Grounding Speakers

I believe the idea behind the ground connection on Tannoy’s is to reduce unwanted radio frequency interference.

+1.  That's my belief as well.

Also, while it would seem unlikely that the speaker itself could respond to RF frequencies, at least in a way that would be audible, I suspect that the likeliest way in which RFI picked up by the speaker cables could affect sonics would be as a result of the RFI being injected into the feedback loop of the amplifier, assuming the amp has a feedback loop. If so, the benefit of this ground connection, if any, in addition to being dependent on the RFI environment at the particular location would be dependent on the design of the specific amplifier. Including the amount of feedback it utilizes, its output impedance, its bandwidth, and perhaps other design-dependent variables.

The bottom line being that the only way to know if there would be a benefit in a particular system is to try it in that system.

Best regards,
-- Al

I found a manual for the DC8T online, which includes the following statement that I assume is also applicable to the DC8Ti:

Connection of Earth or 'Ground' Lead:

Use of a shielded or screened loudspeaker cable will offer further performance advantages when used with the five-way terminal panel. The screening termination should be connected to the earth or ground (green) terminal on the loudspeaker and to the ground or earth connection on the amplifier. Alternatively if you are not using a screened loudspeaker cable but wish to utilise the earthing facility, run a single cable between the earth or 'ground' (green) terminal on the loudspeaker to the earth (ground) connection on the amplifier .

Regards,
-- Al