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Why is the acoustic properties of an environment important?
Noise is audible energy that can adversely affect ones physiological and psychological wellbeing. The use of sound absorbing material reduces sound reflection and will create a comfortable indoor climate.
Stone Wool Acoustic Tiles
Stone wool is by nature a highly sound absorbent material, bringing excellent acoustic properties to our ceiling and wall solutions. This allows you to achieve a high level of acoustic comfort while maintaining a high level of aesthetics. The acoustical ratings of Rockfon products have been tested in independent and certified laboratories.
In schools, up to 70% of the consonants spoken by teachers cannot be heard by pupils(1)
In hospital environments, noise control is very important to the recovery of patients as “unwanted sound” can increase heart rate, blood pressure and respiration rate(2)
In offices, 70% of employees believe that their productivity would be higher if their environment was less noisy(3)
1) “Speech Intelligibility in Classrooms” research project conducted by The Department of Building Engineering & Surveying of Herriot-Watt University in Edinburgh 2) Health Technical Memorandum 08-01: Acoustics 3) Julian Treasure, Sound Business, 2007
How does sound behave in a room?
When a sound wave hits a surface, part of the energy is reflected, the material absorbs part of it and the rest is transmitted. The quality of sound absorption is determined by the layout of the space and the materials used.
By nature, stone wool offers excellent sound absorption properties.
Proper sound absorption
Sound absorption controls the ambient sound pressure level in a room to create comfortable environments in which people can concentrate and work productively without noise-induced irritation or stress.
It increases speech intelligibility making presentation and conversation easier to understand.
It reduces reverberation (echoes) and the ‘cocktail party’ effect where sound levels rise uncontrolled in a room as people talk louder and louder to make themselves heard until everyone is shouting.
How much sound travels from one room to another?
Our stone wool ceilings can help limit the transmission of unwanted sound from one room to another. The total sound insulation of adjacent spaces is expressed by DnT,w, R´w or DnT,A values. It represents the ability of a total construction (partition, ceiling, floor and all connections) to block speech, music or other noise, that is transmitted through the air and through building elements. The higher the value (in dB) the better the performance.
Some regulators prescribe minimum levels of 35-45 dB between offices or 50-60 dB between apartments and dwellings. Mass, air-tightness and absorbing ability are the primary properties that determine the ability of a material to insulate sound. Mass, air-tightness and sound absorption are the primary properties that determine the ability of a material to insulate against sound.
The impact sound insulation between two floors is an expression of the ability of a construction to insulate from sounds generated by impacts e.g. footsteps, slamming doors. It is characterised by the impact sound pressure level L’nT,w and is rated in dB. The lower the value the lower the sound pressure level thus the better the impact sound insulation. Some regulators prescribe maximum L’nT,w (L’nT(Tmf,max),w in the case of schools) levels of 60 dB in classrooms and offices.
Sound transmission paths between adjacent spaces
Rockfon stone wool ceilings can help limit the transmission of sounds from one room to another.
Improved sound insulation
All walls and ceilings, to some degree, limit sound transmission from one room to another.
The use of building elements with superior sound insulation properties contributes to a higher degree of privacy and confidentiality.
Sound insulation contributes to lower sound pressure levels in adjoining rooms, creating more comfortable environments in which everyone can easily concentrate.
What is the sound pressure level an indication of?
Sound pressure level indicates how loud it is in the room. Exposure to continual high sound pressure levels or to high sound peaks can, over time, damage an individual’s health.
Average sound pressure level is important for all environments – from factories to kindergartens. The European Union has defined maximum exposure levels at 85 dB(A), and in some countries, public events like concerts should not exceed 96 dB(A).
The sound pressure level in a room depends on the strength of the sound source, the room shape and the number and quality of sound absorbing surfaces.
Source: United States Department of Labor, Occupational Safety and Health Administration
Industrial environments very often have high sound pressure levels and require specific acoustic corrections. Rockfon offers a selection of solutions like high absorbing ceilings, baffles or wall absorbers.Sound pressure level indicates how loud it is in the room. Exposure to continual high sound pressure levels or to high sound peaks can, over time, damage an individual’s health.Sound pressure level indicates how loud it is in the room. Exposure to continual high sound pressure levels or to high sound peaks can, over time, damage an individual’s health.
What is the reverberation time an indication of?
The most important factor in all regulations is reverberation time, which is defined as the time it takes for the sound pressure level to drop 60 dB below its original level.
In most cases, a low reverberation time improves the acoustical comfort. In some situations, however, such as concerts or conference halls, a higher reverberation time can improve listening comfort.
Reverberation time depends on the size and shape of the space along with the amount, quality and positioning of absorbing surfaces within the space. The more sound absorption in the room, the lower the reverberation time.
What does speech intelligibility indicate?
Speech intelligibility measures how well speech can be heard and understood in a room. It is closely linked to reverberation time.
Many factors influence speech intelligibility. These include the strength of the speech signal, the direction of the source sound, the level of background noise, the reverberation time of the room and the shape of the room.
The common way of expressing speech intelligibility is the Speech Transmission Index (STI) value on a scale from 0 to 1. In a class room, for example, the level should preferably be above 0.6. A simplified (faster) tool for speech intelligibility is the Rapid Speech Intelligibility Transmission Index (RASTI).
What is sound insulation?
Total sound insulation is the ability of a room (partitions, ceiling, floor and all connections) to prevent sound from travelling through the air and through building elements.
The total sound insulation of adjacent spaces is expressed by DnT,w, R’w or DnT,A values. The higher the value (in dB), the better the performance. Mass, air-tightness and absorbing ability are the primary properties that determine the ability of a material to insulate against sound. Some regulators require a minimum of 35-45 dB between offices.
Experience by the user:
30 dB (A) A conversation in the adjacent room can be clearly heard and understood
40 dB (A) A conversation in the adjacent room is experienced vaguely
50 dB (A) The sound in the adjacent room cannot be heard
Impact sound insulation
Impact sound insulation between floors is the ability of a construction to insulate from impact noises such as footsteps. It is characterised by the impact sound pressure level L’nT,w in dB. The lower the value, the better the impact sound insulation. Regulators usually allow a maximum L’nT,w of 60 dB in classrooms and offices.
What are the main indicators for sound absorption?
Sound absorption is measured using the sound absorption coefficient alpha (α), which has a value between 0 and 1.00. Zero represents no absorption (total reflection), and 1.00 represents total absorption of the incident sound. This coefficient is used to determine the commonly used sound absorption indicators explained below:
Weighted sound absorption coefficient (αw)
Alpha W or αw is calculated in accordance with ISO 11654 using the practical sound absorption coefficient αp values at standard frequencies and comparing them with a reference curve. All suspended ceiling suppliers in Europe provide αw for their products.
Stone wool used in Rockfon products offers the highest performances compared to many other materials.
Equivalent sound absorption area (Aeq)
The sound absorption property of islands and baffles is quantified using the equivalent sound absorption area Aeq expressed as m² per object. The Aeq value is measured in accordance with the ISO 354. This is the area of a fictive absorbing surface of αw = 1.00 which would absorb the same amount of sound as the tested island or baffle. There is no standardised “weighted” equivalent sound absorption area, so the best way to compare a plane ceiling with a ceiling of islands or baffles is to calculate the reverberation time for each room and situation.
Rockfon islands and baffles provide high sound absorption where modular suspended ceilings are not suitable.
The international standard ISO 11654 breaks absorption performance into five classes, from A to E. The αp values are compared to a series of fixed reference curves. The range between the reference curves is wide, so absorption classes provide only a rough indicator of sound absorption.
Many Rockfon ceilings offer class A sound absorption.
Noise Reduction Coefficient (NRC)
Calculated in accordance with ASTM C423, the Noise Reduction Coefficient (NRC) provides a single-number rating for sound absorption (higher values are better). It is the mathematical average of the measured sound absorption coefficient αs at 250, 500, 1000 and 2000 Hz frequencies. NRC gives equal weighting across the frequency range, which means it is not as accurate as αw.
What are the main indicators for sound insulation?
Room-to-room sound insulation
The Dn,f,w value in dB quantifies the longitudinal sound insulation provided by the ceiling between two rooms. The higher the Dn,f,w value, the better the room-to-room sound insulation. The Dn,f,w value can be considered equal to the previously-used Dn,c,w value.
Dn,f,w is used by acousticians to predict the total sound insulation DnT,w (R’w; DnT,A) between adjacent spaces.
Direct sound insulation
The direct sound insulation in dB indicated by the sound reduction index (Rw) measures the reduction of sound passing through the suspended ceiling.
Ceilings with high sound reduction index Rw will help prevent noise generated by installations in the plenum from entering the room.
C & Ctr values
To rate the impact of sound insulation in specific conditions, laboratories report Dn,f,w or Rw indicating C and Ctr values. C is the adaptation term for “pink” noise such as speech, music, TV, children playing, etc. Ctr is the adaptation term for traffic noise. The lower the C and Ctr values, the better.
How does sound absorption influence on room-to-room sound insulation?
There is a strong synergy between sound absorption and the room-to-room sound insulation experienced in practice. This is not reflected by the Dn,f,w value measured in laboratories. At equal Dn,f,w value, the use of a highly sound-absorbent ceiling will result in a lower sound pressure level in the receiving room.
The ceiling with the highest αw will do a better job of lowering the sound pressure in both the sending and the receiving room. The impact of sound absorption on the perceived sound pressure level can be calculated and has been verified through in-situ testing.
With an identical Dn,f,w value (in this case 44 dB), a high-absorbing ceiling contributes to a lower sound pressure level than a low-absorbing ceiling.
The Rockfon dB range
Our dB range has been designed to block sound from travelling from room to room, providing a unique combination of both outstanding sound insulation and sound absorption in one panel.