Instruments that play <= 40Hz (E1) include double bass (either standard or with C extension), bass clarinet, and contrabass clarinet.

Percussion also generates frequencies under 40Hz.

And percussion generates sharp transients, which require frequencies below the steady-state fundamental frequency to be reproduced accurately:

https://en.wikipedia.org/wiki/Uncertainty_principle#Signal_p...

Also octobasse and subcontrabass saxophone…although most people won’t get a chance to actually hear those in person.

Piano too if there is one. The fundamental frequency of the low A is 27.5Hz. A Bosendorfer Imperial grand piano goes down to C0, 16.4Hz.

If there's a pipe organ with 64' pipes you can hit 8Hz. Not many of those though.

Plenty of organs go below 20Hz though, and even an otherwise good sound system starts to struggle around 40Hz if it's not built specifically for playing such notes.

Dumb question but how is the piano capable of generating these frequencies? I thought the strings couldn't get nearly long enough and the low frequencies that you heard from piano were just psychoacoustics.

The bass strings are wound with copper wire so that the mass is much higher and the resonant frequency much lower.

The amount of space needed for a certain frequency in air is different to the length needed for that same frequency in a wire.

It might help to see the formula, which is:

Frequency = sqrt(tension/(mass / length)) / (2 * length)

So length, tension, and mass are all factors. Modern upright pianos also string the bass strings diagonally to give them a bit of extra length.

I can almost imagine seeing the low bass string on the longest piano vibrating. The frequency is so low you can pick hear the peaks and valleys.

I imagine it's the space itself resonating more than anything else, being excited by higher-frequency harmonics.

I'd say timpani drums, tubas, largest/lowest pipes on an organ (if the hall has one), and double bass. Contrabassoon, the lowest notes of a piano. Other percussion like a gong.

Basically, by necessity, whatever the largest instruments are in diameter or length. And then it's all being amplified by some mutual resonance with each other and possibly other physical structures like the floor.