Measuring SPL

Music vs Noise

As humans, we generally react differently to noise than to music. 

Noise is as an often uncontrolled, less constrained, statistically random and commonly unwanted sound. 
In contrast, music is a dynamic, multifaceted, and multisensory phenomenon that is 'experienced'. Music contains informationally-rich events that cannot be reduced to simple perceptual dimensions of pitch and rhythm.  

Despite being at similar SPL levels, noise, pleasant musical sounds and unpleasant musical sounds each can yield different effects on our physical hearing mechanisms and our emotional responses. 

Measuring Music vs Noise

Many types of machinery produce a consistent level of ‘noise’. This consistency of SPL can be measured using a simple sound meter to determine the average level and peak. 
The SPL of music is not consistent and varies with every beat, bar, song and act. Establishing the average SPL (LEQ) for music requires a sound meter capable of recording an average SPL over time. ​Measuring the intensity of sound vibrations, SPL, requires metering devices like those shown below. Meters that record LEQ (Average Level) are often more expensive; however, the free iOS NIOSH App, is effective in measuring SPL and Dose.

Measuring SPL, requires metering devices like those shown below. Meters that record Leq (Average Level) are often more expensive; 
However, the free iOS NIOSH App, is effective in measuring SPL ... and dose.

Environmental Noise Measurements - SC Noise Survey

Ear Sensitivity and Weighted Curves

This section explains A and C weighted curves

Human hearing is most sensitive to frequencies that benefit speech and communication. The equal loudness contours graph demonstrates this. To hear the sibilant frequencies within the spoken word around 4 kHz, where we hear ‘s’ and ‘t’, less SPL is required than for other frequencies. 

A and C-weighted curves aim to adjust any SPL measurements to the human experience at various levels of stimulation.

Weightings are an approximate inverse of the equal loudness curves where each weighting relates to a 1 kHz tone at the SPL values shown.

A-weighting - 1 kHz at 40 dB. 
C-weighting - 1 kHz at 100 dB. 
Z-weighting - flat response.

Points to Note:

A, C and Z-weightings are most commonly used in the audio industry. 
Despite the A-weighted scale being the most common live SPL measurement, C-weightings more accurately represent the ear sensitivity at the higher SPLs commonly reached at live-sound events. 
The A-weighted curve is only beneficial below 70 dB. 
A-weighting does not account for low-frequency energy which can cause high-frequency damage. 
Z-weightings more accurately measure SPL peaks than A or C-weighting.

Metering Terms

LAeq and LCpeak

L = Level            A = A-weighted         C = C-weighted
Leq = Average Level (constant equivalent)            
PEAK/MAX = peak/maximum level

Decibel (dB)      	Relative measure of the level of sound. Dose                  	Average SPL (audio 'volume') over the time exposed. Exchange rate    	For every increase in the exchange rate (e.g. 3 dB), the allowable exposure time is halved. L fast                	Used to show varying SPL over a 125 ms time constant. L slow               	Used to smooth the SPL readings to make it easier to read over an approximate 1-second time constant. LAeq                 	Level - A-weighted - constant equivalent (average). For use over the whole performance. LAeq5"             	Level - A-weighted - constant equivalent (average) over 5 minutes. For use throughout a song. LAeq30"            	Level - A-weighted - constant equivalent (average) over 30 minutes. For use over several songs to allow the engineer to make                                changes that could impact SPL readings over a performance. LAeq85              	Level - A-weighted - constant equivalent (average) of 85 dB. LAeq8h              	Level - A-weighted - constant equivalent (average) over 8 hours. Metering Class   	Sound metering equipment accuracy as defined by international standards: IEC 61672-1:2002 (or BS EN61672-1:2003). Class 1             	is a standard for equipment taking accurate calibrated measurements. Class 2               	is a standard for equipment taking calibrated, measurements within an accepted higher tolerance than that of Class 1        
                                devices. SPL                      	Sound Pressure Level, commonly referred to as audio ‘volume’. TWA 	                Time-weighted average.

Measuring SPL

Music vs Noise

Measuring Music vs Noise

Ear Sensitivity and Weighted Curves

Points to Note:

Metering Terms

Stephen Compton