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Defying the laws of physics?!
Old 19th February 2012
Gear interested

Thread Starter
Defying the laws of physics?!

Hi Eveyone,

I'm new to Gearslutz, hope y'all can shed some light on this;

I have my own 'studio' in the attic of our house. The sound has always been pretty good, but last week I deicided to try to make it a little better. At the moment i hardly have budget to buy stuff, but I have quite a bit Rockwool 211 lying around. I read a lot about DIY-basstraps en measuring the room. For now I'm only measuring DB's across the entire frequency range with a DB-meter. I'm not measuring phase, decay etc. with EQwizzard or anything like that (yet) because my only real problem is a little bit too much low end at some frequencies...

Here's the funny thing; When walking around in the room there's very little change in levels at almost all freq's (no standing waves?), but moving around stuff causes a lot of changes, even in the really low... For instance I have a large wooden door that has considerable impact on the levels of some frequencies in the low end. It's a thick door, but it's not like it's that much mass to have that much impact... Also when trying to find the ideal listening position I noticed that moving the spekers only a few inches also has great impact, again also in the low end...
Also, at most listening positions, there are no big spikes and the biggest difference between frequencies is no bigger than 10 DB...

After extensive reading about roomtreatment all this seems to defy everything I've ever read about the subject?! (for an untreated room)

I'm sorry I don't have specified data, but I still wanted to ask if anybody has an idea as to how and why...

The room is as A-symetric as can be, with an L-shaped stone wall in the back and only wood, going round in front, ending in a small pointy ceiling. Pardon my English, I'm from Holland....

My only guess is that, because most of the attic is wood, there are almost no standing waves/room modes, because all the low end goes thru the wood into the open air... Therefore moving stuff around like a wooden door has the same effect as changing the actual dimensions of the room..

Doe this make sense?

I hope to hear from you guys!

Thanx in advance,

Old 20th February 2012
Gear Guru
Ethan Winer's Avatar

Old 20th February 2012
Ethan, do you listen with your wonderful back-receptors?

Gesendet von meinem GT-I9100 mit Tapatalk
Old 21st February 2012
Gear Guru

dries, it does make sense. Newell calls this situation a 'Limp bag'.
i.e. the bass passes through as you described, leading to only low energy modes and boundary reflections.
The result can be quite a bright, even harsh, sounding room.
You will probably need to soften that. At least you will need to treat reflection points. A good eye for snooker, a mirror, or ETC, will help you find those points.

Old 21st February 2012
Gear Guru
Ethan Winer's Avatar


Originally Posted by George Necola View Post
Ethan, do you listen with your wonderful back-receptors?
I have no idea what you're asking.
Old 23rd February 2012
Gear interested

Thread Starter
Okay Guys,

Thanx for replying, I was afraid no one would, because of my totally unscientific approach so far (no real accurate measuring, except db's over the frequency range) :-)

A few questions;

- What do you mean with low energy modes? because it seems that walking through the room pow freq's are pretty much even, except for the really low, then I start hearing nulls... Is that the low energy modes? The really deep freq? (Like F;87 Hz)

- Since I seem to work in a 'Limp bag', Is it even possible to influence the nulls of say 50-150 Hz?

-Is it true that a 'Limp bag' is actually not that bad at all for a start? My room is not harsh sounding, it has enough bass freq left. I mean, it's easier to get rid of mid an high freq reflections than really deep low modes/standing waves, right?

- I'm now experimenting with moving around large quantities of Rockwool 211 (like 10 plates still wrapped in original package), 4 of those packages. I can definitely hear improvement (by ear...), but as soon as I bring in the Rockwool I get a lot of Phase-issues. Bass becomes more hollow, Lead-vocals seem to drown in Reverb. It's like a sort of super-stereo without the 'midlle-part', just extreme left and right.
Does a Limp bag make phase-issues occur sooner than any other type of room?

- I'm sure this has been discussed over an over, but what is the way to go;

1 Find the best listening position (by ear) without any treatment?

2 measure the room

3 Start treating

4 measure

I've attached a very rough sketch of my room; In the back is a stone wall, In front is only 40cm of stone wall, then the wooden makes an angle towards the ceiling (this is difficult for me in English...)

1 Was/is my current listening position,
2 seemed the most 'symetrical', but don't sound to good.
3 is also pretty symetrical and sound pretty okay, but lot of phase issues,
4 Is the only spt where I can hear 50-100 Hz...

- Since even moving a wooden door has so much impact, is it an idea to sort of 'close' the entire right side of the attic by placing wood where the yellow line is, thus making the room more 'logical'?

Thanx for your time, appreciate it!


Any advice on listening position?
Attached Thumbnails
Defying the laws of physics?!-studio.jpg  
Old 23rd February 2012
Gear interested

Thread Starter
Sorry, with the F i meant 43 hz, I need to hear that freq..;-)
Old 23rd February 2012
Gear Guru

Sorry Dries but your descriptions of the sound in the room seem to contradict themselves. I can't even tell if you are hearing enough or too little bass.
Walls and other boundaries that are not hard and massive do not reflect bass, it passes through. A limp bag, like a tent!
Because there are no or only weak low energy reflections there would be only low energy modes and SBIR.
I don't know if you have a Limp Bag or not, attics often are.

As Ethan said, get REW. This will show the sound in graphs (better than the English language ;-) It will make it possible for you to test you various listening positions.
The plastic wrapping on the 211 reflects HF. Not good in a listening zone. I presume that is what you mean by 'phase'.

Get REW or FM!

Old 27th February 2012
Gear interested

Thread Starter
Maybe my posts were indeed too vague ;-) Last few days I been trying to find the best listening position and been bass trapping a bit. I will try to measure with ERW now.

Newbie questions;
Should I measure each speaker at a time or just stereo?

If i'd ask you guys for help analyzing my files, what file is most helpful? Waterfall? Entire freq-range or just 40-300 hz?

To me it's all abracadabra, wouldn't know where to start and how to read those files;-)

Old 27th February 2012
Gear Guru

One speaker. The Meaure Sweep is full range. Chose to look at restricted ranges afterwards.
e.g. Waterfall 20-300 as you said. No Smoothing.
Full range Freq Response will look mad without some smoothing, try 1/12 octave.

And/Or post the files so that anyone here can zoom the graphs to point out the issues to you. You can't post them directly but there are posting websites.
Could someone recommend one they like plse?
Old 27th February 2012
Gear interested

Thread Starter
I think it's best if I just post the file ;-). Tried some measurements, but having problems calibrating and getting clip messages. I think some issues between REW, Mac os x and my RME multiface...

Old 27th February 2012
Gear Guru

The Mac OS doesn't do Java fully correctly, so it can't work with multichannel interfaces.
Use the onboard Mac I/O if you have a stand alone preamp.
This works just fine.
In fact I use my HD192 interface for playback but the Mac Line in.
Calibration and Loopback correction are NOT necessary.
You can get fancy when your skills are up to it.
Turn your speakers up as much as is safe. Wear closed cans. Adjust the mic pre gain for no clipping. It is a bit tweaky, you measure a level, it says OK, then the actual sweep clips due to room peaks. Just dial the gain back.
Old 27th February 2012
Gear interested

Thread Starter
Thanx, this is very helpful! For now, my first (clipped) measurements are telling me what I allready thought I heard...;-) a little weak on the bass, not the sub and I little harsh at high- mid..

For now I'm only measuring at my exact listening position, so approx 1,5 m from the speakers, is it then wise to turn the speakers up as loud as possible? I mean, am I not then only measuring the speakers direct instead of my room?
Btw I'm using a Akg C4000b, omni. Not flat I know...
Old 27th February 2012
Gear interested

Thread Starter
Hmmm, now it's telling me something else... Anyway I keep getting the messge 'impulse response is not where it should be, data... Corrupted...' is that really bad or should I just carry on for now?
Old 27th February 2012
Gear Guru

Bad to useless. That's the Java issue. Use the onboard Input. And output if necessary.
Old 27th February 2012
Gear interested

Thread Starter
So I guess this is my first okay measurement without errors displayed...

I kept the mic (AKGC4000B) in one spot (listening position)
Red = left speaker, blue = right speaker

I think I sort of calibrated at 75DB...

This is the AllSpl file.... 1/12 smoothing

I would love to upload the entire REW-file...

So what does this measurement tell us? (be gentle....;-)

Attached Thumbnails
Defying the laws of physics?!-1st-all-spl.jpg  
Old 27th February 2012
Gear Guru

Glad you got it working. You have used a strong vertical zoom.
Less would make you feel better, a flatter graph.
Or a flatterer graph....
It does appear to be within +/- 10dB and has a downward tilt towards HF which I favour.
People sometimes use some website for uploading the full mdat files.
Perhaps someone could recommend one?

Old 27th February 2012
Gear interested

Thread Starter
Okay Thanx,

So this doesn't seem to bad after some very rough 'treatment'?

The null around 40 Hz bugs me, I understand nulls that low are difficult to change?

I'm now trying to understand the waterfalls and how to make them into a useful, readable graph...

Uploading the files would be great... Anyone?

Thanx again!
Old 27th February 2012
Gear interested

Thread Starter
zip.... ;-)
Attached Files
File Type: zip (4.13 MB, 28 views)
Old 27th February 2012
Lives for gear
kasmira's Avatar

Originally Posted by Mukaku View Post
zip.... ;-)
Great idea!
Old 28th February 2012
Gear interested

Thread Starter
Anyone? I would love t know what my measurements mean... ;-)
Old 28th February 2012
Gear Guru

Try a Waterfall 30-300Hz. You will see that there is dirty looking noise around 90dB and your peaks hover around 130dB. A 40dB range is not enough to show modes are decay clearly.
Looks like you need to drive the room a lot louder to get above the noise.
The sweep should be as loud as the speaker can reasonably do. You will need to block your ears with sealed cans or earplugs.
There is probably some gain or volume control in your computer which is dropping the input level. Go to the sound controlling panels. Turn input levels to 0dB or up full.

With an SLM you can calibrate the levels so your 90dB sweep reads 90 on the graphs. If you don't have one just do it loud and adjust the input gain to read around 90.

Old 1st March 2012
Gear interested

Thread Starter

The last few days I haven't been able to refine my measurements, but there's a few things that bug me for future treatment;

As Dan suggested, my studio might be a Limp Bag to some degree. Allthough not totally, cause there's actually plenty of bass and also some standing waves cause I hear some nulls.
But... most (low) frequencies have very little nulls and peaks when checking throughout the whole room (I guess that's a chatacteristic of a Limp Bag?)

Now my 3 main questions are;
-I if would want to do bass trapping, where do I put the basstraps? (since there seem to be very few 'build-up'-spots..)

-In a Limp bag situation, is it possible basstrapping sort of only makes matters worse? I mean shouldn't I just let all bass freq's 'disappear' through the wood and have as little 'obstruction' (basstraps) as possible?

- If some freq's just seem to 'fly out the window', how do I bring them back? Is there any other way, besides basstrapping, to influence low freq's behaviour?

I hope all this this doesn't seem contradicting (again), but my main worry is; 'How do I even the nulls and peaks on some freq, without affecting the freq that allready seem okay and may be benefiting from some sort of limp bag effect?'

I hope I make myself clear, I think my situation is rather unique, and I'm reading everything I can find about treatment, but still find very situations that might match mine...

I'll try to do some better measuring soon...

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