It’s no secret that the sales of CDs have plummeted in the last decade and are down about 50 percent from their peak. Retailers have been forced to adjust, often by devoting some shelf space to other products. But that has not always meant that retailers have left the music business.

In 2008, Best Buy, the national electronics retailer, began dipping its toe into the world of musical instruments. By late March of this year, the company had opened its 99th and 100th musical instrument departments, at its new stores in Upper Manhattan and in Flushing, Queens.

“We sell many ways to consume music. Why not create?” Justin Barber, a spokesman for the company, said. “It just seemed like a natural extension.”

At the store in Upper Manhattan, customers can select from 45 acoustic guitars, which are kept in a closed, climate-controlled room, ranging from a $99.99 Squier guitar to a $3,999.99, six-string Taylor. (And two ukuleles). Along the red wall facing the customers when they enter the department hang about 80 electric guitars and bass guitars, in a similar range of prices. DJ equipment lines another wall.