[Carlman]

A dentist would like tell me to fill it but I'd like your advice...

I have an 11' w x 13' deep room with 9' ceilings.  I have a bay window behind me and the speakers are along the opposite wall.  There is a wide doorway on the left side wall as I'm sitting on the couch.

The wall where the speakers are has a large closet-sized cavity behind it where there are some stairs that go to 2nd floor of my house.  The only thing dividing my sound room from this cavity is standard sheetrock and the 2x4's it's mounted to.  There is no insulation at all.  I think this may be causing some bass reinforcement in my room but not in a good way.... kind of a slow, pudgy way.

I had the whole room setup 180* opposite the way it is now and I *think* the bass was more detailed.  It's hard to A/B this situation.

I can actually cut a hole and get into the space and fill it with insulation or water balloons... or just about anything.  I'm not going to turn it into a finished space, though.... too much work, too little time.  

Any thoughts on this aspect of the room?  What does a huge cavity under stairs do typically?  Can I somehow use it to improve my sound?

I'd like to remove the sheetrock, cover it with fabric and fille the cavity with fiberglass as an experiment... but that's a whole lotta work for a complete unknown.

Thanks for suggestions.

-C

[Hantra]

I can actually cut a hole and get into the space and fill it with insulation or water balloons... or just about anything.

Actually I heard that if you can pee in the ballons, it's a bit better.  It's kind of like sand vs. lead shot.  All depends on the viscosity of your pee though.  



Nevertheless, if you could snap a pic or two, it would be helpful for us to give you some advice. . .

B

[Carlman]

OK.. here's some photos...

This is the way it WAS... but now the system is right where the couch is... and the empty space is just behind the to AC members sitting on it.


Here's a drawing of the room layout and the current space... The dotted line indicates the empty area (and the little vertical divided line is where the stairway landing is, i.e. where the steps turn on the other side of the wall.)



I'll try the pee trick... can't hurt... it's free..

[Hantra]

Ahhh. . . I see more clearly now than when you were describing this at your place.

I can't give any professional advice, but my first priority would be to enforce that wall so that it flexes less.  Then I'd look at something to fill with if you want.  The flexing is the real problem b/c it is exciting that space behind the wall.  

As far as HOW to do that?  I don't have a clue.  You could add a couple layers of sheetrock and screw them all together.  You could add some MDF, which might work better actually.  Whatever you add back there to reinforce it, make sure you couple it to the sheetrock with screws or whatever.

Just a thought. . .

[rosconey]

if its a crawl space you can get into cut some rock for the back side,double rock would be more ridged for a start,then maybe throw a few rolls of insulation in there for a bass trap.

[BrunoB]

What is the shape of the cavity? If it is not regular, It might help to decrease standing waves.

[MaxCast]

Cut and frame two "cut outs" that you can crawl through.  Build some type of enclosure to hold a given amount of fbrglass in that space.  Cover the holes with framed material...like a Maruska.  Would that work as a bass trap?

[John Casler]

Hi Carl,

I would suggest that the "space" has no bearing on the change in bass and that the Bay Window probably broke up some of the bass nodes when you had speakers on that wall.

Now with the bass traveling in the opposite direction, that "advantage" is not the same, to the actual listening area.

As well the non-parallel walls of the Bay Window, so close to the listening position might be creating some strange interactions bass wise, and the shape looks like it almost "focuses" on your exact listening spot.

For example part of the strongest and direct bass wave from the front "left" speaker is "slamming" almost directly into the bay windows "right" wall.  The exact opposite is happening on the other side.

The angle of deflection is then converging the bass rebound pretty much right at your listening position.  This is going on as the other reflections are happening from the left and right rear corners.

I would say that these interactions (which would require traps to smooth out) are more likely candidates, than the space behind the wall.

Just an opinion

[Carlman]

Hantra, Rosco -  Thanks for the food for thought... I'd never thought about 'stiffening' a wall.
Bruno - The shape is very similar to Harry Potter's room in the first 2 movies... under a staircase.
Max - That sounds like a really good idea but then again... not sure if the experiment would be worth the cost/effort.... but maybe.. requires much thinking and research...
John - I think you may have hit the nail on the head.  It would explain a lot of why moving the speakers has unexpected results.  I have to toe the speakers a lot more to get reasonable imaging now.  Plus, normally toe'ing speakers changes the tonal balance more... not so in this setup.  The bass really booms on a certain frequency.  Before it was a little 'fat' but not a resonating fatness like what I'm hearing.     (a resonating fatness... that just cracks me up..)

Anyway, many, many thanks for the responses.  Now I have to go home and re-arrange my room again.  Ain't experimentation fun?

-C

[John Casler]

You might find that something as simple as moving the couch a few inches forward will make a lot of difference.

I would try 6" at a time and see if it moves you out of the node.

In general breaking up bass waves can be a good thing, since it "softens" the direct nodes, but it looks like you might have moved into the "fryin' pan" when you really wanted the "fiyaaa"