Our address is 7330
Chapel Hill Road, Suite 201, Raleigh, NC 27607. This is actually in Cary at Exit 290 on I-40.
Our New Conference Room
St. Paul's Catholic Church, New Bern
Classroom Acoustics Standard Now
Classroom Acoustics coming to the IBC 2021 Building Code, not 2018
The newly approved
Accessibility standard contains classroom acoustics - This new
version of the standard was approved too late to be referenced in the IBC
2018 building code. It is expected to be referenced in the 2021
model building code. This puts the requirements of ANSI S12.60 into
the model building code used in most states. States can potentially
modify the model upon adoption, and speed of adoption by states
Sound Isolation in the 2018 and 2021 IBC Model Building Code
2018 IBC model building code has two significant changes in Section 12.06.
Previously this section on sound isolation applied only to isolation between
“dwelling units” which were typically individual apartments or condominums
in multifamily buildings. This has now been expanded to “sleeping units.”
This means that these requirements would apply between hotel rooms,
dormitory rooms, hospital rooms and other similar situations. There is also
new language saying “Alternatively, the sound transmission class of walls,
partitions, and floor-ceiling assemblies shall be established by engineering
analysis based on a comparison of walls, partitions, and floor-ceiling
assemblies having sound transmission class ratings as determined by the test
procedures set forth in ASTM E90.” There is similar language for impact
ratings. On the positive side, this could be helpful in some cases where
assemblies have not been tested. However, there is a downside. Even the
most knowledgable people have trouble doing this in some cases, and there is
nothing to keep someone who does not know what they are doing from rendering
a completely erroneous opinion. In the coming months further changes will
be proposed for the 2021 model code. Some of these are necessary
improvements. However, multiple parties plan proposals and some could be
HUD Fixes Medium Truck Calculations in Online
Starting in 2013 an error has been in the HUD
Online DNL Calculator required for use in HUD studies. As of December
2017, that error has been fixed.
Guidelines for Healthcare facilities
There are significant acoustical aspects in the FGI Guidelines in the 2010
and 2014 versions, and this will be improved and expanded to missed areas in
2018. The 2018 Guidelines will be in three books: Hospitals, Outpatient,
and Residential. Noral Stewart was heavily involved in the initial
development of the Residential book as part of FGI Acoustics Working Group
and then seved on the Acoustics Proposal Review Committee reviewing submitted
189.1-2017 adopted with major acoustical requirements.
This revision to 189.1
contains significant improvements and additions to the acoustical
requirements for high performance buildings. Remember that the
International Green Construction Code uses ASHRAE 189.1 now as its reference
technical standard. It
introduces acoustical requirements for sound levels, sound absorption and
isolation into almost all kinds of buildings being built to a
high-performance “Green” standard. This is much more than the basic
isolation requirements for multi-family residential in the basic building
code, and even those requirements are refined in this code. Anyone becoming
involved in Green buildings should become familiar with these new
requirements. Joe Bridger and several other members of ASHRAE TC 2.6
participated in its preparation over the last few years.
S12.70-2016 standard for healthcare speech privacy - (description
It includes important
speech privacy standards for healthcare. Both HIPAA (Health Insurance
Portability and Accountability Act of 1996) and HITECH (Health Information
Technology for Economic and Clinical Health Act, 2009) require
caregiver-patient confidentiality. This is a standard that can be used to
evaluate such privacy requirements.
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.
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.
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
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.
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.
Building Code Requires Sound Insulation –
Uniform Statewide Building Code (USBC) has been modified to include
requirements for isolation from outdoor sound in certain locations.
Specifically this applies in areas greater than DNL 65 near Oceana Naval Air
Station. The code provides two options. The first is that the walls, roof,
and windows meet specified STC requirements
that depend on the extrerior sound level in 5 dB ranges. One difficulty in
this approach is that architects and builders typically depend on test data
for the STC values, and test data are very limited for roof and exterior
wall constructions. Fortunately the STC can be estimated and authorities
accept such estimates. The other option provided is for a qualified person
to analyze the construction plans and provide modifications as necessary to
assure that the interior DNL due to exterior sound is reduced to 45.
Basically, the outdoor to indoor noise reduction has to equal the difference
between the stated DNL on contour maps and 45. This is not a simple matter
of matching STC ratings. Proper analysis requires applying the transmission
loss spectrum of the building components in third octaves to the A-weighted
spectrum of the aircraft sound, considering the effects of the various wall
window and roof areas and the sound absorption within the rooms, and
subtracting 6 dB to account for going from a free-field outdoors to a
diffuse field indoors. This is something that should only be done by an
person very experienced in this kind of analysis. Unfortunately, rather
than language to require the analysis be done by someone really qualified to
do it, the code indicates that the “alternative design shall be certified by
an RDP.” RDP means “registered design professional” which means an
architect or engineer registered in the state of Virginia, very few of whom
are qualified to do the analysis. Thus, it is uncertain exactly what will
be required to meet this alternative more accruate approach.
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
Issue 41 Fall 2018 Posted November 1,
Yes we are now
in our 40th Year.
Noral Stewart Receives Laymon N. Miller
Excellence in Acoustical Consulting
Noral D. Stewart became the fourth recipient of the Laymon N. Miller Medal
for Excellence in Acoustical Consulting at Internoise 2018 in Chicago on
August 29, 2018. This medal awarded in alternating years by the Institute
of Noise Control Engineering and the National Council of Acoustical
Consultants recognizes an “individual who has practiced acoustical
consulting in an exemplary manner over a sustained period of time, to
improve acoustical environments in and around buildings, transportation
systems, work places, recreational and other occupied spaces, such that
the quality of life for citizens and communities is significantly
enhanced.” The award for Dr. Stewart was specifically for “sustained
sharing of his acoustical expertise with colleagues and clients to create
better acoustical environments and standards to evaluate them. The award
is named for legendary acoustical consultant Laymon Miller, known for his
teaching of noise control basics to many, clear communication, and sharing
of his experience with colleagues.
Updated Personal Note from Noral Stewart
As indicated above, we are now in our Fortieth Year. That is a long history, and one of growth and major
accomplishments. As announced last year, I am now working part-time as
I am in my 70's. Joe Bridger is leading our daily operations and John Gagliardi and Sidd Mahjan are doing most of our field work.
I am doing mostly smaller office-based jobs and assisting others on the
staff with the benefit of my experience. We are fortunate to have a
highly experienced staff, totaling over 100 years combined experience
including my own. This does not count our highly experienced
contractors whose total experience is greater than that. Very few firms can
provide that level of experience. We will be looking for additional
staff to meet your needs far into the future.
Bridger is General Manager of Firm,
and now Vice President of NCAC
Joe Bridger has been named General Manager of
Stewart Acoustical Consultants in recognition of his expanded duties in
the operation of the firm. Joe has also been elected as the Vice
President for Finance of the National Council of Acoustical Consultants.
Eric Reuter Chair of ASA TCAA and President
Our affiliated consultant Eric Reuter of Reuter
Associates has been serving as chair of the Technical Committee on
Architectural Acoustics of the Acoustical Society of America, and has been
elected as President-Elect of the National Council of Acoustical
Welcome Sidd Mahajan to our Staff
In 2016 we briefly introduced you to Siddharth Mahajan as one of our
interns. Sidd finished his MS in the summer of 2017 and we have hired him as a
full time professional staff member. He first became involved in the
study of acoustics and vibration as part of his senior project for his BS
in Engineering. As a musician playing several instruments, he had long
had an interest in sound (like Joe). This all led him to NC
State and the program that has trained Noral, John Stewart, Joe,
and Mathew. His thesis on Focusing of Ultrasound using Self Bending Beams
may not seem directly applicable to our work. However, it demonstrates
his ability to do good work and communicate it effectively. Sidd has
strongly impressed us as he has jumped right into doing jobs efficiently.
John Stewart, & others inducted into NCSU Mechanical Engineering Hall of
in industrial and machinery noise and vibration control John
Stewart has joined Noral Stewart in the Hall of Fame of the NCSU
Department of Mechanical and Aerospace Engineering. John is the world
recognized leader in control of noise in woodworking machinery as well as an
expert on machine design. The goal of the Hall of Fame is to recognise the
top 1 percent of graduates of the department based on career achievement.
Around 20 to 40 graduates have been recognized each year since 2013.
Others in acoustics in the 2017 class included Mehmet Caliskan of Middle East
Technical University and MezzoStudyo, and Pat Niskode' retired from GE and
now at Miami University of Ohio.
Acoustical Society of America – North Carolina Chapter Poster Competition
The North Carolina Regional Chapter
of the Acoustical Society of America had a meeting and student poster
competition at NC State University on November 17, 2017. After technicial
presentations by several speakers in the morning, the student competition
featured thirteen posters from NC State, UNC Chapel Hill, Duke and East
Carolina. Awards of $2500 each made possible by a gift from Larry and Julia
Royster were made to Atul Rungta of the University of North Carolina at
Chapel Hill, and Nikhil JRK Gerard of North Carolina State University. The
Royster Awards are part of a national program rotated among regional and
student chapters. Chapter awards of $500 each for graduate students were
made to Kaustav Mohanty of NC State and Zheng (Frank) Fang of Duke. Chapter
awards of $250 each for undergraduates were made to Noah Sonne of East
Carolina and the team of
Steven Jacobson and Simen Omholt-Jensen
from Duke University. Judges for the event were Noral Stewart and John
Gagliardi of Stewart Acoustical Consultants and Laurie Kamper of Threshold
Acoustics. The meeting was hosted by Chapter Chair Yun Jing with
arrangements made by Sidd Mahajan
Stewart, Jing, Sonne, Rungta, Mohanty, Gerard, Jacobson, Omholt-Jensen,&
John S. Stewart,
PhD. Affliliate for Industrial Machinery Noise and Vibration Control
another Stewart, though not related. Noral and John were undergraduate
students at N. C. State at the same time. John stayed and completed his
PhD while Noral worked for a period in industry. John basically wrote the
book when it comes to noise control for wood working machinery. He had a
full-time world-wide consulting career specializing primarily in
wood-working noise before joining the research faculty of NC State to head
a program to develop improved wood-working machinery. During that period
he continued to consult part-time. We referred some wood-working industry
projects to him. He also has experience in other industries, in vibration
control, and in balancing. Since retiring from NC State, he has had a
desire for some part-time consulting. Working with us is a natural fit.
John will be working with Noral on all our industrial workplace noise
control projects with assistance from Chris Eaton as appropriate. He
will also be working on any vibration issues requiring measurement and
analysis beyond the basic guidance for building systems.
John Gagliardi, PhD returns to our staff
remember John Gagilardi working with us on a part-time basis several years
ago. John is now returning part-time at first but working toward a
full-time position. John will be based at his home in Salisbury, NC
but will be in contact with the office almost daily and will be visiting our
office frequently. John did not do his degrees in acoustics but became
involved in acoustics and has been a highly active continuing education
learner. He seems to have been almost continuously enrolled in
acoustics classes from one of the major universities. For the past
several years he has been technical director for a materials manufacturer.
However, before that he was involved in an acoustical consulting firm and an
architectural acoustics test laboratory. John will be working heavily
with Joe on architectural projects but will also be doing field
investigations, especially in the western part of the state.
Holy Name of Jesus Cathedral - Raleigh, NC
“Acoustic Architecture” on UNC TV
NC Science Now
and North Carolina Now
Consultants and AVCON are featured, with key personnel Frank Yarborough and
Eb Strickland of AVCON, and Joe Bridger and Fred Schafer of our firm in this
educational science production (6 minutes), which was born out of the work
being performed on the cathedral.
Stewart Acoustical Consultants teamed with AVCON to design a loudspeaker
solution that would provide optimal speech quality. This was essential
given the strong reverberation in this space, much more than we typically
recommend but demanded by the diocese. Fred Schafer and Joe
Bridger led this effort for our firm. Our interns including Sidd and Mathew George and his staff were integral in the construction of the
EASE acoustics model, and subsequent AURA analysis. The EARS
module was used to develop high quality auralizations that
demonstrated to the Diocese of Raleigh the acoustical character of the space
for music and unamplified speech, and the optimized speech quality provided
by the loudspeaker system design. AVCON provided critical input on client
requirements and is providing the full system drawings and installation. In
addition, our firm was tasked to evaluate the acoustics as designed, and
provide sound isolation and HVAC noise control solutions. The building
was dedicated on July 26th, 2017.
Space Acoustics - Three Decades of Design
Several years ago
we presented several posters on many of our worship space projects at a meeting
in Providence, RI. The plan was for the Acoustical Society of America to
those posters. Well, it
took a while but the book has been published
containing case studies resulting from most of the posters we presented.
The book is published by Springer Verlag and is available from many sources
Realistic Sound Demonstration Equipment
expanded our ability to present high quality auralizations and other sound
demonstrations using specially selected and calibrated headphones and
preprocessing tools. This can be set up with visual walkthroughs and
general visuals to orient the listener. To make auralizations, we take a
carefully selected dry source and convolve it with the room’s impulse
response, to create a binaural sound file with the room’s character now
added. With the new equipment, very realistic demonstrations for multiple
listeners is now easily accomplished
– Advanced Analysis of Environmental Noise
We have been using Soundplan and CadnaA for specific project needs for
several years using short-term licences to calculate and plot sound
propagation outdoors in detail. We have chosen to purchase a fully featured
version of SoundPlan. With this program, we can import from Google Earth
and other sources the geographic information system (GIS) data and
image overlays as well as site plans to develop more precise and complex
noise propagation maps for all kinds of sources, whether building
equipment, transportation corridors, aircraft, outdoor venues (loudspeakers)
or industrial sources. We can properly assess outdoor mass
evacuation systems with this tool. It allows us to more efficiently
problem solve, and develop cost effective solutions and display results in a
way that is easier for everyone to grasp (using color plots and contour
The primary use will be to plot contours of sound radiated from sources in
accordance with ISO 9613. The program also contains a module for
highway sound propagation similar to the FHWA TNM program and
another that allows highway model calculation using the actual TNM
program. Other capabilities include calculation of sound indoors in
industrial spaces and evaluation of the sound escaping to the outdoors.
This program greatly enhances our ability to analyze and illustrate
results for complex outdoor situations.
50 Years for NC Chapter Acoustical Society of America
NC Chapter of the Acoustical Society of America celebrated its 50th
Anniversary with a meeting at the Durham Bulls Athletic Park. A highlight
of the meeting was a tour of the renovated Baldwin Auditorium at Duke
University conducted by Mark Holden, Duke alumnus of Jaffe Holden Acoustics
who converted the room from a mediocre auditorium to a world class
multipurpose space. The photo below is of the chapter chairs (and one vice
chair) who were present, most of whom have connections to us.
Stewart – chair 1979-80, Joe Bridger – chair 2001-02, Chris Eaton – chair
Held – chair 1976-77 (leading sales rep for instruments and materials in
Bailey – chair 1975-76 (a co-founder of this firm, later Dean of Engineering
at three schools)
Hart – chair 1967-68 (NCSU acoustics program founder, later NCSU Provost)
Stewart – chair 1980-81
Stewart – chair 1986-87 (retired industrial audiologist, now a chaplain)
King – vice chair 1969-70 (retired audiology professor at Duke University)
Schafer – chair 1988-89, 2013-15
Cook – chair 1973-74 (retired US Pub. Health Service officer, Nat. Inst. Env.
Honeycutt – chair 1998-2000, 2012-13, John Gagliardi – chair 2009-11
Bailey inducted into NCSU Mechanical Engineering Hall of Fame
nomination by Noral Stewart, Dr. Adnan Akay (left)and Dr. J. Ronald Bailey
(right) were inducted into the NCSU MAE Hall of Fame
in 2016. Akay was Chair of ME at
and a Director
of the US National Science
and is now
professor, chair of ME, and Provost at Bilkent University in Turkey.
Bailey was a professor at NCSU,
helped found this firm, led IBM
Robotics Engineering for several
years, and was Dean of Engineering at three schools before retirement.
Leroy Beranek 1914-2016
Leo Beranek passed away
on October 11 at 102 after a long and productive life. He published his
last paper in the Journal of the Acoustical Society in 2016, 77 years after
his first in 1939, co-authored with Professor F. V. Hunt and fellow student Da You Maa. A few highlights from Beranek's biography.
Becomes interested in
radio as teenager, works way through college in Iowa repairing radios,
wiring houses, and play drums in a band.
Near senior college
year, happens to help a motorist change a tire. Motorist is former Harvard
professor; author of a radio paper Leo had read that morning. Gets help
with scholarship to Harvard.
Works on development of
33.3 rpm Long Playing Record as a student project. Receives PhD 1940.
Went to work in the war
effort, developed ways to quieten the interior of aircraft and make radio
communication with pilots at high altitude possible. Helped develop sound
effects for Phantom Army, in the process building the world’s first Anechoic
Chamber. Commissioned as Captain of the fake USS Beavertail by Navy,
develops way to get radar information more quickly to Navy gunners.
After war, becomes
professor at MIT, publishes first book in 1949, asked to do the acoustics
for the new United Nations building, and founds Bolt, Beranek, and Newman (BBN)
consulting firm which would become largest acoustical consulting firm in
largest muffler for NASA supersonic engine test facility.
When NY Port Authority
bans new jet commercial aircraft, Beranek leads a rush major research effort
to define the differences in sound between jets and propeller planes and
necessary silencing to allow the coming of the jet age.
BBN does many
architectural acoustics projects such as renovation of the Tanglewood
concert shed, and Beranek leads development of NC Curves method of rating
sound in rooms.
Beginning in the
1950’s, BBN leads in the application of digital computers to acoustical
research, buys first computer produced by Digital Equipment Company, invents
the modem, and eventually builds the initial computer network that evolves
into the internet. The email system as we know it is developed at BBN and
the first email with the @ is sent from BBN office.
leads effort to take over license of an existing operator for a TV station,
going three times to the US Supreme Court, then manages the station for 10
years earning the reputation as America’s best TV station before selling it
and making a major money contribution to the Boston Symphony Orchestra.
Retired from BBN and
the TV station, Beranek leads the acoustical design of several highly
successful concert halls in Japan.
In 2012 travels to Hong
Kong to present the Gold Medal of ASA to his classmate Da You Maa who had
become “the Leo Beranek of China.”
Author of at least 10
books, in 2012 at age 98, publishes revision of book first written in 1954.
Starting with a
citation from Harry Truman for his WWII contributions, Beranek has received
almost every award possible in the acoustical world, plus one from the
broadcast industry for station management and the National Medal of Science
from President George W. Bush.
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
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.