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Chapel Hill Road, Raleigh, NC 27607. This is actually in Cary at Exit 290 on I-40.
St. Paul's Catholic Church, New Bern
Classroom Acoustics Standard Now Available Free
Condos – Many Problems Out There - BEWARE - As reported a couple of issues ago the condo market is booming. However, we are seeing many built without good guidance on acoustical issues and this is creating serious problems. The most serious is floor-ceilings that do not meet the basic building code requirements for IIC rating. Such problems are extremely difficult to fix after the building is constructed as impact isolation must be designed into the heart of the floor structure. Tearing into structure after a unit is occupied means relocating people. Getting the materials in and out can be very difficult. Raising a floor to add materials creates problems with doors and counter heights. You might have difficulty getting fire approvals for a design that has never been tested.
Much of the information available from suppliers of materials can be misleading. Some test results may be the best ever achieved with a design and not representative. Laboratory results can differ greatly from expected results in the field because laboratory results do not include flanking of impact sound into walls. Wood-frame structures behave very differently from concrete structures. Some products that can work with concrete structures do not work on wood frame. In one case recently after noticing a test result that was unbelievably good, we questioned the test lab which was embarrassed to find they had forgotten to mention that the system was tested with a ceiling below the concrete slab. The people selling the product did not know enough to recognize something was wrong. Most test data is for either wood-frame or heavy concrete construction. Risk is greater for any other structure type due to lack of information.
The features that provide acoustical quality are not visible or immediately noticeable by a potential buyer. However, those buyers expect the acoustical quality to match the visual quality they see. Reducing the money spent on acoustical isolation is false economy and very risky. We strongly encourage developers and designers to consider their floor-ceiling designs carefully and get independent advice before construction.
Residential Sound Isolation – It’s in the Building Code - We continue to find architects unaware that minimum requirements for sound isolation between residences in multifamily structures are specified in the Building Code. See Section 1206 in the 2002 NC Code. This requires that walls and floor-ceiling structures between dwellings and other dwellings or public/service areas in the building must use designs expected to test at least STC 50 and for floor-ceilings IIC 50 in laboratory tests. Further, the design and construction must be such that results tested in the field after construction including any flanking present will not be more than 5 points less. Be careful in selecting designs based on limited test results since a given design will regularly give results over a range of +/- 2 dB and sometimes more in multiple tests. Some manufacturers publish the highest results ever obtained instead of representative expected results. Also, recognize that achieving the IIC results requires some kind of cushioning agent under hard floor surfaces and in the case of wood-frame structures, batts in the ceiling cavity and a good resilient mounting of the ceiling. Also, these code requirements must be viewed as minimums and not as desirable results. The acoustical design should be of a quality that matches the rest of the structure.
Specifying Sound Isolation – STC is not enough - While the STC of a wall is necessary information for the design of good isolation, the specification and achievement of such requires much more. Specifying STC does not assure good isolation. Isolation depends not only on the sound blockage ability of a partition but also control of sound getting around that partition (flanking), and the relative size of the partition and the amount of sound absorptive material in the spaces. The Noise Isolation Class, NIC, is easily measured in the field and gives an evaluation of the overall isolation actually perceived. Specifying STC alone also can lead to intentional or unintentional use of unrepresentative test results showing higher than expected performance. Designers should identify a wall design that is required after reviewing all available test data and the particular conditions of the project, and then specify the actual construction of the wall along with appropriate details to control flanking.
Pioneers in Acoustical Sales in North Carolina - Many people have been involved in the sales of acoustical products in our area but a few distinguished themselves through their support of the acoustics community. In the 1960’s Ed McKee with Lee Associates represented Bruel & Kjaer, the premier acoustical instrument company selling precision sound level meters. He became active in the NC Chapter of the Acoustical Society and its President. When he left for another career in the early 70’s, he was succeeded by John Held. John had grown up in DC, but was in Massachusetts working for General Radio, the major US manufacturer of sound instrumentation. He took over and then bought out the NC territory of Lee Associates, expanding to carry a wide variety of both acoustical instrumentation and noise control materials, serving primarily the industrial markets. He became active in the Acoustical Society Chapter and was quickly elected President. He has been active ever since and still serves on the chapter board. John retired several years ago and his dedicated professional service is missed. John has a strong interest in railroads and model railroads. One of the major materials companies John represented was first Consolidated Kinetics, then Peabody Noise Control, and today is Kinetics Noise Control. While John served the industrial market, Ed and Allen Tudor set up Southern Kinetics representing these same companies to serve the architectural market. Ed was based in Raleigh, and Allen in Virginia. Ed was always referring his customers to acousticians for help and provided financial support to the acoustical society chapter though he was not active in it. Ed passed away several years ago and Allen continues to serve the southeastern Virginia area.
Origins of Acoustics in the Region- 1940’s-50’s - Over the next few issues we will discuss some of the pioneers who laid the groundwork for acoustics in the Carolinas and Virginia. This time we concentrate on the 1940’s and 50’s. The earliest work we know is that of the Acoustics Branch of the NACA (now NASA) Langley Research Center in Hampton, VA headed by Harvey Hubbard. Early efforts involved silencing propeller aircraft for use on reconnaissance missions. In Blacksburg, Bert Kinzey a young organist and professor in architectural engineering at Virginia Tech was getting interested in architectural acoustics. He would leave to start the architectural acoustics program at the University of Florida, but has recently returned to Blacksburg in retirement. In the early 50’s, a young Bill Manson had graduated from Virginia Tech and joined his father’s business that had started installing tin ceilings in 1915. Bill recognized the importance of acoustics, participated in the first BBN-MIT summer class in acoustics with Leo Beranek, and joined the Acoustical Society of America. Up until this time if you wanted a sound system for a church or auditorium, you went to RCA, the Bell System, or one of a small number of other loudspeaker manufacturers. However, in the late 1950’s, Long Engineering in Winston-Salem became one of the first of a new breed of independent sound systems contractors who could design and install a system using components purchased from various suppliers. The Bell System established a major development and manufacturing presence in the Triad area that included Bell Labs and Western Electric specialists in underwater sound. In Raleigh, two young engineering students were completing their undergraduate degrees without realizing they would quickly in the next decade become involved in acoustics and begin to bring many others into the field.
Book – Sound Ideas, Acoustical Consulting at BBN and Acentech, By Eric Wood and Deborah Melone, order from Acentech, Inc., 33 Moulton Street, Cambridge, MA 02138, $25
This book may have a limited audience but some of us find it intriguing. In the late 1940’s the United Nations approached two young acousticians who had become well know for their work during WWII, Richard Bolt and Leo Beranek. The UN was planning its new building in NY and recognized the need for acoustical guidance. Bolt and Beranek saw the need and opportunity to form a firm for consulting in acoustics. They took on three other partners including their student Bob Newman and formed the firm of Bolt, Beranek, and Newman. They had almost no competition and their firm grew to hundreds of people being the vast majority of all acoustical consultants in the world in this one firm in the 1950’s. Offices were opened around the country, and in 1961 the firm went public and became listed on the New York Stock Exchange. Along the way they became pioneers in the use of computers, buying the first computer made by Digital Equipment Company. They developed the modem, time sharing of computers, the beginnings of the Internet, and email including the first use of @.
This book is primarily about the acoustical consulting business and the people who built it and continue it today as well as those who now head other acoustical consulting firms. It is told as a series of recollections by several of these people. As might be expected, this results in a lot of repetition so the book could be edited heavily without much loss. This repetition and the listing of people over and over gets tedious. However, it is worth it for some for the little tidbits of history on how various projects led to what is the basis of most acoustical consulting today.
One of their employees, JCR Licklider , a past president of the Acoustical Society of America, convinced the US Defense Department that a network of computers around the world could and should be built. When they went to find someone to build the network for the first four sites, all the major potential contractors declined the job. The Army asked Licklider who could do it and he suggested BBN. Thus, this little acoustical consulting firm built the beginnings of the internet. As might be expected, the computer and internet business became larger than the acoustical consulting business. Eventually, many of the acoustical consultants left to form their own firms, and most of the remaining acoustical consulting business was spun off into a new employee owned company, Acentech. Those interested in the beginnings of the internet should read the book Where Wizards Stay Up Late: The Origins of the Internet by Katie Hafner and Matthew Lyon.
NEWSLETTER
Our Latest
Issue 19 Winter 2008 Posted March 14
Issue 18 Fall 2007 Posted December 5
Issue 17 Summer 2007 Posted September 6
Issue 16 Spring 2007 Posted May 4
Issue 15 Winter 2007 Posted February 27
Issue 14 Fall 2006 Posted December 6
Issue 13 Summer 2006 Issue 12 Spring 2006 Issue 11 Winter 2006
Issue 10 Fall 2005 Issue 9 Summer 2005 Issue 8 Spring 2005
Issue 7 Winter 2005 Issue 6 Issue 5
Welcome Chris Barnobi We are pleased to introduce another addition to our staff. Chris Barnobi is a senior in mechanical engineering at N. C. State from Charlotte with a desire to become an acoustical consultant. Though the faculty has told us that seniors these days typically will not take graduate level classes or classes beyond what is needed for graduation, Chris is doing both. He is now taking the second graduate level theoretical acoustics class. He will be assisting us in some project work developing EASE models for room acoustics.
Chris Steve
Welcome Steve Stulgin -We are pleased to announce the addition of Steve Stulgin to our staff as acoustical analyst. Steve is a graduate of the acoustics program at Columbia College of Chicago, a student of professor and acoustical consultant Dominique Cheenne, Ph.D. This is a unique undergraduate program specifically designed to train students to work in acoustical consulting firms. While this program does not provide an engineering degree, it provides a concentrated set of courses in applied acoustics and noise. The program concentrates on building acoustics and environmental noise and Steve has strong interest in both areas. Steve is a native of the Chicago area and a golfer who looks forward to our milder winters.
LEED for Schools - There is now a special LEED certification program for schools that offers points for achievements in good acoustics. The program is tied into the ANSI standards for classroom acoustics which is available free here. To qualify for the LEED certification, the school design must first meet the standard for reverberation time in the classroom. This is easily done by putting the ceiling at 9 feet and covering about 85% of it with an NRC 70 ceiling panel such as the ones available at low cost especially for classrooms. Higher ceilings require greater effort. The classrooms also must meet the requirements for STC 50 walls and floor-ceilings between classrooms and to the exterior. There are some important exceptions to the classroom acoustics standard that still allow the LEED certification: STC 35 windows can be used without limitation on the size, the floor-ceilings do not have to meet IIC requirements, and the HVAC and outside noise intrusion limit is 45 dBA which is quite loud for a critical listening environment. Additional points can be achieved by getting this down to 40 or 35 dBA, the objective in the standard. If the design achieves one of these lower levels in the classroom, then an additional point is available for getting playgrounds down to 55 dBA, and all other school grounds including playing fields down to 60 dBA. It is not clear exactly what these limits mean. It would be most reasonable to apply them to average levels measured without people present, but it leaves questions about whether loud areas immediately adjacent to roads would disqualify a site. Finally, an additional point can be achieved by requiring use of vacuum cleaners, carpet and rug cleaners, floor buffers, leaf blowers, and lawn mowers that produce less than 70 dBA and meet other non-acoustical requirements. It is not clear how the 70 dBA is to be measured.
Green Guide Credits for Health Care Facilities - The Green Guide has introduced a two-point credit (GGHC v2.2 Environmental Quality Credit 9) addressing acoustics in health care facilities. The credit references the 2006 AIA/AHA Draft Interim Sound and Vibration Design Guidelines for Hospital and Healthcare Facilities and follows their organizational structure. The approach advocated by both the Green Guide and the AIA/AHA Guidelines favors acoustical control both at the source and in areas impacted by unwanted noise. The resulting design should, at a minimum, address the following categories: (1) Exterior Noise, (2) Acoustical Finishes, (3) Room Noise Levels, (4) Sound Isolation, (5) Paging & Call Systems, and (6) Building Vibration. For more information, register at www.gghc.com, log in, go to downloads, and look for the technical brief on acoustic environment.
On Allowing Suppliers to Write Specifications – Music Suites -We have found that designers sometimes allow suppliers to write specifications for various parts of a building design. Caution must be used when doing this. A supplier will typically write a specification to favor his products or even to exclude competition. Sometimes it is possible to modify what they have done to allow competition. However, if you are not familiar with all the characteristics of the product or system, you may not recognize requirements that are unnecessary but restrict the specification to a particular product. In some cases it may be necessary to limit a specification to a particular unique product, but when that is not required, it is usually better to provide opportunity for competition among suppliers.
A special case is that of music practice spaces for schools or churches. One particular company is a specialist in this area and can provide complete systems including the design if desired. However, all the components required can be obtained from other suppliers. The difference is that these other suppliers are not set up to do the full room design. They expect the building designer to tell them what they are to provide. Now, the company that can do the complete design usually does a very good job and is an option. However, just realize that if you allow them to write the specification, they are going to write it in such a way that no one else can meet it. Trying to save money by letting a supplier write a specification does not always pay off.
Egan Book Available Again - Professor David Egan before his retirement taught architectural acoustics for many years at Clemson University and the University of North Carolina at Charlotte. His books on the subject developed for his classes have been highly valued by his students and other architects. The out of print books have been known to command premium prices. Now, his last book has been reprinted in paperback by J. Ross Publishing Classics and is available from the publisher and various sources. We have heard rumors that a new version of this classic book may be in the works.
Courtroom Acoustics – History and Technology - Our state has many older courthouses. Over the years many courtrooms have been modernized, but in recent years interest has developed in restoring some courtrooms to their original architecture. A side effect is that the original acoustics of these courtrooms have also been restored including excessive reverberation, but now combined sometimes also with excessive ventilation noise. This makes it more difficult for people to understand what is said in the courtroom. At the same time the technology of court reporting has progressed to where now court reporters often make audio recordings of what is said. They find that in listening to these recordings it is even more difficult to understand what is said than it is when listening live in the courtroom. This is creating problems in generating accurate transcripts. A courtroom is a space where people must be able to hear and understand clearly and make clear recordings, often without benefit of a microphone close to the person speaking. Good acoustical design is essential with care in restorations to provide modern acoustics.
July issue of Sound and Vibration Magazine features local research on Violins
George Bissinger recently retired from the Physics faculty at East Carolina University and David Oliver of Polytec authored an article on 3-D Laser Vibrometry on Legendary Old Italian Violins. According to the editors, “This absolutely delightful article presents state-of-the-art measurements on three “priceless” Italian violins in continuing attempts to discover the “secrets” of their legendary makers.”
Classroom Ceiling Panels - In response to the need for good classroom acoustics at low cost, the three major ceiling manufacturers now offer inexpensive NRC 70 ceiling panels that are especially appropriate for use in classrooms. Using these panels at a height of 9 feet for at least 85% of the ceiling area will assure that the reverberation in the classroom meets the intent of the new classroom acoustics standards ANSI S12.60. These ceilings are the Armstrong School Zone Fine Fissured, the USG Radar Climaplus High CAC/High NRC, and the Celotex Fine Fissured High NRC. Specifying these ceilings with a 9-foot height is the easiest and least expensive route to reverberation control in classrooms.
Resilient Channel Sandwiches – a Recipe for Disaster - We continue to see problems where people have used resilient channel sandwiches, two layers of gypsum with only resilient channel between them. Some people see this as a way to improve an existing wall by adding resilient channel and another layer of gypsum over existing gypsum. Others find it in a catalog of fire-tested assemblies, especially ceilings. This type of assembly may be good for fire, but it is definitely not good for sound blockage. The problem is that the air space is so small that the resonant frequency due to spring of air and RC between the two masses of gypsum is in the range of around 200-300 Hz. This makes the assembly very weak in this range, weaker than it would be without the RC. As noted in the USG Gypsum Construction Handbook, this is “not recommended when sound control is a major consideration.”
Steel Studs – Light Gauge or Load Bearing – Big Difference - We are often called in on situations where walls with steel studs have not given the performance the designers expected. The common problem is that the designers have depended on data for “steel studs” but have used load-bearing heavy gauge steel studs. There are many tables of data for “steel studs” and even some original test reports that make no mention of the gauge of steel used for the studs. In almost all these cases, the data are based on 25 gauge studs. The gauge of the steel makes a major difference in the sound blocking ability of walls when the gypsum is attached directly to a single set of studs. The flexibility of a light 25 gauge studs reduces the structural transmission of sound through the stud. A heavy load-bearing stud will behave much like a wood stud. This difference is reduced when resilient channel is added. The difference is also minimal in double stud or staggered stud arrangements unless bracing is required between studs on each side of the wall. When such bracing is required, performance is deteriorated some with light gauge studs and strongly with heavy gauge studs.
UltraSteel Studs – a New Development - If you have not yet heard of it you will be hearing of “UltraSteel” studs. These have been used in other parts of the world and are now being rapidly phased in to the US market. UltraSteel refers to a light gauge stud made from steel that is actually lighter than the standard 25 gauge, but which have strength similar to 25 gauge and acoustical performance at least as good as 25 gauge studs. The studs have an embossed pattern on them that gives them extra strength with less steel. Advantages are use of less steel and reduced transportation costs. The code agencies have approved their use in all applications that otherwise call for 25 gauge studs. There are some claims that the UltraSteel studs are acoustically superior to the regular 25 gauge studs. Our position is that the data are still not sufficient to be sure of this, but they are at least as good. If you do some searching you may also find reference to a special drywall product that is being marketed with the “UltraSteel” name in conjunction with the introduction with the studs. Do not be confused as the studs can be used with regular gypsum.
Directionality of Transmission Loss, STC and ASTC - In theory, the transmission loss of a wall and the resulting STC or ASTC is a property of the wall independent of the direction of the sound transmission. Thus, the result should not vary with the direction of the measurement, or which room is used as the source or receiving room. However, we have long known that results vary from test to test in different labs or at different times. Now, it has also been observed that measurements in the same lab in different directions can often be different. ASTM E90, the standard for laboratory transmission loss measurement has been changed to allow labs to test in each direction and average results before computing the STC and reporting the results based on the average. This should result in a more reliable result when done this way. However, the standard does not require this bidirectional testing. A proposal has been made to modify the standard for field measurement (ASTM E336) to allow such bidirectional testing, but with a difference. The field standard would require the results in each direction to be reported individually but allow a result based on the average to also be reported.
New Wallboard Products, the light, the heavy and the damped - New wallboard products are being introduced for various reasons and these can have influence on acoustical performance. In past issues we have discussed the Quietrock products that involve thin gypsum panels laminated with other materials to provide damping and move the coincidence effect to a high frequency. National Gypsum has now worked with this company to introduce a similar line of products. The parent company of Quietrock, “Serious Materials” is now planning to offer a lightweight gypsum product on the theory that it takes less energy to transport. Potential users of this and similar product should recognize that reduced weight also means reduced acoustical performance. On the other end of the spectrum, USG has recently introduced their Fiberock line of wallboard. This product is mold resistant without a paper facing, but is heavier than regular gypsum and contains a high percentage of recycled content. In theory the extra weight should help improve sound blockage. However, USG has not thus far provided any test data to examine the benefit. There must be some concern until such data is available as the changes could influence the coincidence effect and affect the mid-frequency performance.
Furring System for Wall Panels - We have often used furring and fiberglass batts behind Tectum panels to obtain better low-frequency absorption, and ceilings with air spaces above provide extra bass absorption. Now, a supplier of absorptive wall panels is offering an optional four-inch wall furring system to enhance the bass absorption. See http://www.thewaveproducts.com/specs/FRRails.pdf. Unfortunately, no test data are yet available.
Acoustics at NC State in the 1960’s and 70’s - North Carolina State University was a leader in acoustics education and research in the late 1960’s and 70’s due primarily to the efforts of two young professors, Franklin D. Hart and Larry H. Royster. After both graduated in 1959, Frank had stayed to continue in graduate school while Larry initially went to work in industry where he became involved in a project on underwater transducers. Larry was able to bring his project with him back to the university as his dissertation subject. Frank spent a brief postdoctoral period with NASA before beginning as a professor. At NASA he became involved in acoustics and saw the possibility of a major acoustics research center at NC State. Back at State he started recruiting students and research grants and establishing courses as part of what was first the Vibration and Sound Laboratory, and then the Center for Acoustical Studies. Upon completion of his degree, Larry also joined the faculty and started a program with some degree of independence but cooperating with the Center. Larry and his wife Julia became international leaders in hearing conservation. Frank recruited Ron Bailey to go to England for a PhD and return to State as a professor, Bill Reiter to complete his degree at State and join the faculty, and Tom Hodgson as faculty member from England by way of Syracuse University. The major thrust of their research was the control of noise from industrial machinery with support from many industries and the federal government. One major program involved the textile industry in cooperation with Professor Paul Emerson of the Textile School. Frank Hart moved up the administrative ladder of the University, leaving as Vice Chancellor and Provost. All those professors are now retired except Ron Bailey a co-founder of our firm who is now Dean of Engineering at UT-Chattanooga. NC State today offers more limited opportunities in acoustics, but over the years has turned out dozens if not hundreds of students in acoustics.
Laboratory Test Reports Can Be Erroneous - We have previously discussed the fact that laboratory test results are not exactly repeatable and can be misleading. We recently reviewed a laboratory report on a type of glue that appeared to indicate miraculous performance in preventing impact sounds when used on a concrete slab with no ceiling below. After sending an email to the lab that did the test we got a quick return phone call after they had reviewed the situation. They had somehow accidentally failed to mention that a well isolated ceiling was installed under the slab during the test. The manufacturer of the glue product was honestly unaware of the very misleading claims made about his product as a result.
Tapping Machine - Impact sound ratings for floor-ceiling assemblies are evaluated using as standardized machine that taps on the floor while the sound is measured below. See photo at right. These machines are rare. We have made arrangements with Fagen Acoustical Consultants of Florida to use their tapping machine at a cost much less than the cost of weekly rental and shipping from other sources.
New Telephone Number - We have added a third telephone line that will be used primarily for making calls out. This is a VOIP line and thus when you get a call from us you will see "unknown" listed if you have caller ID. The number is 919-521-4376.
National Research Council Endorses Quiet Classrooms - At the request of the U.S. Green Building Council and others, the National Research Council (NRC), appointed the Committee to Review and Assess the Health and Productivity Benefits of Green Schools. The committee’s charge was to “review, assess, and synthesize the results of available studies on green schools and determine the theoretical and methodological basis for the effects of green schools on student learning and teacher productivity.” In regard to noise, acoustics, student learning, and teacher health, the committee has found the following:
· Sufficient evidence exists to conclude that there is an association between decreased noise levels in schools and improvement in student achievement.
· Although there is strong evidence that reduced noise levels are most important for younger children because they are still developing speech discrimination, additional research is required to more precisely define possible needs for control of reverberant sound for younger children.
· Some available evidence indicates that teacher health, in regard to voice impairment, may be adversely affected by noisier environments, although the magnitude of the effect cannot currently be estimated as a function of exposure to noise.
The committee then recommended: To facilitate student learning, guidelines for green schools should include requirements to meet American National Standards Institute (ANSI) Standard S12.60, “Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools.”
More information can be found here: http://newton.nap.edu/books/0309101204/html/42.html
ASA Takes Position on Classroom Amplification - The Acoustical Society of America has taken the unusual step of issuing a policy statement regarding the use of amplification in typical small mainstream classrooms and the design of such classrooms. The two part position is 1. Sound amplification should not be routinely employed in typical small mainstream classrooms, and 2. All new or renovated small mainstream classrooms should be designed to conform with ANSI S12.60-2002 to ensure satisfactory speech communication for learning. More information can be found at http://asa.aip.org/amplification.pdf
Products Mentioned on our Website and in our Newsletter - You will notice that we have started mentioning some specific products on this news page an in our Newsletter. These are not intended as general endorsements and are not paid advertisements. These are usually unique products available from only one supplier that meet special needs. Our intent is to make people who have such needs aware of these products that are usually new and that can sometimes be difficult to find. Suppliers with new or unique products should feel free to contact us.