50Hz ring, 60Hz hole, best material to treat?

[Lights]

Hi all:

My room has a ring/resonance at 50Hz and a big dip at 60Hz. In looking at absorption coeficients of things like OC703 and Knauf Ecose, they only list absorption at 125Hz and above. Auralex lists their LENRDs at 100Hz and above. So as a noob trying to figure out what to do to try to treat these issues (and wondering if these issues are even worth treating) I'm hoping I could get some advice.

I'm happy to provide diagrams of the room and waterfall charts to show what I'm talking about if people think that would be useful.

[amishsixstringe]

50-60Hz is quite low, and often a very difficult range to tackle. How much of a dip is there at 60, and how long is the ring at 50? How big is your room, and what is there already as far as treatment? Are you in a house, or in a 'studio'? How much space is there available for treatment? Also, what is your monitor situation like? Do you have a sub/bookshelves/monitors on stands?

These are all pretty important to help you.


Neil

[DanDan]

Deep, very, porous will work. 40Hz, go to hell!
However GS may be at the coal face of innovation right now.
My Experiment with a Metal Panel Absorber
DD

[Lights]

Happy to provide the info. It's the basement bonus room in my house. The diagram with dimensions of the room is attached (the locations marked for treatment are just ideas). The only dimension missing is the height, which is 8ft.

Also attached is the waterfall diagram down at the lowest fequencies, which shows the ring at 50 and the dip at 60. The room is completely untreated in this waterfall, however, neither changed much with Auralex LENRD bass traps installed floor-to-ceiling in the corners of the room marked with the letter A and again with the the corner nearest the right speaker marked A and the corner in the back marked H.

I have been reading lots of the threads on studio acoustics and I have to say I understand only a small percentage of what I'm reading but as you can see from the date of the measurement attached I let that confound and frustrate me for nearly half a year and I'm determined to just go and try to do what I can with my limited knowledge and (hopefully) the help of the good folks here I can make some headway.

My plan was to use a combination of home-made Ecose 3lb PCF fiberboard traps and the contents of an Auralex Project 2 kit to bass trap and create a reflection-free zone and measure the improvement, but after doing the bass-trap-only experiment, I decided to ask for assistance. (Also, the smell of that foam was strong enough that I had to lay it all out in the garage to air out for a few days before trying to install it.)

EDIT: forgot to answer: the monitors are Mackie HR824 (Mark 1, the original kind made down the road a bit in Woodinville, WA, not in China.) While I know it's not perfect, they sit on risers on my desk to the left and right of my LCDs, angled down on mopads. The risers are isolated from the desk by small hand-made sorbothane feet. Attached is a picture of what it looks like where I sit while I'm writing and mixing.

(Hey, I've already gotten tons of flack for having my monitors on a large desk versus on stands behind some very minimal surface, so I don't need to repeat that discussion here unless it's at all related to the issues I'm having at 50 and 60Hz.)

[Lights]

Here are some more captures that I just did. All measurements using just one speaker with a Behringer ECM8000 situated at the listening position pointing directly between the woofer and tweeter.

The "untreated" are taken in a completely bare room.

The LENRD Front Corners waterfalls are taken with floor-to-ceiling LENRD traps placed in the corners marked "A" in the diagram from my previous post.

The LENRD Front Right + Back waterfall (right speaker only, which exhibits the biggest problem) is taken with the corner closest to the right speaker ("A") and the back corner "H" treated floor-to-ceiling with LENRD traps.

(I only have 8 LENRDs, enough to treat 2 corners floor-to-ceiling, so I have been simply propping them in the corners. I do have some T-Pins and could 3 LENRDs in the front corners and 2 in the back from ceiling down if I pin them in place, but since I'm getting almost no improvement I was wondering if I should sell them and try Knauf Ecose (OC703) traps.)

[amishsixstringe]

Ok, thanks for all the info. I don't have a lot of time right now, but I will give you something really quick right now. I can talk to you more in the next couple days or so. Also, the info you gave should help others on here in the meantime.

So, you are treating the space that is your 'mix room', but it is absolutely coupled with what looks like a bedroom. You need to treat the whole place. The front two corners should be trapped as you have. I would also trap the other 90* corners in the whole room if you can. Floor to ceiling. You may also want to do some work with the ceiling/wall corners if you can.

You need to treat your bass problems before worrying about specular reflections arriving at your mix position. That is relatively easy compared to LF modal issues. Your graphs are hard to really see, but you seem to be correct in saying that they look pretty much the same. Those LENRDs are pretty lame, dude. I have never seen them really do anything other than kill the upper mids in a room. It still amazes me at how many 'pro studios' have that stuff.

You will see much improvement with some low density fiberglass or rockwool corner traps. Make them as big as possible and put them in every corner possible. Measure as you go along, making note of what corners seem to do the most good and which don't make much difference. As a hint, you can actually just do a quick test by playing a sine wave thru your speaker at the frequencies you are having trouble with. You can use a dB meter or just use your ears and find the places where the tones are loud in the room and where they are quiet. Use some masking tape on the floor to mark the spots. On the tape write with a sharpie the height from the floor that you are hearing the specific volume change. This will help you place your traps. Where the tones are loud is where traps will be presented with the most energy.

You don't have much space. You also have a pretty irregular shape that makes predicting what dimensions are causing your problems. That is why it is important to just find where the hot spots are and trap those. You want to trap the hot spots for 50 and 60. Realize that 60hz needs trapped. You are also in a basement, so your ceiling is probably thinner than all the other walls in the room, so you are surely coupling your space with the house above you to some degree, making it even more difficult to predict.

You will find that spending a lot of time really understanding your room will go a long way. You don't have much space, so you really need to maximize the efficiency of your traps. Reality is that the Auralex you are using can be improved upon with a better product that takes up the same space. At the same time, use as much space for trapping that you can afford to (monetarily and ergonomically).

Good luck,

Neil

[Lights]

Thanks for replying!

RE: the hard to read graphs, attached is the REW dataset, which you can load up and slice-and-dice any way you want.

I have a line on some Knauf Ecose locally--it's the 3lb PCF variety. Is that sufficient to do the job? When I build the traps, how thick should they be? The boards I can get are 2'X4", and 2" thick, so I could make them any multiple of 2" and use two traps to cover floor-to-ceiling in the front corners.

The room isn't a "bedroom" per se, that's just where I "interview" my prospective backup singers. Hahaha, just kidding We don't really have a guest room (we turned one of the real bedrooms 2 floors up into the kids' playroom), so we threw a bed in the basement bonus room for when grandparents come to visit. The bed (with small bedside table) just squeezes in back there, so there really won't be room for fiberglass traps there. I could potentially use the LENRDs there, but my wife would kill me if I put giant 2x4' framed walls of fiberglass hovering over the bed and there's no space to move the bed forward...

But is there another solution? If you see in my diagram I have a rectangle marked "G" -- I could potentially build some sort of trap on wheels there. The gap is pretty big, though. Would something like that mitigate issues? Should it be hard-backed or no-back? (I assume the corner traps are to be no-back, but a wall that sits in the middle of the room I'm not so sure.)

EDIT: is there a VST that generates a sine wave at any frequency? Cubase comes with one that has some fixed values, but not one that lets me sweep smoothly from 40Hz all the way up through the trouble range.

[amishsixstringe]

Thanks for your response. We will get you going in the right direction a step at a time. I am assuming you are in no serious rush as you have been messing around for half a year already. That is good, because this can take time.

As for the insulation you have available to you, it will work great. It is very similar in testing to OC's 703 line. I would not make panels to trap 50hz. I would make superchunks. You can google them or find tons of people on GS that have made them with very good tutorials on how they were made. Essentially, you take a 2'x4' board of insulation, cut it in half to make 2 2x2 squares. Then cut them into triangles. Each panel makes 4 triangles. Stack them on top of each other in the corners from the floor all the way up to the ceiling. This yields a solid trap that is very capable of trapping very low frequencies. You can cover them with a sort of frame and stretched fabric. They can be permanent or portable. Someone on GS just recently made some portable traps out of cardboard backers. They look awesome. You could even build some of those and throw them in the 'bedroom' corners while you are working and move them back out of the way when you are done.

As for your trap in the 'hallway' area: I have no idea. Again, you can play a sine wave at your target frequencies and move about the room in search of areas with high volume. If that is in that hallway thing it might be helpful to put a portable 'gobo' type trap there, but probably not really. I would most likely focus on corners. You have lots of corners. Like 20.

You don't need to 'sweep' your tones as you are listening. In fact, I would not. Just tune your tone generator to a fixed frequency. Say 50hz. Make notes of hot spots. Tune up to 51hz, and then do the same. If you want a sweep, though, you can do it in REW. Also, I think realtraps has a sweep file on their website that you can download for free.

Good luck,

Neil

[Lights]

I thought about superchunks, but for an 8 foot ceiling at the cost of roughly $100 per box of 2 panels (which is on the low end), that means it's $120 for the fiberglass alone per corner... so all told I could be more than $400 in for the hope that I'd address the problem :(

The only sine generator I have is one that does 4 different frequencies, I can't specify a frequency I just get to choose 4 buttons of common test tones. If someone has a VST or an EXE for PC that generates arbitrary frequencies, that will do the trick.

[DanDan]

REW has a brilliant Signal Generator. Check the frequency follows cursor box and the sine frequency will follow. Slide the cursor over a peak or ridge....
There is another Java one which should work on PCs. The Virtual Minirator, downloadable here.
RealTraps - Acoustics Info
DD

[amishsixstringe]

I realize your reluctance to spend money, but this isn't something that is a gamble so much. The auralex was a gamble, but for some things math, science, and physics don't lie. One superchunk in the corner will improve your room more than all the LENRDs you have right now.

If you really can't afford to put chunks in the corner you can surely put panels there. I would make them 4" thick if you can and straddle the corner. You can even LIGHTLY stuff some unfaced R-30 insulation behind the panel. It will help. You have to understand that 50Hz is pretty low, and has a ton of energy. It is not easy to tame that much energy. It will cost you money. It will also make your music sound good much faster than whatever preamp you bought last.

Dan, your thoughts?

Neil

[DanDan]

Well, maybe the money is gone on the Lenrds.
The 3pcf Ecose is just about right.
I am pretty familar with SSC's. They work. I see the larger 34 inch wide ones making brave attempts at 34Hz with considerable success.
Square traps are probably even better, and may be easier to construct. No cutting.
See GIK Soffit Traps.
The cheapest bestest is probably 3 foot wide SSC frames filled with light cheape attic insulation. Ecose again is nice.

Have no doubt though, or hope. Be sure that babies will improve your LF a lot if they are at the source of your problem.
To be really sure use the Sines. If 50Hz is hottest in those corners, fill em.

DD

[Lights]

I got an incredible deal on the Project 2 kit, so I don't feel too bad about that. If the LENRDs are truely useless, I can sell them for a profit likely. If they have some value, I can use them in things like the wall-to-ceiling corners, etc. I'll keep them until I'm sure I don't need them and I'm likely to use the 24 2'x2' reflection tiles.


If it's not a gamble, I don't mind spending some money, but if there's a cheaper option I'd be into that as well. I could easily make 6" deep panels at a fraction of the cost or, as you say, build 4" panels back-filled with cheaper fluffy stuff (can you tell me what formaldehyde-free product would be good there?). If I'd get similar noise reduction, I'd consider those options. Also, if soffit fitting some of these solutions to the top half of the corners will work, that cuts my cost and work in half.

Once the kids are occupied, I'll try the sine test and see what I find around 50Hz and 60Hz for that resonance and hole. I do hear *something* high-pitch rattling in the low level when I do the sweep so I wonder if that could be part of the ring... I don't know if REQ hears that. Whatever it is, it never does it when REAL music is played. Could be the ceiling mounted lighting fixture or something like that...

[soundoff]

If you are considering the panel straddling the corner approach, then I don't think oc703 or another brands 3 lb equivalent is what you need... You really should be looking at the oc705 or other 6lb per square ft panels. Knauf makes 6#. You can get it in 2" panels... Double it up... And get better low end reach. Also, you'll want to face the panels behind your listen position with Kraft paper or FRK. That too helps a tad more with the lows. I can send you a link when I get home if you want to see the testing done to show this

[amishsixstringe]

If you aren't going to fill all your corners with real stuff, then you could keep the auralex and put it in the remaining corners, but it is obviously not worth anything.

Johns Manville makes formaldehyde free fiberglass insulation. I use them a lot.

The ring that you are hearing, I am sure REW hears as well. Also, if you hear it, it is there when music is playing too. You just can't distinguish it. I assure you it is effecting your listening experience negatively.

Get some fiberblass. You will be happy. Lose the LENRDs.

Neil

[amishsixstringe]

705 is too dense to go down that low. 703 is even a little dense. R30 johns manville just stacked up in a frame and covered would be best, but you may need more of them (more corners treated) to really make any noticeable difference.


Neil

[Lights]

Hey I found this superchunk installation online: Steven P. Helm: DIY Bass Traps

This used mineral wool. What's the least expensive material I can build these out of that's still formaldehyde free?

I'm pretty sure the 6PCF stuff is quite a bit more expensive... I'll have to check with the local dealer--but at that point it's probably similar or less to just build the superchunk... if someone could tell me the least expensive design+material or combination of materials (that are formaldehyde free) I'll go for it

[amishsixstringe]

Price and availability seems to differ from location to location. In my area I can get a box of roxul safe n' sound for 40 bucks from down the street. Find something local that you don't have to pay shipping. You want something light. Not dense. Get as much of it as you can. It doesn't matter if it's rockwool, fiberglass, cotton, whatever. Just get something 3lbs or less. Make some sort of frames or boxes and shove it in. Put in corners. Test. Repeat.

Don't get too caught up in the whole 703 stuff.

Neil

[Lights]

Oh that makes a huge difference. So I just want something that's cheap, formaldehyde free, and 3PCF or lower. That changes the pricing dynamics completely

You said cotton... does it have to be insulation? I mean if I fill a trap with cotton balls, would that do the same job??

[amishsixstringe]

I don't know that anyone has ever tested cotton balls. I assume they would be fine. I also think that you would need like 500 bags of cotton balls, which would cost a fortune.

I have heard of using cotton, but never really looked into it or tested it myself.

Do some searching on here.

Neil

[Lights]

Well, I guess what I meant is if i could use just about any lightweight material that's not insulation, my options are limitless... and I could buy something like the stuff they make couch cushions out of, etc.. I may not have to go to a specialty insulation store... and I could choose things that aren't as potentially toxic as insulation.

[amishsixstringe]

I would try to stick to things that have been tested. For instance...foam is lightweight, but kinda sucks....as you have found out.


Neil

[Lights]

Hahaha... good point. So is there a single thread that lists all the good stuff to use for superchunk style corner absorbers?

[DanDan]

Cotton, as in Ultratouch doesn't do well at low frequencies when it is thick.
Straddling panels say 4-6 inches thick could do with being 6pcf.
However SuperChunks, or big flat ones like in 40Hz go to hell, are fine with cheap light attic insulation. Ecose do that.
DD

[Lights]

Got it. It seems to me like the easiest implementation would be to buy the cheapest fluffy attic insulation possible and somehow stuff it in loose, inexpensive burlap bags. Affix a 2-foot face frame diagonally across the corner, fill behind it with the bag(s) of insulation, and then cover the face frame with some porus fabric.

I may need to place some thin strips of wood or chicken wire or something of that nature to keep the bags from bulging out behind the face frame's fabric.

Any issues with this design?

[DanDan]

Perfect. A facing of laths can look very nice and bounce back a tad of scattered HF. Here's one I prepared earlier....
http://www.gearslutz.com/board/6457886-post91.html
DD

[Lights]

Nice. What if the refractive wood is behind the cloth facing? Not sure I have the skills to pull off the special pattern though.

[DanDan]

The effect of these little laths is HF. Behind the cloth you would lose a little of the highest. These were standard pieces of wood. No cutting needed as best I can remember. The randomness does follow Newell's pattern but I do not believe this is critical at all. Just get three different sizes of lath and make up your own random pattern to look good.
DD

[Lights]

Cool. I thought that you had to cut the strips to specific sizes. That's no problem. Thanks!

So burlap bags are incredibly cheap, now all I need is some suggestion on the least expensive (but not ugly) acoustically transparent fabric that I can get in sizes at least 8.5' x 2.5' and I think i have everything I need to build these corner traps for about $40 each.

[Lights]

Also I assume this is adequate insulation: EcoTouch R-30 Unfaced 9 in. x 15 in. x 25 ft. Continuous Roll Insulation-RU70 at The Home Depot

(This stuff probably has formaldehyde, but just to get my bearings on acceptable insulation.)