what was other-wise a linear freq. response, or mostly one on an infinite baffle).
Basically a grouping of edge sources (particularly equidistant to each other) with different pressures to that of the driver altering the freq. response of the driver.
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Drawing in the data curves doesn't mean there wasn't an actual measurement.
-we take for granted the capabilities we have today with something as simple as a "print screen" command to send to a printer for printing. (..and even more specifically to our area of interest - we take for granted smoothing.)
He could have taken a photo (and likely did from which to trace from, unless from the screen itself).. but it probably wouldn't have been smoothed, and thus not displaying the dominate characteristics he wanted to provide the reader. ..of course this assumes the diffraction analysis was done at point in time where any image was available (..owing to the fact that Olsen's work was modified over a long period of time).
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Sure, if the vector is a straight line. It's not. It's encountering the roundover at some angle of incidence- which can only be 90 degrees in 4 directions. Take a wide, tall speaker as an example- the pathlength firing from a speaker in the middle of a 8' tall by 3' wide speaker to it's edge will vary, from approximately 18" (assume a point source), to 51" or so. A given diameter radius would be adjusted by a similar ratio, in terms of how far that portion of the wavefront must travel to wrap into 4pi space.
2" diameter.... great. Multiply by 51"/18" and you have a nearly 6" roundover approximated, and additionally, the wavefront will have traveled further to get there and thus is lower SPL than a roundover perpendicular to the driver mount location.
At least this is my understanding of the subject.
Where do you have this information from? Any real source, or just a "good guess"?
From what you write here, it seems you claim that the curves in Olson's texts are not even based on calculations, just guesses? Well, in this case at least, the curves are based on measurements: Direct Radiator Loudspeaker EnclosuresOlson's curves do lack the resolution we get so easily today with our computers. But they are from 1950 (the AES paper from 1969 is a reprint from Audio Engineering).
-Bjørn
A resonance that leads to a response curve of similar shape may indeed be a worse offender, but you definitely can hear the effect of diffraction on the response. In general you simply want a flat and smooth response that doesn't change much with angle. My experience is that a speaker that has a very constant directivity within the listening window images better than one that is plagued by diffraction.
What you are describing is interference. The edge-reflection interferes with the direct sound and causes peaks and dips in the response. There is no energy storage involved. These peaks and dips are not the result of resonances. Acoustic resonances and interference caused by diffraction may have some similarities, but they are definitely not the same thing.
But if adding a sphere shape around your "pipes" would "straighten out" the frequency response it would be worth the trouble, right?
I know it was just a proof of concept, but maybe another test with a Styrofoam sphere around the pipes would be worth testing? Just to see if the frequency response would level out...
I know it was just a proof of concept, but maybe another test with a Styrofoam sphere around the pipes would be worth testing? Just to see if the frequency response would level out...