ONBOARD ACOUSTIC GUITAR SYSTEM
9
PHASE, Continued from Page 8
WHAT IS THE PHASE SWITCH FOR?
The phase switch is useful for two reasons:
1. Due to the interactive and changing nature of phase, acoustic amplification
depends on maintaining optimum phase relationships between amplified
instruments, sound systems and venues.
2. Since an industry standard for polarity has not been established for all sound
equipment, the phase switch can compensate for any unintentional differences
that might occur between instrument and sound system.
APPLICATIONS
In any situation where the instrument faces a loudspeaker, there will be an inter-
active phase relationship between the two. This usually occurs with stage amps,
side fill and floor monitors at close distances.
• LOW VOLUME AMPLIFICATION
At low volumes, when an instrument and speaker are at similar levels and are
in
phase,
the sound is full and solid, with the lower frequencies emphasized.
When a mic'ed instrument and speaker are
out of phase
at low levels, the bass
frequencies cancel out to some extent. The resulting sound is somewhat unnat-
ural and unbalanced compared to
in phase.
• HIGH VOLUME LEVELS
At high volume levels, when an instrument and speaker are
in phase,
the sound
pressure from the speaker will excite the instrument's sound chamber, creating a
feedback loop at the instrument's lowest octave. This "cavity resonance" feed-
back can be dealt with by putting the instrument and speaker out of phase or by
adding equalization.
A. USING THE PHASE SWITCH TO REDUCE FEEDBACK.
Inverting the PHASE switch will put the instrument and speaker
out of phase
with each other, cancelling the low frequency feedback.
If you move from your position on stage more than a few feet, you may have to
invert the PHASE switch again to maintain an
out of phase
relationship
between the mic'ed instrument and speaker.
Continued ...
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