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tommac
2008-Nov-03, 02:21 PM
Do sound waves bend from the gravitational pull of the earth? Does sound travelling upward travel slightly slower than sound travelling downward?

mugaliens
2008-Nov-03, 05:28 PM
Offhand, I'd say that sound waves travelling upward travel slower because the air above you is less dense than the air below you, and the speed of sound is proportional to the density of the medium through which it travels.

As for the gravity, I would say no,

tommac
2008-Nov-03, 06:05 PM
If gravity is warped space, it would need to effect a wave the same that it would effect a particle ( like the moon ).



Offhand, I'd say that sound waves travelling upward travel slower because the air above you is less dense than the air below you, and the speed of sound is proportional to the density of the medium through which it travels.

As for the gravity, I would say no,

astromark
2008-Nov-03, 06:19 PM
Sound transmission is not free from the effects of gravitational distortion. Sound is a transmission of a shock wave through a medium, ie; air. As noted, as air density lessons so to would sound transmission fall away. If the medium material was being distorted by a strong gravity well, then yes the transmission of sound through that would be effected. Sound is not a particle stream so would not be effected by gravity. But the mater it is being transmitted through is.

tommac
2008-Nov-03, 06:28 PM
Sound transmission is not free from the effects of gravitational distortion. Sound is a transmission of a shock wave through a medium, ie; air. As noted, as air density lessons so to would sound transmission fall away. If the medium material was being distorted by a strong gravity well, then yes the transmission of sound through that would be effected. Sound is not a particle stream so would not be effected by gravity. But the mater it is being transmitted through is.

Got it!!! thanks.

Hornblower
2008-Nov-03, 06:55 PM
Offhand, I'd say that sound waves travelling upward travel slower because the air above you is less dense than the air below you, and the speed of sound is proportional to the density of the medium through which it travels.
I think you are mistaken, at least to a first approximation. If the speed of sound were proportional to density and the temperature constant, then the pitch of my horn would change with changes in atmospheric pressure. My experience over a wide range of altitude is that there is no audible change. If there is any change as a result of departure of our air from an ideal gas, it is much smaller than a straight proportion.

BigDon
2008-Nov-03, 07:05 PM
Hey, as a sailor and later a boater I can say even the wind changes sound.

A stiff wind will blunt sound sound going against and extend it's range downwind by miles.

Most inland people don't realize how dependant their hearing is on reflected sound (not echos!) until you are somewhere there isn't anything to reflect it it off of.

If we were in the middle of the bay in a largish boat facing away from each other 20 feet apart in a 10mph wind I would hardly be able to shout loud enough to be heard, much less intelligible.

mugaliens
2008-Nov-03, 07:18 PM
But the mater it is being transmitted through is.

True. However, that matter (usually air, or water) has more or less reached isostasis.

cjl
2008-Nov-03, 09:50 PM
I think you are mistaken, at least to a first approximation. If the speed of sound were proportional to density and the temperature constant, then the pitch of my horn would change with changes in atmospheric pressure. My experience over a wide range of altitude is that there is no audible change. If there is any change as a result of departure of our air from an ideal gas, it is much smaller than a straight proportion.
Actually, the speed of sound in air is dependent on exactly one variable: temperature. All other variables are irrelevant. I'm not sure if this also applies to the speed of sound in liquids and solids though.

matt.o
2008-Nov-03, 10:22 PM
Sound transmission is not free from the effects of gravitational distortion. Sound is a transmission of a shock wave through a medium, ie; air. As noted, as air density lessons so to would sound transmission fall away. If the medium material was being distorted by a strong gravity well, then yes the transmission of sound through that would be effected. Sound is not a particle stream so would not be effected by gravity. But the mater it is being transmitted through is.

Sound is not the transmission of a shock wave - I think you mean a pressure wave. A shock wave or shock front occurs when a body is travelling through a medium at faster than the mediums sound speed.

astromark
2008-Nov-04, 08:59 AM
'matt.o ' Did you read my post? did you see the ' As noted ' No mater, I shall try again...
The human ear is equipped to detect the sudden changes in air pressure that are why we are able to detect the noise made by the compression of that medium that we might be in... we hear a sound. Sound is what? detectable changes in pressure. A moving change of pressure is a shock wave. My answer was not so wrong in the first place. Read the O.P. and what I am agreeing with... I do see the use of shock as not as correct as your word pressure and please do not be so pedantic.

'cjl' Your comment regarding temperature might be correct. As temperature changes the frequency of vibration. which is the method of sound transmission through a medium.
Tomacs question has been answered.

matt.o
2008-Nov-04, 09:28 AM
'matt.o ' Did you read my post? did you see the ' As noted ' No mater, I shall try again...
The human ear is equipped to detect the sudden changes in air pressure that are why we are able to detect the noise made by the compression of that medium that we might be in... we hear a sound. Sound is what? detectable changes in pressure. A moving change of pressure is a shock wave. My answer was not so wrong in the first place. Read the O.P. and what I am agreeing with... I do see the use of shock as not as correct as your word pressure and please do not be so pedantic.


There's no need to be defensive. I have just noticed you saying a similar thing before (in the sound in nebula thread), so I though I'd correct you. While a sound wave is a moving pressure wave, it is not the same as a shock front.

astromark
2008-Nov-04, 09:31 AM
That would be Dependant on how fast it is moving... but yes, I agree.:)

BigDon
2008-Nov-04, 09:43 AM
Thank you guys, you gave me my next flightdeck story...shockwaves.

I've been asking people a long time what the difference between sound waves and shock waves were, ever since I had to misfortune to have been caught up in one back in 1981. Shockwaves are unpleasant BTW, that whole "hyper-inflation of the lungs" trauma I could of gone my whole life without experiencing, and not felt deprived. And nobody has given me an answer I liked until now.

Matt, I owe you one.

matt.o
2008-Nov-04, 09:59 AM
No problems BigDon - you don't owe me anything. Shock fronts occur because the medium in front of the body has no time to react. When a body is moving at subsonic speeds, the medium ahead of the body "knows" about the approaching body and has time to react. Since the information of an approaching body travels at the speed of sound in the medium, it stands to reason that when a body is travelling faster than the speed of sound the medium in front of the body doesn't have time to react to the approaching body. Thus, a shock front forms ahead of the body since the medium doesn't "know" to get out of the way. The wikipedia article (here) (http://en.wikipedia.org/wiki/Shock_wave) has some good info.

Incidentally, the properties (density, temperature, pressure) across shock waves can be used to infer velocities of gas motion in e.g. galaxy cluster mergers, supernova explosions and many other astrophysical phenomena.

I can't say I've ever been caught up in a shock wave though - that must have been some scary experience!

hhEb09'1
2008-Nov-04, 06:03 PM
I was going to mention the shockwave thing, but I got distracted :)

I think you are mistaken, at least to a first approximation. If the speed of sound were proportional to density and the temperature constant, then the pitch of my horn would change with changes in atmospheric pressure. My experience over a wide range of altitude is that there is no audible change. If there is any change as a result of departure of our air from an ideal gas, it is much smaller than a straight proportion.cjl mentions below, speed of sound is dependent upon temperature, but I'll bet the pitch of your horn does not change with changes in temperature, right?

sabianq
2008-Nov-04, 06:43 PM
Actually, the speed of sound in air is dependent on exactly one variable: temperature. All other variables are irrelevant. I'm not sure if this also applies to the speed of sound in liquids and solids though.
I would love to see your source on this information, because all of my sources say that there are other factors involved.

are you are saying that if i have a dry day in florida and the same dry day on top of mount Evans in Colorado, and both places have the same temp and humidity, the air density will be the same?


I doubt it..


The speed of sound is dependent on density, humidity and temperature. while temperature can change the density, so can altitude and humidity. it can easily be 70 degrees F on top of Mt Evans in Colorado (14,000+ feet above sea level), but the air density is less than a 70 degree day in the Florida keys even is the relative humidity just happens to be the same.

source:

The air's density depends on its temperature, its pressure and how much water vapor is in the air.
http://weather.n3ujj.com/weather_faq.html

http://www.2-stroke-porting.com/altiden.htm

http://www.cascadeparaglidingclub.org/pages/mm5.php


http://www.atmosphere.mpg.de/enid/1__Understanding_the_stratosphere/pressure___altitude_16h.html


The speed of sound in in any medium is a result of the density and structure (stiffness) of the medium that the mechanical impulse is propagating..



Offhand, I'd say that sound waves travelling upward travel slower because the air above you is less dense than the air below you, and the speed of sound is proportional to the density of the medium through which it travels.

sound actually travels slower as a medium becomes more dense and faster as a medium becomes stiffer
what? did i just say that sound travels slower in denser mediums? sure did.


the actual formula is:
the speed of sound is equal to the square root of the coefficient of stiffness over the density
http://upload.wikimedia.org/math/4/f/f/4ff5693c00111ac2db0b7284dd2aa53f.png
so the speed of sound propagation through a medium is a function of the structure of the medium and the density of the medium.
http://en.wikipedia.org/wiki/Speed_of_sound


This shows that the speed of sound in any given medium depends on how the density varies with pressure (and vice versa). Incidentally, the "bulk modulus" of an elastic substance is defined as K = r(dp/dr), so the speed of sound in a medium with bulk modulus K can be written as .

http://www.mathpages.com/home/kmath109/kmath109_files/image009.gif
http://www.mathpages.com/home/kmath109/kmath109.htm

http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html


I think you are mistaken, at least to a first approximation. If the speed of sound were proportional to density and the temperature constant, then the pitch of my horn would change with changes in atmospheric pressure. My experience over a wide range of altitude is that there is no audible change. If there is any change as a result of departure of our air from an ideal gas, it is much smaller than a straight proportion.


actually there is a change:
Say, in gases of low molecular weight like helium, sound propagates faster when compared to heavier gases, such as xenon. which is why our voices change when we suck on helium.

and the pitch of your horn increases as you go up in altitude, (but i doubt you can tell the difference)

http://www.physlink.com/education/askexperts/ae36.cfm

Helium atoms have a molecular weight of about 4 grams per mole (a mole is 602200000000000000000000 molecules). Air is about 80% Nitrogen which has a molecular weight of about 28 grams per mole; it is seven times havier than helium. This means that a compression wave will propagate faster through helium than it will through air.

sabianq
2008-Nov-04, 06:56 PM
Sound transmission is not free from the effects of gravitational distortion. Sound is a transmission of a shock wave through a medium, ie; air. As noted, as air density lessons so to would sound transmission fall away. If the medium material was being distorted by a strong gravity well, then yes the transmission of sound through that would be effected. Sound is not a particle stream so would not be effected by gravity. But the mater it is being transmitted through is.


This would seem to be correct, as "sound" is a purely mechanical phenomena, meaning that the energy is nothing more than waves of energy in a medium, the only way it could be affected by gravity is if gravity affects the medium that sound passes through.

Ken G
2008-Nov-04, 07:03 PM
I would love to see your source on this information, because all of my sources say that there are other factors involved.cjl is correct, at the level of a simple approximation called the "ideal gas law". However, nothing is ever that simple in real life, so yes, in truth there is some small density dependence to sound speed. But it's not at all the major issue-- the major issue is temperature, just as cjl said. So no, cjl was not saying the air always has the same density, but rather that the density does not matter much. If you climb Mount Everest, where the density is about half what it is at sea level, the speed of sound is not noticeably different. (All your data about bulk moduli and stiffness apply to solids, which are very far from ideal gases.)

Say, in gases of low molecular weight like helium, sound propagates faster when compared to heavier gases, such as xenon. which is why our voices change when we suck on helium.This is of course true, but it is not anything that has to do with density, it is due to the masses of the individual particles. cjl assumed we were talking about normal air. The leading dependence of the speed of sound is on the ratio of the temperature to the mass per particle. The basic proportionality is that the sound speed is similar to the thermal speed, which scales with the square root of T/m.

If you want to get more detailed, note that the sound speed is the square root of the rate that pressure changes as you change the density of gas. Since ideal gases at given temperature have pressures that are proportional to density, the result is a constant that does not depend on density. If the density changes are fast enough, such as with sound waves, that the temperature changes "adiabatically", there is a small correction but it's just a constant.

sabianq
2008-Nov-04, 07:09 PM
but as for the original question, "do sound waves bend", There is a very interesting phenomena where sound can diffract and refract over and through things and pressure and temperature differentials in the space or atmosphere.

This can be annoying when trying to set up a very large sound system outside where the sound may need to be "thrown" a large distance
http://www.britannica.com/EBchecked/topic/555255/sound/63980/Refraction

Diffraction involves the bending or spreading out of a sound wave in a single medium, in which the speed of sound is constant. Another important case in which sound waves bend or spread out is called refraction. This phenomenon involves the bending of a sound wave owing to changes in the wave’s speed. Refraction is the reason why ocean waves approach a shore parallel to the beach and why glass lenses can be used to focus light waves. An important refraction of sound is caused by the natural temperature gradient of the atmosphere...

tommac
2008-Nov-04, 07:15 PM
This would seem to be correct, as "sound" is a purely mechanical phenomena, meaning that the energy is nothing more than waves of energy in a medium, the only way it could be affected by gravity is if gravity affects the medium that sound passes through.

The big question that I was shooting for is how are waves effected by warped space-time.

sabianq
2008-Nov-04, 07:22 PM
i would think that the answer would be the same as how the medium that the waves travel through is affected by the warped space-time.

I don't think the waves themselves can be effected by the "warpage" rather the medium that they travel through would be affected, causing diffraction.

tommac
2008-Nov-04, 07:45 PM
i would think that the answer would be the same as how the medium that the waves travel through is affected by the warped space-time.

I don't think the waves themselves can be effected by the "warpage" rather the medium that they travel through would be affected, causing diffraction.

How do you explain light waves near a black hole?

DrRocket
2008-Nov-04, 07:58 PM
cjl is correct, at the level of a simple approximation called the "ideal gas law". However, nothing is ever that simple in real life, so yes, in truth there is some small density dependence to sound speed. But it's not at all the major issue-- the major issue is temperature, just as cjl said. So no, cjl was not saying the air always has the same density, but rather that the density does not matter much. If you climb Mount Everest, where the density is about half what it is at sea level, the speed of sound is not noticeably different. (All your data about bulk moduli and stiffness apply to solids, which are very far from ideal gases.)

http://upload.wikimedia.org/math/f/0/a/f0aa0a8f1de4bb4cd5c26170954f39b3.png
Correct, and above is the equation for the speed of sound in an ideal gas. I prefer the middle expression in which the terms are:

gamma -- ration of specific heats
R -- universal gas constant
T -- absolute temperature
M -- molar mass (kg/mole)

It is perhaps worth mentioning that this is the speed of sound, not the speed of a real compression wave. The difference being that the speed of sound applies in limit as the amplitude of the pressure wave becomes small. The speed of a compression wave is slightly dependent on amplitude, higher amplitudes propagating a bit faster.

sabianq
2008-Nov-04, 07:59 PM
ha!
I knew where this was heading, into the realm of ATM..

well i have my ideas...

but first, i would bet that the mainstream would say something like this:

well, since light propagates through/on/ or in spacetime, and gravity is a result of the geometrical structure of spacetime (meaning gravity is caused by the way spacetime is bent) then it would seem logical that any light wave traveling through/on/ or in spacetime would merely travel or follow the path of the bent spacetime...

i assume

sabianq
2008-Nov-04, 08:07 PM
cjl is correct, at the level of a simple approximation called the "ideal gas law". However, nothing is ever that simple in real life, so yes, in truth there is some small density dependence to sound speed.

come on, cjl said:

Actually, the speed of sound in air is dependent on exactly one variable: temperature. All other variables are irrelevant.

is that really absolutely true? that [all] Other variables irrelevant?

while Yes, i agree that temperature matters, not air pressure when it comes to the speed of sound as outlined in this source below:
http://www.sengpielaudio.com/calculator-airpressure.htm

is the calculator above incorrect then? if i just change the humidity variable, the speed seems to change (at least on my pc screen)

so it seems to me that humidity also affects the speed of sound, albiet just a bit, but it still seems to affect the speed of sound. is Humidity is not a variable?

While i am no longer disputing the fact that temp is the largest variable, Humidity is a variable that changes c also.

It just comes across as Temperature is the only variable and nothing else matters.

in a forum where the tiniest, littlest, "ittibittest" fact is up for debate, i would think that when someone makes such a bold statement, there would be a bit of hand waving.

alainprice
2008-Nov-04, 08:21 PM
Density and pressure are variables, but they work against each other. As you increase the pressure, you increase the density which sorta cancels out.

Temperature and the material itself(stiffness)is by far the biggest factor.

sabianq
2008-Nov-04, 08:23 PM
hmmm... post 17


the actual formula is:
the speed of sound is equal to the square root of the coefficient of stiffness over the density

Tobin Dax
2008-Nov-04, 08:28 PM
How do you explain light waves near a black hole?

Sound waves and electromagnetic waves are apples and oranges. The apples need a medium to travel through, while the oranges do not. The properties of a sound wave depend on the properties of the medium it travels through.

cjl
2008-Nov-04, 11:11 PM
come on, cjl said:


is that really absolutely true? that [all] Other variables irrelevant?

while Yes, i agree that temperature matters, not air pressure when it comes to the speed of sound as outlined in this source below:
http://www.sengpielaudio.com/calculator-airpressure.htm

is the calculator above incorrect then? if i just change the humidity variable, the speed seems to change (at least on my pc screen)

so it seems to me that humidity also affects the speed of sound, albiet just a bit, but it still seems to affect the speed of sound. is Humidity is not a variable?

While i am no longer disputing the fact that temp is the largest variable, Humidity is a variable that changes c also.

It just comes across as Temperature is the only variable and nothing else matters.

in a forum where the tiniest, littlest, "ittibittest" fact is up for debate, i would think that when someone makes such a bold statement, there would be a bit of hand waving.
Humidity changes the mean molecular weight, which does change the speed of sound. That is a composition change however. As stated above, the full dependence has to do with the ratio of specific heats, the mean molecular weight of the gas, and the temperature. Note, however, that if you ignore the differences that occur from physically changing the composition of the gas, the only relevant factor is temperature.

mugaliens
2008-Nov-04, 11:28 PM
Matt O is right. Technically speaking, a shock wave begins by travelling faster than sound. An explosion creates a shock wave which travels outward many times the speed of sound. Similarly the passage of the supersonic Shuttle creates a shock wave that, initially, is expanding fast than the speed of sound. It doesn't do this for long, though, perhaps a few feet.

As it expands, it slows, until it reaches the speed of sound, at which point it's no longer a shock wave, but simply the wave front of the sound, and it continues to propogate at the spead of sound, growing weaker as it does. It's still referred to as a shock wave, though, as it's the first sound from the source to reach the listener, and it's still the part that packs the most wallop.

A supersonic shock wave has a nearly instantaneous rise slope, and for serious explosions, actually compresses air until it's well past the triple and critical points, becoming a supercritical fluid (doesn't last but a microsecond, though). The rapidly-expanding whiteness you see in videos of large explosions, particularly in humid environments, however, is the trough of the wave, behind the shock front, where the air pressure is nearly a vacuum, and the moisture in the air condenses out. It's the same effect you see on the top of the wing of a fighter (or even an airliner) pulling Gs in a humid environment. For aircraft breaking the sound barrier, we've all seen the picture of the white cone. Same thing. Notice the cone begins several feet behind the leading edge. The shock wave is in front of the cone, where pressure is high - no condensation occurs. The condensation occurs in the region behind the shock front, where the pressure is low. This is why the aircraft appear to be halfway ahead of the "shock wave." The condensation is actually occurring in the trough behind the shock wave.

Once the shock wave has slowed to the speed of sound, that slope slowly becomes more gradual, which is why the Shuttle's "boom-boom" shock wave isn't a CRACK-rumble, CRACK-rumble. It's leading edge has mellowed, somewhat.

Over a long distance, it become nearly sinusoidal, sounding more like the beat of a base drum.

Back to the OP: Any sound wave will be distorted by gravitational gradients just like all other energy-matter phenomena.

tommac
2008-Nov-05, 03:01 PM
Sound waves and electromagnetic waves are apples and oranges. The apples need a medium to travel through, while the oranges do not. The properties of a sound wave depend on the properties of the medium it travels through.


So are you saying that sound waves are only effected by its medium but light waves since they have no medium are in some way more affected by the curvature of space-time?


I mean what I am getting from the rest of the posts is that since the medium is effected by the curvature of space time then by default the waves are also. The medium effects it much more than curvature.

mugaliens
2008-Nov-05, 04:44 PM
The medium effects it much more than curvature.

tommac, where are you going with this? Perhaps if we knew what you were trying to get at, we might have a better answer.

Everything is affected by spacetime. It could be argued that everything is a part of spacetime itself. If spacetime is curved, everything is curved.

It's not a case of something things being affected more than others...

hhEb09'1
2008-Nov-05, 05:23 PM
So are you saying that sound waves are only effected by its medium but light waves since they have no medium are in some way more affected by the curvature of space-time? Light waves are subtly curved by that curvature--we can only measure it in the field of massive objects like the sun, right?
I mean what I am getting from the rest of the posts is that since the medium is effected by the curvature of space time then by default the waves are also. The medium effects it much more than curvature.The curvature at the surface of the earth hardly affects light at all--at least, that we can measure. The same goes for sound :)

You're not talking about the gravity gradient due to, say, mountains and valleys, but the spacetime curvature of Einstein, right?

actually there is a change:
Say, in gases of low molecular weight like helium, sound propagates faster when compared to heavier gases, such as xenon. which is why our voices change when we suck on helium.Changing the speed of transmission doesn't affect the ptich. The reason that our voices change with helium is that the resonant frequency of our vocal chords change in the different atmosphere. The pitch of our vocal chords actually changes, but the medium doesn't change the pitch. If that makes sense.

tommac
2008-Nov-05, 08:04 PM
tommac, where are you going with this? Perhaps if we knew what you were trying to get at, we might have a better answer.

Everything is affected by spacetime. It could be argued that everything is a part of spacetime itself. If spacetime is curved, everything is curved.

It's not a case of something things being affected more than others...

Well it was just a question I didnt understand but was answered. Basically what I didnt take into account was the medium. So from the point of this Q/A thanks for all that have helped answer. I understand better now.

Now ... as with all of my posts ... the questions are usually stemming from ATM at some point. So because you asked I will reply with my thought and confusion etc ...

I watched Nova the other night and it was about fractals. I found it semi-interesting and it actually during parts questioning the usefulness of fractals but also thinking about them too.

One part of Nova was where they were showing how branches on a tree can also represent the general makeup of the forest. I found this a little far fetched and although I sort of see where they were going I wasnt totally on board. I started thinking about e and how e is used commonly in nature and I have seen the same comparisons for e. Then I realized that there may be a fractal of e .... in any case ... Then I started thinking about fractals and the universe and I thought that fractals dont work with the universe because of the dual realities of the macro/micro worlds. I started to think about gravity and how gravity sort of follows a fractal solution. I thought of how the moon revolves around the earth and the earth around the sun and the sun around a black hole in the middle of our galaxie and the galaxie rotating around something else ... and eventually that something else rotating around something bigger. Sort of made sense. Then I thought a little about the microscopic and I do realize that the current understanding is that there is just a totally different reality.

I started thinking about how our universe would look to a super-giant. And was thinking about what would a black hole look like to a super-giant and how clusters of galaxies would look like. Somewhere along the lines I started thinking about the particle wave duality of an electron and sort of envisioned a wave orbiting something complex, with portions of space blinking in and out due to dark objects.

Then I had the question about how waves react to gravitational pull. I posted the question and got the answer. It didnt help the ATM thoughts that I had at all but I learned something.

NEOWatcher
2008-Nov-05, 08:14 PM
Then I started thinking about fractals and the universe and I thought that fractals dont work with the universe because of the dual realities of the macro/micro worlds.
I'm not sure what you mean by dual realities, but I sense you mean the fact that gravity overwhelms in one end but doesn't really apply at the other.
I would probably say that fractals don't apply because there doesn't seem to be enough depth to determine the speed of convergence.
But; my knowledge of fractals is somewhat limited, so maybe there's a way.


It didnt help the ATM thoughts that I had at all but I learned something.
Funny; but those two usually come out that way...:lol:

Edit: let me clarify that last statement to apply only when learning is involved.

sabianq
2008-Nov-05, 08:17 PM
The reason that our voices change with helium is that the resonant frequency of our vocal chords change in the different atmosphere. The pitch of our vocal chords actually changes, but the medium doesn't change the pitch. If that makes sense.

so this is incorrect?
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html#c4


The high speed of sound is responsible for the amusing "Donald Duck" voice which occurs when someone has breathed in helium from a balloon.

and this is wrong?
http://online.physics.uiuc.edu/courses/phys199pom/Student_Reports/Fall03/Erich_Hauptmann/Erich_Hauptmann_P199POM_Final_Paper.pdf

In situations such as
a guitar or vocal cord, wavelength is fixed, therefore frequency must change to balance the
equation when the speed of sound changes.

sabianq
2008-Nov-05, 08:20 PM
why would helium change the speed of vibration of our vocal cords?

is it because the helium escapes faster out of our lungs when we are talking because it is lighter?

but this doesn't make sense because your voice still is high pitched even when you are hanging upside down.

λ = c/f
the wavelength is equal to the speed of sound over frequency

tommac
2008-Nov-05, 08:32 PM
I'm not sure what you mean by dual realities, .

I am talking about how quantum physics diverges from gr near the planck length.

sabianq
2008-Nov-05, 08:44 PM
hold on let me prove this to myself...

λ = c/f
the wavelength is equal to the speed of sound over frequency
say a guitar string vibrating at 100hz is the frequency or (pitch?)
and the speed of sound is 1,088 ft per second,
that give us a wavelength of around 10.88 feet
(I would think that changing the environment would not affect the frequency that the string is vibrating. (i think you said this)
rather the speed of sound changes the wavelength of the frequency)

just by changing the speed of sound to say 2176 feet per second gives us a wavelength of 21.76 feet.
which has a timbre about twice as low as the wavelength of the sample where the speed of sound is slower.
so by plugging in various numbers, we can see that changing the speed of sound does indeed change the wavelength of the sound.


so by increasing the speed of sound, the wavelength of the frequency lengthens.

so how would we as humans perceive that? a lower tone?

BTW the term pitch and timbre are not very concrete and can be ambiguous, frequency and wavelength would/should be more appropriate in this discussion (any discussion actually)

grant hutchison
2008-Nov-05, 09:34 PM
The reason that our voices change with helium is that the resonant frequency of our vocal chords change in the different atmosphere. The pitch of our vocal chords actually changes, but the medium doesn't change the pitch.This isn't actually so. The reason voice frequency changes in helium has nothing to do with the vibration frequency of the vocal cords, which is pretty much unchanged.
What is altered is the resonant frequency of the airways, which act like an organ pipe to select out a base tone and harmonics. Because the speed of sound is higher in helium, pressure waves travel faster, and so the natural resonant frequencies of the trachea, larynx and upper airway are higher.

Grant Hutchison

Hornblower
2008-Nov-05, 11:08 PM
I think Grant is spot on with his post here.

Here is a good reference with some sound samples.
http://www.phys.unsw.edu.au/phys_about/PHYSICS!/SPEECH_HELIUM/speech.html
Note that the low-pitched fundamental from the vocal cords stays practically unchanged while the overtones from air resonances in the throat and mouth go up in the helium atmosphere. The sound is in good agreement with the author's explanation, which in turn is in good agreement with my understanding of the pertinent physics.

Browsing this topic is a good exercise in caveat emptor. I encountered an awful lot of ** (Bad Science) before finding this one.

sabianq
2008-Nov-06, 12:15 AM
so wait,
did i.

get it wrong?



λ = c/f
the wavelength is equal to the speed of sound over frequency
say a guitar string vibrating at 100hz is the frequency or (pitch?)
and the speed of sound is 1,088 ft per second,
that give us a wavelength of around 10.88 feet
(I would think that changing the environment would not affect the frequency that the string is vibrating. (i think you said this)
rather the speed of sound changes the wavelength of the frequency)

just by changing the speed of sound to say 2176 feet per second gives us a wavelength of 21.76 feet.
which has a timbre about twice as low as the wavelength of the sample where the speed of sound is slower.


is this correct?
faster speed = longer wavelength?

grant hutchison
2008-Nov-06, 12:24 AM
is this correct?
faster speed = longer wavelength?It is if you hold the frequency constant.
But in the case of resonant air cavities, it's the wavelength that's held constant, because the physical structures remain the same size and select out only those waves that can "fit" and resonate.
In the case of constant wavelength, frequency scales with speed. So the faster the speed of sound, the higher the resonant frequency of the airways, and the higher the notes they "pick out" and enhance as the vocal cords vibrate. That resonant cavity then couples to the air outside through the nose and mouth, and sends off sound waves into the air with frequencies which matches its new, higher, resonant frequencies.

Grant Hutchison

sabianq
2008-Nov-06, 12:46 AM
c = λ f λ = c / f = c T f = c / λ

so if i have an initial frequency "f" of say 100 hz
and the speed of sound "c" is 1088 feet per second
the wavelength "λ" in the medium would be 10.88 feet.
now if i adjust the speed of sound say through some sort of medium like a strange gas and say double the speed "c" to 2176,
the wavelength "λ" in the medium would be 21.76 feet
and the frequency "f" of the wavelength "λ" would be 50Hz
(Really Low)

(EDIT)"c" 2176 feet per second over λ 21.76 feet = 100Hz
Im sorry i'm such a dope, i didnt mean to make anyone less smart)

1/2

so would we say that frequency "f" and wavelength "λ"are inversely proportional?

:confused:

sabianq
2008-Nov-06, 12:49 AM
how does a longer wavelength and lower frequency translate to a higher resonant frequency?

please tell me what i am missing.

I have been trying to get over this for a very long time
(seriously)

is there something wrong with my math?

please help

sabianq
2008-Nov-06, 12:55 AM
It is if you hold the frequency constant.
But in the case of resonant air cavities, it's the wavelength that's held constant, because the physical structures remain the same size and select out only those waves that can "fit" and resonate.
In the case of constant wavelength, frequency scales with speed. So the faster the speed of sound, the higher the resonant frequency of the airways, and the higher the notes they "pick out" and enhance as the vocal cords vibrate. That resonant cavity then couples to the air outside through the nose and mouth, and sends off sound waves into the air with frequencies which matches its new, higher, resonant frequencies.

Grant Hutchison

wait, wait
are you saying that the resonant cavity actually acts like a high-pass filter?

and only lets the...

hold please
<shakes head vigorously and growls to himself>
...

sabianq
2008-Nov-06, 01:39 AM
how does a longer wavelength and lower frequency translate to a higher resonant frequency?

please tell me what i am missing.

I have been trying to get over this for a very long time
(seriously)

is there something wrong with my math?

please help

yes there is
you are such an idiot!
go suck on a grade school algebra book and see if that helps.
zeech!

grant hutchison
2008-Nov-06, 08:52 AM
yes there is
you are such an idiot!
go suck on a grade school algebra book and see if that helps.
zeech!Um, OK. Glad to have been of help. I think.

Grant Hutchison

hhEb09'1
2008-Nov-06, 08:54 AM
Changing the speed of transmission doesn't affect the ptich. The reason that our voices change with helium is that the resonant frequency of our vocal chords change in the different atmosphere. The pitch of our vocal chords actually changes, but the medium doesn't change the pitch. If that makes sense.

The pitch of our vocal chords actually changes, but the medium doesn't change the pitch.This isn't actually so. I guess I should have said the pitch of our voice box actually changes, but the medium doesn't change the pitch! :)


I think Grant is spot on with his post here.

Here is a good reference with some sound samples.
http://www.phys.unsw.edu.au/phys_about/PHYSICS!/SPEECH_HELIUM/speech.html
Note that the low-pitched fundamental from the vocal cords stays practically unchanged while the overtones from air resonances in the throat and mouth go up in the helium atmosphere. The sound is in good agreement with the author's explanation, which in turn is in good agreement with my understanding of the pertinent physics.I'm trying to envision how this experiment was set up. In the sound files, is he trying to hit a pitch? How does that prove that the pitch was unaffected?


Browsing this topic is a good exercise in caveat emptor. I encountered an awful lot of ** (Bad Science) before finding this one.I'm going to go back to that link that seemed to be a paper submitted for a physics class. :)

Hornblower
2008-Nov-06, 12:56 PM
I based my remarks on the sound of his voice in the spoken samples, in which the low-pitched component from his vocal cords sounded practically the same. Of course he could force that component to a desired pitch when singing even if it would change on its own, so that is not a completely reliable proof. When speaking normally we generally let the fundamental tone settle into a sweet spot.

I am confident in the opinions of those who say that the speed of sound is higher in a gas of lower molecular mass.

hhEb09'1
2008-Nov-06, 01:38 PM
I based my remarks on the sound of his voice in the spoken samples, in which the low-pitched component from his vocal cords sounded practically the same. Of course he could force that component to a desired pitch when singing even if it would change on its own, so that is not a completely reliable proof. When speaking normally we generally let the fundamental tone settle into a sweet spot.I ask because I've seen a couple claims that say the pitch is affected, but nobody seems to know how much.

I am confident in the opinions of those who say that the speed of sound is higher in a gas of lower molecular mass.Was that what any of the dispute was about though?

grant hutchison
2008-Nov-06, 04:21 PM
I guess I should have said the pitch of our voice box actually changes, but the medium doesn't change the pitch! :)And I'm thinking you should have said that the pitch of the vocal-cord vibration doesn't change, but that the medium determines which harmonics are selected by the rest of the vocal tract. :)

Grant Hutchison

Hornblower
2008-Nov-06, 05:17 PM
I ask because I've seen a couple claims that say the pitch is affected, but nobody seems to know how much.Was that what any of the dispute was about though?

My remarks were based on my listening skills as an experienced musician, along with my understanding of the pertinent physics. I recognized a mixture of a low-pitched component directly from the vibrating vocal cords, along with high-pitched components caused by air resonances in the throat, mouth and nose cavities. To my ears there was no obvious change in the former, but a large change in the latter during the spoken samples.

I thought I saw someone say that sound speed is not affected by molecular mass, but I now think I simply misread a confused jumble of remarks about velocity, frequency, wavelength, etc.

hhEb09'1
2008-Nov-06, 05:28 PM
And I'm thinking you should have said that the pitch of the vocal-cord vibration doesn't change, but that the medium determines which harmonics are selected by the rest of the vocal tract. Yeah, I'm undecided. :)

My experience tells me that the pitch changes, but I tend to sextuple-check my experiences. Gonna have to get some helium for Thanksgiving I guess.

Hornblower
2008-Nov-06, 05:46 PM
In these spoken samples our perception of the pitch of the voice is dominated by the high frequency components. I had to listen really carefully to recognize the low component that did not change much if any.