Explaining Acoustic Foam

We here at the Seismic Audio blog, just like you at home, are always looking for ways to improve sound quality.  Sometimes, it is a new technique for your instrument.  Sometimes, it is a new piece of gear.  Today, we’ll look at actually improving the room itself.  We’re going to talk about acoustic foam and how it can make a huge difference not only to your home studio but also to your practice room or your venue.  Anywhere sound is amplified and listened to, acoustic foam can drastically improve the sound quality.


So, what is acoustic foam?  It is a lightweight material made from polyurethane foam, melamine foam and either polyether or polyester.  Okay, but what does it actually do?  It reduces the natural reverb decay time in a room by absorbing sound waves as they reflect off of walls, ceilings and floors.  These reflecting sound waves cause all sorts of phasing issues, frequency resonances and noise.  In your studio, with your extra sensitive microphones, these issues can make it impossible to capture a high quality recording.


You’ll generally find acoustic foams being sold in 2 inch and 4 inch varieties.  The thicker foam is meant for low frequencies, the thinner foam for higher frequencies.  Seismic takes the guesswork out of it and offers a 3 inch foam.  This thickness works across the entire frequency spectrum.


Everyone agrees that acoustic foam is a must in the studio, but what about your practice space or your venue?  There is an old audio engineer axiom that goes, “the best way to make a PA system sound bad is to put walls around it.”  Every indoor venue does this, what does that mean?  Heavily amplified sounds, such as a PA system or guitar amp will bounce off a hard surface at nearly 100% of the original energy it had leaving the speaker.  In the studio or in the club, these sound reflections interfere with the direct sound from the source.  This gives you phasing problems, resonances, and increased noise.  Acoustic foam will eliminate these problems.


We now know it important to use acoustic foam, but how do you set it up?  First, place a healthy amount of your foam on the wall behind the speakers.  Low frequency sound waves are omnidirectional and having them bouncing of the back wall will make it difficult to hear what is actually happening with the low range.


Next, follow the angle of the speakers to where they point at the far wall.  Remember, the monitors should be pointing at your head.  Place another large amount of acoustic foam in these two spots.  Next, cover the corners.  Affix the sheet of foam to each side wall so i forms a gentle curve.  Finally, spread the rest of your foam evenly throughout the room.


Throughout the process, you should be using the clap test.  It is as simple as it sounds.  Simply clap your hands and listen.  You should hear one of three things.  An untreated room will have a harsh metallic reverb, this is what you are trying to eliminate.  You may hear a pleasant and warm reverb as you start treating the room or just naturally if your room has good acoustics to begin with.  This isn’t bad, but you still want to aim for the third thing you might hear: silence.  A properly treated room will practically eliminate all reverb.  This gives you the cleanest recording possible with no reverb tails to trouble you later in the recording process.

It is a simple process but it takes time and experimentation to get the best results.  Have questions?  Want to get an idea how much acoustic foam you’ll need for your room size and shape.  Call one of our experts at 877-347-6423 and they will help you out.

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