Mahipat Singh said:
Could we collect Sound waves in a machine or any sonic instrument ?
If yes, than we can reproduce it in Electric energy !
The answer is, as said earlier, YES - - - BUT.
And that 'but' is so very relevant, because it's all a matter of 'how much energy?' These things are only worth doing if you get back the cost of doing them.
All microphones convert the sound that hits them into electrical energy. If you put a microphone at the focus of a large paraboloid reflector then you will direct more sound energy onto it and, hence, get more electrical energy out of it. However, the principle always applies that you will never get more energy out of a system than is put in.
Having established the principle then you have to consider whether it's a worth while exercise. How much sound power is available? Let's get things in proportion. We sustain permanent hearing damage if we're exposed to sound at a level exceeding 1mW per square metre. To collect just 1W of power from sound at that level, you would need 1000m
2 of collecting area. (Worth it? - I don't think so) And, in any case, where could you fit a collecting area of that size or what source would actually be that loud at a suitable distance where you could fit a reflector that big?
Normal levels of sound noise around us are around one thousandth of this level so, without deafening ourselves, we would get just 1mW from the same collector. People don't seem to realize just how important the actual NUMBERS are in discussions like this.
There are places where the sound levels are higher than the level for hearing damage. A jet engine (an old fashioned noisy type,I suspect), 30m away, produces 1kW per m
2 in the 'loudest' direction but how would you gather it? There's no way you could have a 30m/30m collector anywhere on an airport (start of a runway? Joke) and for how long per day would it be collecting this energy? The fact is that modern jet engine design has vastly improved efficiency, due to the fact that the air flows through it differently and it just doesn't produce so much noise. This has reduced sound noise AND all the time the engine is running on less fuel! There is far more benefit from preventing the production of sound noise than you could ever get by (trendy word coming up) 'Harvesting' sound energy.
People are quite happy to believe that Engineers get it right when designing electronic systems, aeroplanes and electrical power distribution. They get it right because they Do the Sums with the available Figures. They don't say "let's build a power station - I've drawn a sketch of what it will look like so let's get started". They do serious calculations involving structure, fuel supply and expect levels of generation eetc.. If just one part of the design is not right then the power station (aeroplane / TV / city / car) will FAIL and cost someone a lot of money (or a life).
The Figures involved in Harvesting sound energy indicate that it is just not worth it. If someone can suggest a situation where it should be considered and there is actually a significant amount of free, 'concentrated' sound energy around then they need to suggest some figures for just how much power would actually be available and what it would cost to 'collect it'. I am not aware of a single 'sound harvesting' scheme anywhere (and there are some very wacky alternative energy schemes about) and I am not at all surprised, because the numbers just don't add up. When the total energy needed to produce a system is greater than the total energy it will produce over its life then you need to ask questions. (Oh boy, did someone say Nuclear?)