The factory speakers on W/S124s are horrible, so any type of upgrade would help. Although, do not expect to much boom since the largest size you fit front and back are 4" speakers.

I did install 4" midranges at the original factory holes and placed a separate tweeter on top of each. Finally I installed a set of 6" woofers on the front doors, although that did require tampering with the door lining.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]