When shopping for speakers or microphones, you’ll see on the specifications sheet a spec called SPL measured in dB (Decibels); but what is the meaning of SPL in audio specs?
SPL stands for Sound Pressure Level, and it’s a measure used to define the efficiency of a loudspeaker or the sensibility of a microphone to sound.
In this article, I’ll explain what is SPL in audio and why it is so essential when choosing speakers or microphones.
Sound Pressure Level – SPL
In audio, SPL plays an essential role because it is the correct way of measuring the perception of loudness. In other words, SPL measures the strength of a sound wave when emitted from a speaker. It is also used to measure the sensitivity of a microphone to the sound waves’ strength.
SPL reacts differently at various frequencies. Speakers and mics operate between 20 Hz -20 kHz. At each frequency, the SPL response is different. A perfect speaker would react the same at all frequencies. Still, such a speaker doesn’t exist because it’s impossible to have the exact SPL at all frequencies due to physical restrictions.
A very common spec on the datasheet of a loudspeaker is the frequency response graph. In it, you will get the plot of different frequencies versus their respective SPL measurement. Frequency is plotted on the x-axis in Hz (Hertz) and SPL on the y-axis in dB (Decibels).
The image below is a typical frequency response chart for a loudspeaker.
How is SPL Measured
To measure the SPL of a speaker, it is placed inside a sound chamber. A high definition microphone specially designed for precise measurements is placed 1 meter away from the speaker. Sounds are played at different frequencies at 1W of power. The results are then plotted, and you would get the frequency response graph.
When it comes to speakers, SPL is directly proportional to loudness, meaning that the higher the SPL, the louder the speaker is. With microphones, the higher the SPL, the louder the sound it can handle before distortion.
Sound Pressure Level Vs. Sound Power Level
Sound pressure level and sound power level are two completely different things. As explained previously, sound pressure level measures the perception of loudness created by a sound source; and it is dependant on the environment and relative distance from the sound source.
On the other hand, sound power level measures the acoustic energy created by an audio source. If you have a loudspeaker connected to a 100W amplifier that’s playing a 1kHz frequency, the sound power level will be the same whether you are standing close to it or 50 ft away. The reason is that the generated acoustic energy by the speaker is still the same. You might not perceive the same volume, but the generated energy is still the same.
This is why sound pressure level is the metric used when measuring loudness because you want to know what is the perceived volume, not the generated acoustic energy.
SPL Vs. Watts in Speakers
It is frequently believed that the higher the wattage of a speaker, the louder it is, but this is not necessarily the case. Wattage is a measurement of the power a speaker can handle, and this measure doesn’t translate in output volume. When selecting a speaker, you need to look for how well it performs and not how much power it consumes.
For example, if a loudspeaker delivers an SPL of 120dB at 300 Watts and another provides an SPL of 105dB, also at 300 Watts, it means the first speaker is more efficient because it delivers more volume with the same wattage.
Don’t get confused by thinking that higher wattage translates in more volume, instead check the specs to find what is the continuous SPL the speaker can deliver.
Also, beware because some manufacturers use max SPL instead of continuous SPL. The spec you need to know is continuous SPL because that’s the continuous sound pressure level a speaker can deliver. Max SPL is the maximum the speaker can handle for a short time.