I'm building a site that I plan to be on a subdomain to an old authority domain but I also want to use www before the subdomain, i.e. www.subdomain.domain.com. I've noticed though that almost all sites with subdomains don't use www. Is there any difference SEO wise between the the www and non-www version for subdomains?
There is no difference, and if you're building the site with the intention of gaining traffic through search engines, the fact that you're a subdomain of a well established site will be enough to get you moving quickly.
The www is actually a subdomain. For example, in the domain name artists.music.com, "artists" is a subdomain of the larger second-level domain "music.com". This applys to www.music.com, where "www" is a subdomain of the larger second-level domain "music.com". Actually the type of access depends on your server's (webhost's servers) web server configuration. Some hosts provide bot ways of access, as leading to the same content, some not. As far as SEO goes, both are rated exactly the same.
Thank you for the answers. I know www is a subdomain, and I was wondering whether www.sub.domain.com is the same as sub.domain.com or is considered by SE as sub.sub.domain.com, i.e. a subdomain to a subdomain (like rock.bands.music.com for example). Hope I'm making some sense.
Even if it's a sub.sub.sub.domain.com, i don't think you will get any other results than sub.domain.com .