# CTC spacing/comb filtering



## egoaudio (Oct 6, 2008)

Hi everyone,

I've been a lurker for a little while and would like to say thank you to all of those who have asked questions and given great answers in return. I've learned alot from all of you. My turn for a quick Q.

I'm building some three-way towers, this configuration, WmmtmmW. Actively processed (DCX2496) and I need to know about CTC spacing. From what I have gathered you take the CTC distance and find the wavelength of that distance. Do you want to HP vs. LP x-over above or below this to keep comb filter down? What's safe? Do I only take CTC spacing into consideration when considering tweets and mids spacing (I'm guessing no)?

This seems like info I need to know and many people talk about it like it's second nature but it's not to me yet. 

I appreciate any help. 

Best regards,

Erik


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## JCD (Apr 20, 2006)

Ok, I'm working on some serious fuzzy memory here, but for a proper LR crossver, you want the CTC spacing to be (speed of sound)/(crossover point). So, assuming a speed of sound of 1128ft/sec (or 13,536in/sec) and a crossover of 2461, you'd want a CTC of 5.5".

A quick search of the internet, and I found this paper -- Link. Be warned, I only briefly glanced at it and my ears were already leaking brain fluid.

Driver placement also makes difference with the effects of edge diffraction. There is an excel spreadsheet that helps with the optimal placement that I've found.. link.

After that, I think you've exceeded my paygrade... :bigsmile:

Good luck.

JCD


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## avaserfi (Jul 5, 2007)

Ideally, center to center spacing is half of the crossover wavelength or less (the less the better). Now, often times this isn't possible, for example: a 3kHz crossover would require about 2.25" CTC distance. Larger distances can and often times will create anomalies that can be dealt with via crossover implementation. If you do have to go larger than half the CX wavelength try to keep it under 1 wavelength to minimize these anomalies.


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## egoaudio (Oct 6, 2008)

Thanks to both of you gentelmen. I've done some further reading and I can say that I completely understand it now. Thanks for the help. 

best regards,

Erik


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## brianpowers27 (Sep 7, 2008)

There is a nice javascript program out there that helps to visualize the effect of comb filtering as it pertains to phase cancellation.

The flastad wavebox. (Since I am a newbie I can't post the url link yet.)


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## Lucky7! (Jan 7, 2008)

http://www.falstad.com/wavebox/


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