1. I listen to YouTube videos without headphones at night. I can feel it but I think it's more subtle. One of the frequencies I picked wasn't sitting well with me so I let it play a bit but chose another one to play while sleeping.
I'm not sure you'd need or want to turn the volume all the way up to where you need ear protection. They say it's better to listen with headphones but I don't have a comfortable set of headphones to try falling asleep too.
2. You will have some benefit, limited by the frequency range of your speakers - which is generally between 20-20000 Hz. Your subwoofer may deliver lower frequencies than 20 and the tweeter higher than 20000.
In this case, I think it's better to send the frequencies through your speakers than through a headphone, so your whole body receives the sound waves, not only your ears and brain.
(Brain wave attunement sounds with binaural beats and silent message technology requires to listen to those through a headphone. But that's a different story.)
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