Dodge away, dodge away. A myth is a myth unless there is proof. Nowhere on this forum can I find any. If I have missed it, please direct me to it.
I did say that if proof were presented, I'd believe it. I'll not do the homework for those making the claims, thank you very much.
I did say that if proof were presented, I'd believe it. I'll not do the homework for those making the claims, thank you very much.
hom may be a bad word.
How about reflections ?
That you see on horn wavelets and waterfall graphs.
Didn't we have a 31 page thread back in 2009 on how to measure HOMs ?
http://www.diyaudio.com/forums/multi-way/145096-how-hom-measured.html
I don't like the word myself.
I prefer echo-y or even "live", scary use of the word, but once you start knocking down the reflections, the sound has less of a live (reverby) sound.
How about reflections ?
That you see on horn wavelets and waterfall graphs.
Didn't we have a 31 page thread back in 2009 on how to measure HOMs ?
http://www.diyaudio.com/forums/multi-way/145096-how-hom-measured.html
I don't like the word myself.
I prefer echo-y or even "live", scary use of the word, but once you start knocking down the reflections, the sound has less of a live (reverby) sound.
Uhh. To explain wave propagation it is advantageous to introduce the HOM concept.
But I agree with Norman there. To explain harshness experienced by a loud sound that has time-delayed reflections doesn't require the HOM concept, it just confuses people. Just get rid of the reflections and be done with it. (how? By eliminating HOModes 😀)
Its like the whole Higgs particle thing, elusive. Or dark matter.
But I agree with Norman there. To explain harshness experienced by a loud sound that has time-delayed reflections doesn't require the HOM concept, it just confuses people. Just get rid of the reflections and be done with it. (how? By eliminating HOModes 😀)
Its like the whole Higgs particle thing, elusive. Or dark matter.
OK. Let me put it another way. Do you believe HOMs exist in horns and that they are audible? Or do you just like the idea? A nice theory, but is it real?
There seems to be a lot of very smart people here who have jumped on this lime it really exists and is audible. How do you know? What proof is there? Shouldn't this receive the same scrutiny as fancy audio cables?
There seems to be a lot of very smart people here who have jumped on this lime it really exists and is audible. How do you know? What proof is there? Shouldn't this receive the same scrutiny as fancy audio cables?
just had a look at the title and age of this thread
strangely we all seem to know what a HOM is, just don't ask to explain it
but you know when you hear one
ain't this hobby is just great 😀
strangely we all seem to know what a HOM is, just don't ask to explain it
but you know when you hear one
ain't this hobby is just great 😀
Great question. Let me evade that 😀
High order modes are needed to explain certain physical phenomena. They are not needed to explain psycho-acoustic phenomena. You could just as easily lump them with all delayed reflections, AFAIK the hearing mechanism doesn't discriminate between them. So yeah, I think that HOMs are a way of modeling/describing something - a nice theory (that has uses in science AND engineering).
But a huge credit should go to certain individuals for discovering how temporal post-masking in human hearing breaks down depending on playback level. It is widely known that frequency masking actually increases with increasing playback level (thats largely the reason why distortion is inaudible - as the level rises, so does the masking threshold), but temporal masking thresholds were derived too crudely and at a too low level to see a breakdown of the effect (meaning it is assumed that louder signal masks better temporally, now we know that this holds 'up to a point'. But it is illegal to test subjects at a level where this breakdown occurs, so no further study is possible (insert Mengele jokes)). Thats why the issue we have with them pesky horns and their delayed reflections (not HOMs 😀)
PS has anyone developed a model (of human hearing) how this roughness experienced depends on playback level? Maybe the envelope fluctuation of the combined signal is irritating at a certain loudness level to our hearing system, but what mechanism is responsible for that? Our brain, or the Corti organ, that same mechanism that gives ~12dB advantage to the coctail-party-effect, gets overloaded at a certain level (which itself is considered a bogus theory in some circles)? Does any of it make any sense at all?
Pano - I think there are two separate issues: do HOMS exist? Do they matter? There appear to be a couple of AES papers which touch on this from 2004 (On the velocity distribution at the interface of horn driver and horn - Behler/Makarski and Do higher order modes at the horn driver's mouth contribute to the sound field of a horn loudspeaker - Makarski), but it may be easier to search for 'Tools for the professional development of loudspeakers' by Makarski from 2006. I've just found this online and assume it builds on the earlier papers. From my very quick read, the answers are: yes and yes, but much depends on the driver and this is a high frequency issue. There is a lot of information and maths(!) in the paper. Very interesting.
At least someone here has the sense to actually read the material that is available before making bogus claims. Thanks for that.
A big part of the HOM problem is that many do not seem to know what they a actually are. "Delayed reflections" does not quite do it because the main mode can have these as well. It is the fact that the main mode can have them as well that makes sorting out what is an HOM from what is a main mode reflection so difficult.
"How much they matter" has never been sorted out, but that's not the bogus claim that was made. They absolutely do exist, and have been proven to exist, just as I said. "How audible are they?" is an ongoing question. There is some evidence that they will be audible at higher SPLs. But you actually have to read to find that out.
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I would suggest looking at other engineering disciplines where high-order modes are discussed. It's not a new concept, just relatively new to audio.
A couple posts from two or three months back, germane to this discussion:
- The dirty little secret of horns. (post #332)
- Are Most Horns Fundamentally Flawed? (post #227)
And the small nuisance that just rotating a CD on a horn gives different response. Makarski explains that with HOMs in his paper. So it is not correct to deny the existence of HOModes. (and as usual, acoustics gets to be the last discipline where discoveries are made or discoveries from other fields gets incorporated. Something to do with the consumers voodoo-mentality and drawn to mysticism, not verifiable facts? Performance doesn't sell.)
Don Keele had mentioned the driver rotation fact to me as proof before as well. There has never been any doubt that HOMs exist. I don't understand why it was even questioned.
Some questions/comments: am I right in thinking that there are three possible 'sources' for horn HOMs - 1) a driver's failure to produce a flat axisymmetric wave front at the exit of the driver (due to design/manufacturing/assembly problems), 2) the fact that a driver is not a point source and so at some frequency axial modes arise due to cancellation (more on this below), and 3) the horn shape?
Does 1) give rise to radial modes (depending on the asymmetry)?
On 2), I'm sure I don't understand what's happening but I'll ask some dumb questions in the hope that someone explains. I assume that this is to do with the way that sound waves propagate in air when you start with a circular source? Is there a layman's explanation of this I can read that's not too dumbed down, but not so convoluted in maths that I need a maths degree to follow it? Why does Makarski say (if I understand it correctly) that you only need to worry about the first one or two modes as being the ones that carry audible (?) power, at some frequency, higher than that of the main mode? His description in parts also seems to suggest that the HOMs are travelling down the horn along the horn axis, but he also suggests that you can detect the HOMs (in an axisymmetric horn) by way of an on-axis dip and spread in directivity, which means I've misunderstood!
On 3), if HOMs kick in (to maybe being audible) at say c.14kHz for a 1" driver, then maybe I shouldn't worry too much about this in my 1" driver in a tractrix horn, given I cross below that to a 1/2" tweeter driver. (There are other bigger problems with this admittedly, not least that I managed to break the diaphragm of the latter ... Oh well.)
Does 1) give rise to radial modes (depending on the asymmetry)?
On 2), I'm sure I don't understand what's happening but I'll ask some dumb questions in the hope that someone explains. I assume that this is to do with the way that sound waves propagate in air when you start with a circular source? Is there a layman's explanation of this I can read that's not too dumbed down, but not so convoluted in maths that I need a maths degree to follow it? Why does Makarski say (if I understand it correctly) that you only need to worry about the first one or two modes as being the ones that carry audible (?) power, at some frequency, higher than that of the main mode? His description in parts also seems to suggest that the HOMs are travelling down the horn along the horn axis, but he also suggests that you can detect the HOMs (in an axisymmetric horn) by way of an on-axis dip and spread in directivity, which means I've misunderstood!
On 3), if HOMs kick in (to maybe being audible) at say c.14kHz for a 1" driver, then maybe I shouldn't worry too much about this in my 1" driver in a tractrix horn, given I cross below that to a 1/2" tweeter driver. (There are other bigger problems with this admittedly, not least that I managed to break the diaphragm of the latter ... Oh well.)
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1) is a possible cause but it has not been determined to what extent. It is clear that a poor interface between the driver and the waveguide will exacerbate the problems.
2) I don't think this aspect is a concern if the phase plug is done properly (but none are) and if it is not then this aspect is the same as 1) above
3)The non-axisymmetric HOMs can "kick-in" in a 1" driver as low as 4-5 kHz. The axisymmetric ones start at about 7 kHz.
Markaski's comments had to do with the fact that there are only a few modes below 10 kHz. But remember that a 2" throat driver will have twice as many below this frequency than a 1" driver. That's why I use a 1" driver - I don't need the extra power handling.
All HOM travel "down the axis" or "along the axis" but only the main mode travels parallel to the axis. But an on-axis dip need not be because of an HOM since even the main mode will have an on-axis dip if the mouth termination has any diffraction (which is always the case.)
2) I don't think this aspect is a concern if the phase plug is done properly (but none are) and if it is not then this aspect is the same as 1) above
3)The non-axisymmetric HOMs can "kick-in" in a 1" driver as low as 4-5 kHz. The axisymmetric ones start at about 7 kHz.
Markaski's comments had to do with the fact that there are only a few modes below 10 kHz. But remember that a 2" throat driver will have twice as many below this frequency than a 1" driver. That's why I use a 1" driver - I don't need the extra power handling.
All HOM travel "down the axis" or "along the axis" but only the main mode travels parallel to the axis. But an on-axis dip need not be because of an HOM since even the main mode will have an on-axis dip if the mouth termination has any diffraction (which is always the case.)
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