Filter
Top Products
P
REFIX
™ P
RO
B
LEND
9
WHY DO I NEED A PHASE SWITCH ?
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 mic'ed instrument faces a loudspeaker, there will be an
interactive 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 a mic'ed 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
unnatural and unbalanced compared to
in phase.
• HIGH VOLUME LEVELS
At high volume levels, when a mic'ed 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" feedback can be dealt with by putting the mic'ed 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 mic'ed 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
...
F
ISHMAN
P
REFIX
™ S
ERIES
10
Continued from Page 9
Here's why:
A typical guitar has a cavity resonance of about 100 Hz. This is the frequency
that generally feeds back when a mic'ed guitar and speaker are
in phase.
100 Hz has a wavelength of about 11 feet.
Phase inverts 180° for every 1/2 a frequency's wavelength. In this case, 1/2 the
wavelength is about 5 1/2 feet.
If you set your PHASE switch to eliminate cavity resonance
(out of phase)
and
then move 5 1/2 feet towards or away from the speaker, you will effectively put
the mic'ed guitar/speaker relationship at 100 Hz back
in phase;
in the line of fire
for low frequency feedback.
B. USING THE NOTCH FILTER TO REDUCE FEEDBACK
Notching out instrument cavity resonance will eliminate the low frequency
feedback problem completely. The advantages to using notching equalization
are:
• The physical distance from the speaker will no longer be a factor for potential
low frequency feedback.
• The mic'ed instrument/speaker can remain
in phase,
maintaining a more
natural and balanced response at lower volume levels.
DISTANCE:
5' 7"
PHASE INVERTED 180˚ PHASE INVERTED 180˚
11' 4" 17 ' 22' 7"
The PHASE switch on the ONBOARD BLENDER in effect electronically "moves" your instrument's
position relative to the speaker by inverting the phase 180° every time you flip it.