Something I have seen recently, is the parameter SPLO that I have never seen before. I cannot get a straight answer from anyone because they do not know, and all I get is bullshit. These same people is trying to tell me that the sensitivity parameter is the efficiency of the speaker and this is another bullshit statement.
First, the only thing that I found is that this is a SPLO measurement is specific to subwoofers with a measurement in the range with the application (40 to 250 Hz). This parameter is sometimes larger than the sensitivity and can be deceiving. This is because averaged test output for sensitivity is from 500 Hz to 2.5 kHz vs the focus on subwoofers low frequency.
Now the important thing, is to understand the differences between sensitivity and efficiency, and how these are derived.
Sensitivity, sound pressure in dB, is a physical measurement of the on-axis output, using the reference of 1 watt of pink noise in the range of the resonance frequency (Fs) times 10 with a Crest Factor of 6 dB applied and measuring the average sound pressure level at 1 meter. This parameter may not relate to the low-frequency efficiency level of a speaker.
η0 or Efficiency, is referred to as the Reference Efficiency and specified in percent. Comparing drivers by the calculated reference efficiency is more useful than the sensitivity parameter. This reference efficiency, is a calculated function of the electro-mechanical parameters of the loudspeaker and represents the low frequency output range of 300 to 400 Hz range for 12 to 18 inch speaker drivers that directly correlates with the efficiency ratings.
This efficiency calculation used the electro-mechanical parameters that include the resonance frequency (Fs), the speaker’s electrical damping (Qes) and the equivalent volume compliance (Vas).