# Isolation transformer to reduce speaker pop

I have some computer speakers which suffer from the following problem: when switches flip in certain devices in the house, like the thermostat on a radiator or the refrigerator, the speakers will emit a loud popping noise, caused (I believe) by changes in the voltage on the mains.

Would an isolation transformer between the speakers and the mains alleviate this problem?

If so, what capacity isolation transformer should I buy? The speakers are rated at 500W RMS (Logitech Z-5500). I've read that an approximate conversion of 500W to VA comes out to 500*sqrt(2) = 707. If I don't play the speakers at anywhere near maximum volume (certainly less than half the maximum), would a 600VA isolation transformer suffice?

Thanks for any assistance.

• Do you have access to portable power meters such as those kill-a-watt devices? Some of them can measure complex power and the best way to be safe would be to use one of those and measure exactly the power used by your speakers. Also the formula you provided shouldn't be used on the speaker power but on the number that is printed on the power supply. You'll see something like input XXX V and XX A (or mA). Multiply the current by voltage to get the active power and then apply the formula you found. Commented Jun 19, 2012 at 6:32
• I had a similar problem, but with my monitor messing up the picture for a second. These things can best be solved near the source of the problem, by instaling a snubber network across the mains switch. en.wikipedia.org/wiki/Snubber I solved my issue with a capacitor in series with a resistor across the mains switch of the device that made my monitor 'plop'. Can't remember how I did the sizing of this, hence a comment instead of an answer. Check this question: electronics.stackexchange.com/questions/18321/… Commented Jun 19, 2012 at 6:58