Absorber Placement in L-shaped Room

My music room has an 8-foot ceiling, one 10-foot wall, and one 14-foot wall. The room is L-shaped, with a 4-foot open hallway that leads to it. Before I begin treating the room, I'm curious how the hallway will affect how sound builds up in the room. The room is carpeted. Thanks, Nick

Here's what I've done so far: Thanks, Nick

Aloha and welcome to the forum, Nick :D You place looks nice. :wink: Any chance you could post a floor plan, though? Aloha 8)

'm curious how the hallway will affect how sound builds up in the room.

Only way to be sure is to measure. Are you inclined to get into this sort of thing? Warning: it can be addictive! If you are, several of us, myself included, would be happy to teach you all about it. That is a really cool-looking room you've got there!

Aloha David,

Only way to be sure is to measure. Are you inclined to get into this sort of thing? Warning: it can be addictive! If you are, several of us, myself included, would be happy to teach you all about it.

Yes, please teach! :D Aloha 8)

Here's a very rough sketch of the room boundaries: Let me explain the floor plan. I'm in a finished basement: the whole basement is carpeted. I'm in "half" of the basement, in a space that is 8' 4" wide. One side wall is 15 feet long, and the other is 11 feet long. The 4 foot wide corridor connects my "half" of the basement with another room, 10 feet by 20 feet. The ceiling is the same height throughout the basement (7' 9"). All sheetrock. I've put a 2 x 8 absorber made out of 4" OC 703 in each of the three corners of my area. I have a 4" absorber (2 x 6) mounted to the ceiling above my desk, and another 4" absorber (2 x 4) behind me, again, mounted on the ceiling. I've got a 4" absorber (2 x 4) on either side of my monitors, hanging 1" from the ceiling and extending 4 feet down the wall. I've got another 4" absorber (2 x 6) and two 4" (2 x 4) absorbers I hung at the wall/ceiling corners at the back of the room. Thanks, Nick

So, Nick, what, precisely, is the question here? (that's a lot of commas) Is it to find the modal frequencies of the room? If so, to what end? So that you can place treatment accordingly? So far you've only expressed a curiosity in the modes of vibration of this shape. Yhis is the kind of thing that would interest me, and I somehow doubt your as geeky as I am. :D So, if the goal is to treat the room, tell us about your budget, what you're willing to do, and how perfect you need the end product to be, and we'll get you fixed right up. If the goal really is to investigate the modal aspects of the room, then cheers! I'll tell ya... I've seen like one situation similar to this before, and it came out basically like the rectangular prism that is basically is with the width modes weakened, and the 'new' axial width modes (from the 26' exit area) made an appearance. It's a lot like what happens when you open a door in a regular room.

kendale wrote:

Yes, please teach!

You really want me to blather on about acoustic measurement? Since you're a veteran poster here I thought for sure you would have seen this covered before. If you've never done acoustic measurement before and are looking to get into it (you too, Nick), I'd be happy to cover the basics. Like I said, I'm still in shock that it hasn't been covered to death. :shock: 8)

Aloha Nick,

Let me explain the floor plan. I'm in a finished basement: the whole basement is carpeted. I'm in "half" of the basement, in a space that is 8 feet wide. One side wall is 14 feet long, and the other is 10 feet long. The 4 foot wide corridor connects my "half" of the basement with another room, 10 feet by 20 feet. The ceiling is the same height throughout the basement (8 feet). All sheetrock.

Like you, I am in a room of similar working measurements, and side walls of different lengths. Like you, I've treated the room with corner, side and cloud absorbers. And like you, I've had to consider how to address an opening in one of the side walls (which opens up into the dining room, in my case.) To deal with the issues it creates, I've built six stackable absorber units based on John's designs which you can find here: http://www.johnlsayers.com/HR/index1.htm I've found that by closing up the room (and thereby "shortening" the room to about 10' I can create a very dry, controlled environment, and by sliding the rear wall back or apart, thus creating a gap, I am able to allow some measure of "air" to become part of the environment. While it's nice having that option to tune the room, I would prefer to have a bigger overall space to work with. Unfortunately, I am unable to frame in a new wall to accomplish that. You, however, may have that option by either framing in a door in the hallway, thus continuing the side wall to the rear wall, or by placing a stackable, side wall absorber unit in the hallwall, and sliding it out of the way when need. Personally, if it were possibl, I would go with a door. If you were able to fram in another door at the "live room" side, you could creat a nice airlock. Hope this gives you a few ideas on how to approach your solution. Aloha 8)

Aloha David,

You really want me to blather on about acoustic measurement? Since you're a veteran poster here I thought for sure you would have seen this covered before. If you've never done acoustic measurement before and are looking to get into it (you too, Nick), I'd be happy to cover the basics. Like I said, I'm still in shock that it hasn't been covered to death.

Thank you for offering. :D The truth be known, there is so much to learn here, but it's becoming a little difficult to find a post (start to finish) detailing the process, although I've seen lots of bits and pieces. I think it would make a great sticky on its own, as well. In the interest of not taking away cohesiveness from Nicks post, if it were to be better to start a new thread, or a link to one, would you like to start one or shall I? Actually, I think we shall, shall we? :D http://www.johnlsayers.com/phpBB2/viewt ... 2548#42548 Aloha 8)

David French wrote:

So, Nick, what, precisely, is the question here? (that's a lot of commas) 8)

Thanks for the help, guys. My original question? Would the 4' opening on the left side of my room affect how sound (low-frequency sounds in particular) build up in my music space? For me, this isn't rocket science. I've got a couple of decent microphones and a couple of decent mic pres. My guitar amp sounds great, and my new DAW smokes! I would, however, like the room to sound good, so I can record stuff and not have to make excuses about anything except the way I recorded it! That said, I've got a few more of these OC 703 panels I can hang in my room, and I'm unsure where to place them. For instance, should I hang them at a 45-degree angle where the ceiling and wall form a corner? This is all new stuff to me, so I'm definitely open to suggestions. Thanks again, Nick

If I were you, I would replace those 2" panels in the corners with 4" material; the 2" panels handle modes down to about 100 Hz, but with 4" you can get down to about 60 Hz. I also recommend adding 2-4 more of these where the walls meets the ceiling. Once you have about 10 of these thick panels across the corners, the returns start to diminish quick. For dealing with things lower than 60 Hz or so, you're going to either need larger porous absorbers or membrane/resonator devices. Also, you should really get that ceiling absorber and the side absorbers away from the boundaries by several inches - it's free bass absorption. I would use the 2" you took out of the corners and use it for the side walls and ceiling. Also, lower the side wall absorbers - center them around the center of the cabinets in the height dimension. There. I hope that's enough to help.

Oops. To answer this...

Would the 4' opening on the left side of my room affect how sound (low-frequency sounds in particular) build up in my music space?

Yes, It will affect it, I think in the way I outlined in the last half of the firwt paragraph of this post. Like I said before, the best way to find out is to measure.

Thanks for the help, David. I really appreciate your expertise. It's probably too much effort to really dial in this room, becaue I have a lot of stuff crammed into it. My hopes were to tame the room down a bit so I could do a little of everything in here with better results. I record guitar, MIDI instruments, and vocals in this space. I try to mix what I've recorded in this space. I practice my guitar in this space. What I would hope to learn from this exercise is that whether the effort I've gone to in building these absorbers will translate into better recordings, mixing, and practicing. If I can make the room a lot better if I buy another box of OC 703 and double up the corner absorbers, ceiling absorbers, and wall absorbers, I'll do it. This is a little better sketch of my room. Nick

Is there any reason you couldn't make a "door" (a movable panel really) along your back wall that could be closed when the room is in use that could block the opening to the hallway? If you could build it out about 5 or 6" from the back wall, you could mount your absorbant to the back of the moving panel. You could even fashion a "pop out" corner absorber that would only come out when the door was closed. len

len-morgan wrote:

Is there any reason you couldn't make a "door" (a movable panel really) along your back wall that could be closed when the room is in use that could block the opening to the hallway? If you could build it out about 5 or 6" from the back wall, you could mount your absorbant to the back of the moving panel. You could even fashion a "pop out" corner absorber that would only come out when the door was closed. len

Thanks for the help, Len. I could make a door. What I'm wondering is whether I "need" to do that. Put another way, Does this opening cause any problems with my room's acoustics? It sounds like from what I read earlier that I could consider my room to be a rectangle anyway, and make adjustments using treatments, using the rectangular measurements as a guide. Still a little unsure though. Nick

Well, I can't speak to your room exactly (I'm sure others will jump in if I say something wrong here), but I can tell you about my room which is similar. In my thread [url="http://www.johnlsayers.com/phpBB2/viewtopic.php?t=4488"] you can see my whole studio layout. At the back of the control room, you'll see a little alcove (which is like your hallway. If you put on some music, it sounds very well balanced until you walk into that little alcove (I haven't finished the room yet so you still CAN walk in there. Lo and behold, the bass level "rises" dramaticaly when you stand there. That's where all the bass is going. What does this have to do with you and your room? I suspect that you are going to get a lot of sound escaping down the hallway but it's going to be very frequency dependent. In other words, your bass may head down the hall, but never come back. You would try and compensate for that by turning up the bass on your mixer and if you burned a CD and played it in say your car, you would have way too much bass in the music. Been there, done that. :-( len

Interesting. I had no idea that the bass would do that! Nick

It's actually pretty cool (but then, I'm pretty easily fascinated). The effect is not subtle either - it's like you turn the treble to full cut and the bass to full boost and then some. Walk just out of the alcove and everything is back to normal. len

I'm wondering...if I'm trying to reduce bass buildup in my area, would it be a good thing for the bass to exit the room through the hallway? Thanks, Nick

I guess that depends on who's outside in the hallway. :-) I've noticed a change in the sound (frequency response) when I open and close my door. It may all be in my head but I'm sure there is some physical effect.

It's NOT all in your head; that open door leads to a LARGE bass trap. Usually this isn't a BAD thing - but use your EARS; if it SOUNDS good, it IS good... Steve

David French wrote:

...I also recommend adding 2-4 more of these where the walls meets the ceiling. Once you have about 10 of these thick panels across the corners, the returns start to diminish quick...

I'm back at working on the room, and I just wondered about this recommendation. David, did you mean I should take a 2x4 absorber and angle it across the corner created where the wall meets the ceiling? I'm moving the side absorbers out 4" from the wall. Any guesses on what this might do for the absorber's "absorbing" capabilities? Thanks, Nick

Yes, that is what I meant. Moving the absorbers out from the wall will create more low end absorption = a good thing.

Great! Thanks a lot, David. I'm going to place a 2'x4' absorber on an angle, almost exactly across the room from each other, spanning the wall-ceiling intersection. I'll also place a 2'x6' absorber across the back wall's wall-ceiling intersection as well. I'm moving all of my wall-mounted absorbers out 4" with spacers to help absorb more low end. Thanks again for the help, Nick

Well, the semester is over, and I have more time to work on my room. It's sounding pretty good--much better than before--but I've got one issue to deal with: a hump around 70Hz. The room seems to resonate at that frequency. I can't conjure up more OC 703 for my corner traps very easy. Instead, would something like this work? I could buy several rolls of the pink insulation and place them behind the corner traps. Would that help, or should I buck up and drive the 75 miles to pick up more OC 703? Thanks guys, Nick