Foam tiles and acoustic treatment have been described as “no better than hanging a cat up”. Used solely on their own that can be true as they don’t tend to absorb the lower frequencies, not least because they aren't thick enough. But used as part of an overall scheme can they play a useful part? In this article, Mike explains how he has used acoustic foam as part of his studio design.
Not On Their Own
It is our view that a studio acoustic design using just acoustic foam products is unlikely to produce a good sounding room as foam products on their own will tend to absorb the mid and high frequencies much more than the low frequencies so that you end up with a room with a much longer RT60 in the lower frequency bands and shorter RT60 in the mid and high bands. Essentially it will be drier, or less reverberant at higher frequencies and more echoey in the low frequencies. What you need is a multi-solution co-ordinated design.
The Acoustic Design With A Combination Of Solutions Including Acoustic Foam
Having analysed my room I used a spreadsheet to show me what the RT60 would be. In my research I came across a number of spreadsheets into which I could enter the room size and other critical information, such as what I was planning to put on each surface and see how that would affect the RT60 for the octave bands as you can see below...
As I work a lot with speech in audio post I wanted a room with at RT60 of around 0.25 seconds across each band. By choosing different products and solutions and plugging them into the spreadsheet I could instantly see the impact on the RT60 values for the different bands until I got an appropriate design ‘on paper’.
To handle the key room resonances I needed treatment that was tuned to absorb specific frequencies and I choose two solutions - Helmholtz slot absorbers and Helmholtz panel absorbers. Spreadsheets are available so I could find the correct design to handle the problem frequencies in my studio. The calculators I used for my studio design have long gone, but here are links to similar calculators online, like the Helmholtz slot based resonator and the LF Panel Absorber. It is a Russian site but there are a set of English pages. It also has an online variant of my RT60 calculator spreadsheet that you can see below. You can click on the image to see a larger version.
As you can, this is the wall behind my speakers and screens and for this wall I adopted a two pronged approach. I built panel absorbers tuned to handle the lower room resonances and then covered them with acoustic foam tiles, checking all the time with my calculator that I wasn't putting too much in and over-dampening the higher frequencies. In the image on the right, as I hold back the acoustic foam tile, you can see the hardboard which forms the panel absorber, which has rockwool behind that to broaden the range of frequencies it will absorb.
This also helped to reduce the effects of the sound from the rear of the speakers bouncing off the wall and coming back into the room causing a comb-filter effect at the listening position as well as using dead space to handle some of the room resonances.
For the back wall, again there was a two pronged approach with 2 separate solutions. I built a Helmholtz Resonator and positioned it in the centre of my back wall, on what was the chimney breast, having designed it to handle some of the higher resonances in the room. In the two alcoves I used the space on the left hand side to create a computer cupboard, which also doubled as a store cupboard for microphones and other equipment. To the left of the computer cupboard, I used the remaining space in the corner to create a deep bass trap, which I filled with high density rockwool and then covered with acoustic foam tiles.
In the right hand alcove I installed a floor to ceiling 19 inch rack and then to the right of that, in the remaining space I created another deep bass trap, which again I filled with high density rockwool and then covered with acoustic foam tiles.
This wall has a large double glazed window with vertical blinds, which are closed most of the time but still give me daylight. Under the window I have created a storage cupboard which also doubles as a low end absorber.
This wall has the room door, which is a sandwich of a 1/2 hour fire door and the orginal room door so that the door, when closed, matches the other doors on the landing. On this wall there are are also shelves where I store production music CDs and cupboards for other smaller equipment, tapes and microphones. Both the cupboards and shelves will have an impact on the acoustic design so don’t forget to include them in your calculations.
Floor And Ceiling
The ceiling has a suspended ceiling with acoustic ceiling tiles and 150mm of high density rockwool above. This is actually doing a Iot of the work and it is all hidden away behind the ceiling tiles. The floor is a floating floor with thick underlay and carpet.
I cover the design of the floor and ceiling in my article Studio And Acoustic Design. Floor And Ceiling Solutions.
If you are using any foam products in your studio design then you need to consider the fire safety as some foam products are safer than others. You need to make sure that the acoustic foam you use is fire safe.
In my experience you can use acoustic foam products as part of a larger acoustic design scheme. As you can see in my design as well as acoustic foam tiles, I had Helmholtz slot absorbers, Helmholtz panel absorbers with acoustic foam tiles in front. Two rockwool corner bass traps again covered with acoustic foam tiles. All calculated to work together to get a co-ordinated design to produce a room that works for me and the work I do.
What is even better, now you can get acoustic foam products in a range of colours and so you can incorporate the colour scheme into the acoustic design, whereas when I built my studio back in 2001 I could have any colour I wanted as long as it was dark grey!