Below some pictures that show how HOM affects the "sound field" in an infinite conical horn (which will of course be the starting point for the sound field created by a real horn).
Again sims are to be taken with some grain of salt 😉
The sharp diffraction at the horn throat is the reason of strong bouncing wave fronts between walls – or at least for delayed overlaying with the axisymmetric wave front – creating all sort of fancy patterns .
Some (#9) where we even could get the impression that the waves travel backwards through the horn – they don't – it's just the overlay pattern of constructive and destructive interference that isn't stable over time.
The throat is – as Earl is telling us - the most sensitive point of a horn and any mismatch in the shape of the wave front demanded by the horn / wave guide versus delivered by the driver, causes a lot of diffraction leading to HOM
6.) sound field pattern in infinite conical horn with HOM (of low order) overlay of constructive and destructive interference (sinus stimulus):
7.) propagation of wave fronts in infinite conical horn with HOM (of low order) overlay of constructive and destructive interference (sinus stimulus captured at different phase angles):
8.) sound field pattern in infinite conical horn with HOM (of higher order) overlay of constructive and destructive interference (sinus stimulus):
9.) propagation of wave fronts in infinite conical horn with HOM (of higher order) overlay of constructive and destructive interference (sinus stimulus captured at different phase angles):
Except measurement will show otherwise - this brings me closer to the conclusion that HOM is basically a semantic "invention" - to have a incisive term at hand for nothing else what already is described by "standing waves".
Regarding horns / wave guides – as for now – I can't see any more implications sound wise for *HOM* as any other overlay of constructive and destructive interference may have – be it *called* from diffraction, reflection, scattering, standing wave, HOM or whatever.
The "standing wave" / HOM concept does nothing by its own – no implications not to be described by interference and delayed time of arrival - please correct me if I missed something, Earl.
Sure - I can see the benefits of having a sound field which isn't defective as a Swiss cheese of course – but that's true anyway – and *not* necessarily related to the concept of HOM
🙂
Is the Makarski paper somewhere downloadable for free?
Michael
Again sims are to be taken with some grain of salt 😉
The sharp diffraction at the horn throat is the reason of strong bouncing wave fronts between walls – or at least for delayed overlaying with the axisymmetric wave front – creating all sort of fancy patterns .
Some (#9) where we even could get the impression that the waves travel backwards through the horn – they don't – it's just the overlay pattern of constructive and destructive interference that isn't stable over time.
The throat is – as Earl is telling us - the most sensitive point of a horn and any mismatch in the shape of the wave front demanded by the horn / wave guide versus delivered by the driver, causes a lot of diffraction leading to HOM
6.) sound field pattern in infinite conical horn with HOM (of low order) overlay of constructive and destructive interference (sinus stimulus):
7.) propagation of wave fronts in infinite conical horn with HOM (of low order) overlay of constructive and destructive interference (sinus stimulus captured at different phase angles):
8.) sound field pattern in infinite conical horn with HOM (of higher order) overlay of constructive and destructive interference (sinus stimulus):
9.) propagation of wave fronts in infinite conical horn with HOM (of higher order) overlay of constructive and destructive interference (sinus stimulus captured at different phase angles):
Except measurement will show otherwise - this brings me closer to the conclusion that HOM is basically a semantic "invention" - to have a incisive term at hand for nothing else what already is described by "standing waves".
Regarding horns / wave guides – as for now – I can't see any more implications sound wise for *HOM* as any other overlay of constructive and destructive interference may have – be it *called* from diffraction, reflection, scattering, standing wave, HOM or whatever.
The "standing wave" / HOM concept does nothing by its own – no implications not to be described by interference and delayed time of arrival - please correct me if I missed something, Earl.
Sure - I can see the benefits of having a sound field which isn't defective as a Swiss cheese of course – but that's true anyway – and *not* necessarily related to the concept of HOM
🙂
Is the Makarski paper somewhere downloadable for free?
Michael
soongsc said:
Thanks
Seems that we have to "invent" log scale for Y-axis first, if we want to clearly see the interesting details in the impulse response
😀
Michael
mige0 said:
Michael
All I see is a bunch or pretty pictures. Your sims are so far from reality that I don't see them as useful at all, and I don't see anything that supports any of your conclusions. Quite honestly I don't think that you see the point at all.
gedlee said:
Quite honestly, Earl - I have to agree !
There *is* no point in "HOM", IMHO. 😉
As for "a bunch of pretty pictures" – their primary intent was to cut through your "woodoo dancing" when it comes to "HOM" related to horns / wave guides by providing an intuitively understanding of how wave fronts travel and what is the part of "HOM" in the picture.
This - at least – I have provided within my two postings – whereas there was ongoing guesswork since years on the subject you – nor anybody else - were able (or willing) to clarify.
Also the "bunch of pretty pictures" sets a valid starting point for (acoustic impedance) measurements as it provides an overview where we have to expect something to happen and where not.
Same for acoustic measurements.
Don't forget – for you Earl, anything seems to be quite clear – but for the noobs (me too) *nothing* is, actually.
But anyway - we may need to take a step back to look at what you correlate from subjective impressions to "HOM".
What you describe in the significance of delayed arrival is the most interesting part to me – as I can correlate that to my own impressions about impacts of jitter.
Might be, dedicated measurements will help in one way or another...
Michael
Michael, have you compared your 60 degree sims to some done at 90 degrees? In theory, HF reflections off a 45 degree wall (half of 90) can't hit the other wall more than once.
catapult said:
Yes - I originally intended to do a series of horn flares to show this effects.
Also possibly an investigation - within the limits of CARA - about the "deep throat" effects of the wave front transition by the OS contour (maybe CARA would not allow for good enough results anyway - dunno)
"HOM" (as a certain pattern) – by definition – can not occur beyond 90 deg – so its limited to the transition section at the throat in such cases – not to say that it does not affect further wave front propagation.
But meanwhile I'm think I not gonna load Earls thread with any further "bunch or pretty pictures" - there's simply too much time and effort involved 😉
Michael
gedlee said:
What *precisely* IS the point? Seriously.
I've now read through:
1. This thread,
2. The portion on the Beyond the Ariel thread,
3. The Horn vs. Waveguide thread,
4. The How "is" HOM measured thread,
..and most significantly:
*All* of the material you have linked to on your website.
What I don't get is:
-that *if* a "horn" or waveguide has substantially better time-decay performance for any respective domestic sp-level, that the presence of "HOM's" or (mechanically present) Diffraction lenses, (with potentially increased HOM's as a result), should have any relevance.
In other-words I'm looking at this from an EMPIRICAL point of view - or the "end result".
Theoretically (perhaps unlike others) I'm willing to concede that HOM's may well introduce additional time decay for a given sp-level. Further, perhaps even a modest diffraction "lens" will increase HOM's "enormously" (..though I've not seen *any* evidence of this).
For the end user though, theory is fine - but not terribly relevant.
What *is* relevant is the result.
If you say/have tested:
-time-decay is important at varying sp-levels, and may not be "linear" for given waveguide (the 2006 AES paper)
..then that actually *is* important to the Hobbyist (depending on the nature and level of the decay vs. the sp-level a particular user is interested in).
Interestingly enough that one "extrapolation" of the impulse response that others were "discounting" (Cumulative Spectral Decay) displays this behavior in a manner most find "tangible".
What I think this means then for *the hobbyist community* is that rather then spouting some grossly technical theory wrapped in an academic acronym, that instead you should probably be expounding the virtues of:
1. CSD plots and their interpreteation.
2. CSD plots and the need for off-axis (particularly horizontal axis) display.
3. CSD plots and the need for varying sp-levels.
(..and presumably not just for traditional waveguides either - as even a modest baffle for a conventional tweeter actually *is* a waveguide and usually does have a significant diffraction "signature".)
ScottG said:
This appears to be the only point worth responding to, but quite honestly I don't understand what it says. What is it exactly that you "don't get"?
gedlee said:
Try re-reading the *entire* post (perhaps even a few times). It should provide what you are asking for. (..and it isn't like I didn't make an effort to read through all of your material - several times in fact.)
If you still don't get it, ask again and I'll comment further.
>> Is the Makarski paper somewhere downloadable for free?
http://www.akustik.rwth-aachen.de/ITA/Mitarbeiter/mma?&kw=Veroeff
http://www.akustik.rwth-aachen.de/ITA/Mitarbeiter/mma?&kw=Veroeff
"that *if* a "horn" or waveguide has substantially better time-decay performance for any respective domestic sp-level, that the presence of "HOM's" or (mechanically present) Diffraction lenses, (with potentially increased HOM's as a result), should have any relevance."
I also find this unclear, but I think it's saying that HOM aren't relevant if even non-ideal horns can produce the desired in-home SPL w/o them becoming objectionable.
Which is course true by definition, but there's that "if".
I also find this unclear, but I think it's saying that HOM aren't relevant if even non-ideal horns can produce the desired in-home SPL w/o them becoming objectionable.
Which is course true by definition, but there's that "if".
noah katz said:
That's it. The sentence wasn't terribly clear on its own, but it was "reinforced" with the information that followed.
Basically I question the need to look for an underlying problem, (or potential source of a problem), *IF*:
-the measured result is good or excellent.
And yes, there is that *IF*. 😉
Not only is there the "if", but its all a mater of degrees. My old JBL horns sounded harsh even at low levels. They became almost intollerable at higher SPLs. Hence "if" any given horn is "satisfactory" depends on its level of HOM AND the SPL's that are involved. For me, I find them quite objectionable AND I like higher SPLs, hence the extreme need to control them. YMMV.
ScottG said:
The point here is :
“HOM” as a semantic concept was needed for establishing the all new waveguide theory for linguistic differentiation towards old horn theory.
As shown, “HOM” is (only) a specific subset of the laws of physics regarding “diffraction-reflection-interference-delay”, ig “standing waves perpendicular to the axisymmetric wave front”
Not to say that an incisive term like “HOM” my not be of any value - *if* it proves that we can link specific behavior of speakers to that specific pattern – which isn't the case until now IMO.
Until now the specific HOM concept is not needed in any case – as all subjective impressions can be described as well by the mere physics of “diffraction-reflection-interference-delay” - plus the interaction with the driver and possibly specific masking effects of our hearing ability.
Michael
gedlee said:
But is what's "satisfactory" (or not) directly dependent on HOM (and SPL's)?
Do we hear HOM's, or do we hear errors in linear performance at least *in part* as a result of HOMs?
(Note that it isn't really the same thing. Ex. I don't hear room modes, but I do hear the alteration of sound by those modes - particularly freq. dependent spl-differences.)
In other-words I'm positing a slightly different perspective, not to be obtuse or argumentative - but rather to provide a more accessible "position" for readers to form a basis for what is and is not desirable for sound reproduction.
For instance saying: "high levels of HOM's are bad", and then not being able to show any level of HOM "reads" for any given reader pretty much the same as the technical performance aspects of the Enable pattern.
On the other hand saying that something like: "poor linear decay performance vs. SPL is bad", *is* something that a reader can intuitively grasp.
Further - it can be measured.
With such measurements you can also derive designs that are better and worse objectively based on results, not theory. As a DIY'er that *feels* better. 😉
Yes!
From this Makarski paper
http://www.akustik.rwth-aachen.de/pub/mma/mma-daga04.pdf
I got the enlightenment!
"The excitation of higher order modes obviously falls together with the internal membrane breaking up into higher order modes. The observed velocity distributions were nearly independent of being measured with or without a horn coupled to the driver."
"The results show that the fundamental wave dominates the
acoustic behaviour up to the frequency were the mem-
brane starts breaking up massively into higher order
modes and, thus, exciting modes within the junction
area. Furthermore, this behaviour is nearly independent
of having a horn coupled to the driver."
So HOM depends only on the driver. The horn has nothing to do with it!! 😀 😀
- Elias
From this Makarski paper
http://www.akustik.rwth-aachen.de/pub/mma/mma-daga04.pdf
I got the enlightenment!
"The excitation of higher order modes obviously falls together with the internal membrane breaking up into higher order modes. The observed velocity distributions were nearly independent of being measured with or without a horn coupled to the driver."
"The results show that the fundamental wave dominates the
acoustic behaviour up to the frequency were the mem-
brane starts breaking up massively into higher order
modes and, thus, exciting modes within the junction
area. Furthermore, this behaviour is nearly independent
of having a horn coupled to the driver."
So HOM depends only on the driver. The horn has nothing to do with it!! 😀 😀
- Elias
Elias said:
He's specifically addressing HOM's generated at the driver horn interface. I don't think this applies to HOM's generated by refraction in the horn.
Sheldon
gedlee said:
The paper is cited as evidence of the the existence of HOMs, but not in horns/waveguides?
Worse, it doesn't matter what horn is attached?
[Perhaps that's the wrong paper.... 😉 ]
Hello,
From this Makarski paper
http://www.akustik.rwth-aachen.de/pub/mma/AES117paper.pdf
I understand that a horn does not radiate HOM unless there is a coupling for that specific higher order mode from the driver, and a horn does not radiate HOM unless that specific higher order mode is excited by the driver.
Then, what is HOM? It is the break up resonance of the driver membrane!
Hmm.. I thought this was known already before 😀 😀
- Elias
From this Makarski paper
http://www.akustik.rwth-aachen.de/pub/mma/AES117paper.pdf
I understand that a horn does not radiate HOM unless there is a coupling for that specific higher order mode from the driver, and a horn does not radiate HOM unless that specific higher order mode is excited by the driver.
Then, what is HOM? It is the break up resonance of the driver membrane!
Hmm.. I thought this was known already before 😀 😀
- Elias
