I use a VariAC, as well as a light bulb current limiter. The voltage at my house is usually 122-123. I set my variac at 120 so that I get consistent results across the board when testing.... comparing apples to apples so to speak. Also, at trade shows, I've seen line voltages of 130+, so I definitely use my variac there! I don't use it to break in speakers. 60Hz is below the resonance of the speaker, and usually about 7-8dB below the 120Hz response, and the hum is most annoying.