Iowa is one of the few states that does not require the use of a helmet. There are no restrictions on the use of helmet speakers. Iowa allows two motorcycles per lane and has statutes against lane splitting.
Maryland requires helmets. You may ride two abreast in a single lane. Their law on helmet speakers is somewhat roundabout and does not allow you to wear earplugs but does allow you the use of one...
These regulations vary greatly from state-to-state and jurisdiction-to-jurisdiction but are usually contained in the state DMV codes. If motorcycle funeral escorts are done by ANYONE ELSE except law...