Making Our World Sound Better Since 1979

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 Available Free


Classroom Acoustics coming to the IBC 2018 Building Code
The draft of the ANSI A117.1-2015 Accessibility standard contains classroom acoustics) - The last public draft had no comments.  It is expected to be approved in early 2017.  The draft of the IBC 2018 building code has  changed the referenced standard to A117.1-2015 (from -2009).  The IBC 2018 code will be finalized sometime late 2017.  Speed of adoption by states varies.

2018 FGI Guidelines for Healthcare facilities
A summary of changes from 2014 is available here.  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 now is on the Acoustics Proposal Review Committee reviewing submitted proposals

ASHRAE 189.1-2015 1st public draft of proposed significant acoustics additions is available
click here
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.  Joe Bridger and several other members of  ASHRAE TC 2.6 participated in its preparation over the last few years.

ASA/ANSI S12.70-2016 standard for healthcare speech privacy - (description here)
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:  1/8 inch glass  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 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.

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.

Virginia Building Code Requires Sound Insulation –
The Virginia 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 is here


Our Latest

Issue 40 Fall 2016 Posted December 19, 2016


                NEWSLETTER ARCHIVE


 Personal Note from Noral Stewart

Thirty Eight Years.  Yes, we celebrate our thirty-eighth anniverary at the beginning of 2017.  That is a long history, and one of growth and major accomplishments.  I will also be 70 in January 2017.  I realize clients must be wondering where we go from here.   I intend to keep working some as long as my health permits, BUT, I am not going to be working full time.  Starting in 2016, I have been taking 20% time off.  I expect that to increase to 40% in 2017.  I need to slow down and smell the roses some.  I will be taking many long weekends, and much of the summer off.  We have known for many years that this time would come when we have to face the future.  Many of you have come to know Joe Bridger who joined us first in 1993, twenty three years ago.  For several years now, Joe has been managing much of our work.   We expect that Joe will be taking over the primary management of the business.  In 2015, we hired Chris Eaton to begin taking over much of the work I have been doing, and to develop new capabilities we have been relying on contractors for.  He is already doing most of the field work I was doing.  In December 2015 we added John Stewart to our stable of affiliates, primarily to handle industrial and machinery noise and vibration issues.  In November 2016, Dr. John Gagliardi became a full time employee.  This all positions us to allow me to slow down.  I will be available to provide everyone with the benefit of my experience, but I will be managing fewer jobs and doing less field work.  Stay tuned as there could be other changes to allow us to better serve you.

John S. Stewart, PhD. Affliliate for Industrial Machinery Noise and Vibration Control

Yes, 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

Some may 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.



Our Interns – Sidd and Julius

Sidd Mahajan and Julius Elo joined us in the summer as interns.  They are MS students at NCSU in acoustics.  They have had the opportunity to work on and visit jobs with us as well as helping us with many things around the office.  Julius graduated and left us in December but Sidd will be continuing in 2017.  



Holy Name of Jesus Cathedral -  Raleigh, NC
“Acoustic Architecture” on UNC TV
NC Science Now and North Carolina Now (link)

Stewart Acoustical 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.  Fred Schafer and Joe Bridger led this effort for our firm.  Our interns (Siddharth and Julius) 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 dedication of the building is scheduled for July 26th, 2017.

Worship 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 compile a book of 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 including Amazon.



New Realistic Sound Demonstration Equipment

We have 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

SoundPlan – 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 maps). 

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

The 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.

Left to right:
Noral Stewart – chair 1979-80, Joe Bridger – chair 2001-02, Chris Eaton – chair 2016-17
John Held – chair 1976-77 (leading sales rep for instruments and materials in 70’-80’s.)
Ron Bailey – chair 1975-76 (a co-founder of this firm, later Dean of Engineering at three schools)
Frank Hart – chair 1967-68 (NCSU acoustics program founder, later NCSU Provost)
John Stewart – chair 1980-81
Andy Stewart – chair 1986-87 (retired industrial audiologist, now a chaplain)
Burton King – vice chair 1969-70 (retired audiology professor at Duke University)
Fred Schafer – chair 1988-89, 2013-15
Reg Cook – chair 1973-74 (retired US Pub. Health Service officer, Nat. Inst. Env. Health Sci.)
Richard Honeycutt – chair 1998-2000, 2012-13, John Gagliardi – chair 2009-11

Akay and Bailey inducted into NCSU Mechanical Engineering Hall of Fame

Upon nomination by Noral Stewart, Dr. Adnan Akay and Dr. J. Ronald Bailey have been inducted into the NCSU MAE Hall of Fame.  Akay was Chair of ME at Carnegie Mellon and a Director of the US National Science Foundation 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.



Meet Royster Award Winner Nicolas Morales

The ASA North Carolina Chapter held its student poster competition, including the Royster Award, on Friday November 11.  Thirteen posters were submitted.  There were 9 graduate student entries, 5 of which were eligible for the Royster Award, and 4 entries from undergraduate students.  In addition to the $2500 Royster Award, the chapter provided $2000 in prizes open to all graduate students and $500 in prizes for the undergraduate students. Nic’s poster presented a novel approach for optimizing acoustic parameters for computer-aided design and analysis of architectural models. During the meeting Joe Bridger gave a talk entitled “Cathedral Acoustics - a Case Study”. Click here for summary of the awards.



Leo 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 history.

·      Develops world’s 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.

·      Beranek successfully 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.


Welcome Chris Eaton – We are very pleased to welcome Chris Eaton to our firm.  Chris is a native of Davie County (like Noral Stewart) and a MS graduate of the acoustics program in the Department of Mechanical and Aerospace Engineering at NC State.  Chris has had a long and successful career in product acoustics in the automotive and communications industries which has led to 25 issued patents.  He has impressed us with his grasp of acoustical fundamentals, and he brings the skills of a seasoned professional with consulting experience.  His experience in the automotive industry and with HEAD Acoustics included a strong emphasis on the area of “Sound Quality,” a methodology that so far has been applied primarily to products.  We look forward to opportunities to possibly apply some of that experience to the sound quality of buildings and environments.  He has also developed successful award winning audio products for telecommunciations.  Thus, he may assist in audio areas.  However, he will be primarily working with Dr. Stewart in the areas of environmental/community noise and sound isolation.  He has been doing ASTM isolation testing and envirornmental sound measurements as he has been learning new applications of his talents.  As part of this, he will be accompanying us on many visits with clients which will give you an opportunity to meet him.


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.

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.