Choosing The Right Acoustic Foam

Choosing The Right Acoustic Foam

Using acoustic foam in your studio will improve the sound quality of your studio. However with so many companies now selling acoustic foam it is easy to see why many producers venturing into acoustic treatment make the wrong decisions when looking for the right material to treat their rooms. This confusion is brought about by the fact that there are so many companies out there selling cheap packaging and passing it off as specialist acoustic foam. This foam is normally cheaper will have poor acoustic properties and will not be as fire retardant. A common question we are often asked is. “Why is acoustic foam so expensive?” It is because it is a specialist foam grade made with specific properties to enhance sound absorption

Acoustic foam is the room treatment material of choice for many home music producers, and for a number of reasons some of which are;

  • Acoustic foam offers great absorption especially for mid to high end frequencies.
  • Acoustic foam is much more affordable compared to high end options
  • Acoustic foam is also easy to install and can be aesthetically pleasing cut into the performance enhancing shapes

There are three main types of acoustic foam grades made for acoustic applications. These are, in order of increasing price.

  • Polyurethane polyether foam
  • Polyurethane polyester foam
  • Melamine foam

 

Polyurethane polyether foam

Polyurethane polyether foam has a large range of applications and comes in a variety of densities and colours with many different properties. Acoustic applications are best suited to densities which are reliability light between 24 and 32kg/m3 and densities below or above do not perform as well as ones in this density range. To be a good acoustic absorber the foam not only does the foam have to have the right density it also has to have the right hardness, porosity, open regular cell structure and permeability.

Also do not be fooled by manufacturers stating a higher density will work better The NRC Data for a specific tile will let you know which performs better.below is an example of two tiles of the same size and similar construction however one is made in a 30 Kg/m3 foam and one in a 25 Kg/m3 foam the results are surprising

 

Noise Reduction Coefficient NRC Test Data
Frequency (Hz) Hyped Up Acoustics Sonarflex Tile 30KGm3 Pro-Acoustic’s BLOCK45 Tile 25KGm3 BLOCK45 is better by
125 0.09 (9%) 0.10 (10%) 11.1 %
250 0.28 (28%) 0.29 (29%) 3.6 %
500 0.48 (48%) 0.54 (54%) 12.5 %
1000 0.65 (65%) 0.84 (84%) 29.2 %
2000 0.66 (66%) 1.05 (105%) 59.1 %
4000 0.79 (79%) 1.12 (112%) 41.8 %

 

The comparison above shows that a lighter 25 kilo acoustic foam performed better on every audible frequency and has a 33.6% better noise absorption coefficient overall. So who said a denser acoustic foam performs better?

The reason a lighter foam outperformed a heavier one to such a large extent is down to physics. Although the chemical makeup of the higher density polyether foams is the same or very similar to the lower density foam, the open cell structure air permiability hardness and overall porosity of the lighter foam works better in allowing the air pockets to absorb the sound waves impacting on them which increases the observed performance.

More interesting is the performance in the 500 to 100hz range as this is where the majority of the vocal range lies and so is a very important factor when recording vocals, and is often overlooked when acoustically treating vocal booths..

sonarflexblock45-01

The results above were taken from the test data provided on these documents http://www.hypedupacoustics.co.uk/images/stories/sonarflex%20test%20data.png and the reviews are based solely on the tiles acoustic performances

 

Polyurethane Polyester Acoustic Foam

Polyurethane polyester foams have been used traditionally in the manufacture of of acoustic foam grades and come at a premium as the manufacturing process is more costly. Polyester foam has always had a very good regular cell structure which lends itself natrually to being a good property for acoustic foam, however over the years polyester foams younger brother polyether has moved leaps and bounds and acoustic grades in polyether now also have a very good regular cell structure, so the gap has narrowed between the two.

Melamine Acoustic Foam (Basotect)

Whilst not traditionally used in music studios melamine foams are fast gaining recognition as an acoustic treatment option for studio acoustic treatment. Priced higher than polyester and polyether foams melamine foam offers the perfect combination of absorption and light weight.

Melamine foams achieve this extraordinary feat by exhibiting a true 3D filament structure. This structure means that melamine foam doesn’t have any closed cells but rather millions of air chambers which significantly increase its performance in the mid to high frequencies. Although thicker panels will shift the absorption down to the lower end of the spectrum for domestic purposes the cost doesn’t justify the performance.

So where then does melamine foam come in handy? The answer is simple. Firstly the extremely light weight nature of this foam means that melamine foam panels can be stuck on to ceilings of large buildings without any concern of the impact on roof loading. This property means that melamine baffles and blocks are used in large building, factories, gymnasiums, churches and swimming pools.

Secondly melamine foam is available in brilliant white and is the only type of foam which holds its colour without becoming discoloured by polutants in the atmosphere reacting with the anti oxidants in the foams makeup ( known as phenolic yellowing ). This lends it well to use for indoor applications where darker coloured tiles would present an aesthetic challenge. Melamine panels are handy for home cinemas and used for treating walls and ceilings at reflection points as well as treating home studios that double up as work offices.

Melamine foam can be cut into a number of shapes although most popular are flat panels with bevelled edges. Melamine comes in standard White, grey and light grey however the white panels may be spray painted using specialist equipment to any colour.

Finally melamine foam is class 0 fire rated which is lends it well to applications where building regulations mean only materials with high fire ratings can be used without impacting on the aesthetic of the room it is applied to. Other foams can be treated to make them class 0 rated but this involves impregnating them with graphite and carbon which results in black sheets. Not exactly the best for indoor use.

Melamine foam however is quite brittle and can easily get damaged so needs to be handled with caution and costs a small fortune.

Posted in Acoustic Foam.