Adelsberg has secured a "private investment to buy a significant share" in the company. He is joined by Dolan Hewison, who has been promoted from operations director to chief operating officer, and by Owen Laverty whose title has changed from head of insights department Fan Intelligence to director of Fan Intelligence.
The trio will report to Smith and non–executive director Jeremy Patterson. Their focus this year will be to develop Fan Intelligence.
Ear to the Ground has 30 staff and works with brands including England Rugby, Nike, Muller, MBNA, UEFA Champions League, Beats by Dre, Asics, Canterbury and Pringles.
Adelsberg said: "Our agency ambition is to understand sport and music fan bases better than anyone else in the industry. The Fan Intelligence department ensures we stay connected to the revolutionary ways that fans are consuming tech and innovation so that our clients have the edge over their competitors.
"My personal mission is to make Ear to the Ground known for cutting through the marketing bullshit and being the straight-talking agency who come with no ego, just a desire to collaborate with our clients to create brilliant campaigns that actually work."