SOUND TECH
[ HOW LOUD IS YOUR WORSHIP EXPERIENCE? | Kent Margraves ]
The answer is perception based, and may not low frequency information into account, better But slow response metering often correlates
be simple. It’s influenced by many factors. We relating to louder listening levels. Measuring best to human perception.
can measure sound pressure, and it’s useful, SPL with music that includes lots of sub-bass but energy will measure much higher on the C Decibels in sound pressure level measurements
scale than on A. dBs can be relative or absolute and are used in
correlating
that
to
human-perceived
loudness can be confusing. Here’s some clarity
on the topic. A bit of tech talk is necessary first,
then some practical conclusions.
acoustics, electronics, optics, and several other
As illustrated, if listening to a midrange sound fields. Turning a vocal up 3dB is an example of
of 1kHz at 70 decibels, we would need to turn a relative dB change. We don’t need to know
FREQUENCY an 80 Hz bass tone up another 10dB to sound the actual level of the vocal before, or after, only
Loudness is the subjective perception of sound equally loud, and an 8kHz high frequency sound that it changed by 3dB. Absolute dBs refer to
pressure, and it’s influenced by the frequency up about 6dB to sound equally loud. While a known reference (0dB SPL), and must be
content (and duration) of sounds. Our ears are these may sound about the same “loudness”, denoted with the suffix “SPL”. 0dB SPL is the
definitely not flat! They’re quite nonlinear. We’re they measure 70dB SPL, 80dB SPL, and 76dB theoretical lowest human hearing threshold
most sensitive to midrange frequencies and SPL. And again, this curve changes at different and sound pressure levels are measured in
less sensitive to higher and lower frequencies. levels. Notice that at very loud levels (particularly decibels above that threshold. A face-to-face
This is especially true at lower listening levels, 100, 110, and up) our ears are closer to flat conversation may be 60-70 dB SPL and a
and become less true as volume increases. (the “loudness” button on some home stereos diesel truck might be 90dB SPL. Here’s a chart
So, the tonal response of our hearing is rather compensates by boosting the lows and highs of some common SPLs:
complex. Figure 1 is a well-known chart, going and is intended to be used at low listening back nearly a century, that demonstrates this levels). There are also less commonly used behavior by showing the required SPL (in weightings of B, C, D, and Z (which is essentially decibels) for different frequencies to sound flat, or no weighting). No weighting reference equally loud: implies an un-weighted measurement. Clearly,
Fig 2
(Google images)
the non-flat frequency response of our ears is a
Fig. 1
(courtesy chegg.com)
huge factor in measuring loudness.
TIME
Human hearing averages levels
in very short durations. And live
music is constantly changing in
level, sometimes several times
per second. A very loud but brief
repetitive sound (such as a rock
snare drum) may not sound as
loud as a longer or sustained
sound (keyboard pad or rhythm Any meaningful SPL measurement must
guitar) even if it measures, briefly, denote: 1) the weighting curve, 2) the time
at a much higher sound pressure constant, and 3) the reference level. The
level. For this reason, meters statement “I mixed at 92dB” is simply
Sound level meters use weighting curves to should have a time selection - at least a “fast” invalid (and not uncommon). It’s missing the
compensate for this nonlinearity, allowing them and “slow” response option. Fast, Slow, and weighting (or implies no weighting), the time
relate better to human hearing, usually with an Peak, are common modes. Do we want to factor, and the reference level (indicating a
“A” or “C” mode switch. “A” weighting relates know the instantaneous level of the snare strike relative measurement, not absolute). Properly
to rather low listening levels (largely ignores (a few milliseconds) or the average music level expressed, this might look like “92dBC SPL
bass energy) and “C” weighting takes more sustained over a few seconds? Both are useful. Slow”. Stating only “92dB” and comparing that
30
February 2018
WorshipMusician.com