Despite a slow start to the Prime Day summer sales event, U.S. online sales reached $24.1 billion with retailers offering deeper discounts than last year.

The four-day summer sales event officially ends tonight, Friday, July 11. This is the tech giant's 11th Prime Day event during which the online retailer offered up millions of deals over more than 35 categories including electronics and kitchen , apparel and accessories.

We’ve tested thousands of headphones and earbuds — and these are the best pairs to buy on sale during Prime Day.