Other don't believe it simply because someone says so, or claims to have heard it. There are umpteen cable threads here that demonstrate that. 😉
"It's so because I say it's so" doesn't go very far.
"It's so because I say it's so" doesn't go very far.
"Its so" because it was proven. You still don't get it do you. There is a word for that but it is not allowed here.
This is where I first addressed the issue by looking at data.http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-239.html#post1774677
However, that was not good enough for determining the process of improving design. It did show how foam effects and reduces HOM by breaking it up.
If you want to compare designs, you need to measure inside the horn. The measurement should be conducted from as deep as you can go to 1M out of the lip or further depending on size of horn mouth, ideally in increments between 4mm~20mm. If the wave expansion is ideal, all the curves inside the horn should bear the same shape running in parallel to each other. You will never get it perfect, but the less fluctuation in the smoothness of the curves mean you have less HOM. The external part of the measurement is basically for optimising lip design.
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The cable issue is more complicated because it interacts with both ends of the connecting devices. If you look at the schematics and layout of designs, much are poorly decoupled. Then if your speakers are not clean and well designed, you can hear or not hear anything. I vote for total system design integration to get the solution more ideal.
Let's see. Geddes demonstrates in his book and the addendum to it on his website that HOMs are created by changes in a duct's boundary.
Makarski measures them in a horn/waveguide.
Geddes in a paper presented at a AES convention shows that folks become more sensitive to HOMs with rising SPLs. And he did it a way that was scientifically respectable.
He removed possible confounders which include things such as CD time domain artifacts, reflections from horn mouth impedence, refraction from speaker baffle corners, and presented time domain artifacts that HOMs produce, to subjects' ears double blinded and using a musical signal. What's not to like?
That HOMs on the scale of an audio waveguide are really difficult to measure?
So what?
Horns/waveguides that according to Geddes's physics and psychoacoustics demonstrations, should sound inferior at high SPLs to those which produce fewer HOMs, in fact, do sound crappier.😎
Well, how 'bou that? Who'da thunk all thet thar science might mean sompin, Jethro?
Makarski measures them in a horn/waveguide.
Geddes in a paper presented at a AES convention shows that folks become more sensitive to HOMs with rising SPLs. And he did it a way that was scientifically respectable.
He removed possible confounders which include things such as CD time domain artifacts, reflections from horn mouth impedence, refraction from speaker baffle corners, and presented time domain artifacts that HOMs produce, to subjects' ears double blinded and using a musical signal. What's not to like?
That HOMs on the scale of an audio waveguide are really difficult to measure?
So what?
Horns/waveguides that according to Geddes's physics and psychoacoustics demonstrations, should sound inferior at high SPLs to those which produce fewer HOMs, in fact, do sound crappier.😎
Well, how 'bou that? Who'da thunk all thet thar science might mean sompin, Jethro?
I think the subject of this thread is how they are measured, not whether it makes and audible difference or not.
All I'm asking for is to see some measurements of what Geddes is talking about. Why is that so difficult? I feel like I've stumbled into some sort of cult. "We don't need no stinkin' evidence, we believe!" Very unlike the smart people you all are.
At least with a lot of recent prodding there has been some progress, a link to that paper that shows higher order modes at the driver/horn interface. But so far no measurements that show HOMs at the driver mouth, or that one profile has them and another does not. Nor have we seen measurements that show that foam reduces HOMs. We have seen measurements that show a change in frequency response with foam, but that's all. Have I missed those HOM measurements somewhere? If I have, I apologize - but I just can't find them. If you know where they are, please point the way. I've asked Earl Geddes if he has ever measured them, and he remains silent. Why?
Why do these HOM deserve any less scrutiny than any other new audio claim?
Do the HOM fanboys just like the idea (it's a nice one) or is there some other reason that these are exempt from concrete evidence?
At least with a lot of recent prodding there has been some progress, a link to that paper that shows higher order modes at the driver/horn interface. But so far no measurements that show HOMs at the driver mouth, or that one profile has them and another does not. Nor have we seen measurements that show that foam reduces HOMs. We have seen measurements that show a change in frequency response with foam, but that's all. Have I missed those HOM measurements somewhere? If I have, I apologize - but I just can't find them. If you know where they are, please point the way. I've asked Earl Geddes if he has ever measured them, and he remains silent. Why?
Why do these HOM deserve any less scrutiny than any other new audio claim?
Do the HOM fanboys just like the idea (it's a nice one) or is there some other reason that these are exempt from concrete evidence?
Go back and read the first post. 😉
-being able to measure HOM's was simply a "means to an end".
..just the title itself is misleading.
Makarski showed measurements of HOMs at the mouth in one of his papers - he has several.
I am not going to respond to someone who is rude and doesn't listen. There is no point in responding to posts like that.
I am not going to respond to someone who is rude and doesn't listen. There is no point in responding to posts like that.
Am I rude because I ask for measurements? If that's rudeness, then this whole forum will fall apart. Why are we not allowed to ask for measurements or evidence? What is special about HOMs that we don't need to see measurements?
Hi Pano
I can’t say that I have ever gone looking for HOM’s on purpose but I have run into them at least once at a magnitude that demanded investigation.
In the very early days of the full range horns, I convinced my partner to allow an acquaintance Nick, from the DIY audio area to license and sell a DIY version of the Unity horn. We already had the Baltic birch triangle parts and metal driver plate machined to make the horns out of and the deal was we shipped those to him at Lambda to assemble.
I had ours finished off with a ½ inch radius in the corners, a tapered hole in the aluminum plate and finish off with a flap sander which puts a small radius on the transition to the flare angle.
The DIY versions were finished off much more carefully, the corners bondo’d in and painted and a VERY nice looking job, like it was molded. The nicer looking throat area also made the transition to the final angle take place farther from the entrance also.
All was well until measurements of the DIY version came in, on axis, they had a notch in the upper mid which the ones we sold in products didn’t. Ummm very puzzling, so I got one of the DIY horns to play with and sure enough there was the notch dead on axis. I had a TEF machine but it doesn’t tell you what you’re looking at haha.
A slow high rez measurement showed it was a pointy notch meaning (often) a strong reflected signal but also lacking the train of combs one would get with a simple delayed signal.
So lets skip over the boring head scratching, I thought ok, what if here was a frequency dependant radiation within the horn that added spatially on axis ?
I could tape over the mid holes with aluminum duct tape and it went away. This horn had the corners much more filled in than mine, I had found by trial and error that if one made the holes as small as you could get away with and put them into the corner that the effect of that leak becomes negligible compared to that port being closed off. Lower down in the operating range, the holes are no longer leaks as they have active (driven) drivers that are mutually coupled to the upper or lower ranges within the horn, being less than ¼ wl apart where they interact..
To find what thankfully was a solution and might be useful here to find “things”, i used a 5x5x ½ inch sound absorbing foam on a 4 foot dowel rod, I set up a microphone on axis where the notch was and drove the speaker using a very band limited pink noise, I used a speaker controller to limit the band the approximately the width of the notch.
This way, I could watch the SPL and listen while I move around listening and move the stick absorber around the mouth. Band limited pink noise is very useful if you know around where a problem is, much better than a sine wave for “searching” Apparently, the mid holes not being in as much of the shadow of the corners caused a radiation from that point. At a point just past the second bend, that was hitting the inside of the horn mouth and hen summing on axis, partially canceling out the main signal.. As soon as the absorber on a stick (so I wouldn’t be in the way) reached the spot on one face where it was hitting, I saw the SPL jump and I could hear a change. Had there been a somewhat different angle, they would have projected off to the sides instead of bouncing off the horn.
A set of 4 absorbing triangles stuck on the horn mouth in the center, knocked it down to a depression about 2 or 3 dB deep.
Now I wasn’t looking for a HOM, but that is the kind of thing I think of.
Best,
Tom
OK Tom, at least you are providing something. That's a lot more than can be said for many in this thread. It really wasn't so hard, was it?
Tsk, tsk.
You know very well that Makarski's measurements are evidence, not that the the issue of existence is proven. We could just as well have said recently that Neutrino's can travel faster than light because it was "proven" so.
Worse, it's rather obvious that Pano is no longer disputing the simple existence of HOM's:
ie. "..paper that shows higher order modes at the driver/horn interface" from Pano in post #389.
So, who is the one being rude and not "listening"? 😉
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Scott. I have said that the link to the paper was progress, even tho it took some pounding to get it. What's wrong with showing some evidence? Shouldn't we be happy to provide it? Or is that spoiling the fun?
So far we have seen one paper that that shows some higher order modes that occur at the driver/horn interface. Good! That's real progress. OK, let's take it further, let's see some evidence of HOMs at the driver mouth and perhaps in the far-field, where we listen. Wouldn't that be useful? Isn't that the point?
Earl Geddes is right - I don't get it. I don't get why he, or anyone else, would not be happy and proud to provide some simple measurements of HOMs at horns mouths. Why aren't the measurements provided? Geddes insists on measurements for everything else, but not for this. Why? At least someone who shows solid evidence can hold his head high and say "See? I told you so." And it should make you all happy to shut me up. 😉
I promise you - just show some measurements that HOMs are significant* at the mouths of horns (or somewhere in front of them) - and I'll be the first to congratulate and thank you. Honest.
*We can see them or their effects in the measurement and they aren't so far buried as to not be audible. That's the whole HOM idea, we can hear them and they are bad.
So far we have seen one paper that that shows some higher order modes that occur at the driver/horn interface. Good! That's real progress. OK, let's take it further, let's see some evidence of HOMs at the driver mouth and perhaps in the far-field, where we listen. Wouldn't that be useful? Isn't that the point?
Earl Geddes is right - I don't get it. I don't get why he, or anyone else, would not be happy and proud to provide some simple measurements of HOMs at horns mouths. Why aren't the measurements provided? Geddes insists on measurements for everything else, but not for this. Why? At least someone who shows solid evidence can hold his head high and say "See? I told you so." And it should make you all happy to shut me up. 😉
I promise you - just show some measurements that HOMs are significant* at the mouths of horns (or somewhere in front of them) - and I'll be the first to congratulate and thank you. Honest.
*We can see them or their effects in the measurement and they aren't so far buried as to not be audible. That's the whole HOM idea, we can hear them and they are bad.
well, I hope Im not rude saying this
but I always have got the impression that 'dealing with HOM' would put all other horn designs aside
and I almost believed it
I'm just glad there still are other ok alternatives
but what do I know about it ... I like Big Foot too, even if he will eat me 😛
but I always have got the impression that 'dealing with HOM' would put all other horn designs aside
and I almost believed it
I'm just glad there still are other ok alternatives
but what do I know about it ... I like Big Foot too, even if he will eat me 😛
Actually he has given a reason for this several times:
-it's too costly to make these measurements for someone like himself or other hobbyists.
I'm not sure he's gone into any substantive detail on *why* this is the case, but for me it's good enough. 😱
Honestly, Earl's the expert here - if he says that it's very likely that HOM's are occurring under a well-considered condition, then I'll take that as being good enough.
That's not "being a sheep". 😀 That's "betting on the smart money". 😛
I certainly wouldn't fall into the utter BS that anything has been actually proven though. (..an expert shoveling cr@p my way doesn't mean magically transform that cr@p. That takes multiple experts shoveling the same cr@p. 😀 ) On the other hand I do recognize that there is good supporting evidence at this time.
..of course that's just about HOM's existence.
Like the original poster, I too would like to see objective data on HOM's with competing designs, but I'll except that it's unlikely to be available because of cost considerations.
What I won't except however is that HOM's have anything to do with an audible condition in our context, because I've not seen anything to support such a notion (let alone actually being proven).
In fact Earl has repeatedly mentioned that to generate HOM's that are likely audibly objectionable (in a reasonable design context) requires high spl.s.. specifically higher than anything but the infamous "demo". The only real exception to this would be a recording with a very high dynamic range, and in those instances the sound itself is naturally objectionable and usually very limited in duration during those "peaks".
What "erks" me most is that Earl does exceedingly little to disabuse the current proliferation of "HOMo'philes". I understand that it's against his financial interests to do so, but I'd hope that as an expert and particularly as as the expert that started research into this area - that he would do more to enlighten others. 😱
I would like to see more evidence of the problem as well.
I certainly believe that higher order modes exist but am not sure of the extent of the problem. We are told that it is a linear effect (like any frequency or time effect), but that their offensiveness grows strongly with level. For some reason they are hard to measure or hard to issolate, yet supposedly easy to hear.
It wouldn't really matter to me but there seems to be a whole group of followers convinced that HOMs are evil and more detrimental than conventional horn problems such as frequency response problems, poor polars, throat distortion, resonances, etc. The same group will quickly tell you that diffraction slots (indeed, any feature causing diffraction) must be avoided at any cost.
Again, I'm sure they exist but would like to see some concrete measurements in time and frequency response. I would also like to understand how a particular linear effect is more detrimental than any other response aberation steming from more conventional causes.
David
I certainly believe that higher order modes exist but am not sure of the extent of the problem. We are told that it is a linear effect (like any frequency or time effect), but that their offensiveness grows strongly with level. For some reason they are hard to measure or hard to issolate, yet supposedly easy to hear.
It wouldn't really matter to me but there seems to be a whole group of followers convinced that HOMs are evil and more detrimental than conventional horn problems such as frequency response problems, poor polars, throat distortion, resonances, etc. The same group will quickly tell you that diffraction slots (indeed, any feature causing diffraction) must be avoided at any cost.
Again, I'm sure they exist but would like to see some concrete measurements in time and frequency response. I would also like to understand how a particular linear effect is more detrimental than any other response aberation steming from more conventional causes.
David
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