# I've installed bass traps but not sure what to do now.



## 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 10-15db at 130-155hz.
Should I target 90hz with a tuned absorber?
I also have nulls at 490, 600,696,801, 1.4 and 3.4 should I build some diffusers?

I still have a corner on the back wall that I was going to leave untreated because I was going to put my drum kit there and thought there wouldn't be room. However after setting the kit up I see that there is enough room to treat it. After that there is about 1.5 meters of space on the back wall I can treat (including the window). I was advised that more bass traps on the back wall should help the nulls in low bass.
I am concerned that I will suck to many highs out of the room.
Should I install some bass traps on the back wall with diffusers in front of the traps? 
Or apply some facing?
I thought some skyline diffusers on the ceiling behind me and QRD diffusers on the side walls might be a good Idea as well.
I've uploaded FR graph (1/24 oct smoothing), 2 waterfall graphs (40-300Hz and 40-15kHz) and RT 60.
Measurements were taken after bass traps were installed.
My room is L: 3.6 W: 2.7 H: 2.5 meters

Thanks and kind regards
-Matt


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## eclipse911t (Jan 8, 2013)

Matt,


Things look pretty good overall. Can you describe in more detail what treatments you have done and where? A couple room pictures would help.


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## metrobot (Jan 26, 2013)

Here you go,
All the bass traps are superchunk absorbers and they extend all around the room the only space not covered is just above the door.
I used Knauf earthwool universal slab RS60 100mm.
The purple panels are 1.2X 1.2 meters except the one on the right due to the part of the wall that juts out because of the chimney 
They are 100mm thick and spaced from the wall 100mm.
The back wall, back left corner and the side walls remain untreated
As you can see.... I'm not a photographer.
Cheers
-Matt


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## eclipse911t (Jan 8, 2013)

Matt,

That is a great deal of treatment, and the installation looks very good. From an amateur's perspective I would definitely suggest moving panels around and taking some additional measurements. Is the super chunk in the rear framed so it can be moved? If so I would pull it out and remeasure, then try measuring with it on the rear wall center and then the rear wall-floor corner, and then the back of one of the side walls.

Looking at your frequency response I would see how responsive your room is to EQ. It all looks very manageable with EQ, but it's somewhat hard to tell being ever so slightly smoothed. I know it won't help the decay times, but as long as the decays drag on, they take a sizable drop initially.

I've heard excellent things about side wall QRD Diffusors with broadband absorption behind them. This would be for the side walls at or behind the listening position. However, when looking at your problem frequencies, those would be some seriously deep QRD Diffusors.

Hopefully some of the real pros here will step in with some really solid advice. 

One other comment, have you looked at ETC? It most likely has no impact on the discussion here of frequency response or low frequency decay, but it should be considered in your control room. I expect your ETC to be great, but thought I'd mention it.


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## metrobot (Jan 26, 2013)

All of them are framed so they can be moved. Although the ones off the floor are bolted to the walls and ceilings. I'll try moving the one at the back wall and see what happens. So far the bass trapping has done an excellent job compared to what it was before.
When suggesting Eq do you mean a hardware eq put between my speakers and amp or a plug-in on the mix buss?
I haven't looked at the ETC yet but I'll have to figure out what it actually does. I'll do some more measurements this afternoon. I've uploaded the FR with no smoothing.
Thanks
-Matt


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## eclipse911t (Jan 8, 2013)

Matt,
Looking at your unsmoothed graph, everything from 400Hz and down should be pretty responsive to EQ. Typically it's the sharp narrow nulls that are un-EQ-able.

ETC will show you the amount of reflections you have in your room. It focuses on the earlier reflections rather than the decay/reverberation like the waterfall. It is a good quantitative indicator of intelligability and imaging. It's best to get your early reflections as quiet as possible as quickly as possible. The very end of this article talks about it: http://www.realtraps.com/art_measuring.htm
Moving panels is useful in trial work for ETC improvement.

*Edit* Only connect one speaker when measuring for ETC.


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## metrobot (Jan 26, 2013)

I moved the drum kit out and the FR response improved a little plus decay times dropped. No surprise there due to the drums probably resonating.
I also moved the bass trap around as well and the decay times improved some more, FR changed as well.
In some positions (like the other corner) the highs above 12kHz rolled off quite a lot so I think more bass trapping is needed but without absorbing to much above 10kHz. I think the ETC looks good from the limited experience I have with it.

I uploaded FR and waterfall graphs for when the drum kit was removed, when the bass trap was in the other corner and ETC graph for each speaker.
Cheers
-Matt


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## eclipse911t (Jan 8, 2013)

What a great room! You followed the rules and did the work. You earned it. 

I'd drop an EQ on the output bus and smooth out the bottom end. And be done. The extended decay at ~160Hz is too flat to be decay, it's some sort of noise or resonance. The previous resonances/extended decays were pretty far down in amplitude, so they are less worrisome than they look. I chop my waterfalls at -30. Meaning run your measurements at 90 and look at the waterfall from 60 - 100, and run it at 300ms as well as longer values when needed.

There are two things concerning on the ETC. The obvious one is the reflection off the rear wall. It's down 18-20db so it's not bad at all, but some diffusion or absorption back there would help bring it down in line with the rest of the decay. For the record I'm talking about the reflection around 16ms which is about 16 feet. This would be interpreted as the sound from monitor to your ears ears is ~16 feet shorter than the sound from monitor to rear window to ears. Is that close? How badly do you want to cover up your only window :-/

The other thing is the ~2ms reflection that is unique to the purple ETC graph. So this is roughly 2 feet total sound travel longer than a direct sound. A useful way to look at ETC is 0ms - 20ms and 0db to -30db. What could be unique to that speaker at that distance?

-Patrick


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## metrobot (Jan 26, 2013)

Cheers Patrick.
You seem to be on the money with the reflection from the rear wall. The left speaker has the reflection at 16
and its pointing at the un-trapped back corner. I'm going to put some more absorption on the back wall. The window is nice but my back is to it anyway.
I thought the 2ms reflection is either because the absorber on that wall is shorter due to the fireplace. Or the Avantone mono speaker but it seems to be a reflection off the desk as it dropped 3db when I put some foam there. I saw that my speakers were a little off center so I moved them about 50mm.
I got a couple of days off so I'm going to build a few more traps and see how it goes.

Thanks tonnes for your help 
-Matt


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