Sound-Absorbing Drapery: Theory & Application
Sound-control acoustic curtains
Applications
Acoustical drapery is a good option where sound absorption is required and standard 1” or 2” thick wall panels are not possible. It is particularly useful where the material must be retracted, such as over glass, allowing for a clear view during non critical-listening functions.
Recommended applications include:
- As blackout curtains and reverberation control in a home theater with a large proportion of glass/windows
- To provide alterable acoustic conditions in churches that have both classical/traditional “choir & organ” and contemporary “praise & worship” music programs
- To attenuate chatter and din in a large hall or crowded dining room (noise reduction)
- To eliminate sound reflections off recording studio and vocal booth windows
- To provide tunable acoustical control (“live” to “dead”) for listening conditions in a music studio
Note that sound absorption material is often called “soundproofing.” I believe that the term “soundproof” is usually misapplied, which will be discussed in another post. Sound absorption curtains are not able to significantly reduce noise transmission between two adjacent spaces; they are rather designed to improve sound quality and reduce reverberation levels within the room that they are installed.
Material Thickness
The acoustic curtain material must be thick and highly porous. The thicker the absorption material, the more effective it will be against a longer wavelength (lower frequency) of sound. In order to be effective against “bass” frequencies, sound-absorbing acoustical panels typically need to be at least one to two inches thick. Since it would not be practical to have a 2” thick drapery, you must select the thickest, heaviest fabric your budget will allow. I recommend a 32 oz. fabric weight (or greater).
The material must also be highly porous. These pores act as thousands of tiny sound traps, capturing the energy and turning it into heat. A non-porous vinyl, leather, or acrylic-faced fabric will reflect much of the sound energy, reducing the effectiveness of your acoustic drapery. Choose a fabric that could soak up and absorb water, or has a plush, velour surface.
I have had success with the following:
32 oz. Magic Velour
32 oz. Synthetic Velour
If cost is a concern, you could choose a less expensive fabric with 24 oz. minimum thickness. Note, however, that this thinner fabric will be less effective at bass and lower midrange frequencies. Another option would be to use multiple layers of a thinner material (e.g. two layers of 16 oz. fabric).
Pleating
In order to improve the low and mid frequency sound absorption performance of your acoustical curtain, the material must be pleated. This will cause the fabric to be “gathered,” such that it loops in and out (i.e. does not lay flat). The pleating should be as deep as possible in order to expose more sound-absorbing surface, thus increasing effective thickness and improving low frequency sound attenuation.
Minimum pleating at 50% fullness is required; 100% fullness is recommended.
For a more complete explanation of drapery pleating and fullness, please visit:
http://www.rosebrand.com/fabric-stage-curtains-backdrops/Curtain-Fullness.aspx
Distance to Wall
The drapery will also become more effective at absorbing longer sound wavelengths (lower pitches) if it is spaced several inches from the wall or window. Up to a point, the deeper the spacing, the more improvement to low frequency absorption you will see. Consider spacing the drape 6 to 12 inches from the surface behind.
Rigging
The means and mechanism of mounting will not affect acoustical performance but does determine how easy it will be to open and close the drapery. Motorized winching systems are easy to operate but very expensive. For most applications, simple manually-operated rigging is the most cost-effective option. If you purchase your drapery from a theatrical supply house, they can also guide you on the appropriate mounting hardware.
More information on the various rigging systems is available HERE:
http://www.mainstage.com/PDFs/hhrigging.pdf
Suppliers
The following is a comprehensive list of known suppliers of 32 oz. drapery products:
Mainstage Theatrical Supply
Milwaukee, WI
http://www.mainstage.com
Rose Brand
Secaucus, NJ
www.rosebrand.com
Quiet Curtains
San Diego, CA
http://www.acoustic-curtains.com
Please contact me if you know of other suppliers, and I will add them to this list.
Data
The retractable nature of sound-absorbing drapery allows us to easily test its sound absorption performance. Sabine absorption coefficient ratings can be calculated from the average tested reverberation times with and without the material exposed. Onsite acoustical testing data for the above material specification is as follows:
Material: 32 oz. Magic Velour with motorized rigging. Drapery fully retracts into a drywall pocket
Hall: Community Church of Vero Beach – Vero Beach, FL
Acoustical Design: Eric Wolfram
Tested reverberation time, drapery exposed (T30, average of 6 positions):
125 Hz = 2.184 seconds
250 Hz = 1.996 s
500 Hz = 2.000 s
1000 Hz = 1.830 s
2000 Hz = 1.808 s
4000 Hz = 1.462 s
8000 Hz = 1.040 s
Tested reverberation time, drapery fully retracted (T30, average of 6 positions):
125 Hz = 2.350 seconds
250 Hz = 2.142 s
500 Hz = 2.150 s
1000 Hz = 2.040 s
2000 Hz = 1.986 s
4000 Hz = 1.562 s
8000 Hz = 1.106 s
Material Surface Area: 685 ft2.
Room cubic air volume: 266,086.64 ft3.
Material Absorption Coefficient (calculated from above)
125 Hz = 0.62 Sabines/ft2
250 Hz = 0.65
500 Hz = 0.66
1000 Hz = 1.07
2000 Hz = 0.94
4000 Hz = 0.83
8000 Hz = 1.09
Based on the data above and similar tests at other facilities, the sound-absorption qualities are surprisingly good. Although fabric wrapped fiberglass panels provide much better low frequency absorption, this drapery is an excellent option where material retraction is necessary. It is also very effective at altering the reverberation period and acoustic response of a space to support a wide variety of musical styles and instruments.
I need curtains that block outside noise from street traffic and voices. I also need thermal ability for extreme heat, sun and cold as well as light block (reflect?) from outside. Can you suggest material that addresses noise, thermal and light needs, in that order? The noise actually hurts me as I suffer from a chronic pain condition exacerbated by noise, wind, cold and temperature extremes, and restorative sleep is non-exist any in my home!
Thanks!
HTran,
It sounds like the best way may be to consider upgrading to an acoustically rated and thermally efficient window. The drapery will help with the light and maybe heat a little, but it will not be an effective noise barrier. If it is affecting your sleep, I would also strongly recommend getting some uncorded soft foam ear plugs until you can fix the window. Here is a good example:
Howard Leight MAX1 Earplugs Uncorded NRR33 Box/200 Count
I hope this helps!
-Eric
Hello there. Increased quality of life through sleep is so important! I feel your pain with the noise, light and temperature modulation in your bedroom. I also live in a noisy too bright and often cold room (with frequent break ins also) & recently put up actual mirrors in my bedroom window to reduce the light, doubled the curtains and checked the window seals for temperature adjustments. I’ve been sleeping so much better since this. Despite the sacrifice of a window and light in the bedroom, I completely recommend the option of blocking off your windows entirely with foam or velcroed felt etc. you can have light in the other rooms, sleep is too important to well being! good luck!
AcousticsFREQ,
I am comparing the material absorption coefficients of these drapes with the self-made panels (http://acousticsfreq.com/blog/?p=62). Based on these data, it looks like the drapes actually do a better job in the lower frequencies, perhaps suffering slightly at higher frequencies. Does that sound right or am I missing something? Also, do you recall how far the drapes were from the wall? I am looking for sound absorption on a wall for home theater, so the panels may look better for this application, but assembly of drapes would be much less time consuming.
Thanks,
Rick
Rick,
No, the 2″ panels will be much more sound absorptive at low frequencies. Low frequency performance is a function of thickness in porous absorbers. Also, space the drapes several inches from the wall. Anywhere from 6″ to 12″ will work well.
Hi Rick, would sound absorbing drapes help at all with ambulance and/or police sirens? I am installing shades, and purchasing drapes, and I was considering having a second layer of drapes to absorb sounds. Most of the street noise is muffled since I am on a higher floor, but the sirens can be frequent. I rather get new windows as a last resort. I am already using earplugs. Thanks, Alan
Alan,
I am sorry to say that I think they will only make a small improvement to your noise issue. Upgrading the windows and frames to a high Sound Transmission Class (STC) will be what you need to do to solve that problem. Sound absorption treatments (such as these drapes) are intended to reduce reflection of sound within a space.
-Eric
Installing new double pane windows with extra thick glass will tremendously reduce and virtually eliminate outside traffic noise. If you can afford triple pane with extra thick glass, that would be even better. the sound od sirens with the double pane were not eliminated, but muffled. They no longer sound shrill. Hope that helps.
I am trying to block the sound that travels from the open upstairs game room, through the high ceiling (two story) stair well, down into our living room. Every time the kids are upstairs watching tv or playing the Wii, we can hear every word the comes from the tv. We were thinking about installing movie theater style curtains in the room to block the sound. However, the tallest we can find are 108″ and the room is 120″ tall.
David,
I suggest doing more research before making a purchase. Sound Absorption is commonly confused with Sound Transmission Loss. Sound absorption materials do NOT act as a barrier to prevent noise intrusion into your space. It sounds like you need to improve the Sound Transmission Class rating of the partition between the two rooms. That is no easy feat and will probably involve a construction project.
The sound is actually “bouncing” down the carpeted staircase (I’m assuming via the flat drywall) and into the living room downstairs. The sound transmission through the floor definitely would be a construction project. But this is an open air game room (upstairs) into an open living room (downstairs).
So there is basically no way to prevent the sound from transmitting from upstairs to downstairs? I realize that bass sound waves will easily travel thru the sub floor and into the ceiling of the living room. Acoustic Curtains or sound panel will not help then???
Oh, I see. A sound absorption material can help reduce or eliminate sound that is reflected off a wall. In the case of your stairway, it may reduce the noise transmission by stopping that reflection down that corridor. You may want to try something cheap and ugly first to see how well it works. A thick carpet pad, some moving blankets, etc. I just don’t want you to spend a lot of money and then be disappointed.
Awesome!!!
I hadn’t thought of a moving pad as a temporary testing material. My dad owns a moving store. I’m sure he has half a billion of them.
Should they be attached to the wall on the opposite side of the stair corridor from the tv source? Or are you saying to install them across the actual opening in the corridor? In other words, there is one opening where the stair case leads ito the upstairs area. Then there is an additional opening that is on the side of the stair corridor that opens into the game room. Should I block that opening with the moving blankets? Or simply attach them to the opposite wall like an acoustic mat?
David – i have the exact same problem. Open two story living room and upstair a open loft. I want to use the loft as an office room. I have been talking to remodelers to closeout the loft, but wanted to see if any of your drapery idea worked.
Hello!
I live in an apartment. and in my bedroom, there is one shared wall that I have with my neighbors, whom choose that wall to place their bed. I am tired of hearing a squeaking noise. Not sure if its the floor, or their bed. However, i was told that hanging a lot of dropping on that wall will reduce the noise I hear. I am thinking of getting a dresser & and sound absorbing curtains to put against that wall, to block out a little of this noise. Will this help?
Maria, unfortunately sound absorbing materials will not be effective barriers against noise intrusion. In acoustical engineering terminology, Sound Absorption (NRC Rating or Absorption Coefficient) is the ability of a material to prevent sound reflections, echoes and/or reverberation within a room. Sound Transmission Loss (STC rating or TL) is the ability of a material to act as a barrier to sounds that penetrate into the room from an adjacent space. You will need to increase the STC rating of the partition between your neighbors apartment and yours. This is not a simple task and usually involves a construction project!
I have recently put porcelain tiles in my living room and the sound I get from my speakers is just not of my liking. I used to have carpet and the sound was acceptable. I have a balcony that has two doors with glass and wood close to where my stereo system is. I do have curtains on those doors but they are very old. Would new curtains make an important difference in the sound or should I also buy thick rugs to lay down on the porcelain floors? I am not an expert in sound but I know that the tiles have made a big difference in the sound and not for the best outcome.
Nando, this site provides a complete guide to achieving an excellent acoustical environment for a home theater environment. Check it out here: http://acousticsfreq.com/complete-home-theater-acoustics-tutorial/
i have a wedding and event hall .. there are walls but the ceiling is a tent and I’m looking for sound proofing solutions to put on the tent fabric to reduce the sound of music to the neighbors around us ,, do you recommend something or help me figure out what to do .
Muneera, unfortunately sound absorbing materials will not be effective barriers against noise intrusion. In acoustical engineering terminology, Sound Absorption (NRC Rating or Absorption Coefficient) is the ability of a material to prevent sound reflections, echoes and/or reverberation within a room. Sound Transmission Loss (STC rating or TL) is the ability of a material to act as a barrier to sounds that penetrate into the room from an adjacent space. You will need to increase the STC rating of the ceiling to prevent noise from transmitting to the neighbors. This is not a simple task! You may need a professional acoustical engineer. check out http://www.ncac.com
Hi, I am starting a small music venue. Unfortunately there is another bar right next door (adjoining wall) that also has music. I am going to put a curtain on the adjoining wall to alleviate the noise issue. Can you recommend what material I should be using? Thanks!
Chris, unfortunately sound absorbing materials will not be effective barriers against noise intrusion. In acoustical engineering terminology, Sound Absorption (NRC Rating or Absorption Coefficient) is the ability of a material to prevent sound reflections, echoes and/or reverberation within a room. Sound Transmission Loss (STC rating or TL) is the ability of a material to act as a barrier to sounds that penetrate into the room from an adjacent space. You will need to increase the STC rating of the partition between your music venue and the bar next door. This is not a simple task! You may need a professional acoustical engineer. check out http://www.ncac.com
Hi
I weave fabrics on jacquard looms and would like to know that does 32oz fabric mean. Does it mean a fabric weight in terms of GSM should be 900 ?
Assuming that my understanding is correct then fabrics of this GSM can be used in theaters and auditoriums ?
However. such heavy curtains will not be effective to cut outside noise of cars and motor bikes if used in bedrooms and living rooms.
Please inform me if my understanding is correct.
Regards,
Vikas
I want to help my home in anyway I can with sound, do fabrics that call themselves acoustic ( Guilford of Main, Wolf Gordon has 3) give better absorption than regular drapery materials. I am willing to pay for acoustic material vs regular drapery material if it will help more. It all looks the same to me, but Guilford of Maine and Wolf Gordon actually label some as acoustic. I am also looking into having cellolose insulation dense packed into our new homes wall. I wish our architect would have had doe suggestions before we built, about our sound issues. I thank you for your time and any comments you may have. Jean
Jean,
The term “acoustic” could mean a lot of different things. Often, “acoustic fabrics” are materials intended to be transparent to sound (not reflecting or absorbing). These are often used as wraps for sound absorptive panels or speaker grille cloth. Also, “sound issues” could mean a lot of different things and the required treatments may not be what you have in mind. Can you send me an email with a more detailed description of the problem you have and desired outcome? I will try to respond to the best of my ability. The contact tab at the top of this webpage should give you my email address.
I am working on a micro housing college project. If curtains are used as separators for room instead of walls, can they still perform the function of sound absorption. I want to know if it is possible to reduce sound with just curtains without walls in other words, if the interior walls are replaced by acoustical curtains, will it still be an effective strategy?
Suchita,
The draperies described hear will have a high sound absorption (NRC) performance, but a low sound insulation (STC) performance. It is unlikely that you can achieve a high level of sound insulation (transmission loss) with just a drapery. Try a google search for STC rated curtains. There are a few out there. STC (Sound Transmission Class) 50 is a typical target for room to room separation.
We need masking for a theater stage. Would sound absorbing fabric prevent any backstage noise from spilling onto the stage?
If not this fabric, I’d there another fabric you could recommend? Of course, we need the fabric to reflect on stage sound.
Am I asking for a miracle?
LeCee, sorry it will not be an effective noise barrier and will absorb on stage sound. The purpose is to absorb reflected energy.
Hi there, I am hoping you can help me with finding a solution to a noise issue in my condo. I have a small parrot who screams occasionally, and I’d like to prevent this sound from going through my neighbour’s wall and out into the hallway. It’s a rather large, open concept room, approx 24′ x 15′ with 13′ ceilings. What would you suggest as an economical solution? There is only one wall that borders on a neighbouring unit and it is 24′.
Thanks in advance!
Hello, I live in a condo and have a sound system in front of the balcony (glass) door. I want to reduce the reflections of sound coming off the glass door. Would curtains help? Also, if I have some excess curtain in the 2 front corners, are they sufficient as bass traps? Thank you for your help
Jason,
Yes, heavy (thick) draperies are your best option. You want something with a very thick velour material, which is rare. Most residential draperies are too thin for this purpose and are mostly sound transparent.
Hello,
We live in a house with lots of windows near a lake. On summer nights it can get pretty rowdy with noise from boats (mainly bass music reverberating off the water). We installed window inserts, which only seem to amplify the lower frequency sounds because they block out everything else. We have reached a drastic solution – the need to move – but wanted to consider your product as a last resort. Can you please give an honest opinion as to whether your product could help?
Hi,
Will your thick Porous acoustic curtain material block vehicle’s car interior road noise heard while driving on a rough road? The car interior is noisy when driving so i want to block the noise and i do not want to spray any dampening rubber coatings which is messy. I wanted to lay the Porous curtain on the car’s interior, wondering if it will block the road noise ?
Changmin,
No, sound absorbers and sound barriers have a completely different function. This treatment described in the article is not intended (and will not) act as a noise barrier.
I meant i wanted to lay the Porous curtain on the car’s flooring and boot’s flooring, will block the road noise ?
Hello. What would be the best thing to get that is all of the following?
1. Easily movable.
2. Filters sound well, so that a multipurpose gym is has less echoes when set up for a concert.
Also, depending on what type you recommend, how should I set it up for maximum absorption? Also, how much should I get for a gym that is approximately 30 ft by 60 ft? Sometimes we set up the band along the long end, and sometimes we set (a smaller band) up along the shorter end. What could we get that could work for both? Thanks!
NSYC
NSYC, I do think the drapery described in the article would be good for your application. As for the quantity, that is actually not a simple question. An Acoustician will build an acoustical model of your space and introduce a calculated quantity of material to get your reverberation time to the correct length for the type of music and function of the space. 1.5 seconds is probably good for a large, general use space, but it is hard to say precisely without doing the investigatory work. Here is an online tools for the calculation: http://www.sengpielaudio.com/calculator-RT60.htm
Hi, I live in a loft above the living area. There are stairs connecting the two spaces. I’m wanting to block the noise from the tv travelling up to my room. Would installing the curtains you’re talking about at the top of the stairs block out the noise from downstairs?
Hello Collen. The treatment I describe in the article is not intended to act as a sound barrier. It is to reduce reverberation and sound reflections within the room it is installed. Check out my explanation of the difference between sound absorption and sound transmission loss here: http://acousticsfreq.com/sound-absorption-vs-sound-transmission-loss/ Unfortunately there will not be a simple lightweight drapery that can act as a sufficient sound barrier. Impermeable mass (weight) is the fundamental property of sound transmission loss. You will see some benefit by lining the walls of the stairwell with sound absorptive materials, but it will not be a complete elimination of sound.
I live in an apartment and want to block sound coming in through my windows as well as hold heat in. What brand of curtains will be best for this? I’m looking at the reviews in the curtains I find and seeing that some of them don’t really help with blocking noise from outside.
Hello Crystal. The treatment I describe in the article is not intended to improve sound transmission loss of a window. It is to reduce reverberation and sound reflections within the room it is installed. Check out my explanation of the difference between sound absorption and sound transmission loss here: http://acousticsfreq.com/sound-absorption-vs-sound-transmission-loss/ Unfortunately there will not be a simple lightweight drapery that can act as a sufficient sound barrerier. Impermeable mass (weight) is the fundamental property of sound transmission loss. I have also provided a list of noise control products here: http://acousticsfreq.com/noise-control-products/
The Bed Bath and Beyond store sells a sound dampening curtain that has a thin layer of umbrella like fabric attached to the inside of the curtain material , they advertise this extra layer as a sound dampening fabric, I would like to buy this fabric and apply it to the inside of the thick 32 ounce double sided curtains I already have, what is the industry name of this fabric, and does it really work, or is there not much more noise reduction that is achieved with this extra material that It’s not worth the trouble.
… P.S. the 32 ounce curtain I mentioned in my previous post is Velvet, will adding the extra “sound dampening” lining between the double sided velvet curtains help significantly? Will this extra lining that Bed Bath & Beyond and other theatrical curtain shops advertise really add significant additional sound dampening ability or are the velvet curtains I have the best I can do? I’m trying to get a percentage here ( 50% added sound dampening or 10% and not worth the trouble and expense of adding the so-called “sound-dampening-lining”
Hello John. The treatment I describe in the article is not intended to improve sound transmission loss of a window. It is to reduce reverberation and sound reflections within the room it is installed. Check out my explanation of the difference between sound absorption and sound transmission loss here: http://acousticsfreq.com/sound-absorption-vs-sound-transmission-loss/ Unfortunately there will not be a simple lightweight drapery that can act as a sufficient sound barrier. Impermeable mass (weight) is the fundamental property of sound transmission loss. I have also provided a list of noise control products here: http://acousticsfreq.com/noise-control-products/
AF – i’m needing a curtain to go in front of a set of double solid core external doors to help with sound escaping from my studio. Is there a company that I could order custom curtains from? I’m thinking about 32 ounce magic Velour
The treatment described in this article is not intended for Sound Transmission Loss (STC) purposes. It will not help much with that problem.
Thank you for the detailed article. Someone has offered to donate some 14 ounce velour at 50% fullness to our churc but I’m wondering how much it will do for sound absorption as you recommend double the weight in ounces
I’d recommend going with the heavier fabric. However, if you use the thinner draper and leave about 3 to six inches from the wall and use a drapery configuration with a lot of “fullness,” then you should see a decent amount of absorption in the speech frequencies. This can be effective for general reverberation control, but not for attenuating strong, problematic reflections. That drapery will not be good for attenuating low frequency sounds, like amplified drums and bass, however.
Ｈi! Thank you for your article! What will be the best way to sound proof music studios? Will have rooms right next to each other with a wall in between..what would you suggest to put in the wall and in the room that does not cost too much? Thank you!
Usually people refer to “sound proof” as improvement of the sound insulation of the partition wall. Google: “improve the STC of a wall” for a variety of sources on this. Here is my explanation of the difference between sound absorption and sound transmission loss: http://acousticsfreq.com/sound-absorption-vs-sound-transmission-loss/
A lot of noise coming in from the hallway/corridor in condo building. All hard surfaces out there and noisy tourists coming and going. Would hanging theater drapes in front of the door (ie “blocking” and absorbing sound) facing the noisy corridor help?
I’m glad that you talked about how sound absorption curtains are designed to improve sound quality and reduce reverberation levels within the room that they are installed. When my sister was in high school, my family and I attended a play where my sister acted but we could hear sounds coming from behind the drapery before the play started. Thanks for helping me learn more about how acoustic drapery must be highly porous to capture the energy and turning it into heat.
Have a couple of dogs. They bark if they hear the pool man, delivery boy etc. I would like to replace the old verticals with sound proof Something. So the neighbors don’t hear the dogs.
I am searching for a solution to my next door neighbours snoring ! I live in a 16th century listed cottage and there is no sound insulation between the main bedroom wall. This wall contains oak beams in its structure so unable to add sound insulation. Therefore when coming across theatre curtains wondered if this would be the answer to my prayers. The wall however is an odd shape.
I live near a ems depot with sirens noise. The noise reverberates within my bedroom and the common hallway. Will drapes help reduce the sound?
Hi. I am looking for low cost ideas to replace our drapes. We are located in an old theater with concrete walls. Our current drapes go from a high ceiling to the middle of the wall and I think there is some kind of insulation behind them. They are attached to the wall somehow. We do have live music and were told that we can’t just put anything up because it would affect the sound. Do you have any suggestions? Anything would help.
Thanks so much