To complement its larger two-way monitors for studio use, the BBC developed a small speaker for near-field monitoring of the frequency range from 400 Hz to about 20 kHz for its outside broadcasting monitoring. The principal constraints were space and situations where using headphones is unsatisfactory, such as in mobile broadcasting vans. Based on scaling tests done in 1968, and detailed audio work against the LS5/8 – a large "Grade I monitor" already in use at the time – and with live sources, the BBC Research Department developed the LS3/5, which became the famous LS3/5A that was used from 1975 to much of the 1990s and beyond by the BBC and audiophiles alike.