One of the most critical aspects of studio design and construction is undoubtedly controlling sound transmission. Granted, this is just a fancy way of saying “sound proofing’ but nonetheless, it is no less important and when it’s done properly – along with proper acoustic design and treatment – it’s what separates the mediocre studios from the great.
It can be extremely expensive to sound proof a studio and many studios built from the ground up by people who know better often spend a sizeable portion of their budget on sound proofing and acoustic treatment. But why is sound proofing important?

Well, the most obvious reason is to prevent sound from leaking into the outside world and to adjacent rooms. This keeps the neighbours happy but the next and most important application is to prevent outside noise from leaking into the workspace. The way this is traditionally achieved is to build a room within a room with a floating floor and employing absorptive materials into the construction. All constructions should be buffered from the supporting structure by an air cavity (or by some other absorptive filler such as sand or insulation) and as few physical contacts as possible. Additionally, each and every possible point of leakage must be sealed by an acoustic sealant. I can already hear cash registers clanging.
Of course, this is all a challenge. Besides the cost, it requires hiring someone – hopefully a professional – who knows what they’re doing, unless you’re a serious DIY-er who loves getting his hands dirty. This is often what happens when cost is a constraint. In this case, there might be a product that provides a solution and it’s already causing a stir in the sound proofing community.

The product I am talking about is Green Glue, by the Green Glue Company, a subsidiary of Saint-Gobain, now available in South Africa through local importers Kenoran Products, based in Edenvale and Genesis Acoustics in Port Elizabeth.
So what is Green Glue? Well, it’s a compound that looks somewhat like silicon that you would apply with a standard silicon gun around your household except, of course, that it’s green. But before we get into how Green Glue actually works, let’s take a quick crash course on the physics of sound transmission so we can get a better idea of the technology behind it.

Sound travels through a medium (normally air) in waves, which can be termed an airborne vibration. Upon impacting a wall or other boundary, some frequencies will be absorbed, some will be reflected, and some will pass through and be heard on the other side of the boundary. The amount of sound absorbed is termed “transmission loss’ and certain materials are better than others at absorbing certain frequency ranges. Sound Transmission Loss (STL) across specific frequencies can then be defined by the standard unit of acoustic pressure measurement, the decibel, as dB STL. For instance, if a pressure wave is measured as 100dB on one side of a room boundary and 55dB is measured on the other side, we would say that the boundary has a STL of 45dB STL.

Green Glue is a polymeric viscous compound, invented in 2003 and brought to the market in 2004, which effectively converts the mechanical energy of sound into heat. The idea is to sandwich the glue between two layers of dry wall to form a virtually invisible damping system, thus creating a barrier between layers where the sound can be trapped and dissipated into heat. How this compound specifically does this is, understandably, a trade secret.

In addition there is an entire system supplied by Saint-Gobain to aid the installer in taking full advantage of Green Glue technology. This system includes not only the Green Glue compound, but also a clip system for hanging and decoupling the drywall, and a special sealant called Silenseal to seal up the nooks and crannies. Provided you follow their instructions to the letter and use all the components in the system, the Green Glue Company claims that you can eliminate up to a staggering 90% of sound transmission across all frequencies. Needless to say, these are quite tall claims, so does it really work?

Well, one company that is currently using Green Glue as part of their acoustic installation service is Genesis Acoustics, based in Port Elizabeth. I had an opportunity to go to one of their Johannesburg installations where Green Glue was used to make an assessment of the technology. Granted, I would have loved to go to a studio installation but because it’s a relatively new product, there aren’t any studios in this part of the world that have employed it in their construction yet. What we need to remember as well is that studios aren’t the only venues in need of sound proofing and noise control. Restaurants, offices, factories and many other noise-rich environments require this sort of sound transmission control for the purpose of keeping the neighbours happy.

Recently I met Gerald Di Pasquale, owner of Le Bistro restaurant and live music venue in Sandton, to take a look and listen to his installation where Green Glue was utilised. Le Bistro is a quaint French eatery on Rivonia Road that has an adjoining dance club which doubles as a live music venue. The goal there was to create a sound barrier between the outside of the club and the dining areas so that the dance club could rage on while the non-dancing guests could enjoy their dinner without the need to shout at one another. Also, Gerald wanted to control sound leakage as there are other restaurants in close proximity.

Stepping inside the club area, he explained to me that there were three main areas that Green Glue was applied, namely on the kitchen doors, on the main entrance doors and at various points in the building where there were once windows, such as at the east end of the room. In a listening test, Gerald turned on his club system to supply 100dB (measured by my trusty SPL meter) of sound pressure so we could close all the treated doors and take a listen outside. As we did so, Gerald explained further.
“I wasn’t expecting to get figures of 90% transmission loss because we didn’t treat the whole room and we didn’t use the clip system. I just wanted to seal up all the points of leakage and reduce the SPL by about 20 to 30dB. Of course, the low end was the most challenging. It’s the most difficult range to eliminate because of how long the waves are.’

Of course he is completely correct. Low end sound waves – or “bass’ as it is usually called – are omnidirectional, high energy and have the longest wavelengths. This means that they can traverse through almost any non-treated structure and is why we hear a muffled, “bassy’ sound from the outside when noise or music is coming from indoors. We don’t hear the high frequencies because they get absorbed more easily.
Di Pasquale followed the recommendations of the Green Glue company and used two layers of dry wall with a layer of Green Glue between the layers. Indeed, when we listened from the outside, it was clear he got his desired 25dB or so of transmission loss but there was still the obvious leakage of low end. This is somewhat expected, however, and considering there was 100dB pumping inside the room, 75dB SPL is liveable.

But what about a major studio installation where Green Glue was used in its entirety? Well, I was able to interview a studio owner in the United States, Max Dearing of Graham, North Carolina, and he was kind enough to answer some of my questions regarding Green Glue. It had come to my attention through an audio forum that he had used it extensively in the construction of his studio, Dark Pines Studios. He explains. “I’m not going to say that using Green Glue gives you a 90% reduction, as I can’t prove it by my own non-certified testing, but it damn sure kills a LOT of the low frequency transmission through a wall.’
Granted this was a pretty serious construction job and many other materials were used in conjunction with Green Glue.

Dearing continues: “Granted there is indeed a LOT of mass in my studio construction, and the isolation is optimised by each room being on its own independent concrete slabs, so I should get a good bit of isolation and sound attenuation. I can have a full band in the tracking room (drums, bass amp and two guitars) playing full on, and the majority of what little bleed I get into the control room, is through the window. I get very little sound bleeding through the rest of the building into the control room.’
He adds.

“I have walked outside at relatively late hours, when the majority of the world is asleep, and at no more than six feet from the building’s exterior, I cannot hear that typical band playing at anything other than what would be a car radio passing down the road, and at 12 feet from the building, there is not enough sound level to determine it is music. Crickets and frogs in the woods are louder.’
But here’s the qualifying remark: “So, for me, yeah, Green Glue’s a good part of why I have as good isolation and LF attenuation as I do and it saved me from having to put up two to three more layers of 5/8′ gypsum!’

So there you have it. Green Glue was integral in saving space and cost at Dark Pines Studios and Dearing is convinced that without it, he would not have the low frequency transmission loss that he does. I could definitely see how Green Glue can make a serious mark in the acoustics industry and aid customers in saving on costs and space in the construction of their studios, or where ever effective transmission loss is required.