20.11.06

Sound system on ice

AUTHOR: Inavate

A new multipurpose sports venue in Lublin, Poland has been outfitted with a center cluster solution to overcome acoustic difficulties.

In a project that began way back in 2004, Warsaw-based Tommex was asked by the architects from the project company Arconel for cooperation with a range of room acoustic solutions and audio system designs for 'Globus', a multipurpose hall with an ice rink and an audience capacity of 5,000 people.

The planned facility would have the ability to host hockey, volleyball and basketball - and music events. By the time Tommex joined the project team the main building was almost complete. Tommex started by preparing a mathematical model of the hall using EASE 3.0 software and the virtual acoustic reality of the hall was far from good. In every instance, measurements were made using Gold Line DSP 30 B to check the RT60 parameters and the poor measurements confirmed those gained from EASE. The RT60 at some frequencies was almost 11 seconds. This presented Tommex with an enormous challenge to meet the customer expectations of a venue for music events and speech with good intelligibility.

The finance for Globus was already closed but a series of meetings between the client, the architects and Tommex persuaded the client to increase the budget for acoustic treatment. As a result, additional damping material on the ceiling and an acoustic screen above the main loudspeaker cluster were installed to the specification drawn up by Tommex. This resulted in an impressive decrease in average RT60 to below 3 seconds and RaSTI better than 0,5. Tommex admit the room remains less than ideal for music events but it is possible to attain quite good speech intelligibility; a remarkable achievement given the original acoustics and limited budget.

With the reverberation time remaining high and still with poor acoustics, the choice of the loudspeaker system was critical for Tommex. They considered the solution of a multi-point projection system, based on Community R.5 or WET series loudspeakers but there remained two factors that could not be overcome: Firstly the budget for system - more loudspeakers meant more amps and racks to drive them and also more batteries as the system also had to provide voice alarm as a core function. Secondly the budget for installation - more loudspeakers distributed in the hall would mean more cables and more installation work in the almost complete facility. Cables were a significant major cost as they had to meet the certified, fire proof specification.

The chosen solution therefore had to be a central cluster, using Community R2s. After precise simulation Elisabeth Zieliñski of Tommex chose the asymmetrical R2-694X. The well-controlled dispersion of the loudspeaker enabled the design to avoid serious reflections from vertical walls, particularly in the vicinity of corners. Another important consideration in choosing Community R series was the products inherent suitability for an ice arena application. Being weather resistant they would not be susceptible to the usual corrosion caused by the humid environment found in this type of facility.

Seven Community R2-694X and six Community R.5-66TX form the main cluster. The R.5s fire downward and provide good coverage to the central arena with the R2-694Xs covering the audience areas. With this solution the R2s are driven at only 200W, easily meeting the specification for the voice alarm system to have at least 10% reserve power.

Wojciech Zieliñski, heading the Globus project for Tommex, comments, "Final measurements confirmed the accuracy of the simulation and confirmed the importance of being able to use simulation in the design process for acoustically complex buildings. Of course this only works when a manufacturer's data for their products is totally accurate and honest and Community are outstanding in this respect. It makes our job a lot easier and gets better results".

Tommex used a base parameter for the system of 103 dB average SPL for 95% of the audience area with a frequency response of 100 Hz to 10 kHz. Additionally, in accordance with new regulations, such facilities must be equipped with a voice alarm system which must use components certified by the National Institute for Fire Protection Technologies. Because the regulations were entirely new in Poland, the only certified loudspeakers were a few ceiling speakers, sound projectors and 15W horns. Tommex turned to the Institute with the idea of using properly suitable, but not certified loudspeakers for the venue and gained permission to install their designed system with the approval of the Institute. The rest of the system uses pre-certified components.

Zieliñski concludes, "The final result is a unique 2-in-1 system that performs remarkably in this difficult environment and combines a voice alarm system and a sport system. Now installed, the system meets all of the parameters set by the client, the architects and the Fire Protection Department. The average SPL is 105 dB (-2/+3dB) and RaSTI in the worst locations is 0,5. The frequency range is limited to 90 Hz to 16 kHz and the main cluster works as two independent loudspeakers groups: one for seating areas and one for the main arena floor. They are driven separately and have individual equalization. The arrangement of the audience area loudspeakers even allows for up to three to be out of action and SPL drops by only 3 dB".

The system for sports events uses a Midas Venice 160 console. A Sabine FBX 2400 Plus digital feedback eliminator is paired with Beyerdynamic microphones and a Beyerdynamic NE500 D wireless microphone receiver. EQ / processing is performed by a Klark Teknik DN504 compressor / limiter and a KT SQ1 30 band equaliser. It serves two functions: band limiting (and therefore safe use of the R2’s) and fine tuning the system. To prevent unauthorised adjustments to the EQ processing, the SQ1 is fitted with a secure front cover plate.

Commentary for events can be made from four locations: the sound engineering room, the press cabin and two locations on the level of the arena, equipped with on-wall mixers for connecting headsets. The voice alarm system is from Swiss G+M Elektronik AG – a pair of APS 450 on-wall mixers control the remote speakers, driven by BO 250 ev power amplifiers. These, Zieliñski describes as “wonderful”. Rated at 250W RMS they are able to deliver effortless short-term power of 350W. The R2s are driven through Community TRC400 transformers at half power (200W) whilst the R5s are T versions working at 120W nominal power.