I got a problem with the Sub-woofer of my speaker Sony SRS x55. When a bass is high, the sound was cracked and I’m planning to replace this sub-woofer by a new one. I was finding somewhere I can buy the new sub-woofer in the internet but I did not find yet. Do some one know where can I buy it? Or what sub-woofer I could use instead of the original sub-woofer? Thanks!