# Building a Wave Transmitter

1. Jan 2, 2012

### a.glick

How would I go about building a wave transmitter? Like in the noise cancelling headphones. I want to build a transmitter that absorbs sound waves, reflects them, and then shoots them out creating destructive interference.

2. Jan 2, 2012

### Bobbywhy

a.glick, Welcome to Physics Forums!

You need to call things by their correct names! In all sciences, using the correct term is the only way to communicate ideas with accuracy.

1. Sound waves are emitted by a transmitter. Example: a speaker
3. Audio can be amplified by an amplifier.
4. Sound waves humans can hear is known as "audio"

Noise cancelling headphones receive sound from the local environment. The electrical circuits inside amplify and invert that audio. That is, it is phase shifted 180 degrees. Then that audio is sent to the earphones of the person wearing the headphones. When those waves meet up with the incoming waves they should totally cancel out. This is known as destructive interference, as you said. The result expected is the wearer does not hear any sound from the external enviroment.

So, what you want to build is very similar to noise cancelling headphones, just as you said. You need to design and build a receiver, an inverting amplifier, and a speaker.

Last edited: Jan 2, 2012
3. Jan 3, 2012

### a.glick

so essentially i need to attach a microphone to a speaker. what am i supposed to use to create the phase shift of the wave?

4. Jan 3, 2012

### Bobbywhy

a.glick, Visualize a simplified block diagram with 3 boxes:

1. Microphone
2. Inverting audio amp
3. Speaker

#1 feeds into #2 which feeds into #3.

Use the microphone to detect (receive) the sound you want to eliminate. Feed the output of the microphone into an inverting audio amplifier. Send the output of the amplifier to a speaker. Point the speaker towards the source of the sound. The inverted waves transmitted by the speaker will interfere destructively in midair with the sound waves you want to eliminate. Voila! Sound cancellation!

I suggest you consult with someone who can advise you and guide you through this process. It is not too difficult, but it seems to me you will need some help to make it work.

Last edited: Jan 3, 2012