Ken,
If it's a full 88-key keyboard, it depends on how big or good the speakers are in the electronic piano. There might be some output at 28 Hz but I doubt it's audible. Sometimes with some of these very low frequencies from instruments, when you look at the spectrum analysis of the fundamental and harmonics, the actual fundamental is often at a much lower level than the harmonics. That's true of the largest pipe on some pipe organs. Although the fundamental is at 16 Hz, it's at a low level. The 2nd harmonic at 32 Hz is much louder, so that's what we hear even if the speaker doesn't begin to reproduce the 16-Hz fundamental tone. The latter is called "the phantom fundamental".
Alan
