- Why control sound in the first place
- Solving the acoustic problem
- Determining the coverage
- Comparing various acoustic panels
This overview discusses how Primacoustic panels work, how to select the right one for the job, basic guidelines on where to use them and how they compare to others that can be found in the market. This web page is not intended to turn you into an expert but it will provide a general understanding of the science involved and how to apply it.
Why Control Sound in the First Place?
In general terms, controlling sound is all about improving intelligibility or our ability to comprehend what is being communicated. Or more simply stated: taking the clutter out of the sound so that you can clearly hear the message. In a church, this may be the spoken word. In an airport, it may be flight announcements. In a factory, it may have to do with safety paging. In a hotel lobby or restaurant, it may simply be an attempt at controlling the reverberant time to make communication between patrons more comfortable. And in a recording studio, controlling the acoustics allows us to create a predictable outcome so that the recording will translate to other audio systems with relative confidence.
Without treatment, sound will echo off the walls, floor and ceiling and reach a point where the room’s ability to handle and dissipate energy has been exceeded. For instance, a teacher quietly speaking in a classroom is very different than one yelling above a room full of excited kids. Once the room’s natural threshold is exceeded, conversation and communication requires much more attention. This causes an effect known as ‘ear fatigue’ – whereby we have to work hard at listening and speak louder to be heard in an attempt to overpower other competing sounds.
These competing sounds are called reflections. They can be powerful primary or first order reflections that echo off nearby surfaces, or be secondary reflections that create a reverberant field. Controlling the ambiance or reverberant field is generally done by mounting acoustic panels on the walls or hanging them from the ceiling. Adding sound absorption to a room can easily turn a dreadful sounding space into one that is comfortable, quite effective for communication. The following are common types of echo:
The direct or initial sound is the sound coming from your mouth, the instrument being played, or from the loudspeaker. This is the message that is being communicated and usually the most important.
Primary or First-Order Reflections
These powerful reflections occur as sound echoes off nearby walls. Because they usually arrive a few moments after the direct sound, they can interfere causing what is known as phase cancellation or comb-filtering and can make hearing what is being said difficult. Controlling first order reflections is usually the first plan of action. Reducing the reverb decay time is usually a matter of increasing the amount of absorption in the room. The more panels you put up, the more energy you will absorb. While classical music benefits from a long reverb, communication via spoken word vastly improves with shorter decay times.
Flutter Echo or Room Chatter
Clap your hands in an empty room and you will hear the sound ricochet off the walls, ceiling and floor. Flutter echo is mostly caused by reflective parallel surfaces that allow the echo to sustain itself. Reducing flutter echo is easily done by placing panels on opposing parallel walls in such a way that the echo cannot sustain itself.
Secondary Reflections or Reverberation
This is the long trailing echo that you can hear in an old church. Back before the modern public address system, churches were designed with long reverberation to carry the voice. This is particularly effective when listening to choirs or Gregorian chant. Classical music also benefits from a long trailing reverberant field as it allows the instruments to excite the room. Controlling the reverberant time is usually a matter of increasing the amount of absorption in the room. The more panels you put up, the more energy you will absorb. Acoustic music or singing voice benefits from long reverb while communication via spoke word is best with shorter times.
Sound Absorption… a Thermo Dynamic Transfer
When loud music is playing, place your hand on the loudspeaker, floor, nearby furniture or even a window and you will feel the vibrations. Sound energy travels through air, solids or liquids in the form of vibrations and when the medium is set into motion, it inevitably generates heat. Sound absorption is in fact an energy transfer function. The scientific term for this occurrence is called a thermodynamic transfer.
When sound penetrates a Broadway acoustic panel, it causes the minute glass wool fibres in the panel to vibrate. The same thermodynamic transfer occurs only this time, it is very efficient due to the minute size of the glass strands and their ability to vibrate freely with very little energy. By distributing acoustic panels around the room, the echo is quickly attenuated.
In the world of acoustics, bass or low frequencies are difficult to control due to their long wavelengths. With sufficient power, bass will pass through just about anything. This means that it not only requires more energy to generate bass (think elephant versus mouse), it is a lot tougher to stop it once it gets going (think trying to stop a freight train versus stopping a bicycle). High frequencies are much less of a problem as the shorter wavelength is much less powerful.
The easiest way to absorb low frequencies is to increase the thickness of the panel. One can more or less predict the required thickness of an acoustic panel by employing ‘quarter wavelength’ calculations. But actual acoustic testing generally delivers surprising results. Unless the panel is sufficiently dense, bass will pass right through. This is the problem with low density foam; it is ineffective at absorbing bass. On the other hand, if the panel is too dense; the high frequencies will simply bounce off and reflect back into the room. Broadway panels are designed to do both; they provide balanced absorption.
Energy of the reflections
Bass Contains More energy
These two graphs compare low and high frequencies at the same amplitude. Notice that the longer bass frequency contains more energy as depicted by the yellow area. Since more energy is in the sound wave, bass will be more difficult to contain.
Quarter Wavelength Calculation
The math used to predict the low frequency performance of an acoustic panel is known as the ‘quarter wavelength calculation’ whereby the thickness of the panel is equal to 1/4 the wavelength of the lowest frequency plus a factor for the angle of incidence. The panel density plays an important role.
Solving the Acoustic Problem
The actual process involved can be simplified into four steps:
- Determine the problem frequency range
- Select the correct acoustic panels to solve the problem
- Estimate the amount of coverage and budget
- Install acoustic panels in strategic areas for maximum benefit
First, you need to determine where the problems are in the room by identifying the offending frequency range. In other words, you must consider what frequencies you are trying to absorb before you simply put up some panels on a wall and expect them to work.
For instance, in a studio, it is essential that you balance the absorption throughout the audio range so that the recording will translate well onto other audio systems. In this case, you really want to create a neutral listening environment. In a home theater, you want to both create excitement within the room while assuring that the all important center channel that carries the dialogue is crystal clear. In a classroom, boardroom or call center, the human voice is being transmitted and therefore your choice of acoustic treatment must properly address this frequency range.
The following graphs show the frequency range of a typical spoken voice and then how the voice energy shifts depending on how loud it is. You will notice that as the voice level increases, the energy increases in the mid band.
If we take a closer look, we can see that most of the energy in the human voice is centered between 300Hz and 1500Hz. It therefore makes complete sense that when it comes time to select the right acoustic panel for the task, that you want to select one that actually works within this range.
Graph shows range of a typical male voice with much of the energy contained in the mid-range from 400Hz to 1000Hz with harmonics extending to 3500Hz.
Choosing the Right Panels for the Job
Acoustic panels are generally specified by the sound absorption coefficient. What this specification tells us is that if the absorption at a given frequency shows a value of 1.0, the panel will be 100% effective at absorbing sound at that specific frequency. A value of 0.5 would indicate 50% absorption.
The Broadway panel is made from high density 6lb glass wool while most foam panels are made using low density 1.3lb urethane. Because most of the foam is cut away to create an artistic pattern, the density of the foam is further reduced due to the huge air gaps that have been cut away. Most foam ends up with a density that barely reaches 1lb per cubic foot. With only 1/6th the density of a Broadway panel, it is no wonder that urethane foam is unable to absorb bass. This underscores the importance of checking the data and making sure it comes from a reputable independent laboratory. If the manufacturer does not provide independent tests, you are likely getting less than what you are paying for.
If we take this a step further and superimpose the voice energy on top of the acoustic panels, we can clearly see that the Broadway panel will provide 95% absorption down to 300Hz while the foam panel will only absorb 38%. This underscores the importance of marrying the target frequency range of with the correct acoustical panel.(Most reputable manufacturers offer a selection of products. Before you make a decision, always verify the specifications!)
So depending on the sound or noise you are trying to absorb, you will need to select a panel that works within a given frequency range. Acoustic panels are usually offered in choice of 1”, 2” and 3” thicknesses, whereby thinner panels tend to be used to absorb mid range and high frequencies while thicker 3-inch panels provide added low frequency absorption.
|1-inch panel (2.5 cm)||For voice range in offices and restaurants, or flutter echo in studio|
|2-inch panel (5.0 cm)||For general sound absorption and to control first order reflections|
|3-inch panel (7.5 cm)||For music related spaces where broadband absorption is desired|
Example 1: Say you have a problem in an office caused by a dot matrix printer where high frequency tapping is ricocheting off the walls causing annoying flutter echo. As the offending problem is primarily in the upper frequencies, the thinner 1-inch Broadway panel would be a good choice.
Example 2: You have a multi-function meeting space. It is sometimes used for dance classes, other times community meetings. You have a limited budget. Broadway 2-inch think panels will provide excellent control over the voice range and still provide control down into the 125Hz bass region, making these a good choice and very effective for music.
Determining the Coverage
Put one small panel up in a gymnasium and you will likely not hear any change. Put a million panels on the walls and ceiling and the sound will be completely dead. Most room treatment lies somewhere in between. And as simple as it may sound, the more acoustic panels you put up, the more sound you will absorb. This follows what is commonly called the acoustic bell curve.
The acoustic bell curve indicates wall surface coverage versus absorption. As the wall coverage increases or number of panels are used in the room, the effectiveness slowly starts to rise. At one point the room begins to transform from a cavernous echo chamber into a comfortable environment. Then, as more panels are added, the effect diminishes and adding panels no longer provides any appreciable benefit. You have reached the top of the bell curve.
There are no absolute rules when it comes to ‘how much coverage will do the job’. For ‘speech’ where maximum intelligibility is desired, acoustical engineers generally specify a reverberant time of less than 1 second. This can be longer in larger rooms. For a classical music concert hall, long trailing reverberation is usually preferred as the instruments combine with the ambiance to excite the room and audience.
The amount of coverage comes down to application, common sense and preference. For instance if you are treating a studio, you may prefer to mix in a livelier environment. On the other hand, if you are treating a house of worship that switches between spoken word and a lively rock band, you may find it beneficial to have more sound absorption. The wonderful thing about acoustics is that you really cannot go too far wrong. Start with 10% to 20% coverage. If you are not satisfied, simply add more. It really is that easy.
The Acoustic Bell Curve
Common reverberation times in various spaces in seconds
Fire and Safety
Another area that should be of concern is fire and safety. This primarily applies to commercial spaces where people gather or work. Be aware! There is all kinds of misinformation regarding panel fire safety in the market and on the web. For the most part, fire safety is a matter of regional jurisdiction by local government bodies and these will have specific requirements when it comes to putting materials such as acoustic panels on wall surfaces. If you are unsure, always check with your local building authority or insurance underwriter for details.
In the United States, the ASTM E 84-05 test is used to verify smoke development and flame spread. In Canada, a similar test is employed known as the CAN/UL-S102-03. Each test is slightly different which means that one must perform each test independently. In fact, new regulations require these tests be performed three times to average the results. If the tests show a flame spread below 25 with a smoke development under 450, the panel is designated as Class-A or Class-I. The following table shows the classifications and the corresponding test requirements.
|Classification (ANSI/UL723)||Flame Spread||Smoke Density|
|Class-A1 / Class-I2||0 – 25||< 450|
|Class-B / Class-II||26 – 75||< 450|
|Class-C / Class-III||76 – 200||< 450|
1Life Safety Code, NFPA 101 Section 6-5.2.1 and Standard Building Code (issued by SBCCI) Section 704
2Uniform Building Code (UBC) (issued by ICBO) Section 4204 and Basic Building Code
It is also important to mention that even if a raw acoustic panel and the fabric covering have passed separate fire safety tests, the results may be void unless they are tested together as a complete unit. This is due to the additives such as the glue or resin which may alter the individual test results.
Foam manufacturers will often point to a C-117 classification. This in fact is a spec that was developed by the State of California as a means to use foam padding in bedding and chairs. It has nothing to do with using foam in construction or as sound absorption in a commercial building. One ‘very creative’ manufacturer has gone as far as using an obscure Christmas tree lighting test as a means to ‘prove’ their ‘plastic’ urethane panels are safe. These tests tell you that the product may contain some form of fire inhibitor, but they should in no way be ‘assumed safe for use’ in public places. Always consult the local building authority or your insurance underwriter to ensure your acoustic panel installation will not put you in harms way.
At Primacoustic, we pride ourselves in making sure that our products are safe. We spend a lot of money on independent lab tests to ensure Broadway panels meet the most stringent demands and ensure they are safe for use anywhere including public places such as schools, night clubs, auditoriums, churches and hotels.
Comparing various acoustic panels
When treating the acoustics in a room, we are usually trying to control sound reflections by placing acoustic panels on the walls and ceilings where they will be most effective. This is normally done by using absorptive panels. There are several types of acoustical panels to choose from in the market. Each has strengths and deficiencies.
To make product selection as easy as possible, we discuss each product and compare their performance with Primacoustic Broadway panels with our opinion.
The following graph compares various 2-inch thick materials. This data was taken from each manufacturer’s printed test reports on their web sites: Sonex™, Auralex™, Rockwool™ and Tectum™. Although none of these are associated with Primacoustic, in our view, all of these manufacturers are known to produce a good credible product.
The most important aspect in selecting an acoustic panel is absorption and as you can see, each product behaves differently. Even within each category, you will find that there are differences based on density and construction.
|Low frequencies 150Hz +||Very Good||Good||Poor||Poor||Poor|
|Mid frequencies 350Hz +||Excellent||Good||Good||Good||Good|
|High frequencies 2kHz +||Excellent||Very Good||Excellent||Excellent||
The next most important set of issues can be summed us as mechanical: In other words, how easy is it to handle and is it easy to mount on the walls? How about durability? Life span? What about removal and clean up? If you have ever tried to remove urethane foam from your walls, you will know the challenge. If not, you are in for a surprise. It usually costs more to repair the damage caused by the glue than the original cost of the panels!
|Mechanical Attributes||Broadway||Rock Wool||Melamine||Urethane||Tectum|
|Handling||Very Good||Poor (fibrous)||Poor (brittle)||Very Good||Very Good|
|Durability||Very Good||Very Good||Poor (brittle)||Limited||Very Good|
Finally, when installing acoustic panels in public places or in large metropolitan cities, one must be aware that building codes are becoming more and more restrictive due to fire concerns. A recent fire at a night-club in the North East USA was accelerated due to urethane foam being applied to the ceiling. Concerns such as these have caused insurance companies to reconsider policies due to legal liability.
|Fire Safety||Broadway||Rock Wool||Melamine||Urethane||Tectum|
|Class-A Fire Safe||Yes||Yes||Yes||No||Yes|
Comparative Test Charts
Primacoustic Broadway Panels
As a baseline, we will start the comparative study by looking at three Primacoustic Broadway panels. Each panel is made from glass-wool or by the trade name ‘Fiberglas’. Glass wool is made from minute strands of glass that are bundled together into various densities. Loose, low-density Pink Fiberglas is commonly used for house insulation while a higher density versions are used in industrial construction and acoustic sound control.
Broadway panels employ high density 6lb per cubic foot bat as this provides more even absorption, particularly in the low end. Glass wool naturally resists burning so it easily attains the class-A designation making them safe for use anywhere. It is also very stable when subjected to various levels of humidity.
Testing performed by Riverbank Acoustical Laboratories. The test method conformed explicitly with the requirements of the ASTM Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method: ASTM C 423-02a and E795-05.
Broadway panels are available in choice of 1″, 2″ and 3″ thicknesses. As shown here, the thickness of the panel determines the low frequency response with the thicker 3″ panel providing maximum bass absorption. Each panel is fabric covered and a selection of impalers make installation easy. We employs ‘modular approach’ whereby smaller panels make handling and shipping easier, particularly on site. When required, multiple panels are ganged together to create larger absorptive areas.
To make product selection as easy as possible, we have gone one step further to compare primacoustic Broadway panels to other products.It is important to note that all of the companies in these charts produce a quality product and this is in no way meant to undermine what they offer, but only to provide factual data for those interested in making a performance valuation. All data was derived from their published specifications and tests which were derived from their web sites.
Primacoustic Broadway versus Owens-Corning™ 705
Owens-Corning has long set the standard with their 705 panels. Like Broadway, this popular 6lb per cubic foot board offers an excellent balance between full bandwidth absorption and ease of use. Regional acoustic panel fabricators will purchase raw panels and recover them using a fabric such as those made by Guilford of Maine.
The following graph compares a raw Owens-Corning 6lb 705 panel to a Broadway 6lb panel. It is interesting to note that both panels deliver very similar results except in the low frequency region where Broadway panel shows 200% greater absorption at 125Hz. This is likely be due to the Broadway’s added fabric and resin hardened edges.
Primacoustic Broadway versus Auralex™ Studiofoam™ Urethane
For years, low cost urethane foam has been used in home recording studios where less demanding acoustics are acceptable. The wedged shaped `anechoic looking` panels are generally produced from low density 1.3lb foam which will help control highs and upper mid frequencies, but with so much ‘air’ in the design, bass absorption is limited. Reputable companies that produce urethane foams panels will embed them with a fire retardant to provide some measure of safety, but this should in no way be presumed to be fire-proof. Urethane is not acceptable for use in construction as it is not class-A fire safe. The following graphs compares 1″, 2″ and 3″ panels.
One Inch Braodway vs. One Inch Auralex
One inch panels are generally used where voice control is needed. Considering that most of the energy found in the voice is in the 300hz to 1.5kHz region, one should pay careful attention before simply using any 1″ panel. This clearly shows that this 1″ urethane foam panel will not provide effective control in this region.
Two Inch Braodway vs. Two Inch Auralex
Two inch panels are the most common as they provide a good balance between full range absorption and cost. As a rule, one tries to extend the low frequency absorption as far as possible. This graph shows that the urethane foam only provides 10% absorption at 125Hz while the 2″ Broadway panel delivers 450% more.
Three Inch Braodway vs. Three Inch Auralex
Deeper three inch Broadway acoustic panels are the preferred choice for high-end music production. These provide exceptionally balanced and linear absorption throughout. This graph compares Broadway with urethane foam. Again, the density of the product clearly dictates the low frequency performance where the foam attains 20% absorption at 125Hz while Broadway provides near perfect absorption at over 90%.
Primacoustic Broadway versus Sonex-1™ Melamine Foam
Melamine is a chemical that is used to produce the coating on various wood composites and counter tops. BASF formulated a type of melamine foam that is used for acoustic sound absorption. The advantage of melamine over urethane is that it does not sustain a flame and therefore will attain a class-A designation. The down side is that like most foams, it does not have sufficient density to effectively absorb bass.
This graph shows Broadway delivers 300% more absorption in the bass and lower mid range. The other problem with melamine is that it is very brittle and non-elastic… making it easy to damage with very little force. Unless covered, this makes melamine inappropriate in high traffic areas where it may come into contact with people.
Primacoustic Broadway versus Rockwool™
If you have ever taken a T-bar ceiling tile down, you will be familiar with a form of Rockwool. This fibrous material is drawn from quarries, mixed with other substances and bonded together. Because it is fire safe and light weight, it is ideally suited for ceiling tiles. But as an acoustic wall panel, although it is just as heavy, it is not as efficient as the glass-wool and therefore appears to absorb significantly less bass.
The following graph compares 6lb Rockwool panels to Broadway. Both products perform well in the upper frequency range but the 6lb Rockwool only delivers 10% effectiveness compared to Broadway’s 45% making it 400% less effective at low frequencies.
Primacoustic Broadway versus Tectum™ Wall Board
For years, Tectum has been used in high abuse environments such as gymnasiums. This makes tremendous sense as damage to acoustic panels caused by balls turned projectiles requires placing a protective grill on top of the panel. But it is important to note that a ‘hard’ product like Tectum will not provide anywhere near the effective absorption as one would enjoy with a Broadway panel. It is no wonder… Tectum is produced by combining wood and cement.
Much of the energy developed by the human voice tends to begin at around 350Hz with most of the energy toping out at around 2000Hz. When you compare these two products, you will note that while the Tectum is absorbing 40% of the energy at 350Hz, the Broadway panels delivers 100% absorption. Then at 500Hz, the Tectum is still way down at 60% while the Broadway shows nearly double the efficiency. Finally, up in the high frequency range, the Tectum’s hard surface is reflecting energy back into the room causing the severe performance dip at 2kHz.
For those that want the added absorption, but are concerned about panel damage, the solution is easy: simply put a protective metal screen on top of the acoustic panel.
Increasing bass performance by adding air cavity
A wonderful trick that can be used with Broadway panels is to increase the bass performance: you simply introduce an air space behind the panel. When the panel is sufficiently rigid, the extra space acts like a trap which will extend the low frequency performance by as much as one octave below the rated performance.
Broadway panels have been tested with the added air space to verify their performance as shown here. The green graph line repesents a surfaced mounted Broadway panel. The lavander graph line represents the same Broadway panel mounted with Primacoustic Offset impalers. Using Offset impalers will introduce a 3.5″ (9 cm) air space behind the panel.
Primacoustic Offset Impaler creates an air space behind the Broadway panel
Testing performed by Riverbank Acoustical Laboratories. The test method conformed explicitly with the requirements of the ASTM Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method: ASTM C 423-02a and E795-05.
Summary: Broadway glass wool delivers higher performance
As evident by all of these tests, Broadway panels clearly outpace all others when it comes to performance. This does not mean that other panels will not work. They all work, it is more a matter of how many panels you need to achieve the same end results. For instance, if a panel only delivers half the performance at a target frequency, you will likely need two or three times the number of panels to achieve the same results. The tragedy is that as you add more ‘unbalanced’ panels, you are also removing more and more of the high frequencies that provide us humans with a natural sense of space. In our view, there is no substitution for balanced absorption. This is why we engineer Broadway panels to achieve the very highest level of performance throughout the frequency spectrum.