@Mazza: Here you can download the REW project that produced this measurement - DE500-260mmATH.mdat - Google Drive. It is measured at 1 m with UMIK and IIRC no smoothing, only gating just before the first reflection appears in the IR.
Thanks Marcel! Managed to get some modelling, but a simple shape (based on a post from you a few hundred pages back) gave me "better results.
My question is...
With my limited space (6.5" diameter) and considering I am crossing over between 2 and 3kHz, can I get better results than the ones shown in the picture attached?
Attachments
I'd only say that generally, the smaller the size, the wider beamwidth you need to keep DI of the whole system reasonably stable through the midrange and high frequencies. Keep in mind that you need the WG to smoothly blend with the directvity of the 6,5" woofer. But probably there's not much left to improve, given the size constraints, I don't know.
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There is something going on at say 12k. What is that? A "mode" - a resonance of sort? Did anything show in your original standard simulation - I mean in the basic 4 quadrant scart like
https://www.diyaudio.com/forums/att...2753495-acoustic-horn-design-easy-ath4-20-png
There seem to be a wiggle in the blue 00 impedance trace for the 01 event... It's all in the impedance if one dares to look close enough I believe.
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https://www.diyaudio.com/forums/att...2753495-acoustic-horn-design-easy-ath4-20-png
There seem to be a wiggle in the blue 00 impedance trace for the 01 event... It's all in the impedance if one dares to look close enough I believe.
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TNT asks interesting question, are the higher modes visible in the ATH generated chart? Few more (sorry if they were already discussed): where do these modes generate and is there anything one can do to reduce them? Does 1" throat push them higher in frequency or are the modes due to the throat shape or what? 
edit. I don't understand what is it about, simulations of the driving signal means you exite the waveguide with particular mode (from driver) and the graphs show how they behave through the waveguide? or are these modes something the waveguide generates?
edit. I don't understand what is it about, simulations of the driving signal means you exite the waveguide with particular mode (from driver) and the graphs show how they behave through the waveguide? or are these modes something the waveguide generates?
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These simulations show how the device behaves when the input wavefront is not ideal (i.e. has non-flat amplitude). Real wavefront can be approximately described as a weighted sum of these modes - that's what we would like to find in result, based on a real measurement with a particular compression driver.
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No. In the standard report/simulation only mode 0,0 (ideal flat wavefront) is considered (or an ideal spherical wavefront respectively).
This is a nice visualization of what we are talking about: Acoustic modes on a circular duct - GIF on Imgur
Mode 0,0 = ideal pistonic source, i.e. flat wavefront
- Maybe I could measure the first higher axial mode on the PWT, after all (as Earl was suggesting) - seems that it's about the only one that matters in the end. I guess I could return back to this plan now. This mode should still propagate down the tube, i.e. be easily detectable.
Mode 0,0 = ideal pistonic source, i.e. flat wavefront
- Maybe I could measure the first higher axial mode on the PWT, after all (as Earl was suggesting) - seems that it's about the only one that matters in the end. I guess I could return back to this plan now. This mode should still propagate down the tube, i.e. be easily detectable.
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Next question would be to further understand, which of these modes you simulated, Z(0,1) and Z(0,2)? Are these the most important ones in a real compression driver?
For the waveguide design, I guess the throat shape would effect these? What can be done to reduce effects of the first mode, which seems "most offensive", and what are the trade-offs doing so and is it worth it? I guess the driver with its phaseplug design would have most effect on the magnitude of these modes?
For the waveguide design, I guess the throat shape would effect these? What can be done to reduce effects of the first mode, which seems "most offensive", and what are the trade-offs doing so and is it worth it?
I guess the driver with its phaseplug design would have most effect on the magnitude of these modes?
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Yeah, I forgot to mention that explicitly this time. The previous simulation was for the modes 0,0 - 0,1 - 0,2, i.e. the first axi-symmetric ones. To what degree other modes contribute in a real device, I have no clue. Simulation of those would be much more computation heavy, but not impossible.
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Maybe small phase plug would help, a needle in the middle of the throat? I don't know what problems it would bring.
Trying to think about it. So basically on the first mode, middle of the wavefront and circumference move in opposite phase and output of these combine differently on different axis. Small phase plug would try to guide these closer together so they would null out at the throat already? Or would it be more realistic target to try focus the combing to one axis (out of listening axis) or spread out along all axis so that EQ would work on it, mo' diffraction? Do these affect the power response at all, so it just how "the combing" is distributed along the listening window?
The other types of modes would have a bit different "distribution" to each axis than the axial modes in which case a phase plug might help with only some of the mode types and perhaps make others worse? It would help to know what the severity of different modes are with real drivers to find the worst one and try to reduce effect of that. If the modes differ from driver to driver the fix would be per driver basis and not sure worth it.
The effect seems to start about at the 1,4" wavelength ~9,6kHz so 1" throat would already put these to about ~14kHz, the edge of old hearing system.
Sorry if it is all clear for everyone, it is fun to try to think it through
I don't know what problems it would bring. Trying to think about it. So basically on the first mode, middle of the wavefront and circumference move in opposite phase and output of these combine differently on different axis. Small phase plug would try to guide these closer together so they would null out at the throat already? Or would it be more realistic target to try focus the combing to one axis (out of listening axis) or spread out along all axis so that EQ would work on it, mo' diffraction?
Do these affect the power response at all, so it just how "the combing" is distributed along the listening window? The other types of modes would have a bit different "distribution" to each axis than the axial modes in which case a phase plug might help with only some of the mode types and perhaps make others worse? It would help to know what the severity of different modes are with real drivers to find the worst one and try to reduce effect of that. If the modes differ from driver to driver the fix would be per driver basis and not sure worth it.
The effect seems to start about at the 1,4" wavelength ~9,6kHz so 1" throat would already put these to about ~14kHz, the edge of old hearing system.
Sorry if it is all clear for everyone, it is fun to try to think it through
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Quarter wave resonator phase plug Well, lunch break over.
Crude ripple tank demo without resonator and with resonator
Well, lunch break over.Crude ripple tank demo without resonator and with resonator
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