[PeterR]

Quote:

Originally posted by kevin gilmore Dayton Wright electrostatic speakers. The entire speaker was in a plastic bag filled with sulfur dioxide. The sulfur dioxide with 7 times the density of air made the thing much more efficient than any other loudspeaker of that type.

Totally different thing. The reason for the use of the Sulfur Hexaflouride (not dioxide) in the Dayton-Wrights was that it allowed to use a significantly higher bias voltage (15kV and more I think) than conventional electrostatics.

 

[thomas]

(sorry, i was late to this thread so i'm not sure exactly how your project works.... If it creates sound based on resonance like wodgy describes, then it may work, but if it uses the gas to change the frequency of the sound directly, i don't think it will work)

Quote:

Actually, this is an interesting idea. The reason one's voice seems to raise when having breathed helium, is because of the transition from helium to air. See here for a pretty good explanation.

The way I understand this, is very different, ( i agree with the second poster on the physlink site, not the chemistry phd) Can someone please tell me where i'm going wrong, since i haven't studied acoustics since high school physics:

AFAIK, the frequency of a wave is a fixed property that can only be set by the oscilator generating the sound. Once the wave has been generated, the frequency remains constant, and NOTHING can change it. If the medium changes, then the velocity and wavelength of the sound change accordingly,but the freqeuncy always remains the same.

And since your ears hear sounds based on frequency, there is nothing you can do to convert 50hz sound into a 20hz sound, unless you recovered the energy and used it to generate an entirely new wave. (or use resonance like wodgy describes)

A simple way of proving this would be to put on a pair of closed headphones, pump them full of helium or argon, and see if the pitch (frequency) of the sound changes. I would predict that you would hear the exact same thing.

I've heard of a high end speaker that filled the back of the driver with a different gas (maybe it was the dayton writes), but not the front. Changing the density of the gas will have a huge affect on the load presented to the speaker, and most likely change its sensitivity and frequency responce. As kevin gilmore said, you can increase your efficiency and maybe bandwidth of your speaker like this, but probably not enough to turn a 5 watt 3" into a 200 watt sub...

Now if your speaker is actually trying to use standing waves to completely regenerate the sound, ie wodgy's resonsance cavity, i see other problems- AFAIK, resonance cavities can only generate sounds at specific frequencies/wavelengths, and can't generate the full spectrum of sounds needed for audio playback....

Again, i have much less background in this stuff than most others here, so I'm probably making some large mistakes here....

 

[eric343]

thomas - Wavelength and frequency are directly related... Wavelength = 1/f

So if you can change the wavelength...

The reason helium works is it's lighter, so your vocal cords travel at a faster rate through it (less resistance). Using a heavier/denser gas, the driver will move more slowly (reducing the frequency) and affect more air (the denser gas has greater mass).

 

[PeterR]

Quote:

Originally posted by eric343 thomas - Wavelength and frequency are directly related... Wavelength = 1/f

nope, its c/f, with c being the speed of sound...

 

[Czilla9000]

Ok, ok, ok......I am going out of town tonight. I will attempt to build it when I get back.



So currently, I take it, there is no consensus on whether it will work or not?


Looks like experimentation is the only way to figure it out.

 

[thomas]

Quote:

thomas - Wavelength and frequency are directly related... Wavelength = 1/f

see peterR's post....

i think you mixed up the equation for perod and wavelength, period=1/f....


Quote:

The reason helium works is it's lighter, so your vocal cords travel at a faster rate through it (less resistance). Using a heavier/denser gas, the driver will move more slowly (reducing the frequency) and affect more air (the denser gas has greater mass).

But the frequency of the driver is set by the frequency of the AC you send to your driver....There is less resistance with helium, and that could increase the amplitude of the driver's motion, but not its frequency...

I don't know speach works, but i'm assuming its based on standing waves. (ie resonant cavity)... In such a case,a sound is generated at specific wavelengths, which corresponds to the volume of the cavity (lungs? voice box?) So in helium, the same wavelength is generated (since your lungs have the same volume), but it has a higher pitch because that wavelength corresponds to a higher frequecny, since velocity = frequency x wavelength.

This only applies to creating sound through standing waves, once the sound is created, the frequency should be constant.


Quote:

Ok, ok, ok......I am going out of town tonight. I will attempt to build it when I get back. So currently, I take it, there is no consensus on whether it will work or not?

Well, hopefully one of the experts here can say for sure who's right, but you can do my closed headphone experiment, that should show if its possible.... And i'm still not sure what you're project is, can you please repost it so i can steal it.../h/h/h/h i mean help you

 

[thomas]

Ok, i've figured out a way for all this to work....


First, the frequency does not change when passing from argon to air- here's a "thought experiment" that proves it-

send two pulses from a speaker, exactly five seconds apart, in a normal room.... They will arrive at your ears some time later, but the time between the pulses arriving will be exactly five seconds since both pulses travel the same distance at the same speed. If the room was then filled with argon, the pulses will still arrive at your ears five seconds apart- although it will take longer for the pulses to arrive, both pulses have slowed down by the same amount. If the room was divided into two halves, one with argon and one with air, there still wouldn't be any difference in arrival time, since the two pulses always travel equal distances at equal speeds.

This can be translated directly to waves, where each "pulse" is a crest on the wave, and the time between them is the period. The period is always constant, so the frequency must also be constant, since its just the inverse of period. (T=1/f)

So housing a speaker in argon WILL NOT change the frequency of the sound.


HOWEVER, while i was thinking of this i realized there was a way to get the frequency to change- If the boundary between the argon and the air was moved in the same direction as the sound, it could change the frequency. The first part of the wave would spend more time in the fast air, and the end of the wave would spend more time in the slow argon, and the overall freqeuncy would be lower. It seems to work in a similar way to the doppler effect, except neither the speaker nor the listener is moving. ( i've never heard of anyone changing frequencies by moving the boundary between a gas, dunno if its a well known effect )

So in theory, you could build a speaker that used a small driver combined with this to produce low frequencies. (However, the boundary would have to move VERY fast). I'd imagine it would be a thin, long tube with a driver at the end, with an open end facing the listener, and the driver at the back of the tube. Then make a thin airtight membrane that can slide up the length of the tube, and leave it near the driver end of the tube. When you play the speaker, simultaneously pump argon into the back of the tube, causing the membrane to slide up its length.... This moving boundary between air and argon should produce the effect i described Since there is only a short length for the speaker to travel, you could use an array of tubes/speakers and stagger them like a car engine- Send the signal to the first tube, quickly pump it full of argon, when it reaches the end, switch the signal to the second speaker/tube and repeat, while returning the first tube back to its original position...

If you keep the speed of the membrane moving constant, then the frequency shift should also be constant (but non-linear), so you wouldn't need any feedback/correction.....

You could also do the exact same thing with the doppler effect- take a row of 3" drivers, and put them on rails that allow them to slide backwards VERY fast

And while i'm at it, instead of simply returning the driver back to its original position, you could use them both ways- when its moving forwards, its creating bass, when it moves backwards it creates high treble. That would cure both problems of 3" drivers- no highs, no lows, must be Bose....

Anyways, needless to say, its very hard just to get it to work, and impossible to get it to sound decent.... The noise prouduced will probably be louder than the bass you generate, but might be fun to try anyways, and AFAIK, its the only way you can use argon to shift frequency....



Oh yeah, copyright 2003

 

[Dusty Chalk]

Quote:

Originally posted by thomas Once the wave has been generated, the frequency remains constant, and NOTHING can change it. If the medium changes, then the velocity and wavelength of the sound change accordingly,but the freqeuncy always remains the same. And since your ears hear sounds based on frequency, there is nothing you can do to convert 50hz sound into a 20hz sound, unless you recovered the energy and used it to generate an entirely new wave. (or use resonance like wodgy describes)

No, this is wrong, see my explanation below. Quote:

Originally posted by eric343 The reason helium works is it's lighter, so your vocal cords travel at a faster rate through it (less resistance). Using a heavier/denser gas, the driver will move more slowly (reducing the frequency) and affect more air (the denser gas has greater mass).

No, as was explained in a link in my self-destructed post, it works because it starts in helium, and then transitions to air. The wavelengths are traveling at the same frequency they would have if you had not breathed helium, but they are traveling faster. When they get out of the helium, they slow down, and sort of "gang up" on each other, hence lowering the frequency. Quote:

Originally posted by thomas A simple way of proving this would be to put on a pair of closed headphones, pump them full of helium or argon, and see if the pitch (frequency) of the sound changes. I would predict that you would hear the exact same thing.

Yeah, but then you don't get the transition that I describe. So, not really a good experiment.

 

[Tomo]

Thomas,

That is a part of doppler effect. This moving boundary changes the effective path of sound in the frame of reference of the audience.

However, what you suggest is very difficult to do. And you can achieve the same effect by moving transducer in the air. (no need for other gases.) You can change the path of sound much easier.

You are complicating the problem by adding more variables.

T

 

[Tomo]

Hi,

Quote:

No, as was explained in a link in my self-destructed post, it works because it starts in helium, and then transitions to air. The wavelengths are traveling at the same frequency they would have if you had not breathed helium, but they are traveling faster. When they get out of the helium, they slow down, and sort of "gang up" on each other, hence lowering the frequency.

That does not make sense. Wave eqation must be self consistent in both media. Only that they both must be continuous at the boundary. In other words, frequency does not "gang up."

Also, wavelength changes depending on material's propagation constants. What is constant is the frequency. Speed does change because of the change in wavelength.

This phenomenon of sucking Helium* and talking funny is very different. It is the result of change in resonant frequency due to change in media within your resonance cavities. (Your cavities' volumes do not change but propagation constant changes so resonance frequency must change in response to the change in media.)

Tomo

P.S. Tomo turns all red ... * ... "He" doesn't fit there.

 

[Czilla9000]

So I take it that it will not work?

 

[MetalHead666]

Holy Crap. This thread starts as a bomb and turns into a science discussion?? O CRAP!!!


(Is burnt to nothing when the thread explodes, causing a chain reaction to the computer, making it explode, causing projectiles of the PC to fly into my blown up face. . . .)

 

[Dusty Chalk]

Quote:

Originally posted by Tomo That does not make sense.

You're right, it doesn't. I was just quoting the explanation I got on the web, will have to look into it later, when I get back. Quote:

Wave eqation must be self consistent in both media. Only that they both must be continuous at the boundary. In other words, frequency does not "gang up."

Well, for the record, I didn't mean that it would "gang up", I meant that the waves would "gang up". Quote:

This phenomenon of sucking Helium* and talking funny is very different. It is the result of change in resonant frequency due to change in media within your resonance cavities. (Your cavities' volumes do not change but propagation constant changes so resonance frequency must change in response to the change in media.)

This actually sounds more reminiscent of the explanation I got in physics class, so you are probably correct.

That said, if the same driver (your vocal chords) can produce a higher frequency when "submerged" in a lighter gas, couldn't the same concept still work for a driver "submerged" in a heavier gas, producing lower frequencies? I think it would still work. Perhaps the resonant frequency and other characteristics of the driver are all meant for "in air", and they all change in Xenon/Argon. Perhaps czilla wouldn't even need to pitch-shift the incoming frequency. Quote:

Originally posted by MetalHead666 Holy Crap. This thread starts as a bomb and turns into a science discussion?? O CRAP!!!

No, actually, people have been going into their own posts and deleting the content. You missed it.

 

[Czilla9000]

Arg.....so should I go to the effort or not?

 

[thomas]

Quote:

You're right, it doesn't. I was just quoting the explanation I got on the web, will have to look into it later, when I get back.

moral of the story, don't listen to chemists trying to explain physics

My post above appears to be a valid proof that frequency does not change, i'll rewrite it with numbers. It requires no knowledge of wave equations and is based only on the definitions of velocity, period and frequency.

Let X1 rep. the initial time of the first crest of a wave is created
Let Y1 rep. the time the next creast is created.

Period is defined as the time between two successive crests of a wave, so initial period would be Y1-X1

Now, if the sound had to pass through n regions (ie different gasses) , each with a different length and propagation velocity, then the total time for the first crest to reach the end would be:

Xt= X1 + T1 + T2 + .... + Tn

where Tn is the time required for the wave to pass throughthe region. The wave propagates through any region at constant velocity, and we'll assume that the length of the region is fixed. (if it isn't, you'll get the doppler shift i described earlier) Therefore, Tn = Dn/ Vn, simply from the definition of constant velocity.

So Xt = X1 + D1/V1 + D2/V2 + ...+ Dn/Vn

Now you can do the exact same thing with the second crest.

Yt = Y1 + t1 + t2 +... + tn
Note that i used lowercase t's here, so not assuming its equal to T1 for the first crest. But since it is passing through the exact same regions, and each region has a fixed length and velocity, they do turn out to be the same:

Yt = Y1 + D1/V1 + D2/V2 +.... + Dn/Vn

So now calculate the final period:

Yt - Xt = (Y1 + D1/v1 + D2/v2 +....) - (X1 + D1/v1+ ....)
= Y1- X1
= initial period
QED
(frequency is simply the inverse of period, so it also can not change)

Note that you can have any number of regions of any length, the speed can be anything (well, greater than zero, much less than speed of light) and the frequency of the wave still does not change.


Quote:

This actually sounds more reminiscent of the explanation I got in physics class, so you are probably correct. That said, if the same driver (your vocal chords) can produce a higher frequency when "submerged" in a lighter gas, couldn't the same concept still work for a driver "submerged" in a heavier gas, producing lower frequencies? I think it would still work. Perhaps the resonant frequency and other characteristics of the driver are all meant for "in air", and they all change in Xenon/Argon. Perhaps czilla wouldn't even need to pitch-shift the incoming frequency.

I've already explained this in my previous posts. Your speech isn't produced by a "driver", it works on the principal of resonance. But drivers do not resonate, they only respond to the signal they are sent- any resonance in a driver is distortion, and a properly designed driver will have its resonance frequency outside its operating range.

AS i said earlier, you may be able to increase sensitivity and bandwidth slightly, but that's it.

And i've already explained that no speaker can be built entirely on resonance, since it only occurs at specific frequencies- your driver would literally only be able to produce "one-note bass"

Quote:

Yeah, but then you don't get the transition that I describe. So, not really a good experiment.

My "experiment" is to be identical to what you just proposed, except i used headphones and you used speakers

It should clearly show whether there is any pitch change.....