I have a PSB Image series of speakers and Harmon-Kardon amp. My problem started when I connected the ICBM into the system. After that when the system is shutdown the subwoofer will make a large thump. It has a circuit that detects a signal and if none is present after a set time it shuts off same for turn on. It was fine and is fine when the ICBM is not in the circuit. I tried turning the wall wart around to change the polarity but no difference. Any clues would be appreciated. Thank you.

You migh be hearing the turn off thump of the ICBM. I would recommend you try to either leave the ICBM powered up continuously, or turn it off seperately, after your power amps.

I will give it a try with it powered up all the time. Thanks for your timely response.

I moved the wall wart to its own plug where it is on all the time and the thump is gone. Thanks so much.

I know that you have found your solution, just thought I'd put my 2 cents in.


I have been working with sound reinforcement for many years, this is a common 'problem' with lots of different equipment. A general rule is to always power on your amps after all of your other equipment. Shut down in reverse order, amps being powred off first. This 'thump' can actually dammage your speakers. What causes this is the 'surge' when some equipment powers up or down, this is not a problem with the equipment, it is just 'noisy' so to speak when it is powered on or off.

I see no reason to not leave the ICBM on all the time. Mine has not been powred off since I got it.