I plan to watch the inside of my eyelids for a while, as I relax in the sweet spot of my stereo. After about five months, my "new" open air drivers are really sounding good. They are breaking in nicely.
As much as I would like to eliminate the constriction of a sweet spot, there is still a place, roughly hourglass-on-its-side shaped, in front of my speakers where Blumlein's "invention" comes to near perfection. Any good recordings, especially those in jazz, done with proper Blumlein pair pick-up placements sound so large, distinctly separated and well defined, it is almost like real instruments in the room (please excuse cliche). These newish higher Q drivers are better at reproducing lower frequencies than the customised JBL fifteen inch drivers I had been using.
They are not as efficient (by six dB
), but they reproduce a flatter response in their range. I use a simple coil (first order low pass, adjusted for roughly one hundred twenty Hertz - yep, it's huge) in series with the pair of drivers, which are in parallel with each other. The resistance of the coil actually raises the total Q of the pair of drivers to a bit over 0.8 (combined), so the lower frequencies are slightly enhanced. This slight rise in response toward the lower frequencies is offset by the open air design of my baffle (which I am still working on perfecting) and the semi-cardioid propagation pattern is channeled into the room by my Super Secret Squirrel solid diffraction column which sits behind the open back baffles on each side. The actual shape of that truncated triangle column, used in this application, is what I am trying to find a way to patent, because it WORKS.
The drop off in low frequency efficiency is offset by a tiny resistance in series with the eight inch full range driver, which sits atop, angled slightly upward to correct for phase alignment. Of course, the R also raises the total Q of that driver, which now falls in at about 0.72 - really close to perfect!
The only issue is that I hate to lose the incredible efficiency I had enjoyed for a couple of years. I can still use my matched pair of SET two watt tube amplifiers, but the difference in visceral impact when I slap my old McIntosh five hundred watt per channel PA amplifier on them is quite arresting. There is a slight loss in tonality with the solid state McIntosh, compared to the modern SET mono-block amplifiers.
... or were you questioning my break in period. Low frequency drivers usually continue to change for about a year of semi-constant use. They are settling nicely, though.
