The Empire Strikes Back - Movie Acoustic Panel

•Type A (formerly No. 4) – Material placed against a solid backing such as a block wall.

All tests were conducted according to ASTM C 423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method. Sound absorption coefficients for each sample were measured over one-third octave bands and are reported at the preferred octave band center frequencies. In some cases, the measured sound absorption coefficients are greater than 1.00. As recommended by the test method, these values are reported as measured and not adjusted. The corresponding NRC for a material may also be greater than 1.00 according to the ASTM test method. The sound absorption coefficients of these material are not significantly affected by coverings such as expanded sheet metal, metal lath, hardware cloth, screening or glass cloth. When other coverings having less open surfaces are required, consult an Owens Corning sales representative.

NRC = Average Noise Reduction Coefficient

Sound waves that reflect off of the walls (and other surfaces) of your home theater affect the quality of your listening experience. This is because the reflected sound coming from the walls reaches your ears very shortly after the same sound coming directly from your speakers reaches your ears. You may not even notice the effect of this “comb filtering”, but you are hearing the wall’s negative influence on your room audio (frequency response). These reflections damage imaging and clarity of sound to the listening position. Acoustic “absorption” panels are an excellent tool used to significantly decrease or eliminate these sound issues.

Comb filtering is a specific type of frequency response issue that’s caused when a sound source and its reflections combine in the air. Depending on the difference in arrival time to your ear, some frequencies are boosted and others are reduced.

For the purpose of this FAQ we will only touch briefly on some very rudimentary aspects of acoustic panel placement. Although acoustics is a science, using some of these simple rules and techniques can easily help make a dramatic improvement in any listening environment.

Find the “First Reflection Point” by using a mirror. This is done by sitting in the main listening position of the room facing the front speakers. Have a friend place a hand mirror on the left wall. At speaker height have the friend move the mirror on the wall until you can “SEE” the left speaker’s reflection in the mirror. Mark that spot on the wall with tape. Continue moving the mirror until you see the right speaker. Mark that spot on the wall with tape. Repeat this process for the right wall. You now have your first locations for acoustic panels in your room! If you have a second row of seats repeat this for that listening location and mark the wall.

 

A really great video from GIK Acoustics showing this concept can be found here: https://youtu.be/B9u7k2V4YPw

Ultimately the spots you marked on the wall should be the location(s) of your acoustic movie posters! In practice you can approximate the location of your acoustic panels and split the difference with one acoustic movie poster to save on the number of panels needed. It’s up to you! For a simple home theater this seems to work just fine.

For a 20’ x 20’ room we usually suggest one or two acoustic movie posters for the back wall and one or two for the back third of the side walls of the room for aesthetics and other reflection points in addition to the first reflection panels. So as a rule, an average room should have between 5 and 12 strategically placed acoustic movie posters or a mix of acoustic movie posters and acoustic panels.