When we (Arab Instruments) build mother of pearl doumbek, there are some aspects that we need to take into consideration.
We use extra layer of aluminum for all our doumbeks , this is why our "New Generation Darbuka" weigh around 11 lib (5 k"g) and our sombaty plus darbuka weigh around 13.64 lib - 14.3lib (6.2kg - 6.5kg).
This extra layer produces higher quality Arabic sound which make Arab Instruments darbukas to be on the top in terms of sound and quality.