There is an increasing trend for buildings and spaces to have multiple uses, therefore it is critical that designers consider disturbing noise and vibration frequencies and their harmonics as well as the natural frequency modes of the floor and structure to ensure sufficient levels of noise and vibration isolation are achieved.
Vibration control measures can be incorporated to provide vibration mitigation as well as enhance airborne and impact noise reduction. Incorporating mitigation measures for noise or vibration isolation is often far more cost effective than the necessary increase in size and weight of steel or concrete required to suitably stiffen a structure. As the vibration is isolated at source, the acoustic performance is also generally much higher.
Acoustic Isolation of Cinemas
Cinemas play a significant role in modern leisure trends especially in the retail and restaurant mix where they act as the transition between shopping, dining and evening leisure. This trend has meant that cinemas are often situated on upper storeys or on the roof as people are funnelled through the shopping centre into the cinema. Consequently cinema design has had to evolve to overcome significant noise and vibration disturbance challenges from:
- Retail units below
- Adjacent leisure activities such as bowling alleys
- Nearby plant and building service equipment
- Transport noise including that from aircraft
- Closely spaced auditoria
Most modern cinemas cannot rely on a thick concrete structural slab to provide sufficient isolation but instead look to a variety of box-in-box designs to decouple each auditorium from its surroundings. Farrat can help in overcoming these challenges. From outline design all the way through to installation, we have multi-disciplined knowledge and capabilities in place to assist the entire design team. We can provide detailed advice and specification assistance drawing on our wide portfolio of high performance products and solutions. Additionally for installation work, we are happy to recommend AcouStruct Ltd as their highly trained installation team have many years of experience of installing Farrat solutions.
Acoustic Design Considerations
Modern cinema design tends to demand a full box-in-box design for each auditorium to provide the highest level of acoustic isolation properties with the minimum risk of flanking transmission paths. Box-in-box systems consist of an acoustic floating floor, isolated internal walls and ceiling resulting in a room that is completely decoupled from the surrounding building structure. It is imperative that during construction, no solid ‘bridges’ exist between the floating floor, walls or ceiling as they will reduce the effectiveness of the system. For more details on Farrat’s full range of acoustic solution options for floors, walls and raked seating in Cinemas, please download our Cinema Guide.
Acoustic Isolation of Theatres & Concert Halls
Concert halls are an important and popular part of arts and leisure culture where cutting edge technologies are used to provide the best possible acoustics for the music and theatre to be performed. They tend to be constructed in urban environments to allow accessibility which can lead to challenging scenarios where externally induced noise and vibration from road, rail, general urban noise and tightly spaced venues can dramatically affect the critical acoustic experience. Vibration control may be required in a concert hall design due to;
- Externally induced disturbing vibration from transport etc.
- Internal noise transfer between performance, rehearsal/practice and public spaces
Acoustic Design Considerations
The principles of concert hall design are similar to those adopted in cinemas but tend to be on a much larger scale owing to the size of the auditoria and the very high acoustic requirements of the performance spaces. A modern construction method for concert halls is to build the main shell out of in-situ concrete and then construct all the noise critical areas as independent ‘boxes’ supported by high performance acoustic bearings. For large spaces such as main concert hall auditoria and studio theatres the walls and ceiling are supported by a steel frame which is supported at the base of each column by a resilient bearing. That way anything within that space (seating, stage, fly tower etc) is decoupled. Such a method provides high levels of airborne noise attenuation in each space whilst the structure borne vibration levels can be controlled through selecting an appropriate frequency dependent on the disturbing frequency and building structure design. Using steel as the internal frame also facilitates the use of longer spans and complex shapes whilst at the same time minimising weight and cost. The two main approaches to concert hall vibration control are;
- Full building / Base isolation – Used in concert halls around the world to prevent structure borne vibration from entering the structure.
- Box in Box Systems – This system offers benefit if space within the concert hall is constrained (as it often is), by isolating each internal part of the building (main concert hall, second hall, studio theatres, rehearsal studios and gyms etc) from one another.
Acoustic Isolation of Bowling Alleys
Bowling Alleys typically require only one element of high performance sound insulation: a heavy concrete floating floor. Designing a floating floor for a bowling alley is a lot more involved than many other applications for the following reasons: Heavy Impact Isolation: The floor needs to be designed to isolate much lower frequencies than applications requiring airborne sound insulation as a dropped bowling ball transfers a lot more low frequency vibration into a slab than any airborne sound ever could. Damping: In addition to impeding the transmission of low frequency vibration caused by a dropped bowling ball, a bowling alley floating slab needs to provide additional damping to reduce unwanted vibration feedback to the players. Venting: The large surface area to perimeter ratio of a bowling alley floating floor makes it one of the only applications that the often discussed “air-gap stiffening” phenomenon actually has an appreciable effect. A bowling alley slab must be designed so that the air in the cavity formed by the isolators does not become “trapped”. NOTE: Due to the very low frequencies required to be isolated, lightweight floating floors are not suitable for bowling alleys. 100mm of concrete is the minimum slab thickness, and 150mm thickness should always be considered.
Acoustic Design Considerations
Of major importance is also utilising a system that maintains lane level over time and can perform equally well under the wide variation in loads encountered on a typical bowling alley floating slab without tilting.
Acoustic Isolation of Laboratories
There are many types of laboratories that require high performance sound insulation. Typically these are where sensitive machinery such as electron microscopes or coordinate measuring machines are used, however the principle arises anywhere that produces high level of noise and/or vibration, or is particularly sensitive to noise and/or vibration. Due to the fact that there is so much variability in laboratory configuration and usage, there is no one-size- fits-all solution. This is where Farrat’s wide breadth of experience is particularly useful not just in offering advice on products, installation and commissioning in these applications, but also in providing consultancy to assist the design team to ensure appropriate and cost effective solutions are selected.
Cheethams, Manchester Type: Acoustic Box in Box Systems
Vue – Westfield, London Type: Acoustic Floating Floors
Xscape, Milton Keyes Type: Acoustic Floating Floors
VUE – The Rock, Bury Type: Acoustic Isolation System
Why Choose Farrat for High Performance Sound Insulation?
Testing, Standards & Compliance
Farrat acoustic floating floor systems have been laboratory tested in accordance with BS EN ISO 140-4 & 7:1998 in a UKAS accredited laboratory. Our compounds conform with the requirements and testing procedures set out in BS 6177:1982 and BS EN 1337-3:2005. Full test data is available on request.