Some questions about subliminals

[Dr. Strangelove]

To use earphones for overnight listening, you'll want to make sure they have two criteria met. One is frequency range - 20kHz upper limit is a minimum to be effective. Second criteria is comfort, and in case of in ear monitors, smaller is better. I have 4 pairs of high quality in ear monitors which are sonically superb, but can't sleep with them - unless I sleep on my back all night. Too uncomfortable to have in ear, and have ear on the pillow. I bought a 5th pair, Fidue A31s. Not too pricey, sound OK, not too much noise from cord rubbing on pillow, and they are tiny. Change stock tips to better quality foam tips, and you won't even notice they're in.

Sometime (1 night in a week on average) one slips out of the ear while I'm turning in bed. If I'm listening to silent track, I won't even notice until morning. Also, when listening to silent track I was compulsively checking if it's on all the time, or I accidentally turned it off. Running stream track is now all I use for night time.

And then I top that with a few hours during day. More is better.

How will I be able to determine the frequency range?

You'll find this on headphones box/packaging, or on the product's web page. The manufacturers would call it frequency response as well. This is for Fidue model I use:

•Frequency Response : 18Hz-20kHz

Lower frequency (18Hz) refers to bass end to spectrum; less is better for listening to music, but not important for subliminals. Higher frequency (20kHz) refers to higher treble range. Above 20kHz, it's debateable if most people can hear these high frequency sounds. Younger people with their hearing still intact might do. Shannon recommends to get higher range (>20kHz) headphones. Still, 20kHz for upper limit is acceptable. Quote: You should use speakers/headphones/ear buds that have a frequency response range of at least 20 kiloHertz, and higher is better.