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Common DJ Sound
System Mistakes by Mike Starnes
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 you’ll 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 ''listener’s 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 ''harm’s
way.''
See your dentist twice a year and let us know if anything we publish
changes your life…Happy Trails!
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