Wooden 511

[Steve Mac]

Anybody know the math of how large a diameter the lips need to be in order to minimize reflections appropriately for the 511? Anyone else thought about this?

[bfish]

I've forgotten the value (half-wave, full wave?), but it's a simple function of the lowest wavelength vs the circumference (path length). Olson defined it, GM could elaborate.

I ran it once for 511s out of curiousity, but all I remember was the result was too big for anything I wanted to implement, and I could think of no simple DIY method to deal with the radiused horiz. lips. The vertical sides would be easy enough with PVC or sonotube, but the full dimension would way overhang an A7 sides, and throw a big kink in your coax setup too.

The good news is that any rounding/smoothing/edge reduction you do is a good thing, even if it's not theoretically "big" enough.

The "foam at the mouth" UREI trick is another option.

[Russnohio]

Me, I ascribe to the dictum of don't fix what ain't broke.

<font size="2" face="Verdana, Helvetica, sans-serif">Exactly what I say. Altec engineers obviously had good reason for the vanes or they would'nt be there!

....but alas! It's our natural born instinct to tinker!


Russ

[Steve Mac]

Originally posted by Russnohio:
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Me, I ascribe to the dictum of don't fix what ain't broke.

<font size="2" face="Verdana, Helvetica, sans-serif">Exactly what I say. Altec engineers obviously had good reason for the vanes or they would'nt be there!

....but alas! It's our natural born instinct to tinker!


Russ</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">The question centered on mouth reflections not the vanes...

[GM]

JLMMC's math I referenced is probably the most correct, but way back when I had excellent results using the horn's LF cut off radius wrapped around ~270 deg, which is around 12" for a 511 IIRC and good enough at the XO's 500 Hz's ~4.32" radius, though still unacceptably large, so I terminated it on a large flat baffle with high density open cell foam to transition the 'lips' as a practical compromise.

At your 800 Hz XO point's ~2.7" radius, it may be too tight a curl. Regardless, I can't imagine it being of much use to you unless you encase the horns in an aero package/phase plug since there's such a complex reflection field in the big horns that I'm really surprised it sounds worth a toot. For sure my small scale experiments sucked overall.

GM

[Steve Mac]

Thanks GM...that's very interesting.
I think the intention might be to incorporate it in the final chute design. I must say at the levels I'm listening, I'm not hearing reflection artifacts...and I wonder if this may be partly a function of spl. I think the experiment I will try will be to build the chute...apply the rounding...and cover the back driver with a thick sock of sorts. I'm not yet through finishing up on the electronics side and getting a bit impatient to finish things up. But again, thanks so much for providing such valuable insight and experience!