Acoustics Archives - AVL Designs, Inc.

Saratoga Springs High School Acoustic Design

Beautifully repurposed cafeteria

In response to some very positive compliments concerning our cafeteria acoustic design at Saratoga Springs High School, we thought we would share that project news with you.

Saratoga Springs high school cafeteria

Cafeterias are tough, as we explained previously in “Help, I Work In A Cafeteria and I’m Going Deaf!” . Truly, cafeteria space is one of the worst when it comes to conquering the acoustics. Think “tin can.”

cafeteria

This space at Saratoga Springs High School started out as a repurposed gym/classroom, converted into a large upscale cafeteria.

high school cafeteria

Our scope of work was to acoustically compare the existing condition to the architect’s intended design. Their plan was a change for the better but, after modeling the space, we made recommendations that would step up those improvements beyond the original goal, while still preserving the look. We added K13 FC roof deck treatment above the new ceiling clouds, as well as changing wall materials and cloud materials. The school is very pleased with the results.

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Condominium Sound

In the past few years, we have noticed an upswing in the construction of higher-end condominiums. The people who move into these spaces are typically downsizing.

These people are moving from single-family homes into spaces that have residential layouts but are actually single-story dwellings stacked in multi-story buildings.

Many people that have moved into these spaces complain about noise. They are troubled by noise from hallways, from adjacencies, from outdoors as well as from overlying and underlying tenants.

These buildings generally have been designed to typical IBC Based state building code, which requires an STC of 50 (airborne noise control) and an IIC of 50 (Impact Noise Control i.e. Floors).

So, the question that frequently comes up from the architects we work with is “why, since we designed to the standard, are we getting complaints?”

Why the complaints?

In examining the problem, one missing element in these newer builds is the lack of what we in the acoustical industry call “masking” noise.

Masking noise is background noise such as traffic, HVAC, appliance noise, neighborhood noise. Masking helps your ears not notice outside noise sources. Bottomline, these new condos are just too quiet inside.

The quietness is primarily due to more recent energy codes. Older apartment buildings and older houses had windows that would leak heat. Where heat leaks, so does noise. New high R buildings do not leak heat and were by default, better at keeping out noise from outdoors.

Appliances have become significantly quieter. HVAC systems, dishwashers, refrigerators, and other household appliances are now close to silent. In the past, they offered a good level of masking noise in a residential environment. Not so, anymore.

In older buildings, noise from outdoors would mask other sounds, i.e. you didn’t hear the neighbors so much. People also accepted outside noise as “where I chose to live” noise. Not so much in a luxury condo. People want it to feel like they don’t live so close by others.

Standards are out of date.

It is our belief that the standards are out of date. Privacy is determined by a sum of the STC or IIC of physical separations added to background noise. If background noise goes down, construction quality must go up and, yet, this relationship is not addressed anywhere in the code. Background noise is not considered as a factor.

In our opinion, the current standards are off by approximately 10 points when it comes to owner satisfaction. This has been proven in buildings that we have tested. In the ones that were designed at least 10 points above standard, the residents are not complaining. When it comes to the ones that are built at the code standard? People are complaining about the noise.

Beyond STC/IIC

STC and IIC standards do not include low frequency noise, for reasons that will be the subject of another article.

A major complaint we are seeing in a lot of the newer, higher-end condominiums are “elephant noise footfall” complaints, and TV action movie noise when the neighbors have home theater systems.

All of these low frequency sounds fall below the STC and IIC standard. To the chagrin of tenants, a space can test to “spec” and still have these low frequency issues. If you have active people moving around upstairs it can sound like a herd of elephants, which can be considerably troubling.

*Design to control low frequencies is challenging but can be achieved, when done with care.

MINIMUMS

State building code standards are the minimum requirements. The STC and IIC values the codes reference are residential multifamily minimum, which may be acceptable for a college apartment or short term lease , but not a condo high end condo. And the codes are based on an expectation that a wall or floor structure in the field actually performs like the lab test, which isn’t a realistic expectation.

In the lab an assembly is 100% airtight, There are no electrical outlets, recessed lights, ductwork penetrations etc. In the real world, performance is at least 6dB, often 10 dB lower. (To your ear, half as good.)

Solutions

There are solutions but they are not the common methods. Floors have to be stiffened up beyond required structural norms, resilient materials added and, in some cases, low level electronic sound masking added.

—TV’s cannot be attached to demising walls, or demising walls have to be isolated from vibration.

—Some hard floors have to be swapped out for softer options.

—Penetrations and methods need to be changed and treated to be air tight, recessed lighting, HVAC, ducting, bathroom exhausts and other systems need to be built differently than the norm.

These are just a few of the issues. The truth is that all solutions to noise problems will raise costs.

Before you move, ask questions and get guarantees about acoustical performance.

Room Acoustics – Are You Sure That Your Acoustics Are Really Bad?

Room Acoustics

When we get involved in projects to renovate auditoriums lecture halls or classrooms, one of the common complaints we hear from people is “we have bad acoustics.”

Now that statement can have a whole plethora of meanings. So, we start probing. “What exactly do you mean by ‘bad acoustics?’”

As you can imagine, the answers we get back are all over the place. Some people think their room is too live. Some people think their room is too dead. Same room! Some people think that the room has zero sound quality. There is no consistency in what people call “bad acoustics.”

There are rooms that in our expert opinion sound quite good while, in the client’s opinion, the sound quality is bad. There also are rooms that we think sound absolutely awful, but people love them.

Here is a good example: We visited a church that has an exceptionally long reverb time in the main sanctuary – way too long for the spoken word, way too long for any kind of contemporary music – yet, the members just love their acoustics. Reverb time in that room was two and a half seconds in the mid-band, which is really excessive.

The reason they love the acoustics is that they have a choral group and a big pipe organ. For that purpose, the room sounds surprisingly good with a big full sound.

It was just that the listeners were not be able to distinguish the words that the choral group was singing. That, apparently, was not a priority for them. They were happy with it just the way it was.

They wanted better spoken word, but they would not sacrifice any reverberation to obtain it. They wanted a sound system to fix it all.

We have been in other venues where the clients say they “like the acoustics,” yet the room is dead as a door-nail. Often, in those cases, the reason that they like the acoustics is that the primary use for the room is for something like lectures.

However, when they stage a musical event in that same room, it is dull sounding. That is why, when people first say they “like” their acoustics, we ask more questions. Until we know more, we cannot really trust that we know what they really mean.

So, the concept of “good” acoustics is not a standard. There are a lot of standards in the acoustical industry defining what appropriate acoustics are, but for specific uses. A room with good metrics may not be perceived as “good” at all. This is especially true when you get into multipurpose rooms that have more than one function. When the rock band gets booked into the opera house, bad things follow.

Whose Fault Is It, Anyway?

Another real misplacement of blame happens when people add to their “bad acoustics” complaints a discussion about their sound engineer. What they are really talking about is the person running it. But the problem may not be the sound engineer at all. It just could be the performance of the sound system. Or, it could even be both. Obviously, the sound engineer is the final determiner of outcome in any space where sound is being mixed but the outcome will only be as good as the design of the system, and how it works with the room acoustics.

Sound systems must be designed to work with the room acoustics, not against them. Over the years we have seen many sound systems that seem to have been designed completely ignoring basic physics, the layout of the room, the reverb time of the room, the reflections and echoes in the room. Hate to say it but they “slapped something in there” with little thought.

Is the only “good seat” where the sound guy sits?

Sometimes the “good seat” is where the sound guy sits. So, you have a sound guy who is sitting in a location mixing and he thinks he is doing a good job, but the sound he hears is completely different than the sound in the rest of the room.

So, back to the initial complaint, there are a number of things people are not understanding.

The sound engineer needs to be located where he/she actually can hear an average (ideally) of what everybody else is hearing. Or they have to learn how to translate what they hear where they are.
The sound system has to be designed to work with the room’s acoustics.*

*Some sound system companies, the ones that just put in speakers and install equipment without doing any kind of analysis, are not skilled enough at placing loudspeakers and tuning a sound system to get it to work well. In these situations, the sound engineer may not be the one at fault.

So, after speaking for a while with our clients about the difficulty they are having, we arrive to an understanding that…

There is no one room condition that is going to make them happy.
There is not a different sound system that is necessarily going to make them happy.
It is not all the sound engineer’s fault.

…now we can talk about some real solutions.

How do we make a bad sound situation better?

When we design physical acoustics using diffusors, absorbers, reflectors, and various types of structures to guide the way that sound behaves in the room, there are limits to what can be done.

Often, there are budgetary restrictions to what can be done.

Some of the things that might work really well acoustically could be extremely costly. The cheaper ways of adjusting a room acoustically can be kind of ugly. They can look more like you have just randomly attached a bunch of things to surfaces instead of designing a space when you are doing a renovation.

STEREO

So, it can be challenging. First, you must decide what the goal is. What is the room designed for? Speech? Choral? Orchestra? Contemporary music? When you do adjust physical acoustics, you end up with one condition and that condition is the way everything renders in the room. Remember that rock band in the opera hall? …… Not a good option. Better to find some middle ground.

When it comes to the sound system, there are similar decisions to be made. Certain aspects of sound systems design conflict with others.

The idea of left and right is wonderful if you are sitting in the center of the room. Anybody sitting in any seat other than the center line will only hear some of what is on a side of the stereo pair if the sound is panned left or panned right.

If you go with a center cluster, it can be very intelligible and sound great for speech, just as long as it covers all the seats.

There are a couple of problems with using center clusters, however. One is that they are mono and one dimensional, lacking any sense of breadth. Ears hear energy from both sides of the head and the way that energy arrives to your ears gives a sense of warmth, a sense of being enveloped by the sound, which is an important part of the experience. Center clusters tend to be dry sounding. They can be very intelligible but not very musical.

Then you move up to left – center – right, which is a commonly talked about concept that most people do not really understand. In a left – center – right with stereo capability you have to maintain panning consistency so that when something is panned to the left, the entire room still hears the sound and it is perceived as coming from the left.

If your room is wide enough, which most are, there is a time delay problem with trying to send sound from the far left side of the room to the far right side of the room when the far right side of the room has loudspeakers arriving much earlier. So, the way you manage this is your center system ends up having multiple elements and becomes part of the left and part of the right with time delays applied to correct for offsets distances.

In some rooms this arrangement can work fairly well, but the setup and tuning of a system that is true left – center – right with stereo capability is not only complex but more expensive because you practically triple the number of elements required to accomplish the goal. Consequently, what most people tend to do, at least for sound systems in multipurpose rooms is a left – right system that is actually mixed as dual mono.

Comb Filtering and the Haas Effect

Most of the time you never really pan anything full left or full right, correct? You have to have both systems creating the same signal which, inevitably, will cause some phase problems. Depending on where you are sitting you will be hearing both sides of the system somewhat out of phase with each other. The effect that occurs is called “comb filtering.” When that happens, if it is done poorly the room can sound muddy.

So, it requires a lot of skill in placement of those loudspeakers. You must look at time delays to various seats in the room while trying to maintain something known as the “Haas Effect.”

The Haas Effect has to do with the arrival time of energy from two locations to a particular seat. If you are within the Haas Effect, (which various people disagree about whether it is 30 milliseconds or 50 milliseconds) the sound can still be good, even though it is coming from two locations from the same sound source. Once you get outside of the Haas Effect timing, a lot of destructive things happen, quite audibly.

This is all a simplified explanation there is a lot more going on……

So, this is the first segment regarding the basics of room acoustics/ sound systems.

Want some supplemental reading? Go to => Auditorium Acoustic Options

Auditorium Acoustic Options

In the past, auditoriums were generally purpose-built. Opera houses were designed for opera. Orchestras often share the opera house by adding a stage shell that would aid the orchestra acoustically.

Lecture halls were designed for speech. Movie theaters were designed for sound reinforced by audio from loudspeakers.

Churches were designed for various styles of music and use. Some spaces were built around the required characteristics of a large pipe organ. As liturgical spaces are being repurposed for contemporary music and changing congregations, the results are often not very good.

Multipurpose auditoriums were never really multipurpose.

They were a middle of the road compromise.

When preparing to design a space from an acoustical point of view, the first question that has to be answered is:

What type of performances and uses should it accommodate?

Next Question:

Can I target a style or do I need variable acoustics?

Generalized Examples:

Unaided speech requires a quiet room, lower reverberation time and strong early reflections.

Orchestral requires a longer reverb time, extended bass response, and a diffuse room response.

Contemporary music driven by sound reinforcement requires a completely different room character. In order to allow the sound system to control the experience, the room has to be subdued.

Personal Experience:

Dead Room

Live music can be disappointing in the wrong environment. I remember once I was working with a jazz artist and the auditorium we were booked in was entirely covered in thick fiberglass wall panels. It was dead as a doornail acoustically.

Even when using reverb effects, the room still sounded wrong. The reverb was coming from the PA and the stage monitors, not the room. The side and rear walls were absorbing everything, not adding anything to the sound. Not a great experience.

Overly Live Room

I also remember hearing a favorite artist (Jazz/Bluegrass) in an opera hall. The room was so live it was totally muddled. The sound system could not correct for the overly reverberant room.

How About a Variable Room?

If you build a room with no acoustic variability, as and audience member or performer you are stuck with what you have.

Acoustical Variability to some degree can be accomplished with wall covering drop curtains, rotating walls with various materials, and other options. Physical options can be costly and they can take significant manpower to change for each event type.

Electronic Acoustic Architecture

Most people are familiar with movie theater surround sound. THX, Dolby, Dolby Atmos etc…. These systems create spatial locations for sound sources using a multitude of speakers, each receiving specific information to simulate where the sound would be coming from, or to extend the “feel” of an environment.

While these systems are great for movies, they aren’t deigned to work with a live musical source.

Fortunately recent advances in technology have made it possible to go beyond surround sound into fully simulated live acoustic environments. Imagine you are performing in a relatively plain room with a medium reverberation time and not a lot of lateral energy. Walking the seating area, you find that there are dead spots and changes in frequency balance. Your ensemble sounds a bit thin and lifeless.

Like A Concert Hall

What you want for your ensemble is a much larger room with elegantly tailored wood and brick surfaces, diffusive in nature like a concert hall. Features like these are what makes concert halls concert halls.

Imagine, now, an electronic acoustic system that can create the sound of the room that you are not in.

This Is How Electronic Enhancement Works:

A series of prearranged microphones pick up the natural sound of the ensemble, organ etc… from a suitable distance so the sound is well mixed. This sound is then processed by a complex computer algorithm that simulates how the sound would behave if it was occurring in a simulated room. This sound is then precisely distributed and tuned to small loudspeakers located to simulate the room you want to mimic.

Room tunings and character can be changed at will. To the audience, it is entirely natural. It just sounds as if they are in a different room.
When the orchestra takes the stage, the room gets larger and has added bass extension. The choral group gets a longer reverb time with added midrange clarity. For speech, the system switches to a voice lift mode and can improve intelligibility.

All of this is controlled by simple presets: Choral, Organ, Speech etc…

In order for electronic acoustics to work, the ROOM itself needs to be designed carefully from an ACOUSTIC standpoint, but in a different fashion.

Discrete echo has to be controlled. The enhancement system works with the room acoustics, but cannot cancel out physical acoustic defects.

Successful implementation of electronic acoustics requires coordination of the system elements with lighting, ceilings, walls, HVAC, plumbing and other elements throughout the design process. HVAC noise has to be very carefully controlled. Led lighting (much of which is now fan cooled) has to be chosen and placed very carefully relative to microphone locations.

https://www.youtube.com/watch?v=Te5lPxzVR4E

The Physical acoustic conditions have to be designed to work with the system. This is not a sound system, it is an acoustic system and placement of all elements are critical relative to the room in which it is employed.

The results are well worth the effort. Performances are enhanced and audiences experience an enveloping detailed sound quality in auditoriums that were previously not.

Speech Privacy

We get asked quite often about how to achieve speech privacy in office areas, doctors offices etc. It is actually a fairly complex question but here are some basic points to consider:

Speech privacy is a function of many factors. The first and most critical is “how loud is the source?” A loud speech source is more difficult to control than a quiet one. People can talk more loudly than you might expect especially on cell phones.

The next critical factor that comes into play is how well isolated that source is from the area you don’t want to receive the speech in.

In the case of enclosed office spaces, the construction of the space itself is the first line of defense for privacy. If doors, walls, and ceilings are not designed properly speech will transfer into adjacent spaces. These adjacent spaces we call “receiving areas.”

Offices can get noisy #acoustics

If you don’t want speech to be understood in the receiving area, there are other factors in play.

The first is how much sound actually got there, which is a direct function of the quality of the partitions that separate the space.
The second is how much background noise there is in the receiving area. If the receiving area is very quiet, you hear better. It is kind of common sense but it has become a problem. Old desktop computer fans made enough noise to help with privacy. Quiet computers, lack of background music (no one can agree what to listen to), better windows ( high R value equals less outside noise ) and quiet HVAC are actually problems for speech privacy.

If your receiving room is quiet, it is critical that the walls, doors and other construction are built to a higher level to prevent sound transfer.

Some of the things that can degrade the quality or an office are gaps under and around doors, HVAC shared duct paths, back-to-back electrical outlets, and lack of acoustical detailing in wall construction. Some aspects of wall construction are not obvious. The simplest is the insulation in the wall cavity. In the absence of batt insulation, a wall cavity becomes resonant and more sound transfers through.

Tips on speech privacy in office settings #acoustics

The next issue is wall construction. Is it built on 16 inch centers? Is it built on 24 inch centers? Was the gypsum caulked when it was attached to the studs and floor plates? Are the studs wood or metal? These are all factors that play into the quality of the construction.

Doors need to have gasketing. Acoustical gaskets are similar to fire gasketing. It doesn’t need to be fireproof for the sake of a fire rating but if smoke can penetrate around a door, so can sound. The door itself is important, as well. A solid wood door is not a good selection because wood transfers sound well. Preferably, you want a metal door with an acoustical inner core that separates sound from the inside to the outside.

The types of seals that are used around the door affect not only the quality of sealing but also the longevity of the solution. Compression seals tend to only work for a short period of time before developing a memory and start leaking. Magnetically sealed doors, which are considerably more expensive doors to buy, are similar to your refrigerator. They reach out and grab the adjacent surface, creating an airtight seal, as does a refrigerator door. If you use compression seals on a refrigerator, it would tend to leak thermally, which is the same as leaking acoustically.

What if you can’t isolate the receiving room well enough due to factors you can’t control, such as walls that only go up to the ceiling with a big gap above where you can literally see above the ceilings of all the adjacent spaces ? Then you need to look at how to get adequate noise on the receiving side.

It is important that every area considered a “receiving area” is evenly blanketed in some sort of background noise. Background music is one way that used to be done. HVAC in some cases does the job as long as the fans are always on.

Another way is noise masking using shaped pink noise. This type of system is often used in open office plans to achieve a level of privacy. (It works far better if the source rooms are still separate spaces and receiving rooms around them have the noise masking.)

Basically, a noise masking system is a series of small loud speakers placed either in the ceilings or above the ceilings that generate a soft background noise similar to the sound of air conditioning. If done properly it will create a more private environment.