With some of the speaker towers almost 1.5km from the source point, a mean air temperature of 22°C and 50% relative humidity, the audio team were looking at a delay of 4.35 seconds to the most distant tower. Henning Kaltheuner, a senior production planning specialist from Yamaha, volunteered to solve some of the technical issues. "Neumann & Muller preferred to use Yamaha DMEs because of the level of reliability," says Kaltheuner. "We rarely have a chance to join a real world project of this size during its design and performance and we in fact found some software issues to be improved - and these will already be implemented in next version 1.2. The problem was essentially time. Using a single DME delay component you only get 1.3 seconds of delay maximum; for almost every imaginable purpose this is more than enough - 1.3 seconds is approximately 440m . . . But of course with the most distant speakers almost 1.5km away this was problematic."
There were other significant considerations. "The sound system had to fulfil the German regulations for emergency sound systems, the national standard for this is VDE 0828 part 1. The standard insists that the system must be capable of self interrogation, so that a fault on any device or network connection could immediately be monitored from the control room."
This was realized by adding a 20kHz pilot tone to any of the 104 outputs of the main matrix. "Outputs from main matrix were send through the Optocore networks (six networks in total) into DME24 units and further on in analogue domain from DME24s to the speaker towers. The analogue signal arriving at each speaker tower was then returned to the specific DME, and then onward back through the Optocore network to the DME main matrix. This return signal was filtered by some sharp 20kHz band-pass filters and indicated on a user screen with 104m. During normal operation all these meters showed a constant level, a meter with no signal would have indicated a signal path not working."
Naturally, additional fail-safe systems were required. "Thorsten Schulze, an independent planner, developed a backup signal distribution system by RF links to the speaker towers. The signal management for automatic fall-over from regular operation to RF backup was also realised in the DME 24 set-up."
So how did Kaltheuner solve the time delay problem? "The job of the main matrix was to distribute the event program mono mix from a Yamaha PM1D to 104 speaker towers and be simultaneously capable of providing the possibility to address an emergency announcement individually to any of the 104 speaker systems, or specifically to certain groups of these speakers."
"A main difficulty was to provide enough signal delays for the speaker system. A simple cascade of delays could have covered the requirement, three long delays in series would provide 3.9 sec. delay time. This would end in a quite simple hierarchical structure, but the problem is each speaker would require 3 delays - at least for those that far away from stage. DME64 has a limit for delay components, a maximum 32 long delays with 1300msec. Each can be used in one DME64. This limitation is not determined by DSP capacity, DME uses dedicated memory for audio signals per DSP chip, which is totally separate from control memory. This architecture has been demonstrated to be more reliable than a structure in which memory resources are shifted around."
If the main matrix had been designed according to the scheme outlined above, up to seven or eight DME64s would have been required to build the entire 2 into 104 matrix with all the necessary delays. Thi
