ctrl
Major Contributor
This should be possible.I think most people would be interested in at least getting ~100 dB to 105 dB of peak output @ 1 meter with realistic amounts of amplification (~100 to 300W with [email protected]).
According to the manufacturer, the SB15NBAC-8 delivers about 85-86dB, the 4 ohm version about 88dB in infinite baffle @2.83V above 200Hz.
As @TimVG said, the baffle step, for the speaker top, is about -4dB around 200Hz compared to the infinite baffle. So in the worst case the driver in the top speaker cabinet reaches about [email protected]@1m@>=200Hz.

This number also depends somewhat on the baffle size of the bass module. With a 0.26m wide bass module (0.8m height), the sound pressure around 200Hz increases by a little more than 1dB.

Thus, the baffle step loss @200Hz, compared to the infinite baffle, should be a little less than 3dB.
This would put us at around 83dB@200Hz@[email protected] for the eight ohm driver and around 85dB for the four ohm driver.
If the bass module is designed powerful enough, the sound pressure level can also increase by one or more dB, depending on the crossover tuning (slight low bass hump).
In addition, there is another effect which, according to the simulation, is caused by the lateral slots.
The slots radiate the phase-inverted sound from the rear of the driver. Due to the damping and the detour caused by the construction, a frequency-dependent phase shift of the phase-inverted sound occurs.
This leads to the fact that, according to the simulation, the sound pressure level of the driver and slots, in certain frequency ranges, is higher than the driver alone.
Here is the simulation of the speaker top axis frequency response of woofer plus slots:
blue - woofer alone
green - slots alone
red - summed sound pressure level of the speaker top

At 300Hz, the sound pressure level is increased by about additional 1.5dB compared to the woofer alone.
The achievable peak sound pressure level is therefore, depending on the bass module, on the level of large floorstanding speakers, such as a Revel F328be.
Excursus:
You can also see (in the graphic above) very well why the crossover frequency should not fall below 200Hz, because there is sound cancellation due to the phase shift between the driver and slots and therefore the harmonic distortion will increase significantly (when the sound pressure level of the speaker top is linearized below 200Hz).
At 100Hz the cancellation is over -4dB compared to the woofer alone.
It could be that some slotted speaker manufacturer may have overlooked this "feature"
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