Below are two spectral decay (“waterfall”) plots, which show the response behaviour of a loudspeaker. The x-axis shows the frequency response from 1000 to 20.000Hz., the y-axis shows level in dB and the z-axis shows the time in milliseconds (decay).

This is the response of a 2” state-of-the-art” compression driver. It is clearly visible that the initial frequency response changes at around 8kHz. The time-(impulse)response shows that the membrane of the speaker is still generating sound, even after the signal has stopped. This is due to the heavy moving mass of the compression driver, which causes “time-smear” and distortion. A light-weighted 1” compression-driver shows similar behavior, but at a higher resonance frequency.