Main Points
▶ The sound chain begins with the microphone, whose
signal is sent to a console or mixer for routing and then
processed, recorded, and heard through a loudspeaker.
▶ Loudspeakers are transducers that convert electric energy
into sound energy.
▶ Loudspeakers are available in the moving-coil, ribbon, and
electrostatic, or capacitor, designs. The moving-coil loudspeaker
is by far the most common.
▶ Loudspeakers that are powered externally are called passive
loudspeakers. Those that are powered internally are called
active loudspeakers.
▶ A single, midsized speaker cannot reproduce high and
low frequencies very well; it is essentially a midrange
instrument.
▶ For improved response, loudspeakers have drivers large
enough to handle the bass frequencies and drivers small
enough to handle the treble frequencies. These drivers are
called, informally, woofers and tweeters, respectively.
▶ A crossover network separates the bass and the treble
frequencies at the crossover point, or crossover frequency,
and directs them to their particular drivers.
▶ Two-way system loudspeakers have one crossover network,
three-way system loudspeakers have two crossovers, and
four-way system loudspeakers have three crossovers.
▶ In a passive crossover network, the power amplifier is external
to the speakers and precedes the crossover. In an active
crossover network, the crossover precedes the power amps.
▶ Each medium that records or transmits sound, such as a
CD or TV, and each loudspeaker that reproduces sound,
such as a studio monitor or home receiver, has certain
spectral and amplitude capabilities. For optimal results
audio should be produced with an idea of how the system
through which it will be reproduced works.
▶ In evaluating a monitor loudspeaker, frequency response,
linearity, amplifier power, distortion, dynamic range, sensitivity,
polar response, arrival time, and polarity should also
be considered.
▶ Frequency response ideally should be as wide as possible,
from at least 40 to 20,000 Hz, especially with digital sound.
▶ Linearity means that frequencies being fed to a loudspeaker
at a particular loudness are reproduced at the
same loudness.
▶ Amplifier power must be sufficient to drive the loudspeaker
system, or distortion (among other things) will result.
▶ Distortion is the appearance of a signal in the reproduced
sound that was not in the original sound.
▶ Various forms of distortion include intermodulation, harmonic,
transient, and loudness.
▶ Intermodulation distortion (IM) results when two or more
frequencies occur at the same time and interact to create
combination tones and dissonances that are unrelated to
the original sounds.
▶ Harmonic distortion occurs when the audio system introduces
harmonics into a recording that were not present
originally.
▶ Transient distortion relates to the inability of an audio component
to respond quickly to a rapidly changing signal,
such as that produced by percussive sounds.
▶ Loudness distortion, or overload distortion, results when a
signal is recorded or played back at an amplitude greater
than the sound system can handle.
▶ To meet most any sonic demand, the main studio monitors
should have an output-level capability of 120 dB-SPL and a
dynamic range of up to 80 dB.
▶ Sensitivity is the on-axis sound-pressure level a loudspeaker
produces at a given distance when driven at a certain
power. A monitor’s sensitivity rating provides a good overall
indication of its efficiency.
▶ Polar response indicates how a loudspeaker focuses sound
at the monitoring position(s).
▶ The coverage angle is the off-axis angle or point at which
loudspeaker level is down 6 dB compared with the on-axis
output level.
▶ A sound’s arrival time at the monitoring position(s) should
be no more than 1 ms; otherwise, aural perception is
impaired.
▶ Polarity problems can occur between woofer and tweeter
in the same loudspeaker enclosure or between two separate
loudspeakers.
▶ Where a loudspeaker is positioned affects sound dispersion
and loudness. A loudspeaker in the middle of a room generates
the least-concentrated sound; a loudspeaker at the
intersection of a ceiling or floor generates the most.
▶ For professional purposes it is preferable to flush-mount
loudspeakers in a wall or soffit to make low-frequency response
more efficient and to reduce or eliminate back-wall
reflections, cancellation, and cabinet-edge diffraction.
▶ Stereo sound is two-dimensional; it has depth and breadth.
In placing loudspeakers for monitoring stereo, it is critical
that they be positioned symmetrically within a room
to reproduce an accurate and balanced front-to-back and
side-to-side sonic image.
▶ Loudspeakers used for far-field monitoring are usually large
and can deliver very wide frequency response at moderate
to quite loud levels with relative accuracy. They are
built into the mixing-room wall above, and at a distance of
several feet from, the listening position.
▶ Near-field monitoring enables the sound engineer to reduce
the audibility of control room acoustics, particularly
the early reflections, by placing loudspeakers close to the
monitoring position.
▶ Surround sound differs from stereo by expanding the
depth dimension, thereby placing the listener more in the
center of the aural image than in front of it. Therefore,
using the 5.1 surround-sound format, monitors are positioned
front-left, center, and front-right, and the surround
loudspeakers are placed left and right behind, or to the
rear sides of, the console operator. A subwoofer can be
positioned in front of, between the center and the left or
right speaker, in a front corner, or to the side of the listening
position. Sometimes in the 5.1 surround setup, two
subwoofers may be positioned to either side of the listening
position.
▶ 7.1 surround sound, which is growing in popularity, feeds
the two added channels to left- and right-side speakers.
The additional speakers improve sound localization.
▶ As important as personal taste is in monitor selection and
evaluation, calibration of a monitor system is critical to the
objective measurement of the correlation between monitor
sound and room sound.
▶ In adjusting and evaluating monitor sound, objective and
subjective measures are called for.
▶ Devices such as a spectrum analyzer measure the relationship
of monitor sound to room sound. Although part of
testing a monitor loudspeaker involves subjectivity, there
are guidelines for determining performance.
▶ When evaluating the sound of a monitor loudspeaker, it is
helpful to, among other things, use material with which
you are intimately familiar and to test various loudspeaker
responses with different types of speech and music.
▶ Headphones are an important part of monitoring, particularly
on-location. The following considerations are basic
when using headphones for professional purposes: the
frequency response should be wide, fl at, and uncolored;
you must be thoroughly familiar with their sonic characteristics;
they should be circumaural (around-the ear), as
airtight as possible against the head for acoustical isolation,
and comfortable; the fit should stay snug even when you
are moving; and, although it may seem obvious, stereo
headphones should be used for stereo monitoring, and
headphones capable of multichannel reproduction should
be used for monitoring surround sound.
▶ Headphones can be detrimental to hearing because they
are mounted directly over the ears or, with earbuds, placed
inside the ears. Outdoors the problem is exacerbated by
the tendency to boost the level so that the program material
can be heard above the noise floor.
▶ To help reduce the potential of hearing loss is the active
noise-canceling headphone, which detects ambient noise
before it reaches the ears and nullifies it by synthesizing the
sound waves.
▶ Passive noise-canceling can be employed using high-quality
conventional circumaural headphones that fit snugly
over the ears.
▶ The in-ear monitor (IEM) allows a performer to hear a mix
of on-stage microphones or instruments, or both, and
provide a high level of noise reduction for ear protection.
Since their development, IEMs are used for other monitoring
purposes. One company has developed a sound-level
analyzer for the specific purpose of measuring in-the-ear
monitoring levels to guard against excessive loudness