Acoustical question

[36grit]

It's my understanding that sound is a wave that travels through the air. And that waves can cancel each other out.

 

So, I have a couple of thought experiments.

 

Experiment A.

 

If I take two speakers and point them at each other and play the same sound, at the same time, and at the same volume, I assume the waves would cancel each other out and I wouldn't hear anyting.

Here's my questions:

 

1) Are the paper cones still vibrating?

2) If not, are the magnets still vibrating?

And,

3) If I turned up the volume on one of the speakers would I hear the sound?

 

Experment B.

 

If I mount some speakers back to back, and on a track, (No rhyme intended,lol) and I perfectly center them inbetween the other speakers and set the same parameters, sound,time, and volume, I assume the waves would all cancel each other out once again, and I would hear no sound from them.

Here's the questions:

 

4) What would happen if I turned the volume up on the far right speaker?

a) Would I hear some sound?

b) Would the speaker on the track move tothe left? right? or would it not move at all?

 

5) What would happen if the volumes were again equal, and then I turned up the volume on one, say the right, speaker on the back to back, track speaker?

a) same questions as 4)a and 4)b?

 

I wish I had the time and money to perform experments like this. That'd be fun. It'd be super cool to watch the results on youtube!

 

 

 

 

 

 

 

 

[Strange]

If I take two speakers and point them at each other and play the same sound, at the same time, and at the same volume, I assume the waves would cancel each other out and I wouldn't hear anyting.

 

They would only cancel out where the signals are in antiphase. And this depends how far from the speaker you are. So there will be points where the signals destructively interfere (cancel out) and places where they constructively interfere) add together. This is a like a more complex version of the famous "two slit" experiment.

[studiot]

 

2) If not, are the magnets still vibrating?

 

Loudspeaker magnets are big and heavy and do not vibrate.

 

 

1) Are the paper cones still vibrating?

 

 

Yes the cones will still be driven

 

 

Experiment A.

 

If I take two speakers and point them at each other and play the same sound, at the same time, and at the same volume, I assume the waves would cancel each other out and I wouldn't hear anyting.

 

 

I asume you mean on axis cancellation (along the axis between the two speakers)?

 

A good variation of this experiment is to first test along the axis and then try again with different speaker separations.

 

Surely you can do this from a mono source?

 

Note that depending upon the speaker mounting/enclosure there will also be a backward wave so you will never achieve perfect cancellation.

 

 

 

Result for Experiment B will depend upon what you mean by back to back and the same comment about mounting/enclosures apply.

 

One other comment about experimental technique.

There will be a lot of reflections in an enclosed space.

This is why speakers are tested in the open air or an anechoic chamber.

 

Final comment.

There are noise cancelling devices based on doing exactly this for quietening heavy machinery (eg generators).

That is, a loudspeaker outputs an antiphase sound to that produced by the machine which cancels out the machine noise.

They are very effective but rely on being set up exactly right for the machine and its housing.

[Acme]

...

Note that depending upon the speaker mounting/enclosure there will also be a backward wave so you will never achieve perfect cancellation....

This backward motion and the sound it makes is what some Bose speakers employ for their 'enhanced' sound. The speaker is sandwiched between 2 wave guides, one of which is twice as long as the other which puts the backward motion in phase with the forward motion at the plane of the wave guide's termination, i.e. where the sound comes out.

[studiot]

This backward motion and the sound it makes is what some Bose speakers employ for their 'enhanced' sound. The speaker is sandwiched between 2 wave guides, one of which is twice as long as the other which puts the backward motion in phase with the forward motion at the plane of the wave guide's termination, i.e. where the sound comes out.

 

The 'waveguide' (advertiser's version, not a physicist's) only works at one frequency (or a very small range of frequencies)

[Acme]

The 'waveguide' (advertiser's version, not a physicist's) only works at one frequency (or a very small range of frequencies)

Well, a waveguide is as a waveguide does and I can't speak for Bose as to the frequency tuning. Seems I may have got the specific arrangement wrong, as least for the system layout illustrated by Bose here: >> Acoustic Waveguide® speaker technology @ Bose

[studiot]

 

 

 

Bose link

 

Thirty years ago...........

 

Thirty years, ago, sixty years ago these were called labyrinths not waveguides.

[Acme]

Thirty years, ago, sixty years ago these were called labyrinths not waveguides.

Well, Bose calls them waveguides today. It's constructive interference by any other name(s).

Edit: Waveguide(acoustics) @ Wiki

An acoustic waveguide is a physical structure for guiding sound waves.

Edited November 26, 2015 by Acme

[studiot]

 

 

 

Wiki

Other examples include the rear passage in a transmission line loudspeaker enclosure, the ear canal or a device like a stethoscope. The term also applies to guided waves in solids.

 

Right at the beginning of your link.

 

'transmission line'

 

A La Bailey et al.

 

Bose are very late at the gate.

[Acme]

Right at the beginning of your link.

 

'transmission line'

 

A La Bailey et al.

 

Bose are very late at the gate.

None of which contradicts what I was saying about the structure in regard to the OP. Thanks anyway.

[studiot]

Yes there you are the earliest reference I have is

 

The Acoustic Labyrinth

B Olney

Journal of the Acoustical Society of America

Vol 8 , No2 1936

 

So at least 80 years ago.

Edited November 26, 2015 by studiot

[StringJunky]

I think B and W's solution to the rear energy problem is the most elegant; tuned lengths and compression to dissipate the energy.

 

https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTrbTpjEXllGkgg1BA4qCNqTTeOX8rweQNH6hqhXcIrE9RzT3EUjM92nwQ

[studiot]

36grit,

 

You might like to know that the Logitech Z320 speakers we are discussing in this thread

 

http://www.scienceforums.net/topic/92308-trouble-with-ohms-law-and-some-advice-please/

 

include a pair of back to back mounted speakers to create their so called omnidirectional response.

[36grit]

 

They would only cancel out where the signals are in antiphase. And this depends how far from the speaker you are. So there will be points where the signals destructively interfere (cancel out) and places where they constructively interfere) add together. This is a like a more complex version of the famous "two slit" experiment.

 

Well, I kind of figured out the double split experiment by recreating the sub-atomic results using macro world objects. It was really quite simple, I tend to over think things sometimes. I've moved on to trying to figure how magnets work, but mostly I'm trying to figure out a slick way to explain how time travel might work for my sci-fi novel, lol. If I could put together a comprehensive explanation of how the universe is expanding I'd be half way home, I think.

so,

If we have the back to back speakers stationary and the ones on the ends on ball bearing tracks, and we had them set to maximum sound cancelation in the space perfectly centered inbetween them, and then turned the volume up on the middle speakers, would the two on the ends move outwards? If so, relativaly how far?

[Strange]

Well, I kind of figured out the double split experiment by recreating the sub-atomic results using macro world objects.

 

You don't get interference patterns with macroscopic objects. It depends on a relative phase shift between waves: light, sound, ripples in water, etc.

 

If I could put together a comprehensive explanation of how the universe is expanding I'd be half way home, I think.

 

What is wrong with the one we already have?

 

If we have the back to back speakers stationary and the ones on the ends on ball bearing tracks, and we had them set to maximum sound cancelation in the space perfectly centered inbetween them, and then turned the volume up on the middle speakers, would the two on the ends move outwards? If so, relativaly how far?

 

I don't think so. They would be exposed to equal push and pull from the sound waves. So at most they would oscillate back and forth.

[studiot]

 

You don't get interference patterns with macroscopic objects

 

Macroscopic is a term that is relative to the wavelength, ie much bigger than the wavelength.

 

The wavelength of a 100Hz soundwave is 3.4metres.

[Strange]

 

Macroscopic is a term that is relative to the wavelength, ie much bigger than the wavelength.

 

The wavelength of a 100Hz soundwave is 3.4metres.

 

What I meant was, you don't get an interference pattern by sending golf balls or similar through a pair of slits.

[36grit]

I thought the universe was expanding because of dark energy. "Dark" because we don't know the mechanism or where the energy for expansion is coming from.

Double slit, I was thinking a lot of steel bbs and a barrel hooked up to a air compressor with a couple of orbital sanders duct taped to the end of the barrel. Strong magnets on each side of the line of travel to warp the line of travel. Right or wrong the thought experiment helped me to realize the atmosphere the electron exists it. Vibrations, waves, pushing, and pulling constantly.

I've been daydreaming about how natural magnets might have been made. An electro magnetic field probably polorized a vast maority of the particles (relative to each other) at the same time the nuclear fission occured in the star that formed them. But I'm no scientist. Just a day dreamer, lol.

Edited December 1, 2015 by 36grit

[Strange]

I thought the universe was expanding because of dark energy. "Dark" because we don't know the mechanism or where the energy for expansion is coming from.

 

This seems to be a common misconception. The universe would expand without dark energy. It is the recently detected accelerating expansion that requires dark energy.

 

Double slit, I was thinking a lot of steel bbs and a barrel hooked up to a air compressor with a couple of orbital sanders duct taped to the end of the barrel. Strong magnets on each side of the line of travel to warp the line of travel. Right or wrong the thought experiment helped me to realize the atmosphere the electron exists it. Vibrations, waves, pushing, and pulling constantly.

 

I can't see how you would get an interference pattern from that sort of setup. You need waves. Look at Huygen's original version. Or ruipples in water.

http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php

I've been daydreaming about how natural magnets might have been made. An electro magnetic field probably polorized a vast maority of the particles (relative to each other) at the same time the nuclear fission occured in the star that formed them. But I'm no scientist. Just a day dreamer, lol.

 

Natural magnets are formed in rocks by the Earth's magnetic field.

[36grit]

 

This seems to be a common misconception. The universe would expand without dark energy. It is the recently detected accelerating expansion that requires dark energy.

 

 

Little bangs? lol, Perhaps the Eridanus supervoid is reaching the end of if it's inflationary period. Hmmmm

I can't see how you would get an interference pattern from that sort of setup. You need waves. Look at Huygen's original version. Or ruipples in water.

http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php

 

Natural magnets are formed in rocks by the Earth's magnetic field.

 

If you're saying what I think your saying then you should be able to place the slits parallel to the line of fire and still capture the electron. After all, I can still hear the music when my ear is parallel to a speakers axis.

 

I think if my experiment were perfectly tuned it would work fine. The bbs final position would mirror the frequency of the orbital sanders. The magnets are only there to warp the path through the slits.

 

There is another thing though, one we may not have considered. When the electron hits the target it would most certainly send a shock wave through it that would most certainly echo and reverberate. Perhaps this is the interference pattern that we are seeing. Surely somebody else has thought of these things though.

 

 

* Interesting about the magnets.

[36grit]

I actually like the last idea the best. Of course, I always do,lol.

Shooting an electron into a sea of atoms is probably a lot like dropping a buoy into a water tank from a great distance. There'd be a splash, some waves and then the electron would bob around in the troffs until the echoing waves settle and there it would rest in it's final location.

I would guess that when it is not being detected, as the double slit experiment goes, it is spinning very fast when it hits the plate maximumizing the electromagnetic distortion wave that pulses through the material.

When we polorize the electron before it hits the plate it's like a diver, causing very low distortion in the symetry of plate material.

Makes perfect sense. I don't know why I angle. But I do love unsolvable problems and good design. Helps calm me down after a stressful day at work.

[Strange]

It might make a lot of sense to you but:

 

1. Have you calculated the amount of energy the electron has and how much that will disturb the interatomic bonds (after subtracting the energy that is converted to light by the detector)?

 

2. Why would detecting which slit the particle (electron or photon) went through - even if that is done after it has hit the screen - change the behaviour?

 

3. By coming up with an alternative explanation you are effectively saying that quantum theory is wrong. In which case, you also need to come up with an alternative explanation for how all the components in your computer work.

[hoola]

as far as cancellation of sound goes, there is some decrease, most noticable in the bass frequencies if you point two speakers at each other. Another way to cause this decrease is to reverse the phase of one channel, by reversing leads on one speaker, in a normal front-facing arrangement...there is never perfect cancellation of any frequency, but it's easier to detect interfering reductions in the lower ones...

[36grit]

as far as cancellation of sound goes, there is some decrease, most noticable in the bass frequencies if you point two speakers at each other. Another way to cause this decrease is to reverse the phase of one channel, by reversing leads on one speaker, in a normal front-facing arrangement...there is never perfect cancellation of any frequency, but it's easier to detect interfering reductions in the lower ones...

How could obtain a perfect cancelation? 90 percent?

It might make a lot of sense to you but:

 

1. Have you calculated the amount of energy the electron has and how much that will disturb the interatomic bonds (after subtracting the energy that is converted to light by the detector)?

 

2. Why would detecting which slit the particle (electron or photon) went through - even if that is done after it has hit the screen - change the behaviour?

 

3. By coming up with an alternative explanation you are effectively saying that quantum theory is wrong. In which case, you also need to come up with an alternative explanation for how all the components in your computer work.

What does quantum theory say? That it's a wave and a particle at the same time? Relative to what? Other paricles and waves?

[Strange]

How could obtain a perfect cancelation? 90 percent?

 

By very careful control of the frequency, phase and position of the speakers. It is quite easy for a single frequency, more complicated for complex sounds. But this is how noise-cancelling headphones work (in the small space inside the headphones).

 

What does quantum theory say? That it's a wave and a particle at the same time?

 

That is has some wave-like characteristics and some properties we usually associated with particles.

 

Relative to what? Other paricles and waves?

 

Why would that need to be relative to anything? You can take a single photon or electron and measure its wavelength (a wave-like property) or the point it its a screen (a particle-like property).