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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