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Tidal Information System helps sound levels rise in Venice

James McGrath 25 January 2012

The high tides in Venice can have a major impact on day-to-day life – so a new city-wide audio system has just been installed to let the population know when they will need to take action, Paddy Baker reports.

When American humorist Robert Benchley arrived on an assignment in Venice in the 1930s, he famously telegraphed to his office: “Streets flooded. Please advise.” While it’s not known what, if any, advice the office of The New Yorker gave Benchley, the citizens of today’s Venice value being told just how high the waters are going to be every day – and an audio installation in the city is helping to do just that.

Most of us try to catch a weather forecast before we leave for work in the morning, so that we know whether to dress warmly or take an umbrella – but that’s generally as far as it goes. But in Venice, where the canals are tidal, the consequences of a high water level could be rather more severe. Reduced headroom under bridges means that the boats that do the duty of taxis, buses and even lorries in conventional cities may need to re-route; and if pavements disappear underwater, raised walkways may need to be set out. The city’s population – including a sizeable cohort of commuters – are well used to this, but having accurate, timely information is important the necessary adjustments to can be made to keep daily life on track.

A local government department, the Centro Previsioni E Segnalazioni Maree (Tidal Forecasting and Signalling Centre), is charged with monitoring and predicting the water levels, and communicating them to the city. The higher the tide, the greater the proportion of people that are going to be affected. The department has identified four different tidal bands: the lowest, 110-120cm above normal sea level affects 12% of the population, while the highest (140cm and above) affects as many as 90%. (If the water rises beyond 190cm, it impacts the city’s entire population.)  

The Centre has embraced technology in a number of a number of ways to inform the city about water levels: these include a website, a toll-free phone line and even a smartphone app. There are also a number of touchscreen information points at newspaper kiosks around the city.

A siren-based audio system had been in place for a number of years; however, mechanical deterioration had led to it behaving erratically, and it could only broadcast one alert signal. It was decided to replace it with a system that could give more detailed information about water levels.

A clear message
Audio consultant Ing. Umberto Nicolao was engaged to specify the new audio solution. He explains: “The mission that we received was to advise the Venice community without having the possibility to teach them about the signals. So we had to communicate four different levels of the sea by a set of signals that could be understood immediately.”

Nicolao didn’t want to use standard electromechanical sirens in the system. “We tried to work on an audio signal that didn’t have the urgency of a Second World War siren. Here we’re not dealing with a risk to people, we only have to advise them that there is a high water event coming, and what level is foreseen.”

Given that musical notes can be high or low, Nicolao thought immediately that broadcasting different notes could readily be understood as referring to height of water. Also, using a musical tone also fits in well with the city’s musical heritage.

“I studied the characteristics of many acoustical signals, and I found that the sound of the flute is a very pure one,” he continues. “You can recognise it only with the first three or four harmonics. The violin, by contrast, has about 30 harmonics, and you need all of them to recognise the sound of a violin. But with a flute, you only need the four.

“Also, when you have to broadcast a sound a great distance, you have to consider that many of the high-frequency components will not arrive at all. So don’t count on frequencies above 2 or 3kHz.”

So it was decided to use an electronic sound similar to a flute, with the fundamental and just three harmonics. Despite his overall reservations about siren-type signals, he decided to use a siren-like introductory “attention” signal at the start of each signal broadcast; this is followed by between one and four notes, lasting a few seconds each, to denote the predicted height of the incoming tide.

The right tone
The decision about what tones to broadcast came after the system selection process – and that was more complicated than first expected. From the point of view of efficiency, having the fewest speakers to cover the entire city meant having very powerful speakers, positioned where their signals would not be blocked – and that means high up.

“Venice is mainly composed of buildings that are not so high,” explains Umberto. “Only the palaces on the Canal Grande are three or four floors – normally the buildings have only one upper floor. So you need a point above the buildings to cover the area, acoustically speaking.”

Fortunately, Venice is well served with bell towers in its various cathedrals and churches. To investigate the potential sites to install speakers, “We visited at least 50 churches in Venice,” he says. “There was only one church where we couldn’t install the system because of the decision of the priest – he prefers to have an anti-theft system rather than our speakers.”

When it came to specifying the system, Nicolao was in for a surprise. “It’s incredible how little knowhow there is in this field,” he confides. “If you look at the most specialised systems, which come from the US, they couldn’t work here as they radiate mainly in the horizontal plane. If you installed these systems 50m above the ground you would only advise the angels!” His team asked the manufacturers to supply polar diagram data for these systems, especially in the vertical plane, but their own calculations provided better data than the manufacturers could supply. This, along with greater convenience, steered Nicolao and his team towards designing their own solution.

Nicolao felt that there was only one manufacturer that could supply speakers for this installation, which offered a combination of high SPL and weatherproof construction – Community Professional. However, the exact product that Nicolao wanted did not exist.

Ennio Prase, whose company Prase Engineering distributes Community in Italy, takes up the story: “When the designers came to us, we didn’t have the perfect solution in terms of a loudspeaker system. We needed to have something really compact, extremely efficient, extremely powerful in terms of SPL, and preferably light in weight because there are no elevators in these campaniles! Nicolao and his team analysed components and we offered some options – but at the end of the day the best fit was a product that we didn’t have as a distributor.

What was wanted was a compact model with two 2in mid-range drivers. “I had to go to Community and express the desire of having something custom built,” continues Prase. “They liked the idea – we tried to provide a sketched out design to show the concept. They said, ‘Leave it with us, we’ll experiment with some mouldings – and let you know if we can shrink the cabinets and still hold two 2in mid-compression drivers.’ They managed to get the proper result out of it. They created a brand new product – the R.5-V2200.” This has become a bespoke product in the Community catalogue, and has been deployed successfully in other applications.

Unique challenges
It’s not just the weather that the speakers need to withstand, adds Prase: “You have to consider protection from birds in Venice – there are a lot of pigeons. The speakers have a multi-layered weather-tech coating that they also use on the WET series – a multi-layer different mesh density grille that works like Gore-Tex: water can drain out eventually but not get in. Acoustically it’s quite transparent – not a significant SPL reduction. The cabinet is roto-moulded polyethylene, so there’s no molecular stress in the material, and any mounting hardware is stainless steel.”

We visit two installation sites, where the setups are broadly similar. One is La Fenice, a well-known theatre whose name (fenice means phoenix) has ironic significance: it was built in 1792 after the city’s leading opera house burned down nearly two decades earlier. However, La Fenice has itself been destroyed by fire and rebuilt – twice. The current building dates from 2001.

The other install site is an even more iconic Venetian location – the belltower of St Mark’s. This is one of the lowest-lying parts of the city – it begins to fill up when the tide rises more than 80cm above mean sea level. Each of two neighbouring balconies has two Community R-SV2000 speakers stacked vertically, firing out over the city. These are fed by Duran Audio AXYS PB400 IndustryAmps, which take their signal from a Prodytel S-Cluster output box.
Prase explains: “This is a very complex device – it’s an audio streamer, designed for security systems. The audio content – all the different samples – are stored in flash memory inside the unit.” These communicate via WiFi with the control room at the tidal centre, which triggers the playing of the alert signal when required. This link also makes it possible to check that the signals have been loaded properly; although it’s not required here, additional signals could be loaded onto the S-Clusters from the control room.

At one point in the day, as we are walking through the streets, Nicolao says to me: “I found a lot of poetry in this project – and especially the idea to use a musical signal as a warning signal – because everywhere you look there is someone playing a musical instrument.” Literally, at that moment we come across two people in period costume, carrying instruments.

Later on, I ask him: of all the projects he has worked on, which is he most proud of? He replies: “This one, for sure. From the romantic point of view.” Venice, it seems, can capture the hearts of more than just tourists.

www.communitypro.com
www.duran-audio.com
www.prase.it
www.prodytel.de

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