HOW IMPEDANCE AFFECTS POWER RATINGS
People often have questions about impedance. What is it? The root of the word "impedance" is the verb
"impede," which means to block or resist. That's what impedance is
−
resistance to power
.
Solid-state power amps do not have a pre-determined impedance. They deliver power at whatever impedance
the speaker cabinet tells it to. That's why you hear the term "slave amp"
−
amplifiers only do what they're told.
So if someone tells you that they have a "4 ohm power amp," their terminology and understanding of the
concept is way off the mark.
Unlike power amps, every speaker cabinet has a pre-determined impedance rating measured in "ohms." In
most cases this rating is either 4 or 8 ohms (though there may still be some old 2 ohm creakers out there).
The higher the impedance of the speaker cabinet, the more resistance to power it will offer. The lower the
resistance of the speaker cabinet, the less resistance to power it will offer. In other words, HIGHER
IMPEDANCE MEANS LESS POWER CAN ENTER THE SPEAKER CABINET. LOWER IMPEDANCE MEANS MORE
POWER CAN ENTER THE SPEAKER CABINET.
You may be thinking that you've found the solution to the universe
−
just use speaker cabinets with really low
impedances and you can get skull-crushing power out of your amplifier, right? Wrong. There's a catch. Power
amps have limits as to how low an impedance they can drive safely. This is what's known as an amplifier's
"Minimum Impedance Rating." If you try and operate a power amp below its minimum impedance rating, it
will give you lots and lots of power for about five minutes…and then overheat, short out and fail completely.
In other words, THE LOWER THE OPERATING IMPEDANCE OF THE AMPLIFIER, THE HOTTER IT WILL GET.
WORKINGMAN'S 2X10C POWER AMPLIFIER MINIMUM IMPEDANCE RATINGS
Here's what this means to the power amp in the Workingman's 2x10C. Like most combos, the Workingman's
2x10C contains a mono power amp, which makes things fairly simple.
The operating impedance of the
internal speaker system in your Workingman's 2x10C is 8 ohms
, so that's your starting point. When you
add an extension cabinet to the Workingman's 2x10C, invariably the total operating impedance of the
amplifier will get lower.
The Minimum Impedance Rating of the Workingman's 2x10C is 4 ohms
. This
means that you can safely connect to the extension speaker jack:
- One 8 ohm speaker enclosure (4 ohms total impedance)
- Two 16 ohm speaker enclosures (4 ohms total impedance)
Operation at 4 ohms will provide 400 watts, a nice increase over the 260 watts available when used in a
stand-alone configuration. But as previously mentioned, the lower the operating impedance, the hotter the
amplifier will run. An amp that runs at or near its minimum impedance all the time may wear the life of its
components faster than normal. Furthermore, damage to the power amplifier section of the Workingman's
2x10C may occur if speaker enclosures with total impedances less than the minimum loads listed above are
connected to the speaker output section. The owner's manual that came with your speaker cabinet should
state its total impedance. On SWR speaker enclosures, the total impedance is generally indicated on the
speaker's input panel.
So how do you determine the total impedance of two cabinets hooked up to your Workingman's 2x10C?
Here's a quick key of the most common setups:
One 8 ohm enclosure (internal) + one 8 ohm enclosure (extension) = 4 ohms total impedance
This is OK. However:
One 8 ohm enclosure (internal) + one 4 ohm enclosure (extension) = 2.6 ohms total impedance
WORKINGMAN’S 2X10C OWNER’S MANUAL • 11
