I recently completed a Zaph ZRT 2 way build.
The cabinets are 3/4 inch plywood, to the same dimensions as the recommended Madisound enclosure. I ordered the upgrade crossover (with the foil inductor).
I used the default port tuning: 30 Hz, 2 inch port, using only the outer and inner flare.
The speakers sound pretty good to my ears, with one major caveat: lack of bass.
Description of the issue:
My only basis for comparison is my Seas Odin kit, which was hooked up in the same room and to the same amplifiers and sources. The Odin's bass was occasionally a bit boomy (some notes tended to be a bit louder than others), but it was overall quite a bit louder than the ZRTs.
Bass sounds ok (althogh quiet) on the ZRT when only bass instruments are playing, but becomes buried in the mix when other instruments come in.
From doing sweeps with a test program, it sounds like there is major rolloff below 100 Hz and there is very little sound below 70 Hz, at least as compared to the Odins.
Things that I have tried:
I have verified that the woofers are wired in phase.
I have tried putting in a shorter port, using only the front half of half of the port assembly (~1 inch): this seems to increase the amount of bass slightly, but the bass is less precise.
When I remove the port entirely, running the system with the large port-hole in the baffle open, the bass gets much louder. However, it is not controlled and has something of a one-note quality.
I have tried listening through two different amplifiers (a Marantz solid state amp rated at 25 watts in class A and twice that or so in AB, and a Consonance push pull el34 tube amp at ~40 watts) and have found that the speakers exhibit a similar lack of bass response with both amps.
I don't know if it's of any significance, but strangely, with the tube amp, the sound is clearer when the speakers are plugged into the 4 ohm tap than the 8 ohm tap (the ZRTs are 8 ohm speakers I believe). There is mild but audible distortion on the 8 ohm tap which prompted me to try the 4 ohm. I only ever ran the amp with the 4 ohm tap for the Odins.
I had discussed this issue on the diyaudio forum, here, and had tried some of the suggestions: