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Classroom Acoustics Standard Now Available Free

New Developments in Backup Alarms - A backup alarm is an essential safety system for vehicles used at workplaces. Unfortunately, the sound of the traditional backup alarm can be heard far away in quiet places. Since it is a sound designed to get attention, it can be very irritating to those hearing it in places where there is no danger. Systems have been available for years with selectable levels so the alarm could be set to the lowest level still loud enough to provide safety. Also, systems have been available that automatically sense the background level nearby and adjust the signal appropriately. Now some new concepts are available to reduce the degree to which these sounds are heard far from the vehicle.
The first of the new alarms is a broad-band system developed in England. Rather than a beep-beep concentrated at a single frequency, this uses sound over a broad continuous band of frequencies. http://www.reverseinsafety.co.uk/bbs-tek/bbs-tek.html Near the source the higher pitched part of the sound stands out and most people would probably describe the sound from this as a hiss-hiss. The high-frequency parts of the sound die off quickly with distance, and the lower-frequency parts at reduced level blend in with other environmental sound. The developers claim it is also easier for people near a vehicle to localize where it is at. Our clients who have used them verify this. These alarms are now required in New York City.
In the US, the two major suppliers Ecco and Preco have recently merged but each part of the business has a new offering. Ecco has teamed with a San Diego company that specializes in sound sources with strong directional control. Their effort has concentrated on aiming the signal to the back and minimizing the spread in other directions. To some extent this occurs with any signal mounted on the back of a vehicle, so the difference between the new signal and traditional signals is not as great as tests of the signal alone indicate. The Preco Safety division has developed an alarm that is a mix between the traditional pure-tone alarm and the broad-band alarm. It uses sound at a series of individual frequencies, not continuous but closely spaced. This creates a sound that has some of the characteristics of the traditional beep especially near the source, but also some of the characteristics of the broad-band signal especially far from the source.

Interior Storm Windows - As we face more situations of homes offices and other buildings close to roads or other noise sources, we face greater needs to increase the sound blockage of existing windows. The easiest way to do this is usually with a storm window either indoors or outdoors. Such windows can be of acrylic or regular 1/8 inch glass. However, the best performance is achieved with laminated glass ¼ inch thick or in extreme cases thicker. We have discussed this before, but now we are finding more sources of these windows. Here are some:
http://www.stormwindows.com/index.htm  1/8 inch glass
http://www.soundproofwindows.com/photos.html  nothing really soundproof, but these are good.
http://www.maineglass.com/
http://www.citiquiet.com/products.php
http://thermolitewindows.com/noise.htm
http://www.alliedwindow.com/

Alternatives to Fiberglass Duct Liner - We know that some facilities do not allow the use of fiberglass duct liner. The two objections appear to be concerns about moisture retention – mold growth and cancer. We believe these concerns have been addressed. A 1996 study by the University of Nevada Las Vegas confirms the results of numerous earlier studies which showed that fiber content in the indoor air from fiber glass lined systems is insignificant and does not adversely affect the health of building occupants. A 1997 study by Duke University showed that mold is no more likely to grow on fiber glass than on any other surface in the duct system. A second study by UNLV shows that mold grows at the same rate on lined sheet metal, duct board or bare metal. The International Agency for Research on Cancer IARC has established that fiberglass materials of the type used in duct liners are not classifiable as carcinogenic.
Often facilities that do not allow fiberglass lining will allow the use of regular silencers that include fiberglass or mineral wool filler and flex duct that contains fiberglass. This combination can usually get the job done. Some manufacturers are offering silencers with cotton or polyester fiber packing. Silencers are also available with no fiberglass packing, often called “no fill” or “packless” silencers. These are typically less effective than regular silencers. McGill AirFlow makes both round and rectangular double wall duct with perforated inner wall and thicknesses of 1, 2, and 3 inches. They can provide a film between the perforated wall and fiberglass if desired. Alternative duct liners are available in two types of fire safe foam, polyimide and melamine, and in cotton.
 

Wall STC Variation - Over the past several years we have repeatedly discussed the variability of test results for structural sound blockage in the laboratory and in the field. There is an unfortunate assumption that the STC of a wall is a precise and 100% repeatable result. The truth is that in cases where many test results for the same construction are available, a wide range of results are seen. With
enough data a median or average expected result can be established. However, with limited data, one cannot be certain whether the result seen is truly representative or high or low. With so many new products coming available, we have limited data that could be very misleading. Fortunately, for traditional constructions, and now for some of the newer constructions, an acoustical consultant who specializes in sound isolation and does a high volume of testing is
compiling results to get statistical data on performance. For instance, consider wall that most typically performs around STC 51 or 52 in laboratory tests and is widely used in applications where a wall of greater than STC 50 is required with an expectation of greater than ASTC 45 in the field. His data on a very large number of these walls indicates that the wall will usually achieve greater than ASTC 45 in the field, but around 12% of the time it will not, even if nothing
is done wrong in the construction. In our experience, we often find architects selecting walls that would typically achieve only around STC 48 in the laboratory for these applications, based on an unrepresentative test that indicates STC 50. Such walls have a very high risk of being less than ASTC 45 in the field.
 

Proper Installation of Ceilings - Acoustical Performance and Fire Resistance - Discussions at the recent meeting of the Acoustical Society of America shed light on the fact that isolated ceilings using resilient channel or resilient clips are often not installed as required by fire ratings. This may even be the case for some acoustical test results with the differences enhancing the acoustical results but deteriorating the fire performance. Fire rating requirements need to be reviewed carefully for details of the installation. Often, the ratings achieved require the use of additional channels at joints in the gypsum board, so each piece of gypsum is screwed to a separate support channel. If there are multiple layers of gypsum with joints not aligned, this means even more extra channels for those joints. By the time all this extra channel is in place, the cost has increased significantly compared to a simple arrangement of channel 16 or 24 inches on center. Further there is reduced acoustical performance due to the greater number of contact
points and to the reduced loading per clip or channel. Acoustical performance depends on loading the spring-like device for maximum deflection. If more spring devices or longer lengths of channel are added, the loading is reduced, resulting in a higher resonant frequency and reduced isolation. These differences can easily show up in the lower frequencies of the test ranges for IIC and STC, 100 and 125 Hz. Unfortunately, due to the cost involved, very little
comparative test data is available, but the implications are clear in theory. Some manufacturers are looking at different elastomers to use depending on the number of clips and weight of gypsum. Some also have put emphasis on doing fire tests with minimal channel and clips with success. Thus, some products are available that allow the joints of the gypsum to be attached to the same channel, reducing costs and improving performance.

Sliding Doors for Offices - We are seeing increased use of sliding doors for offices and conference rooms without consideration of the privacy issues involved. These doors are usually installed barn style, that it sliding over the wall outside the office, leaving a gap between the door and wall when closed. In some cases these gaps are small and in some they are very large. Often there are no seals of any type. Large unsealed gaps are essentially like having the door open. Sealing systems for such doors are not as readily available as for hinged doors, and the available options will typically not work as well as with a hinged door.

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. 

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.

NEWSLETTER

Our Latest

Issue 24 Spring 2009 Posted June 19

Issue 23 Winter 2009 Posted March 20

Issue 22 Fall 2008 Posted December 16

Issue 21 Summer 2008 Posted September 18

Issue 20 Spring 2008 Posted June 19

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   

30 Years!

Yes, it has been 30 years.  The business was incorporated on December 27, 1978 and opened for business January 2, 1979.

See our Fall Newsletter

              Joe                        Steve                                     Richard

Joe Bridger, LEED AP – Principal Consultant and Associate Principal Joe Bridger has become a LEED Accredited Professional. This indicates that he has demonstrated knowledge of the basic principles of energy efficient and environmentally conscious design of buildings. 

Dr. Richard Honeycutt will Help Us on Worship Spaces - We are pleased to announce an affiliation with Dr. Richard Honeycutt of EDC Sound Services in Lexington, NC. Richard will be assisting us primarily on projects involving worship spaces and auditoriums. We expect him to help manage some worship space projects and provide computer modeling. He brings to us a long and rich variety of experience in acoustics, audio systems, music, and electronics. He has published many magazine articles primarily on audio topics, and two books on electromechanical devices and electronics, and taught electronics at Davidson County Community College for 19 years. Richard has been a member of the NC Chapter of the Acoustical Society of America since 1969 and is a member of AES and ASA.

Welcome Dr. John Gagliardi - We are pleased to announce the addition of Dr. John Gagliardi to our team on a part-time basis. Dr. Gagliardi not only has his BS, MS, and PhD from Marquette University, but has continued his education in acoustics with many classes from Georgia Tech, University of Minnesota, University of Wisconsin, University of Michigan, and Purdue University. He was a practicing acoustical consultant for many years with experience in architectural, environmental, and product noise. In recent years he has been Technical Director at Technicon Industries, and will continue in that position as he works for us. John is initially helping us with HVAC noise evaluations for schools. We will be looking for opportunities for John to assist us with field investigations in the western part of North Carolina, Virginia and South Carolina.

Bridger Named Associate Principal – We are pleased to announce the promotion of Joe Bridger to Principal Consultant, Associate Principal and director of educational, worship, and performance space acoustics.  This recognizes his leadership role in these areas and enhanced role in business development and project management.  Joe has spent his career with us starting with a summer job and working his way up as Analyst, Consultant, and Senior Consultant to his new position. 

Stulgin Full Member of ASA – Steve Stulgin has been accepted into full membership in the Acoustical Society of America.

Sounds of the Past – Have you thought about the sounds of your youth that you do not hear any more except possibly in old movies. Some examples: typewriters, rotary phone dials, the ringing bell of an old phone, the pop of flashbulbs, gurgling percolators, glass bottles in a soda vending machine, the ka-ching of a manual cash register, the shutter and film advance of a film camera, the scratch of chalk on a blackboard, the clatter of a home movie projector, a carousel projector changing slides, and mechanical pin-ball machines. Even the sound of footsteps is now dominated by the softer sound of predominantly rubber soled shoes. New jet engines are significantly quieter than older ones. The sound of most car doors closing is less metallic than older cars. Hybrid cars are quieter at low speeds. So what are the new sounds? Microwave ovens, electronic chimes to signal various functions, and musical ringtones on phones are a few.

Department of Defense Implements Classroom Acoustics Standard - In 2002 the American National Standards Institute developed a standard for classroom acoustics to assure a good learning environment where students can actually hear the teacher well, ANSI S12.60. Several school systems and a few states have adopted this standard in part or in full. The US Department of Defense has now adopted it for all new schools and training facilities under its control. This includes both schools for the children of military families and training facilities for military personnel. A copy of ANSI S12.60 can be downloaded free at this link. http://asastore.aip.org/ Strong progress also has been made by an ANSI working group including representatives of the relocatable classroom industry to develop a special supplement to address the unique problems of relocatable classrooms. Dr. Stewart has been a major contributor to this effort on relocatable classrooms.

Building Code Requirements for Isolation in Multifamily Residential - The requirements of the building code for residential sound isolation are poorly written and not well understood by many. An effort is beginning within the International Codes Council to develop a supplemental document to explain the code and eventually modify it. Members of the acoustical community will be involved in this effort that was initiated by Dr. Brandon Tinianov of Serious Materials.

Virginia Court Decision Strikes Down Noise Ordinances - On April 17, 2009 the Virginia Supreme Court in a case involving a night club held that noise ordinances in the state based on subjective criteria or “reasonable person” standards were vague and unconstitutional. The court essentially held that any noise ordinance in the state must have quantitative and measurable standards. This leaves many communities without enforceable ordinances until new ones can be adopted. The ruling is here
http://www.courts.state.va.us/opinions/opnscvwp/1080998.pdf

Virginia Beach Adopts New Ordinance with Strange Limits - In response to the decision by the Virginia Supreme Court, the city of Virginia Beach has enacted a new noise ordinance http://www.vbgov.com/file_source/dept/planning/3082ord.pdf. It is very strange. The limits for sound in residential areas are 65 dBA daytime and 55 dBA nighttime which would not be unusual. What is unusual is that these are specified to be measured inside the home. There is no averaging or time period indicated. Thus, the limits may have been meant to apply just to an intermittent occasional short duration sound, but with no lower limit for steady sounds someone could be producing about 85 dBA all day outside a home with levels approach 65 dBA inside. This is truly an unacceptable condition. This makes the ordinance dangerous as the producer of such noise could cite the ordinance as condoning it. Unfortunately such unusual ordinances often occur when local governments rush into them without getting competent assistance.

New Ceiling Options - Armstrong is introducing two interesting new products and we have discovered products from Certainteed Ecophon that meet special needs.
Natural Fiber Acoustical Ceiling – Armstrong has introduced a new ceiling panel that is a breakthrough in many ways. http://www.armstrong.com/common/c2002/content/files/54506.pdf The Tierra panel is only 5/8 inch thick but approaches the acoustical performance of a 1 inch fiberglass panel. Further it is a highly GREEN product, made from Jute, a natural fiber that grows very quickly. In fact it is claimed to be the greenest possible ceiling. The fiber for the panel can be grown is less than 90 days. It is very suitable for demanding applications such as open-plan offices or classrooms.

Tin Ceiling – Designers often want to have a historical tin ceiling look but the old tin ceilings reflected sound and created poor acoustical environments. Armstrong has introduced a microperforated tin ceiling panel http://www.armstrong.com/commceilingsna/article52742.html  that is highly absorptive when used with fiberglass or other absorber above it. It is available in a wide variety of colors and patterns.

Glued-up Fiberglass Ceilings – Historically it has not been possible to glue highly absorptive fiberglass ceiling panels directly to a solid ceiling. Certainteed Ecophon has created fiberglass ceiling panels that can be glued up in either their Focus line or thicker more absorptive Master line. Similar panels are also available for a variety of concealed grid options.
http://www.ecophon-international.com/templates/WebProductSystemPage____8181.aspx

http://www.ecophon-international.com/templates/WebProductSystemPage____8202.aspx

AIA Credit Course in Architectural Acoustics Available - Both Noral Stewart and Joe Bridger have been certified by the Acoustical Society of America as presenters of a one-hour course in acoustics that qualifies for health, safety and welfare credit through the AIA. The basic one hour course must follow slides provided by ASA but can be supplemented with the experience of the presenters and special topics of interest to a particular audience. Stewart Acoustical Consultants is pleased to provide this class on a limited basis free of charge to small groups in our office, or to larger architectural firms at their offices in the Triangle Area. We are also open to presenting the class to multi-firm groups of students at locations outside the Triangle area such as at AIA Section meetings. Please contact Noral Stewart or Joe Bridger for information.

United States House of Representatives Passes 21st Century Green High-Performing Public School Facilities Act on May 14th - This was part of the stimulus package (Reinvestment Act) and had been largely removed. Prior to that, it had passed the House in 2008 in similar form. This year, there is a greater chance of success in the Senate where it is awaiting consideration by the Committee on Health, Education, Labor, and Pensions. The House version contains $6.4 billion for the first year (similar $ in the following 5 years) for giving states funding for grants and low-interest loans for schools – uses include to build, modernize and repair facilities to make them healthier, safer and more energy-efficient. This includes LEED for schools and thus acoustics. Specifically from the bill’s summary “Directs local education agencies grantees to use a percentage of their grant, rising in 10% increments from 50% in FY2010 to 100% in FY2015, for public school modernization, renovation, repairs, or construction that meet Leadership in Energy and Environmental Design (LEED) green building rating standards, Energy Star standards, Collaborative for High Performance Schools (CHPS) criteria, Green Building Initiative environmental design and rating standards (Green Globes), or equivalent standards adopted by the entities that have jurisdiction over such local education agencies.” In other words, at least 50% and eventually 100% must be used on green school projects. A separate guidance document approved by the House (though not a part of the bill) encourages school systems to improve classroom acoustics specifically.

LEED for Schools 2009 Requirements - In LEED for Schools 2009, you must meet the prerequisite for HVAC noise (45 dBA) for all core learning spaces, and must meet room acoustics requirements - for rooms under 20,000 cubic feet via calculation meeting classroom acoustics standard requirements or NRC 70 ceiling tile, for larger rooms RT must not exceed 1.5 seconds. No STC requirements for the prerequisite. For a point, you can get enhanced acoustics, but you must lower the HVAC noise to 40 dBA and meet the STC requirements in the classroom acoustics standard. You can further get an innovative design credit for taking additional measures including lowering the background noise to the classroom acoustics standard requirement of 35 dBA for all sources. The sticking point for the enhanced acoustics continues to be the STC 50 requirement and the need for extending all walls to the deck. Stud wall systems must have resilient channel or 24-26 gauge metal studs for to have a shot at STC 50. Masonry wall systems must be sand filled, or heavy masonry, and typically 8” block to achieve STC 50. Typical 6” and 8” lightweight blocks do not do it. Most owners and architects are resisting furred gypsum as a solution.

Stewart and Bridger present papers at ASA meeting in Miami – Both Noral Stewart and Joe Bridger presented papers at the Acoustical Society of America meeting in November. Noral Stewart who has been working with the Modular Building Institute on sound isolation performance of modular classrooms presented current results in an invited paper for a special session on the acoustical issues related to modular classrooms. This paper is pubilshed in the ASA Proceedings of Meetings on Acoustics, POMA.  Joe Bridger presented three contributed papers. Two papers in a session on acoustics of green buildings separately addressed ways to design room acoustics and mechanical systems for classrooms to be Green, affordable, and meet the LEED requirements. Another in a session honoring the late classroom acoustics leader Mike Nixon compared different metrics, criteria, measurements, and calculation methods to address gymnasium room acoustics.

Top 10 ways to foul up a resilient channel installation
In the spirit of David Letterman’s top 10 lists, the 10 most common mistakes in the use of
resilient channel that reduce acoustical performance.
10. Overlap ends of channel several inches, resulting in squeaks.
9. Use double leg channel that is not really resilient
8. Use 20 gauge channel that is not really resilient
7. Install resilient channel in line under trusses instead of perpendicular
6. Install resilient channel upside down
5. Install resilient channel with solid part of web at joists or studs
4. Put resilient channel between two layers of gypsum
3. Use hat channel instead of resilient channel
2. Use long screws from gypsum into wood above
1. Use poor quality resilient channel just because it is labeled RC-1

LEED® growth goes geometric – Acoustical requirements for LEED® for Schools catch designers and owners off guard-Fueled by concerns about climate change and rising energy prices, as well as a general broader interest in sustainable buildings and the environment, “Green” design and construction is growing strongly with many projects using the LEED® Green Building Rating System™ sponsored by the United States Green Building Council (USGBC).  LEED® stands for Leadership in Energy and Environmental Design.  Over the past 15 years this movement has been strongly adopted by corporations, non-profits, and government institutions alike.  Now there is a special LEED® for Schools program.

Schools major growth area- We see the greatest interest in new school projects.  Many school systems are either conducting pilot school projects, or adopting the LEED® system for all their school buildings.  If you want to get a sense of the amount of news on LEED® for schools, go to www.buildinggreenschools.org/news.  Many school districts and several states have adopted the LEED® certification as a requirement for all schools.  There are 370 schools registered for the LEED® for schools program as of this writing (April 20, 2007 through now).  NONE are certified yet.  In the previous year over the same time period, there were only 161 schools (LEED®, but not LEED® for schools).  In the two years before that there were 89 and 61. 

Caught off guard- What many in the architectural community and these school districts do not realize, is that all schools registered for LEED® on or after April 20, 2007 must meet the LEED® for Schools acoustical requirements for reverberation time, noise blockage (STC ratings), and general background noise.  Many architects already doing LEED® schools, under the general LEED® program may not be aware of or prepared for these new requirements.  While the LEED® acoustics program is based on the ANSI S12.60 standard for Classroom Acoustics, the requirements are not exactly the same as in the standard, being less stringent in some regards.  These requirements also caught the LEED® program off guard with the difficulty meeting them as originally written.  The process is changing fast with alternative compliance paths, new interpretations of which rooms must meet requirements, and new decisions on just what will be accepted.  Some recent interpretations are discussed on the next page.

We take the lead – Given this environment, Stewart Acoustical Consultants is taking the lead to provide assistance to architects and school systems participating in the LEED® program.  We are monitoring developments in the process regarding acoustical requirements closely.  Joe Bridger plans to become a LEED® accredited professional to be more knowledgeable of the general LEED® process.  We are also considering firm membership in the organization to play a stronger role in development of the process and requirements.  

Easier LEED® for School Acoustical Prerequisites and Credits – The LEED® program for schools has been revised to provide more options to achieve credits.  Some of these options are easier to do than the original requirements, though they could result in classrooms that are not as good.  The prerequisites and extra points for background sound level can now be obtained based on calculated levels of HVAC noise without regard to other sources.  This is a concern because a calculated level of 45 dBA could result in actual levels even higher and the basic requirement of 45 dBA is far too loud for a classroom.  With this interpretation, we strongly advise clients to go for the extra points with calculated levels of no more than 40 dBA or even 35 dBA.  The credit for isolation between classrooms can now be met based on a measured NIC of 45 between similar rooms as those in the design.  This might be met with walls less than the specified STC 50.   

Classroom Ceilings – an improved inexpensive mineral fiber ceiling– Once the classroom acoustics standard was adopted, we found good mineral fiber ceiling panels that could meet the requirements in classrooms less than 10,000 cubic feet as long as the ceiling was at 9 feet or lower.  Fiberglass panels were required for higher ceilings.  Now, Armstrong has raised the bar by tweaking their mineral fiber School Zone High NRC panel to optimize the performance so it can meet the classroom acoustics standard for a ceiling height of 10 feet.  This is a major advance in making good classroom acoustics affordable.

Unrealistic Wall Test Results –The sound blockage ability and STC of a cavity wall can be improved when the gypsum layers on each side are well isolated from one another using light gauge studs, resilient channels or one of the new resilient clip systems.  However, when only a single layer is used on each side the low-frequency performance is poor and the STC is often controlled solely by the performance at 125 Hz.  That means the STC can vary widely from test to test of the same wall dependent on the 125 Hz result that typically varies widely.  The low frequency performance can be improved even with the light weight if the air space is large enough.  However, we are concerned that some suppliers are publicizing test results with small air spaces and a single layer of gypsum on each side with STC results that are not realistically representative of what can be normally expected.  We have also noticed that a major supplier of gypsum is now publishing the highest test result they can find for wall designs rather than typical results.  Users are cautioned to be careful about results that look too good to be true.  The result may have been achieved in one test, but one test does not verify normal expectations.  

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.”

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.

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.