Allow me to be terse. I know many of you're interested in this section, my English vocabulary is quite poor to desribe my impression.
At first, apply sweep tone by test CD. No peak nor dip is felt around duct resonance.
First impression was that it is dried tone.
Impression in a few day after was a little foggy, less clearness, but energish. Sound of electlic bass is pop. I changed my recognission on 4inch full range driver.
After some more days, It becomes quite good, no problem.
By the way, it is driven by ELEKIT TU-870. At this time, I changed my 6BM8 from Electro-Harmonix to NEC. This NEC tube may some sort of rare item.
These are guessed that manufactured by NEC and OEM'ed to SUMSUNG.
I can't distinguish the difference of tone by each tubes, feeling in depth direction is enhanced.