Experiment IV – Piano

Date of Experiment: September 19, 2011

Purpose + Introduction:

To graphically identify the difference in colour of sound  and amplitude from the vibration of the strings and soundboard to what we hear.

Results + Observations + Data:

The recording below is of an upper C played on the piano split up into 3 different channels:

  • Input 1 (piezo microphone on strings)

  • Input 2 (piezo microphone on soundboard)

  • X/Y H4n recorder microphone (airborne sound).

Shown below are graphs generated from Audacity which show different types of information.

One aspect that is not surprising on all the spectrograms above is the fundamental frequencies are the same, since they all are recording the same note.  Most of the differences that do occur between the 2 piezo recordings.  Note how Input 2 has a stronger ‘white amplitude’ over Input 1.  This is most likely from the better resonance effect of the soundboard over the string.  Input 1 also shows a strange horizontal line and wavers on and off at around 1.5 kHz.  I do not know the reason for that, but I can guess hypothesize that another object, like the pin holding the string, is vibrating at another frequency and is causing deconstructive and constructive waves.

I was very surprised when I saw the difference graphically in the amplitude of the waveform in Input 2.  This is most likely the case of ‘hitting the sweet spot’ – the exact location of where the bridg elies on the soundboard.

Again, I’m not very surprised that the X/Y H4n waveforms look almost exactly the same, but after listening to the audio file I was expecting to see similar waveforms.  I was wrong.  Again, I do not know the answer to this, since all of the audio clips sound like a string vibrating

However, some of these differences in amplitude from one piezo recording to the other is that one is connected to a few strings, while the other is connected to the soundboard, which is in contact with all strings.

Also, taping down the piezo microphone is not the best attachment method for recording.  This may cause additional vibration from the microphone itself, and may not have full contact with the vibrating object.

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