BB93 Archives - MACH GROUP

Case Study – Heathrow Hydrant Operating Company

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Case Study – Heathrow Hydrant Operating Company

9th April 2018BB93, Noise Surveys, Testing

Heathrow Hydrant Operating Company Noise at Work

Mach Testing carried a Noise at Work survey for the Heathrow Hydrant Operating Company. They provide a refueling service to over 100,000 planes a year which land in Terminal two. Employees regularly go out on to the tarmac to refuel the planes, therefore their workplace offers numerous health and safety risks in terms of the amount of noise which they are exposed to.

MACH Testing used a combination Dosimeters and site visits in order to collect data, building up an accurate picture of the noise climate. Our specialist engineers shadowed a number of employees in order to see their work patterns.

Following the assessment, MACH Testing were able to work with Heathrow Hydrant Operating Company to ensure that the noise in their workplace was not putting their employees at risk. We worked with HHOCO to work out a combination of hearing protection and subtle changes to their work schedules which ultimately gave them a risk assessment which was fully compliant with HSE regulations.

If you would like to know more about this project, or you would like a quote for a workplace noise survey, please ring us on 0843 309 4504 or contact us

Posted by IT MACH

Chris cuts though the jargon of Rw and Dw

29th January 2018BB93, Construction

R_w and D_nTw – Knowing the Difference can Save You Money

A common confusion in specifying wall types for a building lies in the difference between R_w and D_nTw. Misunderstanding this can go either way in terms of under or over performance; therefore getting this simple difference goes a long way to ensuring a good result on site, as well as presenting value engineering opportunities.

The Jargon

D_nTwis a term that relates to on-sitesound insulation. This is the target that is measured against in pre completion testing in line with BB93 specified D_nTwvalues. Because it is on site, it accounts for all sound transmission paths including direct through the separating partition and any flanking paths around it (i.e. through ceiling voids, ventilation paths, junction detailing).

R_wis defined as a laboratory rated sound reduction index. Wall constructions should be specified as this, measured in isolation from any other sound flanking paths.

Why is this Important?

The same construction measured in a lab will get the same result every time, but measured on site will vary from room to room, project to project. The conversion from R_w to D_nTw has to account for the size of the separating partition, the volume and reverberation time of the ‘receiving’rooms. It must also incorporate a factor to account for potential flanking transmission on site due to construction quality or inattention to junction detailing.

Therefore it is not a simple case of R_W = D_nTw + X dB. The R_W can vary significantly between partitions, even if they require the same D_nTw. Figure 1 summarises this.

Why does the R_Wvary when the D_nTw is the same?

How does this Help?

Clearly from Figure 1, if the same wall type R_w (say 45 dB) is used everywhere the D_nTw is 40 dB, there will be rooms that fail. On the flip side, if the most onerous requirement of 53 dB R_W is used for all 40 dB D_nTw walls, then some areas will be exceed the required performance by a considerable margin.

Of the two scenarios, it is usually the latter that will occur within a design. Therefore clear cost savings could be made by assigning wall types to partitions based on the required R_W, not simply the D_nTw.

This can all be done whilst retaining the same number of wall types. In fact by careful design and attention to construction details, the build ups of wall types can be engineered to reduce unnecessary overspend on thicker or denser plasterboard products and still maintain the on-site acoustic performance.

Reducing every dB of overdesign quickly sums up when applying over projects, schemes and larger frameworks, particularly those with common shared constructions.

Posted by IT MACH

BB93 Updates – Lean, Green and much much Clearer

29th January 2018BB93

MACH Acoustics aims to lead in the acoustics design of low carbon buildings and open plan teaching spaces, and hence has considerable experience in the design of educational buildings, please see our book ‘Sustainable Acoustics’ found at http://www.machacoustics.com/sustainableacoustics/acoustics-vented-facades.

To achieve the above goal, MACH Acoustics works closely with the Architectural Department at the University of Bath and the Institute of Sound and Vibration, University of Southampton. Currently we are sponsoring a KTP, PhD and two MSc Projects, all linked to the design of low carbon building design.

In MACH Acoustics view, BB93 has been intelligently updated with increased clarity and flexibility towards low carbon and refurbished buildings, whilst providing a more inclusive design approach to pupils within our schools.

Clarity

Clear objective performance requirements are provided in BB93 2014, with many areas being clarified.

For example, the requirements for SEN are significantly clearer, noise levels under natural ventilation and the use of Alternative Performance Standards, have been enhanced and strengthened, with new minimum performance standards being provided.

The challenges in refurbishing buildings have been recognized, with internal noise levels for refurbished projects being relaxed by 5 dB, and sound insulation levels reduced by 5 to 10 dB between spaces, depending upon adjacencies.

An increase of 0.2 seconds in reverberation time has also been provided for non-sensitive teaching spaces. These practical changes will make things considerably easier and encourage the refurbishment of buildings.

Low carbon building design is fundamental to our future buildings, BB93 2014 therefore allows internal noise levels to be increased by 5 dB if natural ventilation is being used, irrespective of ventilation rates. MACH Acoustics research indicates that this could result in 50% more schools being naturally ventilated. To promote cross ventilation, the target across cross ventilators has also been cut back to 32 dB Dnew. This dramatic change will significantly increase the feasibility of using cross ventilation, improving ventilation to teachings spaces and allowing for natural ventilation on noisier sites.

Sound Insulation

Sound insulation has in the main remained unchanged for new builds. The maximum level of sound between exceptionally sensitive spaces has been reduced from 60 to 55 dB DnTw, where this is seen to be a more practical performance standard. Additionally, essential doors between teaching spaces are now allowed, providing a 35 dB door is used.

Reverberation Times

As per sound insulation, reverberation times in the main remain unchanged, with the exception of Sports Halls. The target reverberation time is now a function of its size. Open plan spaces typically gain bad press for their poor acoustics. The tightening and additional new performance requirements relating to speech privacy between work spaces and the reduction in reverberation time, is pleasing to see. These important more stringent changes will result in enhancing the separation between workspaces, reduce occupancy noise levels and enhance communication between teachers and pupils.

Areas of concern

In MACH Acoustics view, BB93 2014 is a significant improvement over the old BB93, providing clearer and possibly more appropriate performance standards. However at this stage, we do not see the need to relax the reverberation times in refurbished buildings, since the Essex Study has shown a clear detriment of increasing reverberation times.

Sports Halls are challenging spaces to design and therefore a clear and detailed calculation process must be provided, such to ensure the on site performance of these spaces.

Finally, with regards to noise ingress, we see that the proposed maximum 55 dBA noise ingress level for the 200 hottest hours of the year, is too lenient, and could result in complaints as a result of communication challenges. The statement relating to the acoustics performance of single sided vented facades and façades to cross vented spaces at 16 and 20 dB, is seen by MACH Acoustics to be simplistic, optimistic and lacking in evidence.

Posted by IT MACH

Lecture Theatre Design with Acoustic Modelling

3rd April 2014BB93, Lecture theatre, Resources, Reverberation time

MACH Acoustics were appointed to carry out acoustic design for the refurbished Clattern Lecture Theatre. MACH created an acoustic model of the lecture space, calibrated by acoustic testing of the existing site. The design report concentrated on the two main factors effecting lecture theatre acoustics:

Speech Ineligibility

A standard requirement for a lecture theatre is to achieve good speech intelligibility of the speaker throughout the whole audience within the space. Speech intelligibility is maximised by increasing the signal to noise ratio, that is by maximising the loudness of speech and minimising the ambient noise level. Thus, the acoustical design of rooms for speech reduces to the consideration of four factors:

Providing optimum reverberation time.
Eliminating acoustic defects such as echoes and flutter echoes.
Maximising the loudness in the audience.
Minimising the background noise level in the room.

Speech intelligibility can be measured by the ‘Speech Transmission Index’, a percentage between 0% and 100%. BB93 requires that areas designed for speech should achieve ‘good’ speech intelligibility, corresponding to an STI of at least 60% across all areas of the audience.

Reverberation Time

Reverberation time is not only important for speech, but also important for audio visual presentations, as well as for amplified speech. For example if a film or a music track is being played from the AV system it is desirable to have a low reverberation time to ensure that amplified sound is clean and intelligible by reducing the build up of reverberant noise that can muddy the sound. This is seen clearly in spaces such as cinemas, which are heavily treated with absorptive material.

Onsite Tests

In order to accurately construct the model, MACH Acoustics carried out tests to determine the current levels of speech intelligibility across all areas of seating. Sound pressure levels were measured at various points around the room with a loud speaker playing in the position of a lecturer. The results are shown below. To put this into context, a 10 dB difference is usually perceived by the human hearing as a doubling in loudness.

The results show that levels in the wider areas, even when at a comparable distance to a position in the centre of the room are significantly lower. Levels at the back of the room are very similar to those as wide seating positions in the first few rows. This occurs mainly for two reasons.

The seating arrangement spreads wide from where the lecturer would typically be stood. Hence the lecturer must constantly turn to address different sections of the audience in order to be heard. Consequently when he or she is facing towards one side of the room, the level heard on the other side of the room is lower. MACH would usually advise that a seating arrangement is a) in front of the speaker and b) has an angle from the speaker to the widest seating position that does not exceed 30○ (currently as much as 70-80○).
The front portion of the ceiling is angled and reflective. MACH would usually advise this type of arrangement, as it aids in reinforcing sound levels towards the rear of the theatre by angling early sound reflections towards the back (as illustrated below). Hence as in this case, the sound is more evenly distributed across the majority of the audience behind the first few rows. This can be achieved by a sloped ceiling as in this case, or by suspending angled reflective panels (available in a range of aesthetically pleasing designs) above the area where the lecturer would usually stand.

Acoustic Model

An acoustic model was created, based upon the test data. The model allows us to assess the space by estimating the reverberation time and the spread of sound across the space, as well as the ‘Speech Transmission Index’ (STI) for speech intelligibility.

Ideally MACH Acoustics will usually target an STI of at least 65%, ‘ideal’ speech intelligibility and it can be seen that this was the case in all areas of the theatre. The reverberation time in the existing space is on the high side for amplified AV presentations. It was therefore deemed desirable to reduce this in the design of the refurbished theatre.

New Design Options

Using the model, MACH Acoustics developed a number of design options for Kingston University, providing varying levels of acoustic treatment to reduce the reverberation time and allow for better travel of speech within the space.

All options offered reduced reverberation time from 0.7s to 0.5s and under, with increased STI at back and room edges.Whilst MACH Acoustics had a recommended best options, the various methods allowed the client to select the best design style for the build.

Posted by IT MACH

Case Study: Llwynderw Primary School

12th March 2014BB93, Case Study, Cross Ventilation, Exhaust Stacks, NAT Vent Attenuator, Natural Ventilation, Sustainable Acoustics, Vented Facades

Llwynderw Primary School is a project in Abergaveny that MACH Acoustics worked on in partnership with Stride Treglown Architects and Willmott Dixon. The school incorporates natural ventilation through a vented facade and openable windows, which cross ventilate classrooms via a central chimney – saving money, building space and simplifying the construction.

An important stage in the acoustic design of a building is an environmental noise survey of the existing site, a service provided by MACH Acoustics. Using the data collected, a dynamic noise map was constructed and used to access the noise levels at each facade and the resulting noise break-in within the teaching spaces. It was clear that the site was not particularly noisy and that an open window would provide enough attenuation at the facade facing away from the roads – simple and low cost.

A ventilation strategy was developed in close coordination with Stride Treglown Architects – using the sound map – which efficiently attenuated noise on each facade. On the noisy road facing facades, a cedar shingles feature created a duct, with intake perpendicular to the ground and containing the NVA. A 90deg arrangement like this increases attenuation and minimises impact on building space – highlighting the bespoke design options that the NVA offers. The quieter rooms with central chimney simply used openable acoustic windows. The central chimney shown above is the highlight of the natural ventilation project. Each stack of classrooms featured a small square chimney, which vented out through natural vent towers on the roof of the building.

A testament to the NVAs versatility whilst maintaining class leading acoustic performance, the build was impressive architecturally whilst naturally ventilating and meeting both BB93 and BB101 requirements as a teaching space. Thanks to a partnership between MACH Acoustics and Strides, the building received a BREEAM ‘Very Good’ rating and was well received by parents, pupils and residents of the area. Click the preview below to download the full case study:

Posted by IT MACH

Case Study: Hertfordshire University

26th February 2014Architecture, BB93, BREEAM, Case Study, NAT Vent Attenuator, Under Floor, Vented Facades

The Law Court at the University of Hertfordshire is a £10M advanced facility, including a full-scale courtroom with public gallery, a working law clinic, a purpose built mediation centre and a dedicated CPD suite, as well as a large number of offices and classrooms. A BREEAM project, the building was to be naturally ventilated. MEP designers AECOM specified the Mach Acoustics NatVent Attenuator to provide a vented facade solution using weather louvres, connected to a raised, vented floor containing the Nat Vent Attenuator.

Installing the NVA under-floor is a veryeffective method when dealing with high noise levels. The vent openings are made within the spandrel panel between transoms. Air passes into the cellular space by passing through a external vent opening, through the NAT Vent Attenuator. The floor void is used as plenum – air enters the rooms above by means of floor diffusers.

Image provided by Aecom

Situated on a busy campus and next to a busy bus route, the natural ventilation strategy needed to be acoustically attenuated. Adding to the challenge was the fact that the building had already be designed for air inflow through the flooring, with acoustic dampers, louvre and bird mesh limiting flow to an already small 1.5m2 face area. Only thanks to the adaptable NVA foam, MACH Products was able to design the attenuator around modulated Kingspan flooring, sitting on pedestals 360mm high, fully filling the void. The profile was designed to the same size as the 600x600mm grid created by the flooring, such that the NVA would be easy to install. By installing in segments like this, we were able to create the required length of attenuator for the noise level at the facade.

Due to the bespoke nature of the NVA, the attenuator could be simply installed in coordination with the modular grid based flooring. The NVA segments were slid into place between the pedestals (1/4 circle sections were added to the corner profile to account for the structure), followed by the matching 600x600mm floor sections. Building services often exist within the flooring void, including a heated element in this case. The NVA foam can be easily adapted on site to accommodate for these items, unlike a common pre-defined attenuators.

Click the preview below to download the full case study:

Posted by IT MACH

Case Study: Dartington Primary School Nat Vent Box

19th February 2014BB93, Case Study, NAT Vent Attenuator, Natural Ventilation, Open Plan Teaching, Vented Facades

Dartington Primary School is located in close proximity to the A384; a large busy road. A number of natural ventilation strategies were developed in cooperation with Arup, including the use of landscaping as a barrier. This inspiring solid timber project presented challenges internally and externally. Natural ventilation is achieved through an external bulkhead cross-venting through the roof.

The first step of any noise break-in assessment is to establish levels across the site. This was done by carrying out noise monitoring throughout the site, over the full operational hours of the school.

A noise map was then created and used to assess the required level of attenuation required by facades of the school. The results indicated that the noise levels at the facades to the classroom block were higher than desirable.

The solution to the high noise levels at the building facade was to naturally ventilate using an external ground floor bulkhead containing the NVA, with hot air flowing out through openable window vents also containing the NVA. This solution allows for natural ventilation when it would otherwise not be possible through an open window for example. In addition to this, an acoustic screen and a strategically placed earth bund were designed to reduce noise levels at the classroom facade. The bund was formed from recycled tires, adding to the sustainability credentials of the building. Dartington Primary School is an inspiring development because a solid timber construction system has been used. BB93 also sets room reverberation requirements and the exposed timber in combination with barn shaped classrooms required some form of room acoustic treatments. The solution used was several acoustic beams provided by MACH Products (below).

The school met all BB93 requirements and BB101 ventilation specifications. Not only this but the finished design was pleasing and added function to the facade besides ventilation. The build was featured in ‘BD Reviews’ sustainability issue, a bow to the innovative design by MACH Acoustics, White Design and Arup. The photo below features the wooden beams put in place to reduce the reverberation. Click the preview below to download the full case study.

Posted by IT MACH

Case Study: Ebbw Vale Learning Zone

5th December 2013BB93, Case Study, Cross Ventilation, NAT Vent Attenuator, Natural Ventilation

The Learning Zone lies at the heart of the regeneration and redevelopment of the former steelworks at Ebbw Vale, the largest regeneration project in Wales. MACH Acoustics worked with Architects BDP to develop a natural ventilation strategy between classrooms.

MF tracks were used to hold the NVA – creating a cost effective bulkhead, with acoustic attenuation and building services able to coexist in the same space.

The case study is a prime example of the NVA’s ease of install and space saving advantages. The render above demonstrates how the NVA installs onto the MF tracking system.Generally a 1100mm depth NVA is used to sit between the standard 1200mm width between MF supports. The foam is positioned within the MF track in layers to form the honeycomb arrangement, which allows air to flow whilst attenuating noise.

Click the preview below to download the full case study:

Posted by IT MACH

Case Study – University of Hertfordshire Law Court

11th October 2013Architecture, BB101, BB93, NAT Vent Attenuator, Natural Ventilation, Under Floor, Vented Facades

The Law Court at the University of Hertfordshire is a £10M building with advanced facilities, including a full-scale courtroom with public gallery, a working law clinic, a purpose built mediation centre and a dedicated CPD suite, as well as a large number of offices and classrooms. Aiming for BREEAM status, the building was to be naturally ventilated. MACH Acoustics provided a vented facade solution using weather louvres, connected to a raised, vented floor containing the NVA.

Situated on a busy campus and next to a busy bus route, the natural ventilation strategy need to be acoustically attenuated. Adding to the challenge was the fact that the building had already be designed for air inflow through the flooring, with acoustic dampers, louvre and bird mesh limiting flow to an already small 1.5m2 face area.

Only thanks to the adaptable NVA foam, MACH was able to design the attenuator around modulated Kingspan flooring, sitting on pedestals 360mm high, fully filling the void. The profile was designed to the same size as the 600x600mm grid created by the flooring, such that the NVA would be easy to install. By installing in segments like this, we were able to create the required length of attenuator for the noise level at the facade.

The vent openings are made within the spandrel panel between transoms. Air passes into the cellular space by passing through a external vent opening, through the NAT Vent Attenuator. The floor void is used as plenum – air enters the rooms above by means of floor diffusers.

Building services often exist within the flooring void, including a heated element in this case. The NVA foam can be easily adapted on site to accommodate for these items, unlike a common pre-defined attenuators.

The build meet the BB93 and BB101 requirements as a teaching space whilst creating a dynamic and pleasant space for students. MACH Acoustics and it’s partners helped the centre become one of the most innovative law schools in the UK and was recently awarded ‘The Most Sustainable Construction Award 2011’ by Building Futures and has been short listed for several other awards.

Click the preview below to download the complete case study (pdf)

Posted by IT MACH

Case Study – Llwynderw Primary School

4th October 2013Architecture, BB93, BREEAM, Cross Ventilation, NAT Vent Attenuator, Natural Ventilation, Vented Facades

Llwynderw Primary School is a project in Abergaveny that MACH Acoustics worked on in partnership with Stride Treglown Architects and Willmott Dixon

The school incorporates natural ventilation through a vented facade and openable windows, which cross ventilate classrooms via a central chimney – saving money, building space and simplifying the construction.

An important stage in the acoustic design of a building is an environmental noise survey of the existing site, a service provided by MACH Acoustics.

Using the data collected, a dynamic noise map was constructed and used to access the noise levels at each facade and the resulting noise break-in within the teaching spaces. It was clear that the site was not particularly noisy and that an open window would provide enough attenuation at the facade facing away from the roads – simple and low cost.

A ventilation strategy was developed in close coordination with Stride Treglown Architects – using the sound map – which efficiently attenuated noise on each facade.

On the noisy road facing facades, a cedar shingles feature created a duct, with intake perpendicular to the ground and containing the NVA. A 90deg arrangement like this increases attenuation and minimises impact on building space – highlighting the bespoke design options that the NVA offers. The quieter rooms with central chimney simply used openable acoustic windows.

The central chimney shown above is the highlight of the natural ventilation project. Each stack of classrooms featured a small sqaure chimney, which vented out through natural vent towers on the roof of the building. Details of the this are shown on the right.

Thanks to a partnership between MACH Acoustics and Strides, the building received a BREEAM ‘Very Good’ rating and was well received by parents, pupils and residents of the area.

Click the preview below to download the full case study (pdf)

Heathrow Hydrant Operating Company Noise at Work

If you would like to know more about this project, or you would like a quote for a workplace noise survey, please ring us on 0843 309 4504 or contact us

Speech Ineligibility

Reverberation Time

Onsite Tests

Acoustic Model

New Design Options

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