On 26 April 2014, M.J. Moore in Cheshire, UK wrote:
"Several years ago I picked up an original loudspeaker 'box' but I couldn't find any information on the spec. of the original speaker. There is a picture in Clausager but you can't tell even the shape of it let alone the size. So I studied the 'box' which is stamped out of 1/8" millboard, and there were two features that I thought could give a clue to the speaker:
1. the speaker fixing holes were punched out of the board and distance apart of these holes (along the board) was 5 1/8".
2. There was an unusual flap about 5/8" wide at the rear of the box which was meant to hinge.
On the first point I started to look on Ebay for loudspeakers with a fixing hole spacing of 5 1/8". Judging from the shape of the aperture in the assembled 'box' it seemed likely that the speaker shape was meant to be elliptical. There seemed to be many 8x5" speakers cropping up on Ebay but their hole spacings were always less than 5" and for the next size up viz. 9x6" the spacing was too great. I didn't come across any circular speakers with this spacing so I was on the verge of giving up when a speaker came up described as 'approximately 8x5'. When I enquired the size was around 8 5/8" x 5 5/8" and the hole spacing was 5 1/8" x 5 1/8" (slotted in one direction).
I bought this speaker and found that the unusual size was because it was based on an 8x5" cone size. The make of the speaker is ELAC. In the 1950s this was a small loudspeaker company based in London just a stone's throw away across North London from the Radiomobile factory. Original factory fitted radios were all Radiomobile.
When I fitted the speaker to the box the reason for the 'flap' became clear. The flap was to cover the protruding part of the speaker at the rear end. I doubt if this was to improve the sound but rather to protect the exposed cone at the bottom.
I've fitted this speaker to the car and it sounds good. It was a bit of a struggle to fit it and it would be much easier to do it before the dashboard is fitted. The top front of the speaker comes very close to the scuttle but there was an elliptical piece of the top hat section at the top of the scuttle cut away, otherwise it wouldn't have fitted. This cut away piece was so well done that it must have been cut before the car body was made.
This size of ELAC speaker appears to be quite rare, and it is the only one I've seen in four years of looking on Ebay. ELAC also do a standard 8" x 5" speaker with the wrong fixing spacing.
One other point about the loudspeaker is that it must be of the correct coil impedance to match the audio output stage of the radio. I believe all the Radiomobile radios required a speaker impedance of 4 ohms. I remember during the 1950s that common speaker impedances were 3, 5 and 15 ohms, so either a 3 or 5 ohm impedance speaker would be suitable, but with a 15 ohm speaker the sound volume would be affected.