| Welcome back from the preceding
thousand years! Was the millennium good to you? How about those
overrated Y2K prophecies? Well here we are in January, and here
it is, the January edition of SCN, just like any other year...nevermind
that this is the January 2003 edition!
Okay, okay, so meeting the deadlines for publication may result
in one writing the column before the event, and missing the
big story, sort of like the Dewey/Truman prediction fiasco (for
you students of journalism or American history). Consequently
the safest thing is to write about something rather immutable,
which also happens to lead right into this month's diatribe.
One of the things that has always amazed me is the famous (or
infamous) "general knowledge" regarding churches and
sound systems. This general knowledge states that churches typically
will have three or four sound systems over the years before
they finally get a system that's right. Of course one's first
thoughts are "What a boon for the manufacturers, a potential
market four times larger than the 'installed base'!" Also
what a bonus for designers and integrators "work"
that trickle-down economy! But perhaps the real nagging question
is "Why?"
The old adage has it that you should never bring up sex, religion,
or politics in a conversation, but is ironic that along with
the obvious factor, another of these topics (your call as to
which one) is so often a part of church projects. Because the
interest in a new audio system is presumably based upon dissatisfaction
with the current situation, one would think there would not
be such an insistence on "holding on" to the very
factors that have resulted in the current displeasure. But the
politics of the environment often work against common sense.
There are relationships involved which are much thicker than
science. How many times have you discovered that a career installing
loudspeakers in automobiles has apparently rendered someone's
cousin knowledgeable in the full aspects of acoustics and audio
systems?
On the other hand, I continue to be impressed at the deep-rooted
faith of many pastors, church committees, and their architects
that the Lord has chosen to suspend the laws of physics from
operating within their sanctuary. How else can one explain the
often adamant stance that nothing shall be seen, nor shall it
be larger than "(fill in the blank with a ridiculous size
which varies with the project, typically in an inverse rela-tionship
with the reverberation time!)." However as far as I know
neither a local repeal of the laws of physics nor an aural miracle
have much chance of occurrence.
And of course this discussion wouldn't be complete without
the apocryphal story of the "church just like ours which
used XYZ and it worked beautifully," where XYZ is a system,
location, device, size, color which makes absolutely no engineering
sense in this project environment. (Just kidding about the color.)
Naturally a visit to the ref-erenced system and church always
brings to light an element which was completely forgotten. Yes
they only had one loudspeaker for the entire church, but there
were only 50 people, or the T60 was under a second or you know
the way it always turns out.
So where does that leave us? Hopefully, along with our justified
frustrations, somewhat humbled, with an understanding that the
sense of personal involvement and ownership runs deep within
church environ-ments. Consequently it is not merely the acoustic
challenge which must be met, but a human one as well.
How to tell the enthusiastic volunteer that the many hours
of work they have cheerfully donated to the church audio system
are worthless? How to tell someone who is interested and well-meaning
that they are irrevocably incorrect, and their past advice has
led to the purchase of expensive equipment which although excellent,
is completely inappropriate for the intended usage? How to take
these people that you have es-sentially held up to ridicule
and insult and make them part of your team, helping them to
understand the engineering behind your recommendations (removing
it from the realm of personal opinion), and bringing them into
agreement and buy-in with the system design and concepts?
Speaking from experience, you ignore this aspect at your peril!
Regardless of how well your system works, if you do not or cannot
solve the human challenges of the situation, your system will
become one of the transitory systems along the route to their
final installation.
So, speaking of transitory, what if a tree falls in a church
without walls or ceiling? Would it generate a reverberant field?
How about if the sound system produced energy that was completely
incident upon the seating area and none of it intersected the
room boundary surfaces? Would it generate a reverberant field?
The answer is that if you fully obey the First Commandment
of Audio (Thou shalt put the Sound where the People Are) and
minimize the sound energy reflecting off room boundary surfaces,
you can effectively reduce the room reverberation which is generated
via the sound system.
Why do we care about that pesky reverberation time? One of
the banes of church work is the dichotomy between music and
speech. From a music standpoint we want the fullness and support
of a fully reverber-ant environment, whereas the signal to noise
demands of intelligibility require us to emphasize the ratio
of direct to reverberant energy. Consequently we add absorption
to reduce the reverberation time, we move loudspeakers closer
to the listeners to increase the direct energy and minimize
the acoustic power energizing the reverberant field, and other
variations on the theme--not always to the benefit of the music.
With the advent of new loudspeaker devices with extremely narrow
vertical cover-age angles (compliments of amplitude shading
and frequency tapering via DSP) the seemingly insurmountable
task of serving two masters (and it's Biblical, look it up)
appears more possible than ever before. It is not merely theory.
We have measured significant reductions in room reverberation
time utilizing these phased array devices com-pared to devices
with minimal pattern control, The result? Intelligibility goes
up via the audio system, while reverberation time for music
remains intact.
So what about those laws of physics anyway? Well one of the
interesting aspects of our times is the sneaky way new tools
turn up which ignore the law you were focused upon, and solve
the problem from another direction. As Pete Townshend says,
the "trick is to walk in backwards like you're walking
out." Got that?
Kurt Graffy (kurt.graffy@arup.com) heads up the San Francisco
office of Arup Acoustics, a global acoustical consultancy based
in the UK. He is the vice-chair for the Audio Engineering Society’s
Technical Committee on Acoustics and Sound Reinforcement, and
has been an instructor at various Syn-Aud-Con special seminars. |
