Determination of parameters of vibroacoustic noise reduction systems.

Determination of parameters of vibroacoustic noise reduction systems ANG-2000, VNG-1020, GSh-01, STENA, VAG-66, VNG-006 when installing their vibration exciters on various elements of building structures of the premises.

2. Estimated parameters.

2.1 Spectral characteristics of vibration oscillations of various elements of building structures when excited by vibration transducers of systems in the frequency range of 0.25 — 6.3 kHz relative to the zero vibration level a0 = 3 * 10-5 g

2.2 Integral values ​​of vibration oscillations au of various elements of building structures in the frequency range of 0.25 — 6.3 kHz relative to a0 = 3 * 10-5 g when excited by vibration transducers of systems.

2.3 Spectral characteristics of acoustic noise emitted by vibration exciters of noise suppression systems installed on various elements of building structures, in the frequency range of 0.25-6.3 kHz relative to the zero sound pressure level p0=2*10-5 Pa.

2.4 Integral values ​​of acoustic noise Lp emitted by vibration exciters of systems installed on various elements of building structures, in the frequency range of 0.25-6.3 kHz relative to p0=2*10-5 Pa.

3. Testing methodology.

3.1 The noise suppression system parameters were measured in a room with internal dimensions of 6.7 m x 5.4 m x 3 m. The area of ​​the wall with a thickness of h=0.5 m was ~ 20 m2, with a thickness of h=0.25 m it was ~ 16 m2, and the area of ​​the ceiling formed by floor slabs with a thickness of h=0.25 m was ~ 36 m2. The noise suppression parameters of the window were measured on a window opening with dimensions of 2 m x 1.5 m.

3.2 To carry out the measurements, the vibration exciters of the noise suppression system were installed on various elements of the building structures in the following sequence.

3.2.1 In accordance with the operating instructions for each system, fasteners for vibration exciters were installed on each of the building structure elements: brick wall h=0.5 m, brick wall h=0.25 m, floor slab h=0.25 m. Then the vibration exciters were installed on the fasteners.

3.2.2 The vibration exciter was also installed on the window opening (glass thickness h=4 mm) in accordance with the instructions for each system.

3.3 Measurements of the parameters according to paragraphs 2.1, 2.2 were carried out in accordance with the block diagram presented in Fig. 1 in the following sequence.

3.3.1 The measuring accelerometer was installed on the elements of building structures at a distance of 3 m from the vibration exciter. The system was switched on.

3.3.2 Using a spectrum analyzer, the accelerometer signal level was recorded in each 1/3-octave band in the frequency range of 0.254-6.3 kHz at the locations where the accelerometer was installed.

3.3.3 The spectral characteristics of the vibration oscillations of the window glass were measured in accordance with paragraph 3.3.2 according to the block diagram in Fig. 1. The distance from the measuring accelerometer to the vibration exciter was 2 m.

3.3.4 The integral values ​​of vibration oscillations au were measured at the installation point of the measuring accelerometer. The spectrum analyzer recorded the signal levels in octave bands in the frequency range of 0.254-6.3 kHz.

3.4 To assess the level of vibration oscillations arising in the elements of building structures from a speech-like acoustic signal, the following was performed.

3.4.1 At the installation location of the measuring accelerometer, a speech-like noise signal with an integral level of 75 dB(A) relative to P0=2*10-5 Pa was reproduced on each element of the building structures.

3.4.2 The speech-like signal levels were recorded and set using a microphone with an acoustic sensitivity of 50 mV/Pa. Then, in accordance with paragraphs 3.3.2 and 3.3.4, measurements were taken from the output of the accelerometer path.

3.5 The parameters according to paragraphs 2.3, 2.4 were measured according to the block diagram shown in Fig. 1 in the following sequence.

3.5.1 Vibration exciters were installed sequentially on each element of the building structure and the noise reduction system was turned on.

3.5.2 The measuring microphone was located opposite the place of their installation at a distance of 1 m.

3.5.3 Using a spectrum analyzer, the signal levels from the measuring microphone in each 1/3-octave band, as well as the integral value of the signal, were recorded.

3.5.4 In the mode of the noise suppression system turned off, in accordance with paragraph 3.5.3, the background noise level of the room was recorded.

Note: for all measurements, the level and frequency response regulators of the generators were set to the maximum position.

4 Test results.

The results of testing vibroacoustic noise suppression systems are presented in Fig. 2, 4, 5 in the form of graphs of spectral characteristics of vibrations of various elements of building structures and in Fig. 6 in the form of spectral characteristics of acoustic noise produced by a vibration exciter on the same elements. The integral values ​​of these characteristics are also presented there.

5 Conclusions.

5.1 The studied vibroacoustic noise suppression systems have approximately the same values ​​of integral levels, but, at the same time, a significant spread of frequency characteristics. Conventionally, according to the type of spectral vibrations of building structures, they can be divided into three groups:

• the first: VNG-006, ANG-2000;

• the second: VNG-1020;

• the third: GSh-01, VAG66, STENA.

5.2 The products of the first group, for all types of building structures used in the tests, provide a noise-signal ratio of 20 dB in almost the entire range of speech frequencies: 0.254 -5 kHz.

5.3 The product of the second group provides a noise-signal ratio of 20 dB in the lower and upper parts of the speech range, but has a “gap” at mid-frequencies of 1-3 kHz.

5.4 The products of the third group provide effective blocking of the speech signal at frequencies above 2 kHz. The interference generated by these devices can be classified as out-of-band.

5.5 When selecting a vibration noise suppression system and determining the radius of guaranteed noise suppression, attention should be paid not only to the integral values ​​of the output levels, but also to their spectral characteristics.

 

1. — vibration exciter;

2. — electronic unit of vibroacoustic protection;

3. — measuring accelerometer;

4. — measuring amplifier;

5. — measuring microphone “Brüel & Kjær”, type 4155;

6. — measuring amplifier “Brüel & Kjær”, type 2610;

7. — digital frequency spectrum analyzer “Brüel & Kjær”, type 2131;

8. — acoustic column, type 10 AC-401;

9. — power amplifier “Brüel & Kjær”, type 2706;

10. — specialized noise generator unit with equalizer

.Fig. 2 Spectral characteristics of vibrations of a brick wall with a thickness of h=0.5 m, excited by vibration exciters of various systems and acoustic speech-like noise with a level of 75 dB(A).

Fig. 3 Spectral characteristics of vibrations of a brick wall with a thickness of h=0.25 m, excited by vibration exciters of various systems and acoustic speech-like noise with a level of 75 dB(A).

Fig. 4 Spectral characteristics of vibrations of a concrete wall with a thickness of h=0.25 m, excited by vibration exciters of various systems and acoustic speech-like noise with a level of 75 dB(A).

Fig.5 Spectral characteristics of vibrations of a 4 mm thick window glass excited by vibration exciters of various systems and acoustic speech-like noise with a level of 75 dB(A).

Fig. 6 Spectral characteristics of acoustic noise generated by vibration exciters of various systems on a concrete wall with a thickness of h=0.25