You are under a severe misapprehension. A 6.5 " driver will not as a rule perform below 50 Hz. The low frequency cut off is determined by the Thiel/Small parameters, especially the free air resonance. For your drivers this number Fs is 37 Hz. Usually frequency output falls off somewhat above Fs. This is the case with your drivers. This is the frequency plot published by Vifa.
Note that output is falling off rapidly below 60 Hz.
Your next mistake is to assume adding drivers will extend the lower frequency limit. It will not. You could have a thousand drivers and the output would not extend lower. It would still fade starting at 60 Hz. What adding drivers would do is increase sensitivity and sound output, but NOT bass extension.
There is nothing wrong with those speakers. They are working as designed. If you persist in driving them with frequencies they can not reproduce, you will just incite useless cone motion and damage the drivers.