# Any help or guidance would be appreciated

Discussion in 'The Projects Forum' started by maxster03, Mar 22, 2014.

1. ### maxster03 Thread Starter New Member

Feb 19, 2009
3
0
Hi Everyone,

Let me first start by thanking you for trying to help.

Okay, I am currently working on a project which is to design a virtual sound barrier by using microphone and speakers. To put it in easy words, I am trying to cancel out noise by creating the same sound in amplitude but in 180 degree phase shift.

I have to design a circuit board which should amplify the sound and phase shift it in 180 degrees. I know how to do the amplification but I am not sure how I can phase shift it 180 degree. Also if you can let me know if it is possible to make it for 2 channels (i.e for 2 speakers).

I would really appreciate it. Any kind of help, documentation or theory is welcomed.

Thank you

With Regards,
Max

2. ### MrChips Moderator

Oct 2, 2009
12,212
3,276
180-degree phase shift means that the signal is out of phase.
Use an inverting amplifier stage.

3. ### maxster03 Thread Starter New Member

Feb 19, 2009
3
0
would a Inverting Amplifier stage also work on a audio signal (sorry for asking such a dumb question, just wanted to confirm it)

4. ### Dodgydave Distinguished Member

Jun 22, 2012
4,762
705
Yes, use a 2nd op amp as an inverter set the gain the same, and add the signals together.

Like this circuit

5. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,561
1,059
Assuming you have identical speakers and identical signal channel gains, sound cancellation should theoretically occur at a 'sweet' point equi-distant from both speakers. However, since speakers have divergent sound patterns the sound will reflect from nearby objects and prevent perfect cancellation even at the sweet point. Elsewhere there will be little or no cancellation; there will even be sound boosting where waves combine constructively. Can you live with that? If not, could you use headphones instead of speakers, to overcome the reflection problem?

6. ### AnalogKid Distinguished Member

Aug 1, 2013
4,281
1,172
Basically you are trying to create the effect of noise-cancelling headphones in a room. Two things.

#1, in a room you will not get the effect you want over a large area. There will in fact be a sweet spot, but unless the offending noise is way over there and the area you want to quiet is way over here, reflections will severly reduce the cancellation effect.

But the fun part is #2 - you do not have to build anything, add an inverting stage, or do anything special to the amplifier. Just reverse the connections to the speaker and the phase of the produced audio will be reversed (shifted 180 degrees).

Try it with your home stereo. Listen to something you know well that has a full stereo image, then reverse the connections to one speaker only and listen again.

ak