sounding board

Reader's Digest 6月号の記事You Are Not Aloneからの抜粋です。
She has made a number of close friends, and they've become travel buddies cheerleaders, and confidantes. Last year, when Rowland was considering surgery to alleviate back pain, these friends were her sounding boards, Then they kept her company during her recovery.
"sounding boards" は文脈からすると話し相手かなと思いますが、辞書で確認します。
・Oxford English Dictionary: A person or group whose reactions to suggested ideas are used as a test of their validity or likely success before they are made public.: I considered him mainly as a sounding board for my impressions.
・Collins Dictionary: If you use someone as a sounding board, you discuss your ideas with them in order to get another opinion.: He needed a sounding board rather than thinking alone.
単なる話し相手として聴くだけではなく、親身な相談相手になってくれるのですね。