THX

Definition

THX home-theater seating uses about a 40° horizontal field of view, which puts you at roughly 1.2× the screen width (or ~0.84× a 16:9 diagonal). The cinema soundtrack reference is 85 dB C-weighted per channel at the mix position, with 20 dB of peak headroom. Living rooms rarely hit that without complaints from the next room. Use THX as a starting geometry, then sit where the picture and the neighbours allow.

Calculators that use this

• 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.

• Screens & projection

  Ideal Viewing Angle Calculator

  Get horizontal and vertical field of view from image size and seating distance. Compare with THX 40° and SMPTE 30°.

• 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.