Earth´s inhabitants can perceive 3D, their senses have not access to many other realms of universal reality. Our sense of hearing relates to space.
We shall not go into time dilation and Einstein´s relativity. (–lucky there–)
Heim can mean home, or indicate heimur, universe, and dallur a huge vessel or it can mean bright and shining. Perhaps Heimdallur covers all of that. Gjöll is a mythical river, gjalla to sound brightly, horn is here most likely a musical instrument. Good to understand multiple layers of words and terms in Icelandic.
Please see also book Stjarnvísi í Eddum by Björn Jónsson on every aspect and meaning of names in bálför Baldurs
and other star-war amusements
Astral aspects of Eddas
planets the actors, askur yggdrasils and other stars the stage !!