About Sound - by Michael

What is the basis of a sound impression?


We hear changes in the pressure of the medium surrounding our ears. The sequence of incoming vibrations provides the information for the sensory perception and the detection and location of the sound sources. This information is the basis for a sound impression.


If something changes in the sequence of the vibrations, the sound changes. Sound transmission is information transmission!


Let's look at natural sound events. The three graphs below are from a percussion instrument. Depending on the type of stroke and the damping of the vibrations, the sound character changes.



A natural sound event begins with a transient, a characteristic sound and then subsides in the direction of the sound source's resonance. The first waves are the loudest sound vibrations in natural sounds. The ear reacts to an abrupt pressure change with greatly increased nerve activity. This is an indication of how important these first sound waves are to our perception. The transients and other short sound events usually reach the listener as direct acoustic sound without influence from the environment.


Clapping of the hands


The first graph below shows the sound waves from clapping. It is an extremely short sound event. Sound events of this length are completely transmitted as direct sound. Spatial influences have no influence on the transmission of the information at all. You've probably already experienced how different speakers sound when reproducing applause. The reason is that applause is a sound with virtually no post oscillation. The pop of hand clapping has no poriodic signal components and the decay is very muted. Loudspeakers must therefore be able to reproduce the correct waveforms within the first millisecond.


For comparison - the step response of a loudspeaker shown in the second graph below is always longer than that of the clapping.



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