Rechor-based fire alarm and voice warning project

Electroacoustic calculation.

The electroacoustic calculation for a particular room answers the questions: "How many speakers, what capacity and where it is necessary to arrange in this room in order to fulfill the requirements that are imposed on the warning system." Knowing the results of the calculations for each room, you can calculate the required power of the amplifiers of the sound warning system for the entire building.

The main requirements for ECSS are given in SP 3.13130.2009 "Fire protection systems. Warning and management system for evacuation of people in case of fire. Fire safety requirements ":

"4.1 EMSS sound signals shall provide a common sound level (constant noise sound level together with all signals produced by the annunciators) of at least 75 dBA at a distance of 3 m from the annunciator, but not more than 120 dBA at any point in the protected room.

4.2 EMSS sound signals shall provide sound level not less than 15 dBA higher than permissible sound level of constant noise in the protected room. The sound level shall be measured at a distance of 1.5 m from the floor level.

4.3 In sleeping rooms, EMSS sound signals shall have a sound level not less than 15 dBA above the sound level of constant noise in the protected room, but not less than 70 dBA. Measurements should be taken at the level of the sleeping person's head.

4.4 Wall sound and voice annunciators shall be so positioned that their upper part is at least 2.3 m from the floor level, but the distance from the ceiling to the upper part of the annunciator shall be at least 150 mm. "

Acoustic calculation in general is quite complex, therefore, in practice, to simplify calculations, the following assumptions are used:

Assumption 1. Based on the geometric dimensions of spaces, all spaces are divided into only three types :

- "Room" (area up to 40 sq.m., length not exceeding 1.75 width),

- "Corridor" (length exceeds width by 2 times or more),

- "Hall" (area more than 40 sq.m.).

A room contains one alert.

In the other two types of rooms - several, evenly located, alerts will be placed.

Assumption 2. The loudspeaker emits a "spherical" wave, i.e. the sound pressure in any direction from the loudspeaker will be the same. At the point of greatest removal (R) from the source of oscillations is the "design point" - the point at which it will be necessary to know the level of sound pressure produced by this source of oscillations .

The initial data for the calculation are:

- loudspeaker characteristics, namely sound pressure level (at rated supply voltage) measured at a distance of 1 m from the loudspeaker;

- geometric dimensions of the voiced room;

- noise level (dBA) in the room;

- method of loudspeakers installation.

The sound pressure level (Usv, dBA) is given in the documentation of the loudspeaker manufacturer.

The noise level (Ush, dBA) in the room is normalized depending on the purpose of the room and is given in the reference literature, for example in SNiP 23032003.

The required sound level at the design point Utr is defined as Ush + 15, dBA.

The attenuation of the sound signal depending on the distance has a quadratic dependence and can be easily determined using an appropriate table or calculated.

Example 1. Classroom measuring 14 x 6 meters.

For such premises Ush is normalized with the value of 35 dBA, (SNiP 23-03-2003

item 6, Table 1).

At that Utr will be 35 + 15 = 50 dBA

According to Assumption 2, this space is a room of type "Hall," subtype "Rectangle." For halls of this type and with an area of ​ ​ less than 100 m2, the installation of 2 loudspeakers located on opposite, narrow sides in the middle is used. The height of wall loudspeakers is 2.3m.

With such room dimensions, the distance to the calculation point will be 14.34 m .

Sound attenuation at this distance is 23 dBA.

The required sound level of the alert is:

Utr. Op. = 50 + 23 = 80 dBA.

Thus, to comply with SP 3.13130.2009 norms, it is enough to use Sonata-T-100-3/1 type alerts, in which Uzv.d is 90 dBA.

Example 2. The school corridor (D) is 23 meters long and 2 meters wide.

For such premises, Ush is recommended to be taken equal to 65 dBA (taking into account the noise made by schoolchildren during the changes).

At that Utr will be 65 + 15 = 80 dBA

Under Assumption 2, this space is a Corridor space. For corridors less than 3 m wide, it is recommended to install alerts along one wall.

It is recommended to calculate the total number of annunciators using the formula:

N = 1 + (D - 2W )/3W = 1 + 3.16 = 4.16.

Round up to 5. The distance between the alerts is 4.6m, from the extreme alerts to the ends of the corridor is 2.3m.

The height of wall annunciators is 2.3m.

With such dimensions of the room and arrangement of annunciators, the distance to the design point will be 3.5 m.

Attenuation at this distance is about 11 dBA.

The required sound level of the alert is:

Utr. Op. = 80 + 11 = 91 dBA.

That is, in order to comply with SP 3.13130.2009 standards, it is necessary to use Sonata-T-100-5/3 type annunciators, in which Uzv.d is 92 dBA.

Having calculated according to the above procedure, we obtain:

• 6 Sonata-T-100-3/1 annunciators with power of 3 W each shall be used for sounding of rooms of zone 0. The total power of the annunciators will be 18 W, i.e. one 50 W amplifier is enough to power the annunciators;

• 17 Sonata-T-100-3/1 type annunciators and 6 Sonata-T-100-5/3 type annunciators with power of 5 W each shall be used for sounding of premises of zone 1. The total power of the annunciators will be 81 W and for their power it is necessary to use 2 amplifiers of 50 W;

• 10 Sonata-T-100-3/1 type annunciators and 9 Sonata-T-100-5/3 type annunciators shall be used for sounding of premises of zone 2. The total power of the annunciators will be 75 W and for their power it is necessary to use 2 amplifiers of 50 W;

• 12 Sonata-T-100-3/1 type and 11 Sonata-T-100-5/3 type annunciators shall be used for sounding of 3 zone premises. The total power of the annunciators will be 91 W and for their power it is necessary to use 2 amplifiers of 50 W;

• 12 Sonata-T-100-3/1 type and 11 Sonata-T-100-5/3 type annunciators shall be used for sounding of premises of zone 4. The total power of the annunciators will be 97 W and for their power it is necessary to use 2 amplifiers of 50 W.

Thus, to power the annunciators of the 1st, 2nd, 3rd and 4th zones in addition to the BAS-4 device (power 50 W), it is necessary to use one BUM1/4 amplifier per zone.