I'm assuming you're talking about Video Ads. As sound matters alot when sponsoring podcasts and doing audio ads on Spotify and Pandora. It would be wrong to assume that sound doesn't matter at all.
Most people don't watch video with sound:
But just because majority of people watch videos without sound does not mean it's not valuable.
It really depends on what you're advertising. Perhaps the most profitable segment of your users watch ads with sound.