Activists speak at the Toronto Community Mobilization Network press conference in Toronto on May 20. ((Nathan Denette/Canadian Press))

The addition of sound cannons to the arsenal available to security forces managing G20 protests comes as no surprise to groups planning to demonstrate in Toronto at next month's summit.

They say it's just one more signal amid an unprecedented security operation that dissenting voices are being muzzled.

"We were expecting the use of sound cannons, sound grenades, Tasers, tear gas — they've been used in the past against Canadian protesters," Sharmeen Khan, spokeswoman for the Toronto Community Mobilization Network, said Thursday.

"We definitely are concerned that this will scare people away."

The sound cannons are capable of emitting ear-piercing and hearing-damaging alerts that can be heard up to 1.5 kilometres away.

Formally known as long-range acoustical devices, they can also be used to broadcast prerecorded and other messages to protesters.

"It will allow our officers to speak to the crowd over and above chanting, yelling, screaming — noise that is most commonly part of protests," said Const. Wendy Drummond, spokeswoman for Toronto police.

"It will allow us to communicate, most effectively, our demands to the crowd."

Toronto police have purchased four of the devices — three hand-held and one mounted — from Vancouver-based Current Corp.

The devices — some call them weapons — use an array of tweeters that work in tandem to produce the high-volume levels.

Used at Pittsburgh summit

They can be pointed at specific targets to minimize the impact on bystanders and have been used around the world for a variety of functions, including against protesters at last year's G20 summit in Pittsburgh.

While the sound cannons can cause hearing damage, police said they planned to follow both manufacturer and internal guidelines in their use, including firing alert bursts of only two to three seconds.

Toronto police bought the devices as part of the $1-billion security effort Canadian authorities are mounting to try to ensure the G8 and G20 summits run smoothly.

The Council of Canadians said Wednesday it would give away earplugs during the G20 to protect people from permanent hearing loss.

"Saying a sound cannon is a tool for communications is like saying waterboarding isn't torture, just a tool for encouraging dialogue," said spokesman Mark Calzavara.

The devices are meant to "intimidate people and make them too scared to protest," he said.

Those involved with security planning are making no apologies.

"This is the largest security event that Canada has ever had," Drummond said.

"We are expecting a large amount of people in our downtown core … just the sheer numbers alone make it a huge event."

Canada is no stranger to ugly clashes between security forces and protesters.

The Commission for Public Complaints Against the RCMP concluded the Mounties used "excessive and unjustified force" to disperse protesters at the 2001 Summit of the Americas in Quebec.

The RCMP was also forced to admit it botched security planning for the Asia-Pacific Economic Co-operation summit in Vancouver in 1997, leading to the pepper-spraying of crowds of protesters and 42 arrests.

The G20 summit in Toronto runs June 26-27.