D27TG-45 with rear chamber replaced with a 2" PVC end cap, stuffed with felt.

Notice how much attenuation there is in Fs (peak dropped from around 14 ohms to 9ohms). The biggest difference is a lowering of the Q. There is only a small increase in the Fs, to around 550hz.

Note also the suppression of the 2k resonance, although there is a bit of a small, very low Q bump at about 1.5khz. I'm not sure what causes this, but it may be that my stuffing job wasn't perfect. I did nearly fill the cap and made sure that a flat piece of felt was pressed against the vent opening. This, I think, is required for the elimination of other non-Fs resonances.

This does seem to argue for the benefit of a larger rear chamber. I didn't actually try it stuffed without felt pressed against the vent, but I believe that the felt should be pressed this way to eliminate the non-Fs resonances.

With the above qualification, this appears to be a useful, cheap modification if done as described.