Protesters are suing the NYPD over a little-known police sound device with a big impact. NY1's Dean Meminger filed the following report.

It's called an LRAD, a Long Range Acoustic Device. Some refer to it as a "sound cannon." It's a powerful portable speaker that emits a piercing sound designed to startle people.​

The NYPD is being sued for using it at a protest.

"I suffered extraordinary pain," said Keegan Stephan, an independent journalist. "I had to leave the area."

Stephan was there in December of 2014 when protesters gathered on East 57th Street hours after a grand jury declined to indict officers in the chokehold death of Eric Garner. The NYPD used a handheld LRAD to clear the street.

On Thursday, lawyers representing six people suing the city over its use of the LRAD told a federal judge the device was developed in part for military use. 

"An LRAD can be used to hurt people so that they leave an area through pain compliance. It is supposed to force people to engage in certain kinds of behavior by hurting them," said Gideon Oliver, a lawyer for the plaintiffs.

The plaintiffs' lawyers submitted an NYPD document that describes the dangers of the device, stating the LRAD emits "piercing sound at higher levels than are considered safe to human ears.....In this dangerous range, the device can cause damage to someone's hearing and may be painful." 

Stephan describes himself as an independent journalist. He says the NYPD's use of the device not only caused him pain, but denied him freedom of press.

"I was trying to record this arrest when I was hit with it," Stephan said. "It forced me away from filming the arrest and the police activity I was trying to film."

The city is trying to get the case thrown out. City lawyer Ashley Garman told the judge police did not use the device as a weapon and were only trying to clear streets to allow traffic to flow. She also pointed out people were throwing bottles and garbage in the direction of police.

But lawyers for the plaintiffs said the department has no guidelines for using the LRAD.

"If we are going to use this in New York City, we need to have testing, we need to have training, we need to have guidelines," said Elena Cohen, a lawyer for the plaintiffs.

The judge will rule whether the case can move forward. Those suing want monetary damages and a clear NYPD policy on LRAD use.