[Simondm]

My period as a BBC Audio Supervisor was the 1980s.

There were various BBC designs that had alternative asymetric enclosures, usually for OB vans of various types. One later design springs immediately to mind, the LS5/8 (I'm trying to remember the earlier designs I encountered like that). They usually had the standard baffle, with a wedge-shaped enclosure of similar volume to the original. Obviously, non-parallel sides would dramatically change the resonances but I assume this was tuned-out in situ.

When there was separate provision, the sound control "rooms" in scanners were extremely small, so even a second human inside would itself make a huge difference - you relied on being close to the monitors, and the distance was usually less than three feet. I much preferred the "leave the bass well alone" philosophy, and, as long as you were prepared to do that, LS3/5As were quite adequate for most things.

Bristol, where I was based, was home to CMCR3 when I started, which possibly had a wedge-shaped LS1/2 on the ceiling above the control desk (sound, vision mixer/director, prod. asst. and Eng. Mgr positions), but it was built by PYE (RCA, Philips/Peto Scott PC 60 camera channels), so may have had the speaker mentioned above. I was a young audio sprog back then, and was rarely allowed in the scanner at all, never mind the control area during production!

M. Hennessy is quite right the LS1/xx series wasn't intended for critical monitoring (and in a VT or TK channel, the noise of motors and vacuum piumps, etc. was considerable). I was told that the 3/xx series was intended for portable (OB) use, and the 5xx series for studio monitoring, however both 3/5As and 3/7s were used for studio monitoring extensively. the 5/xx. I suspect we only had a few 5/8s because of the cost.

In radio vans I never saw the asymetric speakers used. We had speaker stands immediately behind the consoles, with 5/8s or 3/7s clear of the walls angled towards the mix position. It was considered very important though to get the tweeters at head height - the 3/7s were strapped-in upside down for that reason.

On reading the EngInf document, I note that the relay was intended to mute the HF unit during tape spooling. This was very sensible, as we got through quite a few tweeters in my Audio Unit, c/o a senior colleague who insisted on shoving the tape against the heads whilst spooling - earlier monitors, such as the LSU10 didn't have good HF response (BBC 'brown' sound), and, having valve amps, were more robust anyway (soft clipping?). LS3/5As were especially vulnerable, also 3/7s (I have a stack of spare Audax tweeters for mine, just in case).

Finally, of course there were two basic versions of the Spendor BC1, used for monitoring in the late 1970s/early 1980s. One was "self powered", and had a built-in amplifier module fixed to the back panel with a chunky heatsink and volume pot sticking out, and a PO socket for the input. They also had "fragile" tweeters, and the amp was a bit under-powered, which probably didn't help.

When I started, the self-powered BC1s were the main monitors in several radio studio areas (two still used a solitary LSU10 !!!). By the end of the 1980s, every studio was 3/5As, 3/7s, 5/8s, and a pair of 5/9s in the main TV studio (supposed to be the dog's pyjamas, but nobody really liked them apart from the physical size in a small control room).

I worked in the dubbing theatres in Ealing and Lime Grove (on attachment) in the mid 1980s - they were all LS 5/8s, sometimes with Auratones for compatibility checking. We had Auratones in most TV sound areas in Bristol too, by the end of the 1980s, but they mostly got used for talkback, and on rare occasions settling arguments with production about audibility. They only really had relevance in film dubbing (where we also handled video post production sweetening), as in other places you had insufficient time to do much remedial work.

As time progressed, the prevalence of the lower-quality BBC designs diminished, mostly in favour of LS3/5As. It was much easier to keep a stock of them (we had quite a few bookable from audio stores), and as long as the tweeters were actually working, any two made a good stereo pair.

Probably way too much info. Sorry.