By Peter Chupity
Summary: The recent installation of sound absorbing panels in the bar and dining areas has markedly reduced reverberation that has long been a problem. Sound pressure levels in our tests have been reduced some 6-12 dB in the range of speech frequencies.
We tested the acoustic characteristics of the dining area and bar to establish a baseline measurement before any improvements. A powered monitor speaker was driven with a swept, sinusoidal signal over a range of frequencies from150 Hz to 15 kHz. The level was set to 110 dB sound pressure level at the speaker grill with a 1 kHz signal and then a reference sweep was recorded to characterize the speaker and microphone used. The speaker and microphone were then mounted at average mouth and ear level of seated patrons in the rooms with normal furniture configuration in the dining room, and similarly in the bar, with the speaker where the band is normally set up, for the base line tests. The same configuration was repeated for the tests after the treatment was installed, and the test results compared.
In the dining area, the reduction of sound levels was quite noticeable, with a drop of more than 10 dB in the frequencies of 300 Hz to 3 kHz associated with intelligibility of speech (see graph below). Even up to almost 10 kHz there was a reduction of about 6 dB in sound pressure. While we did not explicitly measure reverberation time, it was originally on the order of 1/4-1/2 second, and was largely un-noticeable after treatment. The long reverberation time meant that sound tended to “hang around” the rooms; This “muddied” musical performances, and made conversation fatiguing, with competing, chaotic sound.
Reduction in Dining Area sound levels (in dB)
The results from the bar were similar, but showed slightly less improvement in the range of voice frequencies (see graph below), possibly because the bar is less boxy and had more architectural features so that comparatively less hard surface area was covered in panels. The improvement is still noticeable with more than 6 dB reduction over most of the 300 Hz to 3 kHz range associated with speech intelligibility. One side note that illustrates the improvement is that when we came back to measure the bar, after the panels were in place, we had to turn off the coolers as they were now louder than the signal that we were trying to measure, despite the speaker levels having been set the same as before.
Reduction in Bar Area sound levels (in dB)
While even a 6 dB reduction is a remarkable improvement, the acoustic panels have surpassed that. It might be possible to make some farther improvement by the use of soft decorating material such as drapes or plants, and also by covering some more hard surfaces with absorbing material: From the charts we can guess that the bar would benefit from large absorbers for lower frequencies, while the dining area might be adequately served with smaller absorbers for the higher frequencies.