Responses from hermanv7b9a

Crossover builder
Madisound will design a custom crossover for a given box size and known drivers. They'll even sell you an assembled PCBwww.madisound.com 
How to see if there's DC at my AC outlets?
PS Audio makes a "humbuster". It appears to be a DC blocking device and is reasonably priced (ay least as far as can be said for an audiophile component). PS Audio claims it will quiet mechanical transformer noise. They are designed for high power...