Sound pressure level

Definition

Sound pressure level (SPL) is a log scale: 10 dB is ten times the power, 3 dB is a doubling of watts. THX/cinema calibration aims for 85 dB average at the main seat with peaks to 105 dB. Living-room movies often sit 5–10 dB quieter. Distance from the speaker, room gain and seating off-axis all move the number. Use an SPL meter app only as a sanity check, not as a calibration certificate.

Calculators that use this

• Amplification & power

  Amplifier Power Match (SPL) Calculator

  From speaker sensitivity, distance and target SPL, get required watts and whether a receiver can supply them with headroom.

• Screens & projection

  Screen Viewing Distance Calculator

  Convert a screen diagonal into THX 40° and SMPTE 30° seating distances. Inches on the diagonal; metres (or feet) to the seat.

• Speaker placement & acoustics

  Subwoofer Room Gain Estimator

  Rough in-room bass lift from room volume and how many boundaries the sub sees. Add it to an anechoic SPL.