# Room measured after bass traps installed...What further action should I take?



## metrobot (Jan 26, 2013)

Hi there,
I've recently treated my room with broad band bass traps and there has been a significant difference in the before and after measurements. However, I'm not sure what to do to make further improvements.
I have a gradual null at 55hz that slopes down 10 db to 90Hz and back up 10db at 130hz.
Should I target 90hz with a tuned absorber?
I also have nulls at 490, 600, 1.5 and 3.4 should I build some diffusers?
I was hoping I could upload my REW files and get some opinions from some more experienced users because I'm not confident at what should be done at this point.
Thanks and kind regards
-Matt


----------



## ALMFamily (Oct 19, 2011)

Matt, 

I just finished working with Bryan on my HT, and IIRC he suggested that my 90hz issue was caused by reflections from the rear wall. The way he said to test this theory was to take a measurement from the LP, then move the mic forward about a foot and take another measurement. The part where it gets gray for me (getting older can be such a hassle! ) is what the result should be - it seems that the null should shift if memory serves.

Best bet - check out a few of the latest threads in the acoustics forum - I know someone else had the same issue and Bryan said something along the lines of "if I was a betting man, I would bet it was the rear wall". :bigsmile:

Good luck!

Joe


----------



## metrobot (Jan 26, 2013)

Cheers Joe,
The null shifts down so I'll put a few more traps on the back wall.
I have nulls at 454, 807, 1.6, 3.12..I think that is a room mode.
Cheers
-Matt


----------



## ALMFamily (Oct 19, 2011)

Matt, 

IIRC, Bryan's suggestion is to go 6" thick on the back wall and then face it with 10mil plastic to keep your surrounds lively. I could not manage 6", so I went with 4" and then faced it with some left over MLV I had.

Again, Bryan is a much better resource than I for this - I am just passing along what I can remember from what he told me. 

Joe


----------



## metrobot (Jan 26, 2013)

Hi joe,
Sounds good but I'm new to the forum so I don't know who Brian is. My room is a project studio mixing room so I'm not using surround. I have done a lot of bass traps so far so I thought I should face the remaining ones. Dose the plastic have to be 10mm...seems pretty thick. Is MLV Mass Loaded Vinyl? I thought I would be able to use tin foil or cardboard for the facing.
Cheers and thanks again.
-Matt


----------



## ALMFamily (Oct 19, 2011)

metrobot said:


> Hi joe,
> Sounds good but I'm new to the forum so I don't know who Brian is. My room is a project studio mixing room so I'm not using surround. I have done a lot of bass traps so far so I thought I should face the remaining ones. Dose the plastic have to be 10mm...seems pretty thick. Is MLV Mass Loaded Vinyl? I thought I would be able to use tin foil or cardboard for the facing.
> Cheers and thanks again.
> -Matt


My apologies Matt - Bryan is the moderator of the acoustics forum and works for GIK Acoustics.

MLV is indeed mass loaded vinyl - and 10mm was what Bryan suggested but he also said you could get away with slightly less. To get more directed help with acoustics (much better than I can provide ), I highly recommend posting to the acoustics forum - Bryan will definitely be able to get you are the right track.


----------



## jeff_free69 (Dec 18, 2008)

I'm in a similar boat: small mix room (bit of a sonic nightmare: in basement with low ceiling, cement floor , foundation etc)

Over the years I've done a couple of iterations and ultimately ending up tons of treatment: 
eg 4" OC catty-cornered, floor to ceiling, overhead cloud etc. 
This got the worst peak/nulls down from 15db to more like 8.
The left channel is generally worse, because that is closer to the foundation.

It actually sounds pretty good, but as you know getting the bass exactly right is the hardest part. So I'm getting more serious about measurements.

For the last couple of days I've been moving both the speakers and the listening position back and forth and measuring each L&R channel. Its amazing how even 6" can make a huge difference. At this point I don't care if the speakers end up in middle of the room, I just want it the best it can be!

I;ve got a couple of extra standalone 2" 2'x4' OC panels, so I can play with them to see the effect. IT'll never be perfect, so its a matter of picking the least offensive response. So far moving the speakers closer to the front wall actually helps the most (not what i would have guessed - YMWV) . I may leave my listening position at about 6ft away or move it in to ~4ft (also tried every 6" interval in between and these are the best).

Once I settle on the new arrangement I will setup my new IK Multimedia ARC2 system. Its new to me , but the first test was pretty impressive. Its measured curves closely matched my own. Then a plugin in your DAW creates the inverse curve (up to a point). I could immediatley hear stronger bass tha was getting lost in a null. But I figure the less you ask it to do the better result. You really don't want it trying to pump up +12 db at 80Hz. 

Anyway hope this helps...


----------



## Demsy2000 (Jan 19, 2013)

ALMFamily said:


> My apologies Matt - Bryan is the moderator of the acoustics forum and works for GIK Acoustics.
> 
> MLV is indeed mass loaded vinyl - and 10mm was what Bryan suggested but he also said you could get away with slightly less. To get more directed help with acoustics (much better than I can provide ), I highly recommend posting to the acoustics forum - Bryan will definitely be able to get you are the right track.


Hi, 
I have a question regarding the thickness of the MLV. Joe mentioned that the thickness ideally is 10mil and Matt mentioned it as 10millimeter. Well, 10mm is about 3/8", you could hardly call it as a 'foil'. Jeff, did you mean 10mil as in 3/8 on an inch? I'm sorry for the question, as we here in Indonesia measure in metric system.
Thanks


----------



## ALMFamily (Oct 19, 2011)

Demsy2000 said:


> Hi,
> I have a question regarding the thickness of the MLV. Joe mentioned that the thickness ideally is 10mil and Matt mentioned it as 10millimeter. Well, 10mm is about 3/8", you could hardly call it as a 'foil'. Jeff, did you mean 10mil as in 3/8 on an inch? I'm sorry for the question, as we here in Indonesia measure in metric system.
> Thanks


The mil in "10 mil" refers to the density of the material, not its actual thickness. Sorry for the confusion!


----------



## metrobot (Jan 26, 2013)

Cheers Jeff. Does the plug in you use create an inverse eq curve on the stereo buss? does it do it automatically?
Thanks for the advice. I'll put my questions to the acoustics forum and see what I can get there
Cheers
-Matt


----------



## NoSpeaka (Feb 23, 2013)

If you find that the nulls and/or peaks in your measurement move with monitor movement (ie towards or away from the wall), you can be quite confident that the cause is from a boundary (SBIR) rather than a room mode.
If it stays the same, it's likely a feature of the dimensions of the room 

Hope that helps!


----------



## metrobot (Jan 26, 2013)

It's a big help, Thanks
-Matt


----------



## jeff_free69 (Dec 18, 2008)

metrobot said:


> Cheers Jeff. Does the plug in you use create an inverse eq curve on the stereo buss? does it do it automatically?
> Thanks for the advice. I'll put my questions to the acoustics forum and see what I can get there
> Cheers
> -Matt


Yes - Its basically a home theater Audessy for you computer.
first you run a standalone app that takes measurements as you move the included mic around your listening position. Then you load the ARC2 plugin as the last plug in your 2-bus and load the saved measurement file.

Then it calculates an inverse curve to compensate (up to 12 db). 
I'm still getting used to it - at the moment i only have some nearly completed mixes, so i don't want to just throw it in and start changing everything. You also have to get used to lowering the volume, since a lot of EQ boost will clip the final output (if you're already close to 0) 

As mentioned, i spent the weekend trying all the permutations of positioning speakers, chair and baffles trying to find the best measured response. I changed my mind about putting speakers against the wall. As expected it gave a pretty good deep bass response and also pretty smooth mid and highs. But it put a huge (wide and deep) hole in the mid to upper bass, and everything sounded way too thin. 

After all was said and done, everything ended up within ~6 inches of where its been. But A lot of baffles got moved and adjusted (more towards the reflection points ). And a long table under the speakers got removed . Now they just sit on stands (wood bar stools) .

A lot of work, but at least now I'm sure its not going to get much better (unless I invest heavily in some tuned absorbers) . I used ARTA for most of this and in in non-averaging mode it was fun to move things (including myself ) and see how the response changes in realtime ( just don't forget earplugs). Since its been a good learning experience I'll probably learn to do some measurements in REW too.


----------

