If you ask most jocks/announcers what type of loudspeakers they
would like in the control room, you might hear a response like
“lots of power so I can feel the music.” If you put this
query to the station engineer, you're just as likely to get a different
response with specs on sensitivity and power handling. It's more a
question of personal tastes and desires, than the attributes of any
Since we are mostly concerned with monitoring the quality of our
on-air signal, it stands to reason that a clear and reasonably loud
sound field be maintained at the operator's position. Given the less
than perfect dispersion fields of many speaker units, and no standard
placement in the control room, the clarity of the signal may be muddied
by the acoustics of the room, reflections from various angular surfaces
of the console and nearby equipment, and the quality of the amplifier
driving the system.
Modern materials have improved sonic and
electrical loudspeaker performance.
Many radio studios, and most recording studios, are moving to
nearfield monitors. For a talk-show studio with multiple host and guest
positions, the high-on-the-wall-looking-down position is better. For
voice monitoring, positioning is not so critical as it is for
qualitative listening to the mix of music, jingles, stingers, announcer
voice-overs, etc. Cue speakers are another critical need in the studio.
It is often advisable to place the cue speaker on the floor, behind the
operator or in a position away from the main monitors so that a busy
operator can identify and focus on different sounds during a lively
The usual desires of announcers range from loud to bleeding ears.
Running speakers too loud can cause acoustic leakage to other studios
and danger to hearing health as well. Scale down the type and style of
booth speakers to something reasonable. Judicious attention to
amplifier output rating and possible input signal limiting may be
advisable for booth use. You can also reduce the overall level by
moving the speakers as close to the operator as possible.
Not a plumber's leak
Speaking of acoustic leakage, this has always been an engineer's
nightmare. Concrete blocks, bricks, lead sheeting and pads, rubber feet
and absorbers are among the common materials used to minimize acoustic
leakage. One of the more interesting absorptive mountings that I have
seen had the speakers sitting in box-like enclosures filled with fine
sand; somewhat like indoor planters. It looked strange but did the job
Self-powered nearfield monitors are
gaining popularity in many production facilities.
Acoustic leakage can be attributed to a monitor level that is too
loud in the adjacent studio. While solid architectural and acoustic
designs can minimize airborne sound leakage, a direct physical
connection can nullify any efforts and expense that have already been
made. A mounting bracket or suspension scheme that does not rely on
wall studs or common ceiling joists may be part of the solution.
Well-managed remotes need quality loudspeakers too. The sound
quality of playback direct from air is critical in maintaining good
client relations at the remote site. Self-amped speakers made for PA
and music playback, mounted on heavy-duty tripods, are perfect for
smart-looking remote operations. Since each speaker assembly carries
its own amplifier, proper volume levels can be achieved.
Caring for loudspeakers
Speakers tend to be forgotten once they are installed and
operational. Proper maintenance is important, however. Monthly dusting
of the speaker cone using a soft vacuum brush applied gently is a good
idea. The other threats to speaker longevity are over-powering and
excessive continuous distortion. The first one is simple — do not
install an amplifier with more power than the speaker can handle. Peak
watts, the maximum amount of power that a speaker can safely dissipate
for a fraction of time, are roughly double the RMS value.
When used near video monitors, nearfield
monitors must be properly shielded to avoid magnetic video
Distortion damage can occur even when safe power levels are never
exceeded. The speaker is an electro-magnetic device that wants its
voice coil to move longitudinally over the magnet. When the amplifier
doing its work is driven into distortion by too high an input, or some
other defect, the percentage of square waves delivered to the speaker
drastically increases, causing the voice coil to attempt to move
laterally — sideways rather than in and out. Excessive distortion
delivered to the speaker causes overheating of the coil, since it
cannot self-ventilate as it would in normal longitudinal motion. The
end result is a burned voice coil.
Basic electronics knowledge tells us that a thinner conductor is
more likely to lose energy passing through that conductor as dissipated
heat. We can deliver the most power from amp to speaker by using the
right size of conductor. For the majority of systems under 100 watts,
regular 16-guage lamp cord will do. Phasing is critical for proper
operation. A set of out-of-phase loudspeakers makes it impossible to
derive proper stereo imaging, and the apparent sound field will seem to
wander around the room. It is vital that the “+” terminal
on the amp be connected to the “+” terminal on the
loudspeaker. A way to determine the correct phasing if a phase meter is
not part of your instrument collection is to drive the set of speakers
with a mono source. If the speakers are in phase (both cones moving
outward at the same moment) and aimed properly, the sound field will
appear to originate from a phantom center position.
Phase coherence between channels is important, but absolute phase is
just as critical. The speaker pair in question may be in phase with
each other, but the waveform may be reproduced in reverse. When a bass
drum sound is produced, the speaker cone should move outward and push
air. It should not move inward and pull air.
Some speakers provide digital audio
inputs in addition to a self-contained power amplifier.
Generally, speakers are divided into powered and non-powered
classes. Non-powered speakers require a power amplifier. Powered
speakers have a self-contained amplifier within. With non-powered
monitors, an amp failure can be corrected without removing the speaker.
Likewise, a power amp can be placed in a more favorable position to
allow for physical space limitations. Powered monitors can be much
heavier than non-powered versions. Also, powered monitors require an
electrical power source. For longer cable runs, it is better to run a
line-level signal than a speaker-level signal. Finally, a powered
monitor will also free some valuable rack space and remove a large heat
generator from the confines of the rack.
Many models are also available in shielded models, which reduce the
magnetic field outside the enclosure. This is important when a speaker
is placed near a video monitor because the magnetic field can cause an
undesired effect to the color display.
With the extremely wide and varied assortment of speaker systems,
and the many discrete loudspeaker components and plans/specs for
building one's own enclosures, the broadcast engineer has the daunting
task of choosing an appropriate sound reproducer, and possibly the
right mounting system as well.
Allan Soifer is an audio recordist and production consultant in