You are using a strange construction. Why?Does anyone care to predict what the overall STC of this set-up might be, and predict how much drum sound will leak to the outside?
Using INSUL demo to try and get a rough guesstimate, an STC around 58 dB with the TL at 50 and 63 Hz around 20 dB.
The low end of the drums will be quite audible. Midrange and higher will not.