Architectural Acoustics

Architectural acoustics deal with sound control and acoustical design in large spaces including auditoriums, arenas, theaters, lobby areas, swimming pools, and multipurpose rooms. Typical problems include excessive reverberation (echo), which causes poor speech intelligibility, and excessive noise during events. We try to match acoustical design and acoustical engineering with your design constraints and budget to lower the reverberation time (RT60) for increased clarity of speech and music. To help support our work with architectural acoustics and acoustic designs we have downloadable CAD drawing as well as 3 part CSI Architectural specifications available on our website for over 250 acoustical products, including acoustical wall panels and acoustical wall coverings.

OEM Materials There are many other applications where flexible polyurethane foam is used on a daily basis to control sound and reduce noise levels. Acoustical Solutions offers a variety of open cell and closed cell high density polyurethane foam options. Various thicknesses are available on the polyurethane foam ranging from ¼” up to 12”. Additionally, various facings are available on the flexible polyurethane foam (both open cell and closed cell) such as Mylar, urethane, and tedular. For better sound reduction, a mass loaded vinyl layer can be added in between the high density polyurethane foam layers. Acoustical Solutions can offer competitive bids on existing specs or we can provide a number of design solutions to help make your product run quieter in its end environment.

Noise Control For Architects, Engineers, Consultants and Contracting Firms
Let ArtUSA Noise Control Products be your partner on your next noise control application. You can rely on ArtUSA Noise Control Products to provide you with the in-depth technical expertise necessary to select the most appropriate products and designs for your application. We'll work with you as the project unfolds, in the early stages of planning, specification writing and budget costing to ensure that your and the Owner's requirements are met. With ArtUSA Noise Control Products as your design partner, you can be sure of providing your client with the most appropriate plans and specifications for a wide variety of noise control, soundproofing and acoustical solutions.

Bid shopping and low price awards work fine for commodities and standard building trades but in specialty trades such as noise control they can spell disaster. We'll provide your client with cost-effective products and systems that maintain the performance and construction requirements you have so carefully specified. When searching for a source of acoustical products and systems, you need not look beyond ArtUSA Noise Control Products for a complete line of industrial/commercial products suitable for a wide variety of performance and budget applications. ArtUSA won't let you down – your client will be very satisfied with your choice.

Noise Control in a nutshell (for existing buildings)

Some spaces are not primarily designed with an acoustical function, but acoustics impedes other functions: these spaces are just too loud. The acoustical requirement for noisy spaces, such as cafeterias, work spaces, gymnasiums, and pools is straightforward: make them less noisy. There are two ways to accomplish this goal:

1. isolate the space from noise sources;
2. reduce reverberation.

It is always better, if possible, to control noise by removing a noise source. In the case of a cafeteria or gymnasium, however, the largest source of noise, people in the space, can’t be removed. However, there may be other sources of noise that can be removed to make these spaces quieter, such as air-conditioning units and – very common – drink vending machines with loud, built-in refrigerators.

Changing room surfaces to reduce reverberation is often the only practical solution for quieting a noisy space. The basic problem is to determine how to get in as much sound-absorbing material as possible at a reasonable cost while preserving aesthetics.

The Secret of Architectural Acoustics Revealed

Background Noise

Have you ever noticed that your radio seems awfully loud when you stop your car after listening on the highway? Or have you ever felt that palpable relief when the air conditioner shuts off? We don't notice background noise---but background noise determines what we can hear and understand in the foreground.

Some times we don't want to hear everything. Imagine if you could hear and understand every conversation at your office. It would be terribly distracting. But when we do want to hear every little thing---at a religious service, in an important meeting, at a play, or at a concert---background noise is critical.

During a lecture or sermon, any audible sound not made by the speaker is noise; during a performance, any audible sound not created by a performer is noise. There are, of course, many aspects to excellent acoustical design. However, in any space intended for listening, strict control of noise is fundamental. I call these spaces "critical-listening space."

Sources of noise include traffic, airplanes, machinery, plumbing, lights, and people in other spaces. In a space for listening, the worst offender is usually the heating, ventilating, and air-conditioning system (HVAC).

The (undamaged) human ear is so sensitive that we can detect sounds that displace the eardrum by roughly the diameter of a hydrogen molecule.¹ This means that background noise determines the softest sound that a performer or speaker can effectively utilize. Even in spaces that most people would consider quiet, the background noise level can be twenty to thirty decibels above the threshold of hearing. You don't notice this, but the performer has lost twenty to thirty decibels of dynamic range!

This is illustrated in the graph below, with HVAC noise criteria curves for comparison.²

NC-40 is considered acceptable for such noncritical spaces as lobbies and corridors. NC-30 would be acceptable for a motel room. NC-20 is often given as acceptable for churches or drama theatres.³ But look at how much area there is between the threshold of hearing curve⁴ and NC-20. There is an awful lot of audible sound being covered up by an HVAC system at NC-20.

Speech Intelligibility

When a theatre is truly quiet, an actor can use his entire dynamic range, from a shout to a whisper, and still be clearly understood. Since the quiet moments in a drama are often the most electrifying, strict control of background noise is essential.

The ancient Greek theatres are known for their almost magical acoustics for speech. One can hear a drachma drop from the farthest seats in the theatre at Epidaurus. How can this be so? The answer is that no audible sound covers up the sound of the coin striking stone--and so it is heard.

Music

Similarly for music, a silent background allows a performer to exploit his entire dynamic range. The loud climaxes of a musical performance can be wonderfully stirring, but the quiet moments set off these climactic moments and give them their power. Without the quiet moments, music is all on the same dull level. Furthermore, some of the most intense, magical moments in music are the softest. These moments are only possible when the hall in which they occur is truly quiet.

Recording engineers understand this. They commonly turn off all mechanical systems and most lights while recording.

Speech and Music in the Same Space

Many spaces are used for both speech and music, the best example being church sanctuaries. For such mixed use, a silent background is particularly important. This is because reverberation (the persistence of sound in space) is necessary for music. Without reverberation, music sounds flat and dull. But reverberation can interfere with speech intelligibility by prolonging the sounds of speech, smearing them in time.

A good speaker corrects for this effect by speaking slowly and clearly, working with reverberation to enhance the sound of his voice. However, reverberation amplifies background noise, creating a double difficulty for speech. Contrary to common belief, speech can work quite well in a properly designed reverberant space, but only if background noise is minimized.

Audience Noise

Audience noise is beyond the direct control of the architect or acoustical consultant. However, research shows that audience members are significantly quieter when background noise levels are very low. In the City of Birmingham Symphony Hall, Birmingham, England---a hall with exceptionally low background noise---audience members are so attentive during quiet music passages that they hold their breath to listen.

Examples of Spaces with Low Background Noise

• Meyerson Symphony Hall, Dallas
• Domain Forget, Charlevoix Quebec
• New Jersey Performing Arts Center, Newark, NJ
• Clemens Theatre, Christopher Dock Mennonite School, Lansdale, PA

Gymnasiums, Restaurants, Cafeterias

Listening may not be the primary function in your space. However, people are always hearing, and the acoustics of these spaces can almost always be improved by lowering background noise (as well as other measures). I was recently in a gymnasium, for instance, with horrible screeching noise from the lights. The poor gym teacher who has to work in that space must have a perpetual headache.

The Common Condition

In the vast majority of places where I listen---churches, theatres, lecture halls, recital halls, concert halls---background noise imposes a haze in front of the sound. This noise itself goes unnoticed by most people. Instead, they notice that their experience is diminished: the tone color of the violins is dull; the sound lacks clarity; they can't quite understand the words.

The usual response to the ubiquitous blanketing of desired sound by background noise is to turn up the amplification. Amplification often adds fifteen to twenty decibels above the background noise to the level of the speaker. Wouldn't it be better to reveal the speaker by removing twenty to thirty decibels of background noise?

Furthermore, lower background noise makes the job of the sound system vastly easier.

See and Hear for Yourself

The effect of background noise can be compared to looking through a dirty window; one doesn't notice the dirt on the window, one simply can't make out the view. Clean the window for a striking improvement in clarity. And so it is when background noise is controlled. You can hear this for your self by the following simple experiment. You need two other people to help.

• Two people stand on opposite ends of the room.
• The third person is on hand to manage the noisemakers: fans, ventilation systems, lights, dimmer racks, air-conditioning, etc.
• Turn on all noisemakers. In actual practice not all these devices may be on at the same time, but for the sake of demonstration turn them on to create the greatest contrast.
• Converse with the person across the room. Note the effort necessary to make yourself understood. Note the effort necessary to understand.
• Turn off all the noisemakers at once.
• Listen.
• Proceed with your conversation.
• Note the change in effort necessary to understand and be understood.

Even in rooms that have other acoustical difficulties, the improvement should be clear and palpable.

What Is To Be Done?

When designing a new critical-listening space, consider the location of noise producing machinery such as air-handlers, and the design of a silent mechanical ventilation system from the very beginning. Few people realize that it is possible to supply cool air to a room without creating any noise. It is. However, since this is not the usual practice, such a silent system must be considered from the beginning of design.

An architect once called me to help with the design of a high school auditorium. I discovered that it was too late in the design to move two large air-handlers from their location on the roof of the auditorium. They might just as well have been put on stage! I did my best to help out, but nothing I could recommend for the inside of the room will cancel out the deleterious effect of those two huge noisemakers.

In the case of historic renovation, noise control may be the only option available for improving the acoustics of a space. In some cases, merely quieting a noisy mechanical ventilation system will affect a drastic improvement in the acoustics.

Conversely, many a perfectly lovely space has been ruined acoustically by loud new ventilation systems. When planning the renovation of a worship or performance space, make noise control the first consideration.

Noise control is fundamentally important to the success of any building for listening. It can make the difference between excellent sound and the usual mediocrity. This is especially true on a tight budget. Better to save money by leaving out the seats! After all, these buildings are often meant to last for more than a hundred years.

Conclusion

Since the level of background noise determines what we can hear in a space, it determines the level of acoustical excellence. This is truly the secret of great acoustics. Awareness of this secret in the early stages of design brings excellent acoustics for your new critical-listening space within your grasp. (by Orpheus Acoustics)

In architectural acoustics and environmental acoustics, noise control refers to the set of practices employed for noise mitigation. Within architectural acoustics these practises include: interior sound reverberation reduction, inter-room noise transfer mitigation and exterior building skin augmentation. More specific architectural noise control methods include the installation of acoustical gypsum, ceiling tiles, ceiling panels, carpet and draperies. In the field of environmental sound, common noise control practises include: design of noise barriers, development and enforcement of noise abatement legal codes and urban design.

Materials used in architectural acoustics

Acoustical wall and ceiling panels can be constructed of many different materials and finishes. The ideal acoustical panels are those without a face or finish material that interferes with the acoustical infill or substrate. Fabric covered panels are one way to maximize the acoustical absorption. The finish material is used to cover over the acoustical substrate. Mineral Fiber Board, or Micore, is a commonly used acoustical substrate. Finish materials often consist of fabric, wood or metal. Fabric can be wrapped around substrates to create what is referred to as a "pre-fabricated panel" and often provides the best noise control if laid onto a wall, and require no modifications. Prefabricated panels are limited to the size of the substrate ranging from two by four feet to four by ten feet in dimension. Fabric retained in a wall-mounted perimeter track system, is referred to as "on-site acoustical wall panels" This is constructed by "framing" the perimeter track into shape, infilling the acoustical substrate and then stretching and tucking the fabric into the perimeter frame system. On-site wall panels can be constructed to work around door frames, baseboard, or any other intrusion. Large panels (generally, greater than 50') can be created on walls and ceilings with this method. Wood finishes usually consist of punched or routed holes or slots and provide a warm and natural look to the interior space, although acoustical absorption is not as high.

"A chain is only as strong as its weakest link."

This is a very appropriate saying with regard to sound isolation. We are often asked questions like: "What can I do to this wall to stop the sound going through to the bedroom on the other side?" It's almost incomprehensible to people that the wall may not be (and probably isn't) the only part that is leaking sound to that bedroom. The other parts might well be the floor, the ceiling joists and other shared walls. You could make changes and increase the STC (Sound Transmission Coefficient) dramatically for that wall, but the result might be marginal because the majority of the sound is getting through elsewhere.

In order to deal with sound control one should understand how sound travels. In residential environments it will either be air borne or structure borne. Air borne sound is pretty simple - this is what we hear within the room. A combination of air borne and structure borne approaches need to be considered for sound isolation. One may ask, "But if the room is sealed, isn't all the air borne sound contained?" To a point the answer is yes, but a ½ inch layer of gypsum is not going to stop 50 Hz, just slow it down (i.e. attenuate) and it could become both an air borne wave and a structure borne vibration in the next room.

Let's look at structure borne sound. Have you ever been in a room on a concrete slab where someone is bouncing a golf ball 2 or 3 rooms away? If you are standing on the same concrete slab with no breaks in it, you will hear that golf ball almost as if you were in the same room. You are not getting any air borne sound transmission, this is all structure borne. Many people think that having a high mass will stop all sound, but actually sound travels faster in dense material than in air. The golf ball experiment shows us that mass does not stop the sound at all, rather it transmits it to other parts of the house—quite efficiently too.

So what do we do if we want to isolate sound? The answer is quite simple: Only two things stop sound - mass and space. You need mass to contain the airborne sound, but then you also need space (an air gap or similar unobstructed area) so that the structure borne sound can not be transmitted. You may have heard of sound isolation techniques such as staggered stud walls or resilient channels. These work on those principles - there is a high mass wall, an air gap, and then another wall, making sound transmission difficult.

Simple, right? Well in principle yes, but the devil is in the details. You have to figure out how to actually execute a plan that attacks "the weakest link" effectively. Let's say you're designing a recording studio and there's a train track outside the studio. Well first, it might be smart to consider finding a new location for your studio, but if that fails what are you going to do? You're going to need a lot of mass to stop the noise from a train, like a concrete block building, but structure borne vibration is going to get through that, so you will need an air space and a second high mass wall. How much air space and what type of wall? This is where acoustical engineers come into place, where they can measure what the problem is and at what frequencies and then calculate what size air gap and what mass (walls et cetera) are needed. So you've built that great wall, you should be fine right? Hold it - not so fast. What about the ceiling? You have to use a similar technique there. Now there are doors and windows to deal with. You will need to have "sound locks" to ensure that sound does not penetrate there. So now you've taken care of the walls, the doors, windows, and ceiling. You have a concrete bunker that a nuclear warhead could land next to and everyone would be safe inside. Can you hear the train inside our bunker? You bet! What did you do to the floor? Nothing. The vibration from the train goes right through the ground, into the concrete slab, and right into our studio. You've just built the most expensive fallout shelter known to man, because it's worthless as a recording studio. Your weak link was the floor, and with all the right intentions - nothing was done about it - and to fix it is going to be very expensive.

Fortunately, this was fictional. I don't think anyone has built a serious recording studio next to a railroad track, but there have been many studios built near highways, and floor vibration is very real and very important.

When considering sound isolation there are really 2 aspects. Keeping sound out of the listening environment, and retaining sound within the listening environment. You would think that if you had one you would necessarily have the other, but that's not always the case. First consider the level of noise and the source of noise that might get into the listening environment. Is there a busy road outside? Is there a hard surface floor above the room where people walking will be heard? What about the HVAC (heat and air conditioning system)? Is it a duct system and will sound travel through those ducts, as well as the noise generated by the HVAC system itself? Now we have to determine what type of noise problems are probable with each of these. Are they structure borne, such as a person walking in the room above, or are they air borne such as HVAC generated noise?

Structure born noise is often the hardest to deal with. You need, as stated above, a high mass and an air space, so that there is no positive structural contact. In the case of the hard floor above the listening environment you will need to decouple the floor joists from the ceiling joists. The most common and effective way to do this is to use spring loaded isolation hangers which are suitable for creating a suspended high mass dry wall ceiling (see fig 1). That is not to be confused with the typical suspended ceiling, which has very little mass and will not stop sound from penetrating into or out of the room very effectively.

Fig 1


Now let's look at another type of structure noise - the busy road outside. You might think this is air borne and it could very well be. That noise will penetrate windows quite effectively, but if you are in a basement on a concrete slab, there may be more noise that comes in from vibration. In recording studios this is particularly important and it needs to be dealt with. Kinetics makes a product called a RIM Floating Floor system (see fig 2). This system rolls out onto the sub floor and then you build a standard floor above it. It has a resonance frequency of around 4 Hz, so anything in the audible bandwidth will not penetrate through it, if it is installed correctly. A subfloor (2x ¾" plywood layers or more), the walls, and the final finished floor can all be built on this floor isolation system.

Fig 2


Finally, let's look at air borne noise. This typically comes through thin walls, windows, or as stated previously, the HVAC (one of the most common overlooked issues in a good home theater design). Duct work is like an open channel to transmit sound - a 'flanking path' in Acoustical terms. Have you ever talked in one room and been heard quite clearly in another room, halfway across your house? Were you close to a HVAC duct when this occurred? So what can you do about this type of noise? Actually, it's relatively simple to reduce noise of this type from various parts of the house simply by adding a baffle box and/or plenum that is lined with absorbing material to both the trunk and return of the HVAC unit. A baffle box is basically a large box that has at least two 180 degree turns or a combination of turns to give essentially the equivalent. A plenum is kind of like a muffler, not as effective as the baffle box, but much better than nothing (see fig 3). The second aspect of the HVAC system is the noise it generates by moving air through the ducts and in and out of a room, and the noise of the motors and fans of the unit itself. Most households have relatively small ducts for the volume of air moved. It's fine for most residential applications, but not for our critical sound areas. We need to oversize the ducts and more importantly oversize the diffusers where the air exits into the room. Typically we like to have air velocity into the room less than 225 CFM (Cubic Feet per Minute). An HVAC contractor can calculate the load required for the room and the amount of air exchange needed, and determine the diffuser together with the duct size needed to achieve this. If your HVAC contractor looks at you and asks, "how do I do that?", get another HVAC contractor. It's also a good idea to line the last several feet of ductwork with a sound absorbing material.

Fig 3


Now we have some of the basics covered, let's look at few more areas. First is the interior high mass structure, namely the walls. How will these be constructed so that there is a high mass interiorly and an air gap, a physical space between the two elements of mass? There are many ways to accomplish this. First you need to create the high mass; this can usually be accomplished by using 3 layers of material, generally 2 layers of gypsum with "some" interior layer that they sandwich. I say "some" because there are many interior layers that are suitable depending on the needs of the room. We won't go into the details of these different interior layers, but in general they can be broken down into two categories: Homasote or Celotex, a low density sound board, or a damping layer such as  The second aspect is the air gap, which can be done either by a resilient channel, or by creating a separate or staggered stud wall. The greater the air gap and the higher the mass, the better the isolation will be. (see fig 4).

Fig 4


So are we done? Not quite. Windows and doors need to be considered. These are an equally important part of the 'sound envelope' and, as such, can be major sources of sound leakage. They provide another 'flanking path' for unwanted sound. Again, the best way to stop sound is to have (I'll say it again) mass, and air gap (physical space), and mass. So, with windows it would be great if we could have two sets of windows with very thick or substantial laminated glass in each and a nice air gap between them. This is often impractical and we have to look at something more reasonable. A pre-manufactured thermopane window with laminate glass inserts can do a reasonably good job of sound isolation. The laminate glass is basically glass with a thin layer of acrylic bonded to it. This acrylic bonding element between the two pieces of glass reduces the ability of the glass to freely vibrate at their fundamental frequencies, thereby reducing both the ringing artifact from the glass and their ability for effective sound transmission. It's not a perfect solution by any stretch, but it's reasonably priced and is much better than standard glass.

Doors are another area of concern. Those hollow core doors with ¾ inch gap at the bottom found as the interior doors in most homes are just about worthless in terms of sound isolation. You would probably do as well to have a curtain hanging there instead of that door. Sound isolation for doors parallels the cost of the doors. A solid core door will provide more sound isolation, but it still leaks quite a lot at the threshold. An exterior door, with good weather striping and a threshold to seal it when it's closed is better yet. There are doors with a "cam" hinge closure that really seals them shut and offer terrific sound isolation, and if you really want to go for broke, you can always buy a recording studio door, that resembles something like a bank vault door (and costs nearly as much too). The latter is really pretty impractical and virtually never required for residential applications, but I wanted to mention the possibilities just the same. One very clever way of dealing with the door issue is to have what's known as a sound lock. This basically is a small entry area, where there is a door to, for instance, the home theater and another door to the rest of the house. This provides the air gap that is effective at sound isolation. When we use solid core doors with good quality weather stripping and a threshold, this creates excellent sound isolation.

There - now we've covered everything. Ceiling, walls, floor, windows, doors, HVAC. Surely there can't be anything else. Wrong again. There are still two more things to consider in the acoustical criteria of the design: Lighting and Electrical. You have to get these elements into the room, but you don't want to compromise the sound isolation. Electrical boxes should be sealed enclosures and there should not be another box on the opposite wall within the same joist. This is a common pitfall to sound isolation because every electrical contractor knows it's easiest to put electrical outlets for adjoining rooms on a common wall in the same joist bay. Less wire, less work, less cost—don't let them do it this way for the home theater - Another 'flanking path'. You will have just compromised a lot of the hard work and effort you put into sound isolation. Lighting is another caveat. We never use recessed cans in a high mass sound barrier - period. Sometimes we use them in soffits that are not part of the sound barrier. In fact, we sometimes create soffits just for the sole purpose of holding necessary lighting fixtures and/or HVAC ducting, so as to avoid compromising the sound isolation envelope of the room. However, I can not tell you how many times the home owner goes to the electrician and says "You know I think I'd rather have recessed lights here than track lighting." The electrician obliges, and guess what? Well - all that expense you put into creating a sound barrier was just thrown away because it's now been compromised by a bunch of 8 inch holes for lighting.

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