hey friends what would be great options as per SEO Having one forum on single domain for several different topics or Different forums for different topics on different sub domains like Sports Music etc
Depends on the range of topics, if you think that your visitors can have interest in several topics like in your example Sports and music, then I'd go for one forum because members can hang out in different sections and talk on a variety of topics. This would make your forum more interesting and you'll have more loyal members. But if you target more specific topics like 'Search marketing', 'mortgage loans' and 'translation of bible into spanish' then the better option is to create several forums.
Better start a general forum with different topics in it rather than making different sub domains. And also use a domain which sounds nice according to your domain. I have seen some forums with several sections in one forum. - Digital -
usually a single forum has different relevant topics under one domain. but if you have totally different topics, then you need to use different domians or subdomians