Thanks for taking the time to try and answer my questions. I used ABEC for the modelling which came from the same developer after the AKABAK you used.
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How were you able to determine the shape of the wavefront from the different compression drivers?
Hi
How to sus the output shape from a compression driver or other sound source?.
In the late 80's and 90's one of my jobs was to develop sound sources for acoustic levitation. These generally run at a bit over 20KHz and making a directional source was imperative as the intensity needed was quite high, levitation began around 155dB.
Sound is both pressure changes AND velocity of air molecules separated by 90 degrees in phase or quadrature.
I developed a way to "see" the velocity in such a sound field, attached is a photo of a levitator sound field at 21KHz.
Dark is loud haha.
When there is an interference pattern (lobes and nulls), one see's it in this kind of scan .
The down side is this requires the driver to be pretty loud which may or may not be a problem
One can also probe the sound field with a capillary tube (tiny diameter tube) attached to a 1/8 inch microphone, for a compression driver, scanning across the opening can show amplitude and phase vs postion. This is a tedious process while the image in the picture took about 15 seconds
The TDS approach also allows one to measure arrival time or "distance" the same way.
To gather the Time information TDS uses a linear sweep signal as the source which is multiplied against the returning mic signal. The result of multiplication (modulation) of two signals is a sum and difference frequency and given the sweep rate and resulting difference Frequency (as the mic signal is always a little behind in frequency) , when converted one has the time it took for the signal to emerge after arriving at the terminals or distance.
It's been a while since I looked at this stuff but I did observe a trend.
When you look into the driver, past the bug screen, generally speaking, the smaller in diameter the passageway gets, the more likely it is to radiate a simple shape or contour as that small acoustic dimension forces / leans towards simple radiation.
For the normal "ring" style phase plug, that can be more complicated and Celestion for example has taken a good hard look at what emerges from the phase plug. The larger drivers like 2 inch exits tended to be the "least simple".
The ring radiator compression drivers tend to direct the energy to the center where it begins the conical horn shape at a small dimension.
I am not up to speed on ABEC and it took a while to get the hang of AKABAK but it has proven to be very useful.
Best,
Tom