here's some guideline for electronic and pickup cavity shielding with copper tape.

so, why do we need to shield the cavity?
- the answer is: to reduce hum and noise.  The most common causes for hum and noise on an electric bass are either improper grounding, or bad shielding.  Or there could be defective part or components on the electronic itself.

My scenario this time is that the after the bass had been plugged into an amp, there was hum whenever my hand left the string or hardware.  Then the hum was gone once I had my hand placed on the string, or metal parts such as bridge, tunner, or output jack plate.  This tells me that the bass is grounded properly, and it was actually my body that was receiving all these interferences that affects the electronic of the instrument.

The concept of shielding is to use the copper tape to make a box around the pickup and electronic.  This metal box is then connected to the ground wire so it blocks all the interferences and dump the noise and signal to the earth ground.  All cavity shield are connected with wire.

let's check out the pictures: