Vancouver will modify powerful audio equipment that critics say could be used as a sonic gun against protesters at next year's Winter Olympics, and stop any chance of using the device as a weapon, Vancouver police said on Tuesday.

Police had said they planned to use the so-called long range acoustic device (LRAD) as a public address system to communicate with large crowds, and not as a weapon. But they will now disable its tone capability.

The British Columbia Civil Liberties Association had said police could use the LRAD as a sonic gun to disperse protesters during next year's Winter Games in Vancouver.

The group said the LRAD could emit a blast loud enough to damage hearing and cause temporary vision disruption, and not enough was known about the possible safety risks.

It's a very positive development, David Eby, the civil rights group's executive director, said of the department's announcement.

The LRAD can blast sounds of up to 152 decibels within one meter (three feet) of the device and issue warnings over water to vessels up 3 km (2 miles) away. Sounds louder than 120 to 140 decibels can cause pain and damage to human hearing.

Manufacturer American Technology Corp says the LRAD is not a weapon, but that it allows military and police forces to broadcast information from a safe distance and create standoff and safety zones that may help prevent the use of deadly force.

(Reporting by Allan Dowd; editing by Janet Guttsman)