monitors are often so loud that not even the best sound operator of all time could create a good mix at an acceptable volume . To achieve intimacy and intelligibility , the sound operator would have to push the mains so loud , the volume would only be embraced by the most aggressive audience .
If you want to eliminate volume issues , the first step is to find ways to minimize the stage volume — invest in a good personal in-ear monitoring system .
THE DECIBEL METER The decibel meter is a valuable tool in any live sound environment ; however , it is important that the sound operator understand the usefulness and uniqueness of all userselectable parameters . To simply proclaim that the music team is at 90 dB is somewhat meaningless unless the settings are specified . The sound operator must set the meter to read peak or average levels , the weighting scale must be noted , and the details of how the meter is held and pointed must be considered . All of these variables affect the accuracy of the meter reading .
LOUDNESS AND THE FLETCHER-MUNSON CURVE Loudness is a sound characteristic that involves the listener — it is a perceived characteristic that can be charted and averaged , but it ’ s not simply a mathematical calculation . The common unit , used to quantify loudness , is the phon . Loudness is a subjective , perceptual aspect of sound .
The human ear is not equally sensitive to all frequencies . In fact , as amplitude varies , so does the frequency response characteristic of the ear . The ear is most sensitive between 1 and 4 kHz . This frequency range just happens to contain the frequencies that give speech intelligibility , directional positioning , and understandability . Hmmm , it ’ s almost like it was designed that way . In fact , as the amplitude decreases , our ears become dramatically more sensitive in this frequency range .
So , yes , there is a difference between amplitude and perceived loudness . They are very similar at a certain point , though . Two scientists at Bell Laboratories in 1933 charted a survey of perceived loudness . They compared actual amplitude to perceived loudness throughout the audible frequency range ( x-axis ) and the accepted range of normal loudness ( y-axis ).
Their survey involved generating pure tones through the audible frequency and loudness spectrum at a specific amplitude , then asking participants to identify whether the sound was louder or softer than the reference . The results , referred to as the Fletcher-Munson Curve , is a visual representation of why music sounds fuller at loud volumes and thinner at soft volumes .
Each curve on the graph represents perceived constant volume throughout the audible frequency range . This , for example , shows that perceiving 70 phons of loudness at 1,000 Hz requires 70 dB SPL amplitude . However , in order to perceive 70 phons at 50 hertz , 80 dB SPL is required . At 10 kHz , to perceive 70 phons , a similar 10 dB SPL boost is required .
As dB SPL decreases , the contrast becomes even more extreme between loudness and the actual amount of dB SPL required . At 1,000 Hz , 20 dB SPL is equal to 20 phons . In contrast , at 50 Hz on the 20 phons line , almost 65 dB SPL is required to maintain the perceived 20 phons . Analysis of the Fletcher-Munson Curve points us to the dB SPL range at which the human
ear is most accurate throughout the audible frequency spectrum . Notice that between roughly 700 Hz and 1.5 kHz , phons are essentially equal to dB SPL at all volumes . Also , notice that the center of the graph is where more often than not dB SPL is most similar to phons .
From this graph it is generally held that the most sensitive frequency range is from 1 to 4 kHz , although the graph might indicate an extension of that range from about 700 Hz to 6 kHz or so . Because this is a subjective study , some generalities apply , but it is obvious where the consistencies and trends are .
For our recording purposes , it is helpful to find the flattest curves on the graph . A curve with less variation indicates a volume at which the human ear ’ s response most often matches loudness to dB SPL — the level where the most accurate assessments can be made regarding mix and tonal decisions .
The Loudness button on your stereo is an example of compensation for the fact that it takes more high and low frequencies at a low volume to perceive equal loudness throughout the audible spectrum .
The most consistent monitor volume for our recording purpose is between 85 and 90 dB SPL , according to the Fletcher-Munson Curve . Notice on the graph that the 80 and 90 phons curves are the flattest from 20 Hz to 20 kHz .