semantics
Looks like a semantic misunderstanding here. In my mind, sound travels through a medium primarily by compressional waves, wherein, through a unit area, the position of molecules (or atoms) on that surface, relative to their position when no wave is passing, moves closer to the next unit area in the direction of travel during the pressure part of the waveform, and further away from that unit area during the rarefaction part of the waveform. This is the same as compressing the medium during the pressure portion of the waveform and expanding the medium during the rarefaction portion of the waveform, for a unit area, independant of the state of the medium. hence the term compressional waves. The increased (+) pressure in the direction of propagation is a compression relative to initial position, and the decreased (-) pressure in the second half cycle is a local expansion relative to the initial position.
As an example, if sound did not compress liquids, ultrasonic cleaners would not impart any energy into a liquid, and that liquid would not heat up (which it does).
Sorry for the wordy explanation, hope it helps...
I'm trying to get a handle on the waves "leaving the surface of the waveguide"? What does that mean? Seems to me a wave impinging on an interface between solid wall and gas would cause only a reflection and/or partial absorption of that portion of energy transferred across (and into) the interface. Perhaps what occurs with Earl's waveguide is better control of where those reflections continuously produced as a wave traverses the guide go, and how those reflections deemed undesirable are dissipated w/o causing distortion of the original wavefront.
have I got this right?
John L.
Looks like a semantic misunderstanding here. In my mind, sound travels through a medium primarily by compressional waves, wherein, through a unit area, the position of molecules (or atoms) on that surface, relative to their position when no wave is passing, moves closer to the next unit area in the direction of travel during the pressure part of the waveform, and further away from that unit area during the rarefaction part of the waveform. This is the same as compressing the medium during the pressure portion of the waveform and expanding the medium during the rarefaction portion of the waveform, for a unit area, independant of the state of the medium. hence the term compressional waves. The increased (+) pressure in the direction of propagation is a compression relative to initial position, and the decreased (-) pressure in the second half cycle is a local expansion relative to the initial position.
As an example, if sound did not compress liquids, ultrasonic cleaners would not impart any energy into a liquid, and that liquid would not heat up (which it does).
Sorry for the wordy explanation, hope it helps...
I'm trying to get a handle on the waves "leaving the surface of the waveguide"? What does that mean? Seems to me a wave impinging on an interface between solid wall and gas would cause only a reflection and/or partial absorption of that portion of energy transferred across (and into) the interface. Perhaps what occurs with Earl's waveguide is better control of where those reflections continuously produced as a wave traverses the guide go, and how those reflections deemed undesirable are dissipated w/o causing distortion of the original wavefront.
have I got this right?
John L.
In post#5, Dr. Geddes states an equation, but also addresses how compression drivers with large throat drops in frequency response. I think what is additionally important is that if the throat size is large, there will be difficulty diffracting the high frequencies, thus resulting in a narrower beam. Additionally, he addresses that the low end of the driver response is limited by the driver. I think that this low end response should be due to the limited excursion of the driver, and it would be interesting to see how low the frequency can be extended without losing high frequency and power capability.
winslow said:
Bryce H. said:
I have been swamped here with building speaker kits. Until such time as I get caught up with that, waveguides for cars just isn't going to come to the surface. I'll keep it in mind as I scrong arround to see if I can find the mold. Better would be to just buy the mold off of me. That would interest me. I'd need to get at least $500 for it as that what it cost me.
The minimum crossover point would depend on the driver. With a DE500 it would be about 800 Hz, but 1 kHz. would be better.
Re: semantics
This was one of those comments that came from a misguided view of how acoustics works. It doesn't happen. What does happen is that the waves diffract around the bend, rather than "leave the surface" which is not possible. The diffracted wave now has a new "life of its own" and travels not along with the primary wave, but independent of it and it in fact is moving slower along the axis, so it arrives at the listener latter in time. These are the HOM and they are very audible. I can prove that an OS waveguide will have the minimum of these of any contour - a good thing right?
auplater said:
This was one of those comments that came from a misguided view of how acoustics works. It doesn't happen. What does happen is that the waves diffract around the bend, rather than "leave the surface" which is not possible. The diffracted wave now has a new "life of its own" and travels not along with the primary wave, but independent of it and it in fact is moving slower along the axis, so it arrives at the listener latter in time. These are the HOM and they are very audible. I can prove that an OS waveguide will have the minimum of these of any contour - a good thing right?
Water can have two types of waves, and these are being confused. Waves on the surface are shear waves and exist because of the imbalanced interface between the densities of air and water. These waves are critical to boat design etc. These waves also move very slowly - which is why we can see them, because the restoring force is simply gravity (a very weak force).
Sound waves under water are compressional waves, just like in air, and move very fast, because water is very stiff (the forces are molecular, or nuclear and very large).
Sound waves under water are compressional waves, just like in air, and move very fast, because water is very stiff (the forces are molecular, or nuclear and very large).
Move slower?
Dave
This I find curious. I would expect diffracted waves to take a different path hence arrive at different (later) times due to different path lengths from the primary wave, but I would not expect them to actually move slower, unless by "move slower" you mean arrive at a later time due to a path length difference.
Dave
soongsc said:
Sorry once again, thats not what is happening. As the throat gets smaller the HOMs move higher in frequency and at the point where the throat is a point, there are no HOM, but there is also no source that can drive a point. Thats why I use smaller aperature drivers.
An Elliptical waveguide does not reduce the HOM, but it would reduce the axial hole seen as a result of a circular mouth.
Re: Move slower?
YES - I said that they move slower AXIALY, but they still propagate at the speed of sound. It is the greater path length difference that causes the delay.
Its my training to think of what is called the "trace velocity" which is the velocity of proagation along a certain line. For example when sound strikes a surface at an angle it is the trace velocity along the surface that determines its interaction with the surface.
In a waveguide each HOM has a slower and slower "trace velocity" but they all have the same wave velocity.
dlr said:
YES - I said that they move slower AXIALY, but they still propagate at the speed of sound. It is the greater path length difference that causes the delay.
Its my training to think of what is called the "trace velocity" which is the velocity of proagation along a certain line. For example when sound strikes a surface at an angle it is the trace velocity along the surface that determines its interaction with the surface.
In a waveguide each HOM has a slower and slower "trace velocity" but they all have the same wave velocity.
Probably a more correct way of putting it would be transition from the throat to the guide is the source of the strongest HOM. Elliptical OS wave guide will spread the HOM energy over a wider frequency range so that it does not seem audibly as significant as HOMs concentrated at certain frequencies.
I think I have some designing to do.
It seems that actual design process is going to be easier than I thought.
I think I have some designing to do.
It seems that actual design process is going to be easier than I thought.
The problem is, of course, that if you don't understand the principles you are not likely to build the right thing. This is why I have, to date, been the only one (that I know of) who has built a truly effective device (as the reviewers will testify to). I am trying to educate you on these principles, but if you reject them off-hand then you are off to a bad start.
Well, I've heard this ever since I started respoking my bike wheels. I guess people have different ways of learning things. The same happened when I was trying to figure our how to improve CSD of drivers and reducing effects of breakup modes.
Just a few days ago, my car stopped running due to the flooded roads and rain here, sent it to the mechanic, and they said they expect some broken linkages in the engine like another car that was in there. Since the car seemed like it might start but couldn't, I authorized them to open up the engine to have a look. Nothing was broken as I predicted. Sure they were embarrissed. My position is get the car running, and then talk about responsibility of cost.
Basically, I look at the results and determine what is right or wrong and improve from there. I will assume responsibility for being wrong. I'm sure it would be unfair to ask you to assume responsibility if you were wrong and my desired goals could not be accomplished.
Just a few days ago, my car stopped running due to the flooded roads and rain here, sent it to the mechanic, and they said they expect some broken linkages in the engine like another car that was in there. Since the car seemed like it might start but couldn't, I authorized them to open up the engine to have a look. Nothing was broken as I predicted. Sure they were embarrissed. My position is get the car running, and then talk about responsibility of cost.
Basically, I look at the results and determine what is right or wrong and improve from there. I will assume responsibility for being wrong. I'm sure it would be unfair to ask you to assume responsibility if you were wrong and my desired goals could not be accomplished.
gedlee said:
Hi Earl,
I was traveling much of last week and never did get to respond to this post. In no way did I say I didn't want to hear your system, but I generally don't invite myself into someone's home, as I leave that to them. Some listening and chatting would be a welcome break next time I'm in the area.
