[Dixielandjazz] More about hearing onstage (you may safely ignore this one too)

[Edgerton, Paul A]

Bob Ringwald:
"While your technical info is correct, the problem with hearing drums or
other instruments that are 10, 15, 20 feet away an be compounded by the
various echos bouncing around from the ceiling, floor walls, etc......."

Jim Kashishian:
"Paul, I was going to come back to you on the same subject."

Actually, the point I was trying to make is that these hearing problems
aren't caused by too much sound bouncing the stage -- they are in fact a
problem of the sound NOT bouncing back *soon enough*. So-called early
reflections are your friend: they make things sound louder, cleaner and more
present. Late reflections (like  Ringwald's Carnegie Hall echoes) make
things mushy, indistinct and hard to sort out. This is why you often see a
band shell or a reflective screen in use on a really big stage. It's also
why many musicians don't like to play open-air venues. We really crave those
early reflections.

Sound obeys the inverse square law, which is just a fancy way of saying that
the farther away you are, the softer it sounds. Sound bounces around inside
rooms and we call that reverberation. In every room, there is a point where
the volume of reverberation is as loud as the sound coming directly from the
instruments. This is called the critical distance, and in a very live room
such as a concert hall or gymnasium, that distance might only be a few feet.


The audience is almost always beyond the critical distance, so what they are
actually hearing is mostly the room. It turns out that we *like*
reverberation, so if the room is good, the sound is good. When the room
*isn't* so good, we may attempt to make up for it by using a sound system to
make the direct sound louder than the reverberation. This works okay for the
folks who are sitting close to a speaker. But in most real-world venues, it
usually just creates more reverberation and a not very satisfying result for
at least some part of the audience.

Back on the stage, the musicians might be within the critical distance.
That's a good thing because it helps them hear each other clearly. But as
the critical distance gets smaller (that is, as the room gets bigger) it
becomes more and more important to have those good, early reflections I
mentioned above be substantially louder than the evil, late reflections.

This is where a good monitor system plays an important role. Even though a
musician might be standing clear across the stage from you, his microphone
is still right in front of him. We can send some of that mic's signal to a
monitor on the floor right in front of you and you'll be able to hear him as
though he were nearby. We have accomplished electronically what we might
have otherwise done physically: brought the two of you closer together.

Of course there's no free lunch. Adding monitors raises the overall volume
on stage, thereby increasing reverberation that you have to fight. We don't
normally listen to instruments from a distance of a few inches, so the sound
picked up by the mic is inaccurate. Then we splatter that inaccurate sound
all over the place, including where *other* mics can pick it up again. It's
easy for this whole mess to get to get out of hand.

Doing a good job of setting up and running a sound system is largely a
matter of juggling conflicting needs and values -- just like any other kind
of engineering. You can build a good bridge by making it much stronger than
any possible load (at great expense) or you can analyze the hell out it and
make each part exactly as strong as it needs to be, while hoping that you
didn't leave anything out of your calculations. You can put a speaker near
everybody in the audience (at great expense) or you can analyze the hell of
it and put a few speakers in exactly the right places so that everybody gets
to hear both the direct sound from the musicians and smooth, well-balanced
reverberation from the room. 

In the real world, not everything can be known in advance, so engineers
build bridges with a safety margin, but also have to meet a given budget.
Likewise, not every venue can be known in advance, and sound systems have a
finite number of mics and speakers. In a fixed installation like a church,
you have the opportunity to match the system to the room and the needs of
the music. In a portable system, you select equipment suitable for a variety
of situations. It's all a compromise, and the skill of the soundman is
usually the key factor in sorting it out.

It's sad that some people think owning sound equipment qualifies them as an
expert soundman. That's just like claiming that owning a trumpet qualifies
them to play the lead book. There's slightly more to it.

-- Paul Edgerton
Who reminds you that speakers don't cause feedback -- people do.