Hello, and welcome to Sysnative,
HDMI is fiddly and unreliable when it comes to connecting PCs to TVs, at least in my experience, and especially in relation to sound. There have been laptops I've had physically in front of me and been unable to get connected to a TV via HDMI. Sometimes I manage to run a separate 3.5mm cable from the headphone port to the back of the TV and jury rig it that way, sometimes I just haven't been able to get it to work :noidea: 
You're not alone and sadly I don't think I'll be able to offer you a magic bullet which will solve everything.
Having said that playing around with drivers is your best and pretty much only bet. It's essentially and almost certainly a driver problem at some level but whether the manufacturer has managed to create reliable, stable drivers which actually work in practice is hit and miss.
I suggest you give the stock Intel (generic) drivers a go. Similar to Microsoft's generic drivers they tend to be less feature rich but significantly more stable and reliable than some of the OEM drivers. The risk posed by installing them should be minimal. So I suggest you give them a try. Similarly install any offered graphics/"VGA" drivers which often have a significant impact on HDMI function.
If no luck, go back to the Acer website and make sure to update - audio, VGA, and chipset drivers. All of these could be having an effect here.
Finally, go back to the Acer website one more time and this time go to the Windows 8.1 drivers. Oftentimes manufacturers push their latest and best drivers only to the driver download page for the latest version of Windows download but in practice they work perfectly well on previous versions of Windows too. I notice indeed that there is a more up to date version of the Realtek driver offered through the Acer website for your particular netbook. I suggest you download and attempt to install it. If it installs happily - as it often will - that's great. If the installer fails with a "not compatible with this version of Windows" or words to the effect of, don't force the issue. It is still worth trying though, I've seen a number of issues get fixed by trying this.
Best of luck.
Richard
