Room Treatment

J

JPickman

New member
Hello All,

I could use soem help on some ideas on treating my room...once it is complete...

it will be about 12X19 with around 8' Ceilings down the middle and 6 feet on each side lengthwise due to framed in ductwork....

In fromt of the console I would like to soffit mount my mains....

I also have a soffit in the back for a 2" tape machine that I figured I would just foam the whole inside to kill the machine of the tape as much as possible.......


Thanks for the help....Pick Man
 
First, go here and click on EVERYTHING - especially acoustics, absorbers, and construction...

http://www.saecollege.de/reference_material/index.html

Then go here

http://www.homer.com.au/phpBB2/index.php

Next, go here

http://www.johnlsayers.com/

If you check out all those, you will have more focused questions and will understand the answers better... Steve

Oh, I just ran the modal response on your dimensions and you will have coincident modes at 141 hZ and 282 hZ - better check out the info on slat absorbers at the SAE site so we can discuss that too...
 
Quick and easy

You might also want to check out Microcosm acoustic panels. This is a pretty quick and inexpensive treatment. I went with their 1024 panels myself and I've found them to be quite effective.
 
Thanks Knightfly.....you answered exactly want I wanted.....

I just didn't know yet which frequencies were going to cause problems........I have read over all of these documents a million Times....good stuff...there are just so many different types of things out there for treatment....

Was looking at bulding a slot resonater on the rear wall....bass traps in the front corners under the soffit mounted monitors....possible some burlap wrapped OC 703 panels on the cieling and the sidewalls.....how does this sound to you guys?

Hopefully the control room will be done soon and I can post some pics!....


Thanks a Million!

Pick Man
 
PickMan, your room seems long enough (assuming your speakers/desk are on the SHORT wall) to be able to get the speakers far enough from the walls and still have at least 11 feet from your head to the rear wall - if not, anything reflective on the rear wall (behind you) isn't a good idea. Causes early reflections back to you, muddies the stereo imaging)

If you CAN get the necessary 11 feet or more, slots on the rear should be fine - they take care of the low mid/upper bass that makes most rooms muddy, and will slightly diffuse the highs.

I would probably alternate slots with a couple of home-built quadratic diffusors 10-12" deep, given you have the 11-12 foot (kor more) gap from your head to the back wall.

There is a simple spreadsheet I wrote about 12 years ago here

http://www.prorec.com/prorec/downloads.nsf/category

If you have Excel or Lotus, download the file "roomtune" - it is a self-extracting file with both versions of the spreadsheet and a basic docs file, it will tell you what the primary modal frequencies of your room are. Generally, you want at least 5 hZ between modes, and not more than 20 hZ.

There is a more complex one that includes Tangential (4 surfaces) and Oblique (all 6 surfaces) modes, as well as Bonello distribution charts (explained briefly in the spreadsheet itself) that I found last year (thankfully BEFORE I started to expand on mine) located here - the directions embedded in the first page of the spreadsheet explain the basics of how to use - I got tired of converting to inches, so I changed the feet cells (right of the inches cells) from a formula to an entered #, and saved it under a different name - now, I can use either.

http://www.studiotips.com/tools/MODESv2p.zip

Or, if that link doesn't work, go here and click on the file

http://www.studiotips.com/

when you get there, click calculation tools, and the first file on top is the one.

Be sure to follow the directions on the sheet - if you don't do a [ctrl][shift]S, [ctrl][shift]C after changing dimensions, it won't update info and you'll be looking at incorrect data.

Also, a quick way to find out if your room has problems with this sheet is to look at the Bonello chart page - you want taller blue than red in each band, otherwise it's a problem... Steve
 
Just ran your room thru the second spreadsheet, and assuming an 8 foot ceiling you have some modes that are coincident (not good) but if you assume a 7 foot average that goes away. The room still would have a slight dip at around 40 hZ, but overall not bad.

That was just in case you don't have Excel or Lotus, and were considering going out and buying it just for this... Steve
 
Thanks Knightfly...

one question though.......

I am not real bright when it comes to certain things......How do I read the spreadsheet.....Once I put the L,W, & H in........? I am not a big physics or math person....example Do you tell coincident nodes by the L-1,W-1, H-1 all being the same or very close to each other or too far apart? Or do you want them all the same numbers or as close as possible? Any help on this would be appreciated......also one you figure out what they are....what is the best way to treat them.....is it by Frequency with Bass Traps and Absorbors or by other methods?



ps.......Thanks A Million for all the Help.....


Pickman
 
Hey, JP - I just re-read the docs I included with roomtune - I think I'm going to have to re-write them, it's been about a year since I wrote that and I need to change some of the statements to reflect things I've learned since.

However, the information you asked for is included in the doc file that is packaged with roomtune - here it is -

"each harmonic of each axial mode should be about 4hZ wide at the 3dB point. The goal is setting room dimensions so that there are no coincident harmonics, (at least 5-6 hZ apart) no harmonics further than about 25 hZ, and as even a spread between adjacent harmonic frequencies as possible"

What this means, is that no two bars on the chart should be the same height (frequency) - they should be at least 5 hZ different, not more than about 25 hZ from each harmonic to the next highest frequency, and as evenly spaced as possible.

In most rooms, the bars in the chart from left to right will NOT be increasing evenly, or even in order. You will probably see conditions where the L2 harmonic is lower in frequency than the preceding, H1 harmonic. This is not a problem. what IS a problem, is if each taller bar (higher frequency harmonic) is either the same as any other, within 4-5 hZ of any other, or farther apart than about 25 hZ from the closest frequency to it.

In other words, if you were to re-arrange the bars in the chart so that they were successively taller from left to right, each successive bar should be at least 4-5 hZ taller than the previous one, and NOT more than about 25 hZ taller than the previous one.

As far as treatment, if possible prevention is the best cure. In other words, if the room has yet to be built, choose LWH ratios that give the most even spread of modal harmonics. I believe this to be advantageous EVEN IF you are lucky enough to be able to build a room with non-parallel walls, but it is REALLY desirable if the room has to be rectangular.

Here is an example: open roomtune, and enter these values for L, W, and H - L=13, W=11, H=9 - be sure and hit the ENTER key after entering the last #, so the sheet can re-calculate.

Note that from the left of the chart, over to about the 4th harmonics, each bar is at least 4-5 hZ apart but not MORE than 25 hZ. (Keep in mind, that you have to skip around to get the next tallest bar after W3 - ) Beyond that, this size room has some minor gaps in modal response - in other words, too wide a gap in frequency between successively taller bars. These gaps, since they are 4th or 5th harmonics, probably won't cause serious problems.

It's really hard to get a small room looking any better than this, because the shorter dimensions make it so the gaps are usually farther apart. Once the room is built (or if it already is) these "gaps" or coincidences will tell you what frequencies need to be absorbed - generally, wideband absorption works better, though - there are other factors that enter into room responses, such as wall resonances, reflections from furniture/racks/etc, so that the best way to figure out how to treat a room is to listen to it with music being played thru the speakers.
 
Okay I get it know....


Thanks......Here is a diagram for the room it is not perfectly square though, it actually gets about a little over a foot wider in the rear.......


I thought I uploaded it with the first post but just know realized it wasn't there...

So here it is

Do you think I will still have the same problems?


Thanks,

Jeff
 

Attachments

  • design6.gif
    design6.gif
    22.8 KB · Views: 239
Actually no - the splayed walls will smooth out what few modal problems the room might have had - also, that little alcove at the top right of the drawing would make a great place for a bass trap - if you're using it to store stuff, no problem as long as what's there doesn't rattle or resonate -

You could just put a sealed door on the alcove, made of cloth-covered 2" rigid fiberglas such as Owens Corning 703 or similar Knauf product - if you wanted, you could use a pre-hung interior door, and cut out the middle section, replacing it with the fiberglas and sealing around it with good silicone caulk.

I wouldn't recommend that type of caulk for most studio use, but remember you WANT a bass trap to leak some, so a tiny crack from shrinking caulk would just make a "mini-slot" resonator of sorts, not causing a problem.

If your computer monitors really are not centered between the speakers, I'd move them - you want your mix position to be as symmetrical left to right as it can be.

Once you had the door in place, it wouldn't matter what you store in there as long as it didn't rattle, so you wouldn't lose storage space... Steve
 
Thanks Knightfly..


Yeah the little alcove is the soffit for a 2" Tape Machine.....so I wasn't going to put a door there..........I was going to cover the walls inside that alcove completely with foam, to try to keep the noise from the tape machine down....is there anything else that I could do in their without closing it off and still get a 2" machine in there?



Thanks!

Jeff
 
Yeah, if there's room overhead you could use whatever space is left for a bass trap - placed in a ceiling corner, it would have the most effect. Just a framed box, with 2" 703 or equivalent lining, and preferably DOUBLE 703 on the front. Just make sure you leave enough operating room for changing tapes without hitting your head (Im assuming it's a horizontal transport?)

Just make sure you have plenty of air circulation where necessary for cooling on the tape machine. Completely lining the alcove with 2" absorbent, preferably the 703 type, will keep any of the machine noise from coming back off the inner wall surfaces - If that isn't enough, maybe a movable, absorbent "gobo" in front of the machine... Steve
 
When making a portable bass trap panel to mount on the wall using Ethan's design. Instead of using Rigid Fiberglass can I get away with using the pink Polyfoam with R7.5 rating? If not, does the Polyfoam have any use at all be sound treatment?
 
Haven't tried any of this pink poly stuff myself yet, but from what I've read it's a closed cell foam, and generally worthless for acoustics (might not be too bad for pads to sit stuff on that vibrates, if you're into pink...)

About the only luck most people have had in finding the 703 stuff is to check the yellow pages for local COMMERCIAL insulation contractors, and see if they will sell you some. Owens Corning isn't interested in selling to individuals - they only seem to want pallet-load sized orders on the rigid stuff... Steve
 
Smith,

> can I get away with using the pink Polyfoam <

As Steve suggested, that stuff is useless for acoustics - whether inside or outside a bass trap.

--Ethan
 
Thank You.

Is Armstrong 770 and USG 2310 with a rating NRC of 55 the same as the Owen 703? The acoustical tile sales guys told me it was and I want to double check with some pros.
 
Couldn't find anything on the USG stuff, and the only info on Armstrong looked like some 2' x 2' ceiling tiles. If so, then not the same stuff... Steve
 
You must log in or register to reply here.
Back
Top