What is loud? Why do I need to know about dB SPL?

Perception of loudness is a complicated subject. Every person will perceive loudness differently, as everyone’s ears are different. In fact, everyone’s ears have a slightly different frequency response.

This is why, in sound engineering circles, there is a need to quantify sound pressure levels to define what is loud, and what is quiet. Or perhaps that should be; what is too loud and what is too quiet. The unit of measurement is the dB SPL (decibel). There are also more accurate measurements of loudness called phons, and subjective loudness, called sones, but these are rarely used and are outside the scope of this course!

For convenience we normally measure dB SPL from the mix position, but it can be useful to measure from other areas such as the front row and the stage.

For those new to dB SPL here is an idea of how different sounds compare in level:-

Recording studio	30dB SPL
Conversational speech	60dB SPL
Noisy office	80dB SPL
Church concert (contempory worship)	95dB SPL
Loud rock concert, front row	120dB SPL
Threshold of pain, average young person	130dB SPL
Concord take-off from runway side	140dB SPL
.357 Magnum handgun, (peak impulse)	165dB SPL
Under a Saturn 5 Rocket on take-off!	194dB SPL

This article was taken from my web site, you can read more about PA Hire and dB SPL here.