 ## Sound Silencer function and Counting Method Resonance Room

Silencers to overcome the echo in the room and how to calculate the resonance in the room. After getting to hear the ideal dimensions of space, the next step is to measure the hearing room reverberation and echo neutralize hearing room. Each room has an echo with echo characteristics different to one another. Character echo in this room is determined on three parameters, namely the level of echo, reverberation time and frequency reverberation.

To make the hearing room with good acoustics is that we should be able to apply the proper acoustic treatment composition. Thus, we get a room with the level of echo, reverberation time and frequency reverberation flat at each level of frequency. The room with the right level of echo will give the room an atmosphere of live music was good when we

### 1. Understanding RT60 (Reverberation Time)

There are various methods of measuring the echo time but most often used is Reverberation Time 60dB better known by the term RT60. Definition RT60 is the time (seconds) it takes for the sound to weaken as much as 60dB.

To make a room with good acoustics results we need to calculate:
(1) The amount of reverberation (RT60) on average in the room (seconds)
(2) The amount of reverberation (RT60) at a certain frequency (seconds)

The ideal reverberation time (RT60) for the hearing room with a volume of 10 cubic meters is 0.9 seconds and 500 cubic meters is 1.4 seconds. If the numbers (RT60) room was much smaller than the benchmark figure above, we will feel the room is likely to die (dead room). Or, if the number (RT60) space well above the benchmarks above, we will feel that too reverberant space.

For example, you have a room with a size of 29m3, the ideal echo time (RT60) is 1.15 seconds. However, if the room has a reverberation time (RT60) of 1.7 seconds, then the room will require sound absorption material. Or vice versa, if the room has a reverberation time (RT60) of 0.7 seconds, then the room we could call the dead room where the room is a lot of sound absorption material.

### 2.  RT60 Formula

Each material has the character of absorption and reflection are different for different frequencies. For example, cement material tends to reflect the high tones and low tones to be forwarded. While carpets tend to absorb high tones and low tones continue. Often I see people make room studio or audio space by installing carpet on the floor and walls. A room like this tend to provide sound effects “boomy” (drone) with detailed sound that is not good.

RT60 calculation formula is as follows:

RT60 = (0.161 x V) / (A x S)

V = volume of the room (m3)
A = area of the surface material (m2)
S = the absorption coefficient of the material (m / s)

### 3.  RT60 Calculation Example

Here are examples of questions the calculation of reverberation frequency hearing room if we have the hearing room with dimensions:

Length 6.6m; Width 4.8m; high 2.4m

Floor surfaces: Concrete
Surface wall: Cement
Surface ceiling: Cement

With the above data, we first need to calculate the volume of the room.
To calculate the volume of the room, the formula is: length x width x height.
Then we can calculating the volume of space = 6.6m x 4.8m x 2.4m = 76.032m3

The second step is to calculate the area of each surface of each ingredient is in the room. In an example of this problem, we need to calculate the total area of the concrete surface and the total surface area of cement.
The total area of the surface of the concrete = (6.6 x 4.8) = 31.68m2
The total area of the surface of the cement = total wall + ceiling area = 2 (6.6 x 2.4) + 2 (4.8 x 2.4) + (6.6 x 4.8) = 86.40m2 From the above data, let’s make the calculation table:

Description calculations:

1. S125, S250, S500, S1000, S2000, S4000 is the absorption coefficient of materials (cement / concrete) at a frequency of 125Hz, 250Hz, 500Hz and next.

2. S125 x A is the absorption coefficient multiplied by the 125Hz bandwidth absorbency. From the above table S125 x A = 0.317 for concrete materials

3. RT60 for certain frequencies in the room gained from the numbers 0161 x volume of space for a total of S x A. From the table above, we get the RT60 to 125Hz frequency is 0.482 seconds.

4. If all the numbers have been calculated properly, we can make the frequency response of the room to be like the example below. The graph above gives an overview:
1. On 1000Hz frequency, reverberation (RT60) lasted for 2,993 seconds and echo at a frequency of 125Hz for 0.482 seconds. This causes the phase difference and the time difference to the sound at a frequency of 125Hz and the frequency of 1000Hz.
Negative factors for the above are damaged stereo sound imaging and comfort in listening to dialogue or music to be reduced.
2. RT60 average of 1.776 seconds. The figure of the ideal figure RT60 recommended for such rooms.

B. Step Acoustic Treatment

To get the ideal RT60 we need to do:
1. Reduce the RT60 up with numbers that are ideal for rooms with volume on top.
2. Reduce RT60 at a frequency of 1000Hz with the right combination of acoustic material.

C. The Acoustic Treatment Ideal

Having analyzed and accounted for, the chosen acoustic material with the composition:

1. The floor carpet with a surface area of ​​31,68m2.
2. Walls and ceilings MDF with a surface area of ​​76,40m2.
3. Acourete Fiber Panel with a surface area of ​​10m2.

Let’s see the difference by making a calculation table and a graph like the one below.  Grafik Frekuensi Gema Setelah Treatment Akustik

Graph Frequency Gema After Treatment: pink line depicts reverberation time (RT60) room before treatment at different frequency levels. Dark blue lines depict reverberation time (RT60) room that has been in-treatment.

From the above chart, the conclusion can be drawn:

1. RT 60 average space has been reduced from 1.776 into 0.426.
2. Graphics RT 60 for each level becomes more gentle frequencies ranging from 0.3 to 0.6 seconds compared to the previous graph between 0.4 to 2.5 seconds.

Thus this brief article about the silencers to overcome the echo in the room: Room Reverberation Time RT60 room reverberation and calculations, including examples about how to resolve the issue.

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