Just a Bunch of Noise about Noise?

Steven Ferry & Ulf Wolf

January 2008

If you go back far enough, say a couple of millennia, pretty much all the builder was interested in was keeping the rain out and the heat in or out.

Yes, there was a Roman architect named Marcus Pollio—we’re talking first century B.C. now—who wondered about reverberation and interference, things like that, then wondered some more, then pretty much left it at that.

Things have changed since then.

Starting in the mid-19th century, American physicist Joseph Henry took a serious look at the way sound behaved in buildings and spaces. One of the things he observed was the difference between direct sound (the sound issuing from the source itself, say a voice, or a door slamming shut), the early reflection (the sound that bounces off walls and objects in a room within a 10th of a second or so), and reverberation (what’s still alive after the early reflection).

His research, however, was not carried forward until engineers at Germany’s University of Göttingen took it up in the 1950s.

Today, it can be argued that acoustics range up there with the thermal properties and aesthetics of a room or a building. Some even argue that acoustics will soon become a major focus for our industry.

When one bids a project, the acoustics involved may not be the first thing to consider, but the correct management of sound in new construction may spell the difference between a satisfied and an unhappy customer.

Acoustics (from the Greek "to hear”), generally speaking, is the science or study of sound. Of late, however, it has come to mean architectural acoustics—how you construct an enclosed area so as to enhance the hearing of speech or music, or control noise. In our industry acoustics normally comes in the guise of "noise pollution,” "leakage,” "interference” or "STC levels.”

Buildings, when all is said and done, are used and occupied by people, and people have ears, a crucial if now-and-then overlooked fact. The correct handling of acoustics can set the tone or mood of a building, can facilitate privacy, can improve working conditions and can enhance communication.

As a rule, the worry of the architect—and sometimes even an acoustics engineer, an acoustician—spills down to the subcontractor—primarily the wall and ceiling contractor—who has to implement the architectural design successfully, perhaps even solving problems arising from poor designs. So what are the elements involved in this success?

Terms and Factors—Acoustics 101 When dealing with acoustics in construction, the following terms and factors need to be known and considered:

Reverberation. Areas or rooms that sound unfamiliar seem unnatural. That is why there has to be some reverberation in a space or it will sound dead. The time it takes for a sound to fade to one millionth of its original volume is called reverberation time. For an auditorium, you want the reverberation time to be between one and two seconds; for a living room much less than that, though still discernable.

Much of what the architect or acoustics engineer, and by extension the contractor, does is modify the anticipated reverberations. To do this he uses either sound-absorbent or sound-reflecting materials to coat the surfaces of ceilings, walls and floors, and sometimes even modifying the shapes of walls and ceilings.

Interference. Interference is caused by a difference in the distances traveled by the direct sound and its reflection and can produce dead spots in which certain ranges of frequencies are canceled out. Though more pertinent to concert halls or studios, it can have a bearing on how natural a space sounds.

STC. Sound Transmission Class is roughly the decibel reduction in noise a partition provides. If an 80 dB sound on one side of a wall/partition is reduced to 50 dB on the other side, the partition is said to have an STC of 30. As an example, a typical interior wall in a home (two sheets of half-inch drywall on a wood stud frame) has an STC of about 33.

New multi-family dwellings such as condos are now required by building code to meet a minimum STC of 50 in-between units. This is enough to block normal speech but falls short of blocking a home theater system or a loud stereo, which can reach 110 dB or more, and which could require an STC of 70 or better.

CAC. The Ceiling Attenuation Class measures how well the acoustical tile blocks the transmission of sound through the tile. The highest quality tiles offer a CAC rating in the 40-to-44 range.

NRC. The Noise Reduction Coefficient measures how much noise is absorbed when sound waves hit the surface of a ceiling tile. Tiles are available that offer NRC ratings of up to 80 percent.

The point of this is that excessive reverberation time of a room can lead to poor speech intelligibility. Consider, for example, the difference between a modern, large office meeting room (usually designed with acoustics in mind) and the traditional 1960s or 1970s classroom with hard surfaces all around. Where would you rather hold a conversation, or work?

And if you’re sitting on one side of an office wall with a low STC rating, you’ll be able to hear exactly what is going on, or worse, what is said, in the room or office next door—and two doors down if the STC is out the bottom.

There are three ways to improve workplace acoustics and solve workplace sound problems—the ABCs.

A = Absorb (usually via ceiling tile, or sometimes wall panels)—something you will come across daily.

B = Block (via workstation panels, wall placement and workspace layout)—again, you will encounter this pretty much day by day.

C = Cover-up (via electronic sound masking)—this is normally the domain of the owner once the space is occupied, and does not really concern the contractor.

Computer Aided Acoustical Design Over the last decade or so, and to underscore the importance that acoustics is taking in the construction of new buildings, Computer Aided Acoustical Design is becoming the norm more than the exception in the design of the sound landscape of critical areas, such as auditoriums, conference rooms and even condominiums—where by regulation an STC 50 should be achieved in the demising walls.

A CAAD program allows the architect or acoustics engineer to enter the exact dimensions of a room, including windows, mirrors, doors, floors—and whether carpeted or VCT [vinyl composition tile]—and ceiling design, and simulate exactly how the room will perform acoustically. The engineer can "fill the room with people” and see how this changes the room; he can add angled ceiling panels, or what some call wing walls to increase the wall surface area, to see how this will affect the acoustical properties of the room.

When this is thoroughly and correctly done, drawings and specs will more than likely achieve the exact effect desired, and if followed and implemented exactly, will make for a very pleased end user.

The Contractor’s View Seeing what acoustics is and does, and the growing importance of sound management, how do we approach it on the site?

From conversations with many contractors across the country it was found that the importance of, and attention to, acoustics is far more prevalent in high-end projects, in auditoriums, airports, schools and hospitals, than in medium-to-low range projects, although these are increasingly paying attention to acoustics, too.

Several issues surfaced for the contractors, as follows:

Responsibility: Who is responsible for the end product meeting the owner’s expectations?

The majority of those we spoke to agreed that the architect of record, or the acoustics engineer, is the responsible party.

As a Maryland contractor puts it, "Acoustics engineers design all this stuff, put it in their drawings, and I build to their design.”

A New Jersey contractor expands on this: "If we bid a job that specifies Joe Blow ceiling material, we give what’s specified, per contractual obligation, even if we know it won’t work or we think there’s a better product out there. We would never jeopardize our client’s relationship with the end user; we just do what we’re told. After 30 years of being in business, you learn not to rock the boat.”

Another New Jersey contractor agrees as does a North Dakotan: "We just follow the specs. If you start value engineering, you don’t get the bid.”

A Tennessee contractor couldn’t agree more: "The owners, the architects and the engineers are responsible, and for us to recommend would put us in an engineering position. We are not engineers.”

Another New Jersey contractor has a different slant, though: "If the documents are clear as to what they want, then that’s what they want. If we think there’s a design problem, we may offer an alternative, such as to extend the wall to the deck, leaving it up to them to make a decision. But, I’m talking private work; if it’s public work, you go by the docs.”

An Ohio contractor concurs: "If it just flat isn’t shown whether the wall should go to the deck or not, we’ll ask the question, either of the GC or of the architect. We can only bid what’s drawn, and we’ve got to get the work in order to do it.”

Another New Jersey contractor sums things up succinctly: "Really, we like to call ourselves ‘dumb contractors,’ we do whatever they tell us to do. We just completed a hospital project, for instance, where, in meeting after meeting, we argued that the walls should go all the way to the deck and be topped out. We were told, as many times, to build what’s on the plan, which is what we ended up doing. When the owner moved in, they discovered they had a sound problem, that people in the labs could hear the people next door, their television and conversations. We were forced back out to the job, and we’re still fighting it out. That’s why I say we prefer just to be ‘dumb contractors.’”

Drawings and Specs: How reliable are the architectural drawings and specs? Do they, as a rule, achieve the prescribed standard acoustically?

Generally, the answer to the question above is "yes,” but as with everything else, quality of work varies from one firm to the next.

One Florida contractor recalls, "The sound in a new auditorium was so bad during basketball games and pep rallies that you couldn’t hear the person next to you, nor understand the announcer. We had to hang baffles from the ceiling to stop the sound bouncing around.”

When asked whether tests for STC levels at the completed project ever fail to reach the specified levels, a Maryland contractor answers, "I can’t recall them failing on any job I’ve done in 20 years.”

An Illinois contractor has this to say: "I worked a medical building where all interior partitions were designed to go just above ceiling, but not to the deck, and I was concerned about the CAC and sound transfer from one room to the next. Consulting my supplier rep, he sent me a better performing tile with an STC of 45 or 55. Upgrading to the new tile we managed to keep the sound transferring between offices at an acceptable level.”

A New Jersey contractor shares this experience: "A few years ago, I worked an auditorium project. It had a floating hardwood floor, mirrors on two of the walls, a block wall, and glass windows on the remaining wall, with a 24 foot-high ceiling. The owners came to test the sound a week before moving in, only to realize the music was unintelligible. To solve this issue, we performed a basic reverberation test and found it to be more than five seconds. The solution was to mount several wall panels, which brought the reverberation down to about two and a half seconds.”

A Tennessee contractor adds, "If they provide criteria that we don’t think will meet expectations, we usually raise the flag to the general contractor. We don’t recommend a solution, however, as that would put us in an engineering position, and we’re not engineers.”

Challenges: What challenges do you run into when implementing acoustical designs?

The main challenge voiced by our contractors is coordination with other trades.

A contractor in Washington reports, "The problem is that you have doors, windows, electrical outlets … you have floors that are dirty and the sound caulking does not stick to the floors. Everyone has to do their part. If, for example, the electrician isn’t putting sound putty packs on the backs of his electrical boxes, you’re going to have sound transmitting through the box.”

A New Jersey contractor has the same issues: "Our biggest challenge is coordination with the other trades. We’ve had situations where we’ve had to place sound putty packs on the backs of electrical boxes for electricians. We don’t like to; the trade that is responsible for the penetration of the wall should be responsible for the acoustic aspect.”

One Washington contractor brings up the lack of efficient product. "We don’t have good enough products out there for what the owners really want. I think the risk is now placed on the subcontractor, who must meet the specs. You can test the acoustic properties once the job is done, and if they asked for an STC of 50, you have to deliver, and they don’t really care how you do it.”

He goes on to say, "When an architect indicates STC 50 in his wall type description, as a general contractor I would know that this wall has to run full height, even though the plans show it just going past ceiling grid.”

Acoustics—of concern or not? How great of a concern is acoustics, or should it be, for our industry?

There is no doubt that the attention of both owners and architects is being placed more and more on acoustics, especially for high-end projects such as auditoriums and lecture halls. But as sound pollution in offices and call centers is making its way toward the front pages—sometimes as a nuisance, sometimes as a health hazard, and as regulations are now specifying stringent STC levels in multi-unit dwellings, there is little doubt that acoustics is, or should be, of concern to the contractor.

A Washington contractor raises this particular flag by saying, "My personal opinion is that the next big defect claim lawsuits that our industry is going to see is sound. It’s going to go from mold to sound transmission. Why? Because when it comes to acoustics, it is very easy to prove that something wasn’t constructed properly—you just measure it. And here’s the interesting part: If you really drill down on this subject, you find what I call the new generation contracts: most subcontracts today say that the most stringent conditions shall apply. It’s really a tough one, because if you are the low bidder and you find out that there is a problem: the wall should have gone full height—even though the drawings did not show it—and you have a contract that says the most stringent conditions shall apply, then you’re liable. You have to fix it. It’s a very big topic and an interesting one.”

A Florida contractor elaborates, "The architects and acoustic engineers are going to aim for the highest possible STC and NRC. That’s the first thing for any hotel, convention center, a Disney, Sea World, Universal—any place where you have a tremendous amount of people and traffic. They’re shooting for the highest rating they can.”

An Ohio contractor adds, "I’ve recently completed several offices where they specified covering the entire ceiling with acoustic insulation, or taking all walls to the deck. Sometimes you’ll see this in schools, as well.”

A Massachusetts contractor, however, begs to differ, "We have a lot of people from the acoustical tile manufacturing business saying everybody wants this and everybody wants that. So on the right hand I hear them saying ‘Everybody wants this,’ on my left hand saying, ‘Hey, I ain’t got the money and the budget for what they think I want. I don’t want that, I want this. This is my budget.’ I hear more and more cry for money than I do for sound acoustics.”

Acoustics, as an element of building design and construction, is becoming increasingly relevant; it’s not just a bunch of noise about noise. It’s a smart contractor who studies the subject and maybe even re-examines his role or responsibilities at the bidding stage where the plans do not add up to the desired or stated result.

About the Authors
Clearwater, Fla.–based Steven Ferry and Los Angeles–based Ulf Wolf write for the construction industry as Words & Images.