voigt pipe and tqwp new concept?

[midrange]

I have kept some records of designs (and results) and thought an experiment I did a few years ago would interest fellow diyaudio members.
This particular experiment involved a plain straight sided tube about 28" long, about 6'' square, closed at one end, with 2 Monacor spp 110 drivers mounted opposite each other a few inches down from the closed end, one on the front and one on the back, both pointing in the same direction and connected in phase. The back driver had an optimum closed box mounted behind it (probably about 4 litres) stuck on the tube like a square wart. The tube had no sound deadening in it (to maximise the effect)

Note the 160Hz, 400Hz, and 630Hz responses. Above 800Hz the measurements are identical. From 160Hz up the both driven figures are +/- 1dB.

Top line; 1/3rd octave warbled input centred on the following Hz
Measurements taken about 6' in front of front driver

Hz 50 63 80 100 125 160 200 250 320 400 500 630 800

Front driver only 54 63 68 69 71 73 68 68 68 71 68 72 68

Both drivers 54 63 68 70 71 68 66 67 67 66 68 68 67

I would have thought that by choosing the closed box characteristics of the rear driver (sensitivity needs to be the same) that the bass "boost" of a voigt pipe could be used and the frequency of the cancellation in the pipe could be optimised.