Mercedes has run a 'megaphone' exhaust during testing in Barcelona in a trial to improve the sound of the 2014 engines.

The new power units are noticeably quieter than their V8 predecessors, leading to complaints from race promoters who told Bernie Ecclestone during a meeting on Saturday that they want the noise issue addressed.

In response to the concerns, the teams agreed to trial a way of increasing the noise, with Mercedes running a 'megaphone' exhaust on the rear of the W05 on the second day of testing at the Circuit de Catalunya. Nico Rosberg carried out a number of aero tests at the start of the day but later ran at full throttle with the exhaust, which didn't result in much audible difference when listening trackside.

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Mercedes has now confirmed to that it will not be running the exhaust again today as Rosberg continues with the team's test program on the final day in Spain.

Force India's Dani Juncadella followed Rosberg for a spell and said there was no obvious difference between the two exhausts.

"I drove behind him once, but I didn't really hear much," Juncadella said. "There is obviously not a lot of sound on the engines, but I heard someone say there is not a big difference (between the megaphone and regular exhaust pipes.) We will see if it changes, but for the moment it looks like it is not a big problem. It is just something very new for everyone."