7
Every speaker cabinet has an impedance rating listed in ohms. Think of the
impedance as the speaker cabinet’s resistance to an amp’s power. The
higher the cabinet’s impedance, the more the amp has to work to push
power through it. The goal in any amp/cabinet configuration is the match
the amp’s speaker output impedance with a speaker’s impedance
(sometimes called “load”).
JCA20HV has outputs on the back marked “16 ohm” and “8 ohm.” Use the
correct output for your speaker configuration. If your speaker cabinet is
listed as “16 ohms” use the “16 ohm” output from the JCA20HV.
Speaker cabinets often have a set of ¼” jacks labeled “series” or “parallel.”
This allows you to run a speaker from your head to one cabinet and then
from that cabinet to another one. When you use the “series” output, the
load increases so you add each cabinet’s impedance to determine the
overall load (two 8-ohm cabs in series = 16-ohm load).
When you use the “parallel” output, the load decreases. If all cabinets have
the same impedance, then divide that impedance by the number of
cabinets (two 8-ohm cabs in parallel = 4-ohm load). If the cabinets are of
different impedance, then multiply the impedances together and divide this
by the sum of the cabinet impedances (one 8-ohm cab and one 16-ohm cab
in parallel = 5.33-ohm load). In case of an awkward number, default to the
impedance closes to, but lower than, the number (for a 5.33-ohm load, use
the 4-ohm output).
