Evolution not revolution- Public address and voice alarm.

In keeping with the AV industry’s continuing trend towards IP and other digital technologies, this month’s public address and voice alarm feature looks at the trend towards digital audio processing and distribution. We ask if the days of the 100v line are numbered.

The principles of digital sound processing or DSP have been well established for a few years now. The benefits of being able to take a number of different audio sources pump them into a digital matrix and then distribute them to selected, addressable, output zones are apparent. EQ effects and delay can be tailored on a zone by zone basis leading to great advances in the intelligibility and efficiency of audio systems.

However, things are now progressing even further. More than just using digital technologies to process audio, we are now seeing a rise in their use for the distribution of that audio.

As the number of zones included systems increases, the case for digital solutions becomes more compelling. Recent months have seen the major public address and voice alarm system manufacturers introducing digital processing and distribution systems to cope. The latest additions to Bosch’s Praesidio system allow it to cope with in excess of 500 zones. A more powerful processor and the new Multi Channel Interface mean that the maximum possible system size has increased from 240 zones.

Lars Van Den Heuvel from Bosch explained the rational here. “The largest system we’ve installed to date is actually divided over 20 subsystems. That’s at Bangkok International Airport – they’ve recently opened new terminals and this made good use of our system. We use a decentralised system over multiple locations, which are linked together over Cat5 cable or fibre. When it comes to upgrading a system or expanding it, this decentralised layout makes it a great deal easier. Also, in a situation like an airport you have to make use of the available facilities in terms of rack rooms. The distances between them can be quite large so you have to sub-divide. We distribute the audio between these sub-systems via CobraNet and control them via Ethernet.”

Bosch are not alone in the decentralised approach, several other PA and VA manufacturers have introduced, or are planning to introduce, digital backends to their systems.

TOA’s Ian Bridgewater described the steps they have taken. “We’ve just released a digital 250 Watt amplifier in a 1U rack space. This is a dramatic rack space saving for this kind of power.
“Next from us will be a new networkable PA system that we showed at Prolight & Sound in 2006. Unlike our previous offerings this will be able to operate in a decentralised manner networked over Fibre or Cat5.”

Baldwin Boxall are also in on the act. Marketing Director Nick Baldwin detailed the company’s plans in the digital domain: "We’ve already developed a new DSP controlled routing matrix, and now along with that we’re working on a network card to go into the back of it. That’s going to allow fibre optic or other Ethernet connections into the matrix. Our outputs remain 100 volt line as we believe that this is the most cost effective solution - to have digital loudspeaker lines will dramatically increase the cost of the system, whereas the digital backbone will allow us to run a decentralised system of racks."

Whilst things are moving rapidly into the digital domain behind the amplifier, things are a little more difficult on the output end. Before looking at the problems, it’s worth looking at a company who is doing it already. It, in this case, being the delivery of audio via a digital bus all the way to the speaker itself.

Klotz Digital’s Varizone system has a digital speaker bus, which sends 8-channels of audio to local amplification modules attached to each speaker. The power and control are both delivered over the same cable. Product manager Martin Krauss: “With the digital speaker bus you can monitor and control every single speaker in the system, and you don’t have a separate control system. On the other hand you also have flexible zone creation. Right now, in 100v systems, zones are created by speaker runs. In our case you can just build your structure, and then with the software you can dedicate amplifier modules to zones. Theoretically you can have a zone size of one, but more interestingly a matrix of zones is possible.”

By making each speaker individually addressable, they can be a member of more than one zone at the same time. For instance a speaker on the third floor of a stairwell could be a member of both the 3rd floor zone, and the stairwell zone. This has important implications for localised paging.

However, in order for systems such as Klotz’s to work there need to be some enabling technologies in place from the loudspeaker manufacturers. Penton loudspeakers is at the forefront of this with its work on more energy efficient products based on advanced magnetic materials.

Peter Audbrey-King commented: “We’ve been looking at higher density, neodynium magnets for our loudspeakers. These are more efficient and in some cases we’re seeing improvements of 3-5dB. In PA terms that’s a improvement of 100%.

“We’re working with a major fire safety manufacturer to produce a completely addressable system. They have developed amplification electronics to be attached to our new, more efficient speakers.

“In order to make the modules of a sensible size, they’ve really had to scale back the power from each one which is why we’ve had to work on improving efficiency and reducing the wattage needed to get enough sound pressure.”

So the technology is there to do the job, but it’s not quite that simple. Public address has long gone hand in hand with Voice Alarm / Voice Evacuation. In Europe there is no specific need for a separate system for applications such as background music and emergency systems provided they are compliant with the relevant VA standards - that means EN 60849 : Sound systems for emergency purposes, which apart from dealing with intelligibility and announcements also makes demands on the survivability of a system. That includes things like fire proof cabling. Fire proof / standards compliant Cat5 type cable is pretty hard to come by at the moment.

The general issue of standards compliance is one that rears its head as soon as one steps away from the conventional methods of designing a voice evacuation system. Vision Systems Business Development Director Neil Voce explained: “The big issue of the day is what we term risk assessed performance based design. We’re using TCP/IP based technologies to achieve something which is equivalent to compliance with BS 5839 part VIII. We’re basically trying to shoe-horn IT technology and equipment into a fire alarm standard situation, looking at how we can do dual redundancy and asses the risks involved. The biggest projects that are on-going are sharing raw technologies with the IT industry.”

Penton’s Aubrey-King shares this view, he sees direct parallels between public address systems and CCTV. “I’m convinced these addressable, active, loud speakers will come to the fore. Once you're at that point, you can access your speaker over a network. For someone like a banking organisation you can put these systems in every building around the world, and then page into them from anywhere over the network infrastructure.”

So what does the future hold for 100v solutions, are they on the way out? For the foreseeable future the answer is simply no. The issues around standards compliance, cost and indeed practical need for fully addressable systems mean that 100v is here to stay.

Sasha Reidling, marketing manager of IC Audio still sees great demand for standards compliant 100v products - particularly in the new EU member states who are keen to demonstrate their commitment. “They are pulling really hard in this sector. In fact they are choosing to comply with BS 5839 rather than EN 60849 because in some respects it’s even stricter.”

Klotz Digital’s Martin Krauss stated: “There’s not always a need to control every speaker or to have a totally digital system. Sometimes it’s cheaper and easier to have one speaker run. What is more likely is a hybrid system where you have a digital system for the parts where it makes sense – meeting rooms, and then 100v for larger areas. The two can coexist happily.”

No one is yet predicting the end of 100v technology. There’s a good reason it’s been around so long – it does its job well. However what is clear is that over the next year or so we’ll see digital technologies continue grow strongly in applications that make the most use of the advantages they can offer namely ease of installation, flexibility of system design, scalability and efficiency.

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