Measuring and voicing waveguides v.s. flush mount tweeters

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I'm about to begin my first measurements/crossover design of a system with a waveguide. I was wondering if people who've worked with waveguide designs do anything different when taking measurements and designing the crossover. Here's the measurements of the tweeter on a flat baffle and in the waveguide: As you can see there's quite a bit of "droop" in the response off axis response for the WG compared to the flat baffle. I'm thinking if I approach this like a standard design the end result is going to sound dull/rolled off because of this. If I'm used to using on axis driver measurements for crossover design, should I use off axis measurements (let's say 30-40 degrees) for a project like this and plan on pointing the speakers more or less straight ahead? (I usually measure and listen about 5-10 degrees off axis to my non-waveguide designs.)
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It depends on the waveguide, and your techtalk link is broken, but the answer to using 30-40° off-axis measurements is almost definitely no. If the -6dB pattern is close to constant directivity, you'll probably want a gently falling (3-6dB) response on-axis, and if the pattern is narrowing at HF maybe a more flat response on-axis.
Looks like you could treat it as an approximation of an 80° constant directivity waveguide to me. I'd design on-axis, incorporating compensation to flatten the on-axis response in your measurement to something like this below, and crossing over to where the midwoofer has an approx. 80° pattern, i.e. -6dB at +/-40°.


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The best way to do it is to find a woofer at the particular size where it's directivity (due to beaming) matches that of the waveguide in the proposed crossover region. You can study this design for reference:

The Seas ER18DXT ported two way

There is considerable variation for woofers' directivity but if I was to give a very general reference (for a 60degree directivity) a 10" driver should cross well to a waveguide around 1kHz, 8" @ 1.5kHz, 6.5" @ 2kHz, 5.5" @ 3kHz, 4" @ 4kHz.
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To keep matters flowing, once you decide whether the drivers can be matched, and where (possibly 3k5), then you might go ahead and design a crossover in the usual way. The downward droop with the tweeter response isn't a bad thing regarding why it happens, but you should still straighten it up or maybe leave some of the downward trend if it sounds better.
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