Thickness of acoustic treatment

spiderjazz

After scoring some Rockwool from B&Q (10 euro per roll), I'm going to make up some acoustic treatment for my room. The room is approx 4m x 4m x 4m, with the side walls going up 3m straight, and the final metre at a 45deg angle to the ceiling.

From what I've read, bass is going to be the biggest issue to deal with, so I'm going to make 24" by 48" x 4" bass traps for the 4 corners. Then I was going to deal with the first reflections by having 2 panels to my rear (same measurements as before), and 2 panels at the side, halfway between my listening position and my speakers. For these panels, would people recommend making them 2" inches thick, or should I go with having them 4" thick as well, for extra bass trapping? If I did go with 4" for the first reflection panels, would it have any negative effect on absorption for the mids and highs?

I'm also planning on making a cloud above my listening position, by getting some fabric, attaching it to the ceiling and putting some rockwool into it. There will be nothing behind the monitors, bar a curtain covering a window.

Would anyone have any changes/recommendations to make to the plan I have?

madtheory

Your room is pretty much a cube, you should really try to use a different room if possible. Cubes are disastrous because the modes are identical on each dimension, you get huge pile up which is very very bad.

Simply stack two rolls of rockwool in each corner, and cover with something pretty. Very easy and very effective superchunks.

The rolls of RW are not really dense enough to make good panels. Use the denser RW3 that comes as rectangular sections. Check the specs, you're looking for kg/m3

Do 3 panels, one for overhead, and one for each mirror point. Each as big as you can make them. See Ethan's article linked below for mounting tips. Then two smaller ones, one in front of you, the other behind. Then see where you are (measure it), it's possible that the room might turn out too dead but I doubt it.

http://www.ethanwiner.com/acoustics.html

spiderjazz

madtheory wrote: »

Your room is pretty much a cube, you should really try to use a different room if possible. Cubes are disastrous because the modes are identical on each dimension, you get huge pile up which is very very bad.

Simply stack two rolls of rockwool in each corner, and cover with something pretty. Very easy and very effective superchunks.

The rolls of RW are not really dense enough to make good panels. Use the denser RW3 that comes as rectangular sections. Check the specs, you're looking for kg/m3

Do 3 panels, one for overhead, and one for each mirror point. Each as big as you can make them. See Ethan's article linked below for mounting tips. Then two smaller ones, one in front of you, the other behind. Then see where you are (measure it), it's possible that the room might turn out too dead but I doubt it.

http://www.ethanwiner.com/acoustics.html

Thanks for the reply.

No chance of a different room unfortunately, I've the use of the spare room in rented accommodation so I'm trying to make the best of what I have on a budget. As you said it's pretty much a cube, only I have 8 wall faces rather than 6 (with the 45" angle wall on two sides)

That sounds good about the rolls in the corner, is it okay to leave these in the plastic wrapping (as in leave the plastic wrapping on and then put some fabric over them)?

By the mirror points, do you mean the positions at the side of me? I have a window in front of the desk at the moment so I won't really be able to do much there. I have a wooden floor in here as well so there's probably not much chance of it being too dead

Any recommendations for somewhere to get RW3 around Cork?

spiderjazz

Also, is there any particular preference in the type of fabric you should use for covering the panels? I gave a quick look in Hickey's today, and they have just plain fabric for 4 euro a square metre.

madtheory

I got the flat, denser RW3 in co-op superstore in Midleton, had to go out into the warehouse to find it- they don't stock it much so were not familiar with it! Anyone can order it in though, RW have an Irish base and fast distro.

The fabric doesn't really matter much as long as air passes through it easily. I used dust sheets (the ones used for painting), very cheap and look nice when stretched onto a frame for the panels. I plan to stretch white cotton sheets tight across my superchunks (the rolls) coz it will look cool in a white painted room to have roundy corners.

Yes you can and should leave the wrapping on the rolls, and I think it's a good idea to cover each end with plastic. Keeps the dust in! Acoustically it's slightly better without, but that will be very awkward for you to handle, and is way down the list of priorities in your room, not least because you will need to remove the things at some stage.

Ethan's article will explain mirror points for you- they're the first reflections from the speakers.

Can you post a plan or pic of the room- sheer curiousity!

i57dwun4yb1pt8

dont worry , you can treat a cube room just fine

make sure the bass traps are at least 8 inches deep or better , idelaly fill the corners wall to ceiling as deep as possible

dont bother with the cloud , do the reflection points and maybe the back wall - if the ceiling is problem then put some foam over the mix position

the cloud will make things too dead in a small room

you want to ideally here a good bass response and a bit of room liveliness

a hard floor is good to have , and along with deep filled corners will make the room sound very acceptable .

if you really want to go hard on the low end , then fill the ceiling / wall corner meeting with 6 inches of trapping

dust sheets are good , just make sure no fibre is getting out into the air
you dont want to breathe this stuff

spiderjazz

madtheory wrote: »

I got the flat, denser RW3 in co-op superstore in Midleton, had to go out into the warehouse to find it- they don't stock it much so were not familiar with it! Anyone can order it in though, RW have an Irish base and fast distro.

The fabric doesn't really matter much as long as air passes through it easily. I used dust sheets (the ones used for painting), very cheap and look nice when stretched onto a frame for the panels. I plan to stretch white cotton sheets tight across my superchunks (the rolls) coz it will look cool in a white painted room to have roundy corners.

Yes you can and should leave the wrapping on the rolls, and I think it's a good idea to cover each end with plastic. Keeps the dust in! Acoustically it's slightly better without, but that will be very awkward for you to handle, and is way down the list of priorities in your room, not least because you will need to remove the things at some stage.

Ethan's article will explain mirror points for you- they're the first reflections from the speakers.

Can you post a plan or pic of the room- sheer curiousity!

From the (poor) pictures, the measurements are:

Picture 1 - 11.42 ft wide by 7.92 ft high

http://dl.dropbox.com/u/15798771/Pic1.jpg

Picture 2 - 9.42 ft wide by 5.67 ft up straight with another 3 ft going up to the ceiling at a 45 deg angle.

http://dl.dropbox.com/u/15798771/Pic2.jpg

I used to have the desk facing down the longer length of the room, but I found it sounded "better" where I have it placed now. I also plan on getting speaker stands to get the speakers off the desk and spread a bit further out.

Thanks for the Ethan's article, great information in there. I'll have to get the OH up here to help me find the mirror spots, I think she's already questioning things enough though when I wandered in with the rockwool earlier on!

spiderjazz

DaDumTish wrote: »

dont worry , you can treat a cube room just fine

make sure the bass traps are at least 8 inches deep or better , idelaly fill the corners wall to ceiling as deep as possible

dont bother with the cloud , do the reflection points and maybe the back wall - if the ceiling is problem then put some foam over the mix position

the cloud will make things too dead in a small room

you want to ideally here a good bass response and a bit of room liveliness

a hard floor is good to have , and along with deep filled corners will make the room sound very acceptable .

if you really want to go hard on the low end , then fill the ceiling / wall corner meeting with 6 inches of trapping

dust sheets are good , just make sure no fibre is getting out into the air
you dont want to breathe this stuff

I'm going to go with the rolls of rockwool in the corners, I'm thinking of maybe getting another roll or two, halfing them and putting them on top of the full rolls to extend the bass traps up a bit.

I'm going to give a look for RW3 tomorrow, and make 2 ft x 4ft x 4 inch panels for the reflection points.

There's a bed in here as well to the right of the speakers, not much I can do with that. I know it's not a great layout in here, so it's more a case of trying to do the best I can with what I have.

madtheory

It didn't occur to me that you're in an attic! the 6 sides business threw me.

If you're not sleeping in the bed then put it on its side, it'll make a useful broadband absorber. With that window in there I don't think you will end up with too dead a room, but that hypothesis can only be tested by you in the actual room.

I'm guessing it sounded bad on the long dimension because you did not follow the 33% rule when positioning your head and the speakers, so you ended up in a bass null. Ethan's article will explain that issue too.

Just make broadband absorbers using rockwool- vastly superior to foam. The stud partition and ceiling is already a bass trap.

PaulBrewer

The Thickness of acoustic treatment is inversely proportional to the thickness of the lad putting it up.

johnnylakes

I believe that the 38% rule actually assumes that the speakers are built into the wall, but I guess it's a good starting point!

spiderjazz

I've built some panels for the room and wrote up a blog there about the process if anyone is interested

http://talesfromthepartydungeon.wordpress.com/2011/11/04/therell-be-no-first-order-reflections-in-these-here-parts/

For a quick summary, treating the room has made a huge improvement to the room.

madtheory

Looks great. I'd love to see a measurement before and after. Just do a sweep, mic it up and post the picture of the recording.

spiderjazz

I'll actually have to move the stuff out of the room either tomorrow or Monday so I should be able to do a before and after measurement. I can get a loan of a measuring microphone to do it, I assume a dynamic mic is no good to me?

I'm gonna use Room EQ wizard to measure it, will it be the "All SPL" tab that you need the picture from?

i57dwun4yb1pt8

you need to use an spl meter or room analyser .

just a mic wont cut it.

to be honest - fix the room first , then play a bass sweep with REW at about medium conversation volume from 40 to 340 hertz. sit at your proposed mix spot and listen

if you hear any drops or raises in volume during the sweep that are quite large - then the room is still dodgy - if the changes arent too bad - then its usuable .

the radio shack meter is a good one to get - i use this .

http://www.audiophilia.com/hardware/spl.htm

spiderjazz

Right, got a loan of a measuring mic. This is the freq chart I have of my listening point, with bass traps in the corners (there is another foot of treatment to go on top of each of them, to cover more of the corner towards the ceiling). I also have three 4" panels up to deal with first reflections. How would you rate this in overall usability/suitability for mixing? Any solutions to help improve things?

I assume my big problems areas that I should look to solve are the nulls at around 110hz and 2.3k. Also, should I have more mids/highs in the 3-8k region? I'll be putting extra bass trapping in the corners, and another two 2" rockwool panels on the rear wall which should hopefully smooth things out a bit.

http://i.imgur.com/BeR5G.jpg

madtheory

The biggest dip is at 2.3kHz or so, that's your biggest problem because it's right where the ear is most sensitive. Hard to say what's causing it. Is your computer screen inside the equilateral triangle that the speakers form with your listening position?

The 110Hz is probably easily solved, just a regular null- move your head a few inches left or right! Assuming you put the mic in the listening position?

I think you need to put more absorbers in, and you need to measure the room without treatment also so you can get a better idea of what's required.

What speakers are you using? They also have a part to play.

spiderjazz

madtheory wrote: »

The biggest dip is at 2.3kHz or so, that's your biggest problem because it's right where the ear is most sensitive. Hard to say what's causing it. Is your computer screen inside the equilateral triangle that the speakers form with your listening position?

The 110Hz is probably easily solved, just a regular null- move your head a few inches left or right! Assuming you put the mic in the listening position?

I think you need to put more absorbers in, and you need to measure the room without treatment also so you can get a better idea of what's required.

What speakers are you using? They also have a part to play.

Thanks for the reply.

I've made a sketch up of the room to hopefully illustrate things better. The only thing different is that the panels are not up on the back wall yet. The first reflection panels are up. There is also a picture of a sweep and waterfall graph I've just done.

http://imgur.com/a/mtsxz#0

and here's the google sketchup http://sketchup.google.com/3dwarehouse/details?mid=aadaad03033ebecc5961fdf809d1d0fd

I'm using Yamaha HS50m's on the desk, with the laptop inbetween them. There's 24" between the tweeters, I'm hoping to get stands soon so give them a bit more distance.

I've moved the speakers back and forward, left and right, and the null seems to have decreased the amount of the null, but increased the range of the low end that is being affected. The speakers are around 9" inches from the wall/15" inches from the window at the moment.

I'll upload a reading of the room without treatment later.

i57dwun4yb1pt8

actually your low end from 1 k down aint bad , apart from the 100 hz null
but that could be liveable with just by moving your head a it while mixing maybe change speaker position up or down a bit

the 1 k to 8 k looks weird as does the 2.3 k null

im thinking its a combo of too much absoprtion , a mesuring mic issue , or a speaker issue

or it could be comb filtering from the desk


if you figure out the 1 k to 8 k issue , id say your room is soudning pretty acceptable - you must notice the low end being much more audible and cleaner already.
also did you actually measure at 95 db spl ?

thats a bit loud , you need to do it around 85 or so .

you should be mixing at around the 70 -75 db level and going up to 85 - 90 just to hear it loud

so try a scan at 75 and see what you get

spiderjazz

Just doing a bit of measuring again today, and I measured the speakers up close (distances ranging from 1/2" inch from the centre of the tweeter and woofer individually to 6" inches inbetween the two speakers) and the rest of the frequency appears flat bar the null in the 2-6khz region. I'm probably grasping at straws here, but is there any chance that the crossover could be set wrong in the speakers? I've moved the desk to another wall in the room and the dip in the mids is still present.

i57dwun4yb1pt8

its either the speakers or you mic any chacne you can try another set of speakers or mic ?


if there is a mid switch on the speakers i would try moving it , it could be some kind of filter - not the crossover.

crossover would have a dip around 2 k, but not down up to 6 k .

its also possible , but not too likey that the speakers need to break in a bit.
have they been used much ?

spiderjazz

I tried measuring there with a Peavey rip off of a 58, obviously not accurate for measuring purposes but I wanted to see if there was any similarity in results. Similar dip in the 2-8k region.

I have a set of M-Audio monitors around the place somewhere, I'll check with them tomorrow to see how they measure. I'm going to move one of the HS50m's to a different room tomorrow and measure and check the results.

There are a couple of different switches on the back alright, I've moved the mid switch up to give it a boost, but there is still a huge dip.

Burn in shouldn't be an issue, I've used them for around 6 months at this stage.

Pretty frustrated with it all at this stage, I think I was happier being ignorant about it all