Paul Mac looks at how expertise from a variety of disciplines and cutting-edge audio technologies come together to make great sounding performance venues.
There is a massive range of purpose-built performance space types that each have very specific requirements for audio excellence. The mixture starts with acoustic spaces without amplification, moving on to small theatrical and spoken word venues, lecture theatres, and so on. In new build churches the ambience in the audience area has to be balanced with intelligibility and suitability for everything from sermons, to choral works, and rock bands. And then there's the grand gestures of large concert halls and civic spaces where architectural impact can seem to claim the lion's share of stakeholders' value assessment.
Thankfully, the variety of venues is matched with a fantastic choice of expertise and enabling technologies. The quality and coverage options of sound reinforcement have undergone exponential improvement over recent years. Those technologies are no longer judged on shortcomings or on basic sound quality criteria, but on positive contributions to most challenges. The most explicit example of that is a steady move towards immersive reproduction in all its current forms - a new type of sound system that might even have the potential to change the design of performance spaces to suit itself.
In all cases though, new sound reinforcement technologies must exist in an acoustic space, so that space has to be designed, built, and equipped by a multidisciplinary team that includes architecture, acoustics, system design, and integration specialists. By looking into those aspects, we can better understand the parameters of performance space design, and how they might progress into the future.
The acoustics
One of the most basic measurable and predictable parameters used when it comes to venue acoustics, and certainly one of the first mentioned whenever the subject comes up, is Reverb Time (RT) - the time taken for a sound to die away by a specified ratio. RT60, for example, is the time taken for the sound level in a space to reduce by 60dB. As a single number, it's quite a blunt instrument and really needs several values across a frequency range to refine it. Even so, it is commonly used to characterise a space, and leads to the perennial question of the ideal reverb time. The answer, unsurprisingly, it depends...
"We think about these spaces primarily from the perspective of the audience, but the artist experience is just as important."
Steve Jones, application support and education at d&b audiotechnik, sums up a few of the many options: "In Europe, a good symphony hall might have a mid-band RT of around two seconds. Then as you get below 200Hz that could go up to 2.5 or 3 seconds, or more in the very low end. But that's the opposite of what you want for amplified music. For most people the defining bit of pop music is a kick drum. If we want to excite an audience and get them tapping their feet, you need to hit them with a sub performance that's tight and defined.”
Patrick Smith [pictured right], principal engineer at the Sandy Brown acoustic
consultancy, concurs, and puts a good RT60 for amplified music down to around 2 seconds, or between 0.7 and 0.9 seconds for the spoken word. He also makes the point that other aspects of building use may need to be considered. In some performance spaces, like churches and theatres, you might want to bring the reverb time up, specifically for the audience: "Those are participatory spaces, and in that case a longer reverb time will encourage the audience to participate more,” he explains.
Israeli consultant Harel Tabibi says: “To start with, [integrators] need good acoustics - to make sure that in the planning and design process the acoustic consultant designs the acoustics to suits to sound system. Usually a dry 0.7-0.9 seconds reverb time is best for amplified systems."
Intuitively, you might assume that shorter reverb times mean higher intelligibility, and that can be generally true in small and medium-sized spaces without other serious acoustic issues. However, there are a number of other factors in play. The classic differentiation of direct sound (coming straight from the speakers) from reverberant sound is important too, particularly when thinking about bigger spaces combined with the longer throws of line sources. "You might have a long reverb time in a large space," notes Smith, "But the difference between the level of the reverberant energy and the direct energy from a loudspeaker might be such that the direct sound stands alone and so intelligibility actually goes up. This is where measurements such as clarity (C80, C50, and so on) become much more important."
Clarity is a measure of the ratio between the diffuse and direct energies somewhere in a room, at a specified time after an audio impulse. C80 is measured after 80mS, and C50 after 50mS. Smith: "C80 is a really nice measure for the musicality of a space, while C50 correlates very well with the Speech Transmission Index (STI) for intelligibility."
Whereas reverb time is simply a measure of a room and the combination of several acoustic properties, Clarity measurements involve a source in a room. Though both are diffuse measurements that address the reverberant or diffuse energy in a room. The other part of the picture are non-diffuse effects such as slap-back echoes, flutter echoes, standing waves, and so on.
"Every room has a character - we don’t have materials that can perfectly absorb sound, so every space must have a character to it."
One of the big challenges common to many spaces is the back wall. In fact, any reflective parallel surfaces can cause big issues. "With an orchestra, by the time the energy has got to the other end of a space that energy will have decayed quite a bit, explains Smith. "Reflection off a back wall won't be too much of a concern. However, with a sound system involved, and especially with the extended throw of a line array, you're potentially focussing quite a lot on the back wall.
"You might hit a snare drum on stage and half a second later you hear it come back at you - an experience made much worse because it's unlikely to be in tempo. A sound engineer would call that 'slap back' and it can be quite a destructive force. We think about these spaces primarily from the perspective of the audience, but the artist experience is just as important.
"We would try to build a venue that is more diffuse, where sound energy can scatter and reflect as evenly as possible, primarily achieved through the geometry of the space."
Choose your sound
The choice of sound reinforcement system for a bespoke performance space is a complex one. Even though we can assume a well-specified acoustic, there are still technical decisions to be made - mostly because no room is the same. Jones: "Every room has a character - we don’t have materials that can perfectly absorb sound, so every space must have a character to it. With that in mind, we need a PA to have a controlled, beneficial relationship with the room."
Choice is helped by a fantastic array of products and some advances in technology that can have real benefits. "We're able to make smaller and smaller sound systems that go just as loud and have just as much directivity," says Jones. "Which is a massive bonus.
"Also, historically, sound systems could only manage to control sounds down to a certain frequency, but with our new d&b audiotechnik SL systems, which can control the entire bandwidth, we are actually able to plan and pretty well control where the sound should and should not be.
"We find that venues are happy to extend their budgets a little bit more for [a 'Tier 1' or rider-friendly installation]."
“The ratio of direct sound to reverberant sound for listeners in the room generally changes as you move away from the loudspeaker. After the first 20% of listeners the rest of the audience may well be hearing more reverberant sound than direct sound. This reverberant sound is highly influenced by the off-axis response of a loudspeaker interacting with the acoustical properties of the room. So, a loudspeaker’s performance in every direction (on axis and off-axis) at every frequency really matters. We always say: want to excite the audience, not the room.”
In more commercial terms, the proposed usage of a space has a large bearing on the system choices. An intimate performance space with great acoustics might just need a small point source system, whereas a larger, flexible space that hopes to grab international acts on the touring circuit needs something more substantial. And everything in between.
Tabibi says: “[The integrator needs to] coordinate with the architect so systems are placed and installed where they need to be, for the best result. They need to be away from reflective walls, and not too high.
“This kind of thing is commercially very important for a venue. A big artist will never want to compromise on the position of the arrays so the space for those arrays must be planned in at the architectural stage.”
Gerry Gavros is brand manager for L-Acoustics with Australian distributor Jands, which has recently put the finishing touches to the new Sydney Coliseum Theatre [pictured below]. "For many venues it's important that they have a system that is versatile and acceptable to touring acts – a ‘Tier 1’ or rider-friendly installation.
"We find that venues are happy to extend their budgets a little bit more for that advantage... We've had a few venues put in budget systems, only to find out that there are occasions where the touring act opts to bring in their own system, so the venue loses revenue on equipment hire. Furthermore, it comes down to important considerations like manual handling regulations, and the health and safety issues that come with pulling down house systems and putting in rented ones. Because of public liability issues, they generally want systems up there that are going to stay up there. As a consequence, there are an increasing number of venues implementing 'Tier 1' brands or rider-friendly systems. The venue then doesn't have to spend more money on renting other system in, and they can advertise themselves as a premium venue for international artists. The return on their initial investment is therefore a more lucrative one."
Another premium option for venues now is immersive and object-based systems such as L-Acoustics' L-ISA and d&b audiotechnik's Soundscape. Aside from the new creative mix options, venues can also choose to apply different environments in a room. One question is whether this trend will grow to the point where acoustic and architectural design will adopt new practices for the immersive audio environment, which could drive basic reverb times down even further, in favour of applying the room in the mix.
Many engineers are finding new creative impetus with these kinds of system, even if they don't go for fully immersive systems. "Sound has long been considered mainly an engineering tool," notes Jones. "It has been left to the engineers, who are often behind video and lighting in the pecking order. Immersive systems are already introducing artists to the idea that there are creative ideas to be explored at front of house."
The story of audio in any new venue starts even before an architect gets an email. It starts with a reason for the space to exist, a performance type, a performer type, an audience demographic, and commercial and/or artistic ambition.
From that point on, it's a complex process of fitting aesthetic, visual, and aural interests together without breaking them. The extent to which that initial intent remains connected to the process, or how the audience experience is prioritised or planned for, and ultimately implemented, is directly connected to the success of that endeavour. Tricky.