OK..., got some RTA screen shots showing the open vs closed back with the 2251Js in ~1/2 cu ft cabinets. The only filtering being used is a 33.6 mfd cap inline with the positive terminal and the speaker is set to "large."
The microphone was placed inline between the two speakers at a distance of 2 meters on a tripod sitting on the couch cushion (legs in). "Close" micing was not performed because this defeats the purpose of the open back. No eq of any type is being used. Of course this does include the effects of the room.
The intent is to run these from ~250 to ~2,500 Hz.
Note that with the closed back, the frequency response "falls" as the frequency is reduced such that between 250 and 2,500 Hz there is a span of about 16 dB (i.e., -83 to -67 dB).
But with the open back, the frequency response remains fairly flat dropping substantially below the crossover point, which is essentially what we want here. The span is reduced to about 9 dB (i.e., -74 to -65). The overall volume is also louder.
It is interesting that even though the closed back
sounds like it has more bass, the open back must by responding with things/reflections in the room causing more deep bass. I am simply switching between the two speakers and recording the results without any provisions to equalize their volume. What you see is what the mic hears.
