Weird speaker problem

surely bad contacts in the volume potentiometer... a current problem ... change the potentiometer if possible, of use a contact spray

It's a high resistance contact somewhere. You haven't given enough information for a more accurate diagnosis but my guess would be that there is an output relay or a connector with either tarnished or worn (low pressure) contacts. Turning up the volume allows the increased voltage to break down the insulating layer for a while.

Giving a make and model might be helpful

Ron

You may be jumping to conclusions. Is the entire stereo sitting on the table or are just the speakers? If the entire stereo is sitting on the table, then I agree with the other poster that th volume control wiper may not be making good contact. When you hit the table the wiper may move over a dead spot on the pot.

It is a Panasonic SA-AK15 mini system. The body (cd changer, tape deck, tuner) is on a shelf and the speakers (two) are hooked through long cables on another shelf, atop my bed headboard.

If, after a couple of second after you switch the unit on, there is a quiet mechanical click. that would indicate a relay (which generally isolates the speakers). That would be my first port of call, checking for low contact pressure or tarnished contacts. Tapping this relay often provides a clue. If the fault always occurs on both channels simultaneously, then I would suspect that the relay isn't the cause

It's easier usually to replace the relay than fiddle around trying to improved the contact arrangements.

I would inspect any ribbon cables especially the flat 'printed' type for tarnished contact areas on the ends.

Another area in which it might be fruitful to look, is any mechanical push switches, tho these are becoming rare on modern equipment.

The other possibility is a dry joint (cold solder joint), which would probably be anywhere in the signal path after the volume control, and somewhere common to both channels.

HTH

Ron