The sensitivity, being the major characteristic, is determined and normalized to 1W input power and a distance of 1m. Below the frequency limit of the anechoic chamber (approx. 100Hz), the curve is joined to an appendix from near field measurements of the membrane and the reflex port. In addition to the magnitude of the sensitivity, the phase is displayed.
The maximum sound pressure level plots the highest possible SPL against the frequency, with a given maximum power and a maximum fraction of non-linear distortion. The measurement is performed with sinusoidal signals, gradually raising the voltage, while SPL and percentage of distortion are being evaluated.
One important and often underestimated characteristic is the directivity. Single parameters like "60° horizontal" only give a vague information about the spatial pattern of the sound emission. The directivity should rather be displayed against the frequency, both horizontally and vertically. To accomplish this, measurements are made with the rotatable arm (ELF-System) or, in case of very large speakers, clusters and sets of line array elements, on a rotating plate.
Standard measurements for data sheets are:
|Sensitivity||Magnitude, phase, average sensitivity
|Impedance||Magnitude, phase, minimum, if applicable: tuning frequency
||at 3% and 10% THD, calculated maximum SPL from sensitivity
|Directivity||horizontally and vertically
Additionally the following measurements can be included in the data sheet:
- Sensitivity, impedance and directivity of the individual channels
- Frequency response of the passive crossover network
- THD(f) (Total Harmonic Distortion) at multiple input voltages
- Power compression