5 Final Assignment

The room is rectangular with a door in one of the long walls leading to a corridor outside and a window on the left side of it [if looked at from inside the room]. Both this wall and the shorter wall next to the window are made of painted brick, whereas the other two walls are plastered and painted. Both the floor and the ceiling are made of painted concrete and there are 8 protruding lights on ceiling, that are spaced out evenly through the center of the room. There are also 10 parallel metal pipes above and to the right side of the door [about 2/3 of the room length] and 3 ventilation pipes on the other.

room measurements → 7.5m (width) x 30m (length) x 3m (height)

room volume → 7.8m x 12m x 3m = 280.8m³
short walls [each] → 7.8m x 3m = 23.4m²
long walls [each] → 12m x 3m = 36m²
floor and ceiling [each] → 7.8m x 12m = 93.6m²
window → 3m x 0.5 m = 1.5m²
door → 1.2m x 2m = 2.4m²
cardboard → 1m x 1.5m x 6 = 9m²
lights → 1.2m x 1.2m x 8 = 11.52m²

There is are three metal racks; two lower ones on either side of the door and one that reaches up to the ceiling on the short plaster wall. They are used to store things and to put the models. 6 cardboard rectangles are placed next to each other on the long plastered wall to pin up stuff and there are two horizontal pipes right below it. There are 8 movable tables made of metal and pressed wood, and two smaller ones made entirely of pressed wood. Lastly, there is a canvas on the short brick wall and there are a bunch of plastic and wooden chairs scattered across the room.

The room is very live and loud, even with little noise input. This is due to all the hard and reflective surfaces and the lack of absorbtive materials. The room is a brick-concrete box with flat parallel walls that reflect the sound, and there is only little diffusion of the sound inputs through the spaced out pipes, lights, tables, chairs, equipment and models. This might seem like a lot, but due to those things also being made of reflective materials (except for the models), the room becomes even more live. Due to the moderate size of the room, the reverberation time is not too bad and speech is intelligible, which is aided by the reasonable distance between the speaker and the listener.

*When recording, I was the only person in the room and I created some noise on purpose. All I did was roll around in my chair, cough and move around some paper.

Legal Standards

SUVA

Industry and commerce, Group 2: Activities with temporarily or consistently high demands for concentration, such as monitoring tasks in the context of production as well as quality control.

noise exposure level → LEX,8h < 65 dB(A)

DIN 18041

Reverberation time – rooms for speech communication

A3 type of usage: “teaching/communication” (up to 1000m³) as well as “speech/lecture included” (up to 5000m³)

SIA 181 – sound insulation

High noise exposure, but low noise sensitivity → 52dB

*not very relevant in this case since it is an enclosed space underground

Calculations

current reverberation time:

targeted reverberation time:

equivalent absorption area – calculated with Sabine Equation:

current absorption area – calculated with Sabine Equation:

Acoustic Treatment

concrete	0.05-0.08 → avg. 0.065
plaster	0.01-0.05 → avg. 0.03
cardboard	0.10-0.50 → avg. 0.30

To get from the current absorption area to the targeted absorption area and targeted reverberation time, a lot more absorbing materials need to be added to the space. There are several reasonable areas to put absorptive measures, but I think some are more suited than others. The room can get very dirty, needs to be somewhat reconfigurable and there is a lot of tear on the floor for example, making it not the ideal to place absorbers. [If it were rubber flooring for example, it could be cleaned easily and reduce the noise input, but the absorption coefficient of it is not very high.] Since treatment of the entire wall is not possible through the metal pipes, but also not necessary, I would substitute the pin walls through felt [which can still serve same purpose] and put two more, in order to absorb a lot of first reflections from that long wall and the reflections of the opposite wall to avoid flutter echoes. The felt is of medium thickness [3cm], since the main target are mid to high frequencies. I would also put absorbtive panels on the ceiling and plastered wall to absorb more of the reflections [especially the ones on the back] and increase speech clarity. This also keeps the shelf and its purpose intact, meaning it can still be used to store, but also display the models. [I initially thought of putting a curtain in front, but abandoned the idea due to the dirt/ dust created by the workshop.]

substitute cardboard with felt [3cm] and put two more panels → α = 0.8

41.09m² – (9m² x 0.3) – (3m² x 0.3) + (12m² x 0.8) = 47.96m²

space out acoustic tiles on ceiling center → α = 0.75
put acoustic tiles on short wall with metal rack → α = 0.75

47.96m² – (20m² x 0.065 + 23.4m² x 0.03) + (20m² x 0.75 + 23.4m² x 0.75) ≈ 78 m²

→ A bit more than targeted absorption area, but can’t hurt to lower reverberation time a bit more. This way, communication and the work climate are going to be more pleasant.

*subtracted areas given up, added replacements