EarlK said:
I was the one trying to connect the two because I wanted confirmation on what HOM are so I used HONK. Since then this thread and Geddes thread have had some great discussion and now I (think) understand the following.
1. HOMs are proven through mathematics
2. HOMs are extremely hard to measure
3. When HOMs are reduced the waveguide sound much, much better BUT no one can describe the imporvement.
Sure, I can describe the improvement, but it's subjective, and until we get agreement on the vocabulary, easily discounted or misunderstood.
If I remember right, Geddes describes an increasing "roughness" of sound with increasing SPLs as the objectionable aspect of linear distortion, (which is what HOMs are). This squares with my experience - at some high level the sound becomes unpleasant.
Clean up the sources of of the linear distortion (things causing diffraction and reflection) and the roughness of sound does not become so apparent at increasing SPLs.
In other words, you can play the speakers much louder before the experience becomes unpleasant and, if you've done a really good job, you can get into dangerously high levels before the unpleasantness becomes apparent, if it becomes apparent at all. 😱
doug20 said:
To 2), they are "hard to measure", requiring techniques that I don't have at my disposal (microflowns on scanning array), but they have been measured (Makarski) and so you should add a point here "2b) HOM have been confirmed experimentaly"
To 3), - "no one can describe the imporvement" is completely incorrect, there is a whole list of people who have reported their impressions of low HOM speakers on my web site.
This also happens when driver breakup modes are cleaned up. So how would one differenciate from reducing breakup mode effect vs HOMs?FrankWW said:
soongsc said:
Because completely different methods are required for the two different issues? I don't see how waveguide contours or foam inserts would affect diaphragm breakup. Nor do I see how changes to a compression driver would influence HOM's.
Sheldon
Sheldon said:
Actually the phase plug does have a substantial effect on the HOM and their creation. But virtually all phase plugs are the same so there is not likely to be much difference between drivers in practice, but there could be.
"I don't see how waveguide contours or foam inserts would affect diaphragm breakup."
Now that you mention it, I don't see why foam wouldn't work as an acoustic LP filter for breakup modes, which are by nature higher freq.
Now that you mention it, I don't see why foam wouldn't work as an acoustic LP filter for breakup modes, which are by nature higher freq.
I think that new ''creative plumbing'' design for a next gen phase plug, plus critical contour matching of its exit angle to the WG entry angle, and a smooth seal between them, can be leading to new HOMless 😎 enough driver+WG systems. Maybe to a point that foam would not be centrally necessary? So not to burn SPL during filtering.
Salas said:
Let's not forget that absolute zero HOM is not possible. You can minimize them, but you cannot elliminate them.
gedlee said:
So the measurements to highlight the HOM problems are known to everyone now??
Completely??? Are you sure?
Subjective listening means nothing to me. There are thousand of very happy BOSE owners out there so I do not care if someone "Likes" the sound of anything 😉 Do the proper DBTs and post those results with people that do not worship at your feet besides that we could post reviews from ALL comercial websites and have a drinking party with adjectives used on each site 😉
Let me rephrase then to exclude very subjective opinion...
3) no way to describe the improvement in a detailed matter except people saying, "Hey that speaker sounds awesome".
Thinking of a drinking game, I could have one with how many times Geddes posts "You are completely incorrect" 😱
For all the professed confidence in objective data, there would appear to be an inordinate reliance upon subjective opinion as relates to the significance of HOMs....
gedlee said:
Your correction Earl, is not correct.
As "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” – as outlined in detail in your thread – there is no evidence that the improvement anybody has described by listening to your design is related to “HOM” specifically.
Meaning, the perceived improvement of your design can be described completely *without* any need of the specific "HOM" concept 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
I'm not sure you get it.
I said some other things in that post.
What I did say, which is important, is that, if we reduce levels of linear distortion (including HOMs) by reducing their causes, then we can play the speakers at higher SPLs before they start to sound unpleasant. This may be subjective experience but we can measure it objectively with a Ratshack sound meter.
Subjective judgements are fine. We just have to be clear about the objective correlates for each term used.
Some terms are pretty easy to correlate to physical phenomena. For instance, there are "bright" and "dark" sounding voices, instruments, and, yes, loudspeakers. It depends pretty much on the energy distribution through harmonic structure above and below the fundamental note. In voices and instruments "bright" and "dark" characteristics may be desirable, but never in loudspeakers.
Nah, there's all sorts of ways to describe the improvement. Here's one:
Voices and instruments may change their characteristic sounds as they play louder and this may or may not be desirable, but we don't want this behaviour in loudspeakers.
We especially don't want loudspeakers to sound "harsh", "rough" or "unpleasant" as they play louder. So how loud can a speaker play before it sounds nasty? Loud? Really loud? Really, really loud? There is nothing so subjective about this that it can't be sufficiently objectified with an SPL meter.
Horns and waveguides have a desirable characteristic : they can dynamically match and even exceed the lower frequency drivers' output. This is why they've been used for years, but for a long time, until serious researchers like Geddes got to work, their obvious distortion ("harshness", roughness", "unpleasantness") made them unsuitable as high fi speakers except at unrealistically low SPLs.
I don't see your point in patronizing Geddes.
You are assuming he hasn't done that.
mige0 said:
I don't get this. The time delays introduced by higher order modes are of the same order as those introduced by edge diffraction. What particular characteristics of HOMs leads you to think they would not be at play in human nonlinear perception of linear distortion?
I thinks what Michael is trying to say is that HOMs is just another name for existing phenomena, which I kind of agree with.FrankWW said:
Very interestingly is that the name HOM has been associated with characteristics horn honk, harshness, etc. It seems to me that horn honk is somewhat related with acoustics impedance nature of the horn design which can also be viewed via CSD. Harshness can also be associated with diaphram breakup modes. Both of which can be reduced when you insert foam or alter waveguide/horn design. There has yet to be any specific evidence to separate HOM from other characteristics via data and associated sonic signature.
FrankWW said:
I still don't get it then, you guys love saying that 😕
Nothing you or Geddes has posted defines the sound of HOM.
As for patronizing Geddes? As I posted above Im not the one posting "You are completely incorrect" all over forums in every other response to every other member. Kind of a unique way to convince everyone that his speakers are the best 😉
I also find it funny because is "Completely Incorrect" have more meaning then "Incorrect" 😉
I believe he partonizes everyone that disagrees or has an opinion that differs. Heck my post was merely a subjective observation that didnt need actually what I think is an overly pendatic correction.
He tried to correct my opinion by saying people love his speakers???? How does that remotely answer what HOM sound like.
gedlee said:
Makes sense.
noah katz said:
To the extent that the breakup modes are above about 10kHz, the foam would attenuate them. But it won't attenuate them selectively. Since the typical application is to equalize the system after the foam is applied, then output from breakup modes would not see any net relative reduction.
Sheldon
This thread is a bit odd. I have speakers with the foam insert, and they sound wonderful. I've also tried putting it in tractrix horns of my own design, and again, a huge improvement.
So subjectively, it's well worth the trouble.
Yesterday I did measurements of a waveguide with and without the foam, and the improvement in the impulse response was obvious.
In some ways, the impulse response reminded me of what happens when you treat a room; it cleans up the sound.
So objectively, the difference was impossible to miss.
I'm honestly surprised there's such debate over this; what's the downside here? So you lose a couple of DB in sensitivity. Compression drivers have sensitivity to burn.
As DIYers, we should be ecstatic over this, it's an easy way to improve our horns and waveguides. And it's not like it's expensive; a sheet of the foam is $40.
So subjectively, it's well worth the trouble.
Yesterday I did measurements of a waveguide with and without the foam, and the improvement in the impulse response was obvious.
In some ways, the impulse response reminded me of what happens when you treat a room; it cleans up the sound.
So objectively, the difference was impossible to miss.
I'm honestly surprised there's such debate over this; what's the downside here? So you lose a couple of DB in sensitivity. Compression drivers have sensitivity to burn.
As DIYers, we should be ecstatic over this, it's an easy way to improve our horns and waveguides. And it's not like it's expensive; a sheet of the foam is $40.
"Nothing you or Geddes has posted defines the sound of HOM."
Hello Doug20
Well the catch word seem to be harshness that gets worse with SPL. The only problem I see using it to describe the anomaly is this characteristic is not unigue to Waveguides or Horns. I have heard dynamic speakers get harsh with SPL when pushed too hard. So a hornless speaker can exhibit the same characteristic of getting harsher with SPL that is being used here to differentiate between Horns and Waveguides.
So do dynamic drivers mimic what HOM's sound like when they are pushed hard and the break-up modes become audible?? Is that what we should be listening for?? Looking at the work that shows them at the mouth of the horn it reminds me of some of the break-up mode pictures I have seen made using a laser of dynamic speaker break-up modes.
Rob🙂
Hello Doug20
Well the catch word seem to be harshness that gets worse with SPL. The only problem I see using it to describe the anomaly is this characteristic is not unigue to Waveguides or Horns. I have heard dynamic speakers get harsh with SPL when pushed too hard. So a hornless speaker can exhibit the same characteristic of getting harsher with SPL that is being used here to differentiate between Horns and Waveguides.
So do dynamic drivers mimic what HOM's sound like when they are pushed hard and the break-up modes become audible?? Is that what we should be listening for?? Looking at the work that shows them at the mouth of the horn it reminds me of some of the break-up mode pictures I have seen made using a laser of dynamic speaker break-up modes.
Rob🙂
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