Sound Level Meter microphone, positioned 10cm above the hammer strike, next to mic 7.
Four notes, C2, C3, C4, C5, were sounded by the electronic striker at three velocities, v20 p, v54 mf , v81 f. The calibrated velocities of the electronic striker ensured a consistent strike velocity for each of the piano sounds, Sound level metre & Electronic striker Fig 3.3

The directivity of sound projection is the direction in which the sound is radiated out from the instrument. The directional passage of travelling sound waves influences how the sound is humanly perceived.

When we hear music, the perceived tonal impression is caused by sound carried to our ears by the air. Relevant in this context are the minute pressure variations which are superimposed on the stationary pressure of the air surrounding us. The pressure variations propagate as waves in space. These more or less periodic deviations from the stationary mean value, comprise the so called sound pressure variations, for which in practice the shorter term ‘‘sound pressure’’ is used. ²²⁰

Sound pressure is measured by decibels, (dB) which is an algorithmic scale that measures sound pressure with the vast and intricate range of human hearing, 16Hz- 20,000Hz. Sound pressures converted to the decibel scale are called sound pressure levels, abbreviated Lp.

The levels of loudness recorded by microphones in the arrays were calculated by the VSLM in two categories-

1. Lp : the measure which describes the peak pressure levels in dB, to register how the sound power of the source is radiated within the array.
2. leqA – Equivalent Continuous A-weighted sound pressure , which gives a reasonable approximation of the human perception of loudness, averaged periodically over the designated duration of the note, measured in dBA_A.

Inside the piano, a sound level microphone is positioned to record the sound pressure level of the instrument in Leq, equivalent continuous sound pressure level [dB] a calculation performed on time domain data, to provide a level of the instrument’s volume.

²²⁰Meyer,1.