The Calculated Maximum SPL is typically recorded by a manufacturer at the most sensitive input frequency for their speakers or projection device. Usually, this is in the range of 2 KHz to 3 KHz. So, if a calculated maximum SPL for a given powered loudspeaker is given as 147 dB SPL, this number represents the single highest frequency input signal probably between 2-3 kHz.
For the Maximum SPL number in particular, manufacturers often have their own way of reporting the specification. They can use various methods, and each manufacturer tends to choose the one that makes its particular product look the best. Unfortunately for the customer, this makes comparing two products on paper very difficult.
To get an accurate “real” picture of the output of the system, the dB needs to be measured using an integrating sound level meter that averages the amount of dB at all the frequencies over a measured or linear period of time. The continuous RMS or Leq measures the average dB SPL over a linear period of time. Thus all frequencies and amplitudes of the message or tones are measured and averaged.
While we’re at it, let’s clear up one other misconception: Peak Sound Level is not the same as Maximum Sound Level. Peak Sound Level records the peak of the original pressure wave, not the ‘rectified’ result. This is commonly associated with C or Z frequency weighting, but has no time weighting. If the noise being measured is impulsive, such as a hammer being used, then the Peak level may easily be 20dB higher than the maximum sound level. This is due to the time weighting being applied to the max sound level. To give some scale, the maximum permitted acquisition time of Peak is 100 milliseconds. The Peak level should not be confused with Maximum level as Peak levels are measured without exponential time-weighting and can be several dB higher or lower than the Maximum levels measured using time-weighting. Maximum SPL being time weighted is measured within time constants of 125 milliseconds and 1 second.
Naturally, we believe that a loudspeaker system has to pass the “ear test.” Will the sound be loud enough to be heard under the conditions in which you’ll use the speaker? Will the warning tones and voice messages be clear enough to be easily understood? If the answer is “yes” to both questions, you’ve covered the purpose for which you are buying your sound system.
We can help you specify the right loudspeaker system for your needs – whether they’re tactical, deployable or fixed for any emergency mass notification need. Contact us for more information about which SoundCommander system best meets your requirements and arrange for a demonstration. We can also custom engineer a sound solution that meets your operational needs and budget.