# Small room acoustics advice



## jtm45 (Nov 12, 2011)

Hello Everyone!

I am converting a spare bedroom to a 2 channel mixing/D.I. recording room, and need some advice on what to do acoustically with it. I have measured the room with an ECM8000 as I have added traps one by one, and the REW file and a couple of photos I took during the measurements are here:

https://www.dropbox.com/sh/pxwt3hdpn0zeuhv/m3KxkoW7Az

The room is definitely not ideal, but its the only one I've got.  Also, it is a rental flat and I am not allowed to make holes in the walls so everything I do needs to be "portable". Hence the frame for the ceiling RFZs. I have 19 panels accessible in total, and they are all 2x4 feet. 18 that are 4" thick and one 2"thick. The speakers are Neumann KH120.

The dimensions of the room are 11.48 x 8.03 x 8.69 feet (converted from meters). The listening position is 38% from the back wall since there would not have been enough space to have it 38% from the front. I have not started looking for the best speaker placement yet, and the frame to attach the ceiling and side RFZs are not permanently in position yet.

Questions:

1. As I have understood RT60 is pretty irrelevant for this size of room, but what I have noticed after putting in all recommended panels (all 4 wall-wall corners, side RFZs and ceiling RFZ), is that the room sounds rather dead (RT60 of around 0.2s). Would it be better to have a bit more "live" room and worse frequency response, or should I not worry too much about the liveliness of the room since it is so small anyway?

2. Does the frequency response look reasonable in test 10 in the REW file? Not sure how I could get rid of those modes at 48 and 135Hz…

3. What else should I look at in the measurements and change in the room? 



Any advice would be greatly appreciated!

Johan


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## AudiocRaver (Jun 6, 2012)

Wow, those Neumanns really crank out the volume.:yikes: That 160 dB SPL has got to hurt.:hsd: Hope the neighbors don't mind.:bigsmile:

Seriously: Nice set of plots, well annotated. Great acoustical detective work, very methodically planned, executed, measured, and documented. That takes a lot of patience, more than I have. I will refer others to this thread in the future as an example of "here is how you go about it," and as a super example of what is possible by trying different treatment combinations in a room. Kudos.:clap:

I agree that plot #10 is the first one that catches the eye as looking really nicely controlled. #13 is _really_ clean, in terms of cleaning up all the little nulls from reflections. That looks like the configuration to go with, unless there is some particular reason to go with #10. Either one would be great.

Your reverb time looks great. The room may sound a bit dead now, but when you get to recording & mixing, you will be glad for its cleanness and neutrality.

All this is with 48th octave smoothing. Look at it with more & more smoothing down to 1 octave, where it is ruler flat, which is good. When you are all done, I believe you would like to be able to look at your final plot at all smoothing settings from 1/48th to 1, and see it as smooth as possible at all those settings. In my experience, as we shift between working modes our hearing is looking at different versions of that line. Sometimes we're listening for the big overview, like one octave smoothing, and that overall evenness will stand out. Other times with more and more detail. If you can accomplish that, you will be very happy that you did.

It is doubtful you can do much else with room treatment, equalization looks like the next step. Call the one octave smoothing line your target line. Go to one third octave smoothing and see that 48 Hz and 340 Hz are the main peaks that need to be brought down a little. Go to 1/12 octave smoothing and you'll see better detail, that 135 Hz will need a little bit of tweaking also but not much. With no smoothing, you can see that the little dip at 500 Hz is the result of a sharp little null (from some reflection?? - don't obsess over it, it will never be perfect). Leave that one alone, you will never hear it, and you will do more harm than good if you try to correct for it.

Assuming you will be using REW to generate correction filters, let it give you a starting point and then refine that a little bit by hand. In general, it is not wise to boost the dips in the response, especially if they have a sharp notch involved. I generally set REW to do no individual boosting, and then only add a little where it seems okay by hand at the end. Because it is fairly smooth and not very deep, the dip at 100 Hz could be boosted a little, I emphasized a _little,_ not very much, just a couple to dB at most. Then the peek at 135, instead of flattening it out completely I would leave it up one or two DB, it will tend to compensate for the 100 Hz dip and help make that one octave smoothing line stay completely flat. Of course smooth out the 48 Hz and 340 Hz peaks, it should only take a few filters to do each. I would probably bring up the high-frequency slope so it was only down three dB or so that 10 kHz, but there are different philosophies about that, go with your personal preference. With your low reverb time, that will not seem overly bright.

As you fine tune, go back and forth between one octave smoothing, third octave smoothing, 12th octave, 48th octave, and no smoothing. Your one octave smoothing line should end up razor flat and the others as smooth as possible in support of it. That is my approach, I think you will be happy with it.

Again, very nice job, I am more than a little jealous of your results. You are going to have a very nice mixing room when you are done, and you are almost there. Keep us posted, we will be wanting to see what your final results look like, and what it takes to get there.


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## jtm45 (Nov 12, 2011)

Hey!

Thank you very much for those kind words, and sorry for not replying sooner. I have been on holiday. 
Yeah, I have done A LOT of testing...  Have learnt a lot in the process so far, which is great!

To be totally honest, using EQ to do the last adjustments hadn't even occurred to me. Somehow I was under the impression that doing that was kind of cheating. Would the room be good enough for mixing without using EQ you think?

Now I think I have almost nailed the treatment of the room, but there are a couple of questions that have come up:

1. When I started looking for the best speaker placement (creating a equilateral triangle) I noticed that the freq response became worse compared to the tests I posted last time. The new tests are here: https://www.dropbox.com/sh/e8d1d7lzcywjcb5/1Tn2Fvfkib In that folder there are also a few photos of the latest placements of the panels... Note that I wrote latest! 
The best placement of the speakers for flat response is very close to the front wall and sides of the room, but this means that the speakers will be quite far away from the listening position (around 4.8 feet), and that also means a lot of reflections from the desk. If I move the speakers further into the room I am getting quite a few peaks and nulls. 

So the question is what to compromise on, the reflections from the desk or the bass response?


2. Placement of the side RFZs. Ideally they should cover the reflections from both speakers right? I have read in a few places that in such a small room it should be enough with 1 panel on each wall, but when I check with a mirror it is not possible to cover reflections from both speakers with only one panel on each side... 

I do have 2 panels left that I could use for that, so I have 2 on each side but that would make the room even more dead in terms of reverb time. Would you put up the extra 2?

Thanks for the great input!


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## AudiocRaver (Jun 6, 2012)

jtm45 said:


> To be totally honest, using EQ to do the last adjustments hadn't even occurred to me. Somehow I was under the impression that doing that was kind of cheating. Would the room be good enough for mixing without using EQ you think?


There are those who would say that it is cheating. I think the compromising starts when you try to use equalization to do a job that room treatment could clearly do so much better. Which I am not above trying or suggesting when room treatment is simply not an option for whatever reason, but in your case you have taken that path about as far as it can go. What is left then can be treated very nicely with EQ, and without the negative effects that you can get when trying to EQ in an untreated room. In your shoes, having accomplished so much with room treatment, even in my own most idealistic moments I would not hesitate to use EQ to clean up the last few problem areas.



jtm45 said:


> 1. When I started looking for the best speaker placement (creating a equilateral triangle) I noticed that the freq response became worse compared to the tests I posted last time..... The best placement of the speakers for flat response is very close to the front wall and sides of the room, but this means that the speakers will be quite far away from the listening position (around 4.8 feet), and that also means a lot of reflections from the desk. If I move the speakers further into the room I am getting quite a few peaks and nulls.
> 
> So the question is what to compromise on, the reflections from the desk or the bass response?


A judgment call. Based solely on your measurements, I favor the "not taking equilateral triangle into consideration" curve for these reasons: Looking at the impulse, the reflections appear so much better controlled. High frequencies are very smooth with a gentle rolloff that you could probably live with just as it is, or perhaps boost a little with shelf EQ. Using that curve with 1/3 oct smoothing as a target, REW gives a very nice resulting curve with only 5 filter values, all addressing room modes. Truly minimalistic filtering with excellent results. See this attached file:
View attachment 20130405-Filters.req
. (With that curve selected and 1/3oct smoothing applied, import the filters into the EQ > EQ Filters screen with Generic equalizer selected.)

By the way, your readings all show 160+ db SPL readings when I look at them. I assume for the sake of your walls, windows, & ears, that is not truly correct.



jtm45 said:


> 2. Placement of the side RFZs. Ideally they should cover the reflections from both speakers right? I have read in a few places that in such a small room it should be enough with 1 panel on each wall, but when I check with a mirror it is not possible to cover reflections from both speakers with only one panel on each side...
> 
> I do have 2 panels left that I could use for that, so I have 2 on each side but that would make the room even more dead in terms of reverb time. Would you put up the extra 2?


If you see that the result is even cleaner measured impulses, I would go ahead and do it. At this point they will probably not affect reverb time significantly.

Keep us posted. I would sure like to hear that room when you are done.:sn:


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