1) A simple SPL calculator, taking into account, not the volume of the room, but the distance to the last row of the audience, and the sensitivity of the speakers.
To calculate the theoretical power requirement for an amplifier you need to know 4 values:
1) The distance from the speaker. This is normally the distance from the speaker to the last row of seats in the room. Type in feet or metres (the metres is calculated from the feet – if feet is used). From this distance the Sound Pressure Level (SPL) loss over that distance is calculated.
2) The SPL required. This is how loud you want the sound to be at the distance specified. Some general levels are:
- 70-80dB for speech only
- 80-95dB for light music
- 95-110dB for heavy music
3) The speaker sensitivity. This is not an indicator of how sensitive the main (human) speaker is, but rather a measurement of the sensitivity of the loudspeaker. It should be available in the specifications for the loudspeaker. It is normally stated as the SPL measured 1 metre in front of the speaker with 1 watt of power driving the speaker. Hence the specification will read something like:
Sensitivity (1W/1m) = 91dB
4) Amplifier headroom. This is an allowance for the amplifier to cope with peaks without distortion. Note that for every 3dB allowance, the power requirement doubles.
Use the calculator below with different values to see the effect a change in any of these parameters makes to the amplifier power required.
An excel file here under, for your calculation
2) A more detailed SPL calculator, taking in to account room size, frequencies, air…
3) From Home Theater, about Maximum SPL:
4) From Crown Harman
5) From mh_Audio, a simulator, taking into account the speaker size.