In our consulting practice Clients often ask the question: how much difference will it make if we install ‘x’ amount of material? Will it make an audible difference? Is it worth the time and expense?
These are all very good questions, and they can be very challenging to answer in a clear and objective way!
For many projects we rely on engineering calculations and computer model predictions to estimate changes in reverberation times for different acoustical treatment scenarios. Even with these tools, however, it remains a challenge to interpret the results and convey them so that they can be clearly understood and used for making important project decisions.
“The results were impressive. Parishioners noticed the difference in intelligibility immediately, although aesthetically the new “wall” seems invisible.”
Fidel Cuellar-Torres, Director of Music and Liturgy, St. Francis of Assisi
A recent project aimed at improving speech intelligibility at St. Francis of Assisi Catholic Church afforded a unique opportunity to compare computer calculations with both measurements and subjective responses from the congregation.
As part of our evaluation of the church’s acoustics and audio system, we measured reverberation times in the space and calculated how much they would change with different extents of treatment in the space. Next, we recommended a phased approach to making improvements to speech intelligibility in the highly reverberant space. Step 1 was to install a sound-absorbing finish to the rear wall of the space.
This single change has made a noticeable and positive improvement to speech intelligibility in the space! Congregation members were surveyed about sound quality before and after the change
These survey results show a significant improvement to the sound system as a result of the rear wall absorption. Note that no other changes were made to the sound system between these two surveys!
Following installation of the treatment on the rear wall, we returned to the church to re-measure reverberation times for comparison to our computer predictions:
Reverberation times decreased by about 0.5 seconds above 500Hz, and this was enough of a difference in this case to produce noticeable improvements in speech intelligibility. Is this enough? Probably not. The space is still VERY live with a mid-frequency RT of ~3 seconds, but another goal for this project is to maintain a degree of liveliness for unamplified music.
Fidel Cuellar-Torres, Director of Music and Liturgy at St. Francis of Assisi, writes “We wanted to improve intelligibility without drying out the space completely and ruining how the reverberation helps the music. Soundpost Acoustics gave us a series of short-term, medium-term, and long term recommendations. So far we’ve acted upon the first recommendation, covering the back wall. The results were impressive. Parishioners noticed the difference in intelligibility immediately, although aesthetically the new “wall” seems invisible. We’ve had many parishioners ask where the insulation is? The contractors who installed the track system did a great job. We know we can still improve the acoustics of the room, but the modeling and recommendations were spot on.”
Every project is unique and has different needs. Every project is also an opportunity to learn and build experience. Now, we can proceed with future phases of this project and other projects with even greater confidence in the tools at our disposal!