Being in the sweet spot means the microphone and the sound source are in a harmony of sorts;
the acoustic information is exciting the microphone in such a fashion that the resulting
reproduction is very desirable, usually without the need of additional equalization or electronic
manipulation.
There are only general rules as to where the sweet spot may be found for any given microphone,
and usually experimentation reveals it. The sweet spot can be extremely variable since it depends
on the quirks of a given microphone and a given room. Once the sweet spot is discovered, this
placement can become a rule of thumb starting point for future microphone placement with
similar sound sources. Remember this: If it sounds good, it’s probably right. If it doesn’t, move
the microphone. It’s often more effective to reposition the microphone than to start fiddling with
knobs. Knob twisting can affect headroom and phase coherency and add unwanted noise.
The following is a list of variables that account for “sweet spot” effect:
1. Frequency response variations due to proximity effect.
2. Frequency response variation due to treble losses as a result of absorption and “narrowing” of
the pattern at high frequencies, causing weakening of highs as the microphone is moved
away from the sound source.
3. Variation in ratio of direct to reverberant sound.
4. Tendency of a microphone to favor the nearest sound source due to a combination of these
items, plus the influence of inverse square law. Inverse square law states that for each halving
of source-to-microphone distance, the sound pressure level
quadruples.
Other Types of Microphones
For the same ratio of direct to reverberant sound, omni-directional microphones must be closer to
the sound source than cardioid or bi-directional microphones. Microphones should generally face
the sound source head-on or treble losses due to phase cancellation can result. The exception
here is for large diaphragm condenser microphones, which often give the flattest response at an
angle of about 10-20 degrees (off axis), where phase loss and diffraction effect offset each other
somewhat.
Proximity Effect and Working Distance
The Sound That Is “More Real than Real”
Ribbon microphones have long been renowned for rich bass. This effect is largely due to the fact
that ribbon microphones generally have excellent bass response to begin with, and at the same
time exhibit an effect known as
proximity effect
or
bass
tip-up.
As illustrated in the following graph, a typical bi-directional ribbon microphone will have a flat
frequency response at a distance of about six feet from the microphone, but at shorter distances
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