That's of course the target state, to simulate the whole device (acoustically) including the compression chamber, which I'm still only slowly approaching with the tool.
But at the moment I'm actually interested in the channels alone, if driven by an idealised source. I think that when terminated with a dampened tube, it can still tell a lot about the performance of such (sub)system. I just want to inderstand this better first.
As for the whole chamber and the mode balancing, I already tried this a long time ago, and I know it will be a nightmare -
https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/post-6196087
(Especially the area around voice coil can have a significantly negative impact.)
But at the moment I'm actually interested in the channels alone, if driven by an idealised source. I think that when terminated with a dampened tube, it can still tell a lot about the performance of such (sub)system. I just want to inderstand this better first.
As for the whole chamber and the mode balancing, I already tried this a long time ago, and I know it will be a nightmare -
https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/post-6196087
(Especially the area around voice coil can have a significantly negative impact.)
Last edited:
I've found one... If you see somewhere a phase plug resembling this, it may be actually a well-thought-out one
https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-6193551
I knew @kessito posted this but I didn't remember it was already so close. Did you pursue also the area progressions inside each channel, Kees? It seems so.
Last edited:
Hi, I tried again with ath 4.8.2 and ath 4.9 and throat extension is not calculated. It calculate complete WG properly but without throat extension.
Any advice?
I've found one
https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-6193551
I knew @kessito posted this but I didn't remember it was already so close. Did you pursue also the area progressions inside each channel, Kees? It seems so.
yes I did.If you keep the expansion rate constant it will work BUT it will cause 2 things;
-all resonant artifacts will become more pronounced ( think of a tube vs a conical horn)
- the distortion caused by wavefront steepening will be much higher. this is a tricky one since its not so obvious at lower levels but will be terrible at higher levels.
I once commisioned a linearray ( proaudio) system where the waveguides where constructed by means of many small channels. It sounded great at low levels but once turned up a little...omg
You are on a very good track here, with the current state of 3d printing and your programming skill it should be possible to make something wondefull.
The design I showed a couple of years back was prototyped and worked fine up to 18khz, but it was discarded because of high manufacturing costs and "good enough" corporate desissions.
regards,
Kess
I knew it
To make this clear, at least for me - to keep the wavefront steepening at a minumum, do I get it right that we need to release the high pressure as soon as possible, i.e. to keep the phase plug channels short and preferably expanding? I never thought about it this way. So does it mean that even a plane wave tube, if driven at high levels, adds nonlinear distortion, the more the longer the path the sound travels through it? Somehow I always had this tied to slowly expanding horns only, don't know why, but it would make sense, as a straight tube is in fact the limiting case of low expansion rate.
I would actually keep the areas constant, i.e. there would be no expansion. But from what you wrote this would mean it would be worse than if expanding. Is that right?
Couldn't this be a linear distortion instead (e.g. not very pretty wavefronts)?
Last edited:
OK, plane wave tubes distort the signal (at very high levels):
https://apps.dtic.mil/sti/citations/tr/ADA027650
I didn't fully realize this.
Whether it's an issue for us, is a separate question, of course. But I can imagine the pressures inside phase plugs can be pretty high.
https://apps.dtic.mil/sti/citations/tr/ADA027650
I didn't fully realize this.
Whether it's an issue for us, is a separate question, of course. But I can imagine the pressures inside phase plugs can be pretty high.
Last edited:
Is a phase-plug so special really? Perhaps the wg/horn starts there really and the phase-plug is really the throat of a multi cell wg/horn, And what is "phase" in phase-plug? Is it a length compensation - to get all energy out at the same time from all "cells"? Or is it a plane2spherical wavefront transformer If so, it should change name to something more descriptive...
Skip all old denominations and start over - there is a membrane and a (small) cavity on both sides of said membrane - now, how to "pump" air back and forth with the least difference (distortion) between the membrane and the air, x mm from the mouth, in all directions.
From the paper above... "When sound waves of large amplitude propagate, the nonlinearity of the propagation process causes progressive distortion of the waveform. In a nondispersive medium this distortion will cause a sine wave to deform into a sawtooth wave, provided, of course, the wave does not first become "infinitesimal" through absorption"
Maybe this is partly cause for the "horn sound" - urrg.. triangle wave.... - it's for very high SPLs but inside a CD there is such situations I suppose..
//
Skip all old denominations and start over - there is a membrane and a (small) cavity on both sides of said membrane - now, how to "pump" air back and forth with the least difference (distortion) between the membrane and the air, x mm from the mouth, in all directions.
From the paper above... "When sound waves of large amplitude propagate, the nonlinearity of the propagation process causes progressive distortion of the waveform. In a nondispersive medium this distortion will cause a sine wave to deform into a sawtooth wave, provided, of course, the wave does not first become "infinitesimal" through absorption"
Maybe this is partly cause for the "horn sound" - urrg.. triangle wave....
- it's for very high SPLs but inside a CD there is such situations I suppose..//
Hi,
sorry I was not clear in my last post, indeed I meant expanding area not expansion rate.
These effect will happen even at home levels, they are the main cause of the 2nd harmonics that are always strong in the higher octaves of compression drivers. A good reason to keep the compression ratio low for home use.
these effects start at relatively low spl (+-135dBSPL) this is easily reached in the compression driver slits.
So yes, keeping the channels as shorts a possible and quickly expanding in area is a good thing.
please see chapter 7 of the excellent thesis of Makarski;
https://publications.rwth-aachen.de/record/61507/files/
sorry I was not clear in my last post, indeed I meant expanding area not expansion rate.
These effect will happen even at home levels, they are the main cause of the 2nd harmonics that are always strong in the higher octaves of compression drivers. A good reason to keep the compression ratio low for home use.
these effects start at relatively low spl (+-135dBSPL) this is easily reached in the compression driver slits.
So yes, keeping the channels as shorts a possible and quickly expanding in area is a good thing.
please see chapter 7 of the excellent thesis of Makarski;
https://publications.rwth-aachen.de/record/61507/files/
Last edited:
Okey, its apparently possible to simulate the horn contributed distortion... from above paper:
"Nonlinear Simulations
The goal of this project was, besides the linear property’s optimization, to reach about 125 to 130 dB on-axis sound pressure at 10% distortion in the mid-frequency range. At high frequencies, about 120 dB should be the minimum. As the driver is not known, the horn has to be simulated assuming an ideal, distortion-free excitation at the throat. The technique to do this is described in Chapter 7. The advantage of this method becomes evident now: it is simply necessary to use the simulated surface pressures and to apply the extended post-processing to estimate the nonlinear properties of the horn."
Something for ATH?
//
"Nonlinear Simulations
The goal of this project was, besides the linear property’s optimization, to reach about 125 to 130 dB on-axis sound pressure at 10% distortion in the mid-frequency range. At high frequencies, about 120 dB should be the minimum. As the driver is not known, the horn has to be simulated assuming an ideal, distortion-free excitation at the throat. The technique to do this is described in Chapter 7. The advantage of this method becomes evident now: it is simply necessary to use the simulated surface pressures and to apply the extended post-processing to estimate the nonlinear properties of the horn."
Something for ATH?
//
When I added a piece of narrow throat extension to a waveguide, I didn't see an increase of nonlinear distortion (NLD) as a result. On the contrary, for a given SPL it helped the driver to be usable even lower due to the excursion reduction. This alone, to me, implies that any horn-induced NLD is simply nothing to be worried about. Certainly not at home listening levels.
Last edited:
In hindsight and with the little bit of understanding of what this is all about, there's still nothing but admiration for this (almost twenty years old) work.
Last edited:
BTW, this is what I have lying around for a while - a 2" exit CD with 4" diaphragm, bought cheap in a sale years ago.
It's nicely shallow. The current phase plug is something ridiculously rudimentary (I can't understand how it can even work - it's there just for the compression, it seems). Can't wait to try this with a proper one.
It's nicely shallow. The current phase plug is something ridiculously rudimentary (I can't understand how it can even work - it's there just for the compression, it seems). Can't wait to try this with a proper one.
Last edited:
Great to see this work being done on the phase plug side of things. I was having a play with the plotter and find it a great way to visualise the CSA vs longitudinal area. I would love to play with some more complex sources, is there a built in way of doing this, say for a sphere and a cone, i.e. dustcap and cone?
I was curious. Is this how cheap (one-piece) phase plugs are commonly designed?
Actually, there's an evident attempt to equalize the path lengths, maybe they are.
This is a quick sketch of the thing (the air path in blue):
This is a 6-slot plug
Last edited:
It's obviously one those "gradual-integration" types, where the channels are not joined all at one place, but they are summed in steps. I can't see a reason why this couldn't work in principle, but the optimization sure won't be easy. It should be possible to simulate this as well, as soon as I have the tool finished.it just looks like a turbulence machine...
Well that's the common (and I guess more expensive) way.
Last edited: