The ceiling

The ceiling is the more complex surface of the construction. On the floor above there are two classrooms and a corridor and some chair's dragging noises comes into the room through the slab. Another problem is the height of the room that is only 3 meters. Is very difficult to fit all the necessary isolation in the available space without compromising the effective height inside the room.
As mentioned previously, the construction can not touch the school's building in order to prevent the vibration transmissions. With this, the ceiling can not be rigidly stuck to the ceiling of the room. The solution chosen relies on wooden beams to support all the weight, fixed to the top of the sand wall.

Cut bricks to fit the beams.

The first step was to put the last row of bricks in a special way. These were cut to give space to the wooden beams. The centers of the beams are apart from each other by 60 centimeters. The beams are about 5.5 meters long with a section of 15 by 7.5 centimeters.

Cutting a brick.

The bricks were cut with a machine because they break easily if hammered and they have to be perfectly sliced, so the wooden beams fit with no gaps. We can not forget that the room have to be air tight as much as we can.

Installing the wooden beams.

After the bricks were all placed, glued to the top of the wall and filed with sand, the wooden beams were installed. The beams have only 15 centimeter and the bricks 19 centimeter.

It was necessary to put some wooden blocks to raise the beams in order to let them aligned with the top of the bricks.

Applying glue to the ceiling.

Once the beams were installed, the first layer of insulation was glued to the ceiling. It should have been mineral wool but it would be very difficult to fix it because of it's structure.

We used reconstructed foam. The acoustical performance and the price do not have any comparison with the mineral wool but for technical reasons we had to use it.

Ventilation tubes between
the wooden beams
and the ceiling.

The space between the ceiling and the beams is very narrow. The main problem is to fit the ventilation system. It was necessary to build costume ventilation tubes, but I will explain that in other post.

Ceiling isolation materials.
(test only)

On top of the wooden beams we will add an isolation "sandwich" with several materials. From top, the materials to use are:

- Reconstructed foam.

- Air space.

- Mineral wool (5 centimeters).

- Plasterboard.

- M.A.D. 4

- Plasterboard.

- PKB2 (between the wooden beams - not in the picture)

All the ceiling will be cover with this "sandwich", and will be glued to the bricks and nailed to the wooden beams.

TESTING THE ROOM

Ceiling with reconstructed foam.

After gluing the reconstructed foam all the surfaces of the room have already the acoustics characteristics expected. It doesn't isolate the sound from the outside because it has no door yet, and the ceiling it's not with all the layers, but the reverberation inside its already as it would be when its finished.

Playing music.

I have played some music inside. It sound great!

The reverberation inside its almost null, but the room it's not uncomfortable and super dry. Muting the music makes the sound disappear instantly. Other test made was turning one speakers to the wall, away from the listener, and the sensation was very similar as setting the stereo balance to the other side; most of the sound just doesn't return. It's not ready yet but is responding as expected, witch is good.