Here is a Top 10 listing of car audio speaker and amplifier brands, ranked by dollar sales to consumers by The NPD Group (Jan-Sept 2014).
You can see that JL Audio moved up from second to third place in speakers this year and Rockford Fosgate also gained in share.
In amplifiers, Kenwood gained in share as did Boss Audio and Jensen.
The NPD Group, Inc. (formerly National Purchase Diary) is a market research company. The NPD Group consistently ranks among the top 25 market research companies in the independent Honomichl Top 50 report, which the media and the research industry acknowledge as a credible source of information on the market research industry. For 2010, NPD ranked 10th according to this report. NPD was founded in 1967 and provides market information and advisory services to companies. Using actual sales data from retailers and distributors as well as consumer-reported purchasing behavior, NPD offers consumer panel and retail sales tracking services, special reports, analytic solutions, and advisory services. Covered industries include automotive, beauty, consumer electronics, entertainment, fashion, food/foodservice, home, luxury, mobile, office supplies, sports, technology (commercial technology, information technology, displays, solar), toys, and video games.