Sound cannons operated by police may be used only in short bursts during G20 protests in Toronto, a judge has decided. (Frank Gunn/Canadian Press)

A judge has dismissed a motion that sought to ban police use of so-called sound cannons to control crowds during the G20 summit in Toronto.

Ontario Superior Court Justice David Brown's decision allows police to use the devices, but also places limits on how they can use them. Police must conform to Ontario Provincial Police operating rules for the cannons, the judge said. The voice function of the devices is OK to use, but an alert function, which emits an ear-splitting noise, can only be used in certain circumstances.

In Friday's decision, Brown also dismissed arguments from civil liberties groups that said allowing the use of sound cannons would infringe on the ability of people to protest.

Toronto police will abide by the court's ruling, said Chief Bill Blair.

The sound cannons, known formally as long-range acoustical devices, are capable of emitting sounds that can be heard up to 1.5 kilometres away.

In arguing for the injunction, the Canadian Civil Liberties Association and the Canadian Labour Congress said Toronto residents should not be used as "guinea pigs" to see whether so-called sound cannons are safe.

The groups accused police of relying on manufacturer studies about safety, rather than independent research.

Lawyers for Toronto police argued the sound cannons are needed to communicate with a crowd so noisy it may drown out the sound of a traditional megaphone. They compared the maximum decibel level to that of an ambulance siren or leaf blower.

With files from CBC's Steven D'Sousa and The Canadian Press