ČSN EN ISO 10140-4 - Akustika - Laboratorní měření zvukové izolace stavebních konstrukcí - Část 4: Měřicí postupy a požadavky

3.5 continuously moving microphone

microphone that, with respect to a fixed point,

a) moves with approximately constant speed in a circle, or

b) sweeps, over a fixed time period, to and fro along the arc of a circle, which is as large as possible, but is not to be less than 270°

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Measurement procedures and requirements

Frequency range

All quantities shall be measured using one-third octave band filters having at least the following centre frequencies, in hertz:

100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1 000, 1 250, 1 600, 2 000, 2 500, 3 150, 4 000, 5 000.

If additional information in the low-frequency range is required, use one-third octave band filters with the following centre frequencies, in hertz:

50, 63, 80.

For additional measurements at low frequencies, guidance is given in Annex A.

Measurement of sound pressure levels

General

Obtain the energy average sound pressure level using a single microphone moved from position to position, an array of fixed microphones or a continuously moving microphone.

Minimum separation distances for microphone positions

The following separation distances are minimum values and shall be exceeded where possible:

a) 0,7 m between fixed microphone positions;

b) 0,7 m between any microphone position and the room boundaries;

c) 0,7 m between any microphone position and any diffusers;

d) 1,0 m between any microphone position and the test element;

e) 1,0 m between any microphone position and the sound source.

Averaging times

Fixed microphone positions

At each individual microphone position, the averaging time shall be at least 6 s for each frequency band, with centre frequencies in the frequency range of 100 Hz to 400 Hz. For bands of higher frequencies, it is permissible to decrease the time to not less than 4 s.

Continuously moving microphone

The averaging time shall cover a whole number of traverses and shall not be less than 30 s. Using a moving loudspeaker, the measurement period shall equal the time of movement of the loudspeaker which shall be at least 30 s.

Energy average sound pressure level

Fixed microphone positions

The energy average sound pressure level is determined using Formula (1).

where

 

p1, p2, ..., pn

are root-mean-square (r.m.s.) sound pressures at n different positions in the room.

In practice, the sound pressure levels are usually measured and the energy average level, L, shall be determined using Formula (2).

where

 

L1, L2, ..., Ln

are the sound pressure levels at n different positions in the room.

Continuously moving microphone

The energy average sound pressure level is determined using Formula (3).

where

 

p

is the sound pressure, in pascals;

 

p0

is the reference sound pressure and is equal to 20 µPa;

 

Tm

is the integration time, in seconds.

Correction for background noise level

Measurements of background noise levels shall be made to ensure that the observations in the receiving room are not affected by the background noise. Extraneous sound, such as noise from outside the test room, electrical noise in the receiving system or electrical cross-talk between the source and the receiving systems all contribute to the background noise level. The background noise level shall be at least 6 dB (and preferably more than 15 dB) below the level of signal and background noise combined at each frequency band.

If the difference in levels is smaller than 15 dB but greater than 6 dB, calculate corrections to the signal level according to Formula (4):

where

 

L

is the adjusted signal level, in decibels;

 

Lsb

is the level of signal and background noise combined, in decibels;

 

Lb

is the background noise level, in decibels.

If the difference in levels is less than or equal to 6 dB in any of the frequency bands, use the 1,3 dB correction. For each frequency band where this is the case, it shall be clearly indicated in the report that a 1,3 dB correction has been made and these values are the limit of measurement.

To check the electrical noise in the receiving system or electrical cross-talk between the source and the receiving systems, replace the microphone by a dummy microphone or replace the loudspeaker by an equivalent impedance.

Measurement of airborne sound insulation

General

Sound shall be generated in the source room using loudspeakers in at least two positions or a single loudspeaker moved to at least two positions or a moving loudspeaker. The qualification procedure for loudspeakers and loudspeaker positions specified in ISO 10140‑5:2021, Annex D shall be used to determine the minimally required number of loudspeakers and their most suitable position for a given source room/receiving room combination. The sound pressure level shall be measured using microphones in fixed positions or using moving microphones.

Measurements with fixed microphone positions

a) When using more than one loudspeaker at the same time or a moving loudspeaker, a minimum of five microphone positions shall be used in each room. These shall be distributed within the maximum permitted space throughout each room. No two microphone positions shall lie in the same plane relative to the room boundaries.

b) When using a single loudspeaker, a minimum of five microphone positions shall be used in each room for each loudspeaker position (additional sets of microphone positions may be different from the first set of positions). Each set of microphone positions shall be distributed within the maximum permitted space throughout each room. No two microphone positions shall lie in the same plane relative to the room boundaries and the positions shall not be in a regular grid.

Measurements with a continuously moving microphone

a) When using more than one loudspeaker at the same time or a moving loudspeaker, at least one measurement with a continuously moving microphone shall be used. The sweep radius shall be at least 1 m. The plane of the traverse shall be inclined in order to cover a large proportion of the permitted room space and shall not lie in any plane that is less than 10° to any room surface (wall, floor or ceiling). The duration of a traverse period shall be not less than 15 s.

b) When using a single loudspeaker, a minimum of one measurement using a continuously moving microphone shall be used for each loudspeaker position. The sweep radius shall be at least 1 m. The plane of the traverse shall be inclined to cover a large proportion of the permitted room space and shall not lie in any plane that is less than 10° to a room surface (wall, floor or ceiling). The duration of a traverse period shall be not less than 15 s.

The location of the fixed point about which the continuously moving microphone moves may be changed for each loudspeaker position. The same number of measurements shall be taken at each location.

Measurement of impact sound insulation

General

Sound shall be generated using the standard tapping machine. Requirements for the tapping machine are specified in ISO 10140‑5:2021, Annex E. Not less than four tapping machine positions shall be used for any measurement.

Measurements with fixed microphone positions

The number of microphone positions shall equal the number of tapping machine positions or integer multiples of the number of tapping machine positions.

The same number of microphone positions shall be used for each tapping machine position.

If four or five tapping machine positions are used, at least two measurements of impact sound pressure level shall be made for each tapping machine position. Measurements shall be made in at least two microphone positions for each tapping machine position.

If six or more tapping machine positions are used, at least one measurement of impact sound pressure level shall be made for each tapping machine position. Measurements shall be made at a different microphone position for each tapping machine position.

Continuously moving microphone

The same number of measurements shall be taken for each tapping machine position and at least one measurement shall be made for each tapping machine position. The sweep radius shall be at least 1 m. The plane of the traverse shall be inclined to cover a large proportion of the permitted room space and shall not lie in any plane that is less than 10° to any room surface (wall, floor or ceiling). The duration of a traverse period shall be not less than 15 s.

The location of the fixed point about which the continuously moving microphone moves may be changed for each tapping machine position. The same number of measurements shall be taken at each location.

Measurement of reverberation time and evaluation of the equivalent sound absorption area

General

In accordance with ISO 3382‑2, the engineering method is the preferred procedure although the precision method may be used. The evaluation of the reverberation time from the decay curve shall start at 5 dB below the initial sound pressure level. The preferred evaluation range is 20 dB. The bottom of the evaluation range shall be at least 10 dB above the overall background noise of the measuring system.

Measurement of reverberation time

General

Reverberation time shall be measured using the interrupted noise method or the integrated impulse response method as described in ISO 3382‑2 and ISO 18233.

The use of an omnidirectional radiating sound source can be beneficial in generating a suitable sound field, but other types of source may be used.

Interrupted noise method

For fixed microphone positions, the minimum number of measurements required for each frequency band is six. At least one loudspeaker position shall be used with three fixed microphone positions and two measurements at each position, or six fixed microphone positions and one measurement at each position.

For a moving microphone, the minimum number of measurements required for each frequency band is six. At least one loudspeaker position shall be used with six measurements distributed along the microphone path.

Integrated impulse response method

For the integrated impulse response method, measurement of reverberation time shall use fixed microphone positions.

Using an impulse source, the minimum number of measurements required for each frequency band is six. At least one source position and six fixed microphone positions shall be used.

The reverberation time shall be calculated by reverse-time integration of the squared impulse response.

Equivalent sound absorption area

Calculate the equivalent sound absorption area, A, in square metres, from the reverberation time using Sabine's formula given in Formula (5).

where

 

V

is the receiving room volume, in cubic metres;

 

T

is the reverberation time, in seconds.

Measurement of structural reverberation time

The measurement of the structural reverberation time shall be made in accordance with ISO 10848‑1:2017, 7.3.

The relation between the total loss factor, ηtotal, and the structural reverberation time, Ts, of the element is given by Formula (6).

where

 

f

is the one-third octave band centre frequency in hertz.

The total loss factor includes the internal losses, the structural coupling losses and the radiation losses.

NOTE Lower limits for reliable results caused by filter and detector are given in ISO 10848‑1.

Measurement of radiated sound power by surface velocity of elements

The sound power radiated by the test element and the flanking elements may be used to determine the maximum achievable sound reduction index in the test situation (see ISO 10140‑5:2021, Annex A). This can be calculated from vibration measurements on these elements.

If the critical frequency of the test element or of the flanking elements is low compared with the frequency range of interest, the power, Wk, radiated from a particular element, k, with area Sk into the receiving room may be estimated by Formula (7).

where

 

is the spatial average, mean square velocity that is normal to the surface;

 

σk

is the radiation efficiency, which can be assumed to be equal to 1 above the critical frequency;

 

ρc

is the characteristic impedance of air.

The average surface velocity level, Lv, of the element is given by Formula (8).

where

 

v1, v2, ..., vn

are the r.m.s. normal surface velocities at n different positions on the element;

 

v0

is the reference velocity (10−9 m/s).

In building acoustics, the reference velocity of 5 × 10−8 m/s is also in use. Therefore, the reference velocity used in Formula (8) should always be stated. The reference vibration velocity of 10−9 m/s is preferred for the purposes of this document.

The spatial average of the mean square of the normal surface velocity in Formula (7) follows from this by Formula (9):

If the surface velocity of an element is measured using an accelerometer, the accelerometer should be securely attached to the element’s surface and its mass impedance should be sufficiently low compared with the driving-point impedance of the element’s surface.

NOTE Flanking transmission can also be measured using the intensity method (see ISO 15186‑1).

Sound insulation measurements

General

Measurements can be conducted using fixed or continuously moving microphones, and moving or fixed loudspeakers.

There shall be no significant change in room absorption between measurements.

It is preferable that simultaneous measurements be made in the source and receiving rooms.

General procedure for the determination of airborne sound insulation

General

Select one of the following four options described in 5.2.2, 5.2.3, 5.2.4 and 5.2.5.

Fixed microphone positions and multiple loudspeakers operating simultaneously or a moving loudspeaker

Measure the sound pressure levels in both the source and receiving room (see 4.4.2). Calculate the energy average sound pressure level in both the source and receiving rooms [correcting for background noise (see 4.3)] and determine the sound reduction index or element-normalized level difference as given in ISO 10140‑2.

Fixed microphone positions and a single loudspeaker operated at more than one position

Measure the sound pressure level in both the source and receiving rooms for the first loudspeaker position (see 4.4.2). Calculate the energy average sound pressure level in both the source and receiving rooms [correcting for background noise (see 4.3)]. Calculate the sound reduction index or element-normalized level difference for this loudspeaker position as given in ISO 10140‑2. Both source and receiving room levels shall be measured before the loudspeaker is moved.

Repeat the procedure for the other loudspeaker positions. Calculate the average sound reduction index or element-normalized level difference using Formula (10) or (11):

Continuously moving microphone and multiple loudspeakers operating simultaneously or a moving loudspeaker

Measure the sound pressure level in both the source and receiving rooms (see 4.4.3). Calculate the energy average sound pressure level in both the source and receiving rooms [correcting for background noise (see 4.3)]. Determine the sound reduction index according to ISO 10140‑2.

NOTE If the moving microphone moves about only one fixed point in each room, the measured levels corrected for background noise are the average energy levels in the source and receiving rooms.

Continuously moving microphone and a single loudspeaker operated at more than one position

Measure the sound pressure level in both the source and receiving rooms for the first loudspeaker position (see 4.4.3). Calculate the energy average sound pressure level in both the source and receiving rooms for the first loudspeaker position [correcting for background noise (see 4.3)]. Calculate the sound reduction index or element-normalized level difference for this loudspeaker position as given in ISO 10140‑2. Both source and receiving room levels shall be measured before the loudspeaker is moved.

Repeat the procedure for the other loudspeaker positions. Calculate the average sound reduction index or element-normalized level difference using Formula (10) or (11), as appropriate.

General procedure for the determination of impact sound insulation of floors

General

Measurements may be conducted using fixed or moving microphones and the standard tapping machine.

It shall be ensured that there is no significant change in room absorption between measurements.

The minimum number of tapping machine positions is specified in ISO 10140‑1:2021, Annex H, or in ISO 10140‑3. Each set of measurements shall be made with as many tapping machine positions as are necessary to yield a reliable mean value.

Fixed microphone position

Measure the sound pressure level in the receiving room at each microphone position (see 4.4.2). Calculate the energy average sound pressure level [correcting for background noise level (see 4.3)]. Determine the normalized impact sound pressure level according to ISO 10140‑3.

Continuously moving microphone

Measure the sound pressure level in the receiving room at each moving microphone position (see 4.4.3). Calculate the energy average impact sound pressure level [correcting for background noise level (see 4.3)]. Determine the normalized impact sound pressure level according to ISO 10140‑3.

NOTE If the moving microphone moves about only one fixed point, the measured levels corrected for background noise are the average energy levels in the receiving room.

(informative)SEQ aaa \h SEQ table \r0\h SEQ figure \r0\h Additional procedures for measurements at low frequencies

General

In low-frequency bands (below 400 Hz in general and especially below 100 Hz), the sound field in the test rooms is not diffuse, especially when room volumes of only 50 m3 to 100 m3 are considered. The general requirement that the room dimensions should be at least one wavelength cannot be fulfilled for the lowest frequency bands.

The excitation of the room modes is highly dependent on the source locations. The sound reduction index depends strongly on which room modes are excited. Even if the repeatability is satisfactory at low frequencies, the reproducibility and comparability with test results from other rooms can be very poor and the test results become dependent on the test facility.

In order to reduce the spread of the measured results, additional effort is necessary with regard to the excitation and sampling of the sound field in the rooms and the special requirements that the rooms have to meet.

Rooms with small volumes and unfavourable dimensions are not usable for low-frequency measurements. At least one room dimension should be of one wavelength and another of at least half a wavelength of the lowest band centre frequency and there should be the space to position the source and the microphones according to the requirements.

Minimum distances

A significant increase in sound pressure level is measured towards the room boundaries from a distance of about a quarter of a wavelength. The minimum separation distances (see 4.2.2) should therefore be doubled for measurements down to the 50 Hz one-third octave band. For the distance between the microphone positions and the room boundaries, approximately 1,2 m should be the minimum value. This is also valid for the distances between microphone positions and the surface of the test element.

Sampling of the sound field

In order to obtain a reliable average of the sound pressure levels in the room volume, the number of microphone positions should be increased. The microphone positions should be spread uniformly throughout the allowable volume of the room. If a moving microphone is used, it should sample all parts of the allowable volume as uniformly as possible. At very low frequencies where the room dimensions tend to be in the range of half a wavelength, extremely low sound pressure values are found in the centre part of the room. Therefore, suitable microphone positions should also be found outside this area.

Loudspeaker positions

The lack of diffusivity in small rooms at low-frequency measurements can be partly compensated by exciting different sound fields one after the other and by averaging the results. Therefore, the number of loudspeaker positions should be increased; the minimum number should be three. The use of a continuously moving loudspeaker is recommended.

Averaging time

Due to the smaller absolute filter bandwidth and low modal overlap, the averaging times should be increased to not less than 15 s for measurements in the 50 Hz band (about three times compared to the requirements for measurements at 100 Hz). When using a moving microphone, the averaging time should not be less than 60 s.

Reverberation time

At very low frequencies, test rooms with hard surfaces tend to have long reverberation times (see ISO 10140‑5).

Bibliography

[1] ISO 15186‑1, Acoustics — Measurement of sound insulation in buildings and of building elements using sound intensity — Part 1: Laboratory measurements

[2] HOPKINS, C. Sound insulation. Amsterdam: Elsevier/Butterworth-Heinemann, 2007, 622 pp.