Double Bass Acoustic Image - less bass with extension speaker

[akdor1154]

Hey all,

Just bought a used Acoustic Image Coda R3 with a Contra EX. When I add the contra ex, my bass response dives significantly. My first thought was phase cancellation. I have yet to go home and play around with placement, but on googling I can't find a single instance of people worried about placement of these combos+extensions, so I'm doubtful.

Is there anything else this could be? Is there any way to disable the internal speaker of the Coda R3 so I can listen to the response of the EX on its own?

I'm in Australia (and as said, bought it used) so sending them off to AI is probably not gonna happen!

Additionally, I'm getting some buzz on a low B (and Bs in the octaves above, though progressively less) from the Coda itself when driven at medium volumes (in an empty wooden room, so probably a lot less loud than at your average gig). Again I have yet to spend a huge amount of time with it to ensure it's not something else in the room, but TalkBass's best armchair diagnosis of this?

Cheers
Jarrad

 

[brianrost]

My Coda sIII has an internal speaker on/off switch on the rear panel. But my Contra sIII does not.

The user manual PDF at the AI website does not show a switch.

 

[Francois Blais]

Hey all,

Just bought a used Acoustic Image Coda R3 with a Contra EX. When I add the contra ex, my bass response dives significantly. My first thought was phase cancellation. I have yet to go home and play around with placement, but on googling I can't find a single instance of people worried about placement of these combos+extensions, so I'm doubtful.

To get low frequency phase cancellation, the two speakers should be very close I think, so I don't think it's the case either.

Additionally, I'm getting some buzz on a low B (and Bs in the octaves above, though progressively less) from the Coda itself when driven at medium volumes (in an empty wooden room, so probably a lot less loud than at your average gig).

Maybe the bass driver's cone is hitting the grill.

 

[jmlee]

I have a Coda and the matching EX extension. Mine's an earlier version and so has a very short speakon cable between the amp and speaker of the Coda which enables disengagement of the speaker if you care to do that. I'm guessing that the R3 version doesn't have that option. In any case, adding the EX to mine greatly increases available volume and bottom end. I've used the pair with my upright and a pretty loud jump blues band with 4 horns, drummer, and guitar player: live off a club stage with no PA support for the bass. If you get *less* bass when you attach the EX, it's possible that you have an electrical inversion in the cables connecting the two speakers. That is, they're constantly out of phase with each other producing destructive interference. This would be a much greater effect than just acoustical interference associated with speaker placement in the room. If you have another speaker cable, try that or use an ohmmeter to make sure the cable is wired correctly.

 

[lz4005]

. If you get *less* bass when you attach the EX, it's possible that you have an electrical inversion in the cables connecting the two speakers. That is, they're constantly out of phase with each other producing destructive interference. This would be a much greater effect than just acoustical interference associated with speaker placement in the room. If you have another speaker cable, try that or use an ohmmeter to make sure the cable is wired correctly.

That was my first thought too. Very easy for it to happen if the used cab has been opened and worked on by an amateur.

After trying a 2nd speaker cable, if OP doesn't have an ohmmeter he could do the 9v battery test, or just open the new cab up and reverse the internal speaker wires to see if that fixes it.

 

[akdor1154]

Thanks for the replies all. For testing the cab cable, am I just checking for conductivity between matching pins on each speakon plug? Or are the pins meant to be connected symmetrically opposed?

EDIT: Cable indeed appears wired in reverse, assuming identical pins on each plug are meant to be connected. Nice sleuthing guys!