SWR Sound 350x owner manual Speaker Output Section, How Impedance Affects Power Ratings

SPEAKER OUTPUT SECTION

This section of the manual will deal with the proper connection of speaker cabinets to the power amplifier in the 350x. Some of this ground has already been covered in the “Getting Started – Connecting Your Speaker Cabinets” section in the beginning of the manual. This is meant to supplement that section and provide information in greater detail, as power amplifiers, impedance and speaker cabinets are all crucial in determining how best to operate your new 350x.

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.

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 imped- ance 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.

350x Power Amplifier Minimum Impedance Ratings

Here’s what this means to the power amp in the 350x. As mentioned previously, the 350x contains a mono power amp, which makes things fairly simple. The Minimum Impedance Rating of the 350x is 2 ohms. This means that you can safely connect:

•One 8 ohm speaker enclosure

•Two 8 ohm speaker enclosures

•Two 16 ohm speaker enclosures

•One 4 ohm speaker enclosure

The optimum operating impedance for the 350x is 4 ohms. This way you get a good amount of power from the amp (350 watts) without operating too closely to the minimum impedance—or, in simple terms, with- out running the amplifier too hot. That having been said, the 350x is rated to operate safely when connect- ing:

•One 8 ohm and one 4 ohm enclosure (2.6 ohms total)

•Three 8 ohm enclosures (2.6 ohms total)

•Two 4 ohms enclosures (2 ohms total)

These three hookups will provide between 400 and 450 watts of power, but as previously mentioned, your amplifier will run hotter, the fan will run constantly, and an amp that runs at or near its minimum imped- ance all the time may wear the life of its components faster than normal. Furthermore, damage to the power amplifier section of the 350x 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 imped- ance is generally indicated on the speaker’s input panel.

So how do you determine the total impedance of two cabinets hooked up to your 350x? Here’s a quick key of the most common setups:

12 • 350x OWNER’S MANUAL