[jgubman]

Hi,

hoping to get some room advice from Ethan and the resident acousticians around here. My system is a multi use HT/2-channel listening room. My wife has relegated me and my gear to our basement, the bottom 2/3rds of the room is 100% concrete, the upper 3rd are cripple walls that I've covered w/ 1/4" laminated plywood. The ceiling are floor joists that have also been covered w/ 1/4" laminated plywood.

Here are photos of the front wall before and after.

Before:



After:



My main problem in the room is bass (naturally). In the first photo, you can see a brick wall that has big symetrical holes on both the left and right corners that provides access to the house's crawlspace.

I'm wondering if I should replace the plywood boards that I installed to cover the holes with just an open frame covered w/ fabric. It would provide ultimate absorption, but is it overboard? Would I be better off building some kind of complicated fiberglass trap that fits into the hole but has some boundry behind it?

Any other easy wins you guys can see to get the bass response a little more even? I have big 15db swings centered around 80hz and 40hz.

Other photos of the room are:
http://www.audiocircle.com/circles/modules.php?set_albumName=album34&op=modload&name=gallery&file=index&include=view_album.php


Thanks!

[JLM]

Nice look!

IMO a simple opening into the space behind is an invitation to create all kinds of resonances with the floor structure beyond.  I'd use those cavities to build helmholtz resonators tuned to those problem frequencies (not that I know how to design them).

Is that an on-demand water heater?  How do you like it?  Does anyone in your area know how to fix it?

[jgubman]

Thanks,

yeah that is a tankless on-demand water heater. It works great, takes less than a minute to get the water heated (it's only about 50-80 feet of pipe from the heater to the shower) and the hot water never runs out!

I blew it though on the installation, such a dummy. The minute we finished running the pipe and the gas line and started to hook up the heater, we realized that we could have just as easily installed the heater on the OUTSIDE of the house!! Doh. Oh well, it's only a problem when my wife insists on doing the laundry while I'm using the room, and it really doesn't get that loud. As for servicing, most of the parts are pretty accessible, but yeah, hopefully there's someone who can take it apart and put it back together if it ever really breaks doen. Haven't had a problem yet, but even if I have to replace it outright, it's worth it for the piece of mind -- I'd hate to have a 50-gallon tank down here rust out and pour it's contents all over the room. W/ this thing I only have to worry about a pipe bursting.

Back on topic, yes, creating weird resonances is definately what I'm worried about. I was thinking that since the openings open up to the entire length of the house (close to 1,000 sq. feet behind the opening) that it woudn't be too much of a problem. No?
I could also put some replace the panels w/ some 705 fiberglass covered w/ fabric, maybe that would catch any returning resonances??

[Ethan Winer]

JG,

> Here are photos of the front wall before and after. <

Wow, great job! (The after photo )

I see those big holes in the corners as a great opportunity. If you pack them with fiberglass you'll damp resonances and also create some pretty decent bass trapping. The corner location only helps. You could just buy bales of fiberglass and leave them in their plastic bags, and stack them up in the opening. For best results you'll want more bass trapping than that, but this is a solid start.

--Ethan

[JLM]

Here in the great white north of Michigan we'd probably install the heater inside as they're only rated to -20 degrees.  

[warnerwh]

Some 3" acoustic wedge foam on the back wall and ceiling at least a couple feet out will help greatly.  You'll be glad you did considering the small outlay of cash.

[jgubman]

Yeah, I've got 3" acoustic foam wedges sprinkled throughout the room. Right now the back wall looks like:



In the cavity underneath the stairs, I've filled w/ 3" acoustic foam. I'll probably shove some fiberglass bales under there also. I have a 2'x4' foam in the left corner. I've been thinking of replacing the 8th nerve treatments w/ the foam. However, right now echo doesn't seem to be my biggest problem, it's definately the somewhat flakey bass response.

Thanks for the advice, Ethan. I'll try to frame up some hollow panels, cover them w/ fabric and stick some fiberglass rolls inside the openings to the underneath of the house.

[John Casler]

JG,

> Here are photos of the front wall before and after. <

Wow, great job! (The after photo )

I see those big holes in the corners as a great opportunity. If you pack them with fiberglass you'll damp resonances and also create some pretty decent bass trapping. The corner location only helps. You could just buy bales of fiberglass and leave them in their plastic bags, and stack them up in the opening. For best results you'll want more bass trapping than that, but this is a solid start.

--Ethan

I agree with Ethan regarding those openings.  

Bass is a funny frequency.  The room and its boundaries can assist in its propagation or destroy it.

If your in the mood to fool around, take your RM40 boxes and place them in the rear corners of the room with their angled corner into the corner angle and keep them about 3" out from the wall corner so there is space for the sound wave to be captured in the corner.

Place something heavy like a couple telephone books on top.

Listen to some bass passages (Flight of the Cosmic Hippos works) and see if you hear any difference.

Try this in various positions.  Even lie the boxes down flat along the rear wall a few inches out. (make sure and add weight)

Try them agains the side walls (right up against the wall) a foot or two in front of the rear corners.

Also lie them down along each side wall almost to the corner.

And even try them both in one corner at a time.

All of these positions can provide "interuption" of the bass energy traveling along the floors and walls.  

If any of these help, then it is time to either build your own traps or order up from Ethan.  

While cardboard boxes "are not" sophisticated traps, they can provide enough interuption to help you (in an easy tweaky sort of way) to begin to know your room.

Try all the angles, and intersecting surfaces that you can think of and give a listen.

I accidently discovered this when I had a large shipment of equipment delivered and I stacked them almost to the ceiling in a "single" corner of my room.  That whole week my bass was better.  Then when I took the boxes to the job site, I noticed my bass was not as good.

But do remember they need to have a bit of weight to them.  Empty boxes don't do much.

I might also mention that it worked even better if I took couple a 24" x 48' x 3" and shoved them into the corner, and then placed the weighted boxes.

No guarantees, and YMMV.

[John Casler]

Hi Jon,

I posted the above before I saw the new picture, but you could still try the suggestions.

Also a good portion of your bass shyness may be the low ceiling.  You might find that the treating the side and rear wall ceiling intersections helpfull.

I know you use the Foam Factory.  They have some corner bass traps that can be mounted at the ceiling/wall intersections. (as well as the floor wall and all four corners)




They also make some male and female broadband absorbers and the female can be cut in half making some mini-bass absorbers which can be used along wall/ceiling intersections

[jgubman]

Thanks John,

the RM-40 boxes is an interesting experiment I'd never thought of. I'll get on that, should be an easy enough checkup.

I'd seen those corner bass trap thingies before, but I've always been a bit confused by their corner options. Do you think the wedges are more effective than their "block" solutions?
http://www.foambymail.com/CornerSolutions.html

Thanks for the great suggestions, my wife starts rolling her eyes when I talk about bringing in more foam, so I'm going to start w/ the openings and a roll or two of fiberglass underneath the stairs.

If that doesn't do the trick, I'll try the foam corners, although my wife might get me a straight-jacket to go w/ my padded cell!!

[Ethan Winer]

JG and John,

> Do you think the wedges are more effective than their "block" solutions? <

Foam is not a very effective absorber for low frequencies. One bale of fiberglass from Home Depot will absorb about ten times more than a piece of corner foam at 100 Hz and below.

--Ethan