@chdsl
The second sentence states
“As an object vibrates, it sets the surrounding air in motion, sending alternating waves of compression and rarefaction radiating outward from the object.”
Where it states ‘setting the surrounding air in motion ‘ it is describing the pulse of sound travelling through the medium, the compression and rarefaction event. It is not referencing ‘wind’ or physical movement of the air. You described this phenomena yourself referencing other media like steel. I am not sure why you find this sentence wrong but as always I am happy to learn.
Burnt
The second sentence states
“As an object vibrates, it sets the surrounding air in motion, sending alternating waves of compression and rarefaction radiating outward from the object.”
Where it states ‘setting the surrounding air in motion ‘ it is describing the pulse of sound travelling through the medium, the compression and rarefaction event. It is not referencing ‘wind’ or physical movement of the air. You described this phenomena yourself referencing other media like steel. I am not sure why you find this sentence wrong but as always I am happy to learn.
Burnt
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I just received the Dayton exiters. feel much more solid than I thought.
We have some unwanted guests in the attic. You can hear them right behind the hardwood wall. so I want to try to expel the little mice with high frequencies in the 13 to 15 khz range. I tagged one of the exiters onto the hdf panel.
I am really amazed!
there is fine fullrange sound. Judged just by ear there is only a little eq needed for really flat sound. the 35 hz sine signal is full and solid. 30 hz is also there.
I don‘t know about the hf as my hearing ends at 14khz. would have to do some measurements to erruate this. hope it is good enough for the mice.
the side panels are about 3mm thick hardwood of about 8ft length.
This is only one exciter, so only mono. but for backgound music or audiobooks this would be perfect as it is.
I am thinking about using this also as a subwoofer for tv sound.
really invisible speakers in this case.
We have some unwanted guests in the attic. You can hear them right behind the hardwood wall. so I want to try to expel the little mice with high frequencies in the 13 to 15 khz range. I tagged one of the exiters onto the hdf panel.
I am really amazed!
there is fine fullrange sound. Judged just by ear there is only a little eq needed for really flat sound. the 35 hz sine signal is full and solid. 30 hz is also there.
I don‘t know about the hf as my hearing ends at 14khz. would have to do some measurements to erruate this. hope it is good enough for the mice.
the side panels are about 3mm thick hardwood of about 8ft length.
This is only one exciter, so only mono. but for backgound music or audiobooks this would be perfect as it is.
I am thinking about using this also as a subwoofer for tv sound.
really invisible speakers in this case.
Attachments
It doesn't set the surrounding air in motion.
The road is ~300m away from my flat at an angle. The wall in front of me is 61cm thick. There's 3 story housing building 12m wide, situated 15m away from my block completely blocking my flat. There are few old tall trees between that block and the road, and also two 2 story buildings. A few minutes ago, I heard an ambulance going to my right on that road. That road goes away from my flat. I can't see the road from where I am.
None of the buildings, or trees can hear. Most probably, the sound came to my ears, through the window. There's nothing to reflect the sound on my right, where the window is, only tall trees. And, trees usually block sound than reflect.
Sound doesn't bend and go around buildings or trees. All it can do is reflect. Some of which will be absorbed. It is winter, so not much leaves on the trees. Otherwise, I might've not heard the ambulance. Of course, it is a high pitched noise, but not that high pitched to annoy people.
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The sound pulse, the compression and rarefaction of the air, travels through the air the same way it travels through any medium. In an urban environment sounds reflects from surfaces and where the object is smaller than the wavelength diffracts around the object. In this sense sound waves can and do go around corners. That pulse eventual ends up moving the structures in your ear which converts the pulse to electrochemical signals. This is all well researched and understood and has been for years. At no point did anybody I am aware of suggest that inanimate objects can hear. That is a bizarre notion
Burnt
Burnt
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That's what I see too, Steve.
chdsl.
But regardless of whether or not the cone is touching the glass, I don't understand the point you are trying to demonstrate with this example.
Eric
chdsl,
I fail to understand how this example demonstrates that "it doesn't set the air in motion".
Certainly you are correct that vibrating structures don't create "wind". But they absolutely do set the air in motion, and that's pretty much the only way the sounds that we hear are generated.
Here is a great animation of the effect.
https://www.acs.psu.edu/drussell/Demos/EvanescentWaves/EvanescentWaves.html
Scroll to the bottom part of the page where there are six different examples. In each, a flexing plate (represented by the dark line at the bottom), sets in motion the air above it, represented by the array of moving dots.
Eric
chdsl,
Yes, I absolutely agree that the exciter itself has pistonic motion. But that doesn't mean that the panel to which it is attached is also moving pistonically.
When we speak of "bending waves" in the context of flat panel speakers, we don't mean that any waves are being bent. Rather we mean that the sound waves in the air are caused by bending waves (also know as flexural waves) of the panel.
The animation in this link shows very well what we mean by bending waves. In addition, it gives an excellent description of the difference between pistonic speakers and dml/bending wave/flat panel speakers.
Eric
https://tectonicproaudio.com/about-the-technology/
Sound is energy expended on and transmitted by a medium. No energy no sound. No transmission medium no sound. In all media the energy is transmitted by the local movement of the atoms and molecules that make up the media.
Burnt
Sure, we see the polystyrene sheet jumping about when connected to the exciter, actually 2 exciters, but what happens, when the heavy 6mm glass panel placed over it? (2nd image here) Was there any waves "bending' the glass panel surface to pass those waves to air? That 6mm thick glass panel was ~4kg.
Energy cannot be expended. It is just transferred from one form to another, doing work in the process.
Yes there are waves. Just as, in your previous example, there were waves travelling along the steel rail you referenced. No, you can’t see them, but you can hear them. The movement you see in PS foam is displacement and therefore pistonic ( depending on the mounting arrangement) and the panel is also in DML mode. You can watch a conventional bass driver moving ( pistonic mode) but you can’t see the higher frequencies it reproduces because they are in DML mode. There was a whole thread on this where a big cheap paper woofer was tested in a batch of expensive mid range drivers just for fun and the woofer did very well despite being operated well into cone breakup. Cone break up is DML mode.
Burnt.
I said expended on, I did not say lost. I can expend energy on anything and it will be diffused through the medium until, ultimately, it is transformed to heat and, in this highly entropic form, can do no further work.
chdsl,
Again, it's not waves that bend the glass (or PS panels). It's that the pistonic motion of the exciter, in combination with the mechanical properties of the panel (i.e stiffness and density, etc) cause flexural waves (bending) in the panel. These flexural waves in the panel create pressure waves in the air adjacent to it.
In your example with the glass on top of the PS foam: Most probably, both the PS foam and the glass have flexural waves imparted to them by the action of the exciter. But I would bet that the bulk of the sound you heard was generating by the bending waves in the PS foam. PS foam radiates sound extremely effectively (much more so than glass). Sure, the glass inhibits the flexural vibration of the PS foam quite a bit, and the bending of the PS foam certainly causes some bending vibration of the glass, but most of the sound is still coming from the bending of the PS foam, I am fairly confident.
The glass plate in this post
https://www.diyaudio.com/community/...ll-range-speaker.272576/page-374#post-7198955
was 5.7 mm thick, and weighs 5.6 Kg. But the pattern of rice on the panel created prove that the panel was bending. I wish I had a movie! The rice that was originally in the center was jumping around like crazy when the exciter was running at 554 Hz, while the rice on other sections of the panel (where it eventually gathered) didn't move the tiniest bit.
Eric
Eric.
Nearly 6mm thick glass, no wonder the exciter died.
Heavy rigid panels take a lot of power to move them.
The 5mm thick, cement coated foam panel, similar to the one I took a photo of a few pages back ,was also hard to drive.
I got a phone call while listening to test tones .
When I came back the foam in the panel had melted away inside the exciter area 🤪
The exciter was still working but I think a few of the coil windings had shorted , it was never the same.
Steve.
Nearly 6mm thick glass, no wonder the exciter died.
Heavy rigid panels take a lot of power to move them.
The 5mm thick, cement coated foam panel, similar to the one I took a photo of a few pages back ,was also hard to drive.
I got a phone call while listening to test tones .
When I came back the foam in the panel had melted away inside the exciter area 🤪
The exciter was still working but I think a few of the coil windings had shorted , it was never the same.
Steve.
@Veleric
We've done that experiment few decades ago.
Speed of sound is a very much higher in glass than in air. Sound then travels through the rice, which too is higher than speed of sound in air. Glass, by the way, is a solid-like substance. Put the rice on the EPS sheet to check if the rice arranges itself the same way as on glass. Or, on an aluminium sheet of the same thickness.
When I put my hands on the EPS sheet, and then on the glass sheet, of course, I feel the vibrations, but if I put earplugs on, I don't hear any sound. It doesn't travel through my fingers, hands to the ear. By the way, ear can 'hear' sounds not only through the ear canal, but through a certain bone behind the ear. Usually laryngologists check your hearing that way sometimes.
Glass surface cannot bend in its solid-like state. To bend it, you'd have to turn it back a liquefied state. Glass can crack if there's too much sound, which happens when there's too much resonance.
We've done that experiment few decades ago.
Speed of sound is a very much higher in glass than in air. Sound then travels through the rice, which too is higher than speed of sound in air. Glass, by the way, is a solid-like substance. Put the rice on the EPS sheet to check if the rice arranges itself the same way as on glass. Or, on an aluminium sheet of the same thickness.
When I put my hands on the EPS sheet, and then on the glass sheet, of course, I feel the vibrations, but if I put earplugs on, I don't hear any sound. It doesn't travel through my fingers, hands to the ear. By the way, ear can 'hear' sounds not only through the ear canal, but through a certain bone behind the ear. Usually laryngologists check your hearing that way sometimes.
Glass surface cannot bend in its solid-like state. To bend it, you'd have to turn it back a liquefied state. Glass can crack if there's too much sound, which happens when there's too much resonance.
My excitors are 40W, 8 Ohm, pretty solidly made. But, if I ever make DMLs for the living room, I'd dismantle solid drivers to get at the 'actuator' part. There are lot of Japanese or Korean speakers available in secondhand market for very little money. The last pair was just 25EUR, 1 woofer, 2 mids and a tweeter in each speaker.
By the way, Morocco just won the quarterfinals, it'd be either England or France at 20:00.