noise canceling circuit

My office is next to manufacturing machinery that makes a continuous noise all day long. The monotonous tone is very distracting while trying to talk on the phone to customers or even thinking by myself. I need a noise canceling circuit. Something to do with inverting op-amps I suppose. I think the input mic level should be adjustable as well as the output speaker level for tuning. Can anyone help a simple circuit design? My electronics experience is probably antiquated therefore simple is better for me.

Thanks

Interesting concept. Noise cancelling for earphones is complex although available from Bose for about $300. Doing this for an entire office would be strange (to me). Theoretically, every sound emitted would be quickly matched with an opposite cancelling sound. So the sound coming through the walls would not be heard. Of course, so would every other sound in the room. Would you be able to hear yourself speak? Weird idea! How about proposing a layer of soundproofing on the wall instead?

If you ever find your way to a pub called the "The White Heart" you may here the story of Arthur Clark's "Fenton silencer" but on a more practical note this might be what you are looking for.

https://headwize2.powerpill.org/projects/noise_prj.htm
Noise cancelling headphones

Noise cancelling works for headphones because the space involved is small. It works by picking up the noise with a microphone, inverting it and playing it back through a speaker. The generated sound waves destructively interfere with the incoming noise and "cancel out" some of it.

Getting this to work for a larger space won't work without hundreds of small set ups across the room and even then you're not going to have much luck.

I read a good article on how airliners use this to cut down on cabin noise. If the noise is a steady drone you might be able to cancel that out same way as the arilines