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Acoustics Academy 2018-11-02T12:50:51+00:00

QUALITY IN ACOUSTICS IS A SOUND INVESTMENT

In this Acoustic Academy you will find general information about acoustics and sound and how these relate to Gustafs acoustic solutions. We will focus on what we are good at – room acoustics, which is mostly about sound absorption to reduce sound levels and to create optimal reverberation times of sound. Other room acoustics  are about reflection, diffraction and transmission of sound. Sound isolation is rather a building acoustic aspect.

The Impact of Sound

Sound affects us all the time, physiologically, psychologically, cognitively and behavioristic. Gustafs provides excellent acoustic solutions that make the individual well being in a room and the experience of a room greater, whether your room is an airport terminal, auditorium, conference center, lobby space, etc.

We always recommend designers to consult with an acoustician in order to achieve the required results at an early stage of the design and construction process.

…..and remember, rooms are made for varying activities which require varying acoustic properties.

The Impact of Sound

Sound affects us all the time, physiologically, psychologically, cognitively and behavioristic. Gustafs provides excellent acoustic solutions that make the individual well being in a room and the experience of a room greater, whether your room is an airport terminal, auditorium, conference center, lobby space, etc.

We always recommend designers to consult with an acoustician in order to achieve the required results at an early stage of the design and construction process.

…..and remember, rooms are made for varying activities which require varying acoustic properties.

GENERAL ACOUSTIC CONCEPTS

Five Principles of Acoustics

Reflection

reflecting wooden panel for interior
Sound reflecting decorative panel

Fiber Gypsum Panels are often used to reflect sound, as electric amplifying is often not preferred. The hard and high density surfaces of these panels are a decisive factor in the room’s total acoustic profile. For good reflecting of sound, a stable and non-vibrating surface is essential to carry the sound waves to the audience.

Absorption

Acoustic absorption for wooden panel
Sound absorption for decorative acoustic panels

Sound absorbing surfaces will reduce disturbing noises and shorten the stressing reverberation time. The key of wall and ceiling solutions, like panels and linear ribs, is that the can cover large surfaces of the room, resulting in a superb total sound absorption. Read more about sound absorbing in the other sections of this acoustic academy.

Transmission

Transmission of sound with acoustic wooden panel
Sound transmission for decorative acoustic panels

Sound transmission is an important aspect when it comes to acoustic design in a building/room. Sound transmission measures the level of sound insolation in wall or ceiling claddings. Transmission and simultaneously the isolation of sound is a typical building acoustic aspect.

Diffraction

Example of sound diffraction with wooden wall panelling
Sound Diffraction for decorative acoustic panels

Just like any wave, soundwaves do not stop when it bumps into an obstacle. Instead, the sound passes around the barrier in its own way. Short wave length sounds are less capable of diffracting compared to long wave sounds. Standing outside a concert hall you will more likely hear the low frequency bass sounds (drum) than the high frequencies (guitar).

Diffusion

Diffusion of sound with wooden cladding
Sound Diffusion for decorative acoustic panels

A diffuser is an element which purposely reflects and spreads a sound source. Placed properly, the diffuser will improve the overall sound quality in the room while avoiding added sound effects such as echo or reverberation.

An optimal diffuser must avoid regular patterns in the surface structure. Diffusers are used to create ”depth” in the sound and improve the sound experience of the room, the room feels bigger than it really is.

About Sound Absorption and Reverberation Times

EU ABSORPTION CLASSIFICATION (EN ISO 11654 )

Sound absorption coefficients are measured according to ISO 354. The weighted sound absorption coefficient (αw) and the sound absorption class as shown in the table below have been calculated according to ISO 11654.

Absorption class Weighted absorption coefficient Description
A αw 0,90 – 1,00 Extremely absorbing
B αw 0,90 – 0,85 Extremely absorbing
C αw 0,60 – 0,75 Highly absorbing
D αw 0,30 – 0,55 Absorbing
E αw 0,15 – 0,25 Hardly absorbing
No Class αw 0,00 – 0,10 Reflecting

US NOICE REDUCTION COEFICIENTS (ASTM 423)

NRC (Noice Reduction Coefficient) is determined as a value that comes from the average value achieved on the following frequencies: 250, 500, 1000 and 2000 Hz. Approximate translation from αw to NRC:

αw NRC
A NRC>0,75
B NRC>0,75
C 0,5 < NRC < 0,75
D 0,5 < NRC < 0,75
E 0,25 < NRC < 0,5
No Class NRC < 0,25

Please note that using sound absorbing materials with for example class B not automatically results in a room with class B, the whole room could actually be classified higher or lower.

REVERBERATION TIMES

The reverberation time is the time it takes for a sound to become non-hearable, or more exact the time it takes to reduce the sound with 60 dB. A long reverberation time is experienced as disturbing and makes it difficult to understand the speaking word, stay concentrated and creates stress.

Doubling the amount of absorption halves the reverberation time. It needs twice the surface of a α=0,50 absorber compared to a α=1 to achieve the same reverberation time.

Low frequencies will have a longer reverberation times than high frequencies. Different types of rooms will also have different ideal reverberation times:

Church  4 – 8 seconds

Class room  0,6 seconds

Office room  0,5 – 0,8 seconds

Concert hall  2 seconds

Reverberation time with acoustic wooden panel

Room acoustics and the reverberation time depend mainly on three factors:

1.  The volume of the room. A larger room means a longer reverberation.

2. The surfaces of the room. More absorbing surfaces gives a shorter reverberation.

3. The objects in the room. More objects result in a shorter reverberation.

The total sound absorbing effect of the surface materials in a room is the result of how well the material absorbs sound, multiplied by the total area of the walls and ceilings covered.

Gustafs provides wall and ceiling solutions with very good sound absorbing qualities and they can cover large surfaces of the room, the ideal combination.

About Sound Absorption and Reverberation Times

EU SOUND ABSORPTION CLASSIFICATION (EN ISO 11654 )

Sound absorption coefficients are measured according to ISO 354. The weighted sound absorption coefficient (αw) and the sound absorption class as shown in the table below have been calculated according to ISO 11654.

Absorption class Weighted absorption coefficient Description
A αw 0,90 – 1,00 Extremely absorbing
B αw 0,90 – 0,85 Extremely absorbing
C αw 0,60 – 0,75 Highly absorbing
D αw 0,30 – 0,55 Absorbing
E αw 0,15 – 0,25 Hardly absorbing
No Class αw 0,00 – 0,10 Reflecting

US NOICE REDUCTION COEFICIENTS (ASTM 423)

NRC (Noice Reduction Coefficient) is determined as a value that comes from the average value achieved on the following frequencies: 250, 500, 1000 and 2000 Hz.

Approximate translation from αw to NRC

αw NRC
A NRC>0,75
B NRC>0,75
C 0,5 < NRC < 0,75
D 0,5 < NRC < 0,75
E 0,25 < NRC < 0,5
No Class NRC < 0,25

Please note that using sound absorbing materials with for example class B not automatically results in a room with class B, the whole room could actually be classified higher or lower.

REVERBERATION TIMES

The reverberation time is the time it takes for a sound to become non-hearable, or more exact the time it takes to reduce the sound with 60 dB. A long reverberation time is experienced as disturbing and makes it difficult to understand the speaking word, stay concentrated and creates stress.

Doubling the amount of absorption halves the reverberation time. It needs twice the surface of a α=0,50 absorber compared to a α=1 to achieve the same reverberation time.

Low frequencies will have a longer reverberation times than high frequencies. Different types of rooms will also have different ideal reverberation times:

Church  4 – 8 seconds

Class room  0,6 seconds

Office room  0,5 – 0,8 seconds

Concert hall  2 seconds

Reverberation time with acoustic wooden panel

Room acoustics and the reverberation time depend mainly on three factors:

1.  The volume of the room. A larger room means a longer reverberation.

2. The surfaces of the room. More absorbing surfaces gives a shorter reverberation.

3. The objects in the room. More objects result in a shorter reverberation.

The total sound absorbing effect of the surface materials in a room is a result of how well the material absorbs sound, multiplied by the total area of the walls and ceilings covered.

Gustafs provides wall and ceiling solutions with very good sound absorbing qualities and they can cover large surfaces of the room, the ideal combination.

GUSTAFS SOUND ABSORBERS

In the following sections we will describe and explain 5 types of sound absorbers regarding how they work, their unique properties and how they relate to Gustafs sound absorbers.

1. Sub Resonance absorbers (Membrane)

2. Mid Resonance absorbers, Panels (Helmholtz)

3. Mid Resonance absorbers, Linear Rib (Helmholtz)

4. Nano absorbers (Nano + Helmholtz)

5. Porous absorbers

Absorption frequencies for acoustic wooden panelling

This illustration shows the approximate frequency bands in which the various types of absorbers have their peak performance.

For example Gustafs “PD8” and “Nano” are different acoustic solutions but have similar absorption coefficients.

acoustic academy learn difference between perforated panels
Sound absorption with micro perforated wooden and mdf panel

1. Sub Resonance Absorbers (Membrane)

Membrane absorbers are used to reduce low frequencies. The elastic front (4) of the panel starts to resonate when influenced by sound and transforms sound energy into heat energy. The absorption increases if the distance to the wall is enlarged. Membrane absorbers do work over a short band of frequencies, but this can be enhanced by filling the air void (1) with a porous mineral wool (1).

Recommended Gustafs products: (alternatively Nano-B, contact us for more information)

Gustafs Subcoustic

Sub absorber for decoratice acoustic panels

2. Mid Resonance absorbers, panels (Helmholtz)

Helmholtz absorbers are used to reduce mid frequencies. The Helmholtz construction contains a “chamber” (1) (the void) which is connected to the room trough a “neck” (2) (the perforation hole). The air in the neck is influenced by sound and puts the air in the chamber in resonation, which transforms sound energy into heat energy. The sound absorption increases if the distance to the wall, and by that the chamber/void is enlarged. Helmholtz absorbers do work over a shorter interval of frequencies, but this can be improved by filling the void with a porous mineral wool (1) and putting an air permeable felt (3) directly behind the “neck”.

Recommended Gustafs products: Standard, Slot and Stripe perforations.

Mid resonance absorbers for wall and ceiling panelling

1. Sub Resonance Absorbers (Membrane)

Sub absorber for decoratice acoustic panels

Membrane absorbers are used to reduce low frequencies. The elastic front (4) of the panel starts to resonate when influenced by sound and transforms sound energy into heat energy. The absorption increases if the distance to the wall is enlarged. Membrane absorbers do work over a short band of frequencies, but this can be enhanced by filling the air void (1) with a porous mineral wool (1).

Recommended Gustafs products: (alternatively Nano-B, contact us for more information)

Gustafs Subcoustic

2. Mid Resonance absorbers, panels (Helmholtz)

Mid resonance absorbers for wall and ceiling panelling

Helmholtz absorbers are used to reduce mid frequencies. The Helmholtz construction contains a “chamber” (1) (the void) which is connected to the room trough a “neck” (2) (the perforation hole). The air in the neck is influenced by sound and puts the air in the chamber in resonation, which transforms sound energy into heat energy. The sound absorption increases if the distance to the wall, and by that the chamber/void is enlarged. Helmholtz absorbers do work over a shorter interval of frequencies, but this can be improved by filling the void with a porous mineral wool (1) and putting an air permeable felt (3) directly behind the “neck”.

Recommended Gustafs products: Standard, Slot and Stripe perforations.

3. Mid Resonance absorbers, Linear Rib (Helmholtz)

Helmholtz absorbers are used to reduce mid frequencies. The Helmholtz construction contains a “chamber” (1) (the void) which is connected to the room trough a “neck” (2) (the spacing between linear ribs). The air in the neck is influenced by sound and puts the air in the chamber in resonation, which transforms sound energy into heat energy. The sound absorption increases if the distance to the wall, and by that the chamber/void is enlarged. Helmholtz absorbers do work over a shorter interval of frequencies, but this can be improved by filling the void with a porous mineral wool (1) and putting an air permeable felt (3) directly behind the “neck”.

Recommended Gustafs products: Linear Rib.

Gustafs Linear Rib

Mid resonance sound absorber for linear cladding

4. Nano absorbers (Nano + Helmholtz)

Nano absorbers are used to reduce mid to medium high frequencies. Nano absorbers work according to the Helmholtz mechanism, but do not need the traditional “chamber” (the void) to absorb sound. Sound energy is already transformed into heat energy when sound is penetrating the extremely narrow Helmholtz “neck” (2) formed by the Nano perforation holes (300.000/m²) with a diameter of only 0,5 mm. The sound absorption will although improve when an additional Helmholtz “chamber” (5) is added to the panel core behind the Nano perforated layer and when an air permeable felt (3) is applied to the back of the panel. When installed with a distance to the wall or ceiling, preferable filled with a porous mineral wool (1), the sound absorption will increase once again. When installed as described above, Nano solutions will combine several acoustic mechanisms leading to an outstanding absorption class B.

Recommended Gustafs products: Nano.

Gustafs Nano Perforation

Micro absorbers for acoustic wooden panels

3. Mid Resonance absorbers, Linear Rib (Helmholtz)

Mid resonance sound absorber for linear cladding

Helmholtz absorbers are used to reduce mid frequencies. The Helmholtz construction contains a “chamber” (1) (the void) which is connected to the room trough a “neck” (2) (the spacing between linear ribs). The air in the neck is influenced by sound and puts the air in the chamber in resonation, which transforms sound energy into heat energy. The sound absorption increases if the distance to the wall, and by that the chamber/void is enlarged. Helmholtz absorbers do work over a shorter interval of frequencies, but this can be improved by filling the void with a porous mineral wool (1) and putting an air permeable felt (3) directly behind the “neck”.

Recommended Gustafs products: Linear Rib.

Gustafs Linear Rib

4. Nano absorbers (Nano + Helmholtz)

Micro absorbers for acoustic wooden panels

Nano absorbers are used to reduce mid to medium high frequencies. Nano absorbers work according to the Helmholtz mechanism, but do not need the traditional “chamber” (the void) to absorb sound. Sound energy is already transformed into heat energy when sound is penetrating the extremely narrow Helmholtz “neck” (2) formed by the Nano perforation holes (300.000/m²) with a diameter of only 0,5 mm. The sound absorption will although improve when an additional Helmholtz “chamber” (5) is added to the panel core behind the Nano perforated layer and when an air permeable felt (3) is applied to the back of the panel. When installed with a distance to the wall or ceiling, preferable filled with a porous mineral wool (1), the sound absorption will increase once again. When installed as described above, Nano solutions will combine several acoustic mechanisms leading to an outstanding absorption class B.

Recommended Gustafs products: Nano.

Gustafs Nano Perforation

5. Porous absorbers

Porous absorbers are normally made of mineral or polyester wool (1) covered by a highly air permeable layer, for example a fabric (6). Porous absorbers are good in reducing high frequencies. Sound energy is transformed into heat energy while penetrating the wool twice, in and out. The sound absorption increases if the distance to the wall, and by that the total void is enlarged.

Typical porous absorbers: Fabric solutions covering a mineral or polyester wool.

Fabric Absorber

Porous sound absorber for decorative acoustic panels

5. Porous absorbers

Porous sound absorber for decorative acoustic panels

Porous absorbers are normally made of mineral or polyester wool (1) covered by a highly air permeable layer, for example a fabric (6). Porous absorbers are good in reducing high frequencies. Sound energy is transformed into heat energy while penetrating the wool twice, in and out. The sound absorption increases if the distance to the wall, and by that the total void is enlarged.

Typical porous absorbers: Fabric solutions covering a mineral or polyester wool.

Fabric Absorber

The optimal combination of absorption and reflection

Certain sounds need be reduced or eliminated, others to be directionally steered and carried out towards the audience, all the way to the back of for example an auditoria.

Gustafs panels and Linear ribs let you combine good absorption with good reflection, something normally desired in auditoria, concert halls and similar rooms. Especially acoustic panels have a relatively low open area for the absorption, leaving a large reflective area. The reflection will be well balanced by the non-vibrating, hard and high density cores of Gustafs solutions, starting from 15 kg/m². The medium absorption coefficients of our reflective solutions are compromised by the large visible surface that they can cover on both walls and ceilings.

Studied effects of a good sound atmosphere on Health Care

  • Sleep is essential for patient recovery – rooms with good sound absorption can cut sleep awakenings by up to 40%.
  • In rooms with little noise and short reverberation times, stress and blood pressure levels will drop.
  • Noise reduction in emergency departments and operating rooms increases accuracy by up to 50%.
  • Noise reduction showed less need for medication.
  • Noise reduction increases staff well being and performance.

Studied effects of a good sound atmosphere on Education

In education it is essential to reduce the disruption from background noise and to have a good sound setting overall. If achieved, there will be substantial benefits for both students and teachers:

  • Better speech clarity and greater understanding. (3)
  • Better working memory.
  • Enhanced reading ability.
  • Lower stress levels and blood pressure.
  • Better focused students and less fatigue. (6)
  • Higher test scores (1)
  • Makes student speak lower. (2 & 5)
  • Students feel more encouraged to cooperate and to be inclusive (4)

1. Shield, B.M. and Dockrell, J.E.: The effects of environmental and classroom noise on the academic attainments of primary school children. Journal of the Acoustical Society of America 123(1), 133-144, USA (2008)

2. MacKenzie, D. J.; Airey, S.: Classroom Acoustics – A Research Study, Heriot-Watt University, United Kingdom (1999)

3.Klatte, M.; Lachmann, T.: [A lot of noise about learning: acoustic conditions in classrooms and what they mean for teaching] Germany (2009)

4. Canning, D.; James, A.: The Essex Study – Optimized classroom acoustics for all, United Kingdom (2012)

5. Tiesler, G., Oberdörster, M.: Bremen University [Acoustic ergonomics in schools], Germany (2006)

6. Schönwälder, H.-G.; Ströver, F.; Tiesler, G.: [Health promoting influences on performance ability in school education] Germany (2008)

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