Sensgard has rolled out its ZEM headphones. They come with a simple amplifier that will reproduce purer sound and cancel background noise using a proprietary technique from acoustic researcher Dr. Jozef Zwislocki. The noise cancellation doesn’t require any power, instead using a physics-based sound filter which reduces noise in low and high frequency ranges.
Since there is no electronic gear involved with that, the cost and weight of the headphones are reduced. A few small, electro-magnetic receivers work as electro-mechanical amplifiers, delivering a frequency response between 20Hz and 20,000Hz and a sensitivity of 110.5dB at 1,500Hz.
You can get the Sensgard ZEM headphones for $90.