TexLnt® and Dynamic Noise Monitoring at the North Sea Jazz festival
As audio challenges go, staging the longstanding (since 1976) three-day North Sea Jazz festival, with 14 stages and hundreds of top artists over a July weekend, in the sprawling environs of the Ahoy exhibition center in Rotterdam, must rank among the toughest.
When the decision was made in 2006 to move the prestigious event from its traditional multi-theatre home in The Hague, the organizers knew that serious work would have to be done to turn the modern, bare glass, steel and concrete halls of the Ahoy into spaces that would satisfy 70,000 of the most discerning music fans in the world. Not to mention the neighbors, for the Ahoy sits amid a busy residential district.
Event Acoustics’ audio consultants were immediately hired for their expert knowledge on audio design. Advising on how to improve the acoustic situation and how to provide the best sound insulation between various stages for one of the most reputable festivals in the Benelux.
The Ahoy complex includes a 15,000-capacity arena, the city’s regular international concert venue. Including six multifunctional exhibition halls, a congress center and the Ahoy Plaza food court, Ahoy offers capacity for 30,000 people. Although its logistics and access are ideal for the festival, a major challenge were the acoustics of the exhibition halls that house many of the festival’s stages, some with reverberation times of more than 12 seconds.
In 2008, Event Acoustics installed their production version of a modular low frequency baffle system, TexLnt®. Having to address two key issues: room acoustics, and environmental noise emissions, the team worked alongside colleagues from sister, Public Address (PA), company Ampco. Ampco deployed own and others' equipment within the Synco Europe Network, to service all the stages.
Dynamic noise monitoring
Working closely with the local authority, Event Acoustics’ audio consultants, Peter van der Geer and Kees Neervoort, installed multiple full-frequency sound level measuring points in and around the Ahoy complex.
With wireless monitoring providing instant comparison of specific locations, and separate bass monitoring allowing differentiation between music spillage, traffic and other non-festival noise sources,
as well as between individual stages, Van der Geer says it was a far more accurate system than measuring overall dB(A) – and led to less stress for sound engineers.
The key problem areas were identified as spillage from doors and connecting walkways, the alignment of stages and their PA’s, some of which were re-aligned to minimize spillage, and external stages.
“It meant that rather than asking a sound engineer to reduce the overall sound level, we can just ask them to reduce, for example, a bass frequency by a certain amount. By measuring noise at so many places wirelessly, we can assess a problem and respond quickly and minimize stress for everybody.
“We call it ‘dynamic monitoring and allocating’ – we divide the ‘acoustical space’ over the stages of the festival and allocate headroom throughout the day to the stages where it’s most needed.
“It’s a great tool for the sound engineers. They call us if they need more headroom, and at the end of each evening people were thanking each other for the co-operation.”
The team also expanded its acoustic analysis and measurement toolkit, which included writing dedicated virtual array software for low frequency dispersion predictions used by Ampco. As well as the stalwart EASE room analysis program, the newest offering by EASE’s creators, Ahnert Feistel Media Group, was brought in – EASERA SysTune.
The latter measures both time-domain and frequency-domain information simultaneously using live program material. Crucially, it allows reverberation times and speech intelligibility to be measured while an audience is present.
Woolly acoustics
The main issue inside the halls were the reverberation times. High and mid frequency reverb could be relatively easily dealt with by careful use of drapes, but the troublesome low frequencies were another issue entirely. Among last year’s experiments by Event Acoustics was the use of specially created TexLnt® low frequency acoustic baffles. Made of sheep’s wool and specially configured for acoustic use, they proved invaluable at taming the low-frequency roll-around.
Van der Geer commented: “The sheep wool baffles have a number of important handling and storage advantages over conventional acoustical materials. If well designed, the baffles have excellent acoustical properties in the sub- and low-frequency ranges where ordinary curtains are ineffective. As modern music is highly rhythmically orientated, the lower frequencies are of crucial importance.”
Early 2008, the team had refined the TexLnt® low frequency baffle system for a commercial launch at Frankfurt Pro Light & Sound trade show where it featured in a distinctive blue acoustic booth, walled with the new material.
The R&D effort had also focused on TexLnt®’s practical aspects. Besides absorbing low frequencies it had to meet all standard safety and handling requirements. In a portable, modular, rentable format (the material can also be produced upon special order for permanent installation) the multi-layer woolen absorber is covered in Soundwool cloth (a class 1, ISO certified flame retardant) and each section is fitted with mounting rings or, for backdrops, a combination of zippers and Velcro strips.
The promoter was provided with modular TexLnt® baffle sections that were fitted by the Event Acoustics crew in key areas throughout the Ahoy. These included the rear of the main arena’s bleachers, several connecting walkways and venue walls that were closest to residential areas – supplementing the standard black drapes.
Protecting crews’ hearing was also a key consideration. Ampco uses the full range of Synco by Martin Audio line array systems, and Martin’s Longbow. Although acoustic energy is well focused there’s inevitably a backwash from the PA hangs into working areas alongside and behind the stage.
Event Acoustics recommended strips of TexLnt® baffles, hung directly behind each line array, to absorb this rearward energy, cutting work area sound levels to around 80dB and improving on-stage clarity. Specially configured cardioid sub-bass arrays further improved directional control of the PA.
With a line-up including Cleo Laine, John Dankworth, Herbie Hancock, Al Jarreau, Sergio Mendez, Angie Stone, Bootsy Collins, Alain Clark, Lee Ritenour and Jill Scott, it was a complex electro-acoustical solution that reaped major dividends for an iconic event.