run pulseaudio as root

$ cat /etc/group

root:x:0:
daemon:x:1:
bin:x:2:
sys:x:3:
adm:x:4:ubuntu
tty:x:5:
disk:x:6:
lp:x:7:
mail:x:8:
news:x:9:
uucp:x:10:
man:x:12:
proxy:x:13:
kmem:x:15:
dialout:x:20:
fax:x:21:
voice:x:22:
cdrom:x:24:
floppy:x:25:
tape:x:26:
sudo:x:27:ubuntu
audio:x:29:pulse,ubuntu,root
dip:x:30:
www-data:x:33:
backup:x:34:
operator:x:37:
list:x:38:
irc:x:39:
src:x:40:
gnats:x:41:
shadow:x:42:
utmp:x:43:
video:x:44:
sasl:x:45:
plugdev:x:46:
staff:x:50:
games:x:60:
users:x:100:
nogroup:x:65534:
input:x:101:
systemd-journal:x:102:
systemd-timesync:x:103:
systemd-network:x:104:
systemd-resolve:x:105:
systemd-bus-proxy:x:106:
crontab:x:107:
netdev:x:108:
ubuntu:x:1000:
ssh:x:109:
messagebus:x:110:
bind:x:111:
sambashare:x:112:
net_bt_admin:x:3001:
net_bt:x:3002:
inet:x:3003:ubuntu,root
net_raw:x:3004:ubuntu,root
net_admin:x:3005:ubuntu,root
winbindd_priv:x:113:
pulse:x:114:ubuntu,root
pulse-access:x:115:ubuntu,root
rtkit:x:116:
scanner:x:117:saned
colord:x:118:
saned:x:119:
redis:x:120:

add root to audio, pulse, pulse-access for pulseaudio

sudo usermod -G audio -a root
sudo usermod -G pulse -a root
sudo usermod -G pulse-access -a root

Switch to root, and try to run it

pulseaudio --start
or
pulseaudio --start --log-target=syslog

aplay xxx.wav to test, it should works