Quote Originally Posted by RothwellAudio View Post
If I'm not mistaken, stuffing a cabinet with absorbent material will change the effective box volume (it acts as if it was a larger box), so a reflex design will have all its box/port tuning parameters changed and thrown off alignment. Ideally the stuffing and the port tuning need to be designed together, or at least the port tuning needs to adjusted after stuffing.
The Ditton 15 is not exactly a reflex design, but used an auxiliary bass radiator (ABR) which is tuned to the box volume and bass/mid, so I agree that it is not a good idea to alter the box parameters too much.

Rather than changing stuffing, I may consider an internal brace or two between the front and back walls could help the boxes structural rigidity. These could start from between the tweeter and min/bass to rear and between the mid/bass and ABR to rear.
If they were cut so as to be a tight fit and then glued in place, they could be beneficial without changing the box volume too much.

With speakers of this vintage, I would also think about replacing the capacitors in the crossover.