# Fun with waveguides



## drumdude (Aug 26, 2007)

I have been reading on here and elsewhere about waveguides. What got me interested in them was noticing many commercial studio monitors have them. I had a pair of old speakers laying around with 2" cone tweeters in them. I never liked the sound of the cone tweeters so I had nothing to lose by opening them up to experimentation. They appear to have a proper crossover ie no single cap on tweeter/full range mid. the tweeter wasw set back apparently for some time alaignment. I also had some old 1" dome tweeters laying about. So I hooked them up in place of the cones... already sounds better. tweeters are a bit laid back though, they must be less efficient.










Hmmm I have been waiting for an excuse to play with waveguides. and I could use an efficiency boost and a midrange boost. I know they are supposed to be best used on compression drivers but I have heard them on domes too, so after banging a rough guide out of some scrap, here is what I have. [img]http://www.parkersburglive.com/video/waveguide.jpg[/img] Ugly isn't it? I see no sense worrying about looks till I find out the result. So I fire it up. and give a listen. Midrange sounds more detailed, highs less harsh. Just to make sure I am not weighing my afternoon of work on my opinion I hooked up the modded and un modded speaker side by side. covered then with an acousticly transparent cloth, and dragged my wife out to the garage. I them proceded to A/B the hidden speakers. Her exact words were "the midrange is more clear on the one on the right". I think this is turning out well. So I pull out the trusty Radio Shack SPL meter and fire up REW. Here's what I end up with. 













*Before*
speaker with dome tweeter measured top to bottom. on axis, 15 deg off axis, 30deg off axis, 45 deg off axis with 1/3 octave smoothing.









*After*
speaker with waveguide measured top to bottom. on axis, 15 deg off axis, 30deg off axis, 45 deg off axis with 1/3 octave smoothing. the dip in the midrange seems to have moved down in frequency but less severe, the highs are tamed a bit too. Still looks like a bumpy ride to me, but I'm a newb so what do I know:coocoo:

I know you are supposed to design the crossover for the speaker, not the other way around:hide: But I still think I learned a bit from this experiment. I may try to make an improved wave guide if anyone has any suggestions.


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## Bill Fitzmaurice (Jun 14, 2008)

The difference between a horn and a waveguide is mainly whether or not the throat is smaller than the driver cone or not. Otherwise they behave in much the same way, most especially in acting as low-pass filters. That accounts for most of the difference between your two results.


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## drumdude (Aug 26, 2007)

Thanks for your response Bill. The tweeter used is a 1" dome. The current model has a 1 1/2" throat which matched with the cutout in tweeter front plate the closest. It looks like an 1 1/4 throat would meet closer to the actual size of the tweeter. any theory on how this would affect response, or would it be so minimal as to be insignificant?


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## Bill Fitzmaurice (Jun 14, 2008)

drumdude said:


> Thanks for your response Bill. The tweeter used is a 1" dome. The current model has a 1 1/2" throat which matched with the cutout in tweeter front plate the closest. It looks like an 1 1/4 throat would meet closer to the actual size of the tweeter. any theory on how this would affect response, or would it be so minimal as to be insignificant?


 Where the throat is a wavelength or more across it's not loading the driver as a horn, which is why you're not getting gain above 9kHz or so. Smaller will raise the frequency of loading, but that's got nothing to do with the cone size. An Sd to throat area compression ratio isn't a necessity, it's just usually done that way to allow more driver Vd.


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## drumdude (Aug 26, 2007)

So if I understand correctly, if I can get the throat down to 1 1/4" or less I might get up to 11kHz or so before the top starts rolling off. I will have to try it.


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