Description

This article is from the Car Audio FAQ, by Ian D. Bjorhovde (ianbjor@mobileaudio.com) with numerous contributions by others.

5.5 What is "rear fill", and how do I effectively use it? [HK, JSC]

"Rear fill" refers to the presence of depth and ambiance in music. A
properly designed system using two channels will reproduce original
rear fill on the source without rear high frequency drivers. Since
recordings are made in two channels, that is all you will need to
reproduce it. What is captured at the recording session (coincident
pair mics, Blumlein mic patterns, etc.) by a two channel mic array will
capture the so called rear fill or ambiance. Many of the winning IASCA
vehicles have no rear high frequency drivers. Also a lot of this has
to do with system tuning. If rear high frequency drivers are added,
however, the power level of the rear fill speakers should be lower than
that of the front speakers, or else you will lose your front-primary
staging, which is not what you want (when was the last time you went to
a concert and stood backwards?). The proper amount of amplification
for rear fill speakers is the point where you can just barely detect
their presence while sitting in the front seat. Separates are not a
requirement for rear fill; in fact, you may be better of with a pair of
coaxial speakers, as separates may throw off your staging.

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