Did you happen to update your clover install? If so it could be the cause of your black screen. Latest builds tend to remove OsxAptioFix2Drv-64.efi from the drivers64UEFI folder. Just restore the file & you're back in business.
After installing the driver download and run toledas audio_CloverALC command. I have the same issue you're facing after major updates, this clears it up for me.
You can download it here. https://github.com/toleda/audio_CloverALC/blob/master/audio_cloverALC-130.command.zip
This is still working great for me after 10.13.4 update.
For most of you the onboard (motherboard) audio drivers will need to be re-installed after these major updates. Be sure you do that. None of my outputs including HDMI are available until the onboard drivers are installed.
Still working for me with the latest release. Make sure you're following the latest instructions & not what's shown in the video. Doesn't hurt to install your motherboard audio drivers either. I'm using OSX default graphics driver for my invidia card.
Firstly make sure you're installing it to the correct EFI folder. Some systems use extra/efi folder on their system partition while others reference an EFI partition. Try removing the 10.12 folder. In sierra the kext needs to be placed in the "other" folder. I also had to restart my system twice.
Unfortunately this is just the way OSX works. There are a handful of utilities to enable the function, I'd search the forum and find one. I've tried soundflower but wasn't too happy with the performance.
Updated 07/3/2018. This solution works in High Sierra 10.13.6 as well as several previous versions of MacOS. I didn't create the tools I only figured out how to use them. Credit for the kext goes to andrejkw at macrumors. Your mileage may vary but this is the easiest solution I've found. I've...