Side branch Hermoltz resonator....

[SeleMatt]

Evening all,

Some time ago, I fitted a pair of Novitec rear mufflers and a stainless cylindrical resonator to the mid pipe of my 2.2 Brera. It fantastic when it's not droning...when it's droning it's almost unendurable...atrocious...
4 cylinder hatch's and hatch type coupes are notorious for acute cabin drone. I have a few ideas on how to fabricate an adjustable side branch Hermoltz resonator but I thought it'd be wise to check and see if anyone else has already done this homework (which is essentially what length it needs to be).
Other than this dilemma, loving the car. Bought it last August and nearly done 10,000k's in it already. 
Thanks again for your pm reply Sportiva if you're reading this....just fleshing this out some more to see who else may have had a crack at one. 
Any advice much appreciated.