I have 4 speakers linked up to a A-229 Pioneer stereo amplifier. Two of which run fine and the other two have run into an issue. They were being used by themselves and a song with a lot of bass was being played. The speakers cut out and when turned on again played with a very low volume and no bass. I've used other speakers on the amp so I think the amp is fine there is something wrong With the speakers but not sure what. Any help much appreciated.