Hi Hassan,
You have several options:-
1) Do nothing (VERY bad idea, as your speakers will sound terrible and are likely to suffer damage due to lack of air resistance in the cabinet).
2) Ask an expert such as Dillen to re-foam the ABR panels (assuming that you still have the metal panels)
3) Ask your local B&O dealer for a Tuned Port kit (see the end of the following thread for details) at a cost of around £60 per pair. This makes the RL60 sound AWESOME, a BIG improvement and well worth the money!
http://forum.beoworld.org/forums/thread/42542.aspx
4) (Last resort) patch up the ABR holes with thick wooden panels cut to size so that no air escapes. This will mean you lose a little bass response, but will save you damaging your speakers.
I went for option 3 (Tuned Port conversion) and did a capacitor upgrade at the same time. As you will see from the linked thread above, I am very pleased with the result!
Best regards,
Steve.
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