The exact mechanism of the waveguide widening above 10 kHz is still not completely clear to me, apart from a very vague intuitive understanding.
But it must be a coincidence (a local optimum), as the beamwidth does not increase further with the further widening of the waveguide.
But it must be a coincidence (a local optimum), as the beamwidth does not increase further with the further widening of the waveguide.
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It would be normal to see diffraction here, that is supposed to happen with this horn.
The elliptical shape is one thing that confirms it.
I actually don't see any more elliptical shape. Don't be misled by the different field mesh boundaries.
I'm not being misled.
If you could fold back a horn without diffraction, then I'd be concerned. Don't fear it.
If you could fold back a horn without diffraction, then I'd be concerned. Don't fear it.
The explanation was incomplete. The issue is further reaching than Marcel has indicated, as I have explained.
I'm afraid you haven't explained anything but I won't participate any further in this nonsense.
Closer to the source in more detail -
It is my understanding that the waveguide simply helps to build up the pressure towards the sides of the diaphragm, which alone is not capable of, due to its axial motion. With a waveguide there's less volume for the available velocity.
- But then I don't understand how exactly the on-axis pressure drops. So,... (maybe the diffractions off the WG walls reduce the axial pressure?)
The fact is that the waveguide widens the polar pattern considerably, compared to a flat baffle. But how exactly it does that, remains a mystery to me.
I would accept that "it's all diffraction" but then that's still very abstract.
It is my understanding that the waveguide simply helps to build up the pressure towards the sides of the diaphragm, which alone is not capable of, due to its axial motion. With a waveguide there's less volume for the available velocity.
- But then I don't understand how exactly the on-axis pressure drops. So,... (maybe the diffractions off the WG walls reduce the axial pressure?)
The fact is that the waveguide widens the polar pattern considerably, compared to a flat baffle. But how exactly it does that, remains a mystery to me.
I would accept that "it's all diffraction" but then that's still very abstract.
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We could assume its interference. On flat baffle, the on-axis is the only observation axis where sound from all points on the dome are relatively equidistant compared to wavelength, so sound from any point of the dome is relatively in phase. This makes relatively high pressure on-axis compared to off-axis where path lengths from various points of the dome spread out (compared to wavelnegth) and pressure averages out, beaming.
Since the dome on both your sims is the same, there must be something else to it, some other sound source that affects the interference.
Now lets choose one point on the dome and imagine how sound emanating from there would travel. Lets take for example sound form tip of the dome. Sound propagates to all directions, so sound from tip of the dome goes towards the baffle as well. Sound that propagates toward the baffle would reflect from it. When baffle is flat it would be a specular reflection with very high incident angle ( as dome doesn't protrude that much from the baffle ) and basically the sound just continues escaping the system somewhere close to 90deg off-axis angle.
Now when you start to fold in the baffle (waveguide) the reflection incident angle drops. When you have suitable angle / curvature to the profile this sound that would have escaped the system is now reflected back towards the listening window. Now it interferes with direct sound on-axis, perhaps out of phase reducing pressure while at some other angle its boosting some. This is our secondary sound source.
I think this is visible in the observation field of the waveguide sim, if you look exactly on-axis each color is either shrunk or bulged a bit, which to me looks like path length difference varying with angle.
Of course the waveguide is 3D, sound from any point of the dome would propagate to all directions, reflect to various angles with various path length differences and and the observation field is just 2D so its quite hard to actually imagine the whole system. But I think the basic thing is roughly that the high frequency sound is now reflected back toward the listening window instead of letting it escape toward 90deg off-axis with flat baffle, which makes interference.
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Yeah, you are right I think. Put this way it sounds simple after all. I like the notion that the waveguide "doesn't let the sound to escape so easily", that's actually pretty intuitive.
And you're right that the sound field within the waveguide is noticeably less smooth...
And you're right that the sound field within the waveguide is noticeably less smooth...
Yeah sound is quite simple, it just propagates to all directions, reflects, diffracts and refracts. But, as the objects are 3D it gets quite complicated fast. This kind of simplifications to two dimensions are nice thought experiments and kind of help to see some of it, how it likely plays out.
Got it 😀
So as the total radiated power must stay the same, on average the pressure will simply correspond to that... And it's a consequence of the waveguide shape that this is the result, i.e. more or less uniform radiation in all directions...
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Simplicity is there that its all predictable and quite well defined for practical purposes, its just pressure wave. Proved by the fact there is mathematical equations that describe what would happen, and simulators that are build on those which quite accurately illustrate what happens by visualizing it 😀 Same thing can be done with imagination, of course its all in the head and not by numbers but some kind of a simplification, so just matter of learning / developing some kind of intuition to it 🙂 Of course use computer simulation / maths to confirm but simplified simulation can be done in the head to some extent just by assuming that sound propagates to all directions, reflects and diffracts from objects. Luckily refraction doesn't seem to relate to loudspeakers mucho 🙂
I can imagine a reflection (I think) but certainly not diffraction along a curved surface, as that is something highly frequency dependent (evanescent waves, etc.). There it stops working for me...
^^ Yeah reflection is easy, since sound propagates as a bubble, you can inspect any direction equivalent, just draw a line and reflect it specularly from any object that is big enough in size to wavelength to see how sound travels that particular direction 🙂 Horn stuff gets too complicated, lots of things I don't even understand and haven't bothered to dig into, especially on the deep ones. Surely sound would still reflect and diffract the same no matter what object there is. For example the evanescent wave, perhaps some combination or perhaps there is something completely different stuff that happens. Math explains it I'd quess.
Sharp edge diffraction is kinda to imagine though, and by sharp I mean sharp relative to wavelength. Some round over would be sharp edge to some wavelength. Edge makes secondary sound source with delay which is in opposite phase to the direction sound came from, while direct sound would continue as usual. Direct sound has some attenuation which went to generate the back wave, or vice versa, energy conservation or something. Waveguide mouth reflection for example, if the mouth edge changes abruptly relative to wavelength back wave emerges back toward the throat, spherically to any direction from any single point at the edge.
^ We get clean impulse response only when there is no secondary sounds, in other words when all points of a transducer ( sound source(s) ) are equidistant to our observation point. In case of multiple source some delays can be used and so on. Thats my non academic view on it 🙂 When wavelength is short and you observe flat piston from an angle and impulse isn't good anymore because sound from closest point of the transducer arrives significantly before sound from the furthest point.
Well, this is just kind of framework to think about this stuff and needs to be related to what is audible and what is not in order to take full advantage. If not knowing what is audible we can just try and get as clean as possible, avoid secondary sound sources or make them do work, like improve polar pattern since good polar pattern seems to be a thing.
Sharp edge diffraction is kinda to imagine though, and by sharp I mean sharp relative to wavelength. Some round over would be sharp edge to some wavelength. Edge makes secondary sound source with delay which is in opposite phase to the direction sound came from, while direct sound would continue as usual. Direct sound has some attenuation which went to generate the back wave, or vice versa, energy conservation or something. Waveguide mouth reflection for example, if the mouth edge changes abruptly relative to wavelength back wave emerges back toward the throat, spherically to any direction from any single point at the edge.
^ We get clean impulse response only when there is no secondary sounds, in other words when all points of a transducer ( sound source(s) ) are equidistant to our observation point. In case of multiple source some delays can be used and so on. Thats my non academic view on it 🙂 When wavelength is short and you observe flat piston from an angle and impulse isn't good anymore because sound from closest point of the transducer arrives significantly before sound from the furthest point.
Well, this is just kind of framework to think about this stuff and needs to be related to what is audible and what is not in order to take full advantage. If not knowing what is audible we can just try and get as clean as possible, avoid secondary sound sources or make them do work, like improve polar pattern since good polar pattern seems to be a thing.
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Or not? If you attenuate (with the foam) the waves/modes that should help you to achieve the radiation pattern you want, how do you then keep that radiation pattern you want? I actually still don't understand it (at all, I assume)....
I'm not sure what the higher order modes are, zeroth order mode would be "direct sound" and any mode past that would be any reflected/diffracted wave at any point, just mode higher than 0?
The foam pluck would be effective when the secondary sounds, a reflection or diffraction back wave travel a long way in it, much longer than the direct sound. For example diffraction from horn mouth back to the device and then out again has traveled two times the distance within the foam than direct sound, spent more time in it attenuating more.
The kind of "useful" reflection you show above, which happens very near the sound source, would spend similar time within such foam pluck as direct sound and wouldn't be that much attenuated.
The foam pluck would be effective when the secondary sounds, a reflection or diffraction back wave travel a long way in it, much longer than the direct sound. For example diffraction from horn mouth back to the device and then out again has traveled two times the distance within the foam than direct sound, spent more time in it attenuating more.
The kind of "useful" reflection you show above, which happens very near the sound source, would spend similar time within such foam pluck as direct sound and wouldn't be that much attenuated.
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Yeah, that sounds quite reasonable (again)...
I should ask you more often.
- So the foam plug is actually much more effective for the mouth-related issues than the throat-related. I don't know why but I always assumed it the other way around. So with a reflection-free mouth the foam has typically a very little merit, hasn't it?
I should ask you more often.
- So the foam plug is actually much more effective for the mouth-related issues than the throat-related. I don't know why but I always assumed it the other way around. So with a reflection-free mouth the foam has typically a very little merit, hasn't it?
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