DC offset level to avoid speakers damage-

Bob_bundas. You found my goofup before I got back to fix it. Yes...divided by R. So it is even less of a problem.

I had occasion to adjust bias only once when I fixed a 60 watt Tandberg receiver output stage. I don't remember what the output bias spec was, but I do remember that I had no problem getting it down to less than 5 millivolts. I think that designers/manufacturers set the spec high because it is not critical.

Tks everybody, very clear reply (as usual I should say)
Cheers

The maximum dc offset tolerated by a speaker is a percentage of the linear excursion of the driver that is acceptable, usually 10 to 15%. The formula used is:

Vdc(max) = % excursion x excursion x driver impedance/[Force Factor x Suspension Compliance]

All these parameters are found in the manufacturer's spec sheets. Using a Scan-Speak 21W/8555-0 driver, the maximum dc offset at 10% of driver excursion is:

Vmax = 10/100*6.5mm*5.5-ohms/[8.2*1.34] = 400mV.

Most amps specify dc offset at less than 100mV. So a 50mV offset is not "high". And a lot of drivers tolerate up to 500mV.

Not to worry - a 50mV output offset calculates to 3 microwatts dissipation in an 8 ohm load or 6 microwatts into 4 ohms.

Per Ohm's Law, power is voltage squared DIVIDED by the impedance

POWER = VOLTAGE^2 * RESISTANCE

0.050^2 * 8ohms = 0.02 WATTS.

You don't have a problem!