A ten-phon level reduction halves perceived loudness

Evidence

Figure 9.6 shows results for three loudness reductions. A 10 phon reduction from a high “reference” level (a) is a substantial change (approximately half loudness), but one that is not at all uncommon. Most people would still consider this to be “foreground” listening. A 20 phon reduction (b) yields “background” music, and a 30 phon reduction (c) is for “ambiance”. It is immediately obvious that no single loudness compensation curve can work for music that has significant dynamic range. The low-frequency boosts are substantial to maintain audibility of low-level sounds, and these would render high-level sounds grossly bass heavy. — Toole, Floyd E, Sound reproduction- the acoustics and…, 916