Am i right in thinking that said pipes noise can only be heard by Dogs?
or is this another pipe?
I know its 64'. but no other voices except the Diapason come to mind, being 64'

Dogs are high frequencies aren't they? A 64' Diapason would be extremely low at bottom C - a few cycles (Hertz) - one of those things you would just 'feel' rather than 'hear'...

£5 says you're watching the proms...

i was. i caught the '64' foot pipe makes the room vibrate, only dogs could hear it' bit

Incidently, a talking fiver is pretty rare!

It's not a genuine 64' - its an accoustic 64' - i.e a 32ft pipe which has harmonics making it 64'. on mander someone put a very good explanation

ooh right
i think theres a full 64' in the atlanta convention hall, it might be a 32' though i guess

Sydney Town Hall has a full length 64'

There are only two true 64' stops in the world - as mentioned, they are at Atlantic City Convention Hall (Diaphone Profundo) and Sydney Town Hall (Contra Trombone).

So are all the Gravissimas dotted about the place complete fakes?

No, as Dave mentioned, they are resultants - i.e. low C is not a single 64' pipe, but two pipes - one sounding an octave above the resultant tone (32' length), and one a fifth above that (around 20' length?) - so the resultant frequency generated from the sum and/or difference of the two frequencies gives the impression of a 64' rank.

It is better explained here:

Resultant