Calculation of the number of wall sounders. Taking into account the type and design features of loudspeakers. Accepted design assumptions

Good day.

We have already said that the requirements for SOUE (warning and evacuation control systems) are regulated by volume SP 3.13130.2009. "Set of rules. Systems fire protection. Warning and management system for evacuation of people in case of fire. Requirements fire safety».

The main requirement for sound systems is that they must provide a minimum level sound pressure at a level of 1.5 m from the floor (i.e. at the height of the average person’s ears) 15 dB above the average noise level in the room, but not less than 75 dB. Wherein maximum level The sound pressure created by the SOUE should not exceed 120 dB: this is the pain threshold, then it’s still useless - only harm can be done. Therefore, if the noise level at the facility is, say, 110 dB, then your SOUE should squeal no quieter or louder than 120 dB, and increased efficiency should be achieved through all sorts of lighting effects - stroboscopes, for example. In bedrooms, hotels, hospital wards etc. The sound level is measured at the height of a sleeping person's head.

There are many options for placing sound sources. You can attach a horn-type “bell” loudspeaker of terrible power in the corner of the hall and let it scream “throughout the whole forest.” As a result, at the far end of the room the sound will meet the requirements, but near the sound source people will go deaf. So I forgot to add: the “Code of Rules” also requires uniform distribution of sound (clause 4.7. Installation of loudspeakers and other voice alarms in protected premises must exclude concentration and uneven distribution reflected sound).

Therefore, ceiling speakers are widely used in large rooms - they allow you to create just the same uniform distribution of sound pressure. There are many designs for installation in dropped ceilings, there are pendant speakers that look like chandeliers.

In the corridors and small rooms Wall-mounted speakers are quite suitable; their placement is strictly regulated: not lower than 2.3 m from the floor, but not less than 15 cm from the ceiling. By the way, there are bidirectional loudspeakers: in the middle of the corridor I attached them to the wall, they speak back and forth.

It should be added that, in order to avoid large power losses on the wires, the amplifiers produce a high-voltage signal, 100-120 V. The speakers are equipped with step-down transformers.

About calculating the SOUE with ceiling speakers:

The number of ceiling speakers for sounding a room is calculated without taking into account power - pure geometry. We assume that the directional pattern of the speaker is 90 degrees; it is necessary that they evenly, without overlap, sound the rooms at a height of 1.5 m from the floor. Those who wish can draw, I’m too lazy, so without any details:

b Take the height of the room minus 1.5m, proudly call the resulting number “h”. We hang the speakers at a distance of 2h from each other, and from the wall - h.

The area covered by one ceiling speaker is approximately:

Now we take the area of the room and divide it by this same S(op), we get the number of speakers. For example, we have a hefty warehouse of 7000 sq.m., height 6m. In this case, h=6m-1.5m=4.5m. S(op) turns out to be approximately 2x4.5x2x4.5 = 81 sq. m. Number of speakers:

N = 7000:81 = 86

Now about the power. Any normal speaker (loudspeaker), among its technical characteristics, has such an interesting parameter as sensitivity, measured in W/m. True, then, for the convenience of calculations, this is converted into dB, those who wish can look for themselves how to convert watts into decibels, this is already a theory, I don’t want to go into details. In short, sensitivity is the sound pressure created by a speaker at a distance of 1 m with a power dissipated at 1 W.

We must create a sound pressure 15 dB higher than the noise level in the room. In order not to run around with a sound level meter, we will use a table of typical noise levels in rooms:

Since we have a warehouse, we take the noise level to 70 dB. Let's take the LPA-6 speaker from Louis-Plus; it has a sensitivity of 94 dB, i.e. with a power of 1 W at a distance of 1 m from it, it creates a sound pressure = 94 dB. We need to obtain sound pressure at a distance of 4.5 m (our distance “h”)

70dB+15dB = 85dB

Let's use the graph of sound pressure attenuation c depending on the distance from the speaker, provided by the same company Louis-Plus:

At a distance of 1 m, the attenuation = 0, and at the 4.5 m we need, it is about 13 dB. Those. from the original 94 dB (speaker sensitivity or sound pressure at a distance of 1 m), we need to subtract 13 dB. We get that with a power of 1 W, our speaker will pump us at a level of 1.5 m from the floor with a pressure of 81 dB. But you need 85 dB.

Let's look at the characteristics of our speaker:

Look, in the column “Inclusion power” there are 3 connection options: 6 W, 3 W and 1.5 W. Those. its matching transformer has several taps, allowing, with a voltage on the transformer of 100 V, to develop a power of 6 W, 3 W or 1.5 W.

And, for complete happiness, one more sign - gain in dB depending on the power dissipated by the speaker:

We need to drive 85 dB at a distance “h” from the speaker. We received a calculated 81 dB, i.e. you need to add 4 dB. Let's see - with a power of 3 W, the sound pressure gain will be 4.8 dB, so if we connect the speaker at a power of 3 W, we will have 85 dB with some margin.

We multiply the speaker power by their number and get the minimum sufficient amplifier power. In our case it is 3W x 86 = 258 W.

Overall, quite confusing at first, but let's recap briefly.

Without being tied to any powers, stupidly based on geometry, we calculate the area that one speaker should sound at a given room height. Then, based on the area of the room, we calculate the number of speakers.
We select a speaker and, based on its sensitivity, calculate what sound pressure it can create at a height of 1.5 m from the floor with a power of 1 W
And, finally, we calculate how much power needs to be developed on the speaker in order to obtain the sound pressure we need at that magical height of 1.5 m. Naturally, if this power is higher than the maximum power of the speaker, we will have to choose another model.

Well, that’s basically all the horror. The second approach is no longer so scary.

And here is the very first formula:

I recommend memorizing it by heart, since it’s not difficult. Imagine, you are inspecting a facility, the customer asks how much the notification will cost. With this formula, you can count on your fingers the number of ceiling speakers and plus or minus bast shoes, adding to them the cost of amplifiers and cables, and at least indicate the scale of prices. The customer likes this efficiency.

Questions - in comments or by email [email protected], news subscription form is below.

In accordance with those that entered into force in 2003. New fire safety standards require design to ensure specified sound levels. The document contains a reference to a method for measuring sound level, but there is no reference to how to correctly calculate the required number and power of loudspeakers.

Let's try to describe the procedure for calculating an alert step by step.

1. It is necessary to determine the number of speakers to ensure even sound distribution.

horn........................................30-45 O
floodlight...................................30-45 o
wall-mounted........................................75-90 O
ceiling........................................80-90 o

Also, based on installation experience, it can be assumed that it is allowed to place ceiling speakers at a distance equal to the height of the ceiling (in this case, the sound uniformity will be quite mediocre, but will satisfy the airborne standards. If uniform sound is required, then it will be necessary to install through “ceiling height - human height "). Wall-mounted speakers are installed at a distance equal to the width of the corridor (room). And horn and floodlights are placed so that crowded places fall into the radiation pattern. When installing wall-mounted and horn loudspeakers, you must adhere to the rule: if you want to install several loudspeakers in the same area, it is better to install them in the center and point them towards different sides than putting them on the walls and pointing them towards the center. Legibility and quality in the latter case will be significantly worse.

2. Determine the noise level in the room. To do this, you can measure it or use a table with approximate levels for various types premises.

3. The broadcast level must exceed the noise level by:

for background music...................................5-6dB
for emergency notification.........by 7-10 dB.
for high-quality music...........................15-20dB

4. To take into account the attenuation of the sound level from distance (within the radiation pattern), you can use the table:

5. To take into account the increase in sound level depending on the supplied power, you can use the table:

6. To calculate the sound pressure level at the required distance, you can use a simplified formula:

SPL (dB) = nameplate SPL - attenuation SPL + increase SPL

SPL (dB) - level at the required distance in the radiation pattern

SPL passport - sound pressure level according to the passport at a distance of 1 m (dB/W/m)

SPL attenuation - level of attenuation depending on distance (see table)

SPL increase - - level of increase depending on the supplied power (see table)

From the above formula you can easily calculate the required power for a single loudspeaker. By summing up the power of the speakers, you can calculate the total power of the amplifier. It is recommended to select the amplifier power with a 20% power reserve. When operating the system, you can verify this.

For example: there is a retail space measuring 20x30m with a ceiling height of 3m. It needs to be voiced with background music, but taking into account the possibility of emergency notification.

For uniform scoring you will need 20:3-1 = 5 rows of 30:3-1 = 9 pcs. total 45 pcs.

The sound level at a distance of 1.5 m from the loudspeaker (ceiling height - the height of the shortest person) must be at least 63 + 7 = 70 dB. Therefore, if you use ART-01 (Inter-M) loudspeakers with a power of 1 W, (according to the passport, the sound pressure level at a distance of 1 m is 90 dB), the formula will take the form:

SPL (Sound Pressure Level) = 90-3+0 =87 dB. Which is more than 70. So, these speakers are suitable for sounding a given room. And in principle, if only emergency notification is needed, then the number can be even less (you can recalculate it yourself).

If you don’t want to bother yourself with “complex” mathematical calculations, then you can always use some program for calculating the number of loudspeakers, for example from the TOA company. When using equipment from other manufacturers, it is necessary to take into account the difference in their sound pressure from the selected type. You can download the warning system calculation program (8.2mb)

ABOUT Determining the required power and sound pressure level of acoustic devices in public address systems has always presented a significant challenge for designers. Some manufacturers of warning systems, trying to make their work easier, provide all kinds of graphs, tables or programs for calculating these parameters. Most often the attempt practical application Such recommendations or programs raise more questions than answers, or are perplexed by the absurdity of the solutions obtained.

For self-study Most designers simply don’t have time for acoustics problems, so it makes sense to present them here basic principles acoustic calculations and selection of sound-reproducing devices.

Calculation of the acoustic parameters of sound-reproducing devices involves selecting the necessary loudspeakers depending on the current level of background noise and the selected sound circuit. The actual background noise level depends on the purpose of the room. It is believed that for qualitative perception speech (dispatcher broadcasts), the sound pressure level of the loudspeaker should be 10-15 dB higher than the background noise level at the most distant point of the room.

For relatively low background noise (less than 75 dB), it is necessary to provide an excess useful signal level of 15 dB; for high background noise (more than 75 dB), 10 dB is sufficient. That is, the required sound pressure level is: Lmax=La+15, dB - for a room with a relatively low level of background noise; Lmax=La+10, dB - for a room with a high level of background noise, where La— the current level of background noise in the room.

LOUDSPEAKER CHARACTERISTICS

The main characteristics of loudspeakers include their directivity, frequency range and sound pressure level,

developed at a distance of 1 m from the emitter.

Omnidirectional speakers are speakers, ceiling speakers, as well as all kinds of audio speakers (although it should be noted that speakers occupy an intermediate position between directional and non-directional systems). The sound distribution area of omnidirectional loudspeakers (directional pattern) is quite wide (about 60°), and the sound pressure level is relatively low.

To directional speakers First of all, there are horn emitters, the so-called “bells”. In horn loudspeakers, acoustic energy is concentrated due to the design features of the horn itself; they are distinguished by a narrow directivity pattern (about 30°) and a high sound pressure level. Horn loudspeakers operate in a narrow frequency band and are therefore poorly suited for high-quality reproduction of music programs, although due to high level sound pressure well suited for scoring large areas, including open spaces.

Selecting speakers by frequency range depends on the purpose of the system. For dispatch transmissions and creating a musical background, the range of 200 Hz - 5 kHz is quite sufficient, which is provided by almost any acoustic devices (horn emitters have a slightly smaller range, but for speech transmissions it is quite enough). For high-quality sound, you should use speakers with a frequency range of at least 100 Hz - 10 kHz.

Required sound pressure level is the only characteristic of a loudspeaker that is determined from the results of calculations. This characteristic causes the greatest number of problems, which are most often associated with confusion between electrical power and sound pressure. There is an indirect relationship between these quantities, since sound volume is determined by sound pressure, and power ensures the operation of the loudspeaker. Of the supplied power, only part is converted into sound, and the magnitude of this part depends on the efficiency of a particular loudspeaker. Most manufacturers speaker systems indicates in the technical documentation the sound pressure in Pascals or the sound pressure level in decibels at a distance of 1 m from the emitter. If the sound pressure is specified in Pascals, while it is necessary to obtain the sound pressure level in decibels, the conversion of one value to another is carried out using the following formula:

For a typical omnidirectional loudspeaker, 1 W of electrical power can be assumed to correspond to a sound pressure level of approximately 95 dB. Each increase (decrease) in power by half leads to an increase (decrease) in the sound pressure level by 3 dB. That is, 2 W - 98 dB, 4 W - 101 dB, 0.5 W - 92 dB, 0.25 W - 89 dB, etc. There are speakers that have a sound pressure level of less than 95 dB per 1 W, and speakers that provide 97 and even 100 dB per 1 W, while a 1 W speaker with a sound pressure level

100 dB replaces a 4 W loudspeaker with a level of 95 dB/W (95 dB - 1 W, 98 dB - 2 W, 101 dB - 4 W), it is obvious that the use of such a loudspeaker is more economical. It can be added that with the same electrical power, the sound pressure level of ceiling speakers is 2-3 dB lower than that of wall speakers. This is because the wall-mounted speaker is located either in a separate cabinet or against a highly reflective rear surface, so the sound radiated back is almost entirely reflected forward. Ceiling speakers are typically mounted on false ceilings or pendants so that sound radiated from the rear is not reflected and does not contribute to the increase in frontal sound pressure. Horn loudspeakers with a power of 10-30 W provide a sound pressure of 12-16 Pa (115-118 dB) or more, thereby having the highest ratio of decibels to watts.

In conclusion, it should be noted that when calculating loudspeakers, it is necessary to pay attention to the sound pressure they develop, and not to the electrical power, and only in the absence of this characteristic in the description, be guided by the typical dependence - 95 dB / W.

CALCULATION OF LOUDSPEAKER POWER FOR CONCENTRATED SYSTEMS

Calculation of loudspeaker power for concentrated systems is carried out in the following order:

1) the required sound level at a remote point in the sounded room is determined:

Where La— current level of background noise in the room, 10 - excess of the required sound pressure level above the background;

Where L— distance from the loudspeaker to the extreme point.

If a concentrated system uses multiple loudspeakers, then:

where n is the number of loudspeakers in a concentrated system;

the value 2 x 10-5 in the denominator corresponds to the level of absolute silence in Pascals;

5) by value Lgp or R1 the required loudspeaker is selected or its required typical power is found.

When selecting typical power, a ratio of 95 dB/W is used.

Example 1:

It is necessary to calculate the loudspeaker power in a lumped system with two loudspeakers.
Initial data:
Distance from speaker to remote point L-15 m, background noise level in the room - La- 75 dB.
Required sound level at a remote point -
Required sound pressure at a remote point:
Required sound pressure at a distance of 1 m from the loudspeaker:

A typical 1 W speaker produces approximately 95 dB SPL, 2 W -
97 dB, 4 W - 101 dB, 8 W - 104 dB. Therefore, each of the two speakers should have a power of about 8 watts.

Example 2:

Calculate the loudspeaker power in a lumped system with a directional loudspeaker.
Initial data:
distance from loudspeaker to remote point L— 80 m,
background noise level - La- 70 dB.

Required sound level at a remote point –

Required sound pressure at a remote point:

Required sound pressure at a distance of 1 m from the loudspeaker:

Sound pressure level that a loudspeaker should develop at a distance of 1 m:

A loudspeaker type 50GRD-3 with a power of 50 W has a sound pressure level of 118 dB, i.e. sufficient to sound an area at a given distance.

CALCULATION OF LOUDSPEAKER POWER FOR DISTRIBUTED SYSTEMS

Calculation of loudspeaker power for single and double wall-mounted chains:

Where La— effective background noise level in the room

2) calculate the sound pressure that the loudspeaker should develop at a remote point:

3) determined

- for a single chain or a staggered chain:

- for double chain:

Where b — room width, D— distance between loudspeakers in a chain.

Instead of D you can substitute the expression:

Where L- length of the room, N— number of loudspeakers along one wall;

4) the sound pressure level that each loudspeaker must provide is determined:

5) by value L2p the required loudspeaker is selected or its required typical power is found. When choosing by typical power, the ratio used is 95 dB/W.

Example 3.

Bank operating room:
The length of the room is 18 m, width is 7.5 m, height is 4.5 m.
It is recommended to use two speakers, one on each side.
Speaker pitch: D= 6 m.
Based on the purpose of the room, the expected background noise level is 60-63 dB;

sound pressure that a loudspeaker should develop at a distance of 1 m:

Loudspeaker sound pressure level:

This sound pressure level corresponds to typical loudspeakers with a power much less than 0.5 W.

Store sales area:
room length: L-25 m, width: b — 18 m, height: h - 5 m, people mostly standing - additional height: hd — 1.5 m. Double wall chain recommended, three speakers per side, chain pitch D— 8 m.
Based on the purpose and area of the facility, the estimated background noise level should be expected in the range of 65-70 dB;
required sound level in the room:

sound pressure that loudspeakers must develop:

sound pressure that a loudspeaker should develop at a distance of 1 m:

Loudspeaker sound pressure level:

This sound pressure level corresponds to a typical loudspeaker with a power slightly less than 1 W,

therefore, speakers of 1 W each can be used.

SPEAKER POWER CALCULATIONS FOR SINGLE AND DOUBLE CEILING RAIN AND CEILING GRILL:

1) the required sound level in the room is determined:

Where La- current level of background noise in the room (with a background noise level of more than 75 dB - Lmax = La + 7, dB);

2) calculate the sound pressure that the loudspeaker should develop at a remote point:

3) the sound pressure that the loudspeaker should develop at a distance of 1 m is determined:

- for a single chain located along midline premises:

- for double chain:

- for the ceiling grid:

Where b- width of the room, D— distance between loudspeakers in a chain;

4) the sound pressure level that each loudspeaker must provide is determined:

5) the required loudspeaker is selected based on the value or its required typical power is found. When selecting by typical power, a ratio of 95 dB/W is used.

Despite the apparent complexity, the given formulas do not represent significant difficulty in calculations and do not require special mathematical training. Moreover, after several calculations, the designer will determine the necessary characteristics of acoustic devices without additional calculations, intuitively.

In conclusion, we can indicate the reason for most solutions that contradict practical experience, obtained as a result of specialized acoustics programs or when using the above formulas. As a rule, it lies in the incorrect setting of the current level of background noise. A number of reference and technical publications provide approximate levels of background noise for rooms of different functional purpose. These data should be treated with extreme caution, since in different sources for the same rooms they can differ by 5-10 dB (which gives a very significant spread in sound pressure), in addition, it must be taken into account that in the event of a fire, due to the panic or structural collapse, the required background noise level should be assumed to be greater than for normal control transmissions.

A. Pinaev Ph.D.,
M. Alshevsky senior researcher Research Institute of Industrial Safety and Emergency Situations of the Ministry of Emergency Situations of the Republic of Belarus

Hello, dear friends! Vladimir Raichev is in touch with you, I have prepared another quite interesting article for you. The fact is that before installing the SOUE, an acoustic calculation of the warning system must be carried out. Did you know about this? I will try to tell you what it is and what it is eaten with.

When constructing many areas of a building, how sound travels through them is critical. Concert halls, theaters – shining example that. The acoustics of these rooms largely determine the attendance and the desire of celebrities to perform there.

Acoustic calculations of such cultural and entertainment institutions are carried out at the design stage, when it is possible to change quite a lot of construction parameters to improve the sound of voices, musical instruments.

It is more difficult if it is necessary to calculate the acoustics of an existing, operated room or building. This is what most often have to deal with those who design (SOUE) in case of unforeseen, emergency situations - fires, explosions, man-made disasters.

It should be clarified that all SOUE can be divided into 2 groups:

Sound warning is type 1 or 2 of systems, where the end devices - alarm signals - are sirens and other sources of sharp, loud sound of various tones.
Speech is 3 (the most common) or 4, 5 types. They use annunciators - loudspeakers, acoustic speakers, horns used for most indoor environments; sound spotlights for large premises; line arrays for broadcasting messages and pre-recorded texts in sports, cultural and entertainment venues, airports, and railway stations.

Typically, acoustic calculations of CO are carried out when designing new construction projects and equipping existing buildings with systems of 3–5 types.

This is due to the fact that types 1 and 2 are used in small premises or buildings in terms of area, capacity, number of seats, building volume, number of floors, where installed sound sirens and tinted signals provide excellent audibility due to the volume, a sharp difference from the level of usual background noise anywhere in the building.

Noise level in rooms, power of acoustic devices

It should be noted that the background noise level in the premises of a building, on the territory of an enterprise, or organization is one of the significant characteristics that determine the acoustic calculation of the warning system, affecting its effective operation.

Based on everyday noise levels, rooms can be divided into the following types:

Low noise – offices of administrative and governing bodies, offices, medical institutions.
With a low noise level – shopping pavilions, shops, airport buildings and railway stations.
Noisy. Super- and hypermarkets, halls of sports, cultural and entertainment institutions, warehouse complexes using electric forklifts.
WITH increased level background noise. Warehouses with equipment with engines internal combustion, places of loading and unloading operations using lifting equipment, industrial premises.
Very noisy. Railway station platforms, music clubs.

Naturally, the sound pressure of voice alarm devices, which determines their volume, must significantly exceed the noise level, which greatly weakens the sound of any loudspeaker similar to it.

Such a solution is not always possible. In the premises of music clubs, concert halls, cinemas, where the normal sound level for them is already close to critical for the hearing organs, it is necessary to reduce the volume or completely turn off the broadcast of a music program, film dubbing before reporting an alarm, or block the SOUE with a sound reinforcement system culturally -entertainment establishment.

Power, type, installation method (ceiling, wall, suspended), their number, as well as distance, angle, radius, maximum possible sound area of acoustic devices, places of their optimal placement in the premises of the building - the main characteristics used and determined during acoustic calculations .

Initial data

First of all, this is the average maximum noise level measured on site or pre-calculated in the room where voice alarm devices will be installed. Here are approximate values for various objects:

Hotels, medical, educational, cultural and educational institutions - 55–65 dB.
Administrative, office rooms, shopping pavilions, shops, warehouses – 65–70 dB.
Large shopping centers, restaurants, train stations, airports – 70–75 dB.
Production workshops of industrial enterprises, concerts, sports complexes - 75–80 dB.

In addition, the acoustic calculation will require the following information:

Geometric dimensions premises.
Sound pressure level of selected notification devices.
Sensitivity, power of sirens.
The width of the radiation pattern of each device, which determines the full warning zone.
Sounding area of the siren (based on technical passport products) depending on the noise level.

All these data serve as the basis for acoustic calculations.

Calculation methods and programs

There are methods and instructions for independently carrying out calculations, which outline a clear sequence for selecting factors, and also provide formulas, tables, graphs, and diagrams necessary to establish the basic parameters of the SOUE for each type of premises and buildings.

In addition, to speed up and simplify the process, we have developed computer programs for acoustic calculation of the warning system.

There are both paid services provided by independent development companies; organizations involved in the design of SOUE, and free programs calculations from manufacturers of products-components of warning systems, sound equipment, which can be downloaded from their official websites.

Basic parameters consistently determined acoustic calculation:

Maximum distance sounding of the selected siren under the conditions of upcoming operation.
Maximum voice radius.
Real radiation pattern angle.
The maximum possible sounding area of the siren.

Then taking into account latest characteristics on the plan diagram of the room to be equipped with a warning system, the placement of all sounders is carried out - loudspeakers, sound speakers, other acoustic systems used in composition of the SOUE, so that anywhere in the room you can hear an alarm message about an emergency situation and actions for safe evacuation from the building.

Required amount sound voice alarm devices, in turn, serves as the basis for calculating the total power of the system, selecting broadcast amplifiers, switching devices, sources backup power in case of power outages of the building, construction of the SOUE diagram as a whole.

Nuances of acoustic calculation

It is not enough to determine the unit, total power necessary devices alerts for a given room or building. There are many subtleties and little details known to design specialists, installation organizations, established both theoretically and from operating experience of voice warning systems that affect its operation:

The distance between adjacent sirens should not exceed twice the maximum sound radius for a given product model.
All acoustic devices selected for use in the warning system should not have external volume or power controls.
In addition to the volume in a voice announcement, clear audibility, legibility and uniformity of information presentation are extremely important. Therefore, you should not try to install one or more very powerful speakers to cover the entire area of the room.
In halls and other rooms large area Distributed warning systems are required, consisting of a large number of evenly distributed sirens, the sound area of which overlaps each other. This will eliminate both excessive concentration and improper distribution of reflected sound.
At the same time, in the corridors, narrow and long rooms It is recommended to use sound spotlights with regulated by specialists sound pressure power to select the optimal perception at each point. This will allow corridor-type buildings to significantly reduce the number of sirens and the required amplifier power for broadcasting messages, and as a result will reduce the cost of the system.

Why you need to entrust acoustic calculations to professionals

But this is just the “tip of the iceberg”. Without doubting the knowledge and competence of technical specialists of enterprises and organizations, they should be warned against independently carrying out acoustic calculations if it will serve as the basis for installing a voice alarm system. There are several reasons for this:

For installation of SOUE, integral integral part which is a sound, speech warning system, in existing, operated buildings, a license from the Ministry of Emergency Situations is mandatory this type works
At the same time, paradoxically, it is possible to design SOUE in such buildings without any permits. However, in practice, a working draft of the SOUE is usually developed by the organization that subsequently carries out installation and commissioning, signs the certificate of completion of the work, including in the territorial body of the Ministry of Emergency Situations (as far as my memory serves, this process is voluntary), and, accordingly, bears full responsibility in accordance with with legislation.
For newly built facilities, the design and installation of an EEMS requires SRO approvals for a legal entity.

In addition, it is quite difficult to reconcile the calculated acoustic values with the technical, electrical parameters, characteristics of broadcast power amplifiers, switching devices, uninterruptible and backup power supplies, special techniques so that the operation of the system is stable, and voice messages and music broadcasts are clearly audible in any room of the building protected by the SOUE.

Therefore, for design, installation and commissioning work, it is better and more expedient to involve specialists from enterprises and organizations that have the appropriate permits and long-term experience in the field of industrial safety.

It will be useful to find out about the objects where they designed and installed a voice alarm system in order to independently verify its effectiveness. Reviews from building owners and premises tenants will also be useful.

They are the most important component of fire protection systems. In the process of designing warning systems, electroacoustic calculations are performed. The basis for electroacoustic calculation is a set of rules developed in accordance with Article 84 federal law FZ-123 SP 3.13130.2009 dated July 22, 2008. This article is based on the following main points of the set of rules.

4.1. Sound signals of the SOUE must provide general level sound (the sound level of constant noise together with all signals produced by the sirens) is not less than 75 dBA at a distance of 3 m from the siren, but not more than 120 dBA at any point in the protected premises
4.2. Sound signals of the SOUE must provide a sound level of at least 15 dBA higher permissible level sound of constant noise in the protected area. Sound level measurements should be carried out at a distance of 1.5 m from the floor level
4.7. The installation of loudspeakers and other voice alarms in protected premises must exclude concentration and uneven distribution of reflected sound
4.8. The number of sound and speech fire alarms, their placement and power must ensure the sound level in all places of permanent or temporary residence of people in accordance with the norms of this set of rules

The meaning of electroacoustic calculation comes down to determining the sound pressure level at design points - in places of permanent or temporary (probable) presence of people and comparing this level with recommended (normative) values.

There is various types of noise in the sounded room. Depending on the purpose and characteristics of the room, as well as the time of day, the noise level varies. Most important parameter when calculating, is the value of the average statistical noise. Noise can be measured, but it is more correct and convenient to take it from ready-made noise tables:

Table 1

In order to hear sound or speech information, it should be 3 dB louder than the noise, i.e. 2 times. Value 2 is called sound pressure margin. In real conditions, noise varies, so for clear perception useful information against the background of noise, the pressure reserve should be at least 4 times - 6 dB, according to standards - 15 dB.

Satisfaction of the conditions set out in paragraphs 4.6, 4.7 of the set of rules is achieved by organizational measures - correct placement of loudspeakers, preliminary calculation:

loudspeaker sound pressure,
sound pressure in design point,
effective area voiced by one loudspeaker,
the total number of loudspeakers required to sound a certain area.

The criterion for the correctness of the electroacoustic calculation is the fulfillment of the following conditions:

Sound pressure of the selected loudspeaker d.b. “at least 75 dBA at a distance of 3 m from the siren,” which corresponds to a loudspeaker sound pressure value of at least 85 dB.
Sound pressure at the design point d.b. higher than the average noise level in the room by 15 dB.
For ceiling speakers, the installation height (ceiling height) must be taken into account.

If all 3 conditions are met, the electroacoustic calculation is completed; if not, then the following options are possible:

choose a loudspeaker with greater sensitivity (sound pressure, dB),
select a speaker with higher power (W),
increase the number of loudspeakers,
change the speaker layout.

2. Input parameters for calculation

Input parameters for calculations are taken from the technical specifications (TOR) (provided by the customer) and technical specifications for the equipment being designed. The list and number of parameters may vary depending on the situation. Sample input data is given below.

Speaker parameters:

SPL
Pgr– loudspeaker power, W,
ShDN– Width of the radiation pattern, degrees.

Room parameters:

N– Noise level in the room, dB,
N– Ceiling height, m,
a– Room length, m,
b– Room width, m,
Sp– Room area, m2.

Additional data:

ZD– Sound pressure margin, dB
r– Distance from the loudspeaker to the calculated point.

Area of the sound room:

Sp = a * b

3. Calculation of loudspeaker sound pressure

Knowing the rated power of the loudspeaker (Pvt) and its sensitivity SPL (SPL from the English Sound Pressure Level - the sound pressure level of the loudspeaker measured at a power of 1 W, at a distance of 1 m), you can calculate the sound pressure of the loudspeaker developed at a distance of 1 m from the emitter.

Rdb = SPL + 10lg(Pw)

(1)

SPL– loudspeaker sensitivity, dB,
RVT– loudspeaker power, W.

The second term in (1) is called the “doubling power” rule or the “three decibels” rule. The physical interpretation of this rule is that for every doubling of the source power, its sound pressure level increases by 3 dB. This dependence can be presented tabularly and graphically (see Fig. 1).

Fig.1. Dependence of sound pressure on power

4. Sound pressure calculation

To calculate the sound pressure at the critical (design) point, it is necessary:

Select design point
Estimate the distance from the loudspeaker to the calculated point
Calculate the sound pressure level at the design point

As a calculation point, we will choose the location of the possible (probable) location of people, the most critical from the point of view of position or distance. The distance from the loudspeaker to the reference point (r) can be calculated or measured with a device (range finder).

Let's calculate the dependence of sound pressure on distance:

P20 = 20lg(r-1)

(2)

r– distance from the loudspeaker to the calculated point, m;
1

ATTENTION: formula (2) is valid when r > 1.

Dependence (2) is called the “inverse squares” rule or the “six decibels” rule. The physical interpretation of this rule is that for every doubling of the distance from the source, the sound level decreases by 6 dB. This dependence can be presented tabularly and graphically, Fig. 2:

Fig.2. Dependence of sound pressure on distance

Sound pressure level at design point:

N– Noise level in the room, dB (N from English Noise – noise),
ZD– Sound pressure margin, dB.

With RR=15dB:

P > N + 15

(5)

If the sound pressure at the calculated point is 15 dB higher than the average noise level in the room, the calculation is done correctly.

5. Calculation of effective range

Effective sound range (L) – the distance from the sound source (loudspeaker) to the geometric location of the design points located within the limits of the sound pressure, the sound pressure in which remains within the limits (N+15 dB). In technical slang - “the distance that the loudspeaker penetrates.”

In English-language literature, effective acoustical distance (EAD) is the distance at which speech clarity and intelligibility are maintained (1).

Let's calculate the difference between the sound pressure of the loudspeaker, the noise level and the pressure reserve.

p– difference between loudspeaker sound pressure, noise level and pressure reserve, dB.
1 – coefficient taking into account that the sensitivity of the loudspeaker is measured at 1m.

6. Calculation of the area voiced by one loudspeaker

The basis for assessing the size of the sounded area is the following setting:

We will carry out the calculation based on the following assumptions: The directional (radiation) pattern of a loudspeaker can be represented in the form of a cone (sound field concentrated in a cone) with a solid angle at the apex of the cone equal to the width of the directional pattern.

The area voiced by the loudspeaker is the projection of the sound field, limited by the opening angle, onto a plane parallel to the floor at a height of 1.5 m. By analogy with the effective range: The effective area sounded by a loudspeaker is the area of sound pressure within which does not exceed the value N+15dB (formula 5).

NOTE: The loudspeaker radiates in all directions, but we will rely on the input data - sound pressure levels within the radiation pattern. The correctness of this approach is confirmed by statistical theory.

Let's divide loudspeakers into 3 classes (types):

ceiling,
wall,
horn.

8. Calculation of the effective area voiced by a wall loudspeaker

9. Calculation of the effective area voiced by a horn loudspeaker

10. Calculation of the number of loudspeakers required for sounding a certain area

Having calculated the effective area sounded by one loudspeaker, knowing the general dimensions of the sounded area, we calculate the total number of loudspeakers:

K = int(Sp/Sgr)

(16)

Sp– voiced area, m2,
Sgr– effective area voiced by one loudspeaker, m2,
Int– the result of rounding to an integer value.

11. Electroacoustic calculator

The overall result obtained in the form of a block diagram:

Fig.6. Block diagram of an electroacoustic calculator

Programming example

In this calculator (written in the program Microsoft Excel) an elementary brief technique has been implemented - the electroacoustic calculation algorithm outlined above. This program can be downloaded from our website.

Fig.7. Electroacoustic calculator in Microsoft Excel

Based on the developed calculation algorithm, the ON-LINE electroacoustic calculator on our website works.

APPENDIX 1. List and brief characteristics of ROXTON loudspeakers

Loudspeaker ROXTON	SPL, dB	R tu, watt	ShDN, gr.	R db, dB
Ceiling speakers
PA-03T - Ceiling loudspeaker	88	3	90	93
PC-06T - Ceiling loudspeaker	90	6	90	100
PA-610T - Ceiling loudspeaker	88	6	90	96
PA-620T - Ceiling loudspeaker	90	6	90	96
PA-20T - Ceiling loudspeaker	92	20	90	101
WP-10T - Ceiling Loudspeaker	92	10	90	98
PA-30T - Ceiling 2-way loudspeaker	90	30	90	104
T-200 - Hanging loudspeaker	92	10	90	102
SP-20T - Hanging loudspeaker	92	10	90	104
Wall speakers
WP-03T - Wall-mounted loudspeaker	86	2	90	91
WP-06T - Wall loudspeaker	90	6	90	96
4.2. Sound signals of the SOUE must provide a sound level of at least 15 dBA above the permissible sound level of constant noise in the protected room. Sound level measurements should be carried out at a distance of 1.5 m from the floor level. 4.3. In sleeping areas sound signals SOUE must have a sound level of at least 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-mounted sound and voice sirens must be positioned so that their top part is at least 2.3 m from the floor level, but the distance from the ceiling to the top of the siren must be at least 150 mm. 4.5. In protected areas where people are wearing noise-protective equipment, as well as in protected areas with a noise level of more than 95 dBA, sound alarms must be combined with light alarms. The use of flashing light annunciators is permitted. 4.6. Voice annunciators must reproduce normally audible frequencies in the range from 200 to 5000 Hz. The sound level of information from voice alarms must comply with the standards of this set of rules as applied to audible fire alarms. 4.7. The installation of loudspeakers and other voice alarms in protected premises must prevent concentration and uneven distribution of reflected sound. 4.8. The number of sound and speech fire alarms, their placement and power must ensure the sound level in all places of permanent or temporary residence of people in accordance with the norms of this set of rules.