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said:

The earthing feature is interesting, but doesn't actually
indicate where the connection is inside.

If I understand the Tannoy website correctly, the earthing connection
is made to the basket of the speakers.

Shielding isn't very effective if the wires terminate outside
an unshielded enclosure, the ends are still exposed to RFI.
RFI is usually a source cable problem and amplified, or a
poor design issue at the circuit component level.

The output of an amplifier can be regarded as an input RFI-wise, when
common-mode RFI supression isn't sufficient.
RFI is then able to travel via the loop feedback to the inverting
input of the amp's differential input stage, where it can wreak havoc.

So far, I have not seen many commercial amplifiers where this was done
right, including "pro-audio" types.

This can be easily demonstrated by holding a working cell phone in the
vicinity of the outputs of an amplifier.
Even before the rattling becomes audible, strange things have happened
inside the amp.

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- Never argue with idiots, they drag you down their level and beat you with experience. -