At least the exact mesurements of the Speaker would be interesting. Since Sonos doesn't repair there are no original spare parts. So it would be necessary to get a mid-woofer or a broadband Speaker from another Company. I find the mesurement Information to buy a Speaker very incomprehensible, so it would be interesting to know about how to get the correct size. I think that if you would buy a good one with relatively high specifications in that category it should be ok. If i find one wich will work, i will let you all know here in the comments.