I really, really wanted to measure these outdoors so i could capture as much of the baffle step and minimum phase response of the woofer without room influence, but it's been a very rainy week and i live close enough to a major highway that i have to find quiet times of the day to do it outdoors without disturbing the neighbors - a paradox in ways. So for now I've temporarily settled for gated indoors measurements spliced with box model sims to derive a usable FRD file. The woofer is extremely well-behaved, whereas the compression tweeter required significant electrical shaping (which is fine as it's a very sensitive ~105+db driver. Normally you don't want to have to shape response too much as this indicated mechanical resonances but in this case it's just the horn-loading and mass-rolloff we're dealing with - both of which are acceptablr to equalize). Measurements were taken at 2M away and with the mic about 41 inches off the ground, where I measured the tweeter, the woofer, and then the tweeter + woofer (the third measurement is used to determine acoustic delay)
Charlie Laub's Active Crossover Designer was used to formulate appropriate biquads for the miniDSP. For a variety of reasons, the acoustic crossover ends up being a symmetrical 6th order in-phase centered around 850hz give or take - although I only really have a 2nd order electrical highpass on the tweeter. Reverse null for now is not the deepest possible, but still an acceptable ~ -20db or so and I was satisfied with the phase tracking in the narrow crossover region. With a steep slope like this, I managed to get the large woofer operating in a band where it is well-behaved, while the tweeter is well-protected. The crossover frequency itself should allow even horizontal polar response, but I will have to measure it to know for sure - which I'd prefer to do outdoors and after other tweaks have been made.
Some quick listening revealed good driver integration as far as I could tell, with a very clean, resolving, tight sound character. The highs have an interesting air to them, which I believe is because the SEOS has wider top-octave dispersion than beaming dome tweeters do. I can't yet compare it to the RAAL on my Phils, as I haven't listened to any "go-to Audition" tracks yet. Regardless, these speakers are extremely easy to listen to - and did I mention how beautiful the lower mids are? The word "clean" constantly kept popping up in our minds. The BA-750 is a fantastic driver as far as I can tell, and the TD15M is a treat to listen to.
As they sit in their final resting place (but no, they're not "100% finished - more on that in a bit)
Here's a runthrough of what's left off the top of my head:
- Settling on... a name.
- cleaning up/organizing their listening area a bit and playing with the crossfire.
- plenty of listening!! I'll post some proper impressions later today. This may also mean that I may, or may not, drop the tweeter level 1db as I couldn't decide what looked nicer in my sims (the ideal is probably 1db below the picture above.)
- further playing with filter designs in ACD until I can avoid using any "gain" filters at all and instead only cuts (which will help me figure out where I need to go with a passive design)
- measuring TD15M impedance in-box to verify tuning as well as for use in a passive crossover design.
- fixing the left speaker's binding posts (the outside parts snapped right off as we were moving them, even though the rest is still right there in the wood.. That's why I'm running wire through the port to the left driver. *sigh*
- Cutting, shaping, and adhering 30 PPI Reticulated Foam to the SEOS-18 to reduce Higher-Order modes within the throat and waveguide. IIRC This will reduce HF by about 2db/decade so that portion will have to be remeasured and of course the crossover will need to be adjusted accordingly to get the same frequency response.
- routing out a baffle for the SEOS so that it doesn't look like it's just sitting on top of the LF section (which it is) and then rounding over its edges. This might change the acoustic center and even diffraction-related frequency respons, so again this will require some remeasuring. This was going to be done by now but I came across quite a few problems - I don't have the right router guide, the plunge on my router seems to have broken and needs to be fixed (I can't even use a roundover bit right now) and I don't really have a lot of practice wood left to mess up on (I don't want to mess up on the little good piece of ply I have left that matches the baffle). I don't know when I'll be doing this, but I'm not in the biggest rush. It is however a notable part of the original design and hasn't been scrapped.
- Aesthetics: getting some red onto the baffle, painting the sides, flush trimming the backsides, sanding, etc. This will have to wait until next summer as these speakers were a pretty massively exhausting effort. I know they're ugly right now, but don't confuse that with me designing them to be ugly. The bright red waveguide should go nicely with the right dye, and I feel the grain on the baffle ply will really get accented as well.
