Mid Bass Modules

[WmAx]

What kind of dampening and bracing should one use in a sealed MBM. I was thinking of 2inches on all sides and 4 on the back.

And a just a few braces in between the back and front baffle with round cut outs. These will be eventually paired with acoustically neutral upper-mids. So I'm very concerned about sonic quality here.

With a MBM(mid-bass module), you only need to worry about shifting the resonant frequency of the panels at least 1/2 octave over the intended low pass crossover point, assuming you use at least a 4th order slope. So, if you are going to cross the mid-bass at 150 Hz, you should shift the first resonance panel mode of the cabinet to start no lower than 225Hz. You can accomplish this by using stout hardwood or metal bracing in a matrix (on x, y and z axis) internally that has spacing of no more than about 4.5"-5" from each other. This should push the 1st panel resonant frequency safely above the intended target point. The thickness of coustical dampening depends on the internal dimensions.

I recommend that mid-bass modules be used only in sealed or dipole(in case of using with an open back speaker system) configurations. Ported configurations, IMO, are only suitable for sub-woofer systems, as the port operation and it's complication with acoustical resonance(s) in conjunction with the acoustical dampening is an issue best avoided if possible when dealing with mid-range bandwidths.

-Chris

 

[lsiberian]

With a MBM(mid-bass module), you only need to worry about shifting the resonant frequency of the panels at least 1/2 octave over the intended low pass crossover point, assuming you use at least a 4th order slope. So, if you are going to cross the mid-bass at 150 Hz, you should shift the first resonance panel mode of the cabinet to start no lower than 225Hz. You can accomplish this by using stout hardwood or metal bracing in a matrix (on x, y and z axis) internally that has spacing of no more than about 4.5"-5" from each other. This should push the 1st panel resonant frequency safely above the intended target point. The thickness of coustical dampening depends on the internal dimensions.

I recommend that mid-bass modules be used only in sealed or dipole(in case of using with an open back speaker system) configurations. Ported configurations, IMO, are only suitable for sub-woofer systems, as the port operation and it's complication with acoustical resonance(s) in conjunction with the acoustical dampening is an issue best avoided if possible when dealing with mid-range bandwidths.

-Chris

I really appreciate the posts.

My crossover is a CX2310 which uses a LR 4th order crossover. So I should be fine. I plan to use an A500 to drive the module and maybe another A500 to drive the LR channels. Though I may need to figure a 3 channel solution.

Of course I'm not doing anything ported above the subwoofers ever again unless I build a Thor TL someday for fun.

I'll be using 13 ply birch ply for the box due to it's lighter weight. And I may have a great deal on a little bench top table saw. It won't be a bosch, but it will suffice for my needs.

We are only talking 0.6 cu ft internal volume. So I think the needs aren't extraordinary for dampening. I was planning to use 2 inch rock wool on every side and 4 inches on the back. It will take the box the size of my mains. Helping the aesthetics a lot.

 

[pjoseph]

Yes, many receivers have 'DIRECT INPUTS' on the back panel to feed external sources directly to all of the receiver's amplifier channels. However, I believe that you will find that you will not be able to feed the receiver's OUTPUT PREAMP JACKS to the DIRECT INPUTS and get the receiver to work in this configuration. It would be easy for the manufacturer to allow this to work with a firmware upgrade, but as it is, you are not likely to find a receiver that will do this. Of course, feel free to try it; maybe you will get lucky.
-Chris

I am confused about why the receiver would not work this way? does it automactcally disable either the pre-outs or the direct inputs?

Either way I plan on getting the crossover in the future after I get the Behringer ep2500, I will find out if it works then.

 

[lsiberian]

I am confused about why the receiver would not work this way? does it automactcally disable either the pre-outs or the direct inputs?

Either way I plan on getting the crossover in the future after I get the Behringer ep2500, I will find out if it works then.

You would essentially be looping the jacks so it's impossible for them to work this way.

You can only use the receiver as an amp or a pre-processor.