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St. Paul's Catholic Church, New Bern
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.
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 is 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.
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 32 Fall 2011 Winter 2012 Posted December 21, 2011
F. C. Schafer Consulting LLC Joins Us
F.C.Schafer consulting, l.l.c.
As many of you know, Stewart Acoustical Consultants has worked closely with Fred Schafer on projects involving sound systems for over 25 years. In fact Fred has also assisted with the room acoustics on several projects including the Squires Recital Hall at Virginia Tech. We are very pleased to announce that Fred has relocated his office from Concord to the Triangle and moved into our office. This signals an even closer working relationship with Fred and his firm, F. C. Schafer Consulting. Having Fred physically located with us will allow us to expand our services and work more efficiently.
Stewart Named Fellow of ASA
Dr. Noral D. Stewart has been named a Fellow of the Acoustical Society of America for contributions to building acoustics and noise control. This honor recognizes career contributions of those named. Dr. Stewart is a member of the ASA technical committees on Architectural Acoustics and Noise. Of those ASA members who designate their first interest as either Architectural Acoustics or Noise, only 113 are Fellows, and only around half of those are available as consultants. The election occurred at the ASA meeting in Baltimore in April, and the fellowship certificate will be presented at the next meeting in Cancun in November.
Stewart Receives Award of Merit and Named Fellow of ASTM International
Dr. Noral D. Stewart received the highest award given by ASTM International, the Award of Merit which carries with it the honorary title of Fellow of ASTM. The award was presented by the Chairman of the ASTM Board at the meeting of Committee E33 in St. Louis on May 18, 2010. The citation reads "For distinguished, dedicated, and outstanding leadership in developing and promulgating acoustical field test and community noise standards in ASTM International Committee E33 on Building and Environmental Acoustics and for liaison service as an expert with other acoustical organizations. Stewart is only the ninth member of Committee E33 to receive this award and is the only recipient still conducting tests such as E336 field isolation or E1007 field impact sound in accordance with E33 standards..
International Green Construction Code –
On May 20 the International Codes Council hearing committee meeting in Dallas accepted the major rewrite of the acoustics section of the proposed International Green Construction Code as submitted by Noral Stewart on behalf of the Acoustical Society of America, the National Council of Acoustical Consultants, the ASTM task group on building codes, the Institute of Noise Control Engineering and ASHRAE TC 2.6 on Noise and Vibration. David Marsh of the Kinsella-Marsh Group represented the acoustical community at the meeting. Unfortunately, the committee also accepted a couple of other proposed changes submitted by others that introduce problems. The ICC appears committed to including acoustics in this code. The work of the acoustical community is to assure that the requirements written are technically correct and reasonably appropriate. Work will continue through hearings in Phoenix in November.
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.
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.
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.
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.