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General Science => General Science => Topic started by: Phoebe on 08/03/2010 13:30:01

Title: Do sounds add together to make louder sounds?
Post by: Phoebe on 08/03/2010 13:30:01
Phoebe asked the Naked Scientists:
   
If there are multiple sources of sound in a particular area - say 20 sources of air conditioning units, each creating about 60 Decibels of sound, does this create more sound (and a louder sound) in the same way that lighting multiple candles creates more light?

What do you think?
Title: Do sounds add together to make louder sounds?
Post by: RD on 08/03/2010 18:07:20
Q. Do sounds add together to make louder sounds?

A. Yes, with the exception of anti-phase sound, as used in noise cancelling headphones (http://en.wikipedia.org/wiki/Noise-cancelling_headphones).
Title: Do sounds add together to make louder sounds?
Post by: doppler1 on 10/03/2010 06:40:33
Nuff said
Title: Re: Do sounds add together to make louder sounds?
Post by: Professor Mega-Mind on 22/04/2019 17:09:38
...one frequency only...
IF the sound-wave peaks match up , then yes .
IF the peaks of one match the troughs of the other , then  no .
The second case results in what is now called "Noise-Cancellation" .
P.M.
Title: Re: Do sounds add together to make louder sounds?
Post by: alancalverd on 22/04/2019 17:45:52
If you have n sources of equal amplitude but random phases and frequencies, the total amplitude is  √n .
Title: Re: Do sounds add together to make louder sounds?
Post by: Professor Mega-Mind on 22/04/2019 18:59:40
...so , IF...
One has two identical speakers , in a perfectly sound-reflective room . Each emits an identical sound-wave , perfectly out of sync . All sound is perfectly cancelled out . Where does the energy put into the emitted sound-waves go ?
P.M.
Title: Re: Do sounds add together to make louder sounds?
Post by: alancalverd on 22/04/2019 21:42:54
Heat
Title: Re: Do sounds add together to make louder sounds?
Post by: Professor Mega-Mind on 22/04/2019 23:13:53
...most excellent !
Sounds (sic) like a good alternative  area heating mechanism , or very focused , internal-target heater . The medical and industrial applications could be many-fold .
 If thine appendix offends thee , cook it in situ , THEN pluck it out !
P.M.
Title: Re: Do sounds add together to make louder sounds?
Post by: evan_au on 23/04/2019 00:29:06
Quote from: Professor Mega-Mind
Each emits an identical sound-wave , perfectly out of sync . All sound is perfectly cancelled out
This is not correct.
The sound emitted by the speakers may be out of sync, but the speed of sound is not infinite.
So the points equidistant from the speakers will have cancellation, but points slightly away from equidistant will not have cancellation.

In fact, the points with zero amplitude will be balanced by the points with doubled amplitude.

Quote
in a perfectly sound-reflective room
You need to do this experiment in a perfectly sound-absorbing room (anechoic chamber).

Otherwise, the sound energy injected into the room will just build up forever, causing the speakers, amplifier and room to eventually self-destruct.
See: https://en.wikipedia.org/wiki/Anechoic_chamber
Title: Re: Do sounds add together to make louder sounds?
Post by: Professor Mega-Mind on 23/04/2019 04:27:42
...the limits of noise cancellation !
Your explanation actually brings in another possible use ; sonar for the blind . The return wave's characteristics would reveal the direction and distance to nearby objects . The subject would hear nothing , until an object approached , then they would hear what YOU said !
So now it's a room heater that also tells you what is in that room .
Unnecessary Zoom , unnecessary zoom !
D.H.
Title: Re: Do sounds add together to make louder sounds?
Post by: evan_au on 23/04/2019 11:16:17
Quote
sonar for the blind . ... . The subject would hear nothing , until an object approached
Some blind people already use sonar by clicking with their tongue and teeth.

They hear little reflection (maybe the path they are walking on) until they get near a pole, building, car, etc, when they hear a reflection.

Quote
The return wave's characteristics would reveal the direction and distance to nearby objects
I saw this blind man on TV walking along the street, successfully recognising cars, tree trunks and shrubs beside the path by the way they reflected sound. Here he is in Brugge...

Title: Re: Do sounds add together to make louder sounds?
Post by: Professor Mega-Mind on 23/04/2019 12:19:37
...on the same page...
If the blind person moves , or turns themselves , the return-patterns should change , thus indicating the object's direction/distance . It is a stereo effect .
P.M.
Title: Re: Do sounds add together to make louder sounds?
Post by: Bored chemist on 23/04/2019 13:50:11
All sound is perfectly cancelled out .
It isn't.
Where does the energy put into the emitted sound-waves go ?
In the limit it either escapes through, or is dissipated as heat in the loudspeakers.
Some will be lose by absorption in the air.