The Green Studio

Traditional acoustic materials from mineral and synthetic sources are subject to environmental concerns and possible health issues. Now there are affordable, 'green' alternatives, but how suitable are they for the home studio?

Green building is a hot topic right now, as many people are considering their impact on the environment when planning a construction project. We humans are part of the environment too, and so enlightened self‑interest has a role to play in studio building (or rebuilding). After all, if your musical or production skills are in demand, you'll be spending a lot of time in the studio, so you might as well make sure that you're going to be healthy, comfortable and happy in your chosen habitat.

Whether we're tracking, mixing or mastering, our number one priority is, of course, that our rooms sound right for the task — with reverberation and echo (the time domain) under control, and without unwanted tonal coloration (the frequency domain). As all Sound On Sound readers know, we achieve this balance using a combination of absorptive and reflective construction materials. Conventionally, absorptive panels have been made of either melamine foam or mineral fibre, which have some similarities in structure. Both types of material trap millions of tiny air pockets within a maze of very fine strands, creating a low‑density substance that is lightweight and relatively easy to cut or shape. The drawback is that large quantities of these light, airy materials can be required to absorb bass energy.

In this article, I'm going to look at alternatives to conventional room treatment materials, with regard to acoustic performance, environmental credentials, fire safety, and suitability for DIY installation. I'm also going to factor in the cost and availability of these alternative materials; if they aren't affordable or easy to find, then they are unlikely to be specified in studio building projects.

Do Your Research

The greenest thing you can do is to plan your studio build carefully, based on solid research. That way, you can be sure that you won't be buying the wrong type or too great a quantity of treatment materials, causing unnecessary waste. Acoustic consultants sometimes have to specify that all existing 'treatment' is removed, as a first step towards improving the sound of a particular room. Correct positioning of acoustic treatment and monitors, or just decent monitor stands, can reduce the amount of absorption required to correct acoustic problems.

Given that every absorption material has a characteristic frequency response, using one type of absorber on every surface will bias the room sound towards that particular response — so you may need fewer absorption panels or tiles than you think. Lining the walls with inappropriate material only serves to make the room smaller, and might even lead to false confidence in your mixes. It's easy to remove too many high‑frequency reflections with absorption, making the room sound dull, and leaving a honking resonance at the bass end.

Because low‑frequency resonances (room modes) are some of the hardest acoustic problems to treat, especially in small rooms, consider the role that digital room correction (DRC) of the uneven frequency response might play. It used to be that DRC meant buying special monitor speakers with built‑in DSP chips, or extra rackmount processors. Now that most people mix on computers with plenty of CPU power available, DRC can be done entirely using free, cross‑platform software such as DRC‑FIR or Room EQ Wizard, using your standard audio interface and an inexpensive measurement microphone, or an SPL meter with an auxiliary output. If digital room correction works for you, you might end up needing fewer bass traps.

Acoustic treatment designs originally intended for broadcast studios, where absorption of reflections in the vocal frequency range was the main issue, may not work in other scenarios — so dispense with conventional ideas about what a studio 'should' look like, and concentrate on the results. Establish a testing methodology before you begin, so you can be sure that your design changes are making a difference in the right direction. To paraphrase the late philosopher Sir Karl Popper, science makes progress through falsification, not induction — so if you have a theory, you should be willing and able to prove yourself wrong. This principle applies whether you are using an objective test such as a waterfall plot of room frequency response against time, or a subjective test (listening to a reference CD through your monitors).

If you don't think you have the budget for an acoustic consultant, consider that one day of an expert's time costs about half as much as a basic room‑treatment kit made up of melamine foam tiles. Whatever your budget, the first step on the path towards acoustical enlightenment is to start by reading your Sound On Sound back issues, including Paul White's 'Room For Improvement' series, which began way back in July 1998. This article, and many other relevant features, are on the Sound On Sound web site (see the 'Web Links' box for all references made in this article).

It may be that the room you have in mind for your studio project is just plain wrong, and will never really be suitable for recording, mixing or mastering with any amount of treatment material. An acoustic consultant, or your own research, will soon establish if this is true. In that case, the best thing you can do for the planet, your wallet and your sanity is to start on a new master plan!

Foam Or Fibre?

Melamine foam is a product of the chemical industry: a synthetic melamine compound combined with formaldehyde to produce melamine resin. Although in theory it can be recycled, it's tricky, if not downright impossible, to actually find a place that will accept it for recycling. It's not all that long‑lasting in heavy use, because it tears or crumbles easily, especially when people or equipment regularly bump into it, and it can discolour over time. Melamine is not particularly toxic unless eaten, but its fibres are abrasive, so you probably shouldn't breathe in the dust when cutting foam acoustic panels. Indeed, the chemical company BASF produces a melamine foam under the trademark Basotect, which is used in some domestic cleaning sponges because its "glass hard microstructure” is abrasive enough to remove permanent marker ink from fridge doors.

Formaldehyde is toxic, can cause allergic reactions, and is a "known human carcinogen” according to the World Health Organisation's International Agency for Research on Cancer (IARC). Whether a significant amount of formaldehyde is released into the studio by acoustic panels after manufacture is hard to establish without laboratory testing. The issue of indoor formaldehyde pollution gained attention in the US after Hurricane Katrina. Some victims of the disaster, who had been rehoused in trailers, complained of breathing problems, headaches and nosebleeds. The mobile homes provided by the federal government were found to contain five times the levels of formaldehyde typical for a normal house. As a result, the materials used in the construction of new trailers supplied for emergency housing have now been changed.

Acoustic treatment manufacturers Auralex have acknowledged the problems of conventional melamine foam with the recent launch of their proprietary Studiofoam 'eco' and Studiofoam 'Pro' formulations, which are both melamine‑free, and said to be much longer‑lasting as a result. The exact compositions of the two foams are an Auralex trade secret, but they are described as a soy‑based hybrid formula made without the use of ozone‑depleting chlorofluorocarbons (CFCs). One difference between the two new formulations is that Studiofoam Pro has a Class‑A fire rating, making it suitable for installation in public buildings and vehicles (such as outside broadcast trucks), whereas Studiofoam eco has a Class‑B fire rating. A box of Studiofoam Wedges made with the 'eco' foam is priced at £143 from Dolphin Music in the UK or $199 from www.truesoundcontrol.com in the US, which gets you 12 60cm‑square, 5cm‑thick pieces. Just launched in the US, Studiofoam Pro panels which are 60cm square and 3.8cm thick have a recommended retail price of $275 for 10. Double‑width, rectangular versions of these panels that are 120cm by 60cm but the same thickness are also available.

Auralex Studiofoam is now made from a soy‑based formula, instead of conventional melamine. Mineral‑fibre products are marketed under many names, including Fiberglas (spelled with one 's', a trademark of Owens Corning) or Rockwool (a trademark of Rockwool International). They are made from abundant natural materials including silica, which are melted at high temperatures and then drawn or spun into long, thin fibres. Formaldehyde is still used as a binder in the manufacture of some glass-fibre products, while other producers have replaced formaldehyde with an acrylic binder. Like melamine foam, mineral‑fibre products can be difficult to recycle locally, although new mineral fibre can be made from recycled glass. A more pressing concern for studio builders is the potential effect of loose, airborne fibres on human health.

Critics of mineral‑fibre insulation point out that the companies who make these products are often the exact same companies that used to produce asbestos, a silicate insulation material now banned from sale in many countries. Owens Corning filed for bankruptcy protection in 2000 after being ordered by a US court to pay millions of dollars in damages, due to liability for asbestos‑related diseases in American citizens. The company emerged from bankruptcy protection in 2006, after setting up a US $5 billion trust fund to pay compensation to asbestos plaintiffs.

It's not in dispute that mineral fibre is irritating to human skin, eyes and lungs, which is why you should always wear overalls, work gloves, protective goggles and a good face mask when cutting or handling the fibres. The unresolved question is whether glass and other synthetic mineral fibres breathed into the lungs are carcinogenic. Insulation manufacturers argue that mineral fibre has a different structure and composition to asbestos fibre, so that it cannot be as dangerous. Currently, the IARC lists insulation glass wool as "not classifiable as to its carcinogenicity to humans”, which means there is insufficient evidence to make such a link. However, the IARC has been criticised for a lack of transparency in the matter of influence by the insulation industry.

Consider that if you line the walls of a studio with the stuff, you're going to be in close proximity to it for many hours of the day or night — particularly in an enclosed space such as a vocal booth. The tiny fibres, each of which is just a few micrometres across, have been known to escape through acoustically transparent fabric (which has to be full of small holes to do its job). If the acoustic treatment is moved or damaged, there is the potential for fibres to migrate directly into the studio's air circulation. Owens Corning point to their product's certification for respirable particle levels from the Greenguard Environmental Institute, but it's a safe bet that the tests were carried out on a building where the insulation was buried in the walls and ceiling, not exposed on the inner surfaces of a studio room.

Auralex have obtained the Greenguard Indoor Air Quality and Greenguard Children & School certifications for their wrapped glass-fibre ELiTE ProPanels, because they have eliminated formaldehyde and phenol from the production process. This new glass‑fibre formulation is set to be introduced to other Auralex products including SonoSuede Panels, ProBaffles and ProBanners. Like formaldehyde, phenol is one of the volatile organic compounds (VOCs) which are thought to cause or exacerbate chronic illnesses in humans — an effect associated with 'sick building syndrome'.

ELiTE ProPanels have achieved two Greenguard certifications because they emit fewer VOCs than conventional glass‑fibre products.A reduction in VOCs can only be a good thing, but when using mineral fibre in an acoustic product, the potential for loose fibres remains. It seems reasonable to assume that ready‑wrapped mineral‑fibre panels would cause fewer fibres to escape into the studio air than a comparable DIY installation, particularly if you're building the home‑made acoustic treatment in the room. While Sound On Sound has always championed the DIY approach, it is worth contemplating that home‑studio builders don't have the same access to air‑filtration equipment or air‑quality testing that the established acoustic treatment manufacturers do.

Subsidised Insulation

In the UK, the government subsidises the cost of certain insulation materials for DIY installation under the Carbon Emissions Reduction Target scheme. These include mineral‑fibre products made from recycled glass. Retail chain B&Q offer two alternative products under the scheme, designed for insulation of loft spaces. One superficially resembles traditional 200mm‑thickness glass fibre on a 4m‑long roll, except that it's greenish in colour. It's made from 90 percent recycled plastic bottles, with the remaining 10 percent made up by a polyester binder. This insulation doesn't itch the skin on contact like mineral fibre does, and B&Q claims that the product is totally free of floating fibres. It costs less than £12 a roll with the government subsidy, which is about three times the cost of equivalent recycled glass fibre rolls under the same scheme. There is also a 150mm‑thick, 5.3m‑long version of the recycled plastic insulation available for just under £9 per roll. In New Zealand, a similar insulation made from recycled plastic bottles is sold under the Autex GreenStuf brand name (which really is spelled with one 'f').

Recycled plastic bottle insulation is designed to be kinder to the skin and lungs than mineral fibre.The other interesting product from B&Q is a 100mm‑thick insulation made from 55 percent sheep's wool, 35 percent recycled plastic and 10 percent polyester binder, on a 6m roll. This also costs less than £12 a roll with the government subsidy. Both types of insulation — recycled polyester and the wool/recycled polyester mix — are supplied in a standard 370mm width. Another wool/recycled polyester roll insulation, known as Thermafleece PB20, is made in the UK by Second Nature, based in Cumbria. It costs £54 plus delivery for a 15.9m roll from on‑line store The Green Building Site; the higher cost than the B&Q product per square metre might indicate that this particular offer falls outside of the subsidy scheme.

Although these subsidised roll insulation products are certainly more pleasant to handle than mineral fibre, and the assurance that fibres do not float away from the surface is very welcome, there is a potential limitation. Designed as they are for thermal insulation rather than acoustic absorption, the density of these products is likely to be lower than typical for the better‑quality foam tiles or mineral‑wool slabs currently used in studio construction. Taking the 200mm thick recycled bottle insulation as an example, it weighs around 4kg per roll. This equates to a density of about 26kg per cubic metre when compressed in the wrapper — about the same density as the cheaper type of melamine foam tile that you might find on eBay. When the packaging is opened and the insulation is unrolled, its thickness doubles to reach the full 200mm after a couple of days — halving the density to just 13kg per cubic metre. Thermafleece PB20 is quoted at 20kg per cubic metre. At these density figures, it's hard to imagine that this type of material would be useful in a passive bass trap. For comparison, Rockwool RW3 is specified as 60kg per cubic metre, and RW5 is specified as 100kg per cubic metre.

Polyester Applications

That Sound On Sound DIY room treatment favourite, the hanging polyester duvet, has a similar density to the plastic‑bottle‑roll insulation from B&Q (duvet fillings typically range from 350g to 1000g per square metre, but are usually only a couple of centimetres thick when uncompressed). This comparison might suggest recycled polyester insulation as a permanently installed alternative to borrowing your Mum's duvet (again). Unfortunately, fixing a material like thermal roll insulation directly to a wall would remove the air gap and negate the limp mass absorption effect, design features which are highly desirable with regard to lowering the absorption frequency cut‑off point.

It therefore seems reasonable to conclude that roll insulation has very limited applications for our purposes, given that double‑sized duvets with a recycled polyester fill, made from waste drinks bottles, are available from UK stores including Marks & Spencer and John Lewis for around £15 each.

While you're in John Lewis, you could consider instead a double duvet stuffed with the down of the third winter coat of the snow goose, from the remote glacial Altai mountains of Russia — a bargain at a mere £780! At that price, I'd expect the duvet to be supplied with a full acoustic performance report from an independent testing lab, but alas, no frequency absorption curve is provided. However, if you do have some roll insulation or an old duvet spare, it can be compressed and stuffed behind the fibre‑slab type of corner bass trap to increase the overall density, relative to leaving a void behind the slab.

In 2009, Auralex launched their EcoTech Acoustic Panel in the US market. This has similar acoustic properties to a mineral‑fibre panel, but is made from a proprietary formulation containing 65 percent recycled polyester. While Auralex are not phasing out glass-fibre products yet, the company have indicated that they hope their customers will specify recycled polyester instead of glass fibre in future. A box of 24 unfinished EcoTech panels, each 60cm square and 2.5mm thick, costs US $599 from www.truesoundcontrol.com. At the time of writing, the EcoTech panels do not appear to be available from UK suppliers.The EcoTech panel from Auralex is made from recycled polyester.

Alternative Fibre Slabs

In the thermal insulation and soundproofing markets, a number of 'green' fibre slab products have been devised which do not contain glass or mineral fibre. Potentially, these products could be used for acoustic treatment, but not all of the manufacturers supply data for the audio-frequency absorption curve. Claims that a product has 'excellent' sound-absorption qualities, or the quotation of a single noise‑reduction coefficient (NRC) averaged across frequency bands, are insufficient for our purposes. Once the slabs are installed in the studio, if they don't perform as expected, return for a refund could prove difficult — particularly if the products have been sold without any detailed claims for their acoustic properties.

Steico Canaflex insulation slabs, made from harvested hemp in Poland, can be put on the compost heap at the end of their life — although the manufacturers say that with proper installation, they should last forever. The density is quoted at 40kg per cubic metre, and the 120 x 57.5cm boards are available in thicknesses up to 240mm. Earlier this year, Second Nature launched a rigid slab insulation product in the UK, under the name EdenBloc35. It is made in Cumbria from 60 percent recycled materials — mostly wool offcuts from the carpet industry. EdenBloc35 is supplied as a 120 x 60cm board in standard thicknesses of up to 100mm, or custom thickness of up to 350mm, with a nominal density of 45kg per cubic metre. It's a pity that frequency absorption data is not made available for either Steico Canaflex or EdenBloc35, as these interesting products are being advertised as acoustic absorbers.

EdenBloc35 could be a good acoustic absorber, but without NRC figures, who can tell?New Zealand not being short of sheep, there is a wool‑based insulation product available there too, under the brand name Latitude. Latitude is claimed to differ from other wool‑based insulation in that it does not include polyester in the mix, although it does use an acrylic binder. The manufacturers, Fibre Bonding Ltd, claim that R2.2 Latitude insulation has similar performance to 75mm‑thick fibreglass for absorption in the typical human‑voice frequency range of 500Hz to 8kHz, when used in a double‑wall or ceiling‑cavity system. Unfortunately, the raw data from the acoustic test is not published on the www.latitudeinsulation.com web site.

By contrast, an independent test report from the University of Salford on the acoustic performance of 100mm thick Thermafleece slabs, with 25kg per cubic metre density, can be found on the www.soundservice.co.uk web site. The bass absorption curve of this wool‑based material is diagonal rather than a steep cliff, beginning with an NRC of 0.99 at 400Hz and delivering a still useful 0.87 at 250Hz. A 14‑slab pack of 60 x 120cm Thermafleece costs £112.52 plus delivery from Sound Service. The company also sell a variety of sound-barrier mats for walls and floating floors, made from recycled car tyres and sold under the Acousticel brand.

Chinese manufacturers Jiangsu KPS have developed a wool and jute mix acoustic panel, available in thicknesses up to 100mm and densities up to 50kg per cubic metre. This product is sold in a larger than average panel size of 240 x 120cm. The company's web site quotes an NRC of 1.05 at 200Hz, for a 36kg per cubic metre density panel of 50mm thickness with a 15cm air gap behind. There is no information about whether these figures were achieved via an independent testing lab. Jiangsu KPS have a minimum order of 100 square metres, and while the company do say that they export to Europe and the US, it's not too clear from their web site if there are any distributors or retailers offering the product in the West.

Cottoning On

In the US, there are rather more cotton plants than there are sheep, and so green insulation manufacturers there have turned to using cotton fibres. Bonded Logic produce UltraTouch insulation from 90 percent post‑industrial recycled denim and other cotton offcuts, which is treated with boron to give it a Class‑A fire rating. Available in various widths and thicknesses, NRC figures are quoted for the R‑19 140mm thickness of 0.97 at 125Hz. A bag of five pieces, each 413mm wide by 2.34m long, costs US $49.99 from www.smartlivingdirect.com, including delivery in California, Arizona or Northern Nevada. Delivery in other areas of the US is available by quotation. UltraTouch does not seem to be available from UK retailers.

Auralex offer the SonoFiber panel, which is 60cm square and 2.5cm thick, made from recycled cotton waste and also featuring a Class‑A fire rating. The absorption figures on the Auralex data sheet for SonoFiber compare well with those for the company's Studiofoam Wedges of the same overall thickness, but they are not bass traps. Auralex says that the SonoFiber panel is tougher than melamine foam, making it more suitable for live rooms, sound stages and nightclubs. The panels can be stacked to improve low-frequency absorption, and do not produce dust or cause skin irritation. A box of 24 SonoFiber panels costs £317 from Dolphin Music in the UK, or $359 from Musician's Friend and B&H in the USA.

Auralex S‑Core is a similar product to SonoFiber, except with a scrim fabric on the front and back of the panel. It has now been discontinued by Auralex, but some suppliers still have stocks — in the US, truesoundcontrol.com currently sell a box of 20 60cm square S‑Core panels for $299.

Auralex SonoFiber panels are made from recycled cotton waste.Another cotton‑based acoustic material is Eco‑c‑Tex, used by manufacturers Audimute in a range of panel products. Eco‑c‑Tex is described as a mix of recycled cotton and cellulose fibres from post‑consumer recycled newspaper, with a class‑A fire rating. The company claim that the material is the greenest alternative to glass fibre available, because it requires a tenth of the energy to produce.

Audimute Panels for wall mounting are 50mm thick and have an NRC of 1.18 at 500Hz, but roll off below that frequency to 0.63 at 250Hz. A 60 x 120cm panel costs $70 from www.audimutesoundproofing.com, with other sizes and various colours available. The Audimute Corner Bass Trap is a 100mm‑thick version of the same panel, which has been independently tested to achieve an NRC of 0.94 at 125Hz. It costs $60 for each 60 x 60cm panel. Shipping outside the US costs extra, of course.

Hanging Fabric Treatments

For absorption further up the frequency spectrum, there are now several purpose‑made alternatives to the traditional duvet. Audimute make two ranges of acoustic blankets; one, the Sound Absorption Sheet, is made from cotton, while the Deluxe Acoustical Wall Covering is filled with Eco‑c‑Tex. Prices start at $40 including US delivery for the basic 114 x 198cm white sheet, which has an independently assessed NRC of 0.97 at 1kHz, rolling off to 0.64 at 500Hz. The deluxe version does a little better, with an NRC of 0.75 at 500Hz when attached directly to a wall. Subjectively, it looks like it might work better still with an air gap. It costs $48 for a 120cm‑square deluxe covering, again including US shipping only.

An entirely different pair of products that make use of the air‑gap principle are the AcouStac and AcouRoll, which at first glance look like large roller blinds. Made by US company AcouStaCorp, these two products use long double drops of wool serge fabric to tame mid‑ and high‑frequency reflections. The AcouStac fabric is divided into segments, whereas the AcouRoll looks more like a long continuous loop of fabric. Both versions can be motorised and remote controlled to adjust the precise amount of absorption required in the room.

The supplied NRC figures for AcouStac banners vary, depending on how far from the wall they are mounted, whether they are installed single or double, and the exact fabric used; they can also be hung from a high ceiling. For one banner hung 15cm from the wall, the NRC for a 6V11 wool banner is 1.0 at 630Hz, dropping to 0.6 at 200Hz. Prices are by quotation, but judging by some of the venues where these banners have been installed, they aren't likely to be cheap. Nevertheless, the idea of retractable acoustic treatment might inspire a more affordable DIY creation for a live room or venue.

AcouStac banners can be remotely controlled to adjust the sound of a live room.Next time you are planning a studio construction project, you'll have far more options for acoustic treatment material than ever before. If you try out any of these green materials in your own studio, we hope you'll write to SOS and tell us how you've got on.