|
|
Part 3
Fidelity
How good do you want that speaker to sound? Today’s professional
speakers all sound pretty good. There are some that aren’t
quite as good as the typical, and there are quite a few which
sound much, much better. However, such fidelity comes with a price
many churches can’t justify. If the standard fidelity system
was to be installed properly and the acoustics of the room were
correct, everyone would be quite happy and it would be a rather
exciting system. The only way they would know any different is
if they were to install the more expensive, higher fidelity system
in the same room.
Bass Boost
If you need more bass, consider a subwoofer. These speakers reproduce
the very low frequencies some of which are often felt more than
they’re heard. Once again, before you decide to add subwoofers
to your system, assess the acoustics of the room. Acoustical problems
will limit how much bass you’ll have in the room. In one
church, they had two twin-18 subs and wanted to get two more.
Remember, doubling the number of speakers only adds 3dB to the
level. Well, for about the same cost of purchasing the two speakers,
amplifiers, cable, and installation time, they improved the acoustics
of the room and guess what – they gained 6dB in the low
frequency range! Not only that, but as a side effect, the choir
now sounded better, the piano and organ sounded better, and the
congregation was able to learn new songs faster. So, once again,
don’t bypass the acoustics of the room thinking you can
solve all of your problems with equipment. It can’t be done.
Where should the subwoofers be located? Should they be on the
floor or up in the air with the cluster? Placing them with the
rest of the cluster helps preserve the time arrival issues for
all of the seating areas. Placing the subwoofers on the floor
results in a more rock-and-roll sound and decreases the gain before
feedback of the system. Some people try to get around this by
feeding the subs a separate signal from a submaster or auxiliary
send off the mixer different than the main mix. Then they simply
dial in which instruments they want in the subs and leave out
any vocal mics. At this point, the subwoofer becomes a special
effect system and not part of the overall system. There are many
components of the human voice than can make use of a properly
adjusted subwoofer system, so deciding to use the subwoofer only
for instruments sets it apart from the main speaker system by
default.
Some designers have been known to set up systems with three and
even four low-frequency speakers, each covering a narrow portion
of the audio spectrum. This results in the ability to choose the
right speaker for each frequency region and gives more control
and power to the system.
The subwoofer system helps extend the frequency response of the
entire system. In a typical setup, the full-spectrum audio is
fed into a crossover which then divides the audio signal into
the bass (subwoofer) frequencies and the remainder of the frequencies
(fed to the full-range speakers). (Some systems are 3-way, 4-way,
or even more; such systems are divided into the subwoofer frequencies,
the low frequencies, and high frequencies.) Another form of wiring
the subwoofer is to feed it from an auxiliary or submaster send
on the mixer. This way, the sound operator can selectively send
specific inputs to the subwoofer (and not others). For example,
you might wish to send the bass guitar and kick drum to the subwoofer,
but not the lead vocal. This type of system setup uses the subwoofer
as an effect, not part of the speaker system as a whole.
Speaker Mounting Safety
How does one mount speakers? That’s another long discussion
we could entertain. The simple answer is this: the best way to
hang a speaker or speaker system is by using a custom made all-steel
bracket which is welded together properly. Such a bracket ensures
the speaker(s) won’t go anywhere. The solid construction
also means that you’re coupling a good portion of the low
frequencies directly into the structure. This results in the sensation
of bass without having to turn it up really high. Thus, the teenagers
are happy since they “feel” the bass, and the older
folks are happy because it’s not so loud.
If you use chain or cable, you need to have a backup support.
That is, if you use chain, you need to have a cable backup. If
you use cable, you need to use a chain backup. This is the safest
way to install them no matter what state laws says. Remember,
playing sound through a speaker will cause the suspension system
to swing. Also a ceiling fan or an air duct can blow enough air
past a speaker causing a slow swing too. Cable or chain suspension
wear out the metal links until the speaker falls. It may take
10 years or longer before the speaker support fails, but it does
happen. It often takes two or three times longer to install a
system with cable or chain than it does with a steel bracket.
It also costs more than the steel bracket. Any cable or chain
system should be inspected yearly to ensure the rigging components
are all in good condition and nothing is wearing out. Will you
have to rent a lift or scaffolding to do such an inspection? Hey,
touring groups check their rigging hardware each time they fly
their equipment. If something looks worn or damaged, they destroy
it and replace it with a new part.
While I’ve not personally seen any speakers fall in churches,
I’ve heard a number of first-hand reports from my associates
in the field. In one case, the contractor used a hydraulic scissor
lift to get up to the peak of a church to replace the speaker
system. When the lift got near the peak, the handrail of the lift
touched the existing speaker and moved it slightly. This minor
bump resulted in the speaker suddenly releasing from it’s
mounting and collapsing onto the floor of the lift basket. Upon
further inspection, the original installation used standard off-the-shelf
hardware which, over the years, had begun to allow the links to
slowly open up, aided by the 24 hour a day, 7 days a week, and
365 days a year slow swinging provided by nearby ceiling fans.
It was only a matter of time that this speaker had before it fell
to the sanctuary floor, causing either massive damage, serious
injury, or even death.
speaker mounted with an all-steel bracket
Finally, make sure the speaker is designed to be flown, many
are not. A speaker box assembled with glue and finishing nails
isn’t going to hold together very well near the roof of
a church where temperatures can be quite high for days and weeks
on end. Some manufacturers will help you in adding the needed
structural support to the box so it can be hung safely. Once again,
the all-steel bracket allows so many possibilities when it comes
to speaker mounting and doing it safely.
Making the Choice
With nearly a dozen big-name speaker manufacturers out there (and
many other smaller lesser-known names), where do you start when
it comes to figuring out which speaker(s) to use in your room?
First, figure out how much sound level you need in the pew. A
church that needs only 90dB maximum can use less expensive speakers
than a church that needs 105dB or 115dB. Yes, this means that
traditional churches can save a few dollars compared to contemporary
churches requiring high levels of amplification for each and every
instrument used. Next you need to figure out your coverage. Will
a 90 x 60 speaker do or do you new 140 degrees up front and only
40 degrees at the back? Will one speaker do the job, or do you
need several to cover different portions of the room or to provide
higher SPL than a single speaker can provide? If the reverberation
time is short, you can use less expensive speakers. If it’s
long or too long and the church won’t change the acoustics,
then be prepared to spend more on your speakers to keep as much
sound on the people and not on the walls. Another point to remember—the
narrower the dispersion a speaker has, the worse it sounds. Have
you ever heard a good sounding bull horn? I didn’t think
so. How much gain is there available in the room? If you only
have 3dB of gain, then keep adding zero’s to the cost of
the speakers. If you have 12dB of room gain, then you can keep
the speaker cost lower. If this all seems overwhelming and you
already have the books and math on audio, then you may need professional
help. If you first limit your speaker choices and system design
based on the math, you will do very well. Then again, a single
slip in the calculations with the math and you can make a big
mistake too. If you choose the speaker because of hype or an emotional
attachment to a name brand, then you might as well do better playing
the lottery.
Click here for Part 4 |
