Need speaker enclosure acoustics info

My question is about speaker enclosures. Given any bass reflex type of speaker enclosure (with only one multi-frequency driver) what would be the effect of putting an internal baffle behind the driver? Just for reference say enclosure is 2X high by X wide by 1.5X  deep and the driver is .5X circumference. (the port is not important to the question) and if there was a round stiff wooden baffle size .5x in circumference that was attached to thin stiff dowels to hold it in place very close to the rear of the driver (inside the enclosure) so that air could go around it and reach the rear of the enclosure, would that baffle compared to no baffle cause a) overall noticeably reduce the dB output of the driver b) overall increase the dB output or c) not change the overall output noticeably? 

This assumes that the baffle would alter the resonance of the enclosure and affect some frequencies and not so much others but ignoring that looking just at the output of the driver what's the effect on the driver dB output overall? 

Thanks if anyone can give this a shot... 




We don’t normally model weird-o requests like this. :D

The question is really whether the internal air suspension would continue to work as a simple spring, and the answer is maybe. Depends.

However, part of your question is easy to answer. The sensitivity of the driver has nothing to do with the enclosure. It’s all in the magnet, voice coil and suspension losses. This is why (contrary to myth) bass reflex enclosures and sealed drivers have the same sensitivity. What’s different, when either can be used, is the -3 dB point will be lower, given optimal enclosures for either.

Put another way, the enclosure size (bass reflex or sealed) only affects the low end of a driver's output. The mid to upper end of the driver's output "ignores" the air space behind it.  At these frequencies the baffle dimensions and type however do come into play.

Having said this, weird-o internal baffles may have frequency dependent effects that may be best built than discussed. I’m sure there are ways to create frequency dependent effects due to reflections and constructive and destructive interference.  It is quite normal to have internal bracing with lots of room for air flow to create stiff enclosures but we must remove their volume when calculating the optimal enclosure space.

Thanks I guess I should have revealed that my actual reason for asking is related not to a speaker enclosure but to the internal workings of a resonator guitar (aka dobro). The resonator guitar has a "speaker" cone in the top of the guitar where a large round hole has been cut out. Then the aluminum cone is suspended on a lip of the top of the guitar cutout and then the strings are strung over a "spider" bridge (looks like a spider web) that rests on the corners of the cone and a tension screw is attached to a hole in the center of the cone and the middle of the bridge and tightened to couple the cone and the bridge. So in essence the guitar becomes a speaker enclosure and the vibrating cone acts like a speaker driver but being mechanically driven by the string excursions. My question relates to a particular dobro design where the reflector I mentioned aka baffle is suspended behind the cone. Other modern designs leave the guitar body open rather than have that reflector baffle and the question is what exactly is that baffle doing? The design was patented by Saga Music instruments and called a "power flex resonator chamber" and I think the idea was that the reflector would create more output from the guitar but this does not seem to work because those guitars have lower weaker sound than ones without that baffle. Someone took out the baffle of a guitar and installed sound posts to keep the top from collapsing from string pressure and the result was a much louder better sounding guitar. I am about to also alter one of those guitars and was curious to know scientifically acoustically what that baffle would be doing in theory. In reality it does not increase the sound vibrations in that system. So I think your reaction to this being "weird" was because it's not actually a speaker cab design. And I believe this baffle system was intended to create a better low end which it does not. Thanks for your answer it helps 

"power flex resonator chamber" and I think the idea was that the reflector would create more output from the guitar but this does not seem to work because those guitars have lower weaker sound than ones without that baffle.

It could be that the idea was a tuned resonant cavity with more output at a particular range, creating a signature sound. Without models and experimentation I have no idea how effective it would be, but go to DIYaudio in the multi-way speaker driver section.  There are some people  there who love to play around with finite-element analysis.

I think you're right they were trying to create more bass response but did not work. Thanks for your reply I'll check that out