Loudspeaker measurement

This measurement is especially important because loudspeakers, being transducers, have a higher level of distortion than other audio system components used in playback or sound reinforcement.

The measuring microphone is normally mounted on an unobtrusive boom (to avoid reflections) and positioned 1 metre in front of the drive units on the axis with the high-frequency driver.

At low frequencies, the ground reflection is always in-phase, so that the measured response will have increased bass, but this is what generally happens in a room anyway, where the rear wall and the floor both provide a similar effect.

all strongly alter the perceived sound, though this is not necessarily consciously noticeable for either music or speech, at frequencies above those dominated by room modes.

Complex effects, such as stereo (or multiple channel) aural integration into a unified perceived "sound stage" can be lost easily.

Thus, there is no assured procedure that will maximize speaker performance in any listening space (with the exception of the sonically unpleasant anechoic chamber).

Horrendous though the resulting curve generally appears to be (in comparison to other equipment), it provides a basis for experimentation with absorbent panels.

This means the microphone must be positioned precisely equidistant from the two speakers if 'comb-filter' effects (alternate peaks and dips in the measured room response at that point) are to be avoided.

Loudspeakers differ from most other items of audio equipment in suffering from colouration, the tendency of various parts of the speaker — the cone, its surround, the cabinet, the enclosed space — to carry on moving when the signal ceases.

Initially, an analysis was performed using impulse response testing, but this 'spike' suffers from having very low energy content if the stimulus is to remain within the peak ability of the speaker.

[5] Using multiple sine wave tones as a stimulus signal and analyzing the resultant output, Spectral Contamination testing provides a measure of a loudspeakers 'self-noise' distortion component.

This 'picket fence' type of signal can be optimized for any frequency range, and the results correlate exceptionally well with sound quality listening tests.