Impedance Selector Switches

"This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation."

That Impedance Switch on Your Receiver is a Lie!

OK, it’s not really a lie, but it limits the output of your AV receiver or amplifier. Some AV receivers have an impedance selector switch on the back (Yamaha is famous for this) that opts between 4-ohm and 8-ohm or 4/8-ohm and 6/12-ohm. The idea is that it is safer to match the impedance of the amplifier to the speaker to avoid overpowering it or creating a difficult load on the amplifiers. The problem is two-fold. One, loudspeakers don’t have “flat” impedance curves. They dip down and swoop up. That means that a 4-ohm speaker may spend a lot of its time in the 8-ohm or greater range. It also means that if you’re using a subwoofer, you may never get down to its lowest impedance dip areas. Second, the only way to really make a system “safer” is by limiting the power output of the amplifier or AV receiver. This is exactly what the setting does. As a result, that little switch cripples, ever so slightly, the output of that brand new AV receiver or amplifier you just purchased. Our recommendation is leave it on the highest setting possible. That will give you the most power output regardless of the speaker impedance rating of your bookshelf or tower speakers.