Effects of "Horn-loading" FRD

[EKwisnek]

Hey guys n' gals,

I'm currently working on a top-secret project utilizing the buyout Tang Band W3-881SI. I've decided to use a sealed .05 cubic foot enclosure given the driver's high Qt and extremely limited Xmax. Through a lot of tape-on baffle testing and some input from my old lady, I've decided to rear-mount the driver. My question is in regards to the overall effect that rear mounting, plus using a 1/2" round over bit on the front baffle. I've essentially "horn loaded" the driver, however minimally. In testing I've noted that mounting the driver in this way had a different effect than I though it would. Instead of increasing off-axis response, the polar response became more beam-like. Perhaps this was due to the driver being recessed and the 1/2" radius not really horn loading the driver in a traditional sense?

Also, given the driver's rather poor sensitivity, would mounting the driver in this way provide a nominal increase in system sensitivity?

Thanks!

EDIT: Also - would mounting the driver in this way affect diffraction?

 

[rjbond3rd]

Instead of increasing off-axis response, the polar response became more beam-like.

In my opinion, you are hearing the predicted effect of a waveguide, that is, a narrowing of the radiation pattern into a smaller solid angle. Thus dispersion is not as wide. So it isn't serving your intended purpose, but that doesn't necessarily mean it sounds worse.

For example, the standard vintage Klipsch tweeter was found to sound and measure a bit worse when front-mounted, because the rear-mounting (which looks atrocious) actually left a little cushion of air that was just barely enough to suppress some bad behavior at its bottom end.

But not all wavelengths are affected equally by the shape of this "hole" you have, and thus you are almost imposing a random tone control on the driver's response. However, I wouldn't lose too much sleep over it, because whatever effect it has is probably dwarfed by the rest of the energy coming off the (presumably untreated) baffle.

So you might consider using a layer of thick (real) wool felt to attenuate the baffle's diffracted energy. That might end up having benefits far in excess of the (slightly?) reduced dispersion.

 

[EKwisnek]

you are almost imposing a random tone control on the driver's response

I don't currently have any plans for treating the baffle because it would ruin any plans I had for these being stealth mini-monitors upstairs (where real people live). I haven't really considered a BSC circuit at this point, but I'm concerned that this new "tone control" would already be coloring the response in an unpredictable way.

 

[rjbond3rd]

It is in our nature, as audiophiles, to worry about all things great and small. But problems should be solved according to their magnitude.

If you need BSC, but choose to skip it, that would be orders of magnitude more significant than rear-mounting. Further, there will be gross distortions of the frequency response due to floor bounce, ceiling bounce, diffraction from that shiny audiophile stand, to say nothing of the grotesque distortions from room modes, which would make your hair stand on end should you choose to measure them.

But if you solve the problems according to their magnitude, you will sleep well at night!