FreeBSD切换声音输出的默认设备

我的电脑上有多个声音输出设备如下:

% cat /dev/sndstat


Installed devices:
pcm0: <Realtek ALC892 (Rear Analog 7.1/2.0)> (play/rec) default
pcm1: <Realtek ALC892 (Front Analog)> (play/rec)
pcm2: <Realtek ALC892 (Onboard Digital)> (play)
pcm3: <Intel Kaby Lake (HDMI/DP 8ch)> (play)

第一个(pcm0)是接的是音响,我觉得它太响就想用耳机; 耳机是pcm1.

% sysctl hw.snd.default_unit=1

hw.snd.default_unit: 0 -> 1