In my own experience is a very interesting experiment to modulate frequencies until it resonates with one's own voice.
I had the privilege of having at disposal a room roughly 5 meters by 4 , which was almost empty and had a square shaped shelf that would host my Bluetooth speaker roughly at the very centre of a wall (blasting the sound/ music longitudinally). Since the room was almost empty ( apart for my desk and maybe two shelfs ) I quickly found out that my mantras would be amplified by the eco , and that in the very opposite extremity of the room , music or frequencies would sound almost louder than near the speaker itself.
TANGENT : I'm pretty enthusiastic about the acoustic proprieties of ancient structures ( such like the king's chamber of the great pyramid in Egypt, or the big corridor leaving up to it ) so it wasn't long until I understood that most probable those structures would've been used as sonic amplifiers , either for the human voice or other natural sources of vibration ( even the Earth itself has a natural constant hum).
Anyhow , back to the experiments : I used a modulation app (nothing special) and casted frequencies ranging from 63Hz to 630Hz ( usually 2 at a time ) in a combination such that it reverberated with my voice while chanting long "IAO"s or other mantras. To my ears it sounded like though my voice split into multiple voices chanting the mantras at the same time. It was pretty cool.
The frequencies I played with most were : 63 Hz , 126 Hz , 81 Hz ( but anyhow most probably the size of the room influenced a lot the choices )
Very cool, thanks for sharing this experiment!!
I can scan the acoustics of a room, and even recreate the natural reverb that is within by creating an IR, or digital "snapshot" of it, that can be used on any future recording. This same technique has been used on many modern albums.
Also, with modern EQ, it is easy to see frequencies from 10Hz to 24Khz, which is about the range of healthy human hearing. Frequencies below that are usually 'felt' rather than 'heard', although a subwoofer (bass speaker) will translate them.
Also, certain objects will vibrate with one another from across a room, such as two guitars. I think this is why we become "attached" to those we love (for better and for worse).
And now that I think about it, there are Mongolian chants that produce two notes at a time (harmony) via 'throat singng.'