FI83117C - FOERFARANDE FOER REGLERING AV LJUDFAELTET, SAOSOM EFTERKLANGSTIDEN, I ETT RUM. - Google Patents

Description

1 83117

A method for adjusting a sound field, such as reverberation time, in a room

The invention relates to a method for adjusting a sound field, such as reverberation time, by means of sound-absorbing elements arranged in the corners of a room. The invention is characterized in that the areas in the corner where the sound field is particularly strong are determined by measurements, after which the sound-absorbing elements are shaped and positioned so as to pass through these areas.

It is known from SE patent application 8 103 345 to use planar diagonal absorbents for adjusting the sound image, such as reverberation time, in a room. However, the frequency response is not entirely satisfactory because it is not smooth enough - see Figure 5b.

According to the invention, the individual sound-absorbing element is shaped so as to be preferably located in the vicinity of the corner where the velocity of the air particles is particularly high, taking advantage of the fact that the velocity of the air particles is particularly high in certain areas.

This enables a smoother frequency flow and allows for optimal adjustment of the reverberation time. In addition, the elements according to the invention are more flexible, so that more architectural solutions become possible.

The invention will be explained in more detail below with reference to the drawing, in which Figure 1 shows a known diagonal absorbent for fitting into a corner; Figures 2a and 2b show a view of the angular stray sound field Ekin / Epot; Figure 3 shows isoabsorption curves (Ekln / Epot constant) with diagonal absorbers installed, with different ratios of size and wavelength; Figure 4 shows the absorption as a function of frequency; Fig. 5 shows absorption 35 as a function of frequency in connection with various designs of absorbent; and Figure 6 shows the flow resistance as a function of density.

2 83117

At frequencies above about 100 to 300 Hz, sound absorption occurs in the diagonal absorber shown in Figure 1 during the movement of air particles in the porous immobile material. The absorbent is fitted in a corner where the velocities of the air particles are high - see Figure 2.

The frequency f ^ at which the absorption is greatest can be determined by theoretical analyzes of the angular sound field, where fi = 140 = 280 Hz 10 d 1 * si n20 where d is the depth of the absorbent in meters, while JLja Θ is given in Figure 1.

At lower frequencies (50 - 200 Hz) and diagonal-15 liabsorbents with 1 less than 2 m, sound absorption occurs mainly in such a way that the sheet material begins to oscillate in resonance and energy is absorbed as a result of ··· loss in the material and along the edges. the material is fixed. In connection with the activation of these resonant oscillations. the sound field is important in areas with large pressure fluctuations.

For a planar diagonal absorbent having a low. . the bending stiffness of the ring compared to the stiffness of the enclosed air 25, a resonant frequency is obtained: fQ * 120 Hz ^ m · 1 * sin (29); · Where m is the mass of the sheet material per unit area 2. * · 30 in kg / m and the length in tonnes per meter. The first 1 mode of action in the case of higher frequencies sets * ·; certain requirements as to size, shape and flow resistance * | Ic. Another mode of action associated with lower frequencies imposes certain requirements on size and massal -.... 35 le per unit area.

1: 3 83117

The highest possible sound absorption is sought in the frequency range 100 to 4000 Hz, and the absorption must take place as evenly as possible in this frequency range.

Experimental studies have given promising results with values of l = 0.90 m and Θ = 30 ° for planar diagonal absorbents. Based on theoretical analyzes, even better results can be expected for specific, non-planar formulations - see Figure 5d. Conversely, uneven frequency passages 10 can be expected with particularly inappropriate designs. If the dimensions remain too small, problems will arise at low frequencies. In addition, the available absorption pressure area is directly dependent on the surface area of the absorbent.

15 Since the resonant frequency f should be approximately 100 Hz and the Coleteta should be in the range 0.90 to 1.80 m, the following requirements per unit area are obtained for the mass: 2 -f- m = 1 - 2 kg / m, ____: 20 where the mass per unit area should be the largest with small values. Experiments have shown that the flow resistance should be somewhat higher than in the case of traditional suspended roofing sheets, namely: “approximately r = 2000 - 2500 Ns / m ^. These quantities depend on the thickness h of the plate and on the actual material parameters according to the following formulas: m = p * h, where p is the mass filling, and r = jET * h, where jB is the characteristic flow resistance.

Thus the formula 30 rs is obtained: -1 to 1,250 s

P

which can be marked as a line on the T-p diagram - see Figure 6. This may indicate that the optimal fiber diameter is somewhat smaller than that of conventional glass wool. Alternatively, a surface coating may be used which suitably increases the flow resistance.

4 83117

Finally, there are limits to how high the resistive flow resistance should be to avoid that higher frequencies are reflected too hard from the compressed surface. The material parameters can be selected within 5 of the following limits: h P 2 20 mm 100 kg / m ^ 125 * 10 ^ Ns / m4 40 mm 50 kg / m ^ 63 -103 Ns / m4.

Figures 5a to 5e show characteristic curves of different embodiments of the absorption element. Figure 5a shows an oval absorption element which gives a non-uniform frequency curve, the frequency curve having a strong recess at d / A = 0.7, corresponding to the absorption element being located in this case where the oscillations are weakest. The diagonal absorbent shown in Fig. 5b also gives a very poor characteristic curve, because in all cases only a part of the absorbent is fitted where the vibrations are strongest. It helps a bit if the diagonal absorbent is adjusted asymmetrically • _ 20 so that one angle deviates from 45 ° C. Figure 3 shows how such an absorbent affects the sound field at different frequencies. It will be seen that the characteristic curve necessarily has a recess (in the case shown at a frequency of about 500 Hz). Figure 5d shows a more ideal embodiment of the absorption element 25, in which the absorption element is placed in areas where the sound field is particularly strong. Figure 5e shows the absorption element as an alternative asymmetric embodiment (asymmetric L-shape).

Figure 6 shows flow resistances as a function of density. for different types of materials.

; The sound-absorbing elements can optionally *: * be changed depending on one or more parameter values in the room, possibly so as to counteract the possible change of these parameter values.

I; 5 83117 Sound-absorbing elements can be used, for example, in a concert hall and can be adjusted according to the special wishes of the orchestra, taking into account, for example, the reverberation time, possibly during the concert.

5 Absorbents are arranged either in one or more corners of the room or along the edges of the ceiling. The absorbent shown in Figure 5e is preferably arranged in connection with a sound-transmitting suspended ceiling, possibly perforated along the edge of the roof, which is in line with the absorbent 10 and supports the overall architectural effect.

Claims (1)

A method for adjusting a sound field, such as reverberation time, by means of sound-absorbing elements arranged in the corners of a room, characterized in that the areas in the corner where the sound field is particularly strong are determined by measurements, after which the sound-absorbing elements are shaped and positioned that they pass through these areas. n 7 83117 For the purpose of regenerating the results of the action, the first of the following steps being taken in accordance with the procedure laid down in this Regulation, man utterar och placerar de ljudabsorberande elementen sälunda, att de utsträcker sig genom dessa omräden.