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Acoustic Treatment Optimise acoustics in your studio environment for accurate mixing - the best advice here..

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Old 13th March 2009 , 01:02 AM
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Default 140Hz -150Hz ??

Hi guys, another acoustic question.

A couple of you may already know that i'm in the process of getting my home studio setup the best I can. So far I have some corner traps installed on the front wall, the two first reflection points I've treated with 75mm Pyramid Tiles and this weekend I'm going to be making some Rockwool absorbers for the ceiling, rear traps and maybe the first reflection points instead of the tiles.

Now, i'm a hobbiest/semi pro so i'm not expecting to or even trying to get everything totally amazing, just better so that I can get my mixes to translate pretty well. So, tonight I did a test with a test tone with constant volume and found that everywhere was reasonably constant apart from around 135Hz - 160Hz where the volume appeared to increase (I know it didn't in reality and it was my room that I was 'hearing'.... I think?)

So I inserted a Parametric EQ on the master bus and knocked off about 6db at around 143Hz and then played back the test tone and everything now seemed good (or at least better). I then played some cd's and A/B'd with the EQ on & off and the difference was very noticable and when the EQ was on it just got rid of the 'boominess'.

I'm not too good with all this acoustic techie stuff so I'm kinda learning as I go and I was wondering if any of you clued up guys could give me your thoughts on things such as....

What does this tell you/me (if anything) about my room treatment so far?

Should/could I mix with the EQ on the master bus and then just bypass it at mixdown?

Will I benefit from Rockwool absorbers rather than the tiles at the first reflection points?

Any advice would be very much appreciated

Thanks

Andy
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Old 13th March 2009 , 06:08 AM
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Quote:
Originally Posted by Andy Senior View Post
Hi guys, another acoustic question.

...
Thanks

Andy
What does this tell you/me (if anything) about my room treatment so far?

It tells you that your room needs some more treatment which will deal with your problem range (bear in mind though that you are never likely to make a domestic room perfect, you can only hope to mitigate the problems). That might mean tuned traps (read up on helmholz resonators). It might also mean your corner traps simply arent thick enough or you havent got the design quite right. Can you post the design and maybe some pictures of them?

Should/could I mix with the EQ on the master bus and then just bypass it at mixdown?

No. You need to hear what's going on in the mix. Better to sort your room out as much as you can and then go the old trusted route of cutting a mix and listening to it in different rooms/on different systems so that you hear the problems rather than assume them.

Will I benefit from Rockwool absorbers rather than the tiles at the first reflection points?

Yes. Though it might be useful to put the tiles back on top of the rockwool panels. Try them with and without
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Old 13th March 2009 , 09:45 AM
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Thanks a lot Trev, appreciate it.

I'm just making the traps this weekend for the back wall and deciding what to do for a bit of diffusion at the back aswell, so hopefully once thats done I'll see in improvement. At least I know what my main problem area is now (I think/hope! lol)

I'll let you know how I get on and there might one or two more questions yet Trev

Cheers
Andy
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Old 16th March 2009 , 05:25 PM
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First, a quick lesson (for everyone) about you shouldn't "correct" a room with EQ. I want everyone to read this eight times and commit it to memory.

You can't fix a time domain problem in the frequency domain.

EQ'ing monitors flat might improve things somewhat but attenuating the room modes works far better.

Think of it this way:

Suppose you're not hearing 90Hz correctly / loud enough because your room dimensions give you a 90Hz reflection that nulls out your 90Hz speaker output right about where your ears are at.

Without any EQ in the monitoring chain, you boost the upper bass going to the MIX until it sounds "right" and then when you listen to your mixes on other systems they sound muddy. Crap!

WITH EQ in the monitoring chain, you try a few 1/3 octave sliders and you find that boosting at around 90Hz seems to help a bit (determined by ear or with a real time analyzer). This is an improvement over no EQ in the monitoring chain because at least you're not EQing your MIX, you're EQing what you're listening to.

BUT - now you have some new problems. Boosting the 90Hz in the monitors not only turns up the direct sound but also causes a stronger 90Hz reflection off the back wall and you still get the same null in your listening position. It's a bit better because you've brought up the overall volume and forced the near field (where you hear mostly direct sound) a bit farther back toward the wall. But you still haven't eliminated that room mode, you're still not hearing the 90Hz accurately, you've limited the headroom on your monitor system, you've boosted other frequencies near 90Hz which have different room mode effects, and the slight benefit you get is lost if you move your head even a foot.

The problem isn't the frequency response of your monitor system (it's probably pretty good already), so changing that isn't a good solution. The problem is the reflections in your room causing standing waves that either cancel or reinforce at various frequencies depending on where you're standing in the room. And those are distance dependant meaning TIME DEPENDANT so your choices are to move the walls and get the time alignment more pleasing (usually not an option) or dampen the walls to reduce the amount of reflected sound.

Now, on to the specific problem. A lobe in that range tells me that the length of your room is probably somewhere around 15' and that the width or height is close to that as well, or is half of that. So maybe your room is 15'L with an 8' ceiling or something. You said that you're going to add some bass trapping, yes? Then you'll be fine, especially in that range. 4" or 6" absorbers will hammer than lobe down in a real hurry.

Frank
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Old 16th March 2009 , 07:12 PM
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A short but sweet thread so far but has enough important info in already to warrant.. a sticky..
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Old 20th April 2010 , 01:12 PM
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Default Resonant boom 140-108Hz

Having read Andy Senior's problems with 140-170Hz freq issues, I was wondering if an inexpensive cure resolved.
My room dimensions are 5.5m x 3.9m x 2.5m. I have no 90* angles, all corners are corrected to 45* and walls taper up to the ceiling at roughly 30* over 80cm. Can this freq boom be sorted with rockwool as the angles aren't parrellel?
This is my first studio build. I would describe as entry-level semi-pro. I have placed foam+wool absorbers either end of the room and suspended 75mm rockwool over the desk and either side of my seated position.
Any advice will be gratefully received!
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Old 20th April 2010 , 01:21 PM
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Originally Posted by Graham's Cat View Post
Having read Andy Senior's problems with 140-170Hz freq issues, I was wondering if an inexpensive cure resolved.
My room dimensions are 5.5m x 3.9m x 2.5m. I have no 90* angles, all corners are corrected to 45* and walls taper up to the ceiling at roughly 30* over 80cm. Can this freq boom be sorted with rockwool as the angles aren't parrellel?
This is my first studio build. I would describe as entry-level semi-pro. I have placed foam+wool absorbers either end of the room and suspended 75mm rockwool over the desk and either side of my seated position.
Any advice will be gratefully received!
75mm isn't thick enough to get down a low as 120-150Hz. The absorbers need to be at least 120mm thick with about that much air gap. Also, what do you mean when you say "foam and wool"? Foam may be okay at the front of the room (though I would argue that your room is too small for it to be very useful), but you really need thick (i.e. 150mm thick) bass traps on the back wall.

Frank
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Old 20th April 2010 , 09:21 PM
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Default Not waving but...

Hi Frank, I knocked up some softwood frames 90mm x 520mm x 148mm, then part filled these with 50mm rockwool slabs faced with 50mm split-cell contoured foam. I mounted four in front leaving a 30mm air gap behind. I have two the same at the other end of the room over a large sofa.
I've used flexi-wool, a rockwool product spray-glued to poly cotton with minimal wood batten to maintain ridgidity and to fix suspension hooks. I'm halfway though mounting these on eyehole screws giving an viod of 90mm from the top of the wall and ceiling. As yet I haven't installed anything in the corners, as they're fairly tight 45* angles (plus a fifth corner inset from the lobby) I'm unsure what's going to sort it.
Do you think I'd get away with doubling-up the rockwool (150mm)?
I've run an audio file downloaded from SOSPUBS (Bass staircase test). Things are reasonably linear except from a bump at 90Hz and then an alarming jump 140Hz onwards!
I really appeciate your feedback. Thanks G
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Old 20th April 2010 , 09:47 PM
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Yes, combining two batts to get to 150mm would work great.

You need more than just the staircase test. You need to shoot the room with a higher resolution program like Room EQ Wizard.

Frank
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Old 21st April 2010 , 11:26 PM
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Hey! It was worth the journey(s) in a car stuffed to the ears in rockwool. They flogged me this stuff called 'Flexi-slab' something or other. Allegedly better than general purpose Rockwool.
I've added 100mm to the pre-existing 75mm and extended the air gap to 150mm.
Definately an improvement, and that's only half the room! I'm quite amazed, there is an apparent shift of energy from 120Hz at high volume, yet the imageing is almost perfect. I've only treated what's infront so far
Thanks for the advice. Will try the other audio test you mentioned. Thanks G
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