Closed Bass Traps

[mattianlaseppia]

Hello

I have a studio with 14 Bass Traps, 5 "double" Bass Traps and the corners filled with rockwool and one wall full of rockwool 4" thick.

Now:

1) I feel the room is "too dead" for my taste

2) I think, even if i used all the precautions closing the traps with fabrics, more layers of different fabrics, the rockwool edges came out and the air isn't so good for me, I think partially it's a "mental" feeling and part it's real.

So I'm considering to close all the Bass Traps and the corners and the wall, with multilayer plywood.

But I'm a bit scared about the acoustic, i don't want to lose the benefit closing the rockwool with multilayer plywood.

I want to use multilayer plywood because it's thicker than normal plywood and it's more solid.

For Bass Traps I'm considering using 0.8" thick multilayer plywood, for the boundaries, the frame, and 0.2" thick for the front and the rear, I'm also considering to put them in a way I can remove the front and the rear if i need more absorption for tracking, and close them during mixing or when I need a more healthy room.. i sleep in this room one month yes and one month no.

Than I'm considering to use multilayer plywood 1.2 thick for the wall and the corners, so I can also eventually mount some absorption in the ER points.

The traps i have behind me and in one side now are a little angled (a very little) I'm thinking to keep them tilted even when i close them, is this useful for ER? because if i close them they will be reflective without absorbing in the ER points, but if they are tilted they should not reflect anyway.. because aren't parallel to each other (L to R Front to Back)

What do you think? Will multilayer plywood compromise my acoustic, specially 1.2" thick multilayer plywood?

Thanks!

[DanDan]

Yes the plywood will change your acoustic totally.
You have constructed an extreme room. Plenty of traps, probably very dead. I suggest that you need to get used to it. Such rooms, with the HF rolled off on the speakers, can deliver great mixes, which translate well to the outside world.
So you propose covering all of those to make it very live. Surely another extreme? Steady. Small rooms very often end up very dead when enough traps are installed to get some control of the room. That's life. If you wish to liven things up a bit there are a couple of in-between options.

1 Install some thick paper or thin plastic sheet on the fronts of your bass traps. This will bounce some HF back into the room, while preserving the bass absorption.
2 Install some wooden strips across the front of your traps, to create a bounce back. The arrangement of strips and gaps should be varied and random. This also creates some diffusion.
www.johnlsayers.com has plenty of examples.
3 Install some Diffusors. Space Couplers and Space Arrays seem good at close range.
DD

[Glenn Kuras]

Just to add you can also add some curved wood in front of the panels for diffusion.

[mattianlaseppia]

Originally Posted by DanDan

I suggest that you need to get used to it. Such rooms, with the HF rolled off on the speakers, can deliver great mixes, which translate well to the outside world.

do you mean i should roll of the HF in the speakers using the built in controls or with an external Eq or software Eq?

So you propose covering all of those to make it very live. Surely another extreme? Steady. Small rooms very often end up very dead when enough traps are installed to get some control of the room. That's life. If you wish to liven things up a bit there are a couple of in-between options.

yes i'm considering these options, but probably i will not realize all them, or at least i will start and measure and see what works and what not, i just have written all the possible solution to have a feedback on what can works and what not.

but i already got an idea, thanks

1 Install some thick paper or thin plastic sheet on the fronts of your bass traps. This will bounce some HF back into the room, while preserving the bass absorption.

do you think a big plastic bag (like the black one for the garbage) could work? i need to find solutions to keep the rockwool inside and multilayer fabric doesn't work very well with all that rockwool...

2 Install some wooden strips across the front of your traps, to create a bounce back. The arrangement of strips and gaps should be varied and random. This also creates some diffusion.
John Sayers Productions has plenty of examples.

the arrangement is totally random or has any kind of logic? do you have a couple of pictures at hand?

3 Install some Diffusors. Space Couplers and Space Arrays seem good at close range.
DD

Does diffusers work in a small room? i've heard you must have at least around 20 feet from speakers to diffusers

Thanks you very much for your suggestions, very appreciated

Originally Posted by Glenn Kuras

Just to add you can also add some curved wood in front of the panels for diffusion.

Thanks Glenn, how much curved? i mean is there any logic even here or it's "random curved" ok, i imagine not too much curved :D

[SAC]

I can certainly understand your frustration.

I know that I will catch heck for the suggestion, but...

How about making measurements of the space - including ETC responses, and getting and idea of exactly what it, or is not, happening?!

Its easy to make 'a bunch' of generic changes - but I suspect that this is exactly how you ended up in the current situation...am I right???

I suspect that little has been done to actually evaluate the room's (original or present) response other than perhaps to determine that you need beau coup bass traps - oh, and of course, lots of absorption to control early reflections. ...An all too common and utterly inadequate treatment of the energy above the critical frequency where modes cease to be an issue.

And while wood is a material that might be utilized in the process, I would hardly use it to impart a "woody" room response - whatever in heck that is! Nor would I suggest simply introducing 'random' specular reflections into the room as a solution to the problem! But they just might be sufficient to distract you from the original issue! And unfortunately, to be sarcastic, many would consider that a solution based upon the number who do exactly this!

But you could use many materials in order to impart a more highly defined ISD and a more diffuse later arriving soundfield.

Then, with an idea of the room response you desire, it is relatively easy to make informed changes, observing their objective and subjective impact upon the response of the space...

You have been down this road before. My suggestion would be to employ a slightly more structured approach with a clear goal...and then use the proper tools (measurement/verification of what is happening, combined with the appropriate use of absorption and diffusion) to define the response necessary to achieve that goal.

And in anticipation of the all to common responses - it is a process of evaluating your space, the actual behavior of the space, and choosing specific treatments sufficient to adjust your specific environment to achieve a desired room response model - in other words, HOW you employ absorption and diffusion, not IF you use them - and not just a canned list of specific foregone treatments that only constitute a potential materials list.

[DanDan]

do you mean i should roll of the HF in the speakers using the built in controls or with an external Eq or software Eq?

Absolutely. See Understanding RTA at Studiotips. From experience, I assure you that curve is necessary in small dead rooms. The same curve appeared on Bruel and Kjaer's QR 2011 test record.

Seems like the wooden strips idea might be best for you as you need some containment. Those designs are well covered (no pun intended) at johnlsayers.com. With the strips and a layer of fabric underneath you will hardly need the plastic.

You could make the strips and gaps according to mathematical formulae, look it up. Practical matters will probably dictate otherwise. Kinda Random would be fine by me.

I wouldn't put impose any specific rules about distance regarding diffusors.
Diffusors vary and so do opinions. I specifically mentioned two products which seem to work well quite close. Particularly the Space Coupler overhead.
DD

[mattianlaseppia]

Originally Posted by SAC

I can certainly understand your frustration.

I know that I will catch heck for the suggestion, but...

How about making measurements of the space - including ETC responses, and getting and idea of exactly what it, or is not, happening?!

I already did measurements and i'm quite flat right now, a bit of boost around 1500 (broad boost, between under 1k to 2k more or less) highs fairly flat, a broad cut between 500 to 70 hz, and a boost between 65 to 58 hz of 7 db.. the room mode.. and nothing under 55 because of the room, the speaker theoretically arrive at 52 hz and i've measured them in other placement and they arrive to around 30hz, but that is the flattest placement i found.

Than I treated the most i could and I ended up in this situation.

Honestly I did thousand of measurements :P moving the traps in the room because it's a particularly strange room and the "theory" doesn't work very well here, so I used a lot of empiricism too.

And I think I'll continue doing so, I mean i will put some plastic around some trap and see what changes, then I will put some plywood and see what changes :P.. I will make small steps, so I can go backward if doesn't work.

I suspect that little has been done to actually evaluate the room's (original or present) response other than perhaps to determine that you need beau coup bass traps - oh, and of course, lots of absorption to control early reflections. ...An all too common and utterly inadequate treatment of the energy above the critical frequency where modes cease to be an issue.

The point is, after firsts attempts "following the theory" I haven't get enough improvements for my taste, so I decided to also experiment moving traps and see what they did. And I've noticed a lot of traps did nothing in certain point (usually "the theoretical points", at least part of them) and I decided to remove them and move them to locations where they get me a better absorption, and a better final result.

Now I still have some of them which doesn't change too much the response, which gave me small changes in the spectrum of about 1 db or less or i notice the midrange changes something, but not in a significative way, i mean the graph changes but isn't better or worse, just different, peaks and dips maybe changes a little, sometimes in different positions.

I also noticed putting the "desks", gear and everything has improved something probably, I mean probably because of their "random reflections", while I've decided to throw away the original desk and now I've "no real desk" just a small "bedside table" for mouse etc, because it gave me a lot of comb filtering in the mid highs and highs.. like sea waves :P up and down, very regular.. I don't know if it's normal or not.. I just preferred to avoid it.

But you could use many materials in order to impart a more highly defined ISD and a more diffuse later arriving soundfield.

How to?

in other words, HOW you employ absorption and diffusion, not IF you use them - and not just a canned list of specific foregone treatments that only constitute a potential materials list.

I understand, but unfortunately consider this is also a bed room (one month yes and the other not) and is inside an apartment and I have some furniture i can't get a rid, that constrict me to some decisions and I can put absorption in some places, almost everywhere now, but now i haven't space for diffusers, for example.

And if I could choose I would choose diffusers everywhere, possibly Ethan diffusers, but they cost a fortune and there isn't a dealer where I live, so I chosen absorption because it's cheaper and it's easier to build a bass trap than a diffuser, plus some people told me you need a big room to use diffuser, my isn't small but not big to, it's rather small than big, like 17 feet to 10/11.

BTW I'm also considering building some diffusers, this kind of diffusers are the easiest to build, for me, http://www.gearslutz.com/board/attac...-0094-copy.jpg

and I think I will build a couple of them, but now I haven't the space to mount them, i mean one wall it's completely absorbent and I can't mount it in there, that's why I thought to cover it with multilayer plywood, so I can also mount some diffuser on it and some absorption only in the ER point.

I could put some of these diffuser over some ceiling traps, and also maybe on another wall I have a small space, but all the rest is occupied with bookshelves.

I can put one of them on the door :P

I mean if I had a dedicated room where I can do whatever I want, I think I would also build "a room in a room" with different shape, and I can put bass traps, diffusers, everywhere I want.. I can't do this.. so I tried to find where the bass traps work best to optimize the space.

Anyway I think I will gain a bit of liveliness taking away the bass traps which changes the response too little.

The main problem is rockwool edges, I mean i can get used to this acoustic, isn't that bad and isn't that dead, I mean isn't totally dead, I mixed in rooms totally dead and not controlled in the low end, mine is quite controlled everywhere and quite dead, but not all dead :P I still have a naked floor :P with real hard wood and some little free space, a window and a two big bookshelves.. plus gear, two small desks.

But I need to make the space more healthy too, that's why I thought to "solve two problems in one" closing some traps with multilayer plywood, other with plastic bags, and the wall and corners with multilayer plywood.

I just thought the corner wouldn't change so much the response if I close them because they are not in the ER points, so the low and mid absorption should remain intact and, about the wall (completely absorbent) at my left, I thought I could close it with plywood and put some absorption in the ER point.

Well, about this wall, I think I will get some multilayer plywood and I will put it in front of it, than I will measure and listen and see if changes a lot or not, in better or worse, than if doesn't change in worse, I will fix it, if not I will remove it...

[mattianlaseppia]

Originally Posted by DanDan

Absolutely. See Understanding RTA at Studiotips. From experience, I assure you that curve is necessary in small dead rooms. The same curve appeared on Bruel and Kjaer's QR 2011 test record.

Seems like the wooden strips idea might be best for you as you need some containment. Those designs are well covered (no pun intended) at johnlsayers.com. With the strips and a layer of fabric underneath you will hardly need the plastic.

You could make the strips and gaps according to mathematical formulae, look it up. Practical matters will probably dictate otherwise. Kinda Random would be fine by me.

I wouldn't put impose any specific rules about distance regarding diffusors.
Diffusors vary and so do opinions. I specifically mentioned two products which seem to work well quite close. Particularly the Space Coupler overhead.
DD

I've seen "Understanding RTA" and I've seen a your post where you define the kind of response "quite flat on the mid, highs and controlled in the lows" as not useful to mix... and I have to say my studio is quite flat in the mid, highs, and controlled in the lows :P a little harsh sounding, the other placement was harsher, but now I've changed it and speakers and seems better, isn't totally flat in the highs, I have the mids quite "in your face" ns10 style, but I have a broad band cut in the lows/mid lows between 400 and 70 hz, of few db (like 4/5, maybe less) and the only boomy note i have is around 60hz (perfect for the kick :P)

I have a question, what would you suggest me to use to cut my highs at 8k (as you say) I haven't a HW eq to fine tune the room and usually I know they cost a lot and I also know they usually haven't a LPF or Hi Shelf.

May I use a plug in? Which plug in could be "perfect"? I mean, uncolored and precise.

Would you use a shelf 3db around 8k or a LPF 6db of slope at around 12k (so I think i will have a -3 at 8k)

Sorry if I ask you to be precise, but I'm worried to make mistakes in this operation, plus I don't know how to monitor the result because I use Room EQ and I can't put a plug in in Room EQ, only in Pro Tools, so I have to "go blind" and an EQ which cuts exactly 3 db instead 6 or 10 (like probably Air Eq :P) and at exactly 8k, would be preferred :P

thank you very much for the suggestions

[mattianlaseppia]

Hey DanDan, during measurements, I noticed if I stay under the tweeters (not with the tweeters at ears level, with the ear lower then the tweeter of about 3" or 4" (I move my head :P) I get less highs and watching the graphs the result (if i remember well) was like using an EQ cutting around 8/10k few db, what do you think? Natural EQ? :P

By hear if I stay with the ears at tweeter level the sound is a little harsher

(I hope it's not suggestion e)

[DanDan]

matt, natural eq is just fine. The big PMC speakers are designed to fire over the head and out a bit from the ears. Dead rooms and flat speakers are too bright. Mixes come out sounding dull. There is history and wisdom behind that 'Understanding RTA' curve.
It is possible to do an Eq with Busses and all sorts of tricks in a DAW, too difficult to explain. I am sure you will figure it out if nature doesn't work out.
DD

[mattianlaseppia]

Thanks Dan!

In fact I like more how they sound without the tweeters direct to my ears :D
I already had this impression, thanks to confirm my feelings :D