In this post we present a calculator that finds the sound pressure level (SPL) at a specified distance for multiple speakers in series.
Enter
- Number of Speakers
- Speaker Sensitivity (usually specified in dB (1W/1m)
- Amplifier Power (Watt)
- Distance (meter or feet)
Background
Speaker Sensitivity
It is a measure of how well power to a speaker is converted to sound energy.
As an example, the sensitivity of a speaker might be rated as 95 dB (1W/1m). This means that speaker produces a level of 95 dB at a distance of 1 meter, when driven with an amplifier that provides 1 Watt of power.
The higher the number in dB, the more sensitive the speaker and the more efficient it is in converting the power output of an amplifier to audio.
Amplifier Power
The amplifier output power is specified in Watt. This is a root-mean-square (RMS) value. Important to differentiate this from the peak power which is more of a marketing number and should not be used for this calculation.
Distance
This is simply the distance away from the speaker (not the amplifier) where the SPL is to be estimated.
When connecting speakers to amplifiers, it’s important to ensure that the impedances are matched. With multiple speakers in series, the total impedance seen by the amp will be greater than any individual impedance.
Example Calculation
Consider a 100 Watt amplifier that connects to three speakers connected in series. The speakers are not concentrated in one area but spread across a room. Each speaker has a sensitivity of 95 dB (1W/1m).
The amplifier delivers an equal amount of power: 33 Watt across each speaker.
The amplified SPL at 1 meter is 110.2 dB. (This makes sense when you consider that 33.33 Watt converts to 15.2 dB gain).
At a distance 30 feet away, the SPL is approximately 91 dB. The attenuation relative to the speaker sensitivity is around 4 dB.
Without the amplifier the loss would be 19.2 dB.
Related Calculators
- Amplifier Speaker Matching – Find the amplifier gain (Watt) required to meet a target sound level at a specified distance from the speaker
- Max SPL Calculator – explore the limits of your audio equipment
- Add Sound Pressure Levels – this tool makes it easy
- SPL Attenuation – A speaker’s data sheet usually specifies the SPL at 1 meter distance when the amplifier provides 1 Watt of power. This tool provides the formula and also calculates the attenuation at a specified distance away from the speaker.
- Speaker Impedance – calculate the impedance of speakers in either parallel or series configuration