The monitor speakers which the BBC developed have two classifications, they are called LS3 and LS5. LS3 is a portable model, and LS5 is the model installed in the studio.
It seems that LS3/7 is a portable model, and has handles on both sides of the speaker. As the stereo image of it is so good, and since it reproduces the wide dynamic range, it was installed at Radio 3. It must be ideal for usse as a monitor speaker at Radio 3, because live classical music tapes, which require a wide dynamic range reproduction, are often played. There were Technics SP-12 turntables with SME3009 arms to play records in the Radio 3 monitor room from where they control sound quality.