Tom
I think that we both see Wayne the exact same way and both have trouble with his way of dealing with the competition. However, I would prefer that this NOT become a bash Wayne thread and that Wayne simply refrain from turning "Geddes on Waveguides" into "Wayne's world".
RCW
The wave equation states that the Laplacian (the divergence of the gradient) of the pressure field must equal k^2 times the pressure. For the divergence to be zero k or p would have to be zero. Since p=0 is a trivial solution then only when k=0 does the wave equation yield Laplaces Equation. Only for a static pressure does the divergence vanish. In some cases, the very low frequency behavior of a system can be gleaned from setting k = 0, but in any real audio acoustics k is never zero, and the divergence does not vanish. You really do need to brush up on your acoustics.
In deriving the wave equation from the equation of continuity of mass one has to linearize it by assuming that the density changes are small and neglect these changes altogether in some terms (terms quadratic in the small changes). But if there where no density changes then there is no wave propagation. This is intuitively obviuos since sound is a compressional wave in the fluid, i.e. pressure changes - not incompressible. If the fluid were truely incompressible then the wave speed would be infinite.
We sometimes think of water as incompressible, and compared to air it is. Its wave speed is about hundreds of times that of air, but it is still finite and so water is still compressible as far as sound propagtion is concerned.
You are talking about something for which you really don't seem to be well versed in as you are getting it all wrong.
I doubt that Putland said that the fluid was "incompressible". He knows better.
I think that we both see Wayne the exact same way and both have trouble with his way of dealing with the competition. However, I would prefer that this NOT become a bash Wayne thread and that Wayne simply refrain from turning "Geddes on Waveguides" into "Wayne's world".
RCW
The wave equation states that the Laplacian (the divergence of the gradient) of the pressure field must equal k^2 times the pressure. For the divergence to be zero k or p would have to be zero. Since p=0 is a trivial solution then only when k=0 does the wave equation yield Laplaces Equation. Only for a static pressure does the divergence vanish. In some cases, the very low frequency behavior of a system can be gleaned from setting k = 0, but in any real audio acoustics k is never zero, and the divergence does not vanish. You really do need to brush up on your acoustics.
In deriving the wave equation from the equation of continuity of mass one has to linearize it by assuming that the density changes are small and neglect these changes altogether in some terms (terms quadratic in the small changes). But if there where no density changes then there is no wave propagation. This is intuitively obviuos since sound is a compressional wave in the fluid, i.e. pressure changes - not incompressible. If the fluid were truely incompressible then the wave speed would be infinite.
We sometimes think of water as incompressible, and compared to air it is. Its wave speed is about hundreds of times that of air, but it is still finite and so water is still compressible as far as sound propagtion is concerned.
You are talking about something for which you really don't seem to be well versed in as you are getting it all wrong.
I doubt that Putland said that the fluid was "incompressible". He knows better.
Tom Danley said:
Didn't say it was a substitute. I did say I would be interested to see how the data on a Unity gathered from a measurement array like that looked.
Tom Danley said:
Perhaps. I know there were a lot of posts about the Unity on Audio Asylum, and several on the Pi Speakers forum as well. They were all promoting the Unity, frankly challenging all others to compare with them. But they had that nasty notch, so they didn't look all that hot.
Mark Seaton was an employee of ServoDrive as I recall. So whether the posts were from you or he, I don't recall but I do know it was from one of you guys. It's just like how Ivan Beaver now posts stuff promoting Danley products. Sometimes he'll claim to be unaffiliated, but he gets his paycheck from the same guy you do. So to me, these kinds of posts are all from the same source.
Tom Danley said:
I have a problem with being insulted, yes. I have a problem being bullied, challenged as if my speakers weren't up to a comparison with a new speaker with response curve showing a cancellation notch right smack dab in the middle of the pattern. You guys picked the fights and passed around the data, then when I pointed out that it wasn't that hot, you took me on as if I were a heretic. And it looks like you still are doing the same old thing.
Tom Danley said:
This BS about riding on coat tails is insulting and makes me angry. If you had said that to my face, we'd be taking this outside right now.
I've been making speakers for a long time. My four Pi is over a decade old and has been virtually unchanged over that time. It has been around longer than your Unity and longer than Geddes Summa. I've made horns of all shapes and sizes for various applications for nearly three decades now. I may be a hobbyist, but my designs perform very well, frankly better than either of yours do. So you can take your coat tails and stick it straight up you know where.
I don't see either you or Earl as being my competition. My website is a hobby site, not a commercial endeavor.
I think that is probably the problem, that some people here see this as a competition, but my website just like this one here that you are both posting on, is a DIY website, not a commercial one.
At any rate, I'll leave you both to your selling. I can see where this is going and I'm outta here.
Wayne Parham said:
It would be nice if you took it outside. Outside these forums that is. Enough please Gentlemen, there's no need for that here.
It would be nice to focus on technical, artistic, manufacturing, etc. rather than bring brand names into the comparison. Getting into who is better gets really personal, but if we can look at the data from different points of view, look at analysis methods, and relate it with what we hear, it really is a more proffessional approach.
gedlee said:
gedlee said:
gedlee said:
This is remarkable. Is it possible to civilly discuss any point with you that is at odds to your own beliefs?
I see what rcw is saying, and I don't think it's "absurd" at all. Sound waves are created by the rapid motion of the speakers cone, dome, diaphragm, whatever and the velocity is high enough for the air to behave like an incompressible fluid. As the waves move outwards through the air they expand and loss energy. This happens in every medium.
gedlee said:
Now who has it wrong? Water is only compressible at extreme pressure and will be completely unaffected by sound waves in that regard. Sound propagtion?
A simple question
A quick google search brought up this page:
Princeton University Link
in which it points out how easy it is for air to be compressed by a bicycle tire. Not the speed of sound, no, very low speed movement that then may remain constant, but obviously highly compressible, quite different than, say, for water. This is not isothermal, of course, but still should be a good example.
The simple question is, are you implying that a driver baffled in a double closed box will not move (a reasonable conclusion I would say)? If it did, how could you then claim air to be incompressible at the speed of sound? If it were incompressible, the speed of sound in air would, I believe, be closer to the speed of sound in, say, steel.
The issue is in no way concerned, of course, with an object attempting to move through air at or exceeding the speed of sound, so that physics is not of concern.
Keep in mind that a driver is not moving at a constant speed, it is in fact cyclical. It's speed is zero at the initial application of the signal when at rest (consider a simple sine wave for now), is zero at the peak of each cycle (maximum deceleration) and must accelerate from zero at these two peak points on each cycle and since air is quite obviously compressible at low speeds (the bicycle pump case), by your contention the response of air from a driver must be constantly transitioning from being compressible (in and near the zero speed points) to incompressible (some nebulous point reached prior to maximal movement at the zero crossing point).
Would you elaborate the details as you see them in this regard or show some data or theory that explains at what point from an acoustics standpoint air can be considered to be incompressible?
Dave
Not being fully versed in the physics of acoustics vis-a-vis the wave equation and such, a simple question comes to mind. If air is incompressible at the speed of sound as you insist it is, then if one were to place a driver on a baffle with a closed box on both sides and apply a signal (at any magnitude of course), by your claim the diaphragm would in essence not move because to do so would require that the air be compressed if it moves at all.MJL21193 said:
A quick google search brought up this page:
Princeton University Link
in which it points out how easy it is for air to be compressed by a bicycle tire. Not the speed of sound, no, very low speed movement that then may remain constant, but obviously highly compressible, quite different than, say, for water. This is not isothermal, of course, but still should be a good example.
The simple question is, are you implying that a driver baffled in a double closed box will not move (a reasonable conclusion I would say)? If it did, how could you then claim air to be incompressible at the speed of sound? If it were incompressible, the speed of sound in air would, I believe, be closer to the speed of sound in, say, steel.
The issue is in no way concerned, of course, with an object attempting to move through air at or exceeding the speed of sound, so that physics is not of concern.
Keep in mind that a driver is not moving at a constant speed, it is in fact cyclical. It's speed is zero at the initial application of the signal when at rest (consider a simple sine wave for now), is zero at the peak of each cycle (maximum deceleration) and must accelerate from zero at these two peak points on each cycle and since air is quite obviously compressible at low speeds (the bicycle pump case), by your contention the response of air from a driver must be constantly transitioning from being compressible (in and near the zero speed points) to incompressible (some nebulous point reached prior to maximal movement at the zero crossing point).
Would you elaborate the details as you see them in this regard or show some data or theory that explains at what point from an acoustics standpoint air can be considered to be incompressible?
Dave
MJL21193 said:
Help me to understand your comment. Are you suggesting that water only begins to compress at extreme pressures or rather (and I think more correctly) that the compression is only readily apparent at extreme pressures?
My understanding it that water compresses at even low pressures, but the reduction in volume is so slight as to be nearly imperceptible (this does not mean it is zero).
A quick search pulled up this brief table.
temp F(C) 0 atm 500 a 1000 a 2000 a 3000 a
32 (0) 1.0000 0.9769 0.9566 0.9223 0.8954
68 (20) 1.0016 0.9804 0.9619 0.9312 0.9065
122 (50) 1.0128 0.9915 0.9732 0.9428 0.9193
Obviously it supports your position that it takes extreme pressures to compress water substantially, but while water's bulk modulus may be high (2.2×10^9 Pa), it's not infinite, so even at 2 atm there is a reduction in volume (on the order of 50 ppm).
Hi Earl
I’m sorry for intruding that way in your thread, I pretty much only reply to him when he says something wrong or provocative about my stuff but, looking back, with 88 prior posts responding to him (only the drafts I saved along the way), I should know better.
I’m not sure why one would say air (or even water) is incompressible; to embrace that idea would prevent one from picturing how sound works.
The fact that it is compressible and that there is ambient pressure makes air something like a class “A” circuit, sound is modulating the pressure slightly above and below ambient pressure or “bias” point.
High power piezo electric and magnetostrictive transducers are often loaded with a large static force and then operated in a range about that point, like air but in solid materials.
Because the “spring force” between molecules is temperature dependent, one finds C is temperature dependent. This was demonstrated to me in a vivid way when I was trying to inject high intensity sound from a levitation source into a furnace through a large temperature gradient. If I recall, at about 1100 degrees C the speed of sound has doubled at 1500C it is very hard to do without having some of the radiator showing (not good), inside is a very radiant heat source.
Anyway, even under normal temperatures one can see the effect of compressibility by examining a high intensity sound wave. The pressure side of the wave has a slightly higher temperature and the low pressure side a lower temp so after some distance, the wave shape precesses into a saw tooth. This was a real problem with those 160dB acoustic levitators and is the main “non-linear” thing in air “throat distortion”.
Another part that wouldn’t be clear with an “incompressible” view is what radiation resistance looks like to the radiator.
Radiated pressure is “in phase” with and proportional to source volume velocity, many people think the maximum radiated pressure is when the cone or radiator is at its farthest excursion point where in reality, velocity is highest as it pass through its rest point.
Anyway, a few thoughts on the mechanical part.
Best,
Tom Danley
I’m sorry for intruding that way in your thread, I pretty much only reply to him when he says something wrong or provocative about my stuff but, looking back, with 88 prior posts responding to him (only the drafts I saved along the way), I should know better.
I’m not sure why one would say air (or even water) is incompressible; to embrace that idea would prevent one from picturing how sound works.
The fact that it is compressible and that there is ambient pressure makes air something like a class “A” circuit, sound is modulating the pressure slightly above and below ambient pressure or “bias” point.
High power piezo electric and magnetostrictive transducers are often loaded with a large static force and then operated in a range about that point, like air but in solid materials.
Because the “spring force” between molecules is temperature dependent, one finds C is temperature dependent. This was demonstrated to me in a vivid way when I was trying to inject high intensity sound from a levitation source into a furnace through a large temperature gradient. If I recall, at about 1100 degrees C the speed of sound has doubled at 1500C it is very hard to do without having some of the radiator showing (not good), inside is a very radiant heat source.
Anyway, even under normal temperatures one can see the effect of compressibility by examining a high intensity sound wave. The pressure side of the wave has a slightly higher temperature and the low pressure side a lower temp so after some distance, the wave shape precesses into a saw tooth. This was a real problem with those 160dB acoustic levitators and is the main “non-linear” thing in air “throat distortion”.
Another part that wouldn’t be clear with an “incompressible” view is what radiation resistance looks like to the radiator.
Radiated pressure is “in phase” with and proportional to source volume velocity, many people think the maximum radiated pressure is when the cone or radiator is at its farthest excursion point where in reality, velocity is highest as it pass through its rest point.
Anyway, a few thoughts on the mechanical part.
Best,
Tom Danley
Tom
I found the whole claim to be so incorrect that I almost didn't respond. That sound is a "compressional" wave is fundamental. How could there be a "compressional" wave in an incompressible fluid?
Could you E-mail me at egeddes@gedlee.com so we could talk. I don't want to ask for your E-mail on line (I don't know how private you are) but mine is open to all. So E-mail me and I'll write you back. (I can't place your E-mail address.)
Thanks.
I found the whole claim to be so incorrect that I almost didn't respond. That sound is a "compressional" wave is fundamental. How could there be a "compressional" wave in an incompressible fluid?
Could you E-mail me at egeddes@gedlee.com so we could talk. I don't want to ask for your E-mail on line (I don't know how private you are) but mine is open to all. So E-mail me and I'll write you back. (I can't place your E-mail address.)
Thanks.
Tom Danley has been generous with his time and knowledge to DIYers and always acted the gentleman at AA.
For what it's worth I never heard better speakers than his Unitys, especially the last phase corrected version Kurt Chang and I heard at Tom's house. Yeah, I've heard things as good but never better. I'm talking hi-fi use.
For what it's worth I never heard better speakers than his Unitys, especially the last phase corrected version Kurt Chang and I heard at Tom's house. Yeah, I've heard things as good but never better. I'm talking hi-fi use.
Re: A simple question
Hi Dave,
First of all, I didn't insist that air is incompressible. I said the air in direct contact with the drivers cone will behave like an incompressible fluid. Think about it - air is obviously compressible, and offers little resistance to this at low velocity. When something is moving very fast, it is encountering significant resistance from the air directly in it's path. The faster the object goes, the more solid the air appears to be. Apply that to a rapidly vibrating diaphragm
Your analogy of the double sealed box doesn't prove anything and really has nothing to do with what I'm trying to say. The air inside of the box will be carry the sound wave, sound will escape. Enough said on that.
How does sound go through steel? It is not very compressible at all. Sound is the result of vibration. When something vibrates, it produces sound. Sound strikes objects and they, in turn, vibrate - transmission of the sound waves through a solid medium.
dlr said:
Hi Dave,
First of all, I didn't insist that air is incompressible. I said the air in direct contact with the drivers cone will behave like an incompressible fluid. Think about it - air is obviously compressible, and offers little resistance to this at low velocity. When something is moving very fast, it is encountering significant resistance from the air directly in it's path. The faster the object goes, the more solid the air appears to be. Apply that to a rapidly vibrating diaphragm
Your analogy of the double sealed box doesn't prove anything and really has nothing to do with what I'm trying to say. The air inside of the box will be carry the sound wave, sound will escape. Enough said on that.
How does sound go through steel? It is not very compressible at all. Sound is the result of vibration. When something vibrates, it produces sound. Sound strikes objects and they, in turn, vibrate - transmission of the sound waves through a solid medium.
amiklos said:
In elementary school science class, we did a little experiment. The instructor filled a small glass bottle with water to the top and capped it. He was very particular about how it should have no air bubbles inside. He then used that bottle to drive nails into a piece of wood, without breaking the bottle.
The point? To demonstrate the near perfect incompressibility of pure water.
If the mechanical force it takes to drive nails and the resulting sound it produces (a rather loud banging, hammering sound) were not enough to compress the water, how will sound do this on it's own?
I think your example shows that water is not easily compressible. Many materials are suitable for driving nails, but this does not mean they are all perfectly incompressible.
Your use of the phrase "near perfect" in describing water's incompressibility acknowledges the message I was trying to convey. Water is compressed by normal pressures, it just compresses by a very small amount, not enough to allow the bottle to deform appreciably in your school example.
I apologize for the off topic digression.
Your use of the phrase "near perfect" in describing water's incompressibility acknowledges the message I was trying to convey. Water is compressed by normal pressures, it just compresses by a very small amount, not enough to allow the bottle to deform appreciably in your school example.
I apologize for the off topic digression.
What I was pointing out is that the fluid dynamics concepts of stream and potential functions normally used as a description of the flow of incompressible fluids, can be usefully applied as an aid to understanding what is going on in horns withought invoking the difficulties of solutions to the wave equation, not debating whether air can be compressed or not.
Descriptions such as this are common because the wave equation cannot be solved analytically in most cases we are considering, and number crunching solutions tend to obscure rather than inform unless accompanied by extensive graphical data as is given by boundary and finite element methods.
Obscuration is of course what some people desire because it allows them to claim esoteric understandings that are beyond the ken of mere mortals.
A friend of mine once observed that in his experience those who would be put on pedestals would be put there so they can urinate on others from a greater height.
I leave it to the reader to decide for them self if any of these last two observations are relevant to any trend they might of noticed in this thread.
This is my last word on these matters in this thread.
rcw
Descriptions such as this are common because the wave equation cannot be solved analytically in most cases we are considering, and number crunching solutions tend to obscure rather than inform unless accompanied by extensive graphical data as is given by boundary and finite element methods.
Obscuration is of course what some people desire because it allows them to claim esoteric understandings that are beyond the ken of mere mortals.
A friend of mine once observed that in his experience those who would be put on pedestals would be put there so they can urinate on others from a greater height.
I leave it to the reader to decide for them self if any of these last two observations are relevant to any trend they might of noticed in this thread.
This is my last word on these matters in this thread.
rcw
Lets put this off-topic topic to rest. The comment on air (and water) being incompressible is incorrect, lets move on.
rcw said:
(post altered by mod as requested)
And just for the record, fluid dynamics using potential functions IS NOT acoustics and it is this approach which is an "obscuration" of the reality. However, the solution that I use for the OS waveguide, HOM and all, IS an exact solution to the wave equation. Thats the point, which you seemed to be missing all along.
gedlee said:
Or what? You'll have us banned too?
You put things to rest by not engaging in or making a closing rebuttal pertaining to the offending topic.
Oh, but of course you know this, as you quite clearly know all.
This thread is a grandstand for you and your ill informed followers. Opposing views are not welcome here.
You either need a few letters after your name or bow down to your superior knowledge to be tolerated here.
Would you guys please return to topic? I am getting tired of jumping in here and asking nicely. Any further transgressions will be met with bin time. And, for any of you who think we take sides here, think again, we will not hesitate to bin any member who crosses the line.
In other words keep it civil or you'll be doing time in the penalty box.
Understood?
Thank you.
This is most definitely on topic:
I am interested in what rcw has to say about using a dome tweeter as the source rather than a compression driver. I think that some others would like to hear what he has to say also, but his posts here have all been on the defensive. He has been roundly brow-beaten and belittled, his opinions and references dismissed as so much garbage. None of this in a civil manner.
There is no room in this thread for a reasonable discussion of a method that is not being endorsed and marketed by the good doctor?
Maybe the best thing to do is to start a new thread where one can discuss the validity of different approaches without being slammed.
Scattering:
Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass.
I am interested in what rcw has to say about using a dome tweeter as the source rather than a compression driver. I think that some others would like to hear what he has to say also, but his posts here have all been on the defensive. He has been roundly brow-beaten and belittled, his opinions and references dismissed as so much garbage. None of this in a civil manner.
There is no room in this thread for a reasonable discussion of a method that is not being endorsed and marketed by the good doctor?
Maybe the best thing to do is to start a new thread where one can discuss the validity of different approaches without being slammed.
Scattering:
Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass.