QEMU-KVM soundhw deprecated how to enable sound in QEMU 4.x series
In QEMU 4 or higher you can no longer use the normal "-soundhw ac97" flag and it is much more complicated but here is a simple copy and paste on Linux that will just work:
-audiodev you have to use -audiodev to specify the driver and id
driver=pa
id=someid
-device you have to specify the same audiodev id you used in -audiodev and driver
-audiodev driver=pa,id=pa1 -devic........
Linux qemu-kvm How To Enable Soundcard in Guestl
Pass QEMU this flag:
-soundhw ac97
Or you could use (for a Ensoniq soundcard):
-soundhw es1370
However on some machines I get this error:
pulseaudio: pa_simple_new for capture failed
pulseaudio: Reason: Connection terminated
pulseaudio: pa_simple_new for capture failed
pulseaudio: Reason: Connection terminated
audio: Failed to create voice `ac9........