I'm creating a post hoping to get some serious answers,
Serious? Hmmmm, somehow, the word "serious" gets diluted when the word "pimping" is used to ask for help.

But, ok, I'll pass on the so called humor. Lets do this. Let me illustrate something. If you want SERIOUS help, try using "pimping"" here and see what happens.
http://forum.studiotips.com/index.php
also trying to show that I'm a friendly, easygoing guy by using words such as "pimping" and sarcastically referring to my music as the "definition of dope"
Good enough.
and you, who I understand can be considered a professional in this field, tell me in this arrogant tone to whisper.
Arrogant? If humor is good enough for you, why isn't it good enough for me?

And btw, I ain't no stinking professional. I'm simply a HR enthusiast whos done his homework.

As to the whispering advice...you're the one with the problem.
I suggested a cheap solution. The fact is, you haven't given us a fucking clue to what your REAL situation is. No info on what the boundarys between you and the neighbors are like, distance, construction, type of building, location and or environment, nor what the fucking construction of the closet is like, materials, adjacency to boundarys or location in the room or how it relates to the neighbors in terms of distance from whatever divides your room from the "neighbors", or even what this building is...an apartment?house?basement? or even if the neighbors are beside you, above you...or below you... fucking ZILCH...ZERO....NOTHING!

so how in the fuck do you expect to get a goddamned rational answer when you won't even take the time to fucking CLUE US IN!!!!
Look Mr. Clueless...take a look at 1000 of my posts and you will find more input, drawings, lengthly explanations and more info than 90% of the respondants here. In fact, if the goddamned owner of this bbs would get off his cloud/could care less about this bbs other than income producing ASS, and make some of my fucking posts a goddamned
STICKY, we might not even be haveing this fucking dialog.

DIG?
How hard can it be to help a struggling guy out with some SIMPLE advice?
How hard can it be to give a stuggling respondant some SIMPLE INFORMATION!! Its like...I have a car. Can you fix it?

Spare me. good grief....why do I do this. I must be masochist.
Also, how the does the fact that I will mainly rap change anything (I will actually also do singing - "underground" doesn't automatically mean no singing)? I will still produce loud noise (maybe even louder than that of singing)
When one recites a poem, it is SPEECH, which uses a different set of muscles/lung expulsion to inflect AMPLITUDE!! When one SINGS..the lungs and larynx use much more power to change FREQUENCY and AMPLITUDE. Hence the advice to WHISPER.
which needs to be dampened and it's reflections killed.
Hmmm, do I detect you might have a clue or two?
And about "pimping". See, there's something called sense of humour. But I don't know, maybe you lost yours when you moved to Asshole-Land.
I moved to ASSHOLE land when I came across the first post on this bbs similar to yours. Look, my post count and the depth of my posts in the past gives me the right to defend my attidude any fucking way I want to. Dig. But just to show that I can be helpful to those who don't bother to give US a clue.....here is some help.
Ok, the simple answer to the exterior "dampening" of the...lets see, what did you call it?...oh yea...a wardrobe(not to mention if its a goddamned freestanding unit, built in closet, trunk, chest or suitcase

or any other simple insight other than dimensions) is MASS. Simple mass. Or better yet, decoupled mass. Which means WEIGHT. Oh, now that you mentioned your place of abode is an appartment, is it on a ground floor or higher..and if higher, what kind of floor is it....wood, concrete etc( some cheap apartments on an upper floor would either not support the wieght of even adding a layer of MDF to an existing piece of furniture such as a "wardrobe"(which btw usually means your CLOTHING Mr. Dunce

) or even if its concrete, would simply allow for structural transmission of vibration EVEN if you applied 10 layers of MDF, unless you "decouple" the so called "wardrobe" from the floor....dig? So....give us some insight and maybe, just maybe we can help you. BTW, adding enough mass to keep even low key rap from transmitting to an adjacent apartment may cause structural failure to a cheap apartment floor.....ie....look out dwellers below!!!
As to the inside....well, I already told you. OC703 or its equivalent(ie...different brand/same specs or foam products. There are other DIY solutions...but you asked, I answered. I'm willing to go into it, but not yet.
Ok, if thats what you wanted to know, cool. If you want more...give more.
Or DO A FUCKING SEARCH on Vocal booths here. I've posted more goddamned drawings and info than you'll find on the net. Just get off your duff and SEARCH!! geeezus.....
And btw, how far into the rabbit hole do you want to go? Here is a detail for a vocal booth door. Try to build this Mr Brilliant.

Or even square cut a simple panel of 3/4" MDF @ 3lbs sq. ft and haul it into an apartment and the n FASTEN 6 panels to the outside of the so called "wardrobe" so every joint is
airproof, not to mention the door.
good luck.
your friend,
Mr. ASSHOLE