Early this morning, Portland police officers used a sonic weapon to drive away protesters.

Speaking to reporters early Friday afternoon, Portland Police Bureau Assistant Chief Chris Davis said sometime after 1:30 Friday morning, officers in the sound truck that broadcasts communication to protesters came under attack.

Davis said the officers in the truck then deployed a tool called a "long range acoustic device," or LRAD, which Davis said "will emit a tone that is very hard to be around."

News reports say the device can generate a sound of more than 150 decibels that can be aimed and projected over long distances.

LRADs were originally developed as a tool to deter pirates but has been adopted by military and some police forces as a crowd control device.

The Police Bureau has used an LRAD before, Davis said today, but he did not specify when. "It's very rare," Davis said. "We haven't always found it to be effective. It's not something we use often because of mixed results."

Mayor Ted Wheeler said today after Davis spoke that he is open to such a ban but wants an alternative crowd control measure that isn't worse.

"It's ugly and it looks ugly," Wheeler said of the use of tear gas. "I stand with those who say we should ban the use of tear gas. I would support the discontinuation of tear gas or CS gas provided there were viable options for dispersal that don't involve higher uses of force."

Critics have argued the LRAD is not a good alternative, saying the intense sound the device emits can cause permanent damage.

A federal lawsuit is pending in New York challenging the use of LRADs by that city's police department, which reportedly began using them as early as 2004. New York appealed the case all the way the U.S. Supreme Court, arguing officers should be shielded by the doctrine of qualified immunity, but the Supreme Court disagreed and sent the case back to lower courts for trial.