Sound Advice: Acoustical Design Matters
By Sita Lakshminarayan
In the practice of architecture, thousands of details must harmonize to form the big picture of how a building is both perceived and experienced by its users. The physical layout of the space, the codes and regulations, the mechanical systems, the types of furnishings – it is the architect’s job to oversee all of these considerations and many more. But one detail that is particularly difficult to conceptualize is how the building will sound. Much of today’s work thrives on interaction, collaboration, and flexibility to achieve innovation. Offices, schools, healthcare facilities, and public spaces are constantly evolving to suit different work requirements and to ensure acoustical comfort of occupants. As designers we cannot know enough about how to reconcile these varying requirements.
With this in mind, I invited Andy Miller to join me for a conversation about the profession of acoustics and how architects and acousticians can work together to design better, more functional spaces. Andy is an Acoustician at BAi, a firm that was founded in Austin in 1935 and continues to provide top-notch acoustical consulting services throughout the world. Below are the excerpts from our conversation, which took place within the 100-year old building that houses the Austin office of BAi.
Tell us a little bit about your background and how you got into the field of acoustics.
When I was small, I was always very interested in playing with radios. There was this one time when my grandparents had some delinquent tenants in one of their rentals, and they had to kick them out. The tenants trashed the place, but they left a whole bunch of audio gear behind. So I inherited a bunch of speakers and stuff that was audio related. It’s funny – you look back after you’ve been in a profession and you see all the things that got you there along the way, but none of it seemed like a big deal at the time. Even the science projects I chose along the way – a lot of them related to acoustics, but I didn’t even really know I was on that path.
When I got to college, I went into architecture and engineering. At the University of Kansas, I met and really got along well with the acoustics professor there, Bob Coffeen. As it turns out, he learned acoustics from Dr. C.P. Boner, the father of the current owners of BAi, Charles Boner and Richard Boner. So BAi just happened to have a guy who left the company, and I came and took that spot.
What motivates you about this profession?
Everything I get to work on from the acoustics perspective seems to be the most interesting aspects of the project, to me at least. So that’s a pretty good motivator. With acoustics, there are a lot of subjective and objective things just sort of crashing together – and we must find the balance in that. And I love that about it. There’s something about that blend of physics and art.
What kinds of things in general are you concerned about in a building?
We take a holistic view of architectural acoustics. Within that broader topic are several key areas of focus:
Room acoustics – which are influenced by the shape and the volume of the room
Noise control – which is related to the building systems, including HVAC, plumbing, and electrical
Sound transmission control – which is all about the constructed assemblies (walls, floor ceiling assemblies, windows, doors, etc.) and how well they block sound
Large spaces requiring amplification – where we look at how to design the sound system and balance that with the acoustics of the space.
All of these things influence one another. For instance, if you lower the background noise level, suddenly you need thicker walls to block the sound transmission and keep it from being audible in the next space. The lower the background noise level is, the easier it is to hear something. If it is a reverberant room, such as a mechanical room, suddenly you have to take into account more sound and increase the wall thickness to keep it from bleeding through, unless you’ve got some soft stuff on the walls that absorbs noise and brings the noise level within the room itself down.
Has the enforcement of the ANSI Standard (S12.60-2002) as a pre-requisite credit for LEED for Schools set a sufficiently high baseline for desirable acoustical quality in learning spaces?
Yes and no. The ANSI Standard is a really well written and well researched standard. I know all of the authors of the standard and I participate in the quality reviews of that standard. As a baseline or reference document for the LEED for Schools criteria, it is very good. However, if you only look at the LEED for Schools requirements, you will miss some things because it doesn’t elaborate on what it does and doesn’t address.
The ANSI Standard uses standard metrics to define what the criteria should be. Standard metrics include a very limited range of frequencies within our full range of hearing. Humans hear from about 20 hertz up to about 20,000 hertz, but the majority of the standard metrics address from about 100 hertz to about 4,000, so it is just a very small range.
Things the ANSI Standard doesn’t address fully are things like music education spaces, core learning spaces with unique considerations such as special education, and locations near mechanical equipment. When you’re designing a wall or floor near a space like that, if you’re just going by the STC, then you will end up with a really unbalanced sound in the classroom next to it. So, there are things you have to be careful about. When we are making recommendations, you’ll find that we’re hitting the STC-50 requirement but we’re probably going beyond it in a lot of instances because we’re trying to address things that the STC doesn’t address.
Should building codes and ADA make the move towards incorporating and thereby enforcing ANSI Standard (S12.60-2002)?
That’s a really interesting question. From an ambient noise perspective there are huge benefits of the ANSI Standard, not just for those with hearing disabilities (which is what ADA would point to), but for everyone. For example, if they were to make this part of the ADA there would be a huge benefit for young learners, for whom it is very important to have a low background noise level. These little kids don’t have a lot of experience and context to fill in blanks that older people have. When they are in an environment where they are learning new things and hearing new words, if the noise level is high enough to mask even part of those new words, they will try to fill it in with context that they do have. Kids in noisy environments have difficulty learning, which increases their stress level and causes them to get exhausted more quickly. There’s also the physiological aspect of it, where subjecting them to higher noise levels increases behavioral incidents. If they can’t hear the teacher and they can’t pay attention, they won’t – and they’ll look for something else to do.
But this runs contrary to how mechanical designs are typically done. A lot of times they will spend more time focusing on the mechanical design of a high school or a college building than they will on an elementary school building, when it is probably more critical to get the background noise level right with the elementary school building. There have been several studies done that show correlation between ambient noise level, reverberation, and performance in the classroom.
School districts are moving towards flexible learning spaces in the approach towards 21st century learning spaces. Classrooms are being designed with movable walls and are opening into commons spaces to allow for team teaching and multiple learning opportunities. How can architects ensure acoustical consistency in each learning configuration?
It is, in some ways, a move back to what architects were doing in the 60s and 70s with the open plan school. We seem to be moving back that way, but with a twist. Of all the older open plan schools that I’ve encountered, they’ve gone back and built partitions between classrooms to address all of the acoustical challenges that came with the open plan. Now we’re seeing a lot of the same challenges to address, but architects are looking at accommodating those challenges with things like movable partitions. There are many more acoustical systems available now than there were back then. So while it is difficult to use movable partitions and meet the classroom acoustics standard, sometimes it is worth it for the flexibility that it gives for the paradigm shift in teaching.
At Round Rock ISD’s Elsa England Elementary, I did a little informal poll with the teachers to see how they were doing their teaching. A lot of the teaching I found is Internet-heavy and research-heavy. The kids are discussing what they were learning, rather than getting the information from the teacher verbally. In that case, when they are not getting the information for the first time during the discussion, the students can tolerate a little bit more ambient noise because they already have the context and are familiar with the information that they are discussing. Of course not all schools operate that way; some are more traditional where the teacher is still lecturing.
Most of the building acoustics are related to volume and surfaces. When we open up the movable partitions, we now have larger openings into to the commons space. What should we be doing on the floor and ceiling?
The acoustical challenges with these common spaces are sound transmission control and reverberation. When you open these spaces up, now suddenly it is a much larger volume. It’s very tempting for the architect to go really high with the ceiling in those common spaces. But as long as that ceiling is low, it won’t behave like a larger volume. The higher you go with the ceiling, the more the walls influence what you hear in the space. When the walls start to influence the acoustics, you have to start looking at treatment for those, and that treatment can be very expensive. It’s probably four times the cost of an acoustical ceiling.
Of course, the natural light you get from higher ceilings is also immensely important in the learning environment. So this is where the architect really has to take the reins on a project. You can get out of control with acoustics, or illumination, or anything – if the emphasis isn’t balanced. The architect must gather input from all of the consultants and use that information to turn it into something amazing. At the end of the day it is about the people who are using the space, not the people who are designing it.
What are the most acoustically neglected areas you most commonly see in a typical school building?
Speech pathology rooms are really acoustically important, but for some reason they just seem to get shoved into the basement. These are rooms where they are trying to teach students who probably have hearing difficulties, and definitely have speech difficulties. The tendency is to say well, it’s a really small room so that’s not hard to deal with. But usually what I find is that those rooms get put near something noisy or they end up with no treatment on the walls. You end up with an environment that is fairly difficult to teach in. Those rooms should always have acoustical wall panels on at least two adjacent, non-door walls, and the middle of the panel should be about where the ears and mouths are when they are working.
Gymnasiums and cafeterias are also neglected a lot. OSHA says if you are at or over 85 decibels for 8 hours, it’s a hazard. At 90 dBA, that duration drops to about 2-1/2 hours. A cafeteria is one of those places that if you don’t treat it well acoustically, then you should be handing out earplugs when the kids come in. I recently measured an elementary school classroom seating 800. It was half full and at about 90 to 95 dBA. When you do acoustically treat it well, the noise level comes down a significant amount, to more like 75 or 80 decibels. OSHA considers that safe for a full day of exposure. Also, if levels are at 85 dBA for any amount of time, employers should be implementing a hearing conservation program where they monitor the noise.
What has been your most challenging or exciting project?
The AISD Guerrero Thompson Elementary School was exciting because they decided to pursue the enhanced acoustics credit within LEED, which is not very common with school projects. We had a really good team that was really listening to each other. We came up with really good solutions to a lot of challenges, and the result was outstanding. The acoustics approach was the way we like it to be – holistic. We looked at the “big picture” – teaching methods were well-investigated and well understood (which greatly impacts the classroom acoustic design). Mechanical systems were designed and implemented in a way that resulted in balanced and well-controlled background noise. Large spaces were designed to manage reverberation. Even site noise influence on each classroom was investigated thoroughly. That was AISD’s first LEED Silver project. It was really rewarding to be a part of that.
I also had the opportunity to work on the new School of Music for the University of South Florida. That was a very exciting project. Within a few months of the concert hall opening, the choral group Seraphic Fire made a recording in there and was nominated for a Grammy. It was very cool to be a part of that. That project was very interesting and very exciting because we were able to do a lot of things we don’t do everyday. It’s the kind of project where acoustics was the #1 thing.
To me, any project where your field is an afterthought is not much fun to work on. On the flip side, any project where you have a design team that is listening and talking to one another – that is an exciting project.
BLGY would like to thank Andy Miller and the staff at BAi for their time and careful consideration of this subject matter. You can learn more about BAi by visiting their website.
ANSI – American National Standards Institute; a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States
ANSI S12.60-2002 – Also referred to in this article as “the ANSI Standard,” this particular standard applies to acoustics in the classroom
LEED – Leadership in Energy and Environmental Design; a program run by the United States Green Building Council aimed at improving performance and sustainability of the built environment
OSHA – Occupational Safety and Health Administration; the arm of the federal government that is responsible for ensuring safety and health protection in the workplace
STC – Sound Transmission Class; a rating of how well a building assembly mitigates sound