How to evaluate my DIY bass traps correctly with REW measurements?

[vroad]

How can I tell from my measurements that did bass traps are making my system's sound better and not messing up at least?
For evaluating time domain performance of bass traps, which graphs should I read and how?
Also, is there good rule of thumb for determining how much should I absorb? I guess I can't do more in my current room, maybe in the future.

I've built and installed 4 DIY porus material bass traps in my living room in the beginning of this year.
Each panel sizes about W60cm x H72 cm x D10cm. For the porus material I've used cellrouse fiber insulation material which weighs about 90kg/m3. I stacked 2 panels in 2 corners.
I know that many people would say that fully stacking in 4 corners is the minimal recommended amount, I just tried my best to treat my room with available living room space and my limited DIY skills.

I re-measured bass traps to see if bass traps are still working as expected, and previous measurements were really showing the perforamnce of DIY bass traps.
I only measured in single position so that the conditions other than bass traps won't change.
This time there are not much changes in frequency response graphs, except for higher bass frequencies like 200-300Hz.

When I measured the traps in the beginning of this year, the SPL at 100Hz was below 50dB at worst positions because of the sharp dip.
Installing traps restored some lost SPLs, increasing the SPL at 100Hz to 55dB or so at any positions.

This time the SPL at 100Hz was 55dB with or without bass traps.

I've only looked at frequency response graphs because that seemed like the easiest one to interpret.
Later I've learned about other types of graphs that shows time domain performance of bass traps such as waterwall, though I was not sure how to interpret correctly.

With or without room correction systems like Dirac and Audyssey, my system still sounds good at least to my ears, I don't think I've heard something weird.

My living room's system is 2.1ch configuration.
For "raw" measurements I've only enabled front speakers and disabled the subwoofer.

I've also included a measurements with Dirac DLBC and subwoofer enabled.
I didn't re-callibrate as that will chnage conditions other than bass traps. (Callibrated with bass traps present)

Using Dirac and subwoofer alone lowered the depth of the dip at 100Hz by large margin.
If you have only single listening position and only want to be able to fix frequency response irregularities, Dirac and subwoofer might be enough?

Amp: Denon AVR-X3800H
Front: ELAC DBR62
Subwoofer: SVS 3000 Micro (Only enabled for measurements with Dirac)

 

[moedra]

It looks like your traps are mostly effective from 160Hz and up. They aren't doing much below that. Either they aren't thick enough, they aren't in the right places, or there isn't a large enough air gap behind them. Not sure what the case is. There is a large reflection in the ETC graph around 12.4 milliseconds in the right speaker response. That may be coming from a rear corner. There are other reflections at 4.2, 6.5, 7.9, and 8.8 milliseconds that you should look into treating. These probably don't have much to do with the bass. You should be looking at the ETC graph to locate reflections in the upper regions, and the step response to see what's happening in the lower frequencies. I can see where Dirac cleared up your inter-channel coherence, but the oscillation behind the peak is a lot stronger in all cases than the initial pulse. There is a lot of energy bouncing around the room there that the traps are not absorbing.

 

[Todd Anderson]

Inflicting much change in the lower registers of bass is really tough to do, unfortunately. What kind trap materials are you using?

 

[vroad]

Inflicting much change in the lower registers of bass is really tough to do, unfortunately. What kind trap materials are you using?

I used cellrouse fiber insulation material made by a Japanese company named Ecopulton.
Because it seemed like the only material that is effective as glassfibre/rockfibre insulation and doesn't cause itchiness.

It looks like your traps are mostly effective from 160Hz and up. They aren't doing much below that. Either they aren't thick enough, they aren't in the right places, or there isn't a large enough air gap behind them. Not sure what the case is.

I guess one of the reasons that traps are not effective in lower frequencies is that I'm not spreading them as evenly as possible. I've only used 2 wall-to-wall corners in front of me. I straddled them in those corners to give some airgap.

Ethan Winer's article "Rigid Fiberglass Density Tests" showed that 12 panels 3 inches thick covering larger area is much effective than 6 panels 6 inches covering narrower area. I only have 4 panels 4 inches thick (10cm thick) now, and those doesn't have FRK facing. Each panel slightly larger than RealTraps panels but the number of panel is probably not sufficient.

To spread traps as evenly as possible I need to sacrifice room space or mount traps in ceiling to wall corner, etc.
Safely mounting 4kg weight trap to ceiling to wall corner don't sound very easy for me.
Also they make me feel the room even narrower. I'd rather avoid that as the room is not a dedicated listening room.
Looks difficult to treat more without moving to another house.

 

[basscleaner]

The first of all, you need to get noise response of your room, because there is suspecting, that power supply (or something else) in your room may causes distortion at this frequency. If not, then you need to choose the best position for stereo only, especially, if they work good in LF range. Word "good" means, that distortion in this range has to be in deviation corridor less, than +-2 dB. This value is due to our ear sensibility, because we can divide closest frequencies approximately 1.5 Hz between each other and +- 2 dB is the compromise (less is better!) to have not big difference between closest. After that you should mark peaks and dips and try to use bass traps consistently and carefully add them while controlling FR changes. It is important to remain yourself into the same seat positions due to measurements, because it influences to results. After you successed in the best stereo position by moving stereo base, seating point, you may to add sub with such a manner, that to regulate FR for deleting of remaining peaks or deeps by sub control features. If your narrow peak or dip still remains, you may to make your own tube resonator, which corresponds to this frequency and try to find zone, where it will work good. If you still want us to get comments, please, send your notes to every picture to understand what conditions were while measured.

 

[Mike Schramm]

I've always wondered: what is the go-to graph for evaluating room acoustics. I have treated areas of my room, but from a measurement standpoint I have no idea if they are actually doing anything to help.

 

[basscleaner]

I've always wondered: what is the go-to graph for evaluating room acoustics. I have treated areas of my room, but from a measurement standpoint I have no idea if they are actually doing anything to help.

There are two methods: to hear and to see. What is difference between them? The thing is that some of changes are difficult to sense briefly. Sometimes you need to have either very sensitive ears or big experience, because aged people have worse hearing, then young. That's why to use measurements may be more convenient, than to have the discussion with yourself. Changes in acoustical treatment become more clear, if to test some acoustical parameters, for instance, RT60 - reverberation time as dependence by frequency or any others. This can help to understand the dynamics of changes, how much to add or delete absorbing materials or use EQ, where to place it more efficient. It is well known fact, that our brain is capable to learn right listening.

 

[Mike Schramm]

So, RT60 is the graph I want to use, but the main way is to simply hear if there is difference?

 

[ddude003]

I suggest more bass trapping, some wide band absorption and diffusion as first steps... Then the next step is DSP EQing...

Hint, Bass builds up in all 3 sided corners, floor and ceiling... And in all 2 sided areas, floor to wall and wall to ceiling... Also need to treat 1/4 to 1/3 of surface area... Yea, I know that's a lot... Here is a good source of information on this... http://arqen.com/bass-traps-101/placement-guide/ Also, get your hands on Master Handbook of Acoustics by Ken C. Pohlmann... You might be able to find a previous edition on line as a pdf file for free...