Acoustics and the built environment: Have our Ears Changed?
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Acoustics and the built environment: Have our Ears Changed?

Acoustic Design, Construction
On an evolutionary scale, it is only recently that we have developed technologies and architecture that allows us to change our immediate environment so significantly that it can have little in common with our original living conditions. This has had an effect on every factor that determines our level of ‘comfort’; however for now I will focus on acoustics, and more specifically, noise.

We can all agree that the natural environment is much quieter than modern man-made environments, and exposure to this increases our daily sound ‘intake’ to a level much higher than what our ears (and brains) have been designed to.

The US National Parks Service have produced a pair of noise maps that predict sounds levels across the US separately for natural noise and man-made noise (https://www.nps.gov/subjects/sound/soundmap.htm). We can see that the scale of noise level across the map from natural to man-made is increased by up to 27dB, with the noisiest areas predictably in city centres.
Acoustics and the built environment: Have our Ears Changed?
Predicted ambient noise levels without man-made noise 

Acoustics and the built environment: Have our Ears Changed?
Predicted ambient noise levels with man-made noise

What is most interesting about these noise maps is when we compare these noise levels to standard guidelines for internal living conditions. Predicted noise levels for the natural environment fall below 30-35dB(A) across the US, and when we compare this with good internal noise levels for resting and sleeping, we can see that there is a strong correlation. Does this perhaps mean that as a species our ears have not yet adapted to our new noisier environment? If so, what impact does this have on our health?

BS8233 and WHO guidelines for good internal noise level

Although exposure to extreme noise levels is universally agreed to cause hearing damage, the effect of prolonged levels of medium/high noise has not been fully agreed upon. Multiple studies link high noise levels to hypertension and decreased performance in education (Stansfeld & Matheson, 2003), whereas others have also shown links to ischemic heart disease (Passchier-Vermeer & Passchier, 2000). 
Either way, high noise levels will not have a positive impact on occupant health, and so the impact of this is a serious consideration to make when considering the design of your building.
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Deconstructing Construction Detailing – easier to use than to say!

Construction, Web based design tools

The MACH Acoustics construction detail finder is an innovative new free online tool that allows the design team to instantly obtain suitable lightweight construction details.  The simple to use navigation system allows the user to first select the approximate level of sound reduction they require, and then the type of detail needed (head/roof, plan and foot/screed).  The user then indicates a frame, soffit and/or ceiling type (when applicable) to find a specific detail.  The image can be downloaded, and the process repeated, quickly building up a selection of details in a matter of minutes.
 
The construction details of floors, walls and junctions in a building are critical to its acoustic performance.  It is important to consider that sound not only transmits direct through a wall, but also through flanking paths around the partition through adjacent walls, floors, ceilings, junctions and penetrations.  Inattention to these details can seriously degrade the level of sound insulation from room to room, leading to unexpected poor performance in pre-completion testing, occupant complaints and the requiring of remedial work.  On the other correct detailing can ensure a level of performance equivalent or better than design targets, giving an excellent acoustic environment.  In some cases this will even lead to cost savings by value engineering of wall and floor types, in the knowledge that the risk of flanking sound transmission has been minimised.

 

 

Deconstructing Construction Detailing - easier to use than to say!


This tool is in development and we are open to all comments and suggestions to help improve the way that we work with our clients.

  

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Chris cuts though the jargon of Rw and Dw

BB93, Construction
Rw and DnTw – Knowing the Difference can Save You Money
A common confusion in specifying wall types for a building lies in the difference between Rw and DnTw.  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
DnTwis 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 DnTwvalues.  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). 
Rwis 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 Rw to DnTw 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 RW = DnTw + X dB.  The RW can vary significantly between partitions, even if they require the same DnTw.  Figure 1 summarises this.
Chris cuts though the jargon of Rw and Dw

Why does the RWvary when the DnTw is the same?
How does this Help?
Clearly from Figure 1, if the same wall type Rw (say 45 dB) is used everywhere the DnTw is 40 dB, there will be rooms that fail.  On the flip side, if the most onerous requirement of 53 dB RW is used for all 40 dB DnTw 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 RW, not simply the DnTw. 
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.
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Case Study – London and West London Acadamies

Architecture, BB93, Case Study, Construction, Cross Ventilation, Eco Buildings, NAT Vent Attenuator, Vented Facades

London and West London Academies, two large £30M+ Academy are both designed around a natural ventilation, incorporating cross ventilation. Both schools were required to meet BB93 and BB101 ‘Ventilation of School Buildings’. MACH Acoustics worked with Fosters and Partners to develop a practical solution. Our findings were that the cost of conventional attenuators along with their size and short falls in performance prohibited the use of these devices but allowed for the NVA.

The academies featured many different imaginative implementations of the NVA as a cross ventilator, all venting into a central atrium. Air passed though the facade via actuated windows through bulkheads at ceiling height containing the NVA.

Case Study - London and West London Acadamies
The main principle was to add an attenuator with 25% free area and a face area of 1.5m2, with small splitter sizes.  The attenuator was to be located above a cupboard spaces as shown below. A flap enable the vent to be opened and closed.

Case Study - London and West London Acadamies
Case Study - London and West London Acadamies

One of the main advantages of the NVA is the ease and simplicity of installation. Once the bulkhead has been constructed, the tessellating foam is arranged into honeycomb pairs by alternating orientation, then simply slid into the duct. Since the foam is malleable and can be cut, fitting around building services or any on-site alternations can be easily achieved. Installation generally takes under one hour – saving money and construction time.

With the window facade bulkhead, we were able to implement cost savings by negating the need for expensive weather louvres, using actuated windows instead. Not only was the cost significantly reduced but the installation was greatly simplified – both points highly valued by the contractor. 

Case Study - London and West London Acadamies

Click the preview below to download the complete case study
Case Study - London and West London Acadamies


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Welcome to MACH Acoustics Blog!

Architecture, Construction, Eco Buildings, Exhaust Stacks, Sustainable Acoustics, Ventilation Systems

The aim of MACH Acoustics is to become one of the leading acoustic consultants in the field of sustainable building design. This aim means that we specifically focus on projects around sustainable architecture and Eco buildings. A considerable portion of our time is therefore spent looking to solve some of the conflicts between acoustics and low carbon, sustainable constructions.

Acoustics and sustainability are not often spoken about together. On the other hand, air conditioning systems are often used to overcome noise ingress issues. Thermal mass cooling; exposed concrete soffits for example, can make buildings sound loud, harsh and noisy. Cross ventilation, exhaust stacks and other air ventilation systems can compromise the acoustic cross talk between office buildings accommodation and teaching spaces within educational buildings. Vented facades in combination with ventilation louvers and other types of air ventilation systems within the fenestrations of a building are often used to prevent noise ingress. Buildings are often built using high mass structures to achieve acoustic requirements.

These factors clearly show the link between acoustics and sustainability. Acoustics can therefore have a significant impact upon the levels of carbon emissions, ventilation system and the level of embodied energy in the buildings frame and other factors affecting the sustainable architecture of a given building. With changes to Building Control Documents Part L and Part E, along with new client expectations, there is an increasing importance to ensure that building designs become more integrated and greener.

MACH Acoustics view is that the best way to overcome the limitations imposed by acoustics on sustainable buildings is to increase our knowledge base. This simple goal is therefore the aim of this blog. We aim to provide a point of reference where detailed information will be regularly uploaded relating to residential buildings and the code for sustainable homes. We will be looking at Eco buildings and acoustic materials which match requirements for sustainable building design. Ventilation systems including vented facades, acoustic ventilation louvers, attenuators within facades, passive house systems, heat recovery systems, exhaust stacks and other air ventilation system will be discussed over time.