Some features of the implementation of passive protection measures in vibroacoustic channels of speech information leakage.

Some features of the implementation of passive protection measures in vibroacoustic channels of speech information leakage.

Part 1

The necessity and importance of carrying out measures to protect premises from leakage of speech information via vibroacoustic channels is extremely relevant not only when fulfilling regulated requirements for the protection of designated premises in which information containing state secrets is processed, but also for any organizations and institutions in which confidential negotiations are conducted [1, 2].

Depending on the mode of ensuring the boundary of the controlled zone, the protection of acoustic and vibroacoustic leakage channels has specific features and limitations that complicate the implementation of effective protection.

In most situations, the use of active measures to protect leakage channels leads to the appearance of disturbing acoustic noise, significantly reducing the comfort of work in the protected and adjacent premises.

In most cases, the use of passive protection measures alone cannot fully solve the problem, provided that the protection index is calculated based on maximum acoustic interference. It is obvious that only the integrated use of active and passive methods and means can provide optimal protection, meeting information protection requirements and simultaneously ensuring a minimum level of disturbing acoustic noise in the premises.

Before analyzing the potential of comprehensive protection of vibroacoustic channels in typical conditions, let us consider the features of active protection in its extreme case.

Active protection

Active protection is aimed at protecting speech information only by the method of additive noise suppression.

In leakage channels formed by elements of building structures, the spectrum and level of interference must correspond to the parameters of the distorted speech signal and the current protection standards.

The limiting case of active protection is the creation of acoustic interference in the space of the protected premises, when protection is provided by the original acoustic speech signal.

If this initial speech signal is already noised in accordance with the protection standards, then with further propagation of the signal through leakage channels, the realized standard indicator of speech intelligibility cannot increase.

Within the framework of the theory of a diffuse sound field in a room, when the source of a speech signal and the source of acoustic interference are located at the same point in space, the signal-to-interference ratio established by the power of the original sound sources will be satisfied throughout the entire volume of the room and, accordingly, beyond its limits.

From the point of view of implementing guaranteed protection, such a solution is the simplest and most effective, if we do not take into account two factors — the possibility of unmasking the fact of speech obstruction outside the room due to the presence of increased acoustic noise and the complication of communication for the participants in the negotiations.

Currently, the market offers for sale intercoms that use this method of protecting speech information.

Due to the specific nature of the method being implemented, intercoms are recommended for protecting negotiations in situations where other activities are impossible due to time limits for measuring security indicators and equipping premises with stationary security equipment.

Such situations arise when conducting negotiations in hotels, in residential apartments, in summer cottages, in cars.

At the same time, if the time of closed confidential negotiations can be controlled and their frequency and duration are small, then such negotiating devices can also be used to protect negotiations in stationary conditions, for example, in work offices.

The acoustic field from a sound source in a room consists of two components: diffuse, which is uniformly distributed throughout the room, and the component of the direct wave field.

The diffuse component of the sound field in a room by sound pressure is determined by the expression [3]:

,

where  — sound pressure on the source axis at a distance of 1 meter from it, Pa, — average sound absorption coefficient in the room, ,  — total area of ​​the room's bounding surfaces, m2,  — axial concentration coefficient of the sound source.

The sound pressure of the direct sound field depends on the distance and is equal to:

,

where — distance from the center of the sound source, m, — directivity coefficient at an angle to the axis of the sound source, that is, in the direction of the point under consideration.

The sound pressure of the total field in the room is expressed as the sum of independent noise components:

.

Then the square of the total sound pressure in the room will be determined by the expression:

.

Since the spatial position of the negotiating persons is uncertain, then for the purpose of evaluation calculations it can be assumed that and , then:

.

Thus, the total sound field in the room consists of a diffuse component, which does not depend on the distance, but only on the acoustic properties of the room, and a direct wave component, which depends only on the distance to the point of sound pressure measurement.

For some large distance, the increase in the direct field will be insignificant, and the sound level will be determined only by the diffuse component.

Figure 1 shows the dependences of the change in the diffuse component of the sound field, the field of the direct wave and the sound pressure of the total field on the distance for a speech signal with a sound pressure level at a distance of 1 meter equal to 76 dB.

Figure 1. Dependence of the sound pressure level

of the acoustic field in the room

From the dependencies shown in Figure 1, it is clear that at distances from the source of about 1…2 meters, the sound pressure level of the direct wave field becomes comparable with the level of the diffuse field, and at distances of more than 2.5…3 meters from the source, the total sound field in the room is determined almost exclusively by the diffuse component.

In the near zone from the source at distances less than 0.5 meters, the sound pressure level of the direct wave field significantly exceeds the level of the diffuse component, therefore the sound pressure level of the total field does not depend on the acoustic properties of the premises.

Therefore, if the intercom is designed to protect against covert monitoring devices located in a room at a significant distance from the negotiating participants, then the sound pressure level of the acoustic interference source should be selected based on the condition of exceeding the diffuse component of the speech signal.

As a first approximation for practical applications, it is advisable to use as this distance the distance at which the sound pressure levels of the diffuse component and the direct wave are equal, the so-called «boom radius»:

.

The dependences of the boom radius on the room parameters are shown in Figure 2.

Figure 2. Dependence of the echo radius on the room parameters

For the most typical variations of room parameters in which negotiations are possible, the echo radius is from 2 to 4 meters, which should be taken into account when using intercoms.

In rooms with a large echo radius, the spatial zone where the direct sound wave exceeds the level of the diffuse component is quite large.

This means that the sound pressure level from an acoustic interference should exceed not only the diffuse component of speech, but also partially its direct component.

The requirements for the magnitude of masking interference are determined by the relative positions of speech sources and acoustic interference. The situation of symmetrical positioning of sound sources relative to the interference source, which is most often implemented in practice, is shown in Figure 3.

The noise level from the interference source is selected so as to ensure the standard ratio between it and the signal level throughout the entire volume of the room.

If, when locating signal and interference sources, the noise sound pressure level is selected so as to ensure the protection standard, including the direct wave zones from signal sources, then, obviously, its level will be excessive and unacceptable.

If the noise sound pressure level is selected based on the condition of ensuring speech protection in a diffuse field, then two leakage zones appear, located in the immediate vicinity of the negotiating participants.

Leakage zone size  depends on the ratio of the volume levels of interference and signals, on the acoustic properties of the room and on the location of the signal and interference sources, that is, the distance .

Figure 3. Location of negotiation participants

Let the sound pressure levels of acoustic interference and signals be determined by the expressions:

where — some excess of the interference level over the signal level.

Since the location of the negotiating participants is unknown when setting the interference level, it is set relative to either the diffuse level in the room or relative to the volume level, which is the same thing, assuming that the condition is met.

From Figure 2 it follows that for most real rooms the echo radius is 2…4 meters, and when negotiating participants are located at distances of 1…2 meters, that is, practically in the zone of the direct wave, if the interference source is located between them, as shown in Figure 3.

Then the expressions for the sound pressure levels of interference and signal in the negotiation zone will take the following form:

To meet the requirements for protecting negotiations, a certain relationship must be satisfied between the sound pressure level of interference and signal:

.

By solving both equations together, we can obtain the following expression for determining the maximum distance at which the regulatory relationship for protection is satisfied:

.

Solving this equation, we obtain the size of the leakage zone:

Of interest is the relative value , which determines the size of the leakage zone as a function of the distance between the negotiating parties.

From the resulting expression it follows that the value  must be greater than 1, that is, the excess of interference over the signal must compensate with a margin for the required standardized ratio for the protection of speech information.

Figure 4 shows the dependence of the relative value of the leakage zone on the total excess of the interference level over the signal level.

Figure 4. Relative value of the leakage zone

To obtain small values ​​of the relative value of the leakage zone, on the order of 10…20%, an additional excess of the interference level over the signal level by 10…12 dB is required.

Depending on the requirements for the operational conditions of negotiations, the requirements for the ratio of the interference level to the signal level can be determined, which can be considered as standard indicators of any intercom. From the equation for we obtain:

where  — excess of the level of the acoustic interference signal over the level of the acoustic speech signal, which is provided by the intercom, dB, — the standard interference/speech signal ratio that ensures the protection requirements, dB, — the specified requirements for the value of the relative information leakage zone.

Figure 5 shows the dependence of the required excess of interference over the signal on the relative value of the leakage zone.

Figure 5. Excess of interference over signal

depending on the size of the leakage zone

Thus, to ensure a small value of the speech information leakage zone of about 0.5…0.6, the required noise to signal volume level ratio is 22…24 dB, which exceeds the standard noise/signal ratio by 10…12 dB.

For the rest of the room, the noise/signal ratio will be equal to , that is, it is obviously significantly higher than the standard value.

On the other hand, the relative size of the leakage zone of about 0.5…0.6 corresponds to an insignificant volume of space in the immediate vicinity of the negotiating participant. If it is reasonable to assume that there are no covert means of covert control in the clothes or personal belongings of the negotiating participants, then such a size of the leakage zone is quite acceptable.

Thus, the TF-012 intercom manufactured by IKMC-1 [4] has a noise suppression system volume level of 90 dB, which, with an average speech volume level of 70 dB, corresponds to an excess of interference over the signal by 20 dB, i.e. the diameter of the leakage zone is approximately equal to the distance to the source of acoustic interference.

Since conducting negotiations via a wired path allows for artificial signal amplification, the volume of negotiations at the minimum level, i.e. about 64 dB, is quite acceptable.

In this case, the diameter of the leakage zone will decrease to 0.4, which at a distance of 1 meter to the interference source is only 40 cm.

Such a small size of the leakage zone actually solves the problem of protecting negotiations not only from covert monitoring devices installed in the room, but also in the immediate vicinity of the negotiating participants.

Further reduction of the leakage zone size is associated with an increase in the volume level of acoustic interference, which has its obvious limits due to the creation of secondary acoustic noise in adjacent rooms.

It can be argued that only the use of passive signal attenuation measures in conjunction with active protection allows us to solve this and other similar problems in the most optimal way.

Passive protection requirements

The easiest way to determine passive protection requirements (speech signal attenuation) is to introduce special acoustic interference for the simplest case of speech information leakage into an adjacent room. Figure 6 shows a diagram of such a leakage channel.

Figure 6. Schematic diagram of the acoustic leakage channel

The sound pressure level of the diffuse component of the speech signal in the protected room is equal to:

,

where  — the volume level of the speech signal, determined by the sound pressure level at a distance of 1 meter from the source, — average sound absorption coefficient in the protected room, — area of ​​the internal surfaces of the protected room.

According to the statistical theory of sound propagation in a room, the sound pressure level in an adjacent room will be determined by the expression:

,

where  — soundproofing capacity of the partition between rooms, — average sound absorption coefficient in a noisy room, — area of ​​the internal surfaces of the noisy room.

It is necessary to understand that the actual sound insulation between two rooms depends not only on the soundproofing capacity of the partition material, but also on the acoustic properties of both rooms.

Thus, the level of the speech signal penetrating into the adjacent room depends on the standardized level of speech in the protected room, the sound insulation of the partition and the acoustic properties of both rooms.

For protection in a noisy room, it is necessary to create an acoustic interference that will exceed the speech signal by an amount sufficient to ensure the standard value of the speech intelligibility indicator.

Moreover, it is possible to optimize the interference spectrum in such a way that the specified intelligibility value is met with a minimum integral interference power [5].

Considering the complexity of such calculations, let us consider a simpler case of protection, when it is necessary to exceed the speech spectrum by a certain value and the level of the diffuse component in the noisy room will be equal to:

.

For normal work of personnel in a noisy room, the level of acoustic noise should not exceed permissible medical standards . Thus, the condition must be met. Taking this restriction into account, the requirements for the soundproofing capacity of the partition between rooms can be obtained as follows:

.

The first three terms of the sum of this inequality are determined only by the normative indicators of two categories — protective and medical.

In this sense, the requirement for sound insulation is also partially normative, and the last term depends on the parameters of adjacent rooms.

Let us first consider the order of magnitude of permissible sanitary standards.

In Russia, the permissible level of acoustic interference is regulated in accordance with sanitary norms and rules [6] and is selected depending on the working conditions.

Table 1 shows the octave spectra of permissible acoustic noise for various categories of workers.

Table 1

Table 1 shows the acoustic noise values ​​for the following categories:

1 — hospital and sanatorium wards, hospital operating rooms;

2 — living rooms in apartments, sleeping quarters in kindergartens and boarding schools, living quarters in rest homes and boarding houses;

3 — doctors' offices in hospitals, sanatoriums and clinics, auditoriums and concert halls, hotel rooms, living rooms in dormitories, hospital and sanatorium grounds adjacent to buildings;

4 — classrooms and auditoriums, conference rooms, reading rooms, theater, club and cinema halls;

5 — residential areas immediately adjacent to residential buildings (2 m from enclosing structures), recreation areas of microdistricts and residential quarters, kindergarten sites;

6 — office workrooms and design bureau premises in administrative buildings;

7 — cafe and restaurant halls, canteens, theater and cinema foyers;

8 — retail areas of stores, gyms, airport and train station waiting rooms, utility rooms.

For most work and office premises, category 6 is suitable, for which the integral level of permissible interference is 50 dB, and the sanitary standard itself is called PS-45 for the value of permissible noise at a frequency of 1000 Hz.

If we take the protective requirements for the value of the interference/signal ratio of approximately 14 dB, then for a speech volume level of 76 dB we get: .

Let's consider the term that depends only on the parameters of both rooms:

.

In real practice, the quantities may have values ​​within the following limits: , , , then the quantity will have a maximum value of approximately 7 dB, a minimum of 27 dB, and an average value of approximately 10 dB. Consequently, the average requirement for the soundproofing capacity of a partition is , however, it can also be weakened by about 13 dB and increased, equal to 47 dB.

Medium and high requirements for the soundproofing capacity of a partition are implemented only by massive building structures made of brick or concrete.

Traditional partitions made of plasterboard, dry plaster and similar materials cannot meet the protection requirements simultaneously with the requirements for the permissible level of acoustic noise in the noise-prone room.

In addition, the noise level of PS-45 is suitable for work areas saturated with personnel. If 1-2 people work in the room, then such a noise level will be uncomfortable for them, which will require an additional increase in sound insulation by 5 … 10 dB.

Therefore, a simple solution to the protection problem without carrying out work to strengthen sound insulation is practically problematic for the simple situation considered, except for cases when the adjacent room is non-working or auxiliary.

Then you can focus on compliance with sanitary standards for the permissible level of acoustic noise directly in the protected room. Taking into account the noise penetrating from the noisy room to the protected one, you can get the following requirement for the amount of sound insulation of the partition:

.

The resulting expression is similar to the previous one in appearance, but has significantly lower requirements for sound insulation, since acoustic noise penetrates back into the protected room with additional attenuation. Taking into account the quantitative values ​​of the standard indicators, we obtain:

.

The second term has a maximum value of 8 dB, a minimum of 19 dB, and an average value of 5 dB.

Therefore, the average requirement for the soundproofing capacity of a partition is 8 dB, and the maximum is 14 dB. In all cases, such requirements are easily met by thin partitions.

Practice shows that when protecting an executive office, the standard acoustic noise equivalent to the requirements of PS-45 is overstated when placing one person in the room.

When targeting noise of the order of PS-35, the requirements for the soundproofing capacity of the partition increase by only 5 dB and will be equal to 19 dB in the worst case.

For situations where it is still impossible to create acoustic noise directly in the adjacent room, a combination of passive and active protection is possible, as shown in Figure 7.

With such a design of acoustic protection, it is possible to ensure compliance with protection standards while simultaneously meeting the requirements for residual acoustic noise levels in both adjacent rooms using sufficiently thin additional partitions with a soundproofing capacity of 14…16 dB.

In particular, such a solution is mandatory when protecting ventilation ducts, which are the most effective acoustic channels for leakage of speech information. Attempts to install an acoustic noise emitter directly into the duct will lead to an increased level of acoustic noise in the protected and adjacent rooms.

Without introducing passive protection means, it is impossible to ensure acceptable conditions for normal operation in adjacent rooms, since there are no sound attenuating elements along the signal propagation path.

The only acceptable solution is to install acoustic silencers in ventilation ducts, which perfectly fulfill the role of sound-insulating elements, and their required efficiency is determined in accordance with the above expressions.

Figure 7. Combined use of passive and active protection

Part 2

The effect of through holes

on the soundproofing capacity of partitions

When implementing passive protection by constructing additional partitions or increasing the soundproofing capacity of existing partitions, special attention must be paid to carefully sealing through cracks and holes, which significantly reduce soundproofing.

It is known [3] that for a partition made of materials with different soundproofing capacity, it is more convenient to calculate the overall soundproofing of the room based on the sound conductivity of the material:

,

where — sound absorption coefficient of the room, — surface area of ​​the room, — sound conductivity coefficient, -th section of the partition, made of a separate material,  — area of ​​the th section of the partition, so that , where is the total area of ​​the partition.

We will consider only the change in the soundproofing capacity of the partition in the presence of through cracks and holes in it. It is known that the sound conductivity of the partition is inversely proportional to the soundproofing capacity:

.

Calculation of the soundproofing capacity of a partition with different sections is based on the average sound conductivity coefficient, which is defined as:

.

For a partition with a through hole or gap with an area of ​​, the calculation of the total soundproofing capacity is carried out taking into account the sound conductivity coefficient of the hole, equal to 1. The amount of reduction in soundproofing capacity will be equal to:

,

where is the ratio of the area of ​​the through opening in the partition to the total area of ​​the partition.

Provided that , and for the condition , that is, there is a decrease in soundproofing capacity by its entire initial value.

Figure 8 shows the dependence of the value of the decrease in the soundproofing partition on the ratio of the area of ​​the through hole to the total area of ​​the partition.

Figure 8. Reduction in soundproofing capacity of the partition

It follows from the given dependencies that even with an insignificant decrease in the relative area of ​​the through hole (up to 0.05%), there is a rapid decrease in the soundproofing capacity of the partition.

With a relative area of ​​approximately 1% for partitions with an initial soundproofing capacity of more than 30 dB, there is a reduction in soundproofing by an amount at which the remainder from the initial is 20 dB, and with an area of ​​10%, regardless of the initial, the final soundproofing is 10 dB. Moreover, the higher the initial soundproofing capacity of the partition, the more significant its reduction.

Therefore, even the best partition can be reduced to nothing by the presence of a small through hole.

The dimensions of such holes in absolute terms are quite large, so with a partition area of ​​10 m2, an opening with a relative area of ​​1% will have a linear size of 30 cm, for example, poorly sealed air duct inlets.

The calculations provided show that solving the inverse problem, i.e. attempts to increase the sound insulation of a weak partition by increasing the sound insulation capacity of its part, will not lead to the expected result.

The obtained calculations clearly demonstrate the fact, well known to security specialists, of the practical complexity of ensuring the task of implementing passive protection by increasing the sound insulation of partitions to create optimal conditions for protection and comfortable working conditions for personnel who require high quality construction and installation work.

Sound absorption capabilities

From the expressions for the level of the diffuse component of the speech signal in the room, which is the initial level for leakage channels of all types, it follows that in any room it can be reduced by sound-absorbing finishing of the room surfaces. This fact is known to everyone as a reduced volume level in a muffled room.

Let's consider the potential possibilities of carrying out such protective measures.

Absorption of sound vibrations for protective purposes can be carried out to reduce the sound level in the following cases:

— reducing the level of the diffuse component of the speech signal from a source in the room;

— using acoustic absorbing screens;

— using sound mufflers in air ducts.

Let us consider the possibility of reducing the sound in a room by means of acoustic finishing of its internal surfaces, which is due to the known dependence of the sound pressure level of the diffuse field in a room on sound-absorbing properties:

,

where — acoustic constant of the room, m2, — equivalent sound absorption area of ​​the room, m2.

Sound absorption in a room can be carried out both directly by its internal surfaces and by objects located in it, therefore it is determined in accordance with the expression:

,

where  — sound absorption coefficient -th surface element, the area of ​​which is equal to ,  — the sound absorption coefficient of a separate object located in the room,  — the number of these objects.

As a rule, sound level reduction is achieved by introducing additional absorbing facings. Local sound absorbers can be introduced into the room, but their installation in any room is unrealistic without appropriate design development of the interior, and this is difficult and expensive. The simplest solution to the problem is to use acoustic finishing of entire surface areas, for example, installing an absorbing suspended ceiling or using soft carpeting.

If all surfaces of the room are acoustically treated, the amount of sound level reduction after finishing can be determined by the formula:

,

where  is the sound absorption coefficient of the material used for acoustic finishing.

Figure 9 shows the dependence of the value of the reduction in the sound pressure level of the diffuse component of sound in the room on the initial sound absorption coefficient for various values ​​of the absorption coefficient of the additional finishing material.

Figure 9. Reducing the sound pressure level of the diffuse component

Thus, with additional finishing of the room surfaces with higher-quality sound-absorbing materials compared to the original ones, it is possible to achieve a significant reduction in the diffuse level of the sound field in the interior volume of the room.

Moreover, the lower the value of the initial sound absorption coefficient, the greater the effect of using additional acoustic finishing, i.e. finishing is most effective in echoey rooms. The degree of «echoiness» of a room can be determined by the value of the reverberation time, which allows you to determine the average sound absorption coefficient of the room.

Usually, due to the presence of people and a small amount of upholstered furniture in offices, the average sound absorption coefficient is about 0.2 … 0.4.

Then, when using sound-absorbing materials with a sound absorption coefficient of 0.9…0.95, the gain due to acoustic finishing will be more than 10 dB. In many cases, such a gain is sufficient to meet the protection requirements.

Moreover, the result is achieved without the use of expensive equipment for creating vibroacoustic interference, and after finishing, the comfort of negotiations in the room is additionally increased.

In practice, it is impossible to implement sound-absorbing finishing of the entire surface area of ​​the room. As a rule, it is possible to introduce an additional area with a sound absorption coefficient . Since the sound pressure level of the diffuse speech signal component is equal to:

,

where is the acoustic constant of the room,

then the expected decrease in the sound pressure level of the diffuse field can be calculated using the formula:

,

where  — constant room before treatment, m2; — room constant after treatment, m2.

The value of the sound pressure level reduction can be rewritten as follows:

,

where  — the relative share of the surface area of ​​the room that is subject to acoustic treatment;  — the relative increase in the sound absorption coefficient of the additional cladding material in comparison with the average sound absorption coefficient of the room.

.

Figure 10. Reducing the sound pressure level

during acoustic finishing of the room

As follows from the obtained dependencies, even with incomplete finishing of all surfaces of the room, it is possible to further reduce the level of sound pressure in the diffuse field.

The amount of sound volume reduction depends on the degree to which the sound absorption coefficient of the additional finishing material exceeds the average sound absorption coefficient of the room, and a noticeable increase begins if the material used for additional finishing has a sound absorption coefficient that exceeds the original by 2…3 times.

The finishing area and the efficiency of the material used have the most significant effect on the amount of sound reduction in the room.

It is necessary to increase the area of ​​the surface being finished to significant values ​​of about 50% of the total surface area of ​​the room. The difference between an average-quality absorbing material (sound absorption coefficient of about 0.5…0.7) and a material with high absorption (sound absorption coefficient of about 0.9…0.95) is 4 dB, which is not small in practical applications.

In addition, additional sound absorption can also occur when individual objects that absorb sound energy are brought into the room. For practical use, Table 2 provides experimental data on sound absorption coefficients of various materials and objects.

Table 2

Table 2 shows the sound absorption areas for individual objects.

Special protected room

The interaction of passive and active measures to protect speech information is most fully realized in a protection option that can be called a «room in a room». The purpose of this protection option is to ensure a guaranteed degree of protection of speech information through all possible leakage channels.

Passive protection via the acoustic channel is achieved using additional sound-insulating structures installed at a distance from the building structures of the original room. Protection against information leakage via the vibration channel is ensured by installing sound-insulating structures on vibration-insulating supports.

Moreover, the soundproofing capacity of building structures can be calculated using the above optimization methods, taking into account the standard speech intelligibility in the space between the original and additional structures and the satisfaction of sanitary standards for the level of side acoustic noise inside the premises.

In order to ensure protection against leakage through ventilation ducts, acoustic noise suppressors are installed in them.

The practice of constructing such premises has shown that high quality protection is achieved provided that all through cracks and holes in the additional building structure are eliminated, and cracks in the structural elements are carefully puttied and sealed.

Currently, the market offers few options for technical solutions for protected premises. The most complete version of a standard project for a protected meeting room «GARANTEE» is offered by ZAO «Protection Group — UTTA» [7]. The schematic design of a protected room is shown in Figure 11.

Additional structures of the original room are made of standard building materials on a frame. Vibration-isolating supports are made of rubber.

The design solutions of the frame, structures, and vibration mounts are optimized from the standpoint of maximum attenuation of audio frequency range signals with minimum structure weight.

Acoustic emitters are installed in the space between the structures of the original and protected rooms. Vibration emitters are installed in places with increased leakage signal strength – pipelines, places where vibration mounts are installed, places where the room is suspended from the ceiling.

Acoustic side noise in the interior of a room never exceeds sanitary standards if the soundproofing structure is made with high quality.

One of the advantages of special rooms is the possibility of constructing a shielding shell in them, designed to reduce the level of electromagnetic radiation from covert or legal emitting devices.

Figure 11. Layout of a protected room

The main parameters of such a room are given in Table 3.

Table 3

Control microphones and accelerometers are installed in advance in the protected room, allowing the level of protection to be established and periodic monitoring of compliance with regulatory parameters to be carried out.

The advantages of a secure room are most beneficial when used as a meeting room for a limited number of people, subject to security measures and access control.

According to experts, normal operation of a secure meeting room is possible for 15…20 years without significant repairs.

Conclusion

In conclusion, I would like to emphasize once again that when carrying out protective measures against leakage of speech information via vibroacoustic channels, it is absolutely necessary to conduct a comprehensive analysis of the situation and optimally choose between passive and active protective measures or a combination of them.

Neglect of passive protection measures in many cases nullifies all work on protection, if it is carried out not according to the standard indicators of protection, but according to the subjective perception of secondary acoustic noise in the protected room.

Work on the implementation of passive protection measures, carried out by experienced specialists, can give a tangible result without reducing the comfort of work in the premises.

In certain situations of conducting negotiations with low frequency, it is enough to offer to use an intercom.

It is also advisable to use it in places where it is simply impossible to carry out protection work — hotels, residential buildings, summer cottages, cars.

It is necessary to take into account the presence of a speech information leakage zone, the security of which should be resolved by organizational measures.

When protecting individual identified leakage channels, only active protection means installed on structures or communications can be used. However, given the expected level of secondary acoustic noise penetrating into the room, it is advisable to have a project for enhancing sound insulation in the leakage channel.

If there is a limited number of possible physical leakage channels, and all of them have an efficiency close to the standard, it is sufficient to carry out construction and architectural measures to increase sound absorption in the room, thereby reducing the sound pressure level of the speech signal.

If there are real concerns that speech information leakage channels can be used from all possible directions, then it is advisable to use a means of protection such as a special protected room that provides guaranteed protection against speech information leakage.

Literature

1. Kargashin V. L. Problems of active protection of vibroacoustic channels//Special equipment, 1999, No. 6.

2. Khorev A. A., Makarov Yu. K. On the assessment of the effectiveness of acoustic (speech) information protection//Special equipment, 2000, No. 5.

3. Iofe V.K., Korolkov V.G., Sapozhkov M.A. Handbook of Acoustics/Ed. by Sapozhkov M.A. – M.: Svyaz, 1979.

4. Intercom «TF-012″/Technical Description//Enterprise «IKMC-1».

5. Kargashin V. L. Improvement of methodological principles for assessing the security of premises from speech information leakage//Special equipment, 2001, No. 6.

6. Designer's Handbook. Noise Protection/Ed. by Yudin E. Ya. – M.: Stroyizdat, 1974.

7. Special protected premises «Garant»/Technical project//ZAO «Protection Group — UTTA».

Kargashin Viktor Leonidovich
Candidate of technical sciences
Special equipment, No. 4, 5, 2002