1.) Mike - sorry, when I say midbass I'm speaking about 100-300hz. Might as well use numbers!
2.) I'm fairly sure that dip at 220 hz is a reflection due to the distance of the woofer to the ground. It shows up in every measurement where I was using the old modified box. If you look at the measurements of the front corner vent cab it's gone because the driver center is lower. Good point about it affecting the polars as it very well could, though I'm mostly concerned about 300hz and up.
3.) I'd like to have my cake and eat it too
, but I just don't see how this is possible. The whole point of this is
the increased directivity and the lower sensitivity is the trade off. I'm willing to trade that for the polar pattern to be honest. I really don't see how this can be improved with this kind of design....it's the nature of the beast. My version with the 8" side drivers did well to control the pattern from 300hz+ while leaving the region below that omni so there's little sensitivity lost where I believe it would matter most: at lower frequencies. The trade-off there is more $$ in drivers and amps. This was the direction I thought I'd go when I started all this but when I saw I could get close with the acoustic resistance box I switched gears.
I tend to listen at about 80-85dB, and you could figure 20-25dB for dynamic peaks on good recordings (to be honest the stuff I listen to isn't that good). Is that 2dB of attenuation really that huge of a deal with quality pro drivers used in the home? These will be high passed at 80hz.
4.) I didn't take the time to eq everything flat because I was working on 5-6 different iterations each time I was out. It would increase the SNR to be sure, but I felt that I was high enough above the noise floor that I could get a good picture of the polar pattern as is.
5.) I increase the angle as I get wider out for a few reasons. One - to spare my neighbors having to listen to 30 sweeps for each set of polars
. Also it saves time. I don't think it's as critical to be as detailed at the wider angles since it's far out of the listening window, but it would be worthwhile to check it out once I get close to a final design. I have a thread about some diy waveguides (quiet now) going over on DIYA, and Geddes mentioned that this is the measurement scheme he uses. To me his reasoning is sound.
I have a lazy Susan turntable I built so doing this is all pretty easy once I have everything setup.