Me too. 🙂
However, please note that the fact that a jet engine produces both sound and airflow is beside the point.
Just because we're just talking about sound here.
Otherwise only things that produce a flow of air should also produce a sound.
But we know that this is not the case.
On the other hand, we also know (or should know) for a fact that a sound does not produce any flow of air at all. 😉
But that's not the issue.
I thought
a) we need a medium, classic objects. They don't have to move in the displacement of woofers, for example, but, as you also linked, they only have to "hit" each other - called in sufficient precision.
b) It was about whether or not frequent pressure can also be understood as "sound", i.e. can be perceived by the ear, and
c) we have explained both wave and pressure as "sound", transmissible.
First and foremost, I was interested in mediating between various rigid assertions.
I give up on you again.
Sorry if I wasn't even able to follow your reasoning or read everything you wrote...
Sorry if I wasn't even able to follow your reasoning or read everything you wrote...
Another example are the lunar craters: often hexagonal, strictly symmetrical, flat, pippus in the center, stepped craters: electrical discharges.
Or Mars, Valles Marineris: a sigmoid, a discharge even more powerful than our Grand Canyon;-)
Electric universe;-)
Attachments
To come back to your hair or candle experiment:
A 16 Hz frequency required a membrane circumference of 20 meters (?) in order to be emitted without bending, diffraction. The surface to be excited would have to be correspondingly large in order to be moved with the same amplitude. We would have to do a lot of experiments to see when and how which things react and how.
A 16 Hz frequency required a membrane circumference of 20 meters (?) in order to be emitted without bending, diffraction. The surface to be excited would have to be correspondingly large in order to be moved with the same amplitude. We would have to do a lot of experiments to see when and how which things react and how.
Since we are talking about pressure here: for example, kettledrums (closed) put the room under negative pressure with the first hit, not positive pressure. The membrane of a loudspeaker that reproduces this first negative excursion is on the inside. In many recordings of open bass drums, it is not at all clear on which side the microphone was positioned. It is often placed in the drum - perhaps it should be written on every cover how the microphones were positioned, how the deflections of the drum diaphragms were recorded;-)
@ulogon I can confirm that if you use a candle flame to attempt to observe low frequency sound from a loudspeaker or a reflex vent and the sound is of sufficiently high amplitude, the candle flame can be observed to move back and forth. A difficulty here is that the eye has “persistence of vision” such that higher frequencies cannot be observed with the naked eye. (A strongly plucked guitar string appears to “blur” in front of your eyes, however that is just a property of our vision and the guitar string is in fact just as solid and well defined as it was before it was plucked. ) Similarly, higher frequencies tend to result in lower cone excursion, so there is less movement to observe.
This experiment was performed over 40 years ago when my brother and I were testing a bass reflex disco speaker we had built and wanted to confirm that the port output was indeed in phase with the front of the speaker cone and that we hadn’t messed up the calculations.
The air clearly moves, but this is a very constrained local movement about a central point. There is no long range “flow” - that is the candle flames was NOT launched across the room at 330m/s and therefore didn’t set fire to the sofa on the other side of the room!
(At that sound pressure the sofa did of course vibrate somewhat!)
A more recent observation about the short range air motion was at an Eels gig in Dublin a few years ago. This was an outdoor concert and the bass speakers were on a gantry that was loosely enclosed in a tarpaulin that had band logos etc on. You could clearly see that this evidently heavy tarpaulin would pulse visibly with each kick drum strike by the drummer.
I think that in this context it is helpful not to think about individual air molecules but that the collection of 100s of thousands of air molecules being stimulated in the same way at the same time.
If we consider that when a large speaker undergoes cone movement, since the cone is not permeable to air, the air molecules coincident to the cone must necessarily move with the cone causing local pressurization of the surrounding air. When the cone reverses, the compression is released and the air will become rarified as the cone completes the cycle. Due to ambient air pressure there is never a complete vacuum.
I use the example of a large speaker just for easy visualization.
I hope what I have written makes sense and correctly aligns with modern science in all regards and is more enlightening than confusing. 🙂
Jeff
This experiment was performed over 40 years ago when my brother and I were testing a bass reflex disco speaker we had built and wanted to confirm that the port output was indeed in phase with the front of the speaker cone and that we hadn’t messed up the calculations.
The air clearly moves, but this is a very constrained local movement about a central point. There is no long range “flow” - that is the candle flames was NOT launched across the room at 330m/s and therefore didn’t set fire to the sofa on the other side of the room!
(At that sound pressure the sofa did of course vibrate somewhat!)
A more recent observation about the short range air motion was at an Eels gig in Dublin a few years ago. This was an outdoor concert and the bass speakers were on a gantry that was loosely enclosed in a tarpaulin that had band logos etc on. You could clearly see that this evidently heavy tarpaulin would pulse visibly with each kick drum strike by the drummer.
I think that in this context it is helpful not to think about individual air molecules but that the collection of 100s of thousands of air molecules being stimulated in the same way at the same time.
If we consider that when a large speaker undergoes cone movement, since the cone is not permeable to air, the air molecules coincident to the cone must necessarily move with the cone causing local pressurization of the surrounding air. When the cone reverses, the compression is released and the air will become rarified as the cone completes the cycle. Due to ambient air pressure there is never a complete vacuum.
I use the example of a large speaker just for easy visualization.
I hope what I have written makes sense and correctly aligns with modern science in all regards and is more enlightening than confusing. 🙂
Jeff
Sorry, but please note that wasn't the addressed experiment. 🙂
Dear Jeff,
Just yesterday I read (and appreciated) your comments on a thread where you talked about class B amplifiers.
I was very fascinated by those talks, even if my lack of specific knowledge did not allow me to fully understand them.
However, please note that the topic here is not to demonstrate the air flowing through a bass-refex speaker port because this fact is already granted.
The tuning of a bass-reflex port (I believe) is done on purpose to make air flow at a certain pressure in order to vary the characteristics of the woofer (I'm not a technician nor an expert in electro-acoustics and therefore please forgive any possible descriptive errors, but I'm sure the substance is still correct), but it has nothing to do with the sound propagation.
So, the fact that a certain flow of air exits and enters from a port of a bass reflex is not in question.
The experiment is actually another, and that's to demonstrate that the sound propagation does not produce an air flow.
As a matter of fact, if you place a thin and light strip of paper (or a hair, the flame of a candle, or anything else of that kind) in front of the diaphragm of a driver (let's say of a woofer, because the movement of the diaphragm is easily visible) when that driver is operating then that strip of paper will not move at any power we make that woofer play.
So, let's please leave out the bass-reflex because it is misleading and refer to a sealed speaker in pneumatic suspension.
Please redo the experiment and kindly report your results here. 🙂
Not to influence the outcome of your own experiment, but it has already been done and the result was exactly what was expected, of course.
Please note that I say "of course" just because this "theory" is not mine (of course), but it is a scientific fact that I only have reported. 😉
https://www.scienceworld.ca/resource/sound-vibration-vibration-vibration/
"When sound waves move through the air, each air molecule vibrates back and forth, hitting the air molecule next to it, which then also vibrates back and forth. The individual air molecules do not "travel" with the wave. They just vibrate back and forth".
Aside:
Once I saw a video, a recording of an Apollo mission: it shows an atronaut hitting something on the moon with a hammer. This hammer hit was audible - but not as a low-frequency vague vibration that was somehow transmitted to the microphone by the hitting body, but as a "high-frequency" sound;-)
Once I saw a video, a recording of an Apollo mission: it shows an atronaut hitting something on the moon with a hammer. This hammer hit was audible - but not as a low-frequency vague vibration that was somehow transmitted to the microphone by the hitting body, but as a "high-frequency" sound;-)
I do have a 12” driver lying around and I’m sure I can find a candle in the house somewhere, however I don’t have a sealed cabinet for that. My main speakers are 5 1/4” and I’d be concerned about flame proximity. 😟
However in the interest of science let me try to repeat the experiment with a sealed box this might not be very soon, but you have piqued my curiosity 😀.
I do however completely agree that the air molecules most definitely do not travel with the wave otherwise I would have sent a fireball across the room with my candle experiment and ignited the sofa.
In the case of a reflex cabinet there is some air flow below resonance, and it is this that causes rapid roll off below resonance, however above resonance there isn’t and we just see a identical wave being emitted from the port that is in phase with the speaker, so in a controlled experiment I believe the experiment is still valid. However I may be proved incorrect!
I’m glad you enjoyed the class B amp chats. I think most members aligned more with Cordell than with Self’s definition of Class B but I like Self’s definition as it is very much suited to audio.
I’ll probably stay quiet on this thread for a while until I have something definitive to say to either backup my assertions or to “eat humble pie” as they say!
(In case anyone is relying on translation software, to “eat humble pie” is to admit that you were incorrect, usually a humbling experience. If I get to eat humble pie this time it won’t be the first time and is unlikely to be the last! Fortunately members here are generally very kind in telling you how wrong you are 😀. )
However in the interest of science let me try to repeat the experiment with a sealed box this might not be very soon, but you have piqued my curiosity 😀.
I do however completely agree that the air molecules most definitely do not travel with the wave otherwise I would have sent a fireball across the room with my candle experiment and ignited the sofa.
In the case of a reflex cabinet there is some air flow below resonance, and it is this that causes rapid roll off below resonance, however above resonance there isn’t and we just see a identical wave being emitted from the port that is in phase with the speaker, so in a controlled experiment I believe the experiment is still valid. However I may be proved incorrect!
I’m glad you enjoyed the class B amp chats. I think most members aligned more with Cordell than with Self’s definition of Class B but I like Self’s definition as it is very much suited to audio.
I’ll probably stay quiet on this thread for a while until I have something definitive to say to either backup my assertions or to “eat humble pie” as they say!
(In case anyone is relying on translation software, to “eat humble pie” is to admit that you were incorrect, usually a humbling experience. If I get to eat humble pie this time it won’t be the first time and is unlikely to be the last! Fortunately members here are generally very kind in telling you how wrong you are 😀. )
Jeff, thank you very much for your very appreciated comment. 🙂
Why some (not you) are so skeptical? I really don't realize that!
Appreciated explanation that enriches my limited English idiomatic phrases number...
Please note that "the flame of a candle" was just a further extreme example due to some hair-splitting from a a few members regarding the choice of a hair rather than a thin paper strip: the really important thing is that the material is light enough to convince even the most skeptical.
Why some (not you) are so skeptical? I really don't realize that!
👍
Exactly.
I think so, but please note that I'm the exact opposite of an authority on the operating class definitions of audio amplifiers... 😛
I'm sure it won't be necessary to resort to that much at all! 😉
Thank you very much!
Appreciated explanation that enriches my limited English idiomatic phrases number...
cumbb,
You might be interested in this mistake that is in some music recordings:
The beginning of the vibrating air at the bell opening of a trombone is the molecules vibrating away from the bell opening.
As seen on an oscilloscope, this shows up as a positive going start of the impulse.
I have seen a few recordings of a trombone, when displayed on an oscilloscope, the beginning vibration impulse is negative (upside down).
It is not due to any special trombone.
Instead, a microphone was wired out of phase, a preamp out versus in is phase inverted, sound boards that invert the signal, and all the process from the recording to the playback (CD or phono cartridge), etc.
This is far different than the case where a microphone is placed on one side or the other side of a drum head.
You might be interested in this mistake that is in some music recordings:
The beginning of the vibrating air at the bell opening of a trombone is the molecules vibrating away from the bell opening.
As seen on an oscilloscope, this shows up as a positive going start of the impulse.
I have seen a few recordings of a trombone, when displayed on an oscilloscope, the beginning vibration impulse is negative (upside down).
It is not due to any special trombone.
Instead, a microphone was wired out of phase, a preamp out versus in is phase inverted, sound boards that invert the signal, and all the process from the recording to the playback (CD or phono cartridge), etc.
This is far different than the case where a microphone is placed on one side or the other side of a drum head.
I think it can also just be a misunderstanding that when one person gives an explanation for information transfer, others implicitly excludes, or does not understand. It should not be understood that way - again and again;-)
Another story about "sound": once an old motorcycle with one or two cylinders passed me and I almost collapsed because of the pulsed pressure. The intake and exhaust were obviously perfectly matched to each other;-)
In general, I also recommend long funnel-shaped horns for intake and exhaust to optimize acceleration and compression. Short "sports filters", for example, are not ideal for adapting to the "radiation pressure" of the air;-)
In general, I also recommend long funnel-shaped horns for intake and exhaust to optimize acceleration and compression. Short "sports filters", for example, are not ideal for adapting to the "radiation pressure" of the air;-)
In 1965, Wide World of Sports televised the racing boats trip down the Rogue River from Grants Pass, OR, to Galice OR, and back again.
All the outboard motors had one thing in common . . . 4 tapered conical horns direct from the exhaust ports of the engine, all tuned to the fundamental frequency when the motor was at max rpm.
Gets rid of all the hot exhaust, and destroys ears all at the same time.
All the outboard motors had one thing in common . . . 4 tapered conical horns direct from the exhaust ports of the engine, all tuned to the fundamental frequency when the motor was at max rpm.
Gets rid of all the hot exhaust, and destroys ears all at the same time.
Ok, so in the interest of science I have repeated my experiment of about 45 years ago, only this time using a sealed 4 litre cabinet with a Monacor 5 1/4” driver and holding a small flame from a barbeque lighter a small distance from central axis of the cone.
My speakers are 3 way and bass EQ is by Linkwitz Transform to 40Hz crossed at 300Hz. There is no shortage of cone excursion when playing music with significant bass content. (These have high excursion limits for such small drivers, one of the reasons I chose them. )
So enough teasing, what does happen?
I played “Gold Dust Woman” sung by Stevie Nicks from the Studio Master edition of Rumours. At a fairly loud level the bass drivers can be seen moving back and forth on Mick Fleetwood’s Kick drum beats. I moved the flame in front of the bass unit about 5cm away from the centre of the cone and could clearly see the flame oscillate back and forth in concert with the kick drum. If I moved it closer than that, the flame was extinguished. The closer the flame is to the speaker the greater the perturbation of the flame.
Based on my findings as a teenager I am unsurprised at this result.
I have no doubt that the same result would be observed with a steady tone, but I’d have to test quickly to prevent burning the voice coil.
Please let me know your thoughts.
My speakers are 3 way and bass EQ is by Linkwitz Transform to 40Hz crossed at 300Hz. There is no shortage of cone excursion when playing music with significant bass content. (These have high excursion limits for such small drivers, one of the reasons I chose them. )
So enough teasing, what does happen?
I played “Gold Dust Woman” sung by Stevie Nicks from the Studio Master edition of Rumours. At a fairly loud level the bass drivers can be seen moving back and forth on Mick Fleetwood’s Kick drum beats. I moved the flame in front of the bass unit about 5cm away from the centre of the cone and could clearly see the flame oscillate back and forth in concert with the kick drum. If I moved it closer than that, the flame was extinguished. The closer the flame is to the speaker the greater the perturbation of the flame.
Based on my findings as a teenager I am unsurprised at this result.
I have no doubt that the same result would be observed with a steady tone, but I’d have to test quickly to prevent burning the voice coil.
Please let me know your thoughts.