coustics is a key part of what makes a great building great. Each building has its own unique acoustical personality made up of a combination of such elements as physical volume, sound reﬂection, absorption, reverberation, background sound from mechanical systems and outdoor traﬃc, and noise from occupant activity.
If you close your eyes as you stand inside a building, your ears will receive the sounds of the building, but what you hear depends a great deal on how you listen. Good acoustics are not just dependent on physical characteristics. Rather, they depend primarily on the activities for which the space is designed and the expectations of the listener — this makes the challenge of achieving “perfect acoustics” a very diﬃcult one. Perfect acoustics in a concert hall are very different from perfect acoustics in a library. In one, you want to be able to hear a pin drop, but certainly not in the other. Perfect acoustics in a concert hall are also very diﬀerent from perfect acoustics in a lecture room, and for good reason. Speech is very diﬀerent from music—and there are as many variations of music spaces as there are types of music. How can we manage these challenges to create spaces with superior acoustics?
Aesthetic opinions and qualitative factors figure strongly into the success of music halls, giving acoustics the reputation of being like the quest for the elusive Holy Grail. This unfairly lends a sense of unreality or chance to a person’s perception of acoustical design. Incomplete paradoxes (if a tree falls in the forest…) just add to the confusion.
In fact, Acoustics is a well-deﬁned science. The ﬁeld of acoustical engineering has developed reliable quantitative criteria, calculation methodologies, and design rules for most acoustical situations. The ﬁeld continues to advance rapidly through both physical and psychoacoustic research. All our spaces deserve acoustical consideration or they can become cold, unfriendly, or unwelcoming. You know those places without closing your eyes!
As technologies advance and building performance expectations change, acoustical engineers are constantly faced with new challenges. In many cases, these challenges are the result of advancement in the eﬃciency and sustainability of new buildings.
LEED sets out a design process with goals of energy eﬃciency and sustainability. This rating system encourages a team approach, awarding points for meeting LEED goals in the ﬁnished design. Since most elements of design and construction are open to interpretation, there can be great LEED designs with good acoustics, and great LEED designs with poor acoustics. The diﬀerence lies with how acoustics are considered in the design process. Scoring LEED points without considering the acoustical implications can result in some fairly signiﬁcant acoustical challenges. For example:
Allowing natural light to penetrate deep within a building suggests the use of light wells, atria, openings in partitions, or large areas of glazing. But in addition to light penetration, openings also allow the propagation of occupant sound from place to place, which can be particularly problematic for mixed client groups or those who need high levels of privacy or conﬁdentiality. The size of glazed areas can also be a problem. Large glazing areas can result in excessive reverberation and occupant noise if not addressed through the creative use of sound absorbing acoustical treatments. The challenge can be compounded if the design includes hard panels or areas of exposed concrete for thermal mass or radiant heating/cooling. Hard surfaces mean sound reﬂection, not absorption, resulting in more reverberation, poor acoustics, poor privacy, and workplace distraction.
Passive heating and cooling or the use of radiant surfaces reduces the need for variable volume, fan-driven systems to control temperature. These systems supply the basic ventilation needs with a more constant volume and with higher energy eﬃciency, with the result that HVAC systems are signiﬁcantly quieter than those designed in the past with the level of background noise reduced to below sound masking levels.
But energy-eﬃcient HVAC systems can also create poor privacy in the oﬃce environment, particularly if ceilings are hard surfaced, oﬃce partitions are low and ﬂoors are tiled. To minimize this eﬀect, radiant perimeter panels, which are generally installed before the interior partitions may be carefully co-ordinated to ensure privacy is maintained. In residential applications the use of a central heat recovery ventilation or energy recovery ventilation (HRV, ERV) system means that washroom exhausts return to a common heat or enthalpy wheel in the AHU/heat exchange system. This may result in common exhaust ducts, which provide an acoustic conduit between suites and hence compromised privacy requiring cross-talk noise control. Note that there are also versions of the concept where the equipment is dedicated to the suite, so that there are no common ducts.
Consider the similarities of an open oﬃce and a library. Are libraries quiet? It’s a question of terminology. When acousticians say that a library is quiet, we are really saying that patrons can enjoy the space free from distraction. A reasonable level of “good sounding” background noise oﬀers freedom from distraction. In a library, you really don’t want to hear every page turn, just as, in an oﬃce, you don’t really want to hear what everyone is say ing. Another consequence of the growing prevalence of open oﬃce environments is that most people must learn to adopt an “oﬃce polite” speech level, and understand that speakerphones are not acceptable unless used behind closed doors. As a result, sound masking systems are becoming an integral part of oﬃce design. In fact, recent research conducted by the National Research Council recommends that sound masking systems be considered as one of the essential elements of open plan oﬃces. At this point in the ongoing development of LEED, sound masking systems are not credited with a point score except in heath care facilities.
The trend toward including lightweight building materials in design projects (condominium buildings in particular) can result in less sound reduction and more noise intrusions. This may apply to the building envelope, with large areas of curtain wall, as well as to interior wall partitions and ﬂoor/ceiling assemblies. Outdoor noise from trains, aircraft, buses, and other vehicles can cause audible intrusions, while indoor noise from home theatres and audio systems can be particularly problematic. Bass sounds are the hardest to control, as there is no real substitute for mass. The sound transmission class (STC) rating of a masonry and a drywall construct may be the same, but the low frequency sound transmission through drywall is greater, a factor building codes do not address. Similarly, impact isolation (footfall or impact noise) is not directly addressed in building codes or LEED guidelines. It is worth remembering that even in well-built condominium units, which meet all code requirements, good neighbours are quiet neighbours.
Be careful of manufacturers’ claims that seem too good to be true. There is no such product as acoustical paint. Claims of acoustical performance should be supported with test results from an accredited acoustical laboratory like the National Research Council in Ottawa or several in the USA. Sound Transmission Class (STC), Impact Isolation Class (IIC), and Noise Reduction Coeﬃcient (NRC) data are reliable if tested using ANSI Standard test methods. If the product does not come with supporting acoustical data, you should ask for it. Most auditoria, lecture theatres, or other spaces where speech must be audible at a distance are provided with sound systems for A/V purposes and designed with the potential to provide some voice lift. It is important to be careful that good natural acoustics are not overlooked because of an over-reliance on such electronic supports.
The natural acoustics of the space should not be forgotten during the design process because sound systems are designed to complement existing room acoustics rather than ﬁx acoustical problems. There are at least two possible negative outcomes from an overreliance on these systems. First,if a room is too reverberant, a sound system will not function well. It will add to the reverberation and eﬀectively make matters worse. Second, if a lecture room or classroom is designed with too much absorption and not enough suitably-placed reﬂective surfaces or appropriately low levels of background sound, the teacher’s voice won’t be heard. This results in sound system reliance with a number of shortcomings. If the class can’t hear the teacher without a sound system, the teacher can’t hear questions from the class. Many persons are intimidated or technically challenged by using microphones and adjusting their volume, etc. Sound systems are designed for people with normal hearing and do not compensate for hearing loss, which aﬀects perhaps ten per cent of the population. In many jurisdictions, building codes require Hearing Assistive Listening systems for public buildings with large occupancies.
This blog has addressed a few of the factors that aﬀect the acoustical character of a building and the acoustical challenges we face as architects and engineers. The LEED rating system, like several others, provides a framework within which the design process can proceed in a manner that respects Green and Sustainable principles. By including an acoustical engineer on the design team some pitfalls may be avoided along the way, leading to more consistent and satisfactory outcomes, and possibly an innovation credit.