Multiway off-axis irregularity - causing midrange distortion (Long post)

[rick57]

Thanks for your thoughts dwk.

"Below this things go omni" - if you're using a box sub.
I'm intending to use SL's "compact W baffle" dipole woofer below about 90 Hz - figure 8 radiation, then cross to a midbass horn 90 - 600 Hz, and am trying to optimise the integration, hence the interest in CD. Perhaps it won’t help me with this.

Cheers

 

[dwk123]

Thanks for your thoughts dwk.

"Below this things go omni" - if you're using a box sub.

Well, I was really just talking about the horn itself. The ability of a horn to control directivity begins to fail below a certain point. I'm still working through this part of the Geddes book, but at a rough estimate that gets bandied about it seems that it's about 90 degrees around the point where the wavelength equals the circumference of the mouth. For 90Hz, this would be about 3'x3'. It will of course just get more omni from there.

I'm intending to use SL's "compact W baffle" dipole woofer below about 90 Hz - figure 8 radiation, then cross to a midbass horn 90 - 600 Hz, and am trying to optimise the integration, hence the interest in CD. Perhaps it won’t help me with this.

Cheers

It depends - if you can use a 'full size' 90Hz horn then it might work. I'm not aware of many folks using full-sized midbass horns, but then I'm pretty new to horns in general. A 3'x3' mouth isn't small, and it seems that most midbass horns use either a 1/2 or 1/4 size mouth and then rely on boundary reinforcement to bring the effective mouth area back up. In this case, I don't think you get much pattern control.

Dipoles and CD horns should work pretty well together, though. I know that John Hancock (who seems to have dropped off the face of the earth) said his Unity horns (60-degree conicals, xover at ~300) never sounded 'right' until he paired them with dipoles from 300 down. If I had more room, I'd be doing this, but unfortunately I'm pretty constrained as to how far I can get things out into the room.

I'm actually going to experiment the other direction - build the speakers into the corner, so that in the bass region the on-axis and power response are the same. Yeah, problems with modes etc, but I'm hoping that room correction techniques will mitigate that somewhat. This will transition around 300 to either a 60x60 or maybe 60x40 CD horn - either a refinement of my unity prototype or a cone-driven mid.

 

[jeff mai]

BTW - I believe that Earl said in another forum that he never patented the OS waveguide forumlation.

He hasn't been awarded the patent, but he did file an application that was recently published on the US Patent database. I found it through the search engine there.