Sound method
To artificially generate a 40Hz frequency within the brain, I've employed wide binaural sounds. This technique involves panning two distinct frequencies, one to the left and one to the right. The brain then synthesizes a third frequency, centered between the two, creating the desired 40Hz effect.
There is more info about binaural sounds on WebMD.
You can use the music also on the Next Wave Physioacoustic chair.
Playback
Due to the low frequency, a high-quality subwoofer or decent headphones is recommended for optimal playback.
Hit the play button and relax.