b) Tone and Definition, by allowing diffusion with minimum use of deflectors over the seating area rather than the platform, and finally c) 'Singing' Tone produced here as in all excellent halls by a substantial height of the auditorium which, in the QEH's case, although the rear stalls are steeply raked, the ceiling is 25 feet above the highest seats to the ceiling. (Trends in Concert-Hall Acoustics and the Elizabeth Hall C. L. S. Gilford The Musical Times Vol. 109 No 1499 Jan. 1968) There have inevitably been many alterations and adaptation of the Hall, particularly in recent years, involving increasing the size of the platform and rigging extra specialised lighting arrays which allow the staging of dance and comedy productions. This had adversely impacted on the Hall's acoustics, in particular in the area of tone and definition by increasing deflection in the platform area. As part of the refurbishment work of 2015-18, a retracting gantry was provided at ceiling level reducing this intrusion when not required. The undercroft The undercroft of the foyer building has been popular with skateboarders since the early 1970s and it is widely acknowledged to be London's most distinctive and popular skateboarding area. Opened in 1967 as a pedestrian walkway, it was first used by skateboarders in 1973 as the architectural features were found to be perfect for skateboard tricks. Unlike skateparks which are designed specifically with skateboarding and BMX in mind, the undercroft is not a skatepark but a found space, and still considered by the users as a street spot. The area is now used by skateboarders, BMXers, graffiti artists, taggers, photographers, and performance artists, among others. A photographic archive of the graffiti can be found at The Graffiti Archaeology Project. Although this informal activity, social and arts scene is a distinctive feature of the Southbank Centre site, it was proposed that the area would be redeveloped. However a statement from the Prime Minister's office (reported in Time Out, in August 2008) cited the importance of the undercroft for these uses. The Southbank Centre, as part of its £120 million proposed Festival Wing development, sought to insert café and shop units in the Undercroft space partly to fund new performance spaces in the new buildings to be built above parts of the Queen Elizabeth Hall and to move the skate space to a new location under Hungerford Bridge about 120 metres away. This