AudioControl SA-3052A, Руководство по эксплуатации

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SA-3052A Owner’s Manual
4-1
®
Perhaps the most important use of the SA-3052A is as an acoustical measuring tool:
e.g. equalizing sound systems. This section of the manual discusses the process and ra-
tionale behind using a real-time-analyzer and an equalizer as an integral part of any sound
system.
Overview (or what we’re trying to accomplish)
The primary reason for using the analyzer with an equalizer is to do what our ears
can’t do reliably: adjust a sound system to a known reference condition. The reason that
we can’t do this “by ear” is our rather poor long term auditory memory. In other words,
our hearing process is very adaptive. Our hearing adjusts to compensate for varying
conditions, sound pressure levels, and tonal balances. When presented with a change,
our sense of hearing can discern that change very readily. This is our short-term audito-
ry memory. On the other hand, our ears are not very good at remembering things over a
long period of time, especially when there are unrelated sounds between the periods of
recall.
Another problem is threshold shift caused by exposure to loud sounds. Without
getting into a lot of detail (don’t worry, we will later), the threshold of hearing (the SPL
where you can sense the presence of a sound) shifts upward when the ear is exposed to
loud sound. The recovery time can be measured in hours to days, depending on the inten-
sity and duration or the exposure. For this discussion, it’s just another problem, or source
of error.
For these reasons, and many more, a real-time-analyzer with a calibrated micro-
phone is one of the most popular methods of measuring the frequency response of a
sound system within an acoustical space.
In a nutshell, a pink noise source excites the space, a microphone picks up the acous-
tical signal and converts it to an electrical signal. The real-time-analyzer (RTA) breaks
the signal up into equal octave-percentage bands, and displays the signal level of each
band individually. The display could be VU meters, a CRT (video monitor or oscillo-
scope), or a LED bargraph. The SA-3052A uses the latter method.
In the real world, very few things are perfect, and expensive sound systems are no
exception. Traditionally loudspeakers are measured in an anechoic chamber (an - not
having, echoic - echoes). An anechoic chamber is a large room, with the floor, walls, and
ceiling lined with acoustically absorbent material. Any sound emitted within the chamber
is absorbed.
Being inside an anechoic chamber is a strange experience. First, you are standing
on a suspended floor made of steel cables. If you are afraid of heights, this is just a good
beginning. Since the walls absorb all sound, it is eerily quiet inside. You can actually
hear your blood coursing through your blood vessels.
At any rate, an anechoic chamber is hardly the same as an average living room.
However perfectly the loudspeaker measured within the chamber, putting it into an
average living room changes the whole ball game. First, the floor, walls, and ceiling are
anything but totally absorbent. This allows the room to have resonances, standing waves,
and a sound of its own. The room interacts with our perfect loudspeaker to produce an
imperfect system.
Chapter 4 - Acoustical Testing with the SA-3052A