Designing for Acoustics with KnollTextiles SOUND IS GOOD; NOISE IS BAD.
Acoustics shape our environment and our experience.
Sound is an important and sometimes neglected aspect of comfort. Noise affects our stress and productivity levels, our ability to learn and retain information, our perception of a space and our overall well-being.
A well-designed interior controls for acoustics in order to contribute to a welcoming and comfortable environment. If reverberation levels interfere with the intended use, then the space becomes uncomfortable.
The way a space sounds gives meaning as to what that space is. Spaces have distinct acoustic needs based on their purpose
OPEN OFFICES need to encourage HOTELS have multiple acoustic concentration, productivity and needs depending on the space and a sense of wellness. The inability its purpose: while a lobby should to have a comfortable conversation be warm and buzzing (but not is the biggest frustration for people cacophonous), a hotel room must working in an open office. In a be peaceful and quiet. Noise is the recent survey, 75% of workers most common complaint at hotels. cited “workplace acoustics” as the worst aspect of their office environment.¹
RESTAURANTS require a delicate SCHOOLS need 100% speech balance between a sense of intelligibility in their classrooms so liveliness and overwhelming noise. that students and teachers can Diners need to be able to hear hear everything that is being said. one another without competing Most schools in the U.S. only have with everyone else’s conversations. 75% speech intelligibility, which means every fourth word that is spoken is not understood.² Noise from reverberation makes it difficult to focus on the teacher and leads to a poor learning environment.
¹ “The Workplace Experience Revolution,” October 2018, Leesman Index. https://www.leesmanindex.com/wp-content/uploads/2018/10/Leesman-EwX-Book.pdf ² “Acoustics in Schools,” Cisca. http://www.cisca.org/files/public/Acoustics in Schools_CISCA.pdf How does sound move in a space?
DIRECT VS. REFLECTED SOUND
There are two types of sound: Direct and Reflected.
Direct Sound reaches your ears SOUND directly from the source.
Reflected Sound bounces off of objects and surfaces before REFLECTED reaching your ears. The amount of time it takes for this type of sound to dissipate in a space is called DIRECT SOUND reverberation time.
Comfort and clarity can be increased by controlling reverberation time with sound absorbing materials. What factors affect the acoustics of an interior?
WITHOUT WITH ACOUSTIC ACOUSTIC PANEL PANEL
Reverberation is a major factor To best mitigate reverberation, affecting the acoustics in an interior a significant portion of reflective Not every fabric has space. surfaces should be made acoustic properties. Specially absorptive. designed acoustic textiles All the surfaces and contents within are either sound absorbing a room, including the furnishings, Materials play an important role or acoustically neutral flooring, window treatments and in minimizing or sustaining sound. (allowing sound to pass even people, affect the amount of Hard surfaces allow sounds to through them). time it takes for sound to dissipate. bounce around the room multiple Ceiling height and angles also have times before they become inau- an effect on reverberation time. dible, whereas textiles can help absorb sound. Improving acoustic comfort with textiles
A strategy of A-B-C—Absorb, Here are a few examples of how Block, Cover—can achieve an KnollTextiles can be a beautiful and Although the best and most acoustically balanced environment. effective part of the A-B-C strategy: cost-effective acoustic solu- This can be achieved by installing tions are planned during the interior products with acoustic Sound-Absorbing Drapery space design phase, it’s of- properties and employing sound- Sound-absorbing drapery, like ten not until after occupancy masking technology when needed. the acoustic sheers offered by that noise is determined to The combination of sound KnollTextiles, absorb up to 75% of be an issue. For this reason, absorption, sound blocking and the sound waves that come into KnollTextiles offers acoustic sound covering is the 1-2-3 punch contact with the fabric. solutions for both pre- and that can make a measurable PRO TIP: A recent trend is to post-occupancy. difference in the acoustic comfort install sound-absorbing drapery of any interior. to create a softer, more flexible PRO TIP: The total absorption subdivision of space. added to a space is the product of ceilings in order to reduce rever- NRC and the area of application, Acoustic Tiles beration and improve speech so low and mid-NRC products Innovative, wall-mounted acoustic intelligibility. are often excellent solutions as tiles like our Impressions line offer PRO TIP: Avoid using fabrics with long as more total area is applied. a turn key acoustic management high percentages of natural fibers, solution with an NRC of 0.55. The rayon or nylon; instead look for tiles are created by “impressing” fabrics made out of polyester classic KnollTextiles patterns (or other hydrophobic synthetics) onto an acoustic substrate and to prevent sagging. turn walls into sculptural, sound-absorbing surfaces. Architectural Products Freestanding acoustic partitions Acoustically Neutral Textiles for that block sound are a good way to Wrapped Panels break up space, add a novel touch Sound-absorbing panels can be and address the “football field” wrapped with an acoustically neutral feel of overly large spaces. Most fabric so that the sound can travel of the options on the market can through the fabric and be absorbed accommodate a wide variety of by the acoustic substrate. These fabrics and wallcoverings, like the panels can be installed on walls or dozens of acoustically neutral fabrics offered by KnollTextiles.
Sound absorbing and acoustically neutral products
Acoustic textiles are designed of four frequencies. An NRC of “0” NOISE REDUCTION to have the primary benefit indicates perfect reflection while COEFFICIENT (NRC) of being either sound absorbing an NRC of “1” indicates perfect or acoustically neutral. absorption.
PERFECT 1.00 Sound absorbing products Some materials can have an NRC ABSORPTION perform on their own within an rating greater than 1.00. How is 0.90 environment. this possible? The data used in the NRC calculation only accounts 0.80 Acoustically neutral products for 2-dimensional measurements are paired with a sound absorbing of the material being tested— 0.70 substrate. length x width. In reality, materials and objects also have depth, 0.60 Occasionally, a textile may which increases a material’s actual perform both functions. For surface area available for sound to 0.50 example, KnollTextiles Tranquil encounter. absorbs some sound on its 0.40 own and is acoustically neutral Example: An NRC rating of .65 when paired with a sound means that 65% of the sound 0.30 absorbing substrate. energy that comes into contact with the fabric is absorbed rather 0.20 Testing for Sound Absorption than reflected. The greater the Sound absorption is measured number, the more absorbent the 0.10 with an NRC rating. fabric is. PERFECT REFLECTION 0.00 NRC Noise Reduction Coefficient Industry best practice is to use (NRC) refers to the amount of fabrics that have been evaluated sound absorbed when a sound by a reputable third party with the wave strikes a surface. It is calcu- industry recognized ASTM C423 lated from the absorption data test and are NRC rated.
Another method of measuring sound absorption is the Sound Absorption Average (SAA). The SAA is identical to NRC, except that twelve one-third octave measurements, from 200 Hz to 2500 Hz, are averaged instead of the four used to ascertain an NRC rating. The other difference is that NRC results are rounded to the nearest 0.05 and SAA results are not. Testing for Acoustic Neutrality interference the fabric caused in the ASTM C423 is used to test for panel’s ability to absorb. Depending sound absorption and acoustic on the level of noise control that ASTM C423, “Standard Test neutrality. Testing for acoustic the acoustician is looking to attain, Method for Sound Absorp- neutrality means determining the it may be necessary to review the tion and Sound Absorption NRC difference between an acoustic full report showing the absorption Coefficients by the Reverber- substrate alone and then a fabric at all frequencies tested. ation Room Method,” wrapped acoustic substrate. is the industry recognized KnollTextiles tests all panel fabrics test for evaluating the sound In order to find the NRC difference, in our line, as well as several absorption of a building the ASTM C423 test is conducted wallcoverings and upholstery fabrics material. The test uses a twice—once with the panel alone for acoustic neutrality. The products reverberation chamber and secondly with a fabric covered that have an NRC difference and measures the rate of panel. The difference is found by between -0.25 and 0.25 are deemed decay of sound waves. subtracting the NRC result of the acoustically neutral and are suitable fabric covered panel from the NRC to be paired with an acoustic result of the panel alone. The closer substrate. this number is to “0”, the less
The “blow through test” is a primitive way to evaluate the acoustic neutrality of a textile.
In this ‘test’ a person blows through a fabric and if they are able to feel their breath on the other side, the fabric is considered acoustically neutral and suitable for wrapped acoustical panel use. The reality is that this methodology has no scientific backing. It can be misleading and may not align with actual outcomes of a true acoustical test.
A listing of all KnollTextiles acoustic textiles and products are available as a resource document at knolltextiles.com. What makes KnollTextiles acoustic sheers ACOUSTIC SHEER 75% Hint sound effective? 8 colorways absorption 0.75 NRC
ACOUSTIC SHEER All KnollTextiles acoustic sheers 65% are made primarily with a Noren sound proprietary Trevira CS polyester 7 colorways absorption yarn that is lightweight, durable 0.65 NRC and offers visual transparency.
This yarn is fibrous, which creates ACOUSTIC SHEER tiny air pockets for absorbing ACOUSTIC SHEERS Bewitched 65% sound when it’s spun together. sound absorption The weave structure of the sheer 7 colorways textile also has an ideal air 0.65 NRC permeability. As the air molecules of sound waves vibrate back and forth through the fabric, the ACOUSTIC SHEER weave and yarn resist and convert 35% In Tune sound the sound energy to minuscule 7 colorways absorption amounts of heat. 0.35 NRC
PRO TIPS Acoustic sheers should be hung at Utmost II Velvet a minimum of 2" from the (curtain) 90% Drapery sound wall for superior sound absorption. absorption 22 colorways Greater sound absorption is achieved by allowing more space 0.90 NRC between the sheer and the wall. OTHER
The more fullness the textile has, 55% the more absorbent it will be. Impressions sound (KnollTextiles tests the draperies for 7 patterns & absorption sound absorption at 100% fullness). 16 colorways 0.55 NRC Reducing reverberation time with Impressions acoustic tiles
1 3 Second Second Reverb Reverb
KnollTextiles Impressions acoustic The illustration above shows tiles have an overall NRC of 0.55 the difference between an ideal while providing almost perfect acoustic environment, where the absorption (0.77 -0.93) at the fre- reverberation time is 1 second quencies where the human voice or less, and a noisy environment, registers (1,000-2,000 Hz). This where the reverberation time is means the tiles are highly effective 3 seconds. at absorbing the sound of voices and reducing the reverberation time (the amount of time it takes for sound to dissipate) in an interior space. KnollTextiles has solutions to help you accomplish a balanced acoustic environment.
Visit knolltextiles.com to learn more about the acoustic offerings.
Contact your local sales representative for full product information. ©2019 Knoll, Inc. All rights reserved.