Marcus Tse
Room – HIL B61
The room in question is the Model and Design workspace of Raplab (HIL B61). It is a multipurpose room that is used for lectures and as a workspace for model building. When used for lectures, the speaker is usually at the corner of the room, next to the projection screen, and the students are sitting in rows in the middle of the room. The big worktables are pushed to the back of the room to make space for the chairs. When used as a workspace, all chairs are stacked and placed at the back of the room, and the tables are grouped in pairs and placed in the middle of the room, leaving room around them for people to sit and walk.
In person room acoustic:
The room’s acoustic is a very boomy, bouncy, and loud room with high reverberation noticeable by normal speaking. The sound reflected is also relatively high frequency. These results are probably due to the hard surface used around the whole room – hard painted concrete. Additionally, using the recorder – the reverberation sound is actually increased when the balloon is popped at the speaker’s position and mic at the student position. Furthermore, I don’t think the boards on the wall are preforming much… I hypothesises that if it was a shaped acoustic foam, it would actually absorb and defuse the sound in the room. The room maybe especially loud when students start to get “hands on” when making the models or breaking materials…
Room Spec:
Room Surface Area: 85.5 m2
Sidewalls: 65m2
Front/Rear: 41m2
Floor/Ceiling: 171m2
Total Area: 276m2
Room Volume: 237m3
Ceiling Material: Concrete
Floor Material: Concrete
Walls: Concrete
Sound Analysis
In person acoustic experience:
Balloon Test Recordings: MAP of recording and sound source
RECORDING 1:
Reverberation Time of 0.96s
RECORDING 2:
Reverberation Time of 1.02s
RECORDING 3:
Reverberation Time of 0.99s
Average Reverberation Time: 0.99s
SIA Norm and RT Target
A3 is the Target Range for “Teaching/Communication” and ‘Language/Lecture inclusive” – which is the appropriate function for Room HIL B61
SIA Norm RT suggestion is = 0.74s
Hence there is a difference of (0.74-0.99) –0.25s in RT for it to be acoustically appropriate for its use.
RT60 Calculator 10Log
After finding out the RT target from the SIA guide. We can do some simple simulation and calculation to see how interventions can reduce the RT and the different frequencies of which the balloon test didn’t accounted for.
For reference, this is the RT graph based on the same room with concrete architectural materials without furnitures. Hence the RT indicated will be longer than the real world recorded test.
Interventions!!!
This is a sketch of the potential intervention we can employ to reduce the reverberation time and resonance sound, especially the high frequency.
Strategy 1: Perforated Timber panels on the ceiling to reduce resonance vibration in the room. This should reduce RT on the mid-high frequency scale. Hence improving speech legibility both from the lecturer and also between students when performing group work.
Strategy 2: Shaped Acoustic Foam on the long side of the wall. This is to absorb sound – reduce RT and reach RT target, but also to deflect the sound waves so it doesn’t create the horizontal and vertical echo – reducing resonance and improve speech clarity.
Strategy 3: Acoustic fabric board at the back of the room to absorb sound horizontally (plan view) – reduce RT and echo – Improve clarity of lecturer’s speech.
Strategy 4: Acoustic foam (tower or panel) on the lecturer’s side of the room. This strategy is employed if the RT is required to further reduce to reach Target RT. However, this should not only reduce RT but also improve clarity speech for the lecturer’s own listening position – and also this will create a complete surrounded absorption of sound for the room (plan view).
Here are the results of the intervention through the online calculator.
RT after the interventions are added. You can see that there is a moderate drop in RT around all frequency but in particularly a significant drop in the high frequency – of which is what is targeted. Showing the success of the intervention on the online simulator.
