I have frequently wondered what the natural sound pressure level is at symphonic concerts, so I brought my sound level meter with me when I attended a concert in the Tivoli Gardens in Copenhagen yesterday. I sat in the middle of the concert hall, about 20 meters from the orchestra. All measurements are C weighted, i.e. made with a nearly linear frequency response.
The first item on the programme was Mozart's Symphony No. 17. The average sound pressure level during the 1st movement of this symphony was less than 70 dB, and the peak level was 85 dB.
The 2nd item on the programme was Prokofiev's 1st violin concerto. The peak level during this concerto was 90 dB.
The 3rd item on the programme was excerpts from Prokofiev's 3 suites based on his own ballet music "Cinderalla". The peak level was here 98 dB, reached during the "Midnight" section. The brass was responsible for this -- they played much louder than other instruments.
High SPLs and excessive treble -- which are tempting remedies with speakers lacking transparency -- aren't called for with proper speakers.
PS1. I enjoyed the concert in the intervals between SPL readings.
PS2. At the recent Roskilde Festival -- see http://www.roskilde-festival.dk/ --, sound pressure levels in excess of 130 dB were measured in the Techno Music tent.