Tag Archives: absorber

Installation of acoustic foam can lead to death

This type of foam can turn deadly in the event of fire.

I was reminded today of a very somber and deadly episode of club music history. The fire at The Station nightclub in West Warwick, Rhode Island on February 20th, 2003, killed 100 people. While certainly the lack of a sprinkler system contributed to these deaths, equally contributory, or perhaps even more so, was the MISTAKEN NOTION THAT ACOUSTIC FOAM IS A SOUNDPROOFING MATERIAL.


It does not prevent sound from transmitting. Not even a little bit.

In a misguided attempt to soundproof the club so that the high volume of music inside would not reach the neighbors, the owners of The Station installed a polyurethane substance that they thought was acoustic foam. (A kind of black foam that is commonly referred to as egg-crate style.) Not only does this type of foam NOT even do ANYTHING to reduce sound, it is flammable, and also emits thick, toxic smoke when set on fire. Polyurethane foam is a packing material, not a soundproofing material.

As someone who has studied and done research on materials that affect acoustics, it angers me that most reporting of the incident describe the polyurethane foam on the walls as a “soundproofing material”. This type of material does NOT function as soundproofing.

That night at The Station nightclub, outdoor pyrotechnics were used indoors, and the sparks emitted ignited the polyurethane foam on the walls near the band. If the foam had not been placed on the wall, there is a chance that the structure might not have caught fire. But with the flammable foam on the walls, not only did it ignite, it filled the entire space with deadly, blinding, and asphyxiating smoke in LESS THAN TWO MINUTES. Here is the Fire Safety Institute’s re-creation of what happened that night. Notice that visibility is near-zero at only 1:30 (90 seconds) after ignition:

With only two exits and black smoke filling the venue rapidly, many people were unable to escape and perished. If the polyurethane foam had not been placed on the walls of the nightclub, there may not have been any fatalities as the space might not have filled with smoke so rapidly. A working sprinkler system would have also delayed the onset of the debilitating smoke.

NEVER USE FOAM to try to sound proof or absorb sound. Period.

Rock wool is a completely inert material

In contrast to “acoustic” foam, rock wool (also known as mineral wool) is naturally inert. (Fiberglass insulation is also naturally inert). Rock wool can withstand a blow torch for more than three minutes and will not ignite. Rock wool is found in the U.S. under the trade name Roxul. Watch this video for proof that a blow torch applied directly for three minutes will not ignite Roxul, and after that much heat is directly applied, the wood behind it is barely warm:

Elsewhere on this web site, I explain how you can make 2′ x 4′ broadband acoustic absorbers using Roxul, fabric and furring strips. For even better flame retardation when making Roxul sound absorbers, use flame retardant fabrics.

Use inert Roxul for sound absorption. 

Never use foam. If you want to reduce echoes and sound ambience in a space such as dance studio, recording studio, or music club, use Roxul as the primary material. Also make sure that a sprinkler system is in place and working.

It is tragic, but there have been several similar fires in music clubs in other parts of the world and the U.S. since The Station tragedy. For all readers of this article, please take heed and use the proper materials to ensure the safety of the people who use your building and spaces. Never, ever put “acoustic” foam on the walls, ceiling or floor of an interior space. Only use rock wool (or fiberglass) insulation.

If you currently have acoustic foam or fabric in your interior space, I urge you to remove it as soon as humanly possible. It is a dangerous fire hazard that could result in loss of life in the event of a fire. If you want to absorb sound, use absorbers made of rock wool. They are relatively easy to build and inexpensive to boot.

The next “prop” your dance studio needs

Have you ever noticed how hard it is to hear clearly in your studio’s rehearsal space? As a teacher, are you constantly having to yell to be heard above the music? There is a reason for that: most dance studios’ acoustic characteristics are about as bad as they can possibly be. Because all the walls are parallel (floor and ceiling of course too), and one or more walls are covered entirely with mirrors and windows, sound bounces around and around and around and around. This bouncing is known as echo or reverb. Often these types of spaces have severe flutter echoes.

The net effect of all this sound-bouncing (reverb and echo) is that it makes it hard to hear things inside the room clearly. And when you can’t hear clearly, it makes you want to turn the volume of the music up much too loud. It makes you have to yell in order for the kids to hear you, and even then, it can be hard for them to understand what you are saying, and also hard to hear the details of the music you are playing.

This is ESPECIALLY PROBLEMATIC FOR TAPPERS! Not only are tap shoes loud to begin with, but flutter echoes and loads of reverb make it really hard to hear the details and timing that your tappers are trying to achieve! No wonder that your tap students are having such a hard time trying to get in sync with each other…. they can’t hear what they are doing!

Another downside to the terrible acoustics inside your dance rehearsal spaces is that by cranking up the music to try to hear it better, you are annoying your neighbors, whether they are other businesses or other dance rehearsal spaces. If it’s another dance teacher in the next room, then they have to turn their music up to drown out yours… leading you to turn up your music even louder to drown out theirs, in a never-ending loudness war.

It’s time to stop the loudness wars in your own dance studio! It’s time to start hearing the music and the instructor more clearly inside the the studio space! It’s time to stop going home at the end of a long night of teaching with a headache and your ears ringing!

Fortunately, solutions are EASY and relatively inexpensive! But the difference, from a sonic perspective, is NIGHT and DAY!

Many dance studios have a cadre of talented and able-bodied Dance Dads who build amazing props for their dance daughters and dance sons. These heroic dads (and of course moms too!) then also have the job of carting said props long distances to various regional and national competitions.

Well, the next “prop” your studio’s dance dads should build is …. drum roll….. broadband acoustic absorbing panels.

Yes, you heard me right. For a total of about $150-$200 in materials, your handy dance dads (and moms!) can build six or eight 2′ by 4′ acoustic panels and hang them in your rehearsal spaces, bringing down the amount of flutter echoes and reverb to a reasonable and comfortable level. The result of which will be:

  1. You can hear the music CLEARLY at a comfortable volume
  2. You don’t have to yell as loud to be heard by your students
  3. Students can more easily hear the instructions you are giving them
  4. You don’t leave the studio with a headache every night from the volume of the sound system
  5. You don’t annoy your neighbors with OONCE OONCE OONCE all night long

If you have the budget, you can purchase pre-made acoustic panels and traps, but dance studio owners can save a few bucks by enlisting the help of capable dance parents! More about how to build these acoustic traps coming up soon, so stay tuned! If you can’t wait another minute to find out more, here’s an example of how it looks/works installed in a dance studio: Acoustic panels in a dance studio. Here’s a nice and short little YouTube video that explains quite clearly how to build them. My only advice beyond this video is to use a nice-looking fabric for the face so that you have something beautiful to hang on your walls instead of burlap.

Here is a PDF describing a case study from a dance studio in Sequim, Washington, where the severe echo problems were tamed with acoustic panels. Here is a PDF which gives NRC ratings at several frequencies for 3″ Roxul Safe and Sound (page 7).