IDEA: cancel elevator music

[hays_r]

Lately, (perhaps because my hearing is going a bit with age), I've become increasingly wishing the ubiquitous music played in stores would just go away.  And I have an idea that perhaps it's possible.

I am not a tech on how noise cancelling headphones work, but I understand they read the ambient noise and find frequency patterns associated with background that they can generate cancelling waves for.  I've also heard that there are now programs that can identify a song from a clip.  So why not have your cell phone listen to the music, identify it, and send cancelling waves to your ears? 

Heck, there might even be a commercial product there if the project is too big for a volunteer effort.  And given the difficulty my wife is now experiencing in hearing, this is a growing problem as the population ages that might even attract development funds from those concerned with those suffering hearing disability.

Have fun with this.

[iphigenie]

You know what, this could make neighbourly relations so much easier 

[4wd]

You know what, this could make neighbourly relations so much easier 

-iphigenie (July 26, 2011, 04:16 AM)

I'd prefer a Woofer Stopper¹ connected to an LRAD-RX² playing Celine Dion³ at full blast.

NOTES:
1. Noise, (usually dog bark), triggered ultrasonic dog whistle.
2. RX version gives you remote control via IP so you can use it from the safety of the other side of the planet.
3. Annoying high pitched noise known to shatter glass and eardrums....although puke-inducing subsonics would be more fun.

[Stoic Joker]

I am not a tech on how noise canceling headphones work, but I understand they read the ambient noise and find frequency patterns associated with background that they can generate canceling waves for.

-hays_r (July 26, 2011, 03:36 AM)

I tend to wonder of the sound waves truly cancel each-other out resulting in silence. Or do they just collide, and raise the ambient sound pressure to a high level of white noise?

I'm guessing directionality is critical. 

[Edvard]

Noise-canceling headphones work very simply; a microphone attached to the headphones (or in close proximity) feeds an amplifier which inverts the signal and feeds it into the headphones, so basically you are hearing the background and it's mirror-image at the same time, which results in cancellation.

Due to various technical considerations (like latency, phase distortion, proximity effect, etc.), noise-canceling is much more effective for low-frequency and continuous noise sources, like trucks passing on the freeway or the low hum of a refrigerator.
Unfortunately, elevator music does not fall into that scope. 

@4wd:
When you said "Woofer Stopper" I thought you meant some way to stop the neighbor's kid from jacking his car subwoofer volume to vitriol-inducing levels. 

[Stoic Joker]

Noise-canceling headphones work very simply; a microphone attached to the headphones (or in close proximity) feeds an amplifier which inverts the signal and feeds it into the headphones, so basically you are hearing the background and it's mirror-image at the same time, which results in cancellation.

-Edvard (July 28, 2011, 11:57 AM)

That's what my earlier question was working off of. if you are hearing/subjected to the primary noise and the anti-noise at the same time is the result truly quiet...or does it just appear that way?

As an example: if you have a 100db sound, and you block it with another 100db anti-sound. is the ambient sound pressure at that point 0db or 200db? Or simply, will you not even hear the sound that shattered your eardrums?

@4wd:
When you said "Woofer Stopper" I thought you meant some way to stop the neighbor's kid from jacking his car subwoofer volume to vitriol-inducing levels. 

-Edvard (July 28, 2011, 11:57 AM)

That's where I went also.

[Edvard]

As an example: if you have a 100db sound, and you block it with another 100db anti-sound. is the ambient sound pressure at that point 0db or 200db? Or simply, will you not even hear the sound that shattered your eardrums?

Due to the sheer physics I alluded to, it would never be 0, nor would it go over the original volume.
As an experiment, take any sound editing program, record something mono, clone it and reverse-phase the clone.
Since it's a perfect mirror, you get silence as a result.
But since the path from microphone -> amplifier -> speaker -> air -> eardrum seriously impedes the generation of a perfect phase mirror, headphones simply give you a substantial attenuation of lower-frequency sounds.

From subjective experience, noise-canceling headphones give one the aural sensation of having a massive head cold or the feeling of needing to "pop" the ears after traveling up a mountain road.
Not at all uncomfortable, and the attenuation effect is startlingly nice.

[worstje]

I fully agree with Edvard, save for the ear-popping being comfortable. On that topic I declare him crazy, as it is a bloody annoying thing if you end up having to do it with any frequency.

Basically the problem is that the theory works, but that practice has far too many variables for it to be implemented in as perfect a manner as we would like. If you assume you have a single sound source that blasts sounds about, you would at the very least need to know exactly what sounds are played at exactly what moment, which is a near impossible task on its own. Additionally, one would need to know the angle/position of the sound source compared to ones ears. Now imagine adding multiple sound sources. Or varying the size, shape or materials of the walls of the room, which determine how sounds bounce around.

Congratulations, at that point you have a system that works in a single room with pre-determined sounds being thrown at you. All you need now is a plug in the elevator for your headphones to get the anti-music from.

[Renegade]

Noise-canceling headphones work very simply; a microphone attached to the headphones (or in close proximity) feeds an amplifier which inverts the signal and feeds it into the headphones, so basically you are hearing the background and it's mirror-image at the same time, which results in cancellation.

-Edvard (July 28, 2011, 11:57 AM)

That's what my earlier question was working off of. if you are hearing/subjected to the primary noise and the anti-noise at the same time is the result truly quiet...or does it just appear that way?

As an example: if you have a 100db sound, and you block it with another 100db anti-sound. is the ambient sound pressure at that point 0db or 200db? Or simply, will you not even hear the sound that shattered your eardrums?

-Stoic Joker (July 28, 2011, 01:30 PM)

In a perfect world, it creates absolute silence. But 100db + 100db is 106db. It's logarithmic with volume doubling every 6db. 50% louder is 3db louder irrespective of the current volume (except 0 of course).

It's like having a signal of 1 and a signal of -1 mix together. It's just everyday wave cancellation.

http://www.mediacoll...ave-interaction.html

I've got some information on the general topic here:

http://renegademinds...bid/112/Default.aspx

There's more there as well if you click around. The help file also gets into the topic a little bit.

[Edvard]

+1

I was also going to say that dB's don't add like normal numbers, but that was aside the main point, so I let it pass.

Actually, the way consumer-grade noise canceling works, you're not adding or subtracting dB's at all; you're adding a reverse-phase signal to the normal signal, which has an attenuating effect which CAN be measured in dB's.
0 dB is actually not silence, but the threshold of human hearing (at 1kHz); roughly the sound of a mosquito at 3 meters away.

Don't worry, as a semi-musician and somewhat aspiring sound engineer, I work in this kind of stuff all the time and it still confuses me.
 

[Renegade]

hehehe Time to talk about SPL?

[Edvard]

 
Sure!: http://en.wikipedia.org/wiki/Sound_pressure^w