Resilient Channels – How Metal Absorbs Sound Waves

Anyone who’s ever shared a wall with someone else has probably wondered if the walls were intentionally thin, or the neighbors intentionally loud. Often the assumption is that the walls between dwellings simply need to be thicker to muffle sound. The fact is that the design of the wall, not the size, can be a contributing factor in transmitting sound from one side to the other.

Consider how walls are constructed in most multi-family housing units. Basically, they are made of gypsum board firmly attached to both sides of a wood frame. When sound waves hit one side of the wall it causes the gypsum board on that side to vibrate. Since the gypsum board is rigidly connected to the frame, the vibration is transmitted right through the framing to the gypsum board on the other side. Those same vibrations traveling through the wall frame can also send sound throughout adjacent floors and ceilings. Noises will radiate through the structure because there’s almost nothing there to cushion or absorb the sound waves.

In order to dampen those approaching sound waves, resilient furring channels can be inserted between one of the gypsum walls and the frame. The resilient channel acts as a shock absorber in this system, muffling vibrations coming from either side of the wall. Resilient channels are routinely used to improve the sound ratings for walls and are especially effective in floor/ceiling constructions.

Resilient channels typically add 3 to 5 Sound Transmission Class (STC) points to an otherwise identical wall or ceiling. This can often be enough to meet the STC and Impact Insulation Class (IIC) ratings required by the project design goals or local codes. In California, the building code specifies minimum lab tested ratings of STC 50 and IIC 50 for partitions in multi-family dwellings.

In fact, the IIC 50 rating required by the building code almost mandates the use of resilient channels to hang the ceiling in a multi-family project. Unless the floors are completely carpeted (which is rare for kitchens and bathrooms), it is very difficult to achieve IIC 50 ratings without using resilient channels and batt insulation in the floor-ceiling construction.

It is important to distinguish acoustically effective resilient channels from hat channels, z-channels, and other lightweight metal furring systems. These other systems may resemble resilient channels, but they afford no movement and are simply too rigid to be effective. Only resilient channels have any acoustical benefit.

As can be seen in the diagram above, resilient channels have two flanges, one wide and the other narrow, with a slotted portion in the middle. These slots create the flexibility which allow the resilient channel to act as an isolator. Every manufacturer has a different design for resilient channels. Assuming they are installed correctly, the ones with the least amount of material connecting the wide and narrow flanges will (in theory) transmit the least amount of sound.

Regardless of which brand of resilient channel is used, it is extremely important to install them correctly. Improper installation will nullify any advantage you would have gained from using them in the first place. On a recent project, it took one unfortunate contractor two tries before he finally got it right. On his first attempt, he mistakenly put in a hat channel system. The second time, he correctly installed three different kinds of resilient channels, none of which was the brand specified in the design. The third time around everything went as planned. Luckily, both of the contractor’s mistakes were caught before the gypsum board had been hung.

There are a few simple procedures that need to be followed when using resilient channels. On walls, the channel should be mounted perpendicular to the framing with the narrow flange along the bottom. This allows the gypsum board’s weight to draw itself away from the framing. For ceilings, the flanges should all be pointing in one direction. This keeps the channels from fighting each other.

When fastening the gypsum boards, the screws must be connected to the channels between the studs or joists. It is critical not to “short out” the resilient channels by screwing into the wood behind them. This inflexible connection destroys the benefit of the channels, and you have now spent a lot of time and money to create a complex rigid attachment.

The resilient channels should be held back from intersecting surfaces about an inch on the side edges, and about 2 to 3 inches at the top and bottom of the wall. It does little good to carefully attach the channels in the middle of the wall when the baseboard screws connect the entire bottom edge to the sill plates. Similarly, it is easy to short out the resilient channels at the top of the wall by screwing into headers. The gypsum boards attached to the channels also need to be held back one-quarter inch from similar intersecting surfaces. If the panels are jammed against the edges, then they will be rendered ineffective. The gaps should then be sealed airtight with a specified acoustic caulking. For a more aesthetic effect, the caulked edges can be painted or covered by a trim.

When resilient channels are properly installed, it should be possible to slightly flex the wall or ceiling surface. A lack of flex indicates that the channels are shorted out by screws fastened into the wood framing. Also, it usually does not matter which side of the wall is resiliently suspended. This makes it easier to accommodate shear plywood and wall mounted cabinets–simply put the resilient channels on the opposite side of the wall in the affected rooms.

Keep in mind that this article only outlines the benefits of correctly installed resilient channels. If you feel that this technology would be useful in an upcoming project, it is advisable to seek help from an experienced consultant. One particular contractor already knows how much easier it is to get things right the first time around.

Sound Transmission Class (STC)–Describes how much sound a wall or floor/ceiling construction will block from one room to the next. STC is applied to situations where speech or office noise constitutes the main sound problem. To determine the rating, an active loudspeaker is placed on one side of the partition, and sound levels are measured on both sides. The difference in levels shows how much sound can be blocked by the partition. The higher the rating, the better the sound insulation properties.

Impact Insulation Class (IIC)–Measures the noise created by foot-falls/impact on a floor through a ceiling. A really expensive but standardized testing device generates the impact sound by dropping 5 hammers which impart a known energy into the floor/ceiling construction. In the receiving room below, the resulting sound pressure level is measured in frequency bandwidths comparable to those used in sound transmission loss measurements. Increasing IIC values correspond to improved impact noise dampening qualities.

96 spring

A hat channel (top) and a resilient channel (bottom) with side views-for picture

Anyone who’s ever shared a wall with someone else has probably wondered if the walls were intentionally thin, or the neighbors intentionally loud. Often the assumption is that the walls between dwellings simply need to be thicker to muffle sound. The fact is that the design of the wall, not the size, can be a… Read more »

Video Conferencing – What Does It Mean For You?

Canon saved about $200,000 during 1993-94…the US Navy’s distance learning network saved over $4 million over a four-year period…and Norfolk Southern Railroad saved $1,080,000 over an 18-month period. How?

By video conferencing! A number of our clients are upgrading their systems, or reconsidering video conferencing. To paraphrase one of our clients, “…a person needs to be there to facilitate the work, not to have a meeting”. With the increase in travel costs and expansion of offices, companies are forced to fully utilize their time and available resources. At the same time, system and communication costs are falling and quality is improving. This is helping video conferencing expand.

New applications, opening in many different fields, are also proving the cost effectiveness of video conferencing: educators use it as a convenient means for interactive access to classes, meetings and learning resources from remote locations, physicians use it to provide consultations, courts use it to increase security of prisoners and conduct video arraignments.

Video Conferencing System Types
There are several different types of systems now available:

• Desktop Systems are the least costly of the three basic types and are now being promoted by Intel and Apple. In its simplest form, this system involves setting up a camera, monitor, microphone, and loudspeaker in two rooms and connecting them together on a computer network. The limitation of this system is that it is designed for use by one person at each end, as opposed to larger groups.

• Roll About Systems can be moved from room to room. Built at a manufacturing facility and shipped to the site, installation teams are usually on-site for less than one day. There is no need for local inspections or approvals and if the client plans to upgrade in the future, the components of this system can typically be integrated into a larger system.

• Fixed Systems are built into a dedicated video conference suite, which houses all of the necessary equipment. This is generally the most expensive option, especially if an existing shell space is being modified. Inspections and approvals are needed and installation and construction teams are usually on-site for extended periods of time.

Image Quality
One of the first things a new user will notice when viewing a video conference for the first time is the relatively low quality of the picture compared to normal TV. Many people do not realize that the actual picture will not necessarily be in real time, either. Companies are upgrading their systems for these very reasons…to obtain better image resolution and faster transfer of video images. As occurred in the computer industry, much of the video conferencing technology is quickly outdated and surpassed by the quality and speed of new equipment.

The perceived picture quality in a video conference is affected by 4 major factors:

  • Frame Rate is the number of individual video “pictures” that are displayed on the screen in a given time period. Frame rates are expressed in frames per second (fps). With higher frame rates the participants look more real and movements are less choppy. Frame rates in video conferencing systems can vary from 5 fps to the 30 fps used in standard TV.
  • Resolution is the number of individual picture “information dots” displayed horizontally and vertically in each frame. The number of horizontal lines that are displayed per frame is a fixed display television standard. The number of information dots displayed in each of these lines is what differs. Similar to a fax machine, video conferencing systems break the video information down into digital data by sampling it many times per second. The higher the sample rate, the more information dots are gathered for each frame and the clearer the picture.
  • Motion Handling is a function of each individual CODEC. To increase performance and reduce the amount of information being transmitted between sites, CODECs do not transmit the whole picture, only the changes in a picture between two frames. This means that pictures with very little movement have only small packages of information to transmit. As the amount of movement increases, the amount of information to transfer from site to site increases.
  • The Data Rate is the number of bits of information that can be transmitted per second. In other words, the data rate is the size of the information pipeline. Determined by cost and availability of equipment, the data rate is a fixed number established at the start of a conference.

Because the CODEC has no control over the data rate or the movement of the participants during a conference, the frame rate and resolution must be adjusted to accommodate the amount of information being transmitted through the information pipeline. In most systems, the resolution is fixed at the lowest usable value and the frame rate is adjusted accordingly. Higher data rates allow either better frame rates or higher resolutions (these can be “traded off” depending on the requirements of the CODEC).

What’s the Bottom Line? Despite their costly beginning, video conferencing systems have now become more affordable. This can be attributed to the significant drop in cost of ISDN data lines. In fact, they now cost about one fifth the amount they were a few years ago. As a result, clients can increase their number of ISDN lines for a reasonable cost, and obtain higher transmission speeds and a more natural image. Our clients have found that three ISDN lines provides an acceptable level of quality. Video conferencing has become a cost-effective media which is proving both profitable and worthwhile in many industries. It provides clear, enhanced communications, reduced travel expenses, and a competitive edge in the technology-driven business climate that lies ahead.

Important Video Conferencing Terms

Analog- A method of sending signals — voice, video, data — in which the transmitted signal is analogous to the original signal. Analog technology uses continuously changing electrical waves to generate voice or low speed data signals.

Bandwidth- The range of frequencies over which signal amplitude remains constant (within some limit) as it is passed through a system.

Broadband- Digital services at rates greater than 1.544 Mbps.

CODEC-  Acronym for COder/DECoder. A video and/or audio bandwidth digital compression device.

Digital-  A method of sending and receiving information.

Transmission-  coded with on-and-off pulses of electricity or light.

Encryption-  Code conversion of digitally coded signal values, performed, in general, without any increase of bit rate, in order to prevent unauthorized reception of a signal.

ISDN-  Integrated Services Digital Network. International Standard for digital services on the public switched telephone network.

MCU- Multipoint Control Unit. A switching device commonly used to switch and control a video conferencing network allowing multiple sites to conference simultaneously.

Canon saved about $200,000 during 1993-94…the US Navy’s distance learning network saved over $4 million over a four-year period…and Norfolk Southern Railroad saved $1,080,000 over an 18-month period. How? By video conferencing! A number of our clients are upgrading their systems, or reconsidering video conferencing. To paraphrase one of our clients, “…a person needs to… Read more »

Audio Considerations in Teleconferencing – “Can You Hear Me?”

Teleconferencing, holding meetings by an electronic means, is one of the fastest growing industries in the world. The word “teleconferencing” means different things to different people. Teleconferencing can range from a conference call with speaker phones to a system with installed overhead speakers and tabletop microphones, to a full scale audio for video conferencing system with satellite feeds.

Regardless of the type of teleconferencing, how the audio portion of your conference is handled will ultimately determine the success of the system and satisfaction with the event. Every meeting starts with “can you hear me?” or thud, thud, thud as a person taps a hand on the microphone.

Remember the last time you went to a movie where the theater had problems with the soundtrack? It’s the same with teleconferencing. Even if you have perfect video, audio problems will destroy the conference. One of the biggest problems in teleconferencing is background noise. When you are in a conference or meeting room and you hear background noise such as duct rumble, diffuser noise, or a computer fan, you for example, individually, tend to block out or ignore the noise because you have been able to identify its source. In a teleconference, however, this background noise is transmitted to the distant location along with the sound of your voice. There is no longer a method for the listeners at the other end to distinguish where that noise came from. The noise becomes distracting and masks over the spoken word.

The proper acoustical treatment of any room with teleconferencing is extremely important to the success of that conference. If more than one microphone is used, it is also very beneficial to have an automatic microphone mixer that limits the number of microphones that are active and turns on the microphone nearest to the person speaking. If the only active microphone is the one closest to the person speaking, the intelligibility of the conference will be much higher. Ceiling-mounted microphones contribute to the attractiveness of the conference room, but at the other side of the conference, it sounds like the participants are not talking into the microphone.

The further someone is from the mic, the greater the chance that background noise will drown them out. The best idea is to place the microphones close to the people speaking.

Another source of trouble in teleconferencing is the phenomenon known as “acoustic echo”. Acoustic echo appears when the conference room is operating with open mics and loudspeakers in full duplex conference mode. A full duplex conference mode is when you and the distant room can have a one-on-one communication without having to wait for the other room to stop talking.

Electronic audio signals are sent in both directions simultaneously. In this situation, your audio goes over the transmission media to the speakers in the distant room. The audio is then picked up by the open microphones in that room and retransmitted to you. The result is that you will hear your own voice coming back to you from the far room, thus the echo. This effect is similar to talking over a public address system in a stadium — highly confusing.

Fortunately, acoustic echo can be minimized. It is very easy to remedy the problem by installing an acoustic echo canceller. An echo canceller looks at the audio coming into the room from the loudspeakers, and compares it to the audio from the microphone. Any audio that “matches” is removed from the transmission. However, to keep your installed in the distant room. This means that you will need an echo canceller in every room that is part of your conference. Remember, an echo canceller compares the audio from the loudspeakers to the audio from the microphones. Your best bet is to put an echo canceller in each room. This will assure that none of the rooms can create an echo condition.

Teleconference equipment can be easily installed in existing conference rooms. The best test for proper operation will be made with everyone’s ears. And don’t forget the audio.

Teleconferencing, holding meetings by an electronic means, is one of the fastest growing industries in the world. The word “teleconferencing” means different things to different people. Teleconferencing can range from a conference call with speaker phones to a system with installed overhead speakers and tabletop microphones, to a full scale audio for video conferencing system… Read more »

Binauralization™ — Now You Can HEAR How it Will Sound BEFORE Construction Starts!

How often have you wondered what a room was going to sound like before it was built? How would it sound if the walls were parallel and not canted? Are all of the acoustical room finishes really required? Will there be echoes? Is the reverberation time too long? What will speech sound like in the room? What will music sound like?

Much has been published on this subject in recent months. A major consumer loudspeaker manufacturer has developed a system to model a room with their loudspeakers. However, at Thorburn Associates, we have been working with this type of technology for over 2 years and have begun offering Binauralization™ as a service to our clients.

Prior to Binauralizations™, modeling was used primarily for large and extremely critical projects such as concert halls. The only way to acoustically model a space was to build a scale model of the room. This is tedious and time consuming. To build an acoustically accurate scale model, the details, the relief, and even the construction materials must be scaled down to match the appropriate acoustical effects. Because the sound waves that we hear range from 56 feet to 2/3 of an inch in length, it is difficult to find materials that accurately scale down to 1/10 inch or 1/4 inch scale models.

Unlike model building for visual aesthetics (where a red barn looks like a red barn) we can’t just paint the surfaces to create the same scaled visual look. We must also scale the acoustical characteristics of the materials used. Computer simulations allow us to address the problems of the scale in a much more effective manner.

Also, unlike scale models, where complex charts and numbers are used to represent the acoustical properties of the room (Figure A), Binauralizations™ let you hear for yourself if the finished project will sound good or bad.

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Figure A. Complex Graphics are no longer necessary to understand the Acoustical Characteristics of a room when using Binauralizations TM.


Some of the questions that always arise when we discuss this new technology with clients are “How accurate is the model?” “Can we adequately rely on what we hear in the computer simulation to reflect what will actually be built?” and “How can we use this new technology to better serve our clients?”

Does it Work?
Prior to offering Binauralization™ as a service, we modeled a number of different spaces, then conducted binaural measurements once construction or retrofitting was completed. What we found is that while it is very difficult to achieve an exact model of the room, the major issues that we, as acoustical consultants, are concerned with and need to communicate to the owners and architects, are very readily apparent. So, yes, it does work!

The first step in developing an acoustical simulation is identifying the finishes within the room, both in type and location. Once the physical characteristics of the model are defined, random rays are sent out from a source location. (Figure B.) These rays simulate sound waves leaving the source and traveling in the room. As the rays hit a surface, the computer determines how much acoustical energy is absorbed by that surface, how much energy is reflected, and in what direction.

spring 95-2
Figure B. Single Ray Tracing showing how sound is both absorbed and reflected throughout a space.

This process continues until the sound ray has traveled a predetermined length of time. The longer we let the calculation go, the more accurate the model. Accuracy is also increased with the number of rays sent out.

With this information in hand, we then post-process audio from a CD or tape or a recording of your own voice, and let you listen to that sound from a specific location in the room.

How Can I Use Binauralizations™?
After the model is built, we can readily change surface materials to allow you to hear just how bad an echo will be if we don’t treat the walls or determine if you need to have an acoustical tile ceiling, prior to construction. Binauralizations™ allow the client to make a subjective decision without relying on us to “verbalize” our recommendations in a meeting or with a report.

We can model any type of facility from churches to theatres to conference rooms to lobbies to casinos to entire theme-parks! Binauralizations™ are for any project where good acoustics are necessary and bad acoustics can ruin its success!

How often have you wondered what a room was going to sound like before it was built? How would it sound if the walls were parallel and not canted? Are all of the acoustical room finishes really required? Will there be echoes? Is the reverberation time too long? What will speech sound like in the… Read more »

Sound Masking

Whether you call it white noise, pink noise or NC systems, sound masking is probably the only time that an acoustical consultant will admit that some noise is good.  The shift to open plan offices and demountable partitions from the traditional “private” office with gypsum board construction has created the need to raise the background sound levels in the work place (in a controlled manner) to cover over or mask distractive office noise.

The trick is to determine how much noise a person can tolerate before their concentration is disturbed. Telephone conversations in adjacent spaces, copiers, printers and impromptu hallway and water cooler conferences generate disruptive noise in the work space.  As discussed in a previous newsletter, when the background noise throughout an office space is uniform (not too loud, not too quiet) a worker’s perception of the acoustical isolation is significantly improved.  If a particular sound is covered or masked by another noise, a person will not be able to understand the quieter sound and it will not be disturbing.  A uniform background sound level can best be accomplished with a sound masking system which fills in and raises the overall noise level in the office during the quieter periods of the day.
There are a number of different ways to provide a uniform background sound level in the work space:

  • The careful design of the supply and return air diffusers systems will work for small areas.  This type of system utilizes the turbulence noise generated by air flow through the diffuser.  This method requires a very careful selection of the diffuser type, quantity, and locations. Very close coordination with the Mechanical Engineer, Architect, and Acoustical Consultant is required, along with an accurate knowledge of the final airflow requirements of the space to allow the selection of a diffuser with the proper airflow-to-turbulence noise rating.
  • Install small self-contained units (noise generators) often supplied by furniture vendors or other sales representatives.
  • Have a sound masking system designed and installed as you would any other technical system, be it electrical, mechanical or structural.

All of these systems must be properly adjusted to work.  System balancing and adjustment helps to minimize the intrusiveness of the system. Far too often, a system is installed then just turned on and not adjusted.

Systems provided by furniture supply houses or turn key pre-manufactured systems are often the worst offender of this problem and are sold as a quick fix.  These “simple” systems are often perceived by the workers as being very harsh or too loud and are usually turned off within a month of installation.

However, a well designed sound masking system will have the ability to control and adjust the background noise spectrum in many different frequency or tonal ranges.  The sound masking system will automatically change the volume over the course of the day, adjusting for quiet, early morning and late night hours as well as busy mid-day hours.  A good masking system will also provide methods to prevent tampering or unauthorized access (computer control, security lockouts, etc.).

A sound masking system makes a open plan office area more functional and acceptable than it would be without it.  However, any system that is not adjusted properly and is a major source of noise will be a problem. Unfortunately, this includes a sound masking
system.

When a sound masking system is properly installed and adjusted, the quality of the work environment is significantly improved.

(c) Thorburn Associates 1994

Whether you call it white noise, pink noise or NC systems, sound masking is probably the only time that an acoustical consultant will admit that some noise is good.  The shift to open plan offices and demountable partitions from the traditional “private” office with gypsum board construction has created the need to raise the background… Read more »

Residential Sound Isolation

We frequently get calls from owners and tenants who wish to improve the sound isolation between apartments and condominiums, particularly in older units.  The call often begins with, “I want something I can spray on to the wall to soundproof it so I don’t hear my neighbor’s stereo…” or “My neighbor’s snoring keeps me awake at night”.  Unfortunately, just putting something on the surface of the walls will not really improve things.

Sound absorbing materials only “color” the sound in the room the material is added to.  Typically in a very absorptive room such as a bedroom, adding more absorption has little effect on things.  Experience has shown there is only a 2 to 4 decibel change in sound levels between an unfurnished room and a completely furnished one.

“But what is a 2 to 4 decibel difference?” is usually the next question.  In a typical setting, the sound level would need to change by 3 decibels for you to be able to hear a change.  An example of this is the change in the sound level if you are listening to two loudspeakers side-by-side and then turn one off then back on.

“Okay, but isn’t there some type of minimum code requirement?”  The answer here is that in 1973 the State of California adopted Title 25, which required that the minimum sound isolation across party walls and floor/ceilings in hotels, motels, condominiums, and any other dwelling area, be at least STC 50.  This code has been adopted, amended, changed and is presently Title 24, Chapter 35 of the California Building Code.  In case you are wondering, STC is the Sound Transmission Class of a partition.  It is a single number rating system which is used to compare the sound insulating properties of different walls, floor/ceilings, doors, etc. primarily in respect to speech and small appliance noise.  In a building the actual construction of a STC 50 partition is approximately equal to 50 decibels of sound isolation.  The higher the STC number the greater the sound isolation properties of the partition.

So how do we reduce the noise if sound absorbing materials don’t work?  If there is no “magic” material to spray on to the walls?  As you might have guessed, the answer is to upgrade the wall or floor/ceiling constructions to increase the STC rating of the partition.  This usually involves removing the existing gypsum board, adding batt insulation, then mounting or hanging new gypsum board on resilient channels. This construction has an STC 50 rating versus an uninsulated wall with an STC 35 rating.  An increase of 15 STC points! (Please see diagrams.) In some cases, when it is not desired to remove the existing gypsum board, a “new” wall can be furred out from the existing wall.

 

su21994a

su21994b

“But how much sound isolation is enough?”  As we have discussed in recent articles this is a “signal-to-noise” issue. The quieter the background environment where you will be listening, the greater the insulating properties required to keep loud noises out.  What works in an urban setting with bus and auto noise will not work in a quiet, rural area with only wind and birds.

(c) Thorburn Associates 1994

We frequently get calls from owners and tenants who wish to improve the sound isolation between apartments and condominiums, particularly in older units.  The call often begins with, “I want something I can spray on to the wall to soundproof it so I don’t hear my neighbor’s stereo…” or “My neighbor’s snoring keeps me awake… Read more »

Residential Sound Isolation

We frequently get calls from owners and tenants who wish to improve the sound isolation between apartments and condominiums, particularly in older units. The call often begins with, “I want something I can spray on to the wall to soundproof it so I don’t hear my neighbor’s stereo…” or “My neighbor’s snoring keeps me awake at night”. Unfortunately, just putting something on the surface of the walls will not really improve things.

Sound absorbing materials only “color” the sound in the room the material is added to. Typically in a very absorptive room such as a bedroom, adding more absorption has little effect on things. Experience has shown there is only a 2 to 4 decibel change in sound levels between an unfurnished room and a completely furnished one.

“But what is a 2 to 4 decibel difference?” is usually the next question. In a typical setting, the sound level would need to change by 3 decibels for you to be able to hear a change. An example of this is the change in the sound level if you are listening to two loudspeakers side-by-side and then turn one off then back on.

“Okay, but isn’t there some type of minimum code requirement?” The answer here is that in 1973 the State of California adopted Title 25, which required that the minimum sound isolation across party walls and floor/ceilings in hotels, motels, condominiums, and any other dwelling area, be at least STC 50. This code has been adopted, amended, changed and is presently Title 24, Chapter 35 of the California Building Code. In case you are wondering, STC is the Sound Transmission Class of a partition. It is a single number rating system which is used to compare the sound insulating properties of different walls, floor/ceilings, doors, etc. primarily in respect to speech and small appliance noise. In a building the actual construction of a STC 50 partition is approximately equal to 50 decibels of sound isolation. The higher the STC number the greater the sound isolation properties of the partition.

So how do we reduce the noise if sound absorbing materials don’t work? If there is no “magic” material to spray on to the walls? As you might have guessed, the answer is to upgrade the wall or floor/ceiling constructions to increase the STC rating of the partition. This usually involves removing the existing gypsum board, adding batt insulation, then mounting or hanging new gypsum board on resilient channels. This construction has an STC 50 rating versus an uninsulated wall with an STC 35 rating. An increase of 15 STC points! (Please see diagrams.) In some cases, when it is not desired to remove the existing gypsum board, a “new” wall can be furred out from the existing wall.

summer 94

“But how much sound isolation is enough?” As we have discussed in recent articles this is a “signal-to-noise” issue. The quieter the background environment where you will be listening, the greater the insulating properties required to keep loud noises out. What works in an urban setting with bus and auto noise will not work in a quiet, rural area with only wind and birds.

We frequently get calls from owners and tenants who wish to improve the sound isolation between apartments and condominiums, particularly in older units. The call often begins with, “I want something I can spray on to the wall to soundproof it so I don’t hear my neighbor’s stereo…” or “My neighbor’s snoring keeps me awake… Read more »

Sound Masking

Whether you call it white noise, pink noise or NC systems, sound masking is probably the only time that an acoustical consultant will admit that some noise is good. The shift to open plan offices and demountable partitions from the traditional “private” office with gypsum board construction has created the need to raise the background sound levels in the work place (in a controlled manner) to cover over or mask distractive office noise.

The trick is to determine how much noise a person can tolerate before their concentration is disturbed. Telephone conversations in adjacent spaces, copiers, printers and impromptu hallway and water cooler conferences generate disruptive noise in the work space. As discussed in a previous newsletter, when the background noise throughout an office space is uniform (not too loud, not too quiet) a worker’s perception of the acoustical isolation is significantly improved. If a particular sound is covered or masked by another noise, a person will not be able to understand the quieter sound and it will not be disturbing. A uniform background sound level can best be accomplished with a sound masking system which fills in and raises the overall noise level in the office during the quieter periods of the day.

There are a number of different ways to provide a uniform background sound level in the work space:

  • The careful design of the supply and return air diffusers systems will work for small areas. This type of system utilizes the turbulence noise generated by air flow through the diffuser. This method requires a very careful selection of the diffuser type, quantity, and locations. Very close coordination with the Mechanical Engineer, Architect, and Acoustical Consultant is required, along with an accurate knowledge of the final airflow requirements of the space to allow the selection of a diffuser with the proper airflow-to-turbulence noise rating.
  • Install small self-contained units (noise generators) often supplied by furniture vendors or other sales representatives.
  • Have a sound masking system designed and installed as you would any other technical system, be it electrical, mechanical or structural.

All of these systems must be properly adjusted to work. System balancing and adjustment helps to minimize the intrusiveness of the system. Far too often, a system is installed then just turned on and not adjusted.

Systems provided by furniture supply houses or turn key pre-manufactured systems are often the worst offender of this problem and are sold as a quick fix. These “simple” systems are often perceived by the workers as being very harsh or too loud and are usually turned off within a month of installation.

However, a well designed sound masking system will have the ability to control and adjust the background noise spectrum in many different frequency or tonal ranges. The sound masking system will automatically change the volume over the course of the day, adjusting for quiet, early morning and late night hours as well as busy mid-day hours. A good masking system will also provide methods to prevent tampering or unauthorized access (computer control, security lockouts, etc.).

A sound masking system makes a open plan office area more functional and acceptable than it would be without it. However, any system that is not adjusted properly and is a major source of noise will be a problem. Unfortunately, this includes a sound masking system.

When a sound masking system is properly installed and adjusted, the quality of the work environment is significantly improved.

 

Whether you call it white noise, pink noise or NC systems, sound masking is probably the only time that an acoustical consultant will admit that some noise is good. The shift to open plan offices and demountable partitions from the traditional “private” office with gypsum board construction has created the need to raise the background… Read more »

Peach Piracy?

Speech privacy (peach piracy) exists when a conversation cannot be understood even if it can be heard.

There are 4 levels of speech privacy; normal, confidential, inaudibility and none.

  • Normal speech privacy exists when someone can only partially understand the telephone conversation or the meeting in an adjacent office cubical without having to stop, listen and concentrate on the conversation.
  • Confidential speech privacy exists when you can only hear mumbling coming from the other side of the office partition. If you can occasionally make out a word, but you cannot understand the context or intent of the conversation then the conversation is confidential.
  • Inaudibility exists when you have no idea that a person is speaking in the adjacent room.
  • There is no speech privacy if you can actively participate, without trying, in the conversation being held in the adjacent work station or office.

So why is there always one individual on a floor or building who complains they do not have enough privacy even though their colleagues seem to be fine? This person thinks that speech from an adjacent office space (open plan or private) is obtrusive and annoying. What they are experiencing is a “signal to noise” ratio problem. The solution is to reduce the ratio for greater speech privacy.

The higher the signal (speech, phone ring, etc.) over the noise (partition sound reduction plus background noise) the more intrusive the sound will be. This ratio of signal to noise varies throughout a floor or building because the building system noise, traffic noise, HVAC system noise, and office equipment noise all vary throughout the floor. It would be similar to having different areas of the floor illuminated with 25 watt bulbs, 50 watt bulbs and 100 watt bulbs. Some individuals will feel that the lighting is too bright in their area while others will feel that it is too dark.

Another important factor is that the quality or type of noise has an impact on its obtrusiveness. Individuals on speaker phones or people with naturally loud or boisterous voices can be particularly irritating.

A particularly boisterous worker could be quieted by a muzzle. But, while this may be an effective and inexpensive solution, it is not really practical. Improving the walls, office partition heights, and increasing background sound levels to a uniform level throughout the office space (sound masking) all significantly improve the perceived sound isolation within offices and speech is generally not as obtrusive.

 

Speech privacy (peach piracy) exists when a conversation cannot be understood even if it can be heard. There are 4 levels of speech privacy; normal, confidential, inaudibility and none. Normal speech privacy exists when someone can only partially understand the telephone conversation or the meeting in an adjacent office cubical without having to stop, listen… Read more »

Front Vs. Rear Projection – Questions and Answers

From an entertainment point of view there is probably nothing more impressive than going to a first run cinema (front projection) and being enveloped by the large screen and catchy plot. That’s great if the purpose is for entertainment or large scale audiences. However, if the purpose is to explain a project topic or concept, a different system may be desired. When we are giving lectures or presentations we tend to move around and interact with our slides and graphics. If we use front projection we often disrupt or block part of the image. If rear projection is used we can interact and discuss the image without causing shadows. The solution as to which is best is determined by how the client will make presentations.

The following list describes the issues we discuss to determine which system is most appropriate for a project.

Front Projection

Advantages

  • Allows a much bigger image.
  • Wide viewing angle.
  • Allows for Keystone correction (where the top of the image is wider than the bottom of the image, see picture below).
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Disadvantages

  • The room lighting for front projection must be carefully designed. The image you view, when front projection is used, consists of light from the projector reflected off the screen. This also means any light in the room will also be reflected off the screen back to you, washing out the image (this is why a cinema is generally very, very dark).
  • Projection equipment is often located in the same room as the screen and unless carefully coordinated creates a new source of noise, glare, distraction, etc.

Rear Projection

Advantages

  • Allows for easy interaction with the projected image.
  • Good for long, narrow rooms such as conference rooms.
  • Can be viewed in a room with normal illumination.
  • Excellent for taking notes and command center types of situations where individuals move around and are doing other activities.
  • Generally provides a cleaner looking system installation appearance.

Disadvantages

  • Screen size is limited to the size of transportable glass.
  • Space is required behind the projection screen. However, this space can be utilized as the audiovisual system equipment room. The use of mirrors can further reduce the depth requirements of the room.
  • Rear projection systems are generally a little more expensive. Rear projection screens are slightly more expensive than front projection roll down screens and the additional cost of the square footage required for the rear projection room can be an issue.

As you can see there are advantages and disadvantages to both systems and both are very effective when used properly.

The key is to evaluate your clients’ needs (both current and future) and select the system that best meets those needs.

 

From an entertainment point of view there is probably nothing more impressive than going to a first run cinema (front projection) and being enveloped by the large screen and catchy plot. That’s great if the purpose is for entertainment or large scale audiences. However, if the purpose is to explain a project topic or concept,… Read more »