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I make my Lyra's out of 5/8 inch Partical Board. I was worried about the Particale board being "too lively" so I lined the insides of the box with a "camping mat" bought at K-Mart for 3 or $4.00. It worked GREAT and my cabinet is just as "dead" as 3/4" MDF.
I built my Lyra's with a Vifa D26 tweeter that I happened to have on hand, they are otherwise "as the Reverend specified".
I like mine a LOT - they are better than described in the Lyra text.