routed sides

A well built butt-jointed cab properly screwed and glued should not fall apart through vibration! However, as Mike pointed out, the more glue-able surface area the better...

Both methods are valid.  The key thing whether you're using rebates or biscuits, or even just butt joints is to make sure they're tight.  Wood glue (PVA based) works best when you have the maximum surface area touching each other and cures with them held tightly together.

An accurately cut and assembled butt jointed cab is probably stronger than one with loose fitting rebates and poorly cut panels.

shagnasty wrote: mykey- wrote: ....even more glue area The bits you use to cut these mitres are really not for hand-held machines, you want a table mounted router with some serious power, also the bits aren't cheap and can't be sharpened...   I rebate folded horns using a 30mm follower and laser cut steel jig, the jig means I don't have to mark out my panels, I just axe up the sheets on a wall saw and them blast out the horn profile, assemble is a peach and it reall makes a nice job.   A cheat is to use a rail mounted festool router and CAD out you sides 1:1 and use the paper as a template, either spray mount it onto the board or make cuts through it with a stanley knife join the dots with a pencil...

Good job my house mate has a Festool 1400 router then!!