The method for adding Dacron to the HSE is to unscrew the back plate of the subwoofer module where the binding posts are located. Gently pull back the plastic plate, and the tuning port is revealed. Start by stuffing a handful of Dacron into the port tube. This method is described in the VR4 Gen III HSE owner's manual.
FWIW, my HSE are in a 16 x 19 room...medium to small by most standards. I measured the frequency response using a Stereophile Test CD and a Radio Shack SPL meter both with and without Dacron. The Dacron reduced the bass response by 2-4dB in the lower frequencies. The worst bass hump I have is at 31.5 Hz (+9 db). With Dacron the hump is reduced to +5 db. At 25 Hz and 20 Hz the measurements with and without Dacron are +2/+0 dB and -4/-6 dB
FWIW, my HSE are in a 16 x 19 room...medium to small by most standards. I measured the frequency response using a Stereophile Test CD and a Radio Shack SPL meter both with and without Dacron. The Dacron reduced the bass response by 2-4dB in the lower frequencies. The worst bass hump I have is at 31.5 Hz (+9 db). With Dacron the hump is reduced to +5 db. At 25 Hz and 20 Hz the measurements with and without Dacron are +2/+0 dB and -4/-6 dB