How loud will it be at the seat?

How the estimate works

Sensitivity is the level a loudspeaker produces 1 metre away with 1 watt. Every doubling of amplifier power adds 3 dB, and every doubling of distance takes 6 dB away. So:

Level at the seat = sensitivity + 10 × log₁₀(power) − 20 × log₁₀(distance) − screen loss

RP22 uses the same method to predict, at the design stage, whether a room will reach its targets. For example, a loudspeaker with 96 dB sensitivity driven by 500 W produces about 123 dB at 1 metre, and about 111 dB at 4 metres.

For subwoofers, RP22’s target is the combined output of all of them at the seat. Identical subwoofers, each with its own amplifier and summing in phase, add up to 20 × log₁₀(number): about 6 dB for two and 12 dB for four. Where the subwoofers also reproduce the bass of the other channels (bass management), RP22 expects around 4 dB more, so the calculator raises the targets by that amount.

What it leaves out

• Power compression. At high power, voice coils heat up and output rises by less than the arithmetic predicts. Published maximum output figures, where they exist, are more reliable than sensitivity plus power.
• The room. The estimate assumes sound falls away as it would in open space. In a real room, reflections add energy, so beyond a few metres the level at the seat is often somewhat higher.
• Power handling. The amplifier power you enter should not exceed the loudspeaker’s programme rating, typically twice its AES rating.
• Headroom. RP22’s figures are peak levels reached without clipping, so use the amplifier’s continuous rating, not a peak or “dynamic” figure.
• Subwoofers in a room. At the lowest frequencies, a room does not let sound fall away as it would in open space, and the walls add gain. Enter an estimate for room gain if you have one; with none, the result is conservative. The gain from several subwoofers assumes they are identical, equally driven and summing in phase at the seat, which alignment in the processor aims for.
• Sensitivity ratings. Many manufacturers quote sensitivity at 2.83 volts rather than 1 watt. For a nominal 8 Ω loudspeaker, the two are the same.

Baffle walls

In a cinema, the screen channels are flush-mounted in a baffle wall: a rigid, damped wall that the loudspeakers sit in, facing the room. A free-standing loudspeaker radiates its low frequencies in every direction, including back around the cabinet. Built into a wall, it radiates them only forwards, into half the space, so output below a few hundred hertz rises by up to 6 dB. RP22 notes that baffle mounting smooths the low-frequency response and increases sensitivity below 300 Hz. It also removes the reflection from the wall behind the loudspeaker, which otherwise cuts a dip into the bass.

Drive-unit sensitivity is normally stated with the driver in a large baffle, radiating into half space. A loudspeaker designed for baffle-wall installation and rated this way already includes the baffle gain, so the calculator does not add it again. For a free-standing loudspeaker, the same figure overstates the output below the cabinet’s baffle step, roughly 115 ÷ cabinet width in metres, by up to 6 dB.

Screen loss

An acoustically transparent screen absorbs some of the sound that passes through it, mostly at high frequencies. Screen manufacturers publish their own figures; enter the loss for the screen you plan to use, or 0 for loudspeakers in front of the screen.

Read next: RP22, explained · How many subwoofers?