I have speakers that come with my computer. Two small desktop speakers and a subwoofer with a base volume control on the back. It's worked for years. I was listening to Spotify on my speakers as loud they would possibly go and with the base turned up to max and suddenly the subwoofer stopped working.

I've plugged the speakers into my Android HTC Desire Z handset and again, the desktop speakers play music but the subwoofer doesn't (even after fiddling with the volume control).

So I figured I'd broken it. I went to Amazon and bought a replacement one. I bought this one: http://www.amazon.co.uk/dp/B002N46YD8/ref=pe_217191_31005151_dp_1 but it doesn't work either, on either my desktop nor my Android phone.

I had a play with alsamixer and the LFE and center controls are switched on and the speakers are okay... but still no base.

Am I unlucky enough to bought a new subwoofer which is already broken out of the box or is there something else which is wrong and I could look into please? Are there any other tests which I could perform to see if the problem is me or not?