quality of burnt cdrw

i have 3 cdroms. 1st. regular cdr 2nd. yamha cdrw
3rd. LG cdrw. the cpu is AMD
making copy of music cd (original in regular cdr)
the quality of the burnt cd is poor. when i play it the sound is not as nice as the original and have problem withthe bass(low freq.)
i am doing the same on other pc and the resoults much better.
i am getting the same resoults on both cdrws, using X4 speed. also i am using the nero and cd creator
what / where can be the problem
thank you
joe