ROOM 1 – DRYING ROOM
Assignment 1&2: Acoustic Profile and Characterization of room acoustic treatments
This is the drying room in my house building, next to the washing machines. It is the only room with a bit of softness. The building is made of concrete, tiles, aluminium frames and glass. The room itself is about 7×5 meters, with 2 blind concrete walls, a windowframeless glass exterior wall and a glass interior wall with a opening to walk through. I recorded late at night so there wouldn’t be sound from the washing machines. There was a unit to make the drying process faster which made a lot of noise, but I could turn it off for the recording.
Underneath is a picture of the route I walked from the microphone:
Interesting in this room is of course the washing that hangs in the middel of the room. You could hear the acoustics change depending on how high or low you kneeled, see pictures below.
Standing to the side, there was quite a lot of reverb, probably especially reflecting from the ceiling and glass facade. It had a clangy sounds, probably fed by the visual impression of cold materials. Underneath the washing the room felt smaller. A lot of reverb cut also, and the room felt warmer. Standing up (with head between the washing) there was almost no reverb.
The washing is of course the clear absorber here. As said, the room has only hard and smooth surfaces, which reflect sound much. The materials of the washing is all very soft and rough. The rougher texture means that the sound gets dispersed more. The softer surface I think means sound is absorbed more. I wonder if, because the washing is mostly wet, the heavier washing has more mass and can therefore absorb more sound.
For reference: the semi-open room next door where the washing machines are has a lot more reverb.
One thing I noticed when walking in: this room feels a bit disorientating. The drying unit on the wall makes a lot of noise, but you can’t see where it is coming from. In combination with trying to manouvering yourself through the washing bowed down, you never quite immediately know where sound is cominf from, which I think is very interesting.
ROOM 2 – PASSAGEWAY
Assignment 1&2: Acoustic Profile and Characterization of room acoustic treatments
The second room is a half-room. It is a part cut out of the building to make a passageway. The opposites end are open, the other two sides are facades, which are made of marble. The floor is street tiles, the ceiling is plastered concrete. The room is quite low. The lenght and depth are about the same which make it a square of about 12×12 meter. The two facades are not entirely parallel, but open up a bit towards the exit. It has a lot of columns all throughout the room. I had to record at night, because in the day you can hear many people and cars passing.
The room feels cold. I must say it was also cold and I was on my slippers. Like the first room, although of course a lot less, this room also does not have a clear overview due to all the columns, which I feel affect the auditory experience.
There is a lot of reverb in the room. In some spots you can hear a clear flutter echo. I think I only got it in the first distance in the recording, and if I remember correctly that is because the source and reciever must be in about the same spot to hear the flutter echo, because then the reflection travels just far enough to have te delay it needs to not be percieved as reverb, but as a seperate reflection.
You can feel the openings on the two sides quite well I think. Facing them while clapping feels like quite a lot of reflection gets lost. If you move throughout the room you pass the columns. They are made out of polished concrete. A hard material, so almost no absorption. The are round though, which disperses the sound. When there were columns between me and the facades, it was harder to spot a flutter echo. The reverb felt like it stayed about the same, but hard to hear. Most of the reflection comes from the ceiling, which as said is made with plaster on concrete. The plaster is not as smooth as the marble, but I think still reflects a lot of sound. The ground is made from street tiles, which have a rougher texture and I think there it does start to make a little difference. All in all everything is very hard materials, so all the absorbing work is done by the two openings. It sometimes is still possible though to hear a second reflection coming from the buildings that are standing next to the openings, especially on one side. I wonder how the amount of reverb would be affected if the marble walls would have a much rougher texture. Then the sound would still all be reflected of course, but I think the dispersion could do a lot in combination with the other dispersers, the columns. Still, quite interesting room I found.
ASSIGNMENT 3 – Empirical and numerical estimation of room acoustic properties
For Assignment 3 I recorded in the first room, the washing room. For the calculation I took the fifth (second to last, at 0:15) clap since it was the best and loudest.
There is quite some reverb. There are no echoes because the room is too small for that. Here is the visual of the sixth clap:
I could get a maximum decay of 30 dB. The time of decay was 1,23-0,47=0,76 seconds. To get to the RT60, the time would be 0,76*2=1,52 seconds.
Below you see the Sarooma site. I didn’t fully understand how it worked, and it gave a lot of errors when I tried to get close to the original room design.
final assignment
Five restaurants at the Hönggerberg campus, but nothing for the poor extremely rich. New campaign: Haute Cuisine at ETH.
Exactly where the food is prepared nobody knows, but it certainly is served in the high profile, state-of-the-art, superbly acoustically engineered HIL D24.1.
The room’s main purpose is facilitating a nice, quiet, afternoon lunch at the campus, for an already overstimulated audience. That means NO high pitched disturbances caused by high heels, clattering cutlery and handbag sized dogs. You have to be able to talk with your dining guests, without being bothered by your neighbours.
According to the DIN 18041, that means this room qualifies as B5, for dining rooms with special needs. Coïncidentally, this is also in a school.
The requirement for a B5 room is A/V ≥ 0.30 m²/m³.
The walls of this room are currently made out of plasterboard, except for the north facing wall, which is entirely made of glass. The floor and ceiling are of concrete. There are some acoustic panels hanging from the ceiling, but they don’t do much.
Above are the measurements of the room in the current situation.
And here is the requirement from DIN 18041:
With the function above and V=630 and h=4,8 we get A≥135.0 m2.
This means the room has to have 135 m2 of absorbing area. For reference, the room has 480 m2 total area. So high requirements.
Currently these are the absorption data:
So that means there is work to be done.
DIN 18041 says the focuspoint for category B rooms is 250-2000 Hz, which is of course the speech range. But we will also focus on reducing high-frequency reflections caused by cutlery and glassware, which are more from 2000 Hz upwards.
Our biggest culprit is the smooth concrete ceiling. For our haute cuisine restaurant, a office ceiling would of course be disgusting. But since everyone is willing to pay for this, a possible solution would be as follows:
These acoustic ceiling clouds have great absorbing quality. and since they are curved, they disperse the sound as well as absorbing. Biggest benefit: they hang above on the whole ceiling, so above every table. Therefore each table will have about the same level of acoustic treatment, and you also have less disturbance from you neighbours.
According to producer Western Noise Control, the sound absorption coefficient are as follows.
As seen in the 2 inch thick one, the coefficient is more than 1 for some frequencies, which seem impossible. But with ceiling cloud this is possible because they hang freely, both sides are free to absorb, and so the edges work with absorbing. So the increased area of the ceiling can absorb more sound than a flat ceiling could.
The second one is really overkill. Using the one inch one gives us these results:
No high pitched shimmer will ever go through this restaurant, which is exactly what we want.
We do have to do something with the lower end of speech though, which is 125 and 250 Hz.
For that we will install helmholtz resonators, tuned to absorb the frequencies between 125 and 250 Hz.
I choose wooden helmholtz panels that not only absorb the 125-250 Hz frequency band, but that also diffuses sound. We still have 2 times 2 parallel walls namely. On the wall opposite of the glass we place these resonators, and also on the east wall of the room. This allows us to not have flutter echoes. Also the wood stripes gives our overstimulated appalingly rich the feeling they are really getting their money’s worth.
alfa125=0,5 ; alfa250=0,6 ; which, applied on one long and one short wall. gives us:
One unexpected thing for me was that now the absorbtion of the other frequencies are now less. This is because the helmholtz panels only absorb the specific frequencies of 125-200 Hz, instead of the greater band that the plaster wall absorbed.
That means we have to go back to the cloud ceiling, and go full overkill with the two inch one.
Since this overshoots our goal, we have to tweak the area of each acoustic treatment a bit. We do de cloud ceiling on 80% of the ceiling area. Also the helmholtz resonators do not go on the full area of both walls, but on 70% of the long wall and 80% of the short wall.
This gives us the following results:
This numbers show us that most of the frequencies are good. Only the loewst frequencies could be improved. This could be done with an additional helmholtz resonator. Here is a impression image that I made with help of generative AI:
In the end perhaps the biggest succes is that, because this room has gotten so insanely expensive, only the richest rich can eat in this room, which is why there are only probably mostly 3 people in the room at once, which means there isn’t much sound produced in the first place. Great succes.
