we can use RF receiver to receive RF signal. but, can we use RF receiver to detect sound wave? Reason why?

Question

i was assigned to detect a sound origin in a closed room. i have to develop a device, which is able to detect the sound origin outside that closed room. the sound source (mono-tone) is from a normal sound generator, with a known frequency, may be is 1000hz, 10khz or 20khz. the wall is a thick masonry wall.

so, is it possible for me to use RF receiver to detect that sound origin outside the closed room? what type of antenna i have to use? what kind of problem i would face?

Answer 1

RF - no, not directly. Other answers have explained why (a sound signal isn't a radio signal - RF is variation in electric and magnetic fields, sound is variation in pressure).

One answer has described what's effectively an electronic sonar system. An alternative is a mechanical sonar : get a directional microphone (or a microphone with a long tube on the front to make it directional) and spin it around in a circle. It'll be loudest when directed towards the source.

If RF is what you want, there is an option - measure the effects of the sound on the walls. They may be "thick masonry walls" but if the sound gets through they must be vibrating. Bounce a high frequency RF signal off them and compare your transmit signal to the reflection. Use high frequency because the wall's vibration will be tiny - you want as short a wavelength as possible to make the effects more obvious. Now spin that around so that you "target" different bits of the wall and look for maximum vibration as with the mechanical sonar. To make things even harder you could go for an electronic system with multiple antennae, but I don't recommend it!

Note that this - and any other solution - ignores the fact that the walls will vibrate most away from joists, so the "source" you see may be the centre of the wall closest to the real sound origin, regardless of where abouts behind that wall the origin really is.

Answer 2

RF (Radio frequency) is an electromagnetic wave.
Sound is a physical movement of the air (you could consider this a vibration, or a pressure change)

An RF receiver detects electromagnetic waves using an electrically conductive element that is of a similar wavelength to the signal - an antenna and amplifies this signal directly as it is electrical in nature. It cannot receive sound directly as it is not electromagnetic energy.

A sound wave will need to be converted to electrical energy via a transducer - commonly a microphone (think of a mike as a sound antenna). so you could connect a microphone to an amplifier (such as your stereo system)
To determine the direction, you will need at least 2 microphones, separated by a distance. Think of the sound wave as a ripple in a pool. If the source is square and centered in front of the 2 microphones, it will reach both at the same time. If it is not, then the sound will reach one microphone before the other. This can be observed by attaching an oscilloscope to the 2 microphones and observing the relative phase of the 2 signals. When the sine waves that you see line up, the sound source is equidistant from the 2 mikes. One thing you have to be careful is to set the separation distance so that less than one wavelength of relative separation occurs, as otherwise the 2 mikes could appear to be receiving a signal in alignment, whereas they are receiving one whole waveform later/earlier. The best rule of thumb would be to separate them by a quarter wavelength.

you could also do this by mixing the 2 signals and listening to the beat frequency rather than using test equipment. If the 2 microphones were attached to a pole on a pivot, you could rotate the assembly until you here a pure tone with no beats, at which point of the source in directly in between the 2 mikes (either in front or behind). To tell whether the source in in front or behind us a directional mike - it will be louder from the front, or use an array of 3 mikes.

you could even do this totally in the sound domain with 2 funnels, and some tube. mix the sound together by connecting an equal length of tube to each funnel and join them both to a third funnel that you listen at.

Answer 3

No. RF is a radio wave, a vibration of the ether. A soundwave is a vibration of the air. Two different media. A RF receiver is commonly known as a radio. Sound is commonly detected by a microphone. If the sound generator and you are separated by a thick masonry wall, then its sound would be inaudible, unless the output of the generator is earsplittingly high. Now, if you're talking about a RF generator with its RF signal modulated by a soundwave, then yes, you can tune your receiver to that particular frequency through the wall, No need to develop the device, just use a portable radio with a built-in ferrite stick antenna and rotate the radio to minimum strength and the ferrite rod end will point in the direction of the transmitter. Do this from two different positions, and where the imaginary lines drawn from the ferrite rod ends cross, that's where the transmitter is located. Hope this helps.