Acoustically Treating a Bomb Shelter

Seriously.  My house came with a 1960s era bomb shelter.  It's a total of 2,200 square feet of Cold War Era awesomeness, basically divided into two 51X21 long rectangular rooms.

It's under a pool and pool house, easily 15 feet down. Hard concrete walls. Huge metal out swing doors that could keep out Bob Dylan looking for a string bean. 

We turned one big room into a giant pantry, wine cellar, and storage room.

The other I softened with hardwood floors, sheet rock (with foam insulation) on walls and ceiling, in that it could make an excellent apartment, being 1000 sf by itself, not counting the kitchen and bath.  And has two entrances, one at each end.  Very airy with good ventilation (and expensive filters).

It's this (now) 50 X 20 room iswhere my listening area is.  Ceilings are 14 foot sloping down (the short way on the rectangle) to 12 feet.

I've divided it into three areas of roughly equal area.  One end has a power rack and tons of free weights and whatnot.  On top of the hardwood is a protective layer, hardwood, and then rubber horse stall mats.  Kitchen and bath beyond that.

The other end is an emergency bedroom, with flip down Murphy beds, etc.  Area rug where the wife does yoga.  At its end are double metal doors, then stairs, then another metal door.

The middle third is my listening area.  Speakers and subs on the higher-ceiling side, although I could flip it.  Set up in the classic 60 degree triangle with a leather couch facing the speakers.  Chairs to the side, and a table I use as a desk behind the couch.  Area rug.  Decor: think Andy Warhol meets Austin Powers.

My thought is I don't get a lot of reflection from either the right or left side, due to the width of the room, and the stuff in each room.  I suspect I mainly get reverb off the back wall.  And perhaps the ceiling, although it is sloped up to the speakers.

I'm thinking all I need is some absorption on the back wall, immediately behind the couch/table (so facing the speakers), as I sit closer to the back wall than the speakers.   Perhaps something on the ceiling about 2/3 of the way across the room.

Thoughts?  I'd like to be informed a tad before I get involved with GIK or one of those groups.


Well, according to the two detectors, no radon!

Re: the poster freaked out about this being a cave.  My wife is, too.

The second owner added a Huvco fibreoptic daylighting system to this, but didn't finish.  He put in the collectors and bought fake windows, but didn't finish the system.  I'm going to run the cables down through the internal wall and stick in the "windows" to decrease the cave effect.


Thank you for the support and unity.  Fortunately, geographically I live in a very safe part of Israel.  I’m in the North, but as they say here in Caesarea, we are South of the North and North of the South.  Too far from the rockets of both Gaza and Lebanon.  All we hear here are fighter jets overhead all times of the day and night, although it’s been a lot more quiet the last few days.  My phone hasn’t stopped blowing up with rocket alerts and real time updates since the war began.  I have a friend in Ashkelon who I check in with all the time.  She tells me she has 2 sons with her, 2 in the IDF, and plenty of food, water, and weed to get her through.  

I’ve posted some pictures on my profile in ‘My Systems’ so you can see what I’m dealing with here on an audio level.  Am Yisroel Chai 🇮🇱🇮🇱🇮🇱 🦾🦾🦾.

Thread title reminded me of a song on Donald Fagen’s album The Nightfly.

If anyone has this album check out the lyrics to the song "New Frontier".

Romance in a fallout shelter plus Spandex jackets for everyone.

Just to update:  talked with a number of audio room advisors who offer consulting services.

Most are just pushing their particular products. 

One, in particular, who I'll call "Dennis" was particularly abhorrent example of the acoustic field.  He may or may not know his stuff (probably is extremely smart), but he was talking fast, pushing hard, and coming to conclusions to sell his product clearly based on simple computer room analysis and not taking into account the odd nature of the walls and actual measurements.

Specifically, because we are deep underground, the "drywall" is not drywall, but a product designed to allow water to pass through, made with little beads and glued together (in the unlikely event of a water event). 

Underneath that is six inches of a dense expanding foam.  Basically, the top sheet is very close to being acoustically transparent.  Not sure what is going on, but from multiple measurements with several different tools now, the walls do not really reflect much (nor produce their own sound) but are mildly absorbent of very low frequency sounds.

Long way of saying, computer room analysis is a great tool, but no substitute for direct measurements.

With that in mind, after talking with the rare consultant who actually listened to measurements, I've decided to go with about 20% bass absorption and 20% dispersion.  Mounted 4" combined bass traps/dispersion immediately behind the speakers/subs (about 1.5 inches from the wall).  (The gap increases the depth of sound absorbed, while decreasing the effect on higher frequencies.)  This made an immediate improvement.

Going to do about 108 sf of combine bass trap and dispersion on the back wall, and a fair bit on the ceiling, depending on results of back wall.

Nothing but a simple thin carpet on the floor.  My problems are low frequencies, and it would take building a pit to have something thick enough. (A carpet with pad will just absorb high/mid frequencies.)  If I need more, I'll double up on the ceiling.

The only other covering I'm doing is on two metal blast doors (on the far right) that have a huge tendency to vibrate with bass and give a solid echo.  Not a fan of acoustic curtains, since like carpet, they mainly just absorb higher frequencies. I've decided to use three layers of curtains -- one a heavy acoustic curtain, one that is pretty and acoustically transparent ---- AND HIDDEN IN THE MIDDLE GODAWFUL BEADS AND COINS.

Why the faux "gypsy" (er, Romani?  If I was Romani, I wouldn't claim it.  It's from Spencers.)  -looking garbage?  Dispersion.  I bought twice as much as needed, and they will hang all "bunched up" and hard, facing random directions, thereby taming down that 10'x7' metal reflector of a blast door.  Even better would be to have hanging wood slats, but I couldn't seem to find any.  Will see what happens.  Cost total of the awful beads and "coins" = $39.  If that doesn't work, I have enough space in the door frame (also a giant slab of steel)  to mount 6" base traps directly to the doors.

Get Room EQ wizard and measure what you got. Then figure out your best strategy