The current data is based on keybed noise tests of my M&H BB piano, conducted for interest as the result of a question on Piano World Forums.
All pictures below are high resolution and can opened in a separate tab for zooming.
The 3D graph below shows the impact noise spectrum from 1Hz to 21,000Hz (horizontal axis) for 8 notes, C1,C2,…C8 that have been dampened using felt or rubber mutes. Each impact has a recorded length of approximately 2 seconds. This impact noise is part of the total piano sound and is an important part of the aural experience.
The piano is, after all, a percussion instrument.
If you listen closely and with the volume turned way up, you can hear the full spectrum noise. It appears that the entire piano structure absorbs and reradiates the key/hammer impact energy over a large and predictable frequency range for this piano.
Selected notes recorded on the piano and shown in graphic form.
The graph on the left of each picture is a DFFT Frequency Domain Spectrum of a single note. It clearly shows the amplitude of each partial ranging from the fundamental (1st partial) to the Nyquist Limit of the Sample Rate.
The 3D graph shows the impact noise ‘fence’ and the decay over the sample length of the various partials. Most of the 3D graphs show two sample periods of the same recording and maybe part of a third. They are obvious and easy to separate.