# What am I hearing when I generate a 10 Hz tone?

Ok my curiosity has gotten the best of me… I’m trying to understand the limits of our hearing, which I know varies but let’s just say it’s at best 20-20k Hz. So if I use my headphones which claim to respond/play down to 10 Hz, and I Generate a Tone (Sine, 10 Hz, 1 amplitude) and crank up the volume, I can indeed hear a low rumble… but if I look at the spectrogram (attached), there’s frequencies that go up to 1 kHz, much more than just 10 Hz audio there. The sine wave is 10 cycles per second, so maybe I’m mixing up different kinds of frequencies? What I’m hearing are the parts that are above 20 Hz probably… Is there a way to generate audio without any frequencies above 10 Hz or are there always going to be extra frequencies like that due to the way sound and speakers work? Oh and I’m using Audacity 2.4.2 if that matters. Thanks

Those multicoloured humps are graphic artefacts - a limitation of FFT analysis. If you increase the FFT “window size” you will see those humps diminish in size:

You are probably hearing harmonics of the 10 Hz sine tone. Basically you can hear the headphones shaking rather than the actual signal.
Interesting fact: Earthquakes are silent - earthquake tremors are typically in single figure Hz, too low to hear. What you actually hear is the things that are being shaken (and broken) rather than the earthquake itself.

You are probably hearing harmonics of the 10 Hz sine tone.

Yeah. That’s the speaker cones rattling.

Have you ever been to a cathedral or very large church during services and heard that soft but powerful, shake-your-shirt, pulsing thunder sound? That’s the 16 foot organ pipes. That’s 33Hz. Half that frequency is going to sound like gentle breeze. It might wake up the cat (no promises). Won’t do a thing for you.

Koz

but if I look at the spectrogram (attached), there’s frequencies that go up to 1 kHz

Those multicoloured humps are graphic artefacts - a limitation of FFT analysis. If you increase the FFT “window size” you will see those humps diminish in size:

I can indeed hear a low rumble…

You are probably hearing harmonics of the 10 Hz sine tone. Basically you can hear the headphones shaking rather than the actual signal.
Interesting fact: Earthquakes are silent - earthquake tremors are typically in single figure Hz, too low to hear. What you actually hear is the things that are being shaken (and broken) rather than the earthquake itself.

sorry for the little offtopic answer but I just couldn’t pass through this info
not all earthquakes are silent
only the ones that are happening deep below the surface
around 60 miles deep

not all earthquakes are silent
only the ones that are happening deep below the surface
around 60 miles deep

Yes, but.

There’s a movie-making experience here. You can’t “show” an earthquake by presenting low pitch tones. The audience, particularly the US West Coast audience, knows immediately you’re presenting a bad fake. Yes, it’s possible to get a low growling sound during a shaker, but you’re much more likely to get a funny feeling in your tummy and look up to see the hanging ceiling light swaying—all perfectly silently.

You know what drives the cat nuts in a pet carrier? The motion. They’re experiencing a 1-3 Hz earthquake.

The other common natural phenomena is thunder, for those that have weather. It’s not all “clap of thunder.” You can also get the windows rattling divorced from the audible rumble. That, too is shock wave below 20Hz.

The auditory phenomena is a lot like trying to listen to a very gentle breeze. Wind is zero Hz sound.

Koz