Noise-cancelling headphones are nice. They use little built-in microphones to pick up the ambient sound, and, along with the music, feed the opposite of that sound into their speakers, thereby cancelling out the noise of the world.
Good headphones also have a lot of passive noise-deadening insulation built into them. Which means that when you do want to listen to the outside world, and you roll down the volume on your music, you can't hear much. So you have to take the headphones off.
This idea is simply to use those built-in microphones to hear outside sounds when needed. Install a switch and circuit in the headphones that lowers the music and changes the mike circuit from "cancel" to "transmit".
The mike circuit should set the sound level to less than the music was, on an adjustable volume setting. The mikes could still filter out high and low frequencies.
(I couldn't find this in a search. It's easily buildable.)-- baconbrain, Mar 02 2008 Sony Ear Buds http://kunarion.com...ry/SonyMDR-NC10.jpgSee the large gray "monitor" Noise Cancelling Cancellation Switch on the amp unit. [Amos Kito, Mar 03 2008] It's a great idea because of the simplicity, but it's not that much of a problem. However, if it could amplify speech and filter out other sounds it would be great for listening in to people's conversations while looking like you are listening to music. Also handy in a light aircraft when the engine is running and you are trying to talk to ground staff.-- marklar, Mar 03 2008 Hm. There are noise-cancelling head phones with a "monitor switch" that stops the music without you taking the headphones off, but I don't know whether they're using the microphone input.-- jutta, Mar 03 2008 I own earbuds with a "monitor" switch, to cancel the noise cancelling (to hear the unfiltered sounds). This is the Sony MDR-NC10, a discontinued model -- and it looks like the newer ones have no such switch! It's surprising, even jarring to hear all the noise suddenly kick in, especially when you accidentally press it.
[jutta], I performed an audio signal test on mine just now (tapping an ear bud mic). I can hear the tap in the other bud speaker. No sound when tapping on the base unit (which houses the switch). So the ear buds use their own built-in microphones when I press "monitor".
Something occurs to me about this switch: When I want to listen to the outside world, I remove the ear buds. More important: When someone speaks to me, I still have to remove an ear bud! Otherwise, the person thinks I'm ignoring him. The switch gets used most, unintentionally.-- Amos Kito, Mar 03 2008 Dang! I never thought of the word "monitor" when I was looking for this. That's one of the fun things about searching the net, you need the right words. Thank you.
I just searched for "monitor switch headphones" and found many examples, and several differences in them. It's not always clear, just from the catalog descriptions, what is involved. Some seem to be set up very poorly, but some probably do exactly as I describe/wish. I certainly thought it was an obvious need and easy to include. "Monitor".-- baconbrain, Mar 03 2008 How does that cancelling thing work ? There must be a time lag between the ambient sound and the anti-phase sound that's supposed to deaden it ?-- Pintsgrove, May 21 2008 random, halfbakery