The efficient measurement method of phonic-absorbent coefficient for construction materials.

Ungur, Petru ; Pop, Petru ; Ungur, Patricia 等

1. INTRODUCTION

The noise is an uncomfortable sound for human body, products by different noise sources by mechanical, hydro and aerodynamic, and electromagnetic action, machine tools, pneumatic installations, cars [Darabont, 1983, Pupazan, 1970].

The nocive action of sounds and noise have diminished by using of phonon-absorbent panels fabricated from composite materials reinforcement with fibres, and modelling [alpha]-plaster materials reinforcement with breakage granules of polystyrene from expandable pearlite. In general, these materials have designed and manufacturing with improved quality and quantity indicators of noise level. The phonon-absorbent materials for construction dissipated absorbent sound energy of phonon-absorbent elements, because of small size of transportable sound energy and get in thermal energy by friction and incident acoustic processes on phonon-absorbent element due to oscillations in porous medium [Pop, et al, 2008].

In practical, the capacity of phonic insulating for construction materials has determined by absorbent coefficient-[[alpha].sub.w]. This paper has goal determination of absorbent coefficient.

2. THEORETICAL ASPECTS

Determination of insulation capacity of construction elements at sounds and noise has basic on sound transmission analysis through different physical medium, by air elements of walls and floor, which partitioned a building [ISO2923-1996].

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The transmission of emitted sound in a room (Fig.1), named of emission-(E) by a sound source-(S) and received in reception room-(R) has realized from two ways [Darabont, 1974, 1983]:

--direct way, from which the energy has transmitted by vibrant element from rooms, formed direct energy-[E.sub.d];

--indirect way, from which the energy has transmitted by collateral ways, formed indirect energy-[E.sub.ind].

The phonic insulation grade between rooms is function of:

--itself phonic insulation capacity of partition element;

--sound level from inner and external room;

--transmissions, that of structure and linkage's partition elements.

For construction materials, that covered phonon-absorbent walls and ceilings has measured phonic absorption coefficient-[[alpha].sub.w]. A simple measurement method is stationary wave method. In this case, it has used a loudspeaker, as sound source for production of stationary acoustic waves into a tub with uniform transversal section, which has determined with a sample of tested material.

Used a steel plate with perfect reflection wall as master, the stationary acoustic waves within a tub have the form presented in Fig.2 [Darabont, 1983].

When the tub has finished with a phonon-absorbent material, the stationary waves from tub have the shape from Fig.3. For determination of absorbent coefficient of tested material, have to measure the minim and maxim of static pressure wave. The quantitative measures got the name of stationary wave ratios (RUS), and defined by relation [Darabont, 1983]:

RUS = Pmax/Pmin = A+B/A-B (1)

Where: RUS--is stationary wave coefficient; Pmax--maxim sonic pressure; Pmin--minim sonic pressure; A--amplitude of incident wave; B--amplitude of reflected wave.

The absorbent coefficient-[[alpha].sub.w] has calculated with relation:

[[alpha].sub.w] = 1 - [(RUS-1/RUS+1).sup.2] (2)

For calculus, the relation (2) can be reducing as:

[[alpha].sub.w] = 1 - [(A/B).sup.2] (3)

[FIGURE 3 OMITTED]

The absorbent coefficient of sample has defined as a ratio between incident total energy and square of sonic pressure. The gage for absorbent coefficient determination has in design phase and execution, as bilateral collaboration between Oradea University and Congips Co. from Oradea [Pop et al, 2008].

3. GAGE FOR DETERMINATION OF PHONIC-ABSORBENT COEFFICIENT

The gage for phonic-absorbent coefficient determination of construction materials it is a lab sound gage, composed in principal, from a long tub with circular section and a loudspeaker at the end. At the other end has mounted a plate of reflected material, or a circular sample from tested phonon-absorbent material. The maxim and minim of acoustic pressure within tub can be received by a microphone type probe, which is get in from a carriage by an axial orifice made in loudspeaker.

In fig.4 has depicted the block diagram for phonic-absorbent measurement by stationary waves with Kundt tub. Where: G-is sound generator, 1,2-filters, 3-sound tub, 4-sample tested, 5-probe, 6-osciloscope, 7-electronic interface, 8-PC computer.

For equipped of installation is necessary a Bruel&Kjaer gage. The instrument of phonic-absorbent coefficient measurement has made from two waves tubs, one with diameter of 100mm for frequencies range of 90-1800Hz, and the second with diameter of 30mm for range of 800-6500Hz [Broch,1975;Bruel&Kjaer2007].

Such as orientation, in Tab.1 has presented the frequencies [Hz] and reference level [dB], in conformity with ISO 717 [Darabont, 1983;STAS6161/1-89; STAS6161/3-82].

For tests and determination of phonic-absorbent coefficient would be use a generator of reference sound level of 70dB. The gage has executed in a bilateral accord between Oradea University and Congips Co from Oradea [Pop et al, 2008].

The novel of gage consists in construction, sound generator and inner cylindrical cavity with reflexion surfaces.

The qualitative graphic of phonic-absorbent curve has depicted in fig.5.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

4. CONCLUSIONS

The method of phonic-absorbent coefficient-[[alpha].sub.w] used stationary waves and Kundt tub is approximately, such as other methods, but has the advantage of small size.

This method of measurement of phonic-absorbent coefficient with stationary waves and Kundt tub is simple and of lab technique.

The installation and gage is not difficult to build up, has great capacity of sound reflection by Kundt tub, assured by special reflection paint, applied on inner surface of cylindrical cavity.

5. REFERENCES

Broch, J.T. (1975), Acoustique Noise Measurement, Bruel&Kjaer

Darabont, A, et al, (1983), Sound Measurement and vibration in Techniques, Technical Editor, Bucharest

Darabont, A. & Vaiteanu, D. (1974), Prevention of Noise Pollution and Vibrations, Technical Editor, Bucharest

Pop, P.A.; Ungur, P.A.; Patcas, E. & Ungur, P. (2008), Recovering, Treating And Using Waste From Expandable Polystyrene By Mechanical Brakeage Process Of Manufacturing Composite Materials, The 9th ASME Conference ESDA2008 July 7-9, 2008, Haifa, Israel, Proceedings of ESDA2008, Paper No. ESDA2008-59176, pp. 1-8, ASME International

Pupazan, C. (1970), Acoustics in Construction. Noise Propagation and Phonic Insulating, Romanian Academy Editor, Bucharest

*** (2007), Measures Aquistiques, Bruel&Kjaer

*** (1996), Acoustique. Mesurage du Bruit a Bord des Bateaux, ISO 2923-1996)

*** (1989), Acoustical in Construction, Methods of Noise Level Measurement in Civil Constructions, STAS 6161/1-89

*** (1982), Urban Acoustic, Methods of Noise Level Determination in Towns, STAS 6161/3-82

Tab. 1. Reference level values of noise in room by ISO 717.

 Frequency [Hz]

Reference 100 125 160 200 250 400 500
Level

Admissible 67 67 67 67 67 66 65
[L.sub.n]
[dB]

Reference 630 800 1000 1250 1600 2000 2150
Level

Admissible 64 63 62 59 53 50 47
[L.sub.n]
[dB]