"bj" wrote in message
om...
It is said that at least 28.5 feet length room is required for the
control room. IMO the reason is derived form which the wave length of
20hz is 56.6 feet

Lots of urban mythology here.

First, a room's acoustical size can be significantly greater at low
frequencies than its dimensions due to the walls not being massive enough to
reflect or even attenuate the sound. Soundproof, well isolated control rooms
have little or nothing in common acoustically with most ordinary rooms.

Second, if headphones can support low frequencies, certainly rooms of any
size can do at least as good a job!

--
Bob Olhsson Audio Mastery, Nashville TN
Mastering, Audio for Picture, Mix Evaluation and Quality Control
Over 40 years making people sound better than they ever imagined!
615.385.8051 http://www.hyperback.com