This is a Larson Davis Class 1 sound level meter. With a response time of under 30 microseconds and sensitivity up to 177dB, this is the sort of instrument needed to accurately measure the sound levels produced by transient events like gunshots.
Since I didn’t want to sink over $3,000 into a sound meter, I was able to rent one from Aimed Research, which has become my go-to company for ballistic research equipment and expertise.
I’ll be posting the results of my research shortly. This post explains the basic science needed to fully understand the methods and results.
We use a decibel amplitude scale to describe sound pressure using the formula
We will be looking at explosive noise events that we will call “pops:” sounds dominated by a single, rapid peak in air pressure. The human ear is not very good at assessing peak “loudness” of short pops.* But the magnitude of that peak can predict both the audible distance of the pop and its potential to damage hearing of nearby listeners.
The distance at which we measure a sound is as important as the dB value, because sound pressure decays linearly with distance. On the decibel scale, this means that the same sound measured from twice the distance will be 6dB lower. As is customary, unless otherwise stated, all dB measurements will be given for a distance of one meter from the source of the sound.
For reference, here are some typical pops and pressure effects.
|Bad Stuff||99% lethal overpressure||205dB|
|1 pound TNT||203dB|
|Tissue damage observed||185dB|
|Gunshots||.338LM 25″ bbl w brake||177dB|
|.338LM 25″ bbl suppressed||145dB|
|.223 16″ bbl||166dB|
|.223 16″ bbl suppressed||132dB|
|.22LR 16″ bbl||148dB|
|.22LR 16″ bbl suppressed||126dB|
|Gun Actions||AR-15 bolt release||123dB|
|10/22 bolt release||119dB|
|AR-15 dry fire||113dB|
|10/22 dry fire||105dB|
|Steel Hammer||Nail into wood||133dB|
*For example, I’ve never been able to hear the “first-round pop” that tends to occur with cold suppressors. But in my test data I did find many cases where the first round peak was 3-4dB higher than subsequent shots.