Standards Acoustic performance

Superscript, subscript.

Signs, letters or diacritical numbers placed in the upper right (superscript) or lower right (subscript) that accompany the symbols of the acoustic quantities and modify their meaning, used to identify the methods of measurement and expression to which the quantity is reports that they are written in smaller letters than the symbol they accompany.

Example: the symbols of the soundproofing power (by air) following R, Rw, and R’W respectively identify:
• R = soundproofing power of a partition, it indicates the difference in sound level that the partition is able to maintain between a disturbing environment and a receiving environment under controlled laboratory conditions (without lateral transmissions)
•Rw= adding the subscript “w “means that it is the evaluation index of the soundproofing power of the partition measured in the laboratory or obtained by calculation (without lateral transmissions) which expresses the value in decibels of the reference curve at 500 Hz after shifting the curve according to the method specified in the ISO717 standard,
•R’w= the addition of the apostrophe to the apex of the symbol means that the evaluation index refers to the measurement in place of the same size and therefore includes the lateral transmissions and in this case it is defined as: evaluation index of the apparent soundproofing power .

 

Sound absorption.

It is the ratio between the acoustic energy absorbed by a surface and the incident one; a smooth and hard surface completely reflects the sound that hits it and echoes are formed in large rooms while a porous and absorbent surface reduces the reflection of noise inside a room by reducing the reverberation time.

 

Forecast calculation.

Evaluation viable through reports regulated by UNI, software, laboratory experiments, on-site tests, prepared to find the correct estimate of the insulating performance of building partitions which will then be measured on site.

 

Compressibility.

Characteristic of a resilient material to deform elastically while maintaining the original thicknesses and mechanical characteristics.

This value can be estimated from laboratory tests following the indications contained in the UNI 12431 standard.

 

Acoustic correction.

Intervention of evaluation, analysis and solution of problems related to a non-uniform perception of sounds (typical problem of conference rooms or cinemas) caused by wrong geometries or wrong choice of covering materials. The remediation of this problem subsequently grants an extremely faithful perception of the sound emissions within the treated room.

 

Decibel Unit of measurement of the sound level, it is the logarithm of the ratio between the measured pressure and the minimum pressure of 0.00002 Pa corresponding to the minimum threshold of audibility held as a reference. The decibel is a mathematical device used in physics to express also other quantities whose range of variability is very wide. However, this measurement system does not allow to linearly appreciate the sum or the difference of two sounds, if tangibly we are able to distinguish a measurement of a 10 m string as a double of a 5 m one, for the sound level measured in decibels this does not it is more possible because it is not a linear measure like the meter but a logarithmic one. As a result, two sounds emitted simultaneously by two adjacent and equal sources, for example two washing machines each producing a noise of 60 dB, do not result in a noise of 120 dB but of “only” 63 dB. Using the logarithmic scale of decibels as the unit of measurement, the doubling of the sound pressure generated by the two washing machines corresponds to an increase of “only” 3 dB.
On the other hand, it must be understood that an insulation that leads to a reduction of 3 dB is no small thing because it involves a halving of the sound intensity as if one of the washing machines had been switched off! Another “oddity” of the decibel is that if the two washing machines above emit a noise that differs from each other by more than 10 dB, the resulting sound is practically that of the loudest washing machine, if one produces a noise of 50 dB and the other of 60 dB the total noise will be 60 dB.

 

Dodecaedro.

Omnidirectional sound source for measuring the acoustic insulation of airborne noise.

 

DPCM.Decree of the Presidency of the Council of Ministers.

 

Sound level meter.

Sound pressure level measuring instrument consisting of a microphone capable of translating the energy of the acoustic vibration into an electric signal which, when suitably amplified, expresses the noise level in linear decibels dB or dB L. If the signal is filtered and corrected by suitable filters that reproduce the “sensitivity curves” of the human ear; for different sound intensities, three types are used:

• A, the one that mimics the sensitivity of the ear for sound levels from 0 to 55 dB
• B, for levels between 55 and 85 dB
• C, for levels above 85 dB

There is also a fourth type D which is used to evaluate the disturbance caused by aircraft noises. The level measured by the sound level meter equipped with filters is then expressed no longer in dB L but respectively in dB (A), dB (B) and dB (C) called ponderal decibels, that is, which take into account the sensitivity of the human ear as if instead of the sound level meter to measure the sound had used the ear. The DPCM 5/12/1997 establishes that the linear dB, i.e. the sound level meter without weighting filters, are used to measure the insulation performance of a partition wall, a facade or a floor while the dB (A) to appreciate the disturbance caused by implants.

 

Sound damping.

Element that reduces vibrations caused by sound transmission.

 

Evaluation index (of the insulating performance of partitions).

The acoustic requirements imposed by the DPCM 5/12/1997 for building partitions are evaluation indices. They are determined with the computation according to UNI EN ISO 717 part 1 and 2: 1997 both for the insulation of airborne noise (717-1) and for footfall noise (717-2) of buildings and building elements, at purpose of converting the results of the sound insulation measurements performed as a function of frequency by third-octave or octave bands (shown in a graph called the experimental curve) into an evaluation index that summarizes, with a single value in dB, the insulating performance of the building partition and allows a quick and practical comparison of the performance of different partitions.
To determine the index, the standard has established the reference values ​​in dB for each band of frequencies which, shown on the decibel / frequency graph, draw a reference curve (limit curve) which has the shape of a line broken into three sections which then it is translated parallel to itself on the graph of the experimental curve until the deviation between measured values ​​and reference values ​​falls within the limits set by the standard. At that point, one and only one reference curve is identified which represents the acoustic insulation performance of the partition whose value in dB at 500 hz constitutes its index.

 

Noise pollution.

Exposure to noise levels harmful to the hearing system (very high levels for short periods, high levels for long periods), deriving from sound sources of different types (70 dB vehicular traffic, 100-105 dB machinery or other).

 

Standardized acoustic insulation of façades (index)

D2m,nTw. acoustic insulation of the façade of aerial noise generated outside the building, expressed in linear dB as an index of the same, which identified by the symbol D2m, nTw represents the difference in sound level, measured on site, that the façade is able to determine between the external environment where a sound source is placed and an internal space delimited by the facade itself. If the sound that can be produced by the speaker used for the test is dominated by the noise present in the external environment, the sound source of the measurement on site will be the prevailing traffic noise. The Prime Ministerial Decree of 12/5/1997 has set the minimum values ​​of D2m, nTw for the insulation of the facades.

 

Acoustic insulation of horizontal and vertical partitions of buildings.

It reduces the transmission of airborne and footfall noise between rooms separated by a building partition (walls and floors).

 

Impact noise level of floors Ln.

• L’n,w normalized (index). Footstep noise insulation between environments measured on site on a finished floor, complete with flooring and insulation, expressed as an index in linear dB, which represents the noise, transmitted directly and sideways, which is measured in the receiving environment (even neighbors on the same floor) when the trampling machine that hits it is on on the floor of the attic above. The Prime Ministerial Decree of 12/5/1997 established the maximum values ​​of L’n, w for the separation floors between distinct real estate units.
  •Ln,w,eq: normalized equivalent (index): level of footstep noises, transmitted only directly, from a bare floor, without the floor and the floating screed on the resilient material, expressed as an index in linear dB, measured in the laboratory or obtained with the calculation, under the test conditions mentioned above.
  • ∆Lw: footfall noise level attenuation (index): expressed as an index in linear dB, characteristic of a floating screed of defined weight and of the type of resilient material considered, it is measured in the laboratory or obtained by calculation knowing the dynamic stiffness of the resilient material. Represents the contribution of insulation made to the bare floor by the floating screed.

 

Absorbent materials.

Porous or fibrous materials used for the coating of the surfaces of walls and ceilings of reception or entertainment rooms capable of absorbing the sound incident on them used for the acoustic correction of the halls themselves. Some absorbent materials are also used to fill the cavities of double walls and false ceilings to improve sound insulation. They are fibrous or porous materials that through the resistance imposed on the passage of air (r = resistivity to the air flow depending on the density of the material) impose a loss of energy dissipated by friction (heat) on the sound emission.

 

Laboratory measurement.

Instrumental measurement procedure of the acoustic insulation of the horizontal and vertical partitions and of the noise of the systems performed in the laboratory compliant with standardized test methods, the results of which are used for the design forecast of the insulation of buildings compliant with standardized calculation methods.

 

Measure in place.

Instrumental measurement procedure of the acoustic insulation of the horizontal and vertical partitions and of the noise of the systems performed in the building for the testing of the acoustic requirements in compliance with the standardized test methods provided for by Prime Ministerial Decree 5/12/1997.

 

 

Subscript: you see “Superscript, subscript”.

 

Auditory perception.

The human ear transforms changes in air pressure into auditory perceptions that do not depend solely on pressure but also on the frequency with which changes in atmospheric pressure occur. While the microphone of the sound level measuring instrument faithfully measures sound pressure at any frequency, the ear is an imperfect instrument that hears sounds that have a frequency between 20 and 15,000 Hz with a higher sensitivity in the range of frequencies including between 500 and 5,000 Hz. In the “sensitivity zone” the ear is more sensitive to high frequency sounds than low frequency ones and for example perceives as the same a sound of 35 dB emitted with a frequency of 4,000 Hz and a sound of 90 dB emitted at 20 Hz . The different sensitivity of the ear to the various frequencies can be represented on the intensity / frequency graph, defined as normal audiogram, by curves of equal sensation (isosensitivity) called “sensitivity curves” with more marked differences for low intensity sounds that gradually they are canceled out for sounds with an intensity greater than 85 dB. At 1,000 Hz, a frequency of good ear sensitivity, the physiological sound level perceived by the ear on the sensitivity curves coincides exactly with the physical level that can be measured with the instrument.

For the same reason the ear has an “audibility threshold” of the sound that varies with the frequency of the same and for example it is able to hear a sound of 8 dB emitted at 250 Hz but cannot hear a sound of 50 dB emitted at 31 Hz. Even in construction, when designing or judging the sound insulation of a wall or floor, we take into account how the human ear perceives sound. The ear is unable to withstand sounds of a higher intensity than a level of 120 dB called the “pain threshold” that cause painful sensations.

 

Soundproofing power (index):

Rw e R’w. Performance of the acoustic insulation of a partition (walls and floors) of airborne noise generated inside the building, expressed in linear dB as an index of the same, which identified by the symbol Rw represents the difference in noise level that the partition is able to determine in the laboratory between the chamber where it is generated and the receiving chamber, completely disconnected from each other, when the noise passes only by direct transmission through it. If, on the other hand, it is identified by the symbol R’w it represents airborne sound insulation between rooms separated from the considered partition, i.e. the difference in the noise level that the partition inserted in the building context is able to determine on site between the room where it is it generates and the receiving room when the noise passes through it both directly and sideways through the neighboring partitions. The relation Rw≥R’w always applies because the lateral noise transmission decreases the insulating performance of the partition when it is mounted on site. The Prime Ministerial Decree of 12/5/1997 has set the minimum values ​​of R’s for the elements of separation between distinct real estate units.

 

Passive acoustic requirements of buildings.

Title of the DPCM 5/12/97; Implementing Decree of the Framework Law on Noise Pollution No. 447 of 1995 which reports the maximum levels of noise of continuous and discontinuous systems and floor trampling and establishes the minimum insulating properties of the facade masonry and of the dividing walls between two units separate real estate, measured on site, forming part of all those buildings listed in table A of annex A of the same decree.

 

Resonance.

Phenomenon whereby in particular conditions the amplitude of the vibrations of a material or system stressed by periodic forces takes on particularly high values ​​which cause a drop in the insulation capacity.

 

Airborne noise.

Noise that is generated in the air and is transmitted through the variation in air pressure (for example speech, and noises from television or radio sets). The building distinguishes those coming from outside, traffic noise, etc., the insulation of which concerns the facade of the building, from those generated by the activities carried out inside the building, radio and television sets, conversation of the inhabitants etc. whose insulation concerns the vertical and horizontal dividing partitions of the different building units of the building.

 

Impact, impact, impact noise.

In a general sense, the term defines impact sounds that is the noise caused inside the building by the mechanical impact of a building element that is transmitted directly by the vibrations of the structural elements of the building (for example: hammer blows to fix a nail on the wall, the dragging of chairs or furniture on the floors). The most common source is the trampling of footsteps on the floor of the attics. Strictly speaking, it also defines the impact noise generated by the “trampling machine”.

 

Background noise.

The sound level and spectrum normally present in an internal or external environment acoustically characterizes both the area considered and the various human activities and can be defined as “background noise”. The noise level caused by traffic is high and the one present in some industrial environments that are considered noisy while we define a rural area as silent is typical of urban centers. The consideration of background noise is also important for the sound insulation of building partitions, think of the insulation of the facade in an environment of intense traffic or near an airport. The background noise often varies during the day, just think of the lower traffic noise at night. The level of the background noise masks the sounds of lower intensity that are produced at the same time in the same environment and that is why during the day we do not hear the sound of the neighbor’s television but at night it disturbs us because the level of the background noise is lowered to the below that of the neighbor’s television. The background noise level can be compared to the water level of a stream which in periods of flood makes the surface of the water appear smooth and regular while in the lean periods the boulders of the bottom of the stream emerge which represent the sources of the noise. which, on the other hand, have not diminished in intensity. Even a variation in the sound spectrum of the background noise can bring out a disturbing sound because the human ear has the ability to qualitatively identify a specific sound of different frequency composition even if this has a quantitatively lower level. The measurement of background noise is an operation that is always performed in the receiving / disturbed environment to assess the feasibility of building sound insulation measurements and determine the corrections to be made to the noise levels measured at various frequencies. Measuring the insulation of the facade is also carried out externally in the emitting / disturbing environment to determine whether or not to use it as a source.

 

Plant noise.

Noise determined by the sound level of continuous operation systems (for example the fan coil) and discontinuous operation (for example the drains or the lift) whose noise is measured in dB (A) and whose limits Laeq and LASmax respectively have been set by the Prime Minister’s Decree of 12/5/1997 as values ​​to be measured in the most disturbed environment as long as it is different from the one in which the noise originates.

 

Mass-spring-mass system.

Physical system model in which two masses are kept decoupled through an interposed spring. In acoustic insulation in buildings, it exemplifies the behavior of double walls (the masses) separated by a blade of air (the spring) which may or may not be filled with an absorbent material, generally of a fibrous constitution.

 

Resilient layer.

A resilient layer is defined as an elastic separation layer between rigid elements whose main feature is that it does not allow the transmission of vibrations in the building structure caused by impacts (for example: foot traffic) on its partitions.

 

Sound and noise.

Sensation of the human hearing organ stimulated by the variation in air pressure generated by the vibration of a body, human larynx, loudspeaker, metal sheet, etc. of characteristics (frequency and level) such as to be heard by the human ear. It is characterized by the pressure level, measured in decibels (dB) and by the frequency, number per second, with which the variations in pressure around the atmospheric pressure occur, expressed in hertz (Hz). The set of sounds with characteristics such as to be unpleasant to the human ear is commonly defined as “noise”, but especially in construction it is more appropriate to define it as “unwanted sound”, not everyone likes to hear a Beethoven symphony that the neighbor listens at one in the morning, but no one could define a symphony as a noise.

 

Reverberation time.

Commonly called the “echo effect”, it measures the time it takes for a sound signal to decrease its energy by a considerable percentage. The reverberation time check is performed in large rooms where too long times prevent the intelligibility of the word or music. The measure is mandatory for school buildings and the limits are those reported in the circular of the Ministry of Public Works n. 3150 of 22/05/1967.

 

Direct transmission.

Main noise path through the partition

 

Lateral transmission.

Indirect propagation of noise through the rigid connections of the partitions bordering the building partition which causes a decrease in the potential insulation foreseeable or foreseen for direct transmission only.

 

Ultrasound, infrasound.

Sounds that are not audible to humans because they are of a higher or lower frequency than the ear sensitivity area. Animals often distinguish both ultra and infrasound that humans do not notice and in some cases are able to emit them as a call or to orient themselves and capture prey. Ultrasounds are defined as those that have a frequency higher than 15,000 Hz while infrasounds are those that have a frequency lower than 20 Hz.

 

Sound propagation speed.

Sound spreads only through what is defined as the “sound propagation medium” which can be of a completely different nature: air, water, metals, building materials, etc. If there is no medium, the sound cannot spread, for example in the void there are no sounds. The speed with which the noise “moves” depends on the medium in which it occurs. In the air the propagation speed is approx. 340 m / s, in building materials it can even reach 5,000 m / s (5,000 m / s for steel, 3,000 m / s in bricks, much lower for insulators).

(source: index spa) http://www.isolantiindex.it