Since the introduction of MacOS 10.13.6 Apple has required users to give permission to install kernel extensions.
During the initial Dolby Audio Bridge installation you should see a System Extension Blocked dialog. Whether or not that appears you have 30 minutes from the installation to approve ("allow") the extension from System Preferences>Security and Privacy.
If more than 30 minutes elapses, you will need to manually remove the DolbyAudioBridge.kext file from Macintosh HD ▸ Library ▸ Extensions and re-run the installers.
The ability to "allow" the extension should appear. In rare cases you may need to disable this feature of High Sierra.
The spctl function can be used from the terminal window to disable the need to grant permissions to load a .kext. This should be re-enabled later as it has security implications for your MAC.