Attic Control/ Live Room Acoustic Treatment Overhaul

Hello again, My name is Greg Hill of Raleigh, NC. (U.S.) I am attempting to acoustically treat my attic recording space in an effort to tame some modal issues I've had ever since it was built. The main problem I'm facing is within the lower frequencies, and after having read John's acoustic page, this seems to be the dominant issue in rooms of this size. (Roughly/ L- 20' 8" X W- 12' 6" X H- 7' 4") I plan on installing slot resonators on both left and right walls. Being that this is an attic, both the left and right walls have a considerable amount of space behind them due to the eaves, which I'm hoping will accommodate the resonators. Also, I plan on placing 2" mid-frequency absorbers on the majority of the doors to prevent flutter echo between parallel surfaces. On both the front and back walls I plan on placing 4" bass traps as I understand this to be the most effective way to flatten bass response. Anyways, enough rambling... here are some pics of the acoustic additions- I'm also debating whether or not to remove the drywall from the ceiling, seal the joists and outer leaf, install rock wool, then cover with cloth to make use of an inside-out ceiling. To some extent I feel that this may be overkill, but having been in this space for several years I believe it is required to obtain the response I'm looking for. Here is the Sketchup file- http://www.mediafire.com/?rxab0xv0dli8k8c This is linked from a separate host as the forum here would not allow me to upload such a large file. It was created using Sketchup 7.1 and consists of multiple layers. Feel free to download and show me your ideas! If there are any recommendations towards taming the response in this space please let me know. I understand the idea is not to kill the room, and I would like to determine if this is the best acoustical layout before I proceed. Thanks for all your help! -Greg

have you made any acoustic measurements to determine what problems you might have? also, consider putting the monitors on stands in front of the wall and move the desk back a bit. put an absorber between the desk and the speakers - i.e. cover the front of the desk with an absorber. this will help eliminate reflections off the desk.

Thanks for the reply Glenn. I think stands would be the best way to go as far as placement, and I will prepare some tests to better determine the room response. What would your opinion be on soffit mounting the speakers in this room? I run a pair of Yamaha HS80M's and a KRK Rockit 10 Sub... I'm terrible with Sketchup- Hopefully this will get the idea across. I'm trying to make better use of the shelved out front wall space and I believe soffit mounts and bass trapping would be a good thing. -Greg

yes, soffit mounting would be very nice and since the existing shelve would "force" some space in front you could benefit from additional trapping there.

Having had a little more time I was able to draw a little more accurate soffit design suited for the front wall of the room. -Greg

very nice.

Thanks Glenn, I've decided to go ahead and make use of a Soffit Wall before I go about making any acoustical measurements. Not only will this allow for a more accurate response but it will look very nice as well. Lately I've been in demolition mode. So far I've taken down what was once the front wall of my room (as seen in the sketchup pictures above). No more shelf! I did have to do some drywall/baseboard work to provide an equal depth on both the left and right walls, and in the process maneuver a door that entered the left eave. So far, so good. Now is the question of the soffit walls design. I did a little searching and came across Sonolinks thread here- http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=11508&p=109479&hilit=soffit+design#p109479 which proved to be very useful. After having read over the thread I was able to get a better idea of how one goes about this sort of thing, and ended up drawing this- This is primarily a rough sketch of the framing and design of the speaker housings and their position. I've made use of neoprene throughout the perimeter of the soffit where it will attach to the existing structure, along with iso-washers/bolts. I've also ordered 4 sheets of sorbothane to accommodate the interior of the speaker housings in order to isolate them from the mdf as you recommended. Thankfully, unlike the Sonolink thread, I plan on mounting my speakers vertically, rather than a downward angle; I have enough geometry issues as is. My questions are- Firstly, are there any major flaws in what I have drawn? Do you believe the speaker housing's will require a base (cinder block/ mdf stand filled with sand) below them, or would it be fine to attach them to the soffit as pictured? Should the housing's protrude the framing in order to meet flush with the applied facing or remain flush with the framing itself? And finally, (more so a generic carpentry question) what is the best way to go about framing the top-sill above the speaker housing's. The two that will be placed at a 30 degree angle horizontally, and roughly a 45 degree angle vertically...where they will attach to the "rafter joists"? That final question may just have to be answered in real time as I place the top-sill section, just wondering if anyone out there knows of any tricks around this sort of thing. Anyways, thanks for stopping by and please feel free to chime in on this design. I will be posting updates as progress is made! -Greg Hill

the design looks good. make the speaker boxes using 1" MDF if possible - mass. leave enough space in the box to add something to decouple the speaker from the box. if powered, leave venting on the back of the box - top and bottom. leave the box behind the front panel and allow the speaker to protrude to be flush - then seal around the speaker.

Thanks for the reply Glenn! I went to Home Depot today to pick up some materials. To make a long story short, after following 4 different employees around the entire store they told me they didn't stock neoprene rolls/mats. (The tried to sell me shower liners?????) Also, the thickest available MDF they had was 3/4". Do you think 3/4" MDF for the enclosures would suffice? Also, where would be the best place online to get neoprene rolls? (1/4" 35-40 hardness around 4" width) I've searched via Google shopping and the results come out to around $200 US for a 4" x 12' roll. On ebay, they vary from $30US for a roll to $300US. Just want to make sure I purchase the appropriate quality material for the most reasonable price. I understand you are busy, so If you're able to find the time please let me know. I really appreciate all your help! Thanks again,

i've found these folks usually have reasonably pricing http://www.rubbercal.com/Soft_neoprene.html

Thanks for the reccomendation. My order is on its way now! I've started ripping 3/4" MDF for the enclosures. I will post pictures soon. :D

As promised, some pictures of things getting done here and there. (Cont.)

If you scroll fast enough this may become a stop animation film. And thats where I am at currently. Tomorrow the rest of the framing gets cut and assembled. 8) Fingers Crossed.

More pictures for your viewing pleasure-

I do apologize about the large images. I assumed they would be loaded as thumbnails that could be opened to larger images but that was not the case... If anyone knows how to fix that please let me know. As you can see from the previous post of pictures I've completed the majority of the framing and insulation. (All perimeter studs are isolated via neoprene on the exterior face and neoprene washers on the interior.) I will begin building the hangers for the rear cavity of the soffit tomorrow. Glenn- I've been jumping back and forth between some posts of yours detailing the placement of the speaker enclosure behind the baffle wall. One showing the enclosure attached directly to the stud wall itself- And the other claiming to separate the enclosure from the wall- In no way do I intend to criticize you by bringing this up but rather clarify the appropriate method. (That is if I understand the two correctly) Which of these two options do you believe to be the best? Or a third option- Would adding an isolated shelf be the best way to support the enclosure as in the picture below? Thanks for your help with this.

the important part is that the speaker is kept decoupled from the box. the balance is to keep the speaker immobile and yet floating enough that vibrations are not passed directly to the front panel. if you couple the box to the front frame and panel, then you need to pay particular attention to decoupling the speaker from the box. (the first drawing) or if you have the option or want to enlarge the trapping space, then supporting the box/speaker separately can help (ala Barefoot's soffit design) or my second drawing. if you check out Genelec, they recommend a concrete soffit mounting with rubber isolators and sandbags for damping and isolations. you design as shown is fine but you will want to use something soft but firm (sylomer, sorbathane, agglomerated foam, etc) to decouple the speaker.

Thanks for the reply Glenn. That clears things up for me. I just wanted to make sure I wasn't missing anything important when I came across both drawings. I purchased 1/8" sorbothane a while back (when I was building the enclosures) and have cut it into 1" squares to place on all interior sides of the enclosure. When all is said and done it totals to 6 squares on top and bottom, and 8 squares on left/right sides. I super-glued the pieces to the enclosure with plastic on their outer faces and did a test fit with my monitor and it slowly slid in. A couple days later I went to remove it and it slowly slid out while I held the enclosure so that the monitor cone was facing down. Once out, I noticed that all the squares I placed were still where they needed to be just missing their plastic coverings and several were shall I say "chewed up". When you recommend sorbothane as an isolator for enclosures would you suggest covering the entire interior with the product, using a lubricant of some sort (thin plastic didn't work), or any particular method so that the monitor is appropriately sealed/isolated but wont be damaged if later it needs to be removed? I also plan to use soft neoprene between the studs and the exterior of the enclosure upon final installation, just to further insure vibrations will not be transferred. Thanks so much for your input,