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All Acoustic Foams Are Not Created Equal

By January 31, 2013No Comments

Open Celled Foams

Acoustic foams or foam that absorb energy usually above 125 cycles are technically called open celled foams. Open celled foams have just what the name implies, open cells. If you look at an open celled foam closely you would see each one of these cells arranged cell to cell with no cap on the end. The cell structure is open in order to allow air movement hopefully carrying sound to enter each cell. The cells in most open celled foams are irregularly shaped.

Lightweight Technology

The goal of acoustic foam is to provide for absorption in a portable and lightweight technology. It is also less expensive than building cabinets or boxes. Absorption is the goal and it begins for foams that are at least two inches thick around 125 cycles. The design goal after these variables are met is to provide as much absorption as one can within that 2 inches of foam and provide it quickly. Most acoustic foams begin absorbing around 100 Hz. and climb through 4,000 – 7,500 Hz.

Active Absorbers

There are two general types of sound absorbers. They are broken down into two main categories based on how they function. Our active absorbers is termed active because it will have a front panel or wall some call it a membrane. Air can also be part of an active absorber such as in the case of a Helmholtz resonator. An example of a Helmholtz resonator is a coke bottle. If you blow across the neck of the bottle you will recreate a resonating system that starts at 185 Hz.

Passive Absorbers

A passive absorber will have no “moving parts”. Well, maybe some kinetic energy working with normal air flow across the surface of our passive absorber material. Examples of porous, passive, absorbing materials would be drapes, couches, or acoustical foam. Air flow through the porous material causes friction between the fibers or cells and acoustic energy is converted heat and transformed forever.

Absorption Coefficient

The term sound absorption coefficient is a number we use to denote the amount of absorption a material exhibits. If 50% of the energy is absorbed by the material, then we would assign it an absorbing coefficient of .50. One square foot of the material would be assigned an absorption coefficient of .50 which would equate to .50 absorption units or sabins. An open window is a perfect absorber. Sound leaves the room through the window and never returns. Each square foot of the window would be assigned an absorption coefficient of 1.00.

Auralex

Auralex is a company that is well known. It offers many room acoustic products that range from low frequency absorbers through middle and high frequency absorption. Lets look at their two inch foam as our example:

TABLE HERE 125 at 11%, 250 at 30%, 500 at 91%, 1,000 at 100%, 2,000 at 100%, 4,000 at 100%.

Sonex

Sonex is a second well known company that also has many sound absorbing products. One of their foam technologies is termed Super Sonex. Here are the numbers:

TABLE HERE 5% at 125, 30% at 250, 80% at 500, 90% at 1,000 95% at 2,000 and 99% at 4,000.

Acoustic Fields

Acoustic Fields is a new company that also has its own foam. Here is the data:

TABLE HERE 125Hz.at 30% 250 at 64% 500 at 90%, 1,000 at 1,000Hz.

Three Foam Comparison

Lets look at all three sets of data. At 125 Hz. Aurelex is 11% and Sonex is at 5%. Acoustic Fields is at 30%. Both Auralex and Sonex are at 30% for 250 Hz. Acoustic Fields is at 64% more than twice as much absorption. All are around 90% at 500 cycles and close to 100 % after 1,000 Hz.

Acoustic Field’s Difference

Aurelex and Sonex perform basically the same from 125 Hz. – 1,000 Hz. but Acoustic Fields’s foam performs differently. It absorbs at higher rates starting at 125 Hz. At 125 Hz. Aurelex is at 11%, Sonex at 5% and Acoustic Fields is 30%. Acoustic Fields foam is 6 times more powerful at 125Hz. than Sonex and 3 times more powerful than Aurelex. At 250 Hz, the trend continues. Aurelex is at 30%, Sonex is at 30% and Acoustic Fields is at 64%. This is twice the absorption at 250 cycles than either Aurelex or Sonex.

ALL THREE IN ONE TABLE HERE

Critical Band: 125Hz.-250Hz.

The 125 Hz. – 250 Hz. band is a critical band for vocals and guitars. It is critical for piano and brass. Our mixes build up in this low middle frequency area and extra absorption is always welcome for clarity and definition. This frequency range is also very problematic in today’s smaller recording studios. Smaller room dimensions create unwanted resonances within the 125 Hz.- 250 Hz. ranges. A smooth even absorption rate and level goes along way to clarity and reduces mid range “muddiness” both in playback and recording environments.

New Foam On The Block

All foams are not created equal. Acoustic Field’s foam technology absorbs at higher rates than other open celled acoustic foams. This increased absorption is centered in the 125Hz. – 250Hz. which is a critical band for our middle frequencies that affect our vocals, guitars, and pianos. This 125 – 250 cycle range is also critical in small room acoustical environments. Our physically smaller project studios almost generate resonances within this area. We need all the absorption help we can get in this frequency range.

Acoustic Fields 1″ foam: 15 30 65 92 90

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