Step 1: The Block Diagram

The signal path can be seen in the block diagram above. First, the noise is passed into the mic where it goes to a preamp then an all pass filter to delay the signal.  Finally the noise is input to the summing amp and added to the music signal. This stage also inverts the noise as a summing amplifier is a special case of the standard inverting amp.  The amplitude of the noise is determined by this stage and must be tuned to achieve proper noise cancellation.  The inverted noise plus music signal is then played through the headphones and cancels out the unwanted noise. The next steps explain each stage further.
<p>Thanks for this useful reply ... </p><p>I have just created an negative voltage power supply using a NE555 IC but it is producing 2 volts less than that of the +ve supply (+9V and -7.8...) and after testing its output to it a producing a tremendous high frequency noise ... </p><p>I cannot understand why it is happening, I have just tested all the values of resistors, capacitors... they are just okay (approx.)... Is that happening for my op amps TL701 s</p><p>Presently I am following that reply creating a supply using two 9 V batteries...</p><p>I that DC noise? I just want to know... please reply... </p>
<p>Great project, thanks for posting. I'm going to build this over the holidays. However, I noticed you are not using audio amplifiers for this but instrument amplifiers. Was this a conscious choice or just what you had 6 of in your tool box? Even the data sheet of the LT1055 is conspicuously lacking audio as a suitable use. Wouldn't something like a high-performance audio OpAmp like the OPA4134 be more suited for this project?</p>
I have just completed one circuit, but cannot understand how to power it, I am using 9V DC battery, could understand the Vcc+ , Vcc- and gnd... can u explain it? And another think is that I am using TL071 OP AMPS in place of LT1056 ... does it works?<br>
<p>MalharC, </p><p>The +VCC and -VCC and GND mean you require <em>two</em> 9V batteries. (<em>If you don't set up a voltage divider shown </em><em><a href="http://www.instructables.com/id/How-to-create-voltage-using-one-power-supply/" rel="nofollow">here</a>)</em><strong>. </strong> The easiest way to set this up with two batteries is to: connect two 9V in series: the + of the first battery becomes VCC+, the - of the second battery becomes VCC-, and the <em>shared</em> connection becomes the GND line. This allows for both + and - current to flow in the circuit. </p>
<p>If i connect another mic to the music input pin, whether the intensity of sound at the speaker will be minimum...?</p>
<p>The music input pin is part of a summing, inverting amplifier, meaning it will add in the signal picked up from the additional microphone. The signal from the additional microphone will also be inverted, however it will not be delayed at all from the all-pass filter, which makes for un-synchronized signals, and would probably just make things louder. Also, it would not be amplified, unless you used microphone breakouts with amplifiers built into them, such as <a href="https://www.adafruit.com/products/1063" rel="nofollow">this one</a> from Adafruit. </p><p>Hope this helps!</p>
<p>i just want to cancel the noise in my room,is it possible to just cancel out the noise in the room without using all pass filter..</p><p>do i require all pass filter to just cancel out the noise? </p>
<p>The all pass filter is a necessary step. If not, the &quot;anti-noise&quot; signal that is being generated here will be produced too quickly to actually match up with the &quot;heard&quot; sound waves. Electrical signals travel near the speed of light, which is ~300 million m/s. The speed of sound is only ~343 m/s. As such, the all-pass is vital to these headphones functioning properly. If not used, the anti-noise and noise signals will not match up, and thus not cancel properly. </p><p>Does this help?</p>
<p>built this with some tweaks. </p><p>attached microphones to regular earbuds and achieved decent results. I did not use the current limiting resistor at the output, however i am only producing the noise cancellation signal, no music added. Also switched R7 to a 5K bourns 10 turn pot, and R6 to 100 to keep the gain ratio of 50:1. The 10 turn pot is expensive, but allows for precision adjustment. R4 has also been changed due to slight distance differences from step 5. Used only ceramic caps for ease of assembly. </p>
can I just produce the counter frequency without the music as input.<br>
<p>Yes, you do not necessarily need the music to be playing. In fact, for initial prototyping and at the early stages of this project we didn't use music to make sure everything was working properly </p>
<p>I have a project I would like to build involving a noise cancellation circuit. Thank you so much for this intractable. I'm not an electrical engineer by any means and this is a great project to start learning circuits. So a couple questions. I'm looking at the full res photo and seeing that there are several versions of the LT1056 chip and while you call for 6 total there are 9 on the board. Several 1222s and 0537s. I don't even know what these numbers mean and I'm having a hard time googling it (likely because I don't even know what terms to use). I'm also looking to build this with speakers instead of headphones (I understand the limitations of noise cancellation but this will be in a small, very controlled environment) so I wanted to ask about how and at which point can I introduce more amplification? Third. Can anyone point me to a good forum that might be able to help a noob with such a build so that I'm not leaving paragraph long comments on great projects like this. Thanks so much!</p>
<p>The full breadboard photo I have 3 opamps that are not in use (I was trying a few things out and forgot to take them off the board). Those other numbers should not matter for this project. In fact, I would think most general purpose opamps would work for this project. I would think that using speakers would be very tough to do because the idea behind this architecture is to use noise that is opposite phase in order to destructively interfere with the noise you hear. This strategy means that the microphone to sense the noise and the speaker/headphone to produce the opposite phase signal must be close to each other. The last stage would probably make the most sense in terms of where to add more amplification (by simply adjusting the resistor ratios to give the opamp more gain). Hope this helps!</p>
<p>I purchased all the parts and they should be here in a few days. You said 6 OpAmps for stereo but in the picture you have 9 it looks like. (I'm completely new to this so i could be wrong)</p>
<p>Hi Vincent, </p><p>In that picture of the breadboard I had 3 extra op amps that are not in use and disconnected. Sorry about the confusion!</p>
<p>Vincent, how did you go with this build? </p>
<p>Is this circuit capable of canceling the human voice over the distance of 10 - 20 meters? (considering, if I place the microphone 2 - 5 meters away from the source)</p><p>I'm trying to come up with a solution to reduce the voice noise coming from a neighbor's small window in a building 10 - 20 meters away from different points of my building.</p><p>Thanks</p>
Is it impractical to raise the noise cancellation above 1Khz? The wavelength at 1K is 33 cm. It would seem possible to raise that to 5K (6 cm) without very much phase distortion. If so, how would the design need to be altered?
We just wanted to set a target maximum frequency for the design, but no it should be relatively straight forward to raise the max frequency which entirely depends on the all-pass. So if you do not even use the all-pass, then the circuit in theory should be able to cancel out any frequency (assuming the distance from mic to ear is negligible). If you do plan on using the all-pass, then you would have to alter R4 and (C2+C3). Once you calculate how much phase delay you need using the equations on step 5 you can use a circuit simulator like LTSPICE to find out how much phase difference there is in the circuit then tweak from there. <br> <br>Great Questions!
I'd be curious how well the circuit would work without the delay, since the wavelengths in question are very small (in the 20Khz range).
We'd be curious too! We added the all-pass because theoretically the noise cancelling signal from the circuit will arrive at your ears faster than the noise (sound) you want to cancel. If the two do not match in amplitude and phase then the cancellation will not work. The delay is small, however, and we'd be curious how much of that you can actually hear.
Did you mean Low Pass Filter? If you are cutting highs, that is the function you need. I.e., &quot;Allows Lows to Pass&quot;. A High Pass Filter cuts low frequencies (below the cut-off frequency).
Yes! I did not mean high pass that's a typo. I'll fix that.

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