Not all speakers sound the same...

Rocker

Quite obvious really but my attempts to make my bass sound 'louder' came to naught.  I use a Markbass Minimark 802 and connected a cab with an Eminence Alpha 12" speaker to the Markbass.  I like the Markbass sound but the combination did not work.  In fact awful is closer to the reality.  I used the DB sound level meter on my iPhone to check if the additional speaker made the sound louder.  It did, slightly, but tonally wrecked it.

We (our band) are playing a dancing gig this coming Sunday.  Dancing as in waltzes, foxtrots, jives, etc. and a set or two of general jump around dancing for those unable to waltz.  As the bass is key to getting people out to dance, I had hoped to sound louder and more prominent.  And our PA does not have bass bins so DI'ing is not an option.  Hoping I will be loud enough..... Wish me luck....

ICBM

Was the Eminence speaker definitely in phase with the Markbass one? Although speakers are supposed to all be, there are exceptions...

If it was out of phase it would sound odd, and probably not good.

If it is in phase, try using a long speaker cable, and put the extension cab where the audience can hear it but you can’t! Use the Markbass as your personal monitor.