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DJ Sound System Mistakes by Mike Starnes |
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What not to do if you want
your sound system to sound good and last long
1. Mismatched power - One of the most common
mistakes made with mixer-amplifier-speaker combinations is
the use of components that are not evenly matched. For
example, say you have a pair of speakers rated at 300
watts continuous power and 600 watts peak. This gives you
an operating range in which to place the amplifier that
youll use. Check to see whether the speakers are eight
ohms or four ohms in impedance. The next step is to check
the power rating on the chosen amplifier at that specific
impedance or ''load.'' It is very easy to do speaker
damage by using an amplifier with insufficient power. The
lack of headroom or reserve power may cause the
smaller amp to clip, sending a distorted signal to the
speaker, resulting in blown woofers or tweeters.
2. Improper speaker placement - There are no
absolutes in speaker placement because of the variations
among rooms at different locations. The basics are only a
starting point.
Imagine your system set up to play. The speakers are to
the left and right of your centrally located console.
Theoretically they are facing away from you toward the
crowd. You want the best starting point for optimum
performance, lateral projection, vertical projection, and
feedback elimination. Thinking right angles (remembering
again that there are no absolutes), draw an imaginary line
from the center of the speaker at stage left to the
speaker at stage right. Your DJ microphone should be at a
ninety-degree angle to that line, facing directly toward
you to achieve maximum announcement volume. The horns in
each speaker may have lateral dispersion patterns as wide
as 90 to 120 degrees and vertical dispersion from 40 to 90
degrees. Imagine yourself standing on top of the speaker
with your thumb on a water hose (please don't try this at
home). If the pattern of the water matches the projection
pattern of the horn, then everywhere the water goes the
consonants you speak also go. The higher frequencies that
are more susceptible to feedback are present in the
patterns of the horns. If the speakers are slightly
farther back or angled inward, the pickup pattern of your
microphone may overlap the projection pattern of the horn.
Another simple hint is to stand mount the speaker to
counteract the fact that most of the audible speech goes
into the navels of your audience rather than into their
ears. Yes, if the speaker is elevated you may lose the
''coupling effect'' that adds bass from the floor. Of
course subwoofers are a better alternative than the
floorboards. There's also a small pointed area between the
speakers, directly in front of you, called ''The Dead
Zone.'' There are limited highs there as well. Ya win
some, and ya' lose some!
3. Improper wiring - The gauge of the wire used to
move the music from amplifier to speaker is also critical.
Remembering that smaller numbers indicate larger gauge in
wire, we recommend that for short runs of 50 feet or less
you use at least 16-gauge speaker wire. 14-gauge is
preferred, but you can get away with 16 in this
application. Since the wire itself has ''resistance,'' a
good rule to follow is larger wire (with smaller numerical
gauge) for longer distances. You may be using 16-gauge
cable at the present time for speaker runs of one hundred
feet, but you also may be sacrificing some of the
performance. You may also be forcing your amplifier to
work slightly harder to get the same level. The same rules
apply to your electrical cables. Did you ever wonder why
they get warm? They are screaming for more copper, and a
thicker gauge. The expense is slightly more, but your gear
will last longer.
4. Insufficient coverage - This occurs when you
have 1,500 screaming teenagers in a gymnasium, two
speakers on the floor, and a 300-watt amplifier. Parting
the hair of the first eight rows of dancers with high
volume music in order to make it audible for those in the
rear of the room is no longer acceptable. Renting,
purchasing, or borrowing two more speakers with stands may
be the difference between one gig and a string of repeats.
Advance the booking, research the numbers, add extra gear
if needed, and save your speakers from damage. Most
amplifiers on today's market will easily handle four 8-ohm
speakers. Please note that their power also increases to
all four cabinets!
5. Imbalanced gain structures - Please note that
with the massive strides in technology in the last few
years that the operation of most sound systems has become
more ''forgiving.'' If an older system were set with the
gain on the power amplifier low and the master volume on
the mixer at a high position the sound would be audibly
distorted. The newer amps and speakers do not exhibit the
same tendencies, but it is usually (the key word here is
usually) better to run the levels on the power amplifiers
higher. Those of you who still run your DJ mixers into a
PA-style amplified mixer (and you know who you are) please
remember that your systems are more prone to preamplifier
distortion through pilot error, since you actually have
two preamplifiers. Run the master on the amplified mixer
high and control the gain with the DJ mixer. As a general
rule, the best performance of Crown, QSC, Peavey, American
Audio, and most of the other current amplifiers is best
utilized at the higher settings on the amplifier, with the
mixer to ''control'' the level.
6. Improper amplifier ventilation - Almost all of
the current amplifiers have two-speed fans that preserve
the sonic integrity of their internal workings. The
switching amplifiers that boast low weights do so without
the use of larger heat-producing transformers so they are
more susceptible to voltage variations than heat. These
internal fans usually pull air from the rear and force it
out the front (or vice-versa). The fans assist in the
dissipation of the heat generated within through the use
of external cool air. If the catering director skirts the
console table, sealing all four sides of the amp rack
underneath, then warm air is re-circulated. Simply raise
the side facing you with pins or clips so that some cool
air gets in.
Will your amp shut off when it gets hot? Probably not,
since the protective devices in most of the newer amps are
electronic rather than thermal, but it will last longer
and work better if it is kept cool. By the same token,
vent panels and open spaces between amplifiers help.
7. Improper equalizer use - An increase of three
decibels on your equalizer can translate to double the
power to horns or tweeters in your speakers. Excessive
exposure to high frequencies can also induce
''listeners fatigue'' and cause your dance floor to
look like an Enron stockholders meeting. Less is more.
Start with the ''flat,'' or straight-line theory, and use
the EQ sparingly. If you ''have to'' use the EQ a lot, it
may mean that your speaker system doesn't sound like it
should in the first place.
8. Poor microphone technique - This is usually
exhibited when your mic falls into the hands of the best
man at the wedding or the class representative at the
reunion. Most microphones designed for speech exhibit what
is called a ''proximity effect.'' This means that in close
proximity to the person speaking they have a full,
bass-heavy sound. People speaking slightly off axis or
farther back tend to get a sound that is thin and more
midrange heavy. In a baritone voice sing an ''ooooh''
sound while turning the mic from side to side and moving
it slightly away from your lips to see this effect. Two
hints would be to get a washable windscreen for your
''Other guy microphone'' and to instruct non-DJs to ''eat
the mic.''
9. Ill-maintained gear - In other articles we have
stressed the importance of preventive maintenance. Here we
go again! On an off day remove grills on your speakers.
Gently clean or repaint the face of the cabinet. This can
be done with a careful vacuuming or with a paintbrush used
for dusting. Remove the input panel to tighten all jacks
and connectors. Touch up all solder connections. If there
are rattles, diagnose and fix them. After cleaning and
drying the small paintbrush, use it to dust off the face
of the mixer. Be careful of switches and knobs. Check to
make sure all grounding posts are intact. Using a
two-prong cable may result in damage to you or your gear.
10. Pilot error - Think about what you are doing.
Remember your turn-on sequences. Don't turn off the
mixer/console with the amp on. (Pow!) If you see someone
banging the palm of his hand on the ball of your
microphone immediately drop the master volume. (Wait until
after the event to Riverdance on his chest.) Such tapping
can actually cause a blown woofer. Watch your bass
settings, and check your overall volumes. Route your
cables out of ''harms way.''
See your dentist twice a year and let us know if anything
we publish changes your life
Happy Trails!
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