Some rooms require special attention to soundproof them well. These particular types of rooms, for example, are audition rooms, theaters, or concert rooms. In order to have the best acoustic experience for their purpose, these types of rooms need to meet a series of conditions in regards to volume and dimensions, room shape and profiles as well as the reverberation time and uniform distribution of sound intensity inside them.
The reverberation span of a room refers to the time it takes the emitted sound to amortize in a proportion that will allow optimal audibility. The reverberation duration is an important characteristic which greatly influences the quality of audition and concert rooms.
The optimum duration of reverberation is set in accordance with the purpose and final function of the room. The usual duration range is between 1 and 1.5 seconds.
The reverberation time is especially dependent on the sound absorption level, and that’s why the best way to correct it, besides choosing the volume and shape, is to soundproof the individual construction elements which limit the room.
To soundproof construction elements, we need to use different types of sound-absorbing structures like:
- Sound-absorbent elements by porosity
- Sound-absorption through the membrane effect
- Resonators and resonant-absorbent structures
Sound-absorbent elements by porosity
Sound-absorbent elements by porosity have a fibrous or granular structure like glass wool, slag wool, felt, different types of porous masses, soundproofing curtains, porous plasters, etc.
In order to prevent dusting and damage, it is recommended to protect them with protective screens made of panels with perforated plywood, textile materials, fabrics of metal. or fiber.
Painting these porous materials diminishes the sound absorption levels. Oil paint particularly causes problems because the pores will close when used. So think twice before painting them.
Sound-absorption through the membrane effect
Sound-absorption through the membrane effect is made of plastic membranes, glass windows, and mounted on a frame. They are kept separate from the construction elements by an air layer or one partially filled with porous soundproofing material.
Resonators and resonant-absorbent structures
These consist, in principle, of a cavity located between a rigid wall and connected to the exterior with a canal (individual resonator).
Most often coupled resonators are used. These consist of a perforated plate supported by a frame. This closes an air-layer between it and the wall.
This space is common to all the perforations (resonators).
To obtain high-quality sound absorption, we can introduce some sound-absorbing things like cloth, crayon, mineral wool, paper glued to the back of the perforated plates, or the like in this space.
The sound absorption level that can be obtained by these depends on their placement inside the room. This placement should be made as non-uniform as possible to obtain maximum soundproofing.
Choosing the materials and sound absorbing structures for their sound-absorption capability depends on:
- their weight
- mechanical resistance
- installation possibilities
- painting possibilities (for example painting with water or oil paint)
- maintenance – do they require maintenance time?
- durability
- fire resistance
- hygroscopic properties (if it tends to absorb moisture from the air)
- light reflex capability
These are the basics of soundproofing acoustic and concert rooms, but let’s jump into the particularities that each room require.
We will begin with theater rooms. Everyone loves to go to the theater, but not everyone knows that they require a lot of work for the sound to be enjoyable. Think about this the next time you go to a theater.
Theater rooms
From the soundproofing standing point, theater rooms are regarded as the intermediary between conference and concert rooms.
They have reverberation spans with medium frequencies and between 1 and 2 seconds. That’s a little more than a conference room.
Modern theaters have a special type of ceiling that is placed relatively low, having a single balcony. That is this way to use sound reflection from the ceiling surface.
Because there is a lot of soundproofing surfaces backstage, it is hard to obtain a sufficiently good reflection from the stage to the room.
The back
To improve the sound intensity in the back of the theater room, it is required to place as many sound-reflecting surfaces as possible behind and on the sides of the area. Also, to improve the quality a little more, the ceiling must be oblique and with the sound reflection to the front of the area.
The back wall of the theater room should be inclined and reflect the sound as well.
The shape of the ceiling should be so made that it will directly and uniformly reflect the sounds to the spectators.
Theater rooms shouldn’t be built too large because of two good reasons.
The first one is that high volume requires a lot of soundproofing work on the walls in order to get the low reverberation time required for such an appliance.
Another reason is that it is hard to obtain a uniform distribution of sound with a high enough volume for all spectators.
Wrap up
Now we know the specifics of theater soundproofing. With some common sense, the methods used above, and the specific tips for theaters, it should be as easy possible soundproof a theater room.
Let’s move to even more serious business: concert rooms. These are usually big rooms and used for singing or playing different instruments. These require even more attention to soundproofing and sound absorption than theater or other rooms.
Concert rooms soundproofing
In concert rooms, the reverberation field must be as independent as possible from the presence of spectators. The concert rooms should have high sound-absorbing chairs. Yes, like the movie chairs, thick ones. These are made of dense fabrics, and the chairs and backrest should be well-padded.
The bottom of the seat should contain a perforated plate which, together with the filling material, act like a powerful sound-absorbent by resonance material.
Spectators shouldn’t be placed too close to the orchestra as it could affect the sound quality.
The orchestra can’t be viewed as a single point in the room but as a permanent stretched position due to the multiple sources of sound. Because of that, the surfaces of the walls nearby need to reflect the sound. It’s not advised to build the ceiling of paraboloids, and it must consist of three sections.
A sound-reflecting surface should be placed above the orchestra to obtain an even distribution of sound to the audience.
The soundproofing of surfaces must be done in accordance with the reverberation time that must be obtained which depends on the type of music that will be played.
Custom adjustments for the type of music played
A large vertical and equilateral prism system with the faces well covered with sound-absorbing materials mounted on the side walls will allow for adjusting them for each type of music that will be played. This way, we can do small adjustments, and the concert room can accommodate different types of genres.
The prisms are made of concrete in order to avoid low-frequency sound absorption.
Also, the perforated wood panels need to be provided with hinges. These allow us to adjust the airspace behind them to obtain maximum sound absorption of the soundproofing resonator at different frequencies.
Another type of soundproofing treatment consists of thin shutters made of slats placed in front of porous mats which, in the case of closed louvers, offer high sound absorption at low frequencies and low sound absorption at high frequencies. The opposite is valid for open louvers.
By using wood wall panels, the reverberation time of sound with a frequency lower than 100 Hz greatly diminishes.
Conclusion
Some types of rooms require special attention, and they are not as easy to soundproof as others. Soundproofing a home apartment room is clearly easier than rooms that need to accommodate multiple persons (some a lot of persons) extra soundproofing. Some of the facts about soundproofing a theater or concert room are not as common sense as soundproofing a normal room. Special attention is required to the reflection of the sound, keeping the reverberation time low enough and reflection of sound to the spectators.
Basically, there are three types of materials or methods used for soundproofing theater, audition, and concert rooms; resonators and resonant-absorbent structures; sound absorption through the membrane effect; and sound absorbent elements by porosity.
