Are There any Space-saving Alternatives?

I’ve turned a room in my house into a sort of all-in-one control room/recording room (mainly drums), I’m still a bit unsure of the best (and easiest) way to acoustically treat it. It’s 11 x 16 feet (height = 10 feet) with an unusually shaped ceiling and parallel walls. I’ve already laid a laminate wood floor. At the moment the room sounds very boomy; my drums sound extremely loud and my cymbals very harsh. I have posted here about this room before, but have since learnt a fair bit by hanging around this forum and have also referred to the John Sayers wall units on the front of this site. Are there any alternative options for treating the room other than the huge bass traps and side absorbers on the homepage of the site? I’ve seen things such as MiniTraps and the use of 2’ x 4’ fabric-covered rigid fibreglass panels mentioned here and I wondered if these would be a valid and sufficient option, especially considering my poor DIY skills(!)? (I’m a complete novice so excuse the lack of thorough understanding) Cheers. Tom. Diagram of the room - shows unusual ceiling shape: http://johnlsayers.com/phpBB2/files/tw_room.gif [/url]

Tom, > Are there any alternative options for treating the room other than the huge bass traps < First, understand that all room acoustic problems are caused by reflections off the walls, floor and ceiling. If a room has 700 square feet of surface area, then you can't expect a tiny bass trap with only, say, four square feet of surface to do very much. You really do need to cover some reasonable percentage of the room's surfaces to convert them from reflecting to absorbing. That said, the most space-efficient design I know of is the wood panel bass trap. You can build these to work as low as 60-80 Hz with a depth of only a few inches. Another option is corner mounted rigid fiberglass or a commercial product like the MiniTraps you mentioned. Although mounting a 2x4 foot panel across a corner impinges on the room, if you put them in the corners where the walls meet the ceiling they'll be up high and out of the way. --Ethan

Thanks for your reply Ethan. Mounted fibreglass panels in the corners would suit me as far as space-saving goes, and would be preferable in that respect to the sealed bass traps on this site’s front page (so long as they are still effective). I’ve gone away and made a VERY rough diagram as a starting point, which should be seen below. (I haven’t considered the front wall yet as it’s just a huge window/door) The light-blue boxes represent 4’ x 2’ wood mounted, fibreglass panels in the room. Can anyone suggest whether this plan would be effective? (I emphasise that it is a VERY rough plan and probably based on fragile understanding!). Thanks Tom

Tom, > Can anyone suggest whether this plan would be effective? < It looks about perfect to me, though you may want to add a few more panels that straddle the partial corners where the walls angle away. --Ethan

Appreciate your advice Ethan. I’ll get to work making a few of these panels in the next couple of weeks and I’ll probably be back then to seek advice about some of the finer details such as ideal hanging distance from wall surface (further away from wall increases lower frequency absorption, right?) Thanks again, Tom.

Ethen wrote:

the most space-efficient design I know of is the wood panel bass trap. You can build these to work as low as 60-80 Hz with a depth of only a few inches.

I am very interested but have not seen a design with the associated design calculations for these. Can you point me in the right direction?

tmwhi - what program did you do that 3d drawing with? I have a 2d CAD system but I am looking for an inexpensive, easy to use, 3d program for illustrating ideas etc. . .

I am very interested but have not seen a design with the associated design calculations for these

I have posted twice in as many days the formula. Once it was even correct! Here is the formula: f=170/sqrt(md) where f= center frequency of absorption m= mass of panel in pounds per square foot d= depth of space in inches If you think you haven't designs with this, study various rooms designed by professionals and look at the room mode frequencies vs wall absorption,

Hmmm. . . I have seen this formula a couple of places within these forums, with and without the square root, but I just don't believe it. . . reminds me of a story. I was managing an electronic manufacturing operation about 10 years ago. I was burning the midnight oil and one of my Manufacturing Engineers (Masters in Mech Eng) was also working late. I walked by his office and stuck my head in to say hello. He had a pile of his books out and was looking frustrated. He told me he was trying to calculate the resonant frequency of a metal plate one of our electronics products was mounted to on a tractor, because we were having field failures and he thought it might be vibration. I asked him the plate size and thickness, then I thought back to the sound of a piece of metal of around that size I remembered hitting to knock flux off after a weld on a home project in the past. I told him it was around 1.6kHz. He laughed, 20 minutes later he dropped my office and said his calculations said it was 1.8kHz, asking how I got so close. I told him it was because I remembered the sound and also said, by the way my answer is closer than yours because I bet you forgot to allow for the metal electronic case bolted to the plate. The next day they tested the real deal on the vibration table and found it was 1.675kHz. I know he still tells this story to new engineers. I must admit there was some luck to it, but experience as well. I am not up on the formulas, which is why I asked above, but I have pounded the palm of my hand on enough walls, resonating panels and speaker cabinets, checking the fundamental, to make me believe there is more to it than. The larger the panel the lower the frequency. . . but I don't see the area of the panel in the equation? I also thought material compliance was part of it as well (low-compliance = low frequency, hi-compliance = higher frequency). I know compliance affects woofers and also affects walls because I know from experience if you screw 2 layers of 5/8 gypsum the wall resonates higher then the same size wall with the first layer screwed and the second layer glued with lots of flexible adhesive. I believe it is because the glued version is not as stiff. I also remember lining a concrete basement with wood studs and drywall for a home studio. I did not want to transfer vibration to the main floor joists so we used metal "L" brackets and screwed them into the concrete wall and attached to the studs. I thought it would be nice to resonate across a few frequencies so I suggested we add an alternate the mounting point so that some had a bracket halfway up the wall in addition to the bracket near the top plate. Once it was all drywalled (Canadian term for Gypsum board mounted) you could walk along the wall, pounding it and hear the frequency change by about an octave difference between the two areas. I know a complete detailed equation model is not practical, but isn't there a little more to it then just the formula below, or am I missing something in my thinking?

f=170/sqrt(md) where f= center frequency of absorption m= mass of panel in pounds per square foot d= depth of space in inches

I am really learning a lot on these forums and my hat-is-off in appreciation to everyone involved. Thanks!

Howard, Now that you have the formula, you'll find specific plans on my web site. Look for "Build a better bass trap" about halfway down the list on my Articles page: www.ethanwiner.com/articles.html --Ethan

I know a complete detailed equation model is not practical, but isn't there a little more to it then just the formula below, or am I missing something in my thinking? Quote: f=170/sqrt(md) where f= center frequency of absorption m= mass of panel in pounds per square foot d= depth of space in inches I am really learning a lot on these forums and my hat-is-off in appreciation to everyone involved. Thanks!

Nice story you wrote. Yes there is a lot of detail involved with system resonances. Depending on what the goal is, the design may focus on Transmission Loss (TL) or absorption, or both. The absorption that we are talking about is the total wall system at low frequencies. A good description of factors involved, focusing on TL is in http://www.domesticsoundproofing.co.uk/tloss.htm As you read it think about the underlying physical concepts, not TL. Enjoy![/url]

Howardk wrote:

tmwhi - what program did you do that 3d drawing with? I have a 2d CAD system but I am looking for an inexpensive, easy to use, 3d program for illustrating ideas etc. . .

It was actually just the little drawing tool in PowerPoint for Mac!

I’ve come up with a better drawing that shows my proposed placement of 4’ x 2’ panels in the room (the turquoise boxes). As shown on the diagram, I have intended to put two directly on the ceiling, and one each at an angle between the end-wall and ceiling boundary (marked *). Any other placement suggestions would be much appreciated. A design for the 4’ x 2’ panels I intend to use comes from the following webpage (for the mid and high frequencies). http://www.bobgolds.com/TrapMartin/home.htm He seems to have made them exactly the same for the low frequencies (except 4 inches in thickness rather than two) and just hung them 45-degrees across the corners without being an airtight unit – does this work effectively? If they will work well, I’ll hopefully make a start this week. Forgive me if I seem to be repeating myself but I just want to make sure of everything before I start, my understanding is still a bit sketchy. Thanks again, Tom

Tom, > just hung them 45-degrees across the corners without being an airtight unit – does this work effectively? < Sure, that's a standard placement for rigid fiberglass. --Ethan

Great. One more final question (honest!) for now at least, I've been searching posts on here for a few hours and just want to make sure: Owens Corning 703 seems to be the preferred material for such panels, but Rockwool will also do the job won't it? The reason I ask is that it seems to be much cheaper here in England and more readily available. Thanks again Tom.

Tom, > Owens Corning 703 seems to be the preferred material < For low frequency absorption my tests show that the denser 705 is better at the lowest frequencies - those below what the published specs report. > Rockwool will also do the job won't it? < Absolutely. All such products are fairly similar, and all come in a variety of densities. --Ethan