Here is how I’ve made some simple but effective noise-suppression headphones.You need a pair of old headphones and a pair of hearing protection earmuffs. My earmuffs were really cheap, 4€, so this will be very cheap noise-suppression headphones.
The active, noise-cancelling headphones are more expensive and they function differently. They use batteries for the noise-cancelling function. A mic (or two?) records the ambient noise. This signal is then processed by the internal electronics into an opposing signal and this signal is feed into the headphones. You ears will hear the noise coming from outside, and the processed noise coming from the headphones. This two sounds cancel each other out and so you hear nothing (silence).
Anyway the prices for active noise-cancelling headphones vary from 100€ to 300€ so let’s build some simpler noise-suppression headphones. From what some people say, the noise-suppression headphones are more effective! (I have no way to know this because I don’t have noise-cancelling headphones).
I removed the foam from the earmuffs and placed the speakers under the foam. This affects a little the quality of sound but you can balance that from the equalizer. Also you could place the speakers on top of the foam if they are not that big and there is room for them.
Be very careful when you work with the tiny wires coming from the speakers. Do not burn them with a flame (to remove the insulation) because the flame will melt the wire.
You also need to figure out which speaker wire is the positive one and which is the negative one. I’ve done this with a dead cell battery (3V). Connect briefly the plus from battery to one of the wires and the minus to the other. If the membrane pops out, then the first wire is the positive one. More information here.
The rest you can figure out from these pictures: