CTC Distance: confusion with dual drivers

[dlneubec]

I'm trying to plan for my first 3way design and am concerned about CTC distance and the crossover points that this suggests.

In my case I'm doing an hybrid omnidirectional. It may have two woofers, firing up and down at each other and two mids firing similarly. The tweeter will be front firing, perhaps with a waveguide and rear firing tweeter (see the prelim plan below.

Here is my concern. When you have pairs of drivers, how do you figure the CTC distance; from the nearest two drivers, the furthest two or from the middle between them? How about in this application where they are up and downfiring?

Secondly, in my prelim looks at it, I get the idea that in order to get the drivers in proper CTC distances, that I can't get the crossover at a good point to avoid mid and woofer floor bounce cancellation. They seem to fight each other, unless I'm missing something (probably). CTC would suggest a max distance of 18" for a 750hz crossover. For example (using BoxyCad2) if I have a ear height of 37" and a distance to listener of 11.5', if my mid is at 35", then my woofer has to be at 9" to get a recommended 750hz crossover, for a CTC of 26". I have to lower the woofer to under 29" and have the woofer at about 11" to get a good match between the two. If the tweeter is within 6" of the woofer, that puts the tweeter at only 35". That seems too low for both. Shouldn't they both be near ear height? :??

Can anybody give me some guidance with these questions? If they do fight each other, which is the most important to go by and how do you resolve these seemingly conflicting issues in a design?

Thanks!

[dlneubec]

Here is a third related question in regards to ideal distances that I forgot to mention in the first post. When you have drivers facing each other as I have in this plan, I assume there would be an optimum distance they should be apart to avoid resonances and/or diffraction issues.

Would you look at the minimum wavelength and make sure the baffle to baffle distance is something less than that? If so, what wavelength? At the crossover point or some db amount below that?

[dlneubec]

Bump.

No one interested in helping?

[Paul W]

Dan,
There are so many things going on with this concept that any "help" I provide may be a bit of an overstatement :roll:

The physical appearance is quite impressive, but a few things seem a bit odd.

-Time alignment seems like a wasted effort with a radiation pattern so broad and variable with frequency. Omni at LF, perhaps a misshaped disk midrange, and narrow front/broad back HF...and everything but LF will change with direction/listening axis.
-The parallel surfaces behind the midrange may introduce unwanted resonance (which rounded convex flares might help).

Results would be more predictable if the design were simpler. For example 4-6-8 or 9 RS-180s in a square, hex, oct, etc cabinet with an equal number of tweeters firing in a circle. Just a big 2-way with low excursion/distortion and great power handling. If you want to do something more complex, make it a 2.5 or 3-way but maintain the same radiation pattern for 360 degrees.
Paul

[joecarrow]

Yeah, Dan- you're starting to swim in the deep end here. I try to lend a helpful comment from time to time, but this is getting pretty out there.

One experiment I'd suggest, however, is to take two RS52s and put them on facing baffles as you've suggested. Based on my best guess, you're going to get some cavity resonances within their passband, and you'll have to change your strategy or play with shapes to control that. You're doing a great job trying new things and measuring the results.

I think you're really going to want to get a woofer close to that mid- they're not quite tweeters, but they sure don't go as low as a cone mid.

[dlneubec]

Hi Paul and Joe,

Yup, it's way out there, but that's what makes it fun! :yeah:

Thanks for trying to help. I did some tests that I posted over in the Mentor II omni thread which makes it look like a single RS52 will work. Maybe you could take a look and see that you think of my results.

Anyway, based on the possibility of using just one RS52, I've worked up a deisgn with a single Rs52 on a 30º sloped baffle (might need to be 15º, but need further testing from behind the sloped baffle). This deisgn is a little more like the Beolab omni. Take a look at the pdf below and see what you think about my questions with this plan in mind. A smaller form factor tweeter would make it possible to reduce the tweeter to mid distance more. I'm thinking along the lines of 600-700hz and 2400-2600hz crossover points. :sos:

[dlneubec]

BTW, I forgot to mention that BoxyCad2 suggests that 570hz is the optimum crossover point from a floor bounce perspective with this latest configuration.