Actually there's a another technique, by varying the length and diameter of the port, maybe inserting a fitting pvc pipe of different length internally. The length of the port (since the diameter is already of fixed size) can alter the bass frequencies. The effective length and diameter of a subwoofer port is seriously taken into the design of a subwoofer for desired frequency response. Nevertheless if the speaker is somewhat boomy (due to manufacturing cost reduction of this RM200 thingy), damping the internals can be to good effect, but to my experience because they used a rather underpowered chip amp, excessive internal damping can seemingly reduce the overall bass dynamics but with tighter bass lines for sure. Its a trade-off for a nicer bass tone in this case for the 4121.

thanks guys for ur guidance.

my vs 4121 warranty sudah habis la.

i'll ask my wives when they r free, to make a cloth cover & then put sponge inside de cover. after that i glue dat cover to the walls of the subwoofer.

thanks again guys. u r all helpful.

if ur fren,wife know...please inform me ya....

told ya there is no hi fi shop...