Study of a Carmelite Monastery

Hi everybody! Last week, I talked about a study of a Carmelite Monastery that I was conducting. I have submitted my report yesterday so I will talk about what I did and how.

Context

At ENSIM, we have a Junior-Entreprise. I often say that a Junior-Entreprise is a school-sized company ruled for and by students. The whole definition can be found here. Its goal is to find missions related to ENSIM’s curriculum, whether in acoustics, sensors, or computer science. Recently, I applied for this mission for the Carmelite Monastery and I was chosen to conduct the project!

Initial Situation

The Carmelite Monastery has a large conference room that is very noisy. In fact, the room is very symetrical and has a very beautiful ceiling vault. It is a beautiful room in terms of architecture, but the client complained about the poor sound quality of the room. Our role was to take measurements and suggest improvements for the room.

Measurements

As you saw in the previous article, we did the measurements last week. We used an omnidirectional source of pink noise. For those who don’t know, a pink noise has the same amount of energy in every frequency band, and it sounds like a road traffic noise. The source was placed at one third of the diagonal of the room. On the second third, we were measuring the sound using a sonometer.

room acoutics measurements

Experimental measurements.

The key indicator for a room is the Reverberation Time (RT). It corresponds to the time the sound takes to decrease from 60dB. Usually, a sonometer can measure a difference of 60dB so it measures a difference of 30dB and extrapolates to get what is called the RT60. In the case of the room, the results were pretty impressive: The Reverberation Time was 2.45s, more than twice as much as what is usually advised for such rooms! The problem with high Reverberation Times is that understanding each other in such rooms becomes harder and has an influence on productivity.

Computer Modeling

To understand and fix this problem, we modelled the room on computer. We used SketchUp to model the room. You mought know this software because it used to be used for the 3D-rendering of Google Maps, . The final result can be seen below. It was really interesting to work on that because it was quite a complex geometry (due to the ceiling vault) but we managed to do it without any problem. When we did the sound measurements, I insisted on taking the dimensions of the room thoroughly, which made things easier when we came to computer modeling.

modele_01

3D modeling of the room using SketchUp

Acoustic Calculations

Now that the room was modelled, we imported the geometry in a software called I-SIMPA. This software performs acoustic calculations, such as Reverberation Time Calculation and also sound propagation calculation which were the two things we needed.

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I-SIMPA’s logo.

The first thing we did was a Reverberation Time Calculation. Our goal was to find a value close to what we measured. In our case, we found the same global RT though the RT in each frequency was a bit different. The second thing we did was to see the diffusion of sound within the room. This part was very interesting to verify the notion of diffuse field, which the main hypothesis of the Reverberation Time Calculation. You can see below how does the sound changes in a few seconds:

isimpa_01

t=0.01s: The sound level is located near the source.

isimpa_02

t=0.09s: The sound field is now diffused.

Improvements

Now that the measurements and the calculations are done, we have to suggest improvements. This part was more difficult than I thought because our only resource was the Internet and there not a lof of discolsed prices. We found a first solution with self-adhesive panels. This solution was great in the way that the end-user can easy put them on the walls. However, in our case, I think it wasn’t the best solution because it implied to cover a lot of surface.

The other solution was to use Pinta Acoustic panels. I am very familiar with this brand because I used to sell them during my internship at West General this summer! With this solution, less surface coverage is needed, which is great! However, it is more expensive than the first solution. We’ll see which one the client choses!

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Example of a Pinta Acoustic foam.

Conclusion

This study was very interesting because it was a way for me to reuse the knowledge I learnt during my internship, whether related to acoustics or to the way a project has to be conducted. But the very interesting thing is that I had an opportunity to improve my skills in computer aided design and acoustics calculation.

I would like to thank Jensim, ENSIM’s Junior-Entreprise, for chosing me and François for being a wonderful assistant during this study!

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