Question about sound proofing: Home Theater in a townhouse

I recently bought a good quality townhouse which has your typical layer of insulation, a layer of fiberglass fire retardant, and a 5 inch gap of air between me a https://9apps.ooo/ nd my neighbor. Anyone with experience living in a similar situation, do you think this is enough sound proofing to avoid a noise complaint from my neighbor? Or should I invest in sound proofing the entire wall?

issue got solved

Decouple from the floor, TOO.  You might be surprised how much that helps your neighbors and YOU.  Subs, and mains... Enjoy the new digs ay...

Regards

Put whatever you want on the wall,it will NOT stop deep bass from thumping away next door..Time for a new headphone rig.

BT headphones with a double BT transmitter for each pair.

you cannot generalize about how effective your situation is unless you test it. unlikely it will be sufficient to allow for reasonable listening without considerable sound leakage. and restrict your sound levels and listening time flexibility. 

if you do want to add a layer of additional sound insulation, i do recommend a product (i have used) which will give you maximum sound attenuation for the depth it will use, that is Quiet Rock 545. it’s an inch and 1/4 thick but will perform like 5 sheets of 5/8" sheetrock. it is heavy and hard to cut for your contractor, but it will do the job.

https://www.quietrock.com/products/quietrock-545

a layer of green glue between the Quiet Rock and current wall will also help insulating.

https://www.greengluecompany.com/

these 2 products should get the job done.....and you should be Led Zeppelin or Beethoven’s 9th ready to boogie.

if there is a crawl space underneath the townhouses you might also erect a barrier there, but that would need to be something engineered for that space. not sure what is appropriate there.