5.2 Performance Standards – BB93, HTM and BREEAM

Performance Requirements
The function of a space governs its acoustics requirements. Spaces which need to be quiet and where speech intelligibility is important require a low reverberation time.

BB93 ‘Acoustics Design for Schools’
Table 1.5 of BB93 provides a comprehensive list of performance requirements for educational spaces. This table is used as a benchmark for many buildings including multifunctional buildings and higher educational facilities.

BREEAM Offices
At present BREEAM Offices does not provide performance requirements with respect to room acoustics, therefore the 1 second reverberation time BB93 requirement for offices is commonly used.

HTM - Health Technical Memorandum Acoustics
HTM states that ‘Sound-absorbent treatment should be provided in all areas (including all corridors), except acoustically unimportant rooms (storerooms etc), where cleaning, infection control, patient-safety, clinical and maintenance requirements allow.

Acoustically-absorbent materials should have a minimum absorption area equivalent to a Class C absorber (as defined in BS EN ISO 11654:1997) covering at least 80% of the area of the floor, in addition to the absorption that may be provided by the building materials normally used. If a Class A or B absorbent material is used, less surface area is needed.

Acoustic absorption is likely to be needed in large open spaces such as atria, particularly in localised areas.

MACH Acoustics advises that an acoustic consultant be appointed to undertake a detailed assessment if an alternative to ceiling tiles is to be used.

3.2 Size and Acoustic Performance Requirements

The length of the NAT Vent Attenuator is a function of the required acoustic performance and the free area requirements for ventilation. If a large free area is needed, the depth of the cross talk attenuator will need to be increased. This increase in depth is required to balance against the increase in sound transmission as a result of a larger face area.

The free area of the NAT Vent Attenuator is typically between 20% and 50%. The calculated pressure drop through this product is minimal due the low air speed experienced with natural ventilation. 20% free area attenuators are used in cases where there is a limited depth for the attenuator. The drawback of this configuration is that a large face area is required to maintain the same free area specified by the M&E engineer. In this instance, the cross talk attenuator typically runs the width of the classroom, office or medical room.

The acoustic performance of the NAT Vent Attenuator is rated between 34 dB Dne,w and 39 dB Dne,w. Through research, it is seen that cross talk attenuators with an acoustic resistance of 34 dB Dne,w provide an equal performance to that of a solid partition containing an acoustically rated door (30 dB Rw). BB93 requires 39 dB Dne,w across a vent within a corridor wall, due to this limitation of the door this is seen as an over specification.

1.1 Introduction

The NAT Vent Attenuator has been designed to overcome the clashes between natural ventilation and acoustics. The NAT Vent Attenuator allows the fl ow of air into and through a building, whilst preventing the passage of sound. This product can easily be incorporated into the facade of a building, allowing for natural ventilation on all sites, irrespective of environmental noise levels. The NAT Vent Attenuator can also be used to prevent cross talk issues when implementing cross ventilation to atriums/corridors. This product can be made to comply with BREEAM, BCO, HTM, BB93 and other standards. 

The concepts and design specifi cations for this product have come from MACH Acoustics consulting experience. Our experience has shown that current products have a limited acoustic performance, are exceptionally infl exible, costly, and are lacking in technical innovation. Through frustration, knowledge and insight, the NAT Vent Attenuator has been designed and produced by MACH Products. The NAT Vent Attenuator is formed from W shaped tiles manufactured from acoustic foam. These elements are then tessellated and stacked together 11, 12 to form the NAT Vent Attenuator 13. The result is a fl exible product which can be fitted into bulk heads to allow for cross ventilation, or incorporated into the facade of a building to prevent noise break-in. 

The key features of the NAT Vent Attenuator are its patented technology based around the honeycomb structure, its novel W shaped splitter arrangement and the materials from which it is made. A simple manufacturing process delivers a cost effective, lightweight product, which is exceptionally flexible and therefore can be made to fit into a wide range of spaces and locations. The NAT Vent Attenuator is designed and manufactured bespoke for each project and tested using MACH Acoustics in-house test facilities 14 meaning that the acoustic specifi cation of this product meets the exact project requirements.