Speaker Impedance; Speaker Polarity (Or Phase); Impedance Selector Switch - Mesa/Boogie Subway WD-800 Owner's Manual

connected to the second pair are simply not used.
The cables to avoid are what are called NL4 bridge mode cables, which are typically 2 wire, and wired 1+/1- on the speaker end and
1+/2+ on the amplifier end (used for pro audio power amps that support this specific bridged termination). These cables SHOULD be
clearly marked but sometimes they are not, so be aware of the possibility when buying or troubleshooting cables.
Why SpeakOn™ cables and not the "old favorite" ¼" (6.35mm) connector? There are several important reasons, the first being that
with updates to global safety regulations, amplifiers like the Subway WD-800 require "touch-proof connections". A second reason is
because the power amplifier's internal topology is BTL (bridge tied load), neither output terminal are at ground potential, so touch-proof
connectors provide an added layer of safety to the system. A third reason is the often poor quality of the 1/4" (6.35mm) connection,
which at low power is not much of an issue, but at higher power levels become a failure point. A fourth reason is that one common
failure mode of amplifiers is when the 1/4" (6.35mm) speaker cable works loose at the speaker cabinet, the tip gets shorted to the
sleeve within the speaker jack's bushing, applying a short circuit to the amplifier's speaker output. While this amplifier is protected
against such faults, it's not good practice to test any amplifier protection on a regular basis.
Never connect the speaker output to anything except a speaker. This especially means not to a DI, even a speaker level DI
because the Subway WD-800 utilizes a BTL (bridged) output power amplifier. On a bridged amplifier, the minus terminal that
is normally at ground is actually a driven output that swings above and below ground at peak currents of up to 30 amps. Using a
DI, the normal shell or ground terminal (pin 1) of the DI is not at ground at the amplifier's end but may be connected to the console
(mixer) circuit ground bus at the console's end which would cause the amplifier to drive dangerous currents into circuitry that does
not expect to see such currents, nor is it generally protected from this fault. So, in addition to possibly damaging your amp, you could
also damage a (potentially) very expensive console.

SPEAKER IMPEDANCE:

that the amplifier is tasked with delivering. The lower the speaker's impedance, the greater the current that the power amplifier must
provide. The lowest impedance that the Subway WD-800 amplifier is capable of driving safely is 2 ohms (with the impedance selector
switch in the 2 ohm position), which is a parallel connection (the standard connection of virtually all speaker cabinets) of either two
x 4 ohm cabinets or four x 8 ohm cabinets. Note that measuring speaker cabinets using an ohm meter will not give accurate results
because ohm meters read DC resistance not AC impedance (technically called "reactance"). AC impedance will always be greater
than the DC resistance, an 8 ohm speaker will typically measure between 5 and 7 ohms, a 4 ohm speaker will typically measure
between 2.5 and 3.5 ohms when measured with an ohm meter (or DMM).

SPEAKER POLARITY (OR PHASE):

dustry standard will move forward when a positive DC voltage is applied to the positive terminal of the speaker. While there are well
established standards, there are also deviations from standards, either by legacy (ie. early JBL drivers), by faulty repair (incorrectly
wired cabinet or defective recone parts) or a manufacturer choosing to ignore the standard. If a multi-driver speaker cabinet or a pair
of speaker cabinets does not appear to have the expected output or low end, it's always a good idea to double-check that all drivers
move forward with positive DC voltage (no more than a 9 volt battery) momentarily applied to the + terminal (this will be the 1+ terminal
on a SpeakOn™ connector, or the tip on a 1/4" (6.35mm) connector). If you find that on a multi-speaker cabinet, one speaker moves
out while the other does not move, it's likely that the non-moving driver has either failed or has become disconnected. If one driver
moves out while the other driver moves in, it's likely that the driver moving in is wired incorrectly (or in a sealed cabinet is failed or
disconnected and is merely being moved in the opposite direction by coupling to the air mass inside the cabinet itself). Being aware
of these possibilities can often help when troubleshooting something that doesn't appear to be performing quite right.

IMPEDANCE SELECTOR SWITCH:

amplifier's drive capabilities to loads below 4 ohms. Whenever using loads of either 2.66 ohms (a 4 ohm load paralleled with an 8
ohm load or three paralleled 8 ohm loads) or a 2 ohm load (a 4 ohm load paralleled with a 4 ohm load or four paralleled 8 ohm loads)
this switch must be set in the 2 ohm position. Failure to do so will result in the amplifier's protection circuits (correctly) shutting the
amplifier down due to an over-current fault condition.
All speakers have a "rated nominal impedance". Impedance is the resistance to AC electrical current
All speakers have "polarity". A speaker that is wired in accordance to the current in-
The SUBWAY WD-800 is equipped with an impedance selector switch to match the
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