I have been told that a non-inductive or inductive resistor used for speakers can only handle 10 watts if it is a 10 watt resistor, which makes no sence because they do use even 5 watt resistor in a 160 watt setup. So my question is how do I know how to tell how much they can truly handle before failing or what is the general rule on how much they can use?
closed as unclear what you're asking by uint128_t, PeterJ, Bence Kaulics, placeholder, Brian Carlton May 30 '16 at 20:10
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There is no such thing as a 'speaker' resistor. A resistor is used for whatever purpose it serves. As a general rule resistors are not used at more than 50% to 75% of their maximum rating so there is some assurance of a long life.
There are wire-wound high wattage (5W to 300W) resistors known as 'non-inductive' that are used mostly for RF and audio 'test' circuits, but could offer some benefits for tweeters, by not inducing inductance into the HPF circuit. A typical wire-wound resistor has some inductance, enough to be a problem with high frequency ultrasonic, RF and pulse circuits.
Most any resistor can take a 50% overload for a second or so. A 10 watt resistor can handle 10 watts, but will last for many decades if run only at 5 to 7 watts. Running a resistor at its maximum rating can cause a 'slow-burn' over 1 or 3 years of continuous use. It may still work OK, but have a discolored look, with any markings burned off.
For smd resistors, the overload margins are smaller and the 'slow-burn' chance is greater as they do not have enough surface area to dissipate extra heat. They are seldom used at more than 25% to 50% of their wattage rating.