Why Do We Measure SPL?

Why Do We Measure SPL?

What is SPL?

Sound Pressure Level is an objective measure of the pressure fluctuations in air caused by a sound wave. It can help to characterize the level of any source of sound or noise.

Why not just “use your ears?”

SPL is an objective measure of the strength of sound waves in air – whereas human loudness perception is subjective and complex. It’s possible to feel completely comfortable while being exposed to dangerous sound levels, and it’s also possible to feel like it’s “too loud” even when it’s completely safe. 

Using an SPL meter allows you to objectively tell if the levels around you are dangerous without relying on the subjective complexities of human hearing perception. 

If SPL isn’t a measure of “how loud,” why measure it?

We measure SPL when we need an objective answer to an objective question. Three common reasons to measure SPL are:

• A tool for the mix engineer. Is this the same level as it was last time? Are we giving the audience a consistent experience every night? A “quality control” measurement.
• Sound exposure. Is this sound level safe? Are we exposing people at this concert to dangerous sound levels? Are we in violation of sound exposure regulations or recommendations such as OSHA or NIOSH?
• Nuisance noise. Are we bothering the neighbors? Are we in violation of local or regional noise ordinances?

Can’t I just use an inexpensive handheld meter?

Most handheld sound level meters (SLMs) are fine for relative measurements – making sure you’re hitting the same level every night. Just keep the placement consistent and the battery fresh. However, if the number on the screen needs to be meaningful, the odds are against you, and many meters that claim to be within +/- 2 dB accuracy on their packaging are actually not (and they can drift significantly over time). More importantly, most handheld SLM can only measure the SPL Fast and Slow metrics, not the Leq metrics that are important for event SPL measurement.

It is possible to take accurate SPL and Leq measurements with professional-grade handheld instruments such as the NTI XL2. As with all calibrated solutions, they tend to be far more costly than the cheaper handheld sound meter options, and should come with calibration documentation.

Can’t I just use my smartphone?

Smartphones can be great for low-level relative measurements, but there are accuracy issues with internal microphones (and the apps themselves) and most phone mics are overloaded at concert levels. Like handheld meters, smartphones and tablets can exhibit a response that varies quite significantly based on how you hold the device. Although mobile apps are fun and handy, they are generally not an appropriate solution for concert SPL measurement.