Bass resonance problem

madtheory · 11-04-2012 06:18PM

USE THE CORNER PANELS FOR THE REFLECTION POINTS. No need for panels and rolls/ fill in, that's a waste of good panels. Fill the corners simply with the rolls. It will work fine in the packaging it comes in. But given that you've unwrapped it, you would do a nicer job building a super chunk of some kind and stuffing it tight with what you call the "fluffy stuff". You'll get slightly better LF absorption that way, without the plastic wrapping. The "breathable" thing is only a very rough guideline, it's not hugely important, especially at the level you're at.

And...I did say this several times already: take out your existing corner panels and use them for the reflection points.

For the size of room you're in, a bigger panel is better (within reason). So build whatever size is most convenient for you.

BTW if you've only done the corners, you've only done the tri corners. There's a bicorner everywhere you've a right angle!

pinksoir · 11-04-2012 06:43PM

Ahaaaa. Bicorners. Of course.

I didn't understand that you were telling me to take out my existing traps and replace em with the rolls. Got it now. I did go off earlier and bought more RW3 though...

Do you think the rockwool rolls turned into sort of superchunks like you described would be better than the RW3 panels I have now or about the same? Cos if they're better I'll build them, but if it's negligible I'll leave it as it could be fiddly enough.

Thanks again.

madtheory · 11-04-2012 06:47PM

Eureka!

The rolls are more effective than panels. And there's no building as such- just stack em in the corners and cover with something pretty. As you say- "sort of superchunks". They measure only slightly less effective than actual superchunks, with zero effort.

A normal room takes two with a slight gap at the top. You can also cut a roll with a saw to make a small fill for the gap at the top.

pinksoir · 11-04-2012 07:09PM

Alright so. I only have one roll of fluffy rockwool though so I wouldn't have enough to superchunk without buying more. I presume it has to be a certain thickness (ie as thick as a roll) for it to be effective?

I'm gonna go ahead and build 4 more panels from the RW3 I got earlier anyways, treat the FR points and go from there.

BTW having a listen to your tune-skis at the mo (vol II). Good stuff.

madtheory · 11-04-2012 07:16PM

Thanks

Just to re-iterate: leave them in their original packaging and just stack them. Normal rooms take 2 in each corner.

pinksoir · 11-04-2012 10:46PM

Good stuff.

I do have the RW3 panels I bought today though. I don't really fancy spending more cash on 3 more rolls of rockwool to do the corners. At this point I guess I have a few options;

1) Stuff what fluffy rockwool I have (one roll) in behind my RW3 panel corner traps to fill the gap. I think what I have will be enough. This'll leave me with 4 RW3 panels to build absorbers from.

2) Build 60cm-faced triangular superchunks from the RW3. This'll leave me with 2 RW3 panels to make absorbers from.

3) Buy 3 rolls of rockwool and stick them in the corner. This'll leave me with 8 RW3 panels to use as absorbers.

As I said I'd rather avoid parting with any more cash so for me number 3 is kinda out. Between 1 and 2 what would be best?

Obviously I'll be building my first reflection points first before I do anything else.

i57dwun4yb1pt8 · 11-04-2012 10:57PM

you need to take the wrapping OFF
and cover them in either cloth that allows air in but no fibres out , or two layers of decorators dust sheets.( cloth )

the plastic wrapping makes them near useless- the air needs to get in .

pinksoir · 11-04-2012 11:05PM

I'm not so sure about that. From what I've found online both EW and the dudes at GIK advise to leave them in the wrapping.

But anyway, I'm not going to be using the rolls so it's irrelevent

i57dwun4yb1pt8 · 12-04-2012 01:39PM

ethan winer said that ?

hmm, surprising - well he's the man , so i stand corrected.

madtheory · 12-04-2012 03:57PM

I guess you missed the extended debates about OC with or without foil backing, and the use of cling film for a membrane absorber? Endless fun...

pinksoir · 12-04-2012 10:11PM

Okaaaay. I built my FR absorbers. The resonance thing is still there, exactly the same.

On the plus side, the FR absorbers are really great.

What now?

madtheory · 12-04-2012 11:19PM

You've done the main reflection points including floor and ceiling? And the bicorners? Have you got exact room dimensions and put them into a mode calculator? I'm not clear on your room size- do you have two equal dimensions? Because that will require a Helmholtz absorber. Have you tried moving the mix position slightly?

pinksoir · 13-04-2012 12:04AM

Okay, here's a breakdown of what's going on.

My room is:

255cm wide (8ft 4")
248cm tall (8ft 2")
559cm long (18ft 4")

I have calculated the modes using EW's mode calculator. They are as follows:

The problem frequencies I am experiencing are:

61-65Hz

123-130Hz

Basically both C an octave and two octaves below middle C, and the Bs below them.

The trapping I have done thus far is:

-Front two corners, floor to ceiling with 100mm (4") RW3 panels.
-Left and right First Reflection points with the same, but not floor to ceiling.

I have two RW3 panels left so I will treat the ceiling tomorrow. I haven't done the bi-corners as I don't have enough panels/cash to do them right now. I can't easily treat the back corners really as there's a ton of stuff there - bookshelves etc.

Looking at the modes from the ModeCalc it looks like the problem frequencies are occurring in the modes from the room length... though I don't really know what I'm doing so I could be wrong.

Cheers

madtheory · 13-04-2012 11:51AM

So let me get this straight... you still haven't done the superchunks made of rolls of RW? You still need to do all four tricorners? And you can move the front corner panels to the ceiling which SAVES YOU BUILDING MORE PANELS. And put a rug on the floor. Then come back to us...

pinksoir · 13-04-2012 12:30PM

I am not going to buy 3 more rolls of rockwool to stick in the corners as they are nearly 30 euro a roll and I have no money left. I explained to you numerous times that I only ever had one roll of rockwool. I don't have 4 rolls to stack in the corner. I do however have the one roll rolled back up into black sacks and packed behind the RW3 panels. It reaches about half way up, stacked, on each side.

If the rear tricorners are the next most important thing to do, then I'll do them today. It will be extremely difficult. I explained earlier in the thread that my back wall is half window, half shelving. And the door into the room is where the back wall meets the side wall. I will find a way to do it.

I have a rug on the floor and it's carpeted anyway.

Thanks again for the help.

i57dwun4yb1pt8 · 13-04-2012 12:55PM

FIGHT ! FIGHT ! FIGHT ! FIGHT !

fitz · 13-04-2012 01:00PM

pinksoir wrote: »

I am not going to buy 3 more rolls of rockwool to stick in the corners as they are nearly 30 euro a roll and I have no money left. I explained to you numerous times that I only ever had one roll of rockwool. I don't have 4 rolls to stack in the corner. I do however have the one roll rolled back up into black sacks and packed behind the RW3 panels. It reaches about half way up, stacked, on each side.

If the rear tricorners are the next most important thing to do, then I'll do them today. It will be extremely difficult. I explained earlier in the thread that my back wall is half window, half shelving. And the door into the room is where the back wall meets the side wall. I will find a way to do it.

I have a rug on the floor and it's carpeted anyway.

Thanks again for the help.

I may be wrong (and I'm sure I'll be corrected if I am), but if you're not going to fill the corners fully, I suspect you'd be better off having those black sacks in the top half of the cavity behind your panels.

I'd also say that the corners near the listening position are more important than the rear corners, if on limited budget.

pinksoir · 13-04-2012 01:05PM

Naww, madtheory's aiight.

I'm looking at treating that tricorner above where the door is. Any ideas on any designs to use? With my RW3.

I can think of a triangular shaped one suspended in the corner, or superchunking, or a 120x30cm (half size panel) suspended lengthways across the bi corner and into the tri corner.

madtheory · 13-04-2012 01:05PM

Yes, fitz is right, the front corners are the most critical, but not by much.

pinksoir wrote: »

I am not going to buy 3 more rolls of rockwool to stick in the corners as they are nearly 30 euro a roll and I have no money left.

OK, but you can't get around the physics of it. If you want get rid of the resonance, you need more absorptive mass in the room.

fitz · 13-04-2012 01:08PM

Would agree with MT, there's no cheap way to treat a room to a high standard.

fitz · 13-04-2012 01:19PM

Quick question pinksoir, the isolated monitor stands you mention in your first post...are they these, on top of the desk?

Or these:

If the monitors are still on the desk, and you're just using the mopad style isolation pads, I'd advise getting stands, and using them in conjunction with the mopads.
Doing that, and using this kind of kit (with some two extra tiles per first reflection point) on a roughly 11 x 10 foot room made a huge difference for me. It's not perfect, but I've no overly problematic resonances.

pinksoir · 13-04-2012 05:24PM

@fitz - It's the stands I have, not the pads.

@madtheory - I understand that I can't get round the physics. But I also can't get round not having money.

What I do have is 6 slabs of RW3 (that is 2 left over from the 4 I bought to make the left and right FRP absorbers, plus the 4 I have in the front corner traps) which I could cut up into triangles to make superchunks for the front corners. That would be 24" (60cm) faced triangles to a depth of 12" (30cm).

This would be in lieu of buying rolls of rockwool and stacking them. It would mean I would have superchunks in the front and then two left & right FRP traps. I could also stack up the fluffy stuff in one corner, floor to ceiling, at the back. Obviously that would mean I'd have used up all my rockwool on just treating those spots.

Alternatively, would it be better for me to keep it how I have it now and instead use my left over slabs to treat other parts of the room, like the back tricorners?

I would just like to know what would be the most effective use of the rockwool I actually have right now - that is 8 slabs of RW3 and one roll of fluffy rockwool.

Alright, scratch that. I see the non-rigid (fluffy) stuff is better at absorbing low frequencies. So I'm probably going to have to bite the bullet and buy some bales when I get the cash. At least I'll have a load of panels spare for other treating.

I'd prefer to actually build superchunks than stack the rolls so is there a particular thickness I should be aiming for? There are space constraints so I'd still be aiming for around 24" (60cm) face with 12" (30cm) depth. I could probably go a little bigger but not much. Would 12" deep be enough?

madtheory · 13-04-2012 08:38PM

Check John Sayers forum, loads of super chunking going on there, should give you the best idea for your room.

pinksoir · 13-04-2012 09:11PM

Cheers, will do.

Looks like the best option is 34" superchunks. I'm just trying to find out whether to use rockwool roll/bale or slabs for it. I can't really understand which is better as people are arguing right from cheap pink fluffy insulation up to RW3 (or its American equivalent). Apparently the less dense stuff is better for lower frequencies. And obviously 1 1/2 rolls of rockwool (2x100mm) will do 2 corners of 34" superchunks vs 3 packs of 4 slabs, so it's way under half the price.

DaDumTish, you said you'd done superchunking. What did you use, slabs or rolls? How deep did you do them? Did you have any problems with room nodes before and did superchunking get rid of them?

i57dwun4yb1pt8 · 15-04-2012 12:21AM

yes, the room was a fcuking mess / nightmare mode wise .

i tried 6 inch deep rockwool filled 2 by 4 acoutisc cloth panels two in each corner wall
to ceiling - thus leaving a large gap behind

wasnt enough so i filled the gap behind the panels with rockwool covered in painter dust sheets
so i have effectively filled the corners wall to ceiling to a depth of about 13 -14 inches .

i have two 4 inch thick 2 by 4 panels left and right at the reflection points

one corner is a door ( = bass trap ) and there is a window in middle of mix wall ( another bass trap of sorts.)

floor room is inch ply on top of thick heavy rubber carpet underlay - and slight damping on the ceiling in areas.

in the attic the ceiling has layers of rock wool on top of the plasterboard.

rest of room is untreated to keep some liveliness.

( i also had a cloud and more panels on back wall , and ceiling , but it became too dead )

its a 7 by 7 by 7 upstairs cube - concrete walls ( two are thin two are very thick )

its a nice little room now , translates very well , modes are there still but way way more under control . some were + or minus 30 db , they are now +- 6 to 8 db )

i think your ceiling is you major problem in your case. but filling each corner thick will make a massive difference.

pinksoir · 15-04-2012 01:06AM

Good stuff, thanks a million.

It's very confusing trying to find out which stuff to use from online. A lot of talk about different densities and which is best. 45kg/m3 is apparently the best for rockwool. The rolls are around 30kg/m3. I think the overriding thing is that more mass=better though, so I'm gonna use the rockwool rolls and compress them so each corner is taking two 4" rolls. That should bring the density up nearer the 45kg mark. And I'll do them as deep as I can with as wide a face as poss (34"). Hopefully that'll do it.

The problem frequencies I'm hearing aren't really near the modes of the room height so I dunno how much of a problem my ceiling is. At least I have a load of RW3 panels to treat it with anyways.

PaulBrewer · 17-04-2012 03:49PM

I've not read all this thread but ....

With two room measurements effectively the same any amount of rock wool isn't going to make much difference.

Even more space efficient tuned membranes probably won't 'flatten' it.

You can easily be looking at peaks/troughs of 20 dB plus.

That's not to say that it's not worth doing - just that the improvement will most likely be slight.

madtheory · 17-04-2012 04:20PM

In theory they're not really close:
255cm wide (8ft 4")
248cm tall (8ft 2")
559cm long (18ft 4")

But in practice, who knows? I think it's doable myself.

PaulBrewer · 17-04-2012 04:38PM

madtheory wrote: »

In theory they're not really close:
255cm wide (8ft 4")
248cm tall (8ft 2")
559cm long (18ft 4")

But in practice, who knows? I think it's doable myself.

In acoustic terms that's VERY close.

Remember all acoustic work is 'broad stroke'

69 hz to 67 hz is, in terms of treatment, the same thing.

I'm not saying don't treat - I am saying the room most likely has major problems - rock wool alone, especially the volumes spoken of here, is a 'minor' solution at best - especially the lower few octaves.

PaulBrewer · 17-04-2012 05:09PM

pinksoir wrote: »

I understand that I can't get round the physics. But I also can't get round not having money.

The latter is the more addressable, may I respectfully suggest.

Bass resonance problem

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