Not including a volume control is user-hostile.
There is no other way to say it.
I have the other sounds on my system set to the way I want them. Along comes a SoundCloud player BLASTING out of the speakers. Pretty much every other player of any kind in a web browser on a PC has a volume control. I do NOT want to turn everything else down to where I can't hear it.
I've searched around, and people have been commenting, complaining and lamenting this for years. The use cases I can come up with where you don't have one are minuscule in number.
Please. Put a volume control on there. I don't care if it defaults on or off. Just, give the sites embedding it an option to include one. If you pay attention, I suspect you'll find 99% of sites will use that option.