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.

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.

Copyright AVLDesignsInc 2021+


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Sound In Schools – Why It’s So Bad

So, today we were at a school that wanted a review of all their technical systems: stage rigging, lighting, audio, video, curtains – everything.

As usual, the first thing that we found was unsafe stage rigging as well as unsafe stage practices such as building sets, suspending sets, etc. [Which is the subject of another little article: Sound in Schools Part 2]

The next discovery was lack of skills in knowing how to do lighting.

But the number one thing that came up, and it almost always does, is bad audio. Years ago someone wrote a book with the title “If Bad Sound Were Fatal, Audio Would Be The Leading Cause Of Death” [authors Don & Carolyn Davis] Yes, bad sound is a universal problem and, truly, the number one complaint from schools for their theater productions, as well as for just day-to-day meetings, lectures, etc.  No one can seem to get audio to work. So, why is that?

Audio is not a Technical Skill

We were trying to explain to them why it is so difficult to get audio to work. And the first misconception that they had, as well as everyone else seems to have, is that audio is a technical skill. Audio is not a technical skill. Audio is a musical skill and, unless you have musical capabilities, you are never going to successfully do audio.

What do we mean by “musical capabilities?”  It means that running audio for any kind of function is similar to learning how to play a musical instrument. On an instrument if you play something in the wrong key everybody knows. It is immediately apparent. They don’t look at you and go “gee, I wonder what is going on with that instrument?” They just go “He’s wrong. Let’s fire that guy.”

In audio, when people get bad results whether its poor tone quality, muddy sound, feedback, screeching – take your pick of aberrations that people get –  it is all bad sound. When people look at how to get this to stop, they think somehow that there is a magic fix to it. Usually, they think it means buying new gear. Wrong.

People assume that in all circumstances getting new gear will fix all audio regardless of who is using a mic, how they are using a mic, what their voice sounds like, what else is going on in the room, etc. That simply is not the case.

Another thing we hear a lot is directors telling their sound people to “get it set” and just leave it alone. Sure, if everything else doesn’t change at all ever. That scenario hardly ever happens.

So, the first misconception is that the fix is a technical skill. It is NOT. It is a musical skill! So that means the person doing audio should be able to play an instrument. They need to be constantly staying top of the changes happening on the source end, level, EQ, etc….on the fly.

That person has to be able to identify frequencies by octave band, at minimum. Third octave band would be even better so that when they hear something they will recognize “ oh, that is this frequency that is out of control. I need to fix that.” 

So, that is the first set of skills. Develop self-ear-training. Ear training is best learned from a musical perspective. You can teach it to a technical person who is non-musical but it is a lot more difficult.

So you get this person, now, and you get him/her to the point where they actually have an idea of what certain frequencies sound like. That way when someone is performing and the sound person hears something they don’t like, they can say “oh, that is 250hz, if I can take some of that out they will stop sounding so “chesty” and the audio quality will be better.”  Or “that squeal I am hearing is 8khz. I can pull the filter out and get rid of the feedback problem.” So they’ve got that skill, that’s great. You are on your way.

That is one microphone, one person. [More to come in our next installment: Sound in Schools Part 2! ]


Copyright AVL DESIGNS INC. 2021+

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Sound In Schools – part 2 – You are part of the band!

In case you missed it=> Sound in Schools: part one

So, you have one mic sounding good. Now let’s start working with multiple microphones, multiple instruments. The nitty gritty of bad audio, if we  were to put it in a nutshell, is  the notion that if you get each channel sounding good by itself and then turn it all up, it will all sound great together.  Based on that premise, if you want somebody to sound more in front of someone else, you just turn them up, right?  Not exactly. Why not?  Because that is not how the human ear operates.

Discovering why sound in school auditoriums is often so bad, and how to fix it! #sound #AVTweeps #audio #performingarts #Highschool

Your ear can only discriminate a certain number of things at any given time. Try this for an example:  play a track of a bass player that sounds good, full and crisp. Now turn on a fan in the room. Bass definition drops off and, oddly enough, it sounds like there is no bottom-end. If, instead of a fan the sound interference was cymbals, it would be even worse. Multiple “anythings” have similar issues. Sounds mask each other.  As the engineer, you have to decide how to deal with that and make music out of it.

So, let’s just take a simple task:  two vocalists as opposed to just one.

Put two people up there and let’s say they have kind of similar voices and you have a hard time figuring out who’s who. When you listened to each voice individually they sounded pretty good – and then when you put them together it is just kind of two-dimensional.

You can’t really tell who’s who when they are singing at the same time.  Now, if they are in a duet or singing parts and they are breaking apart, obviously that changes. But when they are singing together, you’re not really hearing the voices independently.

One of the things people will do, if they are mixing on a sound system that is stereo, is to pan one person to left and the other person to right. And then, if you are sitting in the middle of the room, that really separates them.

In live sound, however, if you are sitting on the right or the left side of the room you won’t hear the other person very well at all. So that approach  is not a viable fix  unless your sound system is a type that hardly any average school has, where the left and right systems completely overlap the entire room and provide true stereo in all seats. [We can talk about why that is complicated to do in a different segment at some point.]

Most live sound is dual mono by default. Separation in the mix is done by other means.

So, let’s get back to the two microphones. We really need to mix them in mono because we need to be sure everybody in the room hears both singers, but we want them to sound distinct. So what should we do? We will take some frequencies out of one mic that we leave in the other mic to make them stand apart sonically.

Let’s say there is a male voice and a female voice. In this instance, the goal is for the male voice to stand out in the low frequency ranges but the female voice has some low frequency content. To make that work, we will pull some low frequencies out of the female voice which will separate the two.

Now, if we then listen to the female when she is singing just her part, we have to bring those low frequencies back in for a while to make her voice sound the way it should as a soloist. But when they go back to singing in unison, in the duet sections, we will have to pull her voice frequencies out to get the whole thing to work from that perspective.

So, it’s a constant movement, like playing an instrument.

You are not leaving things alone. The keyboard player doesn’t just play an F chord and that’s it. When they’ve got to play a B flat cord, they change to B flat. Channel equalization has to change in various songs and parts of songs. In essence, you are part of the band.


Copyright AVL DESIGNS INC. 2021+

Did you miss part one? Catch up here>>> Sound in Schools part 1 Copyright AVL Designs Inc 2020+

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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.

Copyright AVL Designs Inc. 2020+


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The LED Conundrum – LED Theater Lighting

A brief discussion on LED lighting for theater.

“Everybody says they want LED theater lighting, yet we hear many people say that they have it and hate it. Totally believable and we know why – they got the wrong LED’s for their application.”

LED Theater Lighting solutions #lighting #theater

In the old days of analog lighting (meaning incandescent and  halogen lights) lights  pretty much turned on and off and up and down when you told  them to. If you wanted to dim those lights, there were a variety of devices that would  dim them pretty well with the occasional lamp sing noise. (For those of you who don’t know what “lamp sing” is,  it is a buzzing of the filaments in the lamp that is audible. It can be heard as a buzz when the lights are dimming. Good dimmers didn’t produce that noise. Cheap ones produced it in various forms depending on the dimmer.)

Thanks to flat screen TVs, we enter the wonderful world of LED lighting. Yes, that’s right – television is at fault for LED lighting. Somebody realized that a nice flat screen display actually made colors and light all at the same time. That seemed like a good idea for lighting,  which it is except it has a bunch of problems (what a surprise.)

LED accomplishes a variety of things other types of lighting technology could only hope to do. Energy efficiency is one of those things – about 25% of the energy for the same light output. But the best thing about LED is the ability to change color. Being able to pick any color of the spectrum without a gel inserted in front of the fixture is really kind of spectacular. The problem is that getting the color requires a sophisticated array of LEDs and a driver, which is basically a computer telling a variety of LEDs what to do. So now you have a room full of small computers!

Another problem with LEDs was how to get them to look like theatrical lights do.  Most theatrical lighting uses lenses to provide focused tight beams of light. These beams of light have sharp edged capabilities that allow lighting designers to light just what they want to and not have light spilling all over the place.


The first group of LED offerings couldn’t really do that because they were groups of individual LED’s that provided a wash of light not a focused beam. (In the wash of light there were also issues. They had to use individual color LEDs to create the lighting field so the whole lighting  field was not smooth nor consistent.)

LEDs have come a long way and some are just as good as traditional fixtures. Sorry to say, they are NOT the cheaper ones! Just so you know.

Many specifiers select LEDs from catalogs, or the recommendations of manufacturers. LED lights should never be selected without hands-on experience with the specific product plus a full understanding of how they operate and are used in theater.

Some of the problems with LED lighting that were never issues with incandescent:

  • Color Rendering Index– Incandescent Quartz stage lighting has a high CRI in excess of 90. What his means in simple terms is your eyes like it as a white light source. Many LEDs have poor CRI – i.e. your eyes don’t like them.
  • Color Consistency – Pick a few LEDs from different manufacturers and check their red/green/blue base Led colors – they are not the same. This makes it impossible to get various fixtures to match when trying to create white or a specific color. (With some manufacturers, pick two of the same fixture and they won’t even match!)
  • White Light color Temperature – many LEDs do not have a good “white “period.  When the red green blue base colors don’t work, white doesn’t either.
  • Poor dimming
    • Stepping, flickering, etc.….
  • Noise – Some LEDs have fans that kick on that are louder than HVAC noise.
  • Lack of light output when you make the fans quiet. Many “quiet mode “ settings restrict light output by as much as 50%.
  • High frequency noise when dimming, in some fixtures. A squeal or whine when dimming. Changes depending on  the color selected.
  • Colors at the edge of light beams – “rain bowing.”
  • Life spans that are much lower than expected. High output devices for theater are made possible  by overdriving the LEDs so they last much less than the 50,000 hours people expect.  It can be as low as 20,000.
  • Comparing data is not simple as many standards that do exist are not published by many manufacturers. You can’t compare what isn’t published.

Summary – You have to test to select appropriate LED fixtures.

At AVL we test equipment and test fixtures extensively before we specify them. We test fan noise, dimming, color, rendering, dimming noise, and overheat behavior. Based on those tests, we will specify different fixtures for different projects while considering budgets, needs, field conditions etc…..


  • High fan noise isn’t a problem in a mall, but is a problem in a theater.
  • White not a big deal if I’m lighting in blue.

LED is a fast moving industry so we are testing fixtures regularly. The latest offering may or not be an improvement and, in some cases, the latest and greatest have new issues that didn’t exist before.

LED Replacement Lamps and the dimming problem

What about just using LED lamp replacements ? There are many “dimmable” LED replacement lamps on the market. You would think if it fits in the socket and says it dims, it will – right ?  Not so much. Here is a brief discussion….

Incandescent Dimming

  • Incandescent dimming has been easy and, for the most part, reliable. Many dimmer types will dim an incandescent lamp pretty well.
  • The hope has been that LEDs would be better. That is not the case.

Dimming of LED Fixtures or Lamps:

  • LED lamps are called things like “dimmable” and “truly dimmable “ and “really dimmable”
  • Unfortunately, LED lamps  called “dimmable” can mean many things. It may mean they will dim well, not dim well, or not dim at all. Dimming can also shorten the LED lamps life if the drivers and the dimmer type are not compatible.
  • Any dimmable LED solution needs to be a designed solution. LEDs have solid-state drivers within the lamp or fixture, which need to be compatible with the type of dimmer being used. Dimmer types : ELV, MLV, SSR, TRIAC, SINE WAVE AND IGBT dimming are all options, but not all will properly dim a particular LED Lamp or fixture or in some cases a particular quantity of LEDs on a circuit.

Data Control Dimming

  • Some LED fixtures dim directly via DMX data, some with 0-10VDC (which has it’s own issues), some over DALI and other control schemes. These control schemes are more reliable where the fixture is self-dimming, but the solid-state driver circuit boards within the fixtures can be subject to damage from surges and low voltage.
  • In essence these driver boards are mini computers, which need to have protected power and have their power fully shut off when not in use. If this is not done, the fixture life may be shortened by data driver failure.  This requires an additional layer of control in the form of remote control relays or switches to kill the power feeds when the fixtures are dimmed off.

There are also issues of LED consistency device to device.  A row of LED’s where all but one dims well is likely due to a bad LED lamp, not necessarily a bad dimmer. It may also be conductor resistance, a bad LED driver, phase reversal, or a host of other issues.

Substitutes when dealing with LEDs cannot be simply a cut sheet saying a lamp or device is “dimmable.” Specific combinations of LEDs, quantities,  and dimming devices must have been tested as a system to verify they will actually work.

A well written on online resource that describes the issues of LED Lamp dimming is available at: LED Lighting – What You Need To Know

The US Department of Energy has authored this, as they recognize the issues moving forward.  Their basic recommendation is not to use any design without a mock up. Therefore, when a contractor wants to substitute a lamp for a specified LED,  the contractor will need to verify with the manufacturer that they have test data to support the dimming of the lamp in the configuration on the plans with the dimmer types and curve being used.

At AVL Designs Inc. we keep dimmers at our office and test the lamps that we might specify as replacements.

Copyright AVL Designs Inc 2020+


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