Reverb in Acoustic Sound Reinforcement
~ Just replacing what has been lost ~
Copyright ©1999 Howard Coleman
This article describes the reasoning behind my use of reverb -
how I use it and how I justify using it for acoustic gigs. It is
intended to complement information I have given in Acoustic sound reinforcement solution
and Thoughts on how loud an acoustic gig
should be. What I have written applies to live acoustic vocal
and instrumental music. It does not necessarily apply to recorded
music or rock music.
The need for reverb (and why we sing in
the bathroom)
Adequate reverb is vital for the musicians and vocalists. Their
ability to pitch accurately is severely hindered by lack of
reverb. It is as though they need to hear the remains of the
previous note dying away in order to judge the pitch of the next
note. (See Fundamentals of Musical Acoustics
by A Benade.) Performers also find it reassuring to hear
reverb and unnerving not to. That is probably why people sing in
the bath/shower room. They sound better (to themselves!) and find
it easier to sing. (They are also more relaxed and they think
no-one can hear them!) The downside of close miking with
directional microphones is that virtually all the sound picked up
is directly from the source and very little from reflections from
the surrounding walls etc. For the audience this can result in a
very "dry" sound which is unnatural.
My aim with reverb
I do not use reverb as an effect or try to do
anything creative with it. For my acoustic gigs, where
naturalness is the key, my aim is to add reverb only to
compensate for the loss caused by close miking with directional
microphones.
Reverb settings
Choosing appropriate reverb settings is a tricky
business. I could simply use settings that sound nice, for
example ones that I think flatter the singer's voice.
Alternatively, I could be creative and add the type of reverb I
think will help convey the feelings expressed in a song (easy for
songs about being in an underground cavern!) However, my
preference is to add what will make the performance more natural
sounding. I think that the reverb settings should be chosen to
match the characteristics of the room. Trying to improve the
sound by adding longer reverb delays would certainly add to the
spaciousness of the sound - it could make it sound like a large
concert hall - but I think it would be out of context and
therefore unnatural. The room ambience should therefore be the
only reference. I say "should" because, while this is
my aim, I cannot claim it to be easy to achieve.
The quantity of reverb to add is easier to judge in theory than
in practice. As I only use reverb in a subtle way it is difficult
to judge how much is there just by listening to a performance. I
have also found that listening to reverb can deaden my
sensitivity to it. I am sure I am not unique in this; there must
be psychoacoustic reasons. I find it helps to switch it off
completely to hear the difference between the "dry" and
"wet" sounds but, obviously I can't do this during a
performance. Another trick is to make clicking sounds into the
microphone to hear the reverberation in the absence of other
sounds. I would rather err on the side of too little reverb,
since too much, besides sounding unnatural, encourages acoustic
feedback. (The repeats allow more time for feedback to build up.)
With my simple sound reinforcement system I only have two
controls for adjusting the quality of the reverb: "Reverb
Time" controls the length of the decay and "Reverb
Color" controls the brightness of the reverb from bright to
dark. If you are lucky your reverb time control will be
calibrated in milliseconds. In this case you could calculate the
natural reverb time of the room and set the control accordingly.
The calculation can be carried out painlessly by measuring the
room dimensions and feeding them into a reverb time calculator
like the one at mcsquared.com.
If, like me, you are not so lucky you will have to rely more on
your ears. Likewise with reverb colour, experimentation and use
of the critical ear are the keys. I restrict all of this to the
setting up period and soundcheck.
Recommended reading
Some aspects of reverb can be found on the
Internet - mostly as a phenomenon and as an effect.
These can be found at Harmony
Central and at JBL. The
subject is dealt with in much more practical detail in some of the books I recommend.
Last revised: November 01, 1999.