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How to choose audio equipment
most important specifications
response measures the range of tones that your equipment is
able to reproduce. Most people are able to hear tones as low
as 30 Hz and as high as 15,000 Hz, though many can hear 16,000
- 18,000 Hz and a few 20,000 Hz or higher. If you are buying
your equipment to play back or record music, you will find
a wider range makes a noticeable difference in the quality
of what you hear. On the other hand, if youre buying
a cassette deck mainly to do recordings of people speaking,
youll find such ranges unnecessary, as most voices,
in speaking, span a range of only 200 - 2,000 Hz.
important to note that the frequency response of an audio
system is limited to its weakest component. If you use a cassette
recorder that produces a 20,000 Hz high tone with a microphone
that will do no better than 10,000 Hz, youve wasted
the extra quality of the recorder.
to noise ratio measures the most intense video or audio signal
the piece of equipment can reproduce versus its background
noise level. An S/N ratio of 58 dB, for example, means there
can be up to 58 decibels of signal for every decibel of noise.
Higher ratios mean a cleaner signal, and this will be particularly
important in situations where you need to reproduce a pure
tone interspersed with silence. (Thus someone listening to
someone speaking will be much more aware of equipment noise
than someone listening to music.)
harmonic distortion measures all of the unwanted changes in
frequency (tone) in a recorded signal made by the recording
or playback device.
flutter measures unwanted variation in the speed of a tape
recorder or record player, which shows up as changes in pitch.
Wow and flutter exists in CD players, but is so low as not
to be measurable.
range is the ratio of the loudest to the softest sound that
can be reproduced by a piece of equipment. A wide dynamic
range will produce a more lifelike sound only in applications,
such as recording classical music, where theres a large
variation in volume.
expressed in ohms, measures electrical resistance in an AC
system. There was a time when impedance was important to selecting
a microphone, but today, virtually all audio and video equipment
have low-impedance inputs. The only reason to buy a high impedance
mic (or a switchable mic) would be to use with older equipment.
impedance still plays a role. Headset jacks are 8 ohms. Youll
get better volume with a lower-impedance headset if used alone,
but if you have listening centers, you need 600-ohm headsets,
as grouping 8-ohm sets on a listening center can damage the
amp in the source you are using.
In a cassette
deck, frequency response, signal to noise ratio, and wow and
flutter are the most critical measures of quality.
In an amplifier,
frequency response, signal to noise ratio, dynamic range, harmonic
distortion, and maximum output per channel are the critical measures
In a loudspeaker,
frequency response, freedom from distortion, and maximum power
it can accept from an amplifier are critical. When good specifications
are absent, its reasonable to expect larger speakers to
sound better. The best speakers use a crossover circuit to divide
the frequency range: a two-way speaker uses a woofer (for low-frequencies)
and a tweeter (for high), a three-way a woofer, midrange and tweeter.
have an amplifier built in, the more commonly-used unpowered speakers
do not. Youll want a powered speaker for portability or
to use in cases where an amplifier would be expensive or inconvenient
(such as with a personal computer or an engineers station
in a studio).
In a CD
player, sampling rate is the key quality indicator, since
the frequency response of all players is consistently high and
distortion almost nonexistent.
and in analog systems, sound is produced as a continuously varying
set of tones. A digital system, however, can only capture discrete
tones and reproduce them one at a time. The sampling rate denotes
the number of discreet "samples" played per second.
A higher rate is better, though many people will never notice
the difference between high and low sampling players.
In a microphone,
frequency response, pickup pattern, and whether or not the mic
is powered are the critical specifications.
most often find omnidirectional mics, which have a spherical pickup
pattern, and unidirectional mics, which are intended to focus
on your speaker or vocalist. Surface-mounted mics have an extremely
wide pickup pattern and are used to mic two or more people. Shotgun
mics are simply unidirectionals with very tight pickup patterns.
are unpowered, but condenser mics use a battery or phantom power
from the mic mixer. If you want to mic a live speaker, youd
be most likely to use a dynamic mic, because they are easier to
handle and less costly. If you were recording the speaker, however,
or recording music, youd want to use a condenser mics, because
they reproduce sound more accurately.
cost concerns, most stationary mics are wired, but a wireless
system is advantageous if your speaker will be moving around your
stage or set. In a wireless system, the critical specifications
are available frequencies (UHF offering better range, less interference,
better frequency selectivity and better audio than VHF) and whether
or not the system is using diversity antennas (which minimize
radio frequency noise).
A mixer controls
the audio inputs going into your sound system. It can switch between
inputs, control the volume of each input, and control the outputs
to which each input is sent. In a mixer, the number of inputs
and outputs, whether the unit is powered or unpowered (that is,
whether it has its own amplifier built in), its control features,
whether it has phantom power, and its sound quality (shown by
frequency response and signal to noise ratio) are all critical.
mic mixer is a specialized item used in conferences where a large
number of mics are present. An automatic mixer turns mics on as
people begin speaking, thus minimizing feedback and background
noise which would result from having a large number of mics open.
Beyond the basics, youll want to consider if your audio
inputs and outputs. Its very important, for example,
that an amplifier has the connections you need for the components
you plan to use it with, or that a cassette recorder the microphone
or auxiliary jacks you need for the uses you intend.
jacks, which will be important anywhere people need to listen
privatelyfor instance, with students in a classroom
on a cassette deck or record player allows you to use a microphone
and the units amplifier and speaker (or external speakers)
as a public address system.
fine tunes your sound systems frequency response to
a given room. You can use it to adjust bass, treble and midrange
to provide the most pleasing sound and also to minimize feedback.
is sometimes used to provide artificial echo effects, but
its real purpose is to provide extra depth and clarity
to your sound.
controls when the sound gets from the amplifier to each set
of speakers. It should be used whenever you have multiple
speakers in different places in a room, to ensure that the
sound from each speaker reaches the audience at the same time.
or audio limiting circuitry, limits the volume of input sound
to what the system can handle, thus helping to provide an
even output sound and to protect the equipment from damage
due to overload.
speed playback allows you to speed up or slow down a cassette
or record. You would use this in a dance class (usually to
slow down the music to allow beginners to keep up with it),
in an aerobics class (to increase your exercise tempo), or
in a music class (to fine-adjust the pitch of what youre
There are some comparisons that are very difficult to make from
a spec sheet. Youll want to talk to your United account
manager to get a feel for:
Will the component or system work through a critical presentation?
Does its manufacturer have a good reputation? Whats
the warranty? Is it UL listed for business or educational
How long will you have to do without your system if it breaks?
How difficult is it to get parts?