We ran a SPL check in the parking lot yesterday. Shotgun wants to play a gig at a campsite with the limit of 90dB SPL (A-weighted) at 50' from the stage. Since there was limited time, the test was simplified:
Acoustic level of the drums are the limiting factor for how "low" you can take the volume... you can't play any quieter than that!
One guitar was mic'd through the PA system. We piped an MP3 of a song that both the drummer and guitar player knew, and played along with it. A hand-held SPL meter was set to A-weighted measurement, and we measured out 50' from the PA speakers.
At 50', we were able to bring down the volume of the guitar and MP3 to 80~84dB average, with peaks of about 86~88dB. We agreed that the gig should go ahead, and the sound engineer will keep an eye on the meter during the performance.
Some other interesting measurements:
Cranked the MP3 player through the system to achieve 90dB average at 50'. Measured 100dB at around 25 feet and then 110dB at 5 feet. Each of the speaker drivers was able to exceed 120dB at a foot or so. It seemed the mid-high frequency drivers registers the highest levels. This is due to the nature of the A-weighted curve. Since human hearing tends to favor the mid-high frequency range just above 1kHz, the weighting of the meter is actually more sensitive to the smaller speakers. This doesn't mean that they are putting out more sound pressure, just that the meter registers a higher level for the same SPL with this setting.
The speakers used for this test were a pair of 1588's and LS1801's, powered by a DCM2500. which are all shown on our Equipment page.
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