Tag Archives: acoustics

Unique noise control standards developed for mixed-use project

The LegoLand Discovery Center in Assembly Row was designed by Darlow Christ Architects. The development also includes residential, office, and retail space. Photos © Bruce T. Martin

The LegoLand Discovery Center in Assembly Row was designed by Darlow Christ Architects. The development also includes residential, office, and retail space. Photos © Bruce T. Martin

An acoustics consulting firm, Acentech, developed project-specific noise control guidelines for Assembly Row—a new mixed-use waterfront development near Boston.

Located on a 18-ha (45-acre) previously underdeveloped site on the Mystic River in Somerville, Massachusetts,  Assembly Row’s master plan was conceived and coordinated by developer Federal Realty Investment Trust (FRT). It retained Acentech early in the project to address the complex issue of noise control as it related to the mix of uses within four blocks. The acoustic design addressed noise and acoustic issues in buildings and tenant spaces.

Assembly Row’s first phase, includes:
● 450 residential apartments;
● a 12-screen movie complex;
● LegoLand Discovery Center;
● restaurants;
● outlet retail stores;
● 9290 m2 (100,000 sf) of office space; and
● a 2.4-ha (6-acre) waterfront park.

Succinct and prescriptive noise-emission standards were developed and included in the design and technical manual governing tenant fit-outs. These standards included specific design criteria for noise emissions from rooftop or outdoor mechanical equipment, and noise transmission from ground-level retail to residences above. Similar standards were also applied to base building designs throughout the development. These standards were intended to ensure compliance with the municipal noise code, and serve to reasonably protect the various properties from each other’s noise emissions.

“Assembly Row is a new neighborhood designed to foster a 24/7 lifestyle,” said FRT’s Brian Spencer. “Less than 10 minutes from Boston, it is the first neighborhood of its kind in the country, offering outlet retail alongside entertainment and eateries, with apartments and office space above, fostering a true neighborhood feel.”

Consultants worked with architects and developers of specific buildings and tenant fit-outs to design acoustically favorable spaces and comply with the development’s noise emissions standards. The 12-screen movie complex, located above the LegoLand Discovery Center in Assembly Row’s Block 3, presented a unique design challenge.

Acoustic consultants worked to ensure each theater within the movie complex would be protected from noise produced by activities at LegoLand, other building tenants, and mechanical equipment. The resulting design includes floating concrete slabs under every screening room, with certain walls and other features supported from the roof structure above. Through careful coordination with the architecture and building structure, these and other design features ensure the screening rooms are not disturbed by activities in surrounding spaces, and likewise, the cinema’s neighbors are not disturbed by movie noise.

Another challenge was protecting residential tenants in the upper floors of the development from the noise produced by rooftop mechanical equipment serving restaurant and retail facilities on the ground floor. Planning for judicious placement of visual/acoustical screening around rooftop equipment helped reduce noise impacts from HVAC systems on residents of adjacent buildings. Even within buildings—with both commercial and residential spaces—the careful location and vibration isolation of mechanical equipment has helped reduce noise impacts.

Sound Thoughts on Door and Frame Assemblies: Exploring differences between STC and STL ratings

All images courtesy MegaMet Industries

All images courtesy MegaMet Industries

by Edward Wall Jr. and Allan C. Ashachik

When sound control acoustic door assemblies are selected, the usual way is to specify a sound transmission coefficient (STC) rating in accordance with established standards. Derived from testing at a series of frequencies within the range of human hearing, STC is a single number assigned to a door assembly that rates its effectiveness at blocking sound transmission. This sounds simple and logical, just like hourly ratings on fire doors, but the situation is far more complicated.

The challenge with having a catch-all solution in the form of specifying the ‘right’ STC comes down to the range of sound. For example, if a project concerns a high school band’s practice room, the noise that needs to be reduced comes from instruments ranging from the low-frequency (pitch) of a bass drum to the high pitch of woodwinds or chimes. For this application, STC would be appropriate since sounds from many frequencies all need to be blocked or reduced.

However, selecting the right door for a mechanical equipment room at the same school is quite different. Low pitch and constant machinery noise needs to be filtered out. Using the STC rating system for this opening could be much more expensive than necessary to be effective. Fortunately, there is another metric more suited to these situations—sound transmission loss (STL).

The STC rating is actually derived from an average of STL performances. Since STC relies on testing data that establishes the reductions at each individual frequency, the data can be used to determine the STL needed at a specific frequency or frequency range without additional testing.

Setting the stage
This article is not intended as a lengthy discussion of all aspects of sound control, designs, gaskets, or installation. Rather, it seeks to clarify some misconceptions about STC and suggest using alternate values and standards when specifying acoustic door and window assemblies for a particular sound control purpose or requirement.CS_October2014.indd

The authors believe STL is the definitive method of specifying acoustic assemblies, and better accomplishes what the sound-deadening qualities are to be required for a specific opening. On a practical level, this means the building owner gets what he or she really needs, often for less money. To make this argument clear, six myths must be examined.

Myth 1: “An STC rating in accordance with ASTM E90 is all that needs to be specified.”
It is important the reader be a least somewhat familiar with some of the ASTM standards applicable to lab testing and rating of sound control assemblies.

To that end, ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, describes the test chamber, testing method, frequencies to be reported, and other lab requirements. However, it does not contain the method of establishing the rating. A second standard like ASTM E413, Classification for Rating Sound Insulation, or ASTM E1332, Standard Classification for Rating Outdoor-Indoor Sound Attenuation, needs to be included.

ASTM E413 is used to define the 16 frequencies at which sound transmission losses in decibels are measured. It also establishes the sound insulation contour values of those frequencies and the sound transmission loss values for each corresponding frequency. From this, a reference contour can be created to which actual test data can be graphed and compared. Interestingly, the profile of this reference contour remains constant for all graphs and is shifted up or down on the graph to obtain a single STC rating (Figure 1).

ASTM E1332 is used to calculate an outdoor/indoor transmission class (OITC) and covers a range from 80 to 4000 Hz. This standard has an extended lower range of frequencies for which the results are calculated rather than graphed. The additional frequencies are intended to measure STL in decibels for outdoor to indoor sound exposure resulting in a different OITC rating. The calculations generally result in a somewhat lower single rating than does ASTM E413 for STC.

In order to convey the purpose of this article, two fictitious ASTM E90 test results—derived from two different examples—are shown in Figure 2. The columns listed show the 16 STL numbers achieved at each frequency of the ASTM E413 test. Ratings are at random and do not necessarily represent a specific door assembly or manufacturer—however, these sample numbers are not unusual.

Sample 1 would be typical of a less-expensive door assembly with an STC of about 40 while Sample 2 would represent an assembly costing two to four times as much with an STC of over 48. As the image illustrates, depending on the frequency of sound, one can save the client a lot of money by specifying the less-expensive door.












Myth 2: “A higher STC rating is always better, regardless of cost. Therefore, one should always specify an STC rating higher than what the client needs—just to be safe.”
To understand how those STL values relate to real-world conditions, the reference charts of common volume sources and approximate frequencies are provided as examples in Figure 3. Simplistically, to reduce the volume from a busy office with mostly male employees to that of a private office, the assembly should be capable of at least an STL of 40 at a middle frequency range. The lower cost Sample 1 would be sufficient in lieu of the more costly Sample 2 usually specified.

To reduce the noise from a bass drum or low-frequency vibrations, the maximum STL should be concentrated in the corresponding frequency range. Here, Sample 2 would be the better choice. Other noise sources should be evaluated accordingly and the correct door assembly chosen to meet the best STL at a certain frequency range. At higher-frequency ranges, Samples 1 and 2 are not really much different in performance, but substantially different in cost.

Neither ASTM E413 nor ASTM E1332 establishes an STC (OITC) value of the ‘perfect’ acoustic door assembly. To evaluate test results to a single number, they must be compared to this contour. The key to this comparison is referred to as the ‘deficiency’—any measured sound transmission loss (STL) variation below the contour. The STL measurements above are not considered variations. Unless otherwise noted, ASTM E413 limits these deficiencies to a maximum total of 32, and a maximum of eight at any single frequency.

For projects like this IMAX movie theater in Brimingham, Alabama (or the Nashville Sympohny on page 96) choosing a door with the proper acoustical ratings is critical.For projects like this IMAX movie theater in Brimingham, Alabama (or the Nashville Sympohny on page 96) choosing a door with the proper acoustical ratings is critical.

For projects like this IMAX movie theater in Brimingham, Alabama choosing a door with the proper acoustical ratings is critical.

Acoustical doors are available in a wide range of sizes for a wide range of applications, such as this Georgian power plant.

Acoustical doors are available in a wide range of sizes for a wide range of applications, such as this Georgian power plant.

Myth 3: “STC is a single number completely reliable to describe performance.”
Unlike fire door assemblies rated based on a certain time and temperature curve, the method of calculating STC by test data and deficiencies from a sliding reference contour can result in different ratings. The test lab will generally use the most advantageous graph in the test report. This will be the one with the highest STC or OITC rating that falls within the parameters of the deficiencies. This rating, however, may not be the one with the lowest total of deficiencies or the one closest to the reference contour. With that in mind, one can see STC expressed as a ‘single’ number does not necessarily mean it is the ‘only’ number available.

The five graphs in Figure 4 show how the STL remains constant while the reference contour is shifted up or down to determine STC. It is important to remember the STC is the point at which the reference contour (not the STL contour) intersects at 500 Hz. This means even though the STL at frequencies is identical in the five graphs, the sample could have multiple STC ratings depending on the variation parameters. For example, the maximum STC (complying with ASTM E413) of the assembly is 43 (with 30 deficiencies) in the graph in Figure 4a. If an STC of 44 is attempted—as shown in Figure 4b—the result is a failure at 42 deficiencies and nine deficiencies at 160 Hz.

The highest STC values with the lowest total deficiencies are:

  • STC 42, with 21 deficiencies as in Figure 4c;
  • STC 41, with 14 deficiencies as in Figure 4d; or
  • STC 40, with eight deficiencies as in Figure 4e.

STC ratings below 40 result in a lower number of deficiencies when the sound transmission coefficient is the only determining factor. This should demonstrate the rating method has far less reliability than what is associated with fire door ratings where the time and temperature curve is more consistent.

STCDoors_Figure 4a-4e

A: In this two contour chart, the cyan is STC 43 with 30 deficiencies, while the dark blue represents STL 41—both are at 500 Hz, as are all of the other Figure 4 graphs. B: Cyan is STC 44 with 42 deficiencies, and dark blue is STL 41. C: Cyan reprents STC 42 with 21 deficiencies, and dark blue remains as STL 41. D: The cyan line plots STC 41 with 14 deficiencies; dark blue is STL 41. E: Cyan is STC 40 with eight deficiencies; dark blue is STL 41.

























Myth 4: “It is fine to continue putting STC-rated door assemblies in Section 08 10 00.”
Under MasterFormat, Sections 08 11 13–Hollow Metal Doors and Frames, 08 12 13–Hollow Metal Frames, and 08 13 13–Hollow Metal Doors, are intended to describe common applications of swinging hollow metal (e.g. steel) doors and frames. Not all manufacturers capable of fabricating hollow metal doors and frames are also capable of fabricating acoustic door assemblies, especially those over STC 35. They may also not have the up-to-date testing data and technology to fabricate such specialized products. This could lead to a litany of exclusions or qualifications at bid time; difficult to manage and compare for any distributor or general contractor.

The correct section to specify acoustic door assemblies is 08 34 73–Sound Control Door Assemblies, as this incorporates the latest in acoustic door assembly standards (e.g. American National Standards Institute/ National Association of Architectural Metal Manufacturers Hollow Metal Manufacturers Association [ANSI/NAAMM HMMA] 865, Metal Doors and Frames) that describe qualifications, details, and requirements for this specialized product. This ensures the project benefits from the expertise of manufacturers who are familiar with sound control and have conducted a sufficient number of tests in various configurations.

Myth 5: “STC-rated assemblies can do everything other doors can do.”
In order to perform the specialized performance functions required of STC-rated assemblies, the internal construction of doors must be of sufficient mass or innovative design. In some cases, this may conflict with other performance requirements such as fire ratings, universal accessibility, security, life safety, or wind loads.

Documents such as the aforementioned HMMA 865—or HMMA 850, Fire-rated Hollow Metal Doors and Frames, and Steel Door Institute (SDI) 128, Guidelines for Acoustical Performance of Standard Steel Doors and Frames—contain design or other information useful in determining which performance functions are the most important to the project. For example, an STC-rated door assembly also required to have a 1 ½-hour fire rating might be located in an area where a 20-minute fire rating suffices. An STC-rated door assembly where the entire project is also specified as meeting accessibility needs may be in a critical sound-control room where the accessibility is not the main function.

Qualified manufacturers of these specialized products should be well-equipped to discuss and resolve such conflicts so the specifier can decide which is the most critical to the individual opening.

The windows and door for this West Point recording studio needed to meet certain sound requirements.

The windows and door for this West Point recording studio needed to meet certain sound requirements.

West Point University Recording Studio STC Windows











Myth 6: “The STC of the installed opening will have the same STC as the lab test.”
Documents like HMMA 865 and SDI 128 quite clearly dispute this myth. When tested in a lab according to ASTM E90, the instrumentation, room size, calibrations, ambient conditioning, humidity, or other factors—in addition to the installation of the test samples—must be controlled within established parameters. Pre-test inspections and adjustments are common. Such stringent controls are not feasible at the project site.

Although there are accepted standards for ‘field testing’ of STC, the results of such tests could be five to 10 points less than the lab-tested STC.

To be clear, this article does not intend to propose totally replacing the historic STC rating method. It does, however, introduce the option of specifying acoustic assemblies by using a sound transmission loss method at a certain frequency or range of frequencies for special situations. It is important to remember—unlike the STC rating method, the STL lab-tested data does not change.

Edward Wall Jr. is the president of MegaMet Industries, located in Birmingham, Alabama. He was nominated to the technical committee and then the executive committee of (NAAMM’s) Hollow Metal (HMMA) division. Wall is now closing in on two decades of manufacturing hollow metal and developing specialty door products. He can be reached at ewalljr@megametusa.com.

Allan C. Ashachik is an independent consultant, providing services to steel door and frame manufacturers. Since entering the industry as a pencil and T-square detailer in 1968, he has been involved in all aspects relating to steel doors and frames from detailing to final quality assurance in acoustic, windstorm, detention, and fire-protective applications. Ashachik is the 2006 recipient of the A. P. Wherry Award, issued by the Steel Door Institute (SDI) to recognize individuals who have made outstanding contributions to the progress of standard steel doors. He can be reached via e-mail at aashachik@neo.rr.com.

New Arkansas Music Pavilion Opens on a Good Note

This photo shows a view of the Arkansas Music Pavilion at night. The polytetrafluoroethylene (PTFE) cone structures come to life with lighting, while at the same time protect concert attendees. Photos courtesy Birdair

This photo shows a view of the Arkansas Music Pavilion at night. The polytetrafluoroethylene (PTFE) cone structures come to life with lighting, while at the same time protects concert attendees. Photos courtesy Birdair

by Doug Radcliffe

Walton Arts Center (WAC) purchased the Arkansas Music Pavilion (AMP) in February 2011 with the goal of expanding the venue to serve a broader and more diverse audience. The AMP operated at the Washington County Fairgrounds after moving from the Northwest Arkansas (NWA) Mall in 2012. However, after seeing a 200 percent increase in ticket sales in 2012, it was clear a permanent site was required to meet the region’s growing need for arts and entertainment. Further, the lack of a roof meant numerous event cancellations due to weather.

In 2013, the Walton Arts Center council approved plans to build a mid-sized, permanent outdoor amphitheater to attract headlining artists and bigger audiences to Northwest Arkansas. As part of a multi-campus expansion in the region, the new Pinnacle Hills venue serves as a major stop for touring concerts in the mid-south.

The new location, in the city of Rogers, has everything WAC was looking for in a permanent venue, including proximity to a major freeway, multiple access points, ample parking, and a supporting infrastructure. This improvement, as well as the 519-m2 (5590-sf) stage, upgraded technical capacities, an artist lounge, and production offices, is expected to attract bigger acts to the venue. The new AMP will also draw in larger crowds with its seating capacity of more than 6000 people, parking, upgraded concessions, and air-conditioned restrooms.

A look up at the three PTFE cone structures supported by steel.

A look up at the three PTFE cone structures supported by steel.

An orchestrated effort
Architecture firm CORE, Tatum-Smith Engineers, general contract consultant David Swain, and Crossland Construction worked to complete this project. A tent-like, weather-resistant covering for the stage was specified. The three-cone and four-inverted-cone-shaped structure is made of a fabric polytetrafluoroethylene (PTFE) fiberglass membrane, with steel supports. PTFE coats a woven fiberglass to form a durable, weather-resistant membrane.

Raising the roof
The AMP’s three-cone shaped structure creates an open, inviting space. PTFE fiberglass membranes can be used to construct roofs, façades, freestanding buildings, skylights, or accent enclosures.

Fabric roof forms are curved between supporting elements in a manner reflective of the flow of tension forces within the membrane. With the exception of air-supported structures, these curvatures are anticlastic in nature. The curving forms of fabric roofs have dramatic appeal. Another attractive feature of tensioned fabric structures is the enormous range of spanning capability. The aesthetic features and the long-span ability of fabric are particularly appropriate for entertainment facilities like the AMP.

Fabric structures are not only visually appealing, but also environmentally responsible and economically competitive. PTFE fiberglass membrane is Energy Star and Cool Roof Rating Council (CRRC)-certified. PTFE fiberglass membranes reflect as much as 73 percent of the sun’s energy, and certain grades of PTFE membrane can absorb 14 percent of the sun’s energy while allowing 13 percent of natural daylight and seven percent of re-radiated energy (solar heat) to transmit through.

The lightweight membrane also provides a cost-effective solution requiring less structural steel to support the roof or façade, enabling long spans of column-free space. Additionally, the tensile membrane offers building owners reduced construction costs and maintenance costs compared to traditional building materials.

DCRDoug Radcliffe has more than 28 years’ experience in steel, glass, and membrane manufacturing, project management, engineering, and construction business. During his career, he has been an integral member of design-build teams for high-profile construction projects of all sizes. Radcliffe is a tensile architectural systems expert at Birdair. He can be reached at sales@birdair.com.

Designing Stone Wool Ceiling Assemblies

All images courtesy Rockfon

All images courtesy Rockfon

by Cory Nevins

Specifiers have an increasing number of choices for commercial ceiling systems. Among the performance considerations for selecting the most appropriate for a particular application are acoustics, fire performance, humidity resistance, hygienic properties, dimensional stability, indoor air quality (IAQ), and light reflection. Added to these are choices pertaining to design aesthetics, ease of installation, maintenance, durability, sustainability, and cost.

Stone wool ceiling panels and metal suspension systems meet these selection criteria for both new construction and renovation projects throughout North America. The material was discovered on the islands of Hawaii, where it occurs naturally as a by-product of volcanic activity. The primary rock involved is basalt, the earth’s most abundant bedrock. The igneous material forms by the rapid cooling of lava from eruptions on the sea floor. Seismic activity, including the earth’s volcanoes, produces 38,000 times more rock material than is used by the world’s largest producer of stone wool.

The typical production process for stone wool begins with the fusion of this volcanic rock at a temperature of 1500 C (2732 F). Emerging from the furnace, the melt runs out of the bottom and onto a spinning machine, where wool is whipped into thin strands, similar to making cotton candy. The strands form ‘wool,’ held together with minor amounts of organic binders.

Stone wool ceilings offer good sound absorption, high light refl ectance, fi re protection, and humidity resistance. These panels are well-suited to create modular ceiling designs, such as long corridors.

Stone wool ceilings offer good sound absorption, high light reflectance, fire protection, and humidity resistance. These panels are well-suited to create modular ceiling designs, such as long corridors.

Now a fleecy web, the material is gathered and formed; the number of layers varies depending on the final product’s desired structure and density. The layered fibers then move to a curing oven. Once cured, the wool emerges with non-directional fibers that contribute to its multiple performance characteristics of the stone wool products. In addition to ceiling panels, stone wool’s unique combination of thermal, fire, and acoustic properties make it suitable for:

  • blown insulation in cavity walls;
  • rolls of loft insulation;
  • pre-formed and faced pipe sections; and
  • wall slabs.

A mineral fleece and water-based paint are layered on top of the stone wool to produce the finished ceiling panels. The stone wool products proceed to cutting saws, finishing and packing equipment, or are led to off-line equipment for special treatment. The majority of the waste created during the production is fully recyclable.

Use of suspended ceilings
Since the 1950s, drop ceilings have been the preferred method for concealing HVAC vents, electrical wires, plumbing pipes, phone cables, and security lines in interior commercial buildings. These suspended, interconnected ceiling systems consist of a metal grid comprising cross-tees and main runners.

The main runners are suspended by hanger wires from the structure above, and wall channels or angles provide a clean look throughout the perimeter. Panels are used to conceal the plenum—hiding the visible structure, suspension system, HVAC, and other equipment, while providing simple access for future maintenance.

The suspension ceiling system is selected for aesthetics, maintenance, and specialized performance such as fire resistance, seismic mitigation, or limited accessibility in security applications. For all ceiling designs, specifiers should check the suspension systems are manufactured to ASTM International standards. On request, suspension manufacturers may provide reports from the International Code Council (ICC) and third-party seismic performance testing and certification reports.

Corrosion resistance is also a priority for metal suspension systems supporting stone wool and other ceiling panels. The industry standard is 23.8-mm (15/16-in.) galvanized steel for suspended metal ceiling grids; most may be specified with a minimum of 25 percent recycled content.

While the ceiling panel’s size, orientation, color, finish, and edge largely determine the overall aesthetic, changing the size of the grid’s face also changes the appearance. For example:

  • a 14.28-mm (9/16-in.) narrow face diminishes the distinction between grid and panel for a more monolithic look;
  • adding a 3.17-mm (1/8-in.) slender, center regress with a ‘bolt-slot’ design accentuates the shadow between panel and grid;
  • mitered intersections provide crisp, continuous lines for a uniform ceiling plane;
  • wide-face 34.92-mm (1 3/8-in.) ceiling suspension offers bolder expression of the ceiling grid modules, especially at high elevations; and
  • in curved drywall applications, radius systems create concave and convex shapes, including barrel-vaulted ceilings.
When a sound wave hits a surface, part of the energy is refl ected, part of it is absorbed by the material, and the rest is transmitted. Undesired sound from various potential sources can include noise transmitted into the building from the exterior, or coming in from other interior spaces.

When a sound wave hits a surface, part of the energy is reflected, part of it is absorbed by the material, and the rest is transmitted. Undesired sound from various potential sources can include noise transmitted into the building from the exterior, or coming in from other interior spaces.

The noise reduction coeffi cient (NRC) refers to a surface’s ability to reduce noise by absorbing sound. NRC is important in areas where high levels of noise (like a photocopier) are present.

The noise reduction coefficient (NRC) refers to a surface’s ability to reduce noise by absorbing sound. NRC is important in areas where high levels of noise (like a photocopier) are present.












Specifying acoustic comfort
According to the World Health Organization (WHO):

noise seriously harms human health by causing short- and long-term health problems. Noise interferes with people’s daily activities at school, at work, at home and during leisure time. It can disturb sleep, cause cardiovascular and psychophysiological effects, hinder work and school performance and provoke annoyance responses and changes in social behavior.1

Therefore, it could be argued design professionals have a duty to create acoustic comfort and well-being for the occupants of their buildings. Stone wool can help with two primary components of acoustic comfort: speech intelligibility and noise reduction.

The material’s airflow resistance and density contribute to its high noise absorption properties. The fibers’ size and non-directional orientation lead to stone wool’s inherent sound-absorbing qualities. The measures and concepts discussed in this article provide a foundation for understanding the relationship between stone wool’s characteristics as a material and achieving acoustic comfort.

Speech intelligibility
One important component of acoustic comfort and sustainability, speech intelligibility refers to a listener’s ability to hear and understand a speaker in a room or space. It is measured as a signal-to-noise ratio, expressed in decibels (dB). For this application, the signal typically is speech and the noise usually is everything else in the background.

Reverberation time
An important factor for creating speech intelligibility, it is defined as the time it takes for the sound pressure level to decrease 60 dB below its original level. In most situations (excluding unamplified music performance), a lower reverberation time improves speech intelligibility and acoustic comfort. For most rooms requiring speech intelligibility, mid-frequency reverberation time should be between 0.50 and 1.00 seconds when the room is unoccupied.

Noise reduction coefficient
The noise reduction coefficient (NRC) indicates a surface’s ability to reduce noise by absorbing sound. It is calculated by averaging the absorption coefficients from the 250-Hz, 500-Hz, 1-kHz, and 2-kHz octave bands. It varies between 0.0 (i.e. absorbs very little sound) and 1.0 (i.e. absorbs a lot of sound). NRC is one of two important variables in determining reverberation time (the other being room volume). A higher NRC indicates more noise reduction (or sound absorption) and leads to lower reverberation times and greater speech intelligibility. Stone wool ceiling products typically have an NRC of 0.85 or higher.

Background noise
Undesired sound from various potential sources can include noise transmitted into the building from the exterior, or coming in from other interior spaces. It can also include sounds generated by the building’s systems or even those reverberating too long inside the room.

Speech intelligibility
Factors influencing speech intelligibility include:

  • speech signal’s strength and clarity;
  • sound source’s direction;
  • level of background noise;
  • room’s reverberation time and shape; and
  • listeners’ hearing acuity and attention span.

Reverberation time depends on two main variables: the volume of the room and the amount of sound-absorbing materials. As volume decreases or as the amount of sound-absorbing materials increases, reverberation time decreases and speech intelligibility generally increases. Since the volume of the room often depends on functional and aesthetic criteria, reverberation time is often solely dependent on the amount and efficacy of sound-absorbing materials.

In many cases, placing sound-absorbing materials on the walls is not desirable due to its tendency to get damaged, dirty, or worn because of occupant contact. As a result, whether speech intelligibility is poor, fair, or good can highly depend on the ceiling specified. This is why acoustic standards and guidelines for schools, hospitals, offices, and other types of facilities have minimum NRCs of 0.70 and up to 0.90. Stone wool ceiling panels, more than other panels made of less-absorbing materials, help ensure projects comply with acoustic performance requirements in these standards and guidelines.

Even if reverberation time is appropriate, speech intelligibility can be low if the background noise in the room is too loud. Speech intelligibility equates to a high signal to noise ratio. Consequently, it is also important to ensure noise from the exterior, other interior spaces, and from the building’s systems is controlled.

Noise reduction
In other rooms or spaces like open offices, cafeterias, libraries, and gymnasia, speech intelligibility is not the primary acoustic goal; rather, the push is for overall noise reduction for stress relief and concentration. Noise reduction equates to an overall decrease in sound pressure level from loud continuous noise (e.g. traffic noise transmitting into the building), as well as event-specific noise (e.g. a crying baby). The sound pressure level in a room depends on the strength of the sound source, the room’s size, and the quantity and quality of sound-absorbing surfaces.

Just 30 decibels of periodic noise can be disturbing to sleep or concentration. Conversational speech is generally between 50 to 70 dB. Noise with sound levels of 35 decibels or more can interfere with speech intelligibility in smaller rooms. This is demonstrated by a phenomena known as the ‘cocktail party effect,’ whereby as noise levels get louder and louder, people try to talk louder and louder to be understood. Despite their efforts, speech intelligibility decreases and acoustic stress increases. It is not until someone leaves the ‘party’ that they realize just how agitated they were as their muscles begin to relax, heart rate slows, and respiration deepens. Stone wool, because of its high noise-absorbing characteristics, also helps achieve the overall noise reduction goals.

Whether sound reduction is needed for speech intelligibility or overall acoustic comfort, blocking noise that could be in the plenum above the ceiling can also be important in some instances. As more acoustics standards and guidelines place minimum noise control criteria on wall constructions (i.e. sound transmission class [STC]), the need for ceilings to block noise from adjacent spaces traveling via the overhead plenum is becoming less frequent. This is because achieving the minimum STC wall requirements necessitates the walls be extended up to, and sealed against, the underside of the deck above them. However, in the cases where the walls do not extend full height, or where there may be noisy mechanical equipment in the plenum, the ceiling also may need to block noise from transmitting into the space below them.

Ceiling attenuation class (CAC) indicates the ceiling’s ability to prevent airborne sound from traveling between adjacent rooms when the demising walls do not intersect with the structural deck above. CAC is also a good measure to judge how much protection is offered against noisy mechanical equipment in the plenum. The higher the CAC value, the greater the ceiling’s blocking capacity. A CAC value of 35 dB is considered to be moderately high and may be specified for stone wool ceiling panels. When even higher sound-blocking capacity is required, stone wool ceiling panels can be specified with a CAC value up to 43 dB in combination with a high NRC of 0.85.

Insulation infl uences the sound level in the receiving space, helping provide more privacy between rooms and better concentration in the adjacent room.

Insulation influences the sound level in the receiving space, helping provide more privacy between rooms and better  concentration in the adjacent room.

In practice, there is a strong link between sound absorption and room-to-room sound insulation. This link may not be accurately refl ected in laboratory testing. In practice, two ceilings with the same ceiling attenuation class (CAC), but different NRCs, produce different levels of perceived sound insulation. The ceiling with the highest NRC will do a better job of lowering the sound pressure in both the sending and the receiving room.

In practice, there is a strong link between sound absorption and
room-to-room sound insulation. This link may not be accurately
refl ected in laboratory testing. In practice, two ceilings with the same ceiling attenuation class (CAC), but different NRCs, produce different levels of perceived sound insulation. The ceiling with the highest NRC will do a better job of lowering the sound pressure in both the sending and the receiving room.

Total sound insulation is the ability of a total construction (e.g. partitions, ceiling, fl oor and all connections) to prevent sound from traveling through the ceiling void and through building elements. Sound insulation of ceilings is measured using CAC, while walls are measured using the sound transmission class value (STC).

Total sound insulation is the ability of a total construction (e.g. partitions, ceiling, floor and all connections) to prevent sound from traveling through the ceiling void and through building elements. Sound insulation of ceilings is measured using CAC, while walls are measured using the sound transmission class  value (STC).
















Fire performance
Every second counts once a fire has started. Specifiers know choosing the right building materials can delay the spread of fire and provide the vital extra minutes needed to save the occupants and limit the damage.

Given its volcanic origins, stone wool can withstand temperatures up to 1177 C (2150 F). It is non-combustible, will not develop toxic smoke, and does not contribute to the development and spread of fire even when directly exposed to fire.

Ceiling panel products are required to be tested for surface burning characteristics to Underwriters Laboratories (UL) 723/ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials. Testing requires 7.31 m (24 ft) of material to be exposed to a flame ignition source in a Steiner Tunnel Test to determine how far the fire will spread during 10 minutes, and how much smoke is developed during this period.

The test was developed by Al Steiner of UL and has been incorporated as a reference into North American standards for materials testing. The progress of the flame front across the test material is measured by visual observation, while the smoke emitted from the end of the test assembly is measured as a factor of optical density. A Flame Spread Index and a Smoke Developed Index are calculated from these results. Both indices use an arbitrary scale in which asbestos-cement board has a value of 0, and red oak wood has a value of 100.

Many commercial applications require a Flame Spread Index of 25 or less and a Smoke Developed Index of 50 or less. Products labeled “FHC 25/50” (Fire Hazard Classification 25/50) or “Class A” (ASTM E1264, Standard Classification for Acoustical Ceiling Products) fulfill these requirements. Stone wool ceiling panels may be specified to meet the most stringent requirements with a maximum Flame Spread Index of 0 and a maximum Smoke Developed Index of 5.

Humidity and hygienic attributes
Humidity can weaken the structure of certain ceiling materials, causing them to sag and, in extreme cases, even fall out of the suspension system. This often happens in buildings under construction where the building is not yet temperature- and humidity-controlled, or materials have not yet dried. Additionally, humidity levels are naturally high in wet rooms like kitchens and sanitary areas, and moisture problems may occur.

The stone-wool core in acoustic ceiling panels can be specified as hydrophobic, which means it neither absorbs water nor holds moisture. This makes the ceiling panels ‘sag-resistant,’ even up to 100 percent relative humidity (RH) and in temperatures ranging from 0 to 40 C (32 to 104 F). The material is dimensionally stable and does not warp, curl, or cup. It also neither rots nor corrodes. Further, its characteristics remain unaltered over time, maintaining its dimensions and physical characteristics throughout a building’s lifecycle.

Since stone wool is inorganic, it also does not promote the growth of mold or bacteria. North American studies show a relationship between mold and damp conditions, and an increase in allergic reactions, along with eye, nose, and throat irritation.2 They have also been associated with litigious concerns that some commercial building owners have termed ‘sick building syndrome.’

Twenty-three percent of office workers experience frequent symptoms of respiratory ailments, allergies, and asthma. The impact has been an increased number of sick days, lower productivity, and increased medical costs. The economic impact is enormous, with an estimated decrease in productivity around two percent nationwide, at a cost of $60 billion annually.3

Helping maintain cleanliness, stone wool ceiling panels may be specified with a smooth, non-textured finish that can be vacuumed with a soft brush attachment. Specially treated hygienic and medical surface finishes allow cleaning with water and some diluted disinfectants, such as chlorine, ammonia, and quaternary ammonium. In some cases, specially treated surface finishes on stone wool ceiling panels allow for more intensive cleaning, such as steam cleaning twice a year following a defined protocol.

In addition to being composed from the earth’s most abundant bedrock, stone wool ceiling panels can contain up to 42 percent recycled content. When removed, undamaged stone wool products may be reused or recycled for other projects. However, if recycling, one should be observant of recycling plant locations.

Stone wool is an excellent thermal insulator and contributes to energy-efficient buildings. Stone wool ceilings’ reflective, smooth surface also can play a significant role in enhancing energy efficiency through better light distribution. The health benefits of natural light include a more positive mood, improved productivity, and lower absenteeism.4 Maximizing use of natural daylight may allow a reduction in the number of lighting fixtures. The subsequent lowering of electric loads may reduce cooling costs.

Further contributing to sustainable goals, stone wool ceiling panels may be specified with UL Environment’s Greenguard Gold Certification for low-emitting products. Certification is only given to products compliant with the associated requirements, which among others include stringent limits on emissions of more than 360 volatile organic compounds (VOCs).

UL Environment states indoor air can be two to five times more polluted than outdoor air. Greenguard Gold criteria incorporate health-based emissions requirements as denoted by the U.S. Environmental Protection Agency (EPA), the State of California Department of Public Health’s Section 01350, and others.

More than 400 green building codes, standards, guidelines, procurements policies, and rating systems give credit for Greenguard products. Certification also fulfills the low emission requirements of the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) v4 program, and the Collaborative for High Performance Schools’ Criteria (CHPS) for low-emitting materials.

Stone wool, the core material of stone wool ceiling products, can withstand temperatures up to 1177 C (2150 F). It is made from basalt rock and is non-combustible; it will not contribute to the development and spread of fi re.

Stone wool, the core material of stone wool ceiling products, can withstand temperatures up to 1177 C (2150 F). It is made from basalt rock and is non-combustible; it will not contribute to the development and spread of fire.

Stone wool acoustic ceiling products that have been certifi ed to GreenGuard Gold certifi cation standards for low chemical emissions into indoor air during product usage are suitable for environments such as schools and healthcare facilities.

Stone wool acoustic ceiling products that have been certified to GreenGuard Gold certification standards for low chemical emissions into indoor air during product usage are suitable for environments such as schools and healthcare facilities.

Aesthetic design
Beyond sustainability and performance, there are numerous aesthetic considerations in selecting the best stone wool ceiling panels to achieve the desired architectural expression.

The shape of a stone wool panel’s edge significantly contributes to the ceiling’s overall appearance. Demountable options include:

  • square lay-in—cost-effective, provides easy access to the plenum, and mounts in standard suspension systems;
  • tegular—square or angled, hangs on a visible and recessed suspension system that creates a shadow between the tiles, and mounts in standard suspension systems;
  • semi-concealed—appears to float under the suspension system, the profiled edge and deeply recessed grid profiles presents an elegant shadow (an effect emphasized by specifying the suspension system in black); and
  • concealed—hides the suspension system to create a monolithic appearance, but only some concealed panels are demountable.

Another option is the direct-mount assembly, where ceiling panels are directly bonded to the structural soffit or an existing ceiling surface. These systems are for areas where ceiling heights do not permit the use of the suspension setup.

Panels are not limited to two dimensions of squares and rectangles; they may be formed into three-dimensional cubes. Baffles and clouds provide an alternative solution for rooms where contiguous ceilings are unsuitable. They are suited to thermal mass applications where the soffit needs to be left exposed. They can be used as part of a retrofit or to create a design feature.

A wide range of sizes contributes to the design freedom and flexibility offered with stone wool ceiling panels. By combining different module sizes, even small rooms may seem larger and long corridors can seem less distant. The line of a ceiling impacts the perception of a space and creates focal points that may show direction, outline an object, or divide a large space into more comfortable zones.

Horizontal lines convey stability, grounding, and direction. Vertical lines, on the other hand, also communicate stability, as well as pillar-like attributes of strength and balance. Diagonal lines are perceived as dynamic and transformational with overtones of freedom, while curves are considered playful, organic, and soothing.

Texture and color
Based on today’s design styles, stone wool ceiling panels are preferred in smooth and lightly textured surface finishes. This gives the impression the ceiling is lighter in texture, weight, and color. White and neutral tones are the most popular color choices for interior ceilings. For more vibrant spaces, stone wool ceiling panels can be specified in a breadth of other hues.

A viewer’s perception and relation to a color changes depending on whether it stands alone, is dominating a space, or if it is in play with other colors. It also is influenced by the quality and quantity of light hitting it.

Colors evoke physical and psychological reactions, and the brightness or color temperature creates different moods and ambiance: Warm colors—such as red, orange, and yellow—are considered stimulating. Cool colors—like blue, purple, and light green—generally have a calming effect.

Spatial perception is also affected by color. Lighter hues tend to make spaces seem bigger, while darker ones can make spaces feel more intimate. A dark ceiling will seem lower than it really is, or—when installed high enough above—simply disappears.

Color schemes also can indicate the purpose and usage of a space with boundaries and transitions. Consideration should be given to how the visual stimulation in a space will be perceived by the brain to evoke a desired response. This is of utmost importance in environments where varied spaces have different tasks and functions, to avoid any confusion that can cause stress in the occupants.

Segment-specific demands
Color certainly has a place in educational settings, but aesthetics may need to be secondary to performance requirements. Fire performance and indoor air quality are top-of-mind, and acoustics also need to be of primary importance. Classrooms in the U.S. typically have speech intelligibility ratings of 75 percent or less, meaning every fourth spoken word is not understood.5 Loud or reverberant classrooms may cause teachers to raise their voices, leading to increased teacher stress and fatigue.6

In school activity areas, stone wool ceiling panels may be specified with both a high acoustic performance and impact-resistance. The panel’s reinforced surface withstands tougher-than-average wear and tear, as well as frequent mounting and demounting.

Along with durability and flexibility for future redesign, health care facilities seek products with easy-to-clean surfaces to support infection control. Most Methicillin-resistant Staphylococcus Aureus (MRSA) infections occur in people who have been in hospitals or other health care settings and are resistant to the antibiotics commonly used to treat ordinary staph infections.7

Stone wool ceiling panels designed for medical use have been classified Class 5, or better, in accordance with International Organization for Standardization (ISO) 14644-1, Cleanrooms and Associated Controlled Environments−Part 1: Classification of Air Cleanliness. Those that have specially treated medical and hygienic surface finishes also help mitigate:

  • MRSA bacteria resistant to antibiotics and responsible for post-surgery infections and septicaemias;
  • Candida Albicans, which is yeast responsible for skin infections and pneumonias; and
  • Aspergillus Niger, which is mold responsible for pneumonias.

Noise also contributes to patients’ slower recovery times. Studies show high levels of sound have negative physical and psychological effects on patients by disrupting sleep and increasing stress.8

With respect to auditory privacy, acoustic performance not only is relevant to patient decency and respect, but also to the protection of corporate intellectual property, and to increased concentration levels in working environments. After surveying 65,000 people over the past decade in North America, Europe, Africa, and Australia, researchers at the University of California-Berkeley reported more than half of office workers are dissatisfied with the level of speech privacy, making it the leading complaint in offices everywhere.9

From acoustics to fire performance and aesthetics to sustainability, stone wool ceiling systems provide the versatility and attributes to meet the varied requirements of commercial and institutional buildings’ new construction and renovation projects.

1 Visit www.euro.who.int/en/health-topics/environment-and-health/noise. (back to top)
2 Visit www.hc-sc.gc.ca/ewh-semt/air/in/poll/mould-moisissure/effects-effets-eng.php(back to top)
3 See William J. Fisk’s “Health and Productivity Gains from Better Indoor Environments,” from the 2000 edition of Annual Review of Energy and the Environment. Visit www2.bren.ucsb.edu/~modular/private/Articles/Fisk%20HealthandProductivity%202000.pdf(back to top)
4 For more, see Vanessa Loder’s article, “Maybe Money Really Does Grow on Trees,” in the May 4, 2014 edition of Forbes. Visit www.forbes.com/sites/vanessaloder/2014/05/04/maybe-money-really-does-grow-on-trees/2(back to top)
5 See Classroom Acoustics, by Seep et al, published in 2000 by the Acoustical Society of America (ASA).(back to top
6 See Tiesler & Oberdörster’s 2008 article, “Noise: A Stressor? Acoustic Ergonomics of Schools,” in Building Acoustics (15 [3]). (back to top)
7 Visit www.mayoclinic.org/mrsa(back to top)
8 See “Sound Practices: Noise Control in the Healthcare Environment?” published by HermanMiller Healthcare in 2009, and “Sound Control for Improved Outcomes in Healthcare Settings,” by Joseph Ulrich, published in 2004 by the Center for Health Design. (back to top)
9 See John Tierney’s article, “From Cubicles, Cry for Quiet Pierces Office Buzz,” in the May 19, 2012 edition of the New York Times. Visit www.nytimes.com/2012/05/20/science/when-buzz-at-your-cubicle-is-too-loud-for-work.html. Also, visit www.cbe.berkeley.edu/research/index.htm(back to top)

Cory Nevins is Rockfon’s director of marketing, leading the company’s continuing education and training programs to keep commercial building team members updated on acoustic stone wool ceiling panels, specialty metal ceiling panels, and ceiling suspension systems. He has nearly 20 years of experience in the building products industry, the majority of which has focused on ceiling systems, and a bachelor’s degree in marketing from Miami University in Oxford, Ohio. Nevins can be contacted at cory.nevins@rockfon.com.

Improving Floor/Ceiling Sound Control in Multifamily Projects: Sound Testing Practices

by Josh Jonsson, CSI

The sound transmission class (STC) and impact insulation class (IIC) are ASTM-derived single number ratings that try to quantify how much sound a stopped by partition being tested.

Laboratory testing involves an ideal setting for the floor/ceiling assembly—it is isolated from the walls, and there are no penetrations for HVAC, plumbing lines, sprinklers, can lights, or electrical boxes. In the field (i.e. F-STC and F-IIC), the floor/ceiling assembly often sits on load-bearing walls, is connected to the structure, and contains many ceiling and floor penetrations for the items just mentioned. Consequently, the code allows for a lower rating for field scores over those in the lab.

The STC rating essentially tells how much noise is stopped from going through a wall. The test involves blasting loud noise at all the measured frequencies in a room. A Level 1 sound meter measures this exact noise in that room level at all frequencies, as well as the sound in the room on the other side of the partition. These two different levels are then essentially subtracted from each other, with some corrections made for background noise.

The IIC rating is not a comparative test like the STC. Rather, it uses an ASTM-specified tapping machine that sits directly on the floor—more specifically, directly atop the finished floorcovering. (Consequently, an IIC rating always lists the floorcovering with which it was tested.)

The machine has five steel hammers that spin on a cam shaft, falling onto the floor from the same height, no matter what or who is testing. These hammers put a consistent energy into the floor. The sound level meter is taken downstairs below the tapping machine and the sound level is measured at all the frequencies called out in the ASTM standard. These sound levels are plugged into the equations in the standard; a single number is generated summarizing how much sound was stopped.

To read the full article, click here.