Advice on accoustic treatment

doc-phil

I am in desperate need of some acoustic treatment in my home studio. I recently moved house and I'm trying to mix and master in a room with 4 bare walls and a whole ton of boomy-ness and mudiness, depending on where you stand in the room.

Without getting too scientific, what is the best way to go about treating the room acoustically?

My plan at the moment is to have someone I know build about eight 1x1.5 bass traps, using the following as a guide, and to simply stick them up on the walls:

http://www.readyacoustics.com/DIY-BASS-TRAPS-MADE-EASY.pdf

The packages that I have seen online are ridiculously expensive, so I would prefer to DIY if possible. I know a lot is dependent on the room itself and proper advice can only be given after having seen the room and 'listened' to it, but I just want something basic. The major problem is there is only one corner that I could place a bass trap in, the other 3 corners have a door, a cupboard door and a window against the very edge of the wall, so I can't really do anything there.

I know there are absorbers, diffusers and a whole host of other acoustic type things, so can I get away with just using bass traps?

Any advice would be most appreciated.

Jayhell

If you go to Chamdor in Krugersdorp, they sell acoustic carpet. It's actually for cars but it could help with some of the high frequency reflection. It's also black and would look cool on the walls behind you bass traps.

AlanRatcliffe

I've been doing my research lately and am just about to embark on treating my room (or starting to anyway).

Firstly, what are your room dimensions and what are the surfaces? Very important factors. If the floor is carpeted, you already have a fair amount of high frequency absorption, so covering the walls with broadband absorbers will skew the room towards the bass end. You can get away with a three broadband panels to control flutter echo (left, right uppards) at mix position.

Most small rooms suffer from serious problems in the low end, so bass trapping is a must. Even properly made and mounted (that's 10 cm thick and 10cm away from the wall - that's 20 cm off your room width!), your broadband panels are only effective down to about 250 Hz, so don't address the real problem areas in the spectrum. If you flush mount them or make them thinner, your effectiveness in the lower end of the spectrum drops off dramatically (IIRC, a 4" panel will only work down to about 500 Hz when mounted flush with the wall.

However, don't forget that the bass build-up happens at any boundary intersection. Your room corners are best because at the top and bottom they are the intersection of three boundaries. But don't forget your wall/ceiling (and wall/floor - but w/f is not practical for other reasons) boundaries are just as effective a position as wall/wall boundaries. And a lot more out of the way in a small room. Also remember that symmetry is very important for correct imaging

BTW, most rigid insulation is sized at 600mm x 1200mm, the rolls of Cavitylite and Energylite are 1200 mm wide, so factor that into your sizing calculations. The less you have to cut fibreglass the better. Mineral wools are not as good either - you have to up your thickness by 25% to get the same performance as fibreglass.

For some reason, no-one locally seems to stock the 47.5 kg/m3 fibreglass (the one you want for bass and broadband trapping) in 50 mm (2") panels, and to buy direct from Isover, you need to buy in bulk. Please let me know if you find someone who can supply.

AlanRatcliffe

BTW - for those corners in which you can't mount stuff properly - by cupboards, doors and windows - why not make a couple of movable tube traps?

Mixerboy

Isn't it basically around a third of your room needs to be trapped for effective low end absorption?

I read somewhere that the 3" Auralex is about 20% effective at 125hz (with a gap between it and the wall) and when you get down to around 60hz it's practically just aesthetic wall decoration.

Mixerboy

A good idea is to measure your room and use some online calculators to show you at what exact frequencies you'll have modal/standing wave problems which, if you're in a small squarish room, will be many.

If you slap up any old treatment you might actually be adding to your problems by taking away what wasn't an issue in the first place while still leaving the things that are.

doc-phil

Thanks for all the pointers.

I read the section on acoustics in Mixing Secrets for the Small Studio by Mike Senior and various articles, including this one:

http://www.recordingreview.com/blog/recording-studio-construction-acoustics/why-your-bass-traps-dont-work/

It all seems to paint a pretty bleak picture. I don't have space to mount the bass traps 20cm or more off the wall. Even if it is 10cm off the wall, that means the trap itself will protrude 20cm.

The room I am in is also sparsely furnished, and depending where I am sitting/standing, I can hear an audible echo (never mind comb filtering). It doesn't help that my desk is forced into the corner with my right monitor pointing directly into the corner of the wall. Even getting your bass traps to have an effect on the sub 300Hz range seems nigh on practically impossible.

Movable traps for the corners is a good idea, thanks. This has now also got me thinking. If I make all my traps to be mounted on wheels, and keep the studio room sparsely furnished, I could wheel them around wherever I please, and not worry about hanging them on the wall. This may also lessen the chance of me further messing up the acoustics as Mixerboy says by making semi permanent mountings which could hinder more than help.

Jayhell

Wont something like a reflection filter be more usable in this application? Like a SM pro (I think) Mic Thing.

AlanRatcliffe

Yeah there are limitations to small room acoustic treatments. Doesn't mean that you can't improve them at all. Ya works with what ya have and makes the most of it.

A point I tried to make earlier (which I didn't summarise at the time - sorry) is that you get far better results from corner traps than wall-mounted broadband panel absorbers. After all - that's why one is called a bass trap and the other a broadband absorber. Even a panel absorber across a corner is far more effective in the low end than the same placed against the wall. And yes, broadband absorbers basically act as high frequency absorbers when mounted flush against a wall - which can be useful to know in taming a bight room.

Sure, you can go a step further and make precisely tuned panel traps or heimholz resonators for your low end treatment, but you need to know exactly what you are doing to make it worthwhile.

So, get as much corner trapping going as you can (preferably superchunks - easier than panels to do), treat your reflection points to control flutters. That will make a huge difference. Then see how you are doing (get REW for free and invest in a measurement mic) and then take it from there.

BTW: A while back, I drew up a list of coverage for a pack of 15 50mm batts (47 kg/m3). Might help you plan quantities:

One pack batts =
1 x 3m tall "superchunk" bass trap or
2 x 1.5m "superchunk" bass traps or
7 x 120 cm x 60 cm x 10 cm broadband panel absorbers

Two packs batts =
2 x 2m "superchunk" bass traps plus 5 x panels

AlanRatcliffe

Jayhell wrote: Wont something like a reflection filter be more usable in this application? Like a SM pro (I think) Mic Thing.

Not for mixing and mastering, no. ? Even for vocal mics, they only help control the room reverb getting to the mic and do nothing for the low end (which you are mostly filtering out with a highpass filter anyway).

kayDUB

Alan, you might know this already, but I bought rigid fibreglass 47kg/c3 50mm thick 1200mm x 60mm sheets from a guy called Renaldo, I can't remember the company though. Bought them in packs of 15, which I don't consider too "bulk"y ?
If you don't know him I can send you the number.

AlanRatcliffe

kayDUB wrote: If you don't know him I can send you the number.

:yup: Please!

kayDUB

Sent!

Trippp

It's easy to make the mistake of thinking that bass traps (i.e large amounts of rigid fiberglass stacked in your corners or elsewhere) takes care of bass problems alone.

They take care of ALL frequencies - including bass. Building enough bass traps up will help you with your echo problem as well.

Start off with a couple of bass traps and see how it goes. You can never have too many.

Should your high frequencies get attenuated too much, you just cover some of the bass traps with plastic, which allows them to be reflected off the traps.

Next I would worry about creating a reflection free zone (rfz) at your mix position, which you can do with 2 to3broad band absorbers (wallls left and right and a cloud overhead).

All of these items can be built with the exact same materials - rigid fibreglass of about 40kg/m3 density if I remember correctly.

You can start off by simply buying the fibreglass and stacking it in your room, still inside the packaging. That should already take care of your lower and mid freqs and reverb time. You can then "tune" the amount of high freq attenuation by removing some of the packaging. Stacking them as to help create a rfz will then also help with your stereo imaging.

Edit:

Err ... sorry for not reading all of your original post. The link you posted pedants would call broadband absorbers - not bass traps. By standing them off from a wall you do get some lower absorbsion, but still not low bass.

For bass absorbers you can simply cut those fibreglass battons in half (600mm x 600mm) and then in half on the diagonal again, to get triangles. Stack those in all corners possible - floor to roof if you can. you can cover the front with cloth for aesthetics and to keep the fibers at bay.

Something like this:

http://swbg1.tripod.com/corner_stack.jpg
or this
http://nagasakisound.com/how-to-build-corner-bass-trap/

Trippp

kayDUB wrote: Alan, you might know this already, but I bought rigid fibreglass 47kg/c3 50mm thick 1200mm x 60mm sheets from a guy called Renaldo, I can't remember the company though. Bought them in packs of 15, which I don't consider too "bulk"y ?
If you don't know him I can send you the number.

I'll take that number too please ? Hopefully doing something similar in the near future.

doc-phil

Thanks Trippp. For now, I think I am going to go for 3 superchunk bass traps for the corners and about 6 broadband absorbers (provided the person building them for me can source the proper materials - she mainly does set building and design for stage shows) and I'll take it from there!

I don't expect to solve all the acoustic problems that I have, but I'm looking to achieve something workable that can at least give me a decent monitoring set up.

kayDUB

Trippp wrote:
kayDUB wrote: Alan, you might know this already, but I bought rigid fibreglass 47kg/c3 50mm thick 1200mm x 60mm sheets from a guy called Renaldo, I can't remember the company though. Bought them in packs of 15, which I don't consider too "bulk"y ?
If you don't know him I can send you the number.
I'll take that number too please ? Hopefully doing something similar in the near future.

Here's the number for you, and anyone else in the future ?

Renaldo 0215122860
Or
John 0832811221