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[Ivan Beaver]

In this case the existence and the frequency of the abrupt phase shifts appear to vary with angle. I took measurements at roughly 10 deg increments and 10 ft. distance -- optimistically in the far field for this horn. In the image below I overlayed phase plots for 6 measurements, individually adjusting the delay to compensate for the small differences in measurement distance. (I could have overlayed the plots a little better but .01 ms is the delay increment in ARTA, which is a whopping 36 deg at 10 kHz.)

The big question is, can anyone hear it? My guess is no, since from what I've read about perception of phase (in isolation, not talking about coupling of multiple sources), any effect is confined to lower frequencies.

The good news is that since this comes and goes with angle there is nothing to do about it on the processing side. Flatten the average magnitude, play nice music, and be happy.

On measuring drivers without a horn, not that I'm likely to try this anytime soon, do I need a plane-wave tube setup to terminate the driver? I believe that is one way it has been done. It sounds like Art has a "reference horn", which is good for driver comparisons.

Thank you all for your insights.

Best,

--Frank

If it was a reflection in the phase plug-it could show up differently at different angles

I would measure without any sort of termination-just the raw driver and see what you have.

[Art Welter]

In this case the existence and the frequency of the abrupt phase shifts appear to vary with angle. I took measurements at roughly 10 deg increments and 10 ft. distance -- optimistically in the far field for this horn.

The big question is, can anyone hear it? My guess is no, since from what I've read about perception of phase (in isolation, not talking about coupling of multiple sources), any effect is confined to lower frequencies.

On measuring drivers without a horn, not that I'm likely to try this anytime soon, do I need a plane-wave tube setup to terminate the driver? I believe that is one way it has been done. It sounds like Art has a "reference horn", which is good for driver comparisons.

Frank,

Personally, I can't hear the phase differences, and the frequency response deviations where the problem lies are so high that it would take an A/B test (for me) to identify the problem compared to a smoother unit. Some folks are blessed (or cursed) with hearing more sensitive to ragged FR.

Testing the driver raw would show the problem, though diffraction around the driver body can make identification difficult- I have used a 1/8" sheet of plastic (or Masonite) with a driver hole cut in, and the hole rounded to make a relative "half space" comparison. This can be useful to see how wide the phase plug will spread VHF, and expose driver problems, as opposed to horn problems.

The Maltese horns I use for comparative testing are very smooth above 1kHz, only about 1/4 dB of "ripple", with only 13 x 13 degree conical expansion, so any driver will "fill" the horn, with the proper throat adapter. It loads to around 200 Hz, so the LF response of drivers are also easily compared.

Below you can see the HF phase/FR problem with a B&C DE82 compared to a BMS 4552, a trade of cleaner LF for HF.

Art

[Ivan Beaver]

Frank,

Personally, I can't hear the phase differences, and the frequency response deviations where the problem lies are so high that it would take an A/B test (for me) to identify the problem compared to a smoother unit. Some folks are blessed (or cursed) with hearing more sensitive to ragged FR.

Testing the driver raw would show the problem, though diffraction around the driver body can make identification difficult- I have used a 1/8" sheet of plastic (or Masonite) with a driver hole cut in, and the hole rounded to make a relative "half space" comparison. This can be useful to see how wide the phase plug will spread VHF, and expose driver problems, as opposed to horn problems.

The Maltese horns I use for comparative testing are very smooth above 1kHz, only about 1/4 dB of "ripple", with only 13 x 13 degree conical expansion, so any driver will "fill" the horn, with the proper throat adapter. It loads to around 200 Hz, so the LF response of drivers are also easily compared.

Below you can see the HF phase/FR problem with a B&C DE82 compared to a BMS 4552, a trade of cleaner LF for HF.

Art

DAMN TRADEOFFS-------------

Why can't anybody make perfect drivers??
Yeah it is what we "wrestle with" all the time.  Yes we have to give up one area of performance for another.

It comes down to "What is most important about where/how I am going to be using it".

It may not make sense to somebody else who is looking at a different part of the performance.

But, yet another reason loudspeakers are by far the worst part of the whole reproduction chain.

[Frank Koenig]

I have used a 1/8" sheet of plastic (or Masonite) with a driver hole cut in, and the hole rounded to make a relative "half space" comparison. This can be useful to see how wide the phase plug will spread VHF, and expose driver problems, as opposed to horn problems.

Art, Ivan, I'm more of a curious consumer of loudspeaker systems than a developer, except perhaps with respect to the measurement representation and DSP/ASP side of things, which is purely a hobby at this point. But it's extremely helpful to know that I'm running into real phenomena that others have seen and not just chasing artifacts. That purple trace looks familiar. I'll try the infinite baffle trick someday -- thank you Art for that.

Best,

--Frank

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