FISHMAN PREFIX™ ONBOARD BLENDER
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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.
PHASE INVERTED 180° | PHASE INVERTED 180° | ||||||
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DISTANCE:
5' 7" |
| 11' 4" |
| 17 ' |
| 22' 7" |
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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.
B. USING THE NOTCH FILTER TO REDUCE FEEDBACK
Notching out instrument cavity resonance will eliminate the low frequency feed- back 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 nat- ural and balanced response.
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