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Reflections on acoustics and soundproofing

The acoustic qualities of any space - a recording studio, meeting room or home cinema - can be improved considerably through the use of special treatments in the construction process. Kevin Hilton talks to leading experts about how this is done and the differences between sound absorption and soundproofing

The Covid pandemic and the enforced isolation it brought through lockdown periods made people consider many aspects of life they might have previously not contemplated. The most obvious of these were just being able to see family and friends whenever one wanted and the importance of hand washing. Compared to those kinds of personal priorities, acoustics and the need for some form of sound treatments were most likely not on many people’s lists. But the reliance on video conferencing for work and business, as well personal calls, made these hitherto specialist areas important in improving audio quality and making for successful and less fatiguing online meetings.

While using a decent standalone microphone and being close to it was a relatively straightforward first step to a better sound, many people also experimented with putting mattresses or coats against doors to minimise any noise coming from elsewhere in the house. Closing the curtains also helped in both excluding the sounds of the outside world and reducing reflections from the windows. These basic, practical measures no doubt improved the general experience of many conference calls and may have made people think about sound quality a little more, but they also highlight a fundamental misapprehension about the nature of acoustics.

In this particular case, it is mixing up sound insulation, what people might generally think of as soundproofing, and sound absorption. While the mattress against the door will deaden any sounds from outside, it will not exclude them completely. It will, in fact, be more effective in diffusing sound in the room and preventing flutter echo, the ‘tinny’ noise caused by sounds bouncing off parallel surfaces. Chris Parker-Jones, founder and director of ParkerJones Acoustics, comments that real sound insulation can only be achieved when it is built into a space.

“I see this issue a lot with residential soundproofing,” he says. “I get people phoning me about noisy neighbours on floors above, saying they’re surprised there is still a problem because they already had a soundproofing company around to inject insulation into the floor void. The problem is that many of these companies are builders who just read what’s on the label. There are so many products that are [sold as] ‘high acoustic performance’ and ‘soundproof’. There are even things like ‘soundproof’ paint but it doesn’t really exist. Products are only ‘soundproof’ when the constructions they are used with lend themselves to being soundproof.”

A classic example of this is the box-in-box build. This is based around a floating floor and acoustically isolated walls and ceiling, which effectively disconnects the room from the rest of the building. It is most commonly associated with recording studios, which call for a high degree of isolation to prevent the transmission of sound from outside the studio space. While this remains the target for any facility of this kind, budget is always a deciding factor.

White Mark is an acoustic consultancy known for its work in both the music and post-production sectors, but is also heavily involved with what managing director David Bell calls the “educational” market. Radio and television studios and even specialist eSports venues, as well as music recording facilities, are now a key part of schools, colleges and universities. Bell cites the Confetti Institute of Creative Technologies, part of Nottingham Trent University, as an example of a studio building with a high degree of sound isolation. 

“Part of this comes from the layout created, allowing spatial separation of the rooms and the concrete block construction that was possible,” he says, adding that acoustic treatments such as specialist suspended ceilings can also offer economic solutions for the absorption of sound, particularly in dealing with low end frequencies.

While the aim is to create something that is close to, if not on the same level, as a professional studio, Bell observes that the principal thing limiting the quality of acoustic spaces in education is procurement. “Price has frequently become the only issue considered and there is a steadily decreasing consideration of what the performance will be,” he says. 

“Too often the procurement department will consider that professional standards of performance are too expensive. This is not the case and the use of non-application specific acoustic designers, in concert with the limited standards set out in BB93, often leads to the design/build approach elevating budgets to the detriment of the final facilities’ quality.”

The amount of reverberation in a space is a key factor in the acoustic design of a studio, but it should also be high on the list of priorities when it comes to AV installations such as meeting rooms, classrooms and public places – including bars, airports and shopping centres. A low reverb time plays a part in reducing the amount of reflected sound, which can adversely affect the intelligibility of speech.

If this is not addressed as part of the initial construction, it is possible to deal with reverberation problems retrospectively by installing sound treatments. These are able to absorb or deflect unwanted audio elements to produce clearer, more intelligible sound. Among the specialist companies producing treatment systems for education and office environments are Ecophon and Standapart: the former offers a range of free-hanging units and baffles, modular ceilings, acoustic plaster and wall panels/screens; while the latter also produces acoustic screening, wall-mounted blocks, free-standing units and stand-alone ‘pods’ that can be installed in a larger room to create an isolated space.

Pro audio and musical instrument retailer Thomann has produced an online guide to acoustics that is primarily for what it calls home recording enthusiasts, but which is a useful starting place for the uninitiated. Reflections are identified as a major contributor to poor audio quality, causing comb filter effect distortions, room modes, flutter echoes and other problems. To combat these, the use of absorbers such as compressed glass fibre matting and Basotect foam, as well as plate resonators and diffusers, is recommended.

In these days of grand design architecture and interiors, acoustics can often be as a secondary consideration. Many architects and interior designers would no doubt baulk at the idea of putting acoustic baffles or panelling into a swanky hotel lobby, high-end store or exclusive restaurant, but David Yates, founder and chief executive of technology design practice Recursive Digital, comments that simpler, less obtrusive methods of absorbing wayward frequencies and sounds can be employed to achieve a good quality outcome.

“If somewhere has been built from scratch you can specify something traditional, like acoustic ceiling panels,” he explains. “If you’re lucky, the interior design works with that and there might be other interiors to absorb sound, which helps beyond the standard acoustic tool kit. You could have absorbing panels in the walls but you can also put them under tables or change the furniture, for example from wooden seating to something with cushions. If you’re trying to fix the reverberance in a space, sometimes you need to be a lot more creative.”

While a completely dead acoustic is a very strange environment, there is a need to control the behaviour of sound in any space where audio intelligibility and, or, quality is desirable. “On the whole, reflections are bad news,” acknowledges Neil Grant, managing director of acoustic consultants Harris Grant. “But absorption is difficult. No one panel is absorbent across the whole range of frequencies and if you make the room dead, you’re doing nothing about mid and low reproduction.”

As Grant outlines, there are several devices and techniques available to deal with reflections and help create the right acoustic for the job. Key among these is the diffuser, a panel with a non-uniform (in other words, not flat) surface, which prevents direct reflections. A variation on this is the diffractal, usually used to control the low end and often in the form of a layered wooden diffuser. 

When it comes to sound isolation/proofing, Grant says just having a concrete box structure is not enough. “You can’t decouple from that, so you need a set-up of mass [outer wall, floor or ceiling]-air in between-mass [inner wall, floor or ceiling],” he explains.

Attessa III Interior

Harris Grant made its name designing recording studios. One of its notable achievements is Peter Gabriel’s Real World, which broke convention by having no physical divide between the control room and the performance area. Grant observes that while the recording market has changed dramatically over the last 30 years – with many big name studios either going out of business or turned into much more lucrative real estate, such as apartments – the need for good acoustics and sound in other areas, has become more recognised.

“In schools and colleges there is a need to link together multiple spaces, like classrooms and music facilities,” he says. “In large rooms like that, the main issue is high background noise levels. My job is to integrate things like that. Home cinema has its own rules because you’re creating a false environment, with surround/immersive audio formats from 3.1 or 5.1 to Dolby Atmos.”

There is a wide range and variety of acoustic treatments and constructions available at the current time, so selecting the right one for a specific project is crucial. All of the experts agree that not only should time and money be allocated to include an acoustician in the design and building processes, but also state that the clients and architects/designers need to be made aware of the niceties of acoustic design. In this way, a good sounding as well as good looking result is more likely.