Ed's AV Handbook.com
Home Theater & High Fidelity Stereo Audio


Chapter Eight
Home Theater Sound by Design

Page 2

Batting practice for the audio/video pro and a primer for the novice 



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The THX Design
          The ubiquitous THX logo has been seen on a profusion of audio and video product for decades.  Yet many wonder, what is THX?  
        
THX is simply a standard that manufacturers and installers must meet to be certified by THX.  THX was originally a division of Lucasfilm, but now an independent company.
 THX is not a standard such as Dolby or DTS.  Yet THX does outline minimum specifications for amplifiers and speakers such as flat frequency response, low distortion, and low noise.  In addition, THX makes the following assumptions:
  • Movie soundtracks are mixed with a mid-range boost that causes harsh sounding playback in a home theater.
  • Acoustical reflections from the floor and ceiling smear sound fields and distort the       mid and higher frequencies.
  • Compromised speaker placement stimulates room modes which distort sound.
  • Listener placement near room boundaries creates excessive bass.
  • Rear channel effects are often unconvincing via dated surround sound encoding.
               As a result, THX standards institute the following modifications to the electronic                processing and the speaker system:
  • THX processing features “ReEQ” and “Timbre Match” which alter high frequency and mid-range output that results in less harsh sound.
  • THX standards decrease the vertical dispersion of the front speaker system, which should result in less distorting acoustical reflections from the floor and ceiling.
  • THX specifies smaller front and rear speakers and processing that re-routes                     low frequency sound to a sub woofer.   A single source of low bass, the sub woofer, simplifies the management of distorting low frequency room modes.
  • THX applies Boundary Gain Compensation that filters excessive bass for seating           near a room boundary.
  • THX systems implement a rear dipole speaker design that results in more diffused,       less localized rear sound fields.
  • THX offers “Adaptive De-Correlation” which creates a more spacious image from         older rear channel sound mixes.
          For the larger room with many rows of seating consider a horn speaker design.
Though this is not THX prescribed; a mid/tweeter horn array can broaden mid/high frequency dispersion width from the front row to the last.  However, this design will also sacrifice optimum performance at the focal point of the room, which might be your seat.
   
In any case,  if you accept THX assumption
s and concur with their solutions, then this is     your design choice.

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Ed's AV Handbook.com
Batting Practice for the AV Pro and a Primer for the Novice.
Copyright 2007 Txu1-598-288   Revised 2018