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.


Yes, it actually has a lot of dedicated power outlets, already.  With a lightning arrestor, whole facility surge protector (not the same as a lightning arrestor), and filter.  It was originally designed to protect against EMP.  I've replaced the elements due to age, but the amount of copper used was amazing, as is the grounding.

I run my whole rig off a dedicated 20 amp circuit, going through a commercial Furman.

Wifi was futile, outside of one room at a time.  I had to run ethernet cable.

It's still a bomb shelter, I wouldn't want to have a listening room there, just a storage place.

Any acoustic space then any space can be acoustically managed well ...

It does not matter in acoustics science that it was a bomb shelter at all ...😊


Plus, it's not like loud music would bother anyone.

In seriousness, it's a just a very giant empty room.  Not dark or damp or whatever.  Excepting the fact you walk down a flight of stairs and through a mud room (er, "decontamination room" made to look like a mud room), you'd never know you're in a bomb shelter.

Zero noise from anything.

And while we haven't had to shelter from bombs, during a couple of tornado warnings, we have made our way down.

That sounds awesome. I’ve two systems in the basement because it sounds so much better than upstairs. Concrete rocks. Photos would be interesting. 

Cool. You have the enormous advantage of a really low noise floor. One of the great characteristics of my room is it is underground on three sides… it really helps quiet the ambient noise. 

You sound like you already are thinking about the right stuff. If you have a system, move it down there and then make observations… move, dampen areas… move.. experiment. Then you can get into buying expensive treatments. 

Yeah, I’ve got the system there already, although I have a new turntable I need to assemble.  And missing a shelf from my rack.

I’ll post pictures after I get it looking reasonable.

Dave I agree with others that sounds like an awesome situation and never bothering neighbors or family is a win in itself. Regarding room treatments and such your best bet would be to use a program like REW and get yourself a mic and measure your room. That way you won't be blindly spending on treatments that aren't necessary or don't treat your problems.

You have a wonderful opportunity to build a music room that is second to none. The first decision is the exact room dimensions. This matters very much - and there is very much snake out to distract you.

Fortunately, the science has been done, and done in style. The famous Cox, author of my acoustics text, has published a report of his research into room dimensions, the result of a major simulation considering hundreds of thousands of room ratios. It turns out that most are bad. Perhaps a quarter are OK, and a few percent are good.

His research is reprinted on the website of the University of Salford School of Acoustics  (UK). When you read the research, you will note that an inch either side of optimal detracts from the resultant sound. Then there is the rigidity of the walls - not to prevent transmission, but to prevent the walls from flexing like 22nd grade woofers. There was an article on this about 4 years ago in Absolute Sound or Stereophile. I used Quietrock 545, backed by firm styrene over concrete or premium 3/4" plywood, and cases on cases of elastomeric glue from Chemlink.

GOOD  LUCK on a TREMENDOUS opportunity.

So if the ceiling is concrete, that has to addressed as well as the flooring and walls.

But it does sound like a fun project.

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The underlying walls and ceiling are concrete, but I put in a vapor barrier and 1 inch insulation, then 2x4 (2x10s in the ceiling to space for steel I beams) and then 5/8 drywall on top,  The void is expandable foam insulation.  Looks like firm yellow shaving cream.

All of that is not structural.  Just insulating and gave me a place to run conduit and make it look like a normal room.

The main issues I have a acoustically are:

1.  It’s a big room.  Right at 1000 sf.

2.  It’s almost a hallway, being 50 feet long and 20 deep.  And I’m setting up across the short side of the rectangle.  So reflections from L and R are quite distant.

3.  ceiling has a fair slant to it from 14 to 12 feet, which presumably reflects sound back to the speakers, but probably somewhere between the speakers and couch.

4. I’ve got it set up where I listen closer to back wall, which is why I suspect that is my point of unwanted reverb.





What jond said. Perfect enfironment for audio heaven based on the volume. So many things going for you. Room EQ Wizard and $100 recommend micorphone and do some sweeps at your listening position. Go to waterfall chart so you can see decay which is a measurment of your reflections. With that data and your ears you should be able to make good decisions in what will assist you and see as well as hear changes such as throwing a rug down does. You can then take that info to GIK to get input. Plenty of room to push the speaker well away from front wall. Congrats on a wonderful acoustic situation of a dedicated large room. Probably sounds pretty good now.

...after the Great Upgrade, launch with the music from Apocalypse Now....;)

Very cool opportunity.  Any thoughts of going Multichannel?  You have space for some theater seating, lots of space for Atmos speakers and subs. The extra speakers and DSP might help overcome some of the room limitations.  And you’ve got that wine cellar to provide the bevvies when you and the family do watch a movie.

do the normal stuff ... drop a panel on the cieling and a couple of the back wall ... better yet put some sound panels on wheels so you can move them around until you get the schweet spot

We have a home theater already in the house proper.

It’s very typical McMansion stuff put in by the owner of the home between us and the survivalist builder, straight out of the mid-2000s, albeit with a new QLED.  I suspect they walked into Magnolia and just picked the most expensive stuff they sold.  It’s certainly nice enough in a cheesy way. Made watching Into the Spiderverse awesome.

But that is for the kids and currently has a PS5 strewn across the carpet.

This is for me.

+1 on taking measurements with some software like REW and a mic like miniDSP Umik-1 that will work with that software. This way you’ll know where you are starting and can sort out the right issues instead of just putting things up on walls and ceilings. You can send your measurements to somewhere like GIK and get their input as well. I did that and they gave me comprehensive feedback. Doing so, I can make changes, take new measurements and decide what, if anything, else I want to do.

Whatever combination of diffusion/damping needed; I'd look for damping panels that are disguised as windows with an outdoor view- the thought of the room gives me anxiety! 

I have no idea if a product like that exists, but that would be my vision.

Guessing you're starting off with space that's free from external/ambient noise, which is a good thing.

Don't forget the ceiling.

I get that you already have a MC system elsewhere, but I was suggesting MC with DSP as a solution to your unique room issues. You could always have a dual two channel /multi channel by using an HT bypass.  Multichannel isn’t just for video and gaming, it can do a lot to enhance audio as well.  Having some ceiling , rear and sidewalk speakers with DSP might defeat a lot of the oddities of the space 

Mahler -  ah, excellent point.

I am trying to be retro here, to a degree.

It may come to that.  I do have a newish Arcam AVR that is now unused.  And it does have room correction software/mic.

You might want to go the whole Atmos route, but since you already have the Arcam (I am assuming it’s a 5.1) you should start there first

Hey, I would contact Acoustic Fields. They have different levels of things down to DIY depending on your budget. Maybe absorption up to 9 feet from the floor on the sides. Then quadratic diffusion on the front/ ceiling starting at the absorbers/ and the back. I don’t know if you create a faux ceiling at 10’ or just dart wrapping the ceiling down to the absorption foam. I say leave it to the experts. 

It's 2.5 feet of hard concrete and steel under ~15 feet of dirt under a swimming pool or deck.   Pretty sure it's a giant Faraday cage, too.  Cell phones go completely dead, something I very much enjoy.

So, I think we're OK with radiation.  ;-)

On the serious point, my playing with Dirac Live on the Arcam/laptop and a brief online consultation told me the same thing.  Nothing is needed on the left or right side, due to the length of the room.  All that is needed is either diffusion or absorbtion on the back wall, immediately behind the listening area, together with a bit directly above the sofa on the slanted ceiling.  Also pulling out the speakers about two feet from the forward wall (which I had already done).

I have a large (5' x 5') oil painting on the back wall.  I'll see if acoustic foam hidden underneath in the void works.

The slanted ceiling is apparently ideal and a bit of a mini-ampitheater. 




Perfect listening room. Congrats!

Tested for Radon?

Had a friend who spent time in his basement.

Died from radon exposure.

He was  in his 40s.

No test for radon, but it's got radiation detectors of all sorts.  Nada.

Radon is not particularly a problem here (oilfields of West Texas), anyway.

Per Texas A&M map, our county shows up at the second lowest level recorded in basements.

My friend also lived in Texas, and also in the same radon level class as your county. Most homes here with basements have none to low levels of radon. His home had very high levels.

I live up in Washington along the Columbia River. The Missoula Lake flood gravels have a lot of radon. We put in a radon exhaust system. Worth a test, just to verify. 

This has to be the most interesting thread to come up on Audiogon in months. I’d love to see pics of the space.

I’d consider the big Perlisten towers for that space since they can be driven to high output and have controlled directivity. 


Queue Donald Fagen’s New Frontier. 


That's a lot of width, AND you've also got a full 20 feet of depth so it seems pretty ideal. I would try flipping it around just to see how it sounds. It's often recommended to put the speakers on the lower ceiling end. The sound tends to propagate forward better and turn into reverb behind you, which is preferred to having it come from the same direction as the speakers. 

Either way, the wall and ceiling surfaces directly behind you and in front of you between the speakers are good attack points. Those are the earliest reflection points, and the closest parallel wall  surfaces that can create standing waves.

A crosstalk reduction scheme like BAACH would work great in there with the relative freedom from early side reflections. 



Just wanted to make sure you’ve got plenty of food and water on hand at your disposal in case of a real emergency.  That should be priority No. 1, then get your audio system set up.  

I live in Israel in a very safe area away from any rockets landing but I have friends all over the country who have to go into / or stay in their safe rooms for extended periods of time.  

Acoustically Treating a Bomb Shelter

Do you mean muffle the sound of an explosion?  How loud do you play?


1.  Am Israel Chi!  Go do whatever is necessary, please!  Ignore the media.

2.  For clarity, I live in West Texas.  This house was built by an extremely wealthy oil man back in the 1960s during the height of the Cold War.  Very rural.  If I ever have to shelter from bombs it’s because China Russia and the USA have decided to have a massive nuclear exchange.  All in, the shelter is as large as most people’s houses.

3.  Yes, we have plenty of food.  And about 2000 bottles of French, Californian, and even Israeli wine.  All set for the apocalypse.  Also a rather large library.

4.  We are fortunate enough here to not be preparing for said apocalypse, but rather finding something useful to do with a massive room with wonderful filtered electricity and completely silent, if oddly shaped.



Totally joking.  Pretty cool to have that unique story with the space. Living through the cold war with nuclear missiles pointed at each other was frightful. 

Good luck on your room acoustics.

Place absorption panels at first reflection points front wall (the wall you're looking at behind the speakers), side walls, ceiling, and rear wall (the wall behind you).

My dedicated room is treated just that way. Sounds wonderful. Yours will too.


Thanks for the advice.  As noted, the side walls are too far away to be of concern, but I do have a pretty pronounced standing wave.  I’ve bought multiple 4 inch thick panels for the back wall and behind the speakers/subs..  Also a bit just behind the turntable (dead center).

Moving the subs inside the primary speakers also helped immediately, as did widening the distance between the primary speakers from the classic 60/60/60 triangle by about 4 feet.  The Bowers 800s have plenty of “umph” with the big subs and Classe amps to handle being offset.  Really helped with separation.

Because of the canted ceiling, I’ve got 3 hanging baffles (pretty thick) staggered behind the listening position that I’m going to hang this week.

The back panels placed in the center back also incorporate some dispersion elements.





I've got the 803 D3s. Have toyed with the idea of a couple subs. What benefits did you gain from adding them?

It’s the SVS PB16 ultras. It’s a big room and they move a lot of air and just add the required depth to the bottom end.  Very noticeable without overpowering.  Takes some of the burden off the monoblocks.

Set crossover (coming out of the preamp) at 50ish and slope at 24 by ear, which, turns out is exactly what SVS recommends for the 800.

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.