Help interpreting REW graphs

[javamad]

Hi All,

My project is to set up a recording/mixing room in the spare bedroom in my house. It is a typical Irish/UK semi detached house with plasterboard walls. I'm renting and I am not allowed to apply any large fixings to the walls, etc

The room is a bit of an anti-studio but it's what I have to work with. It is an L shape as per the drawing attached.

My intention is to use the room for composition and self recording (should be ok with basic treatment) and I would also like to try mixing for myself and others (I will need a balanced room for this)

I have set up my desk along the longer axis and that leaves me with a window to my right which I intend to block off with a thick plywood board using some foam on the edges to allow me to push-fit the board into the window area and not have to do any permanent install. I will then be adding early reflection absorbers to left and right side but they are not installed yet.

I am trying to get a handle on whether the bass can be tamed in this room and I have put rolls of rockwool, still in their packs, in the two front corners. The room height is 248 cm and each roll is 125 cm so two stacked simply pushes into the corner and holds there.



My Questions:
1. Is the room all that bad? I see on the graph a mode at 150Hz and a null at 85Hz ... but it doesn't look too bad to me.
2. I took measurements from the listening position (132cm) and from 170 and 190 cm from the front wall. The null seems to get worse as you go back but that won't really affect me in my listening position, right?
3. I am unable to understand the waterfall chart ... as I zoom in an out the shapes move around but I am not sure what I'm looking at. What I *seem* to see is a ringing or long decay below 80 at several frequencies. This would suggest I go buy more bass trapping I presume?
4. If I buy more bass trapping for the rear corners .. what do I do with the rear right? there is no corner to speak of....
5. Is my bass trapping effective enough by leaving the rockwool in the packs? Does the wool have to be loose to have more effect?


Thanks,


MDAT file is here : https://www.dropbox.com/s/5ixatg1pkv90o ... t.zip?dl=0

[javamad]

I forgot to post a photo ...

Heres a photo of the room as is now.

[Soundman2020]

1. Is the room all that bad? I see on the graph a mode at 150Hz and a null at 85Hz ... but it doesn't look too bad to me.

considering the very tiny size, it's not too bad overall.

However, you did your REW tests at a level that is way too low. REW shows that you ran the tests at a level of about 65 dB, but you need to do it at 85 dB. So please repeat the tests, after calibrating REW correctly with a proper hand-held sound level meter.

2. I took measurements from the listening position (132cm) and from 170 and 190 cm from the front wall. The null seems to get worse as you go back but that won't really affect me in my listening position, right?

Right. The "null" is actually not the same one! That is SBIR, and is an artifact of the distance between the rear wall and the mic position. So you are looking at a different null in each case, for a different frequency that corresponds to that distance. As you go further away from the rear wall, the "null" goes to a lower frequency, corresponding to the larger distance. So at the listening position you are in one of those nulls, that corresponds to the distance between that location and the rear wall. Fortunately, it isn't that deep at the listening position, and there seems to be a modal peak in the same region too, so they cancel each other out to a certain extent.

I am unable to understand the waterfall chart ... as I zoom in an out the shapes move around but I am not sure what I'm looking at.

You are looking at the decay times for specific frequencies. Click on the "limits" button. Set the parameters so that you are looking ONLY at the low end of the spectrum, from about 20 Hz on the left to about 500 Hz on the right (or even less if you want more detail: maybe 300 Hz on the right). That's the region where all the problematic modal activity will be, as well as SBIR, and other issues. Set the vertical to run from about 35 Hz to about 105 Hz. Next, click on the "controls" button, then click "Apply default settings", and close the controls window. That's a realistic picture of what your low end looks like, warts and all. Or rather, it WOULD be a good picture, if you had done the tests at the correct level. In your case, to view your existing data you'll need to adjust the vertical scale...

What I *seem* to see is a ringing or long decay below 80 at several frequencies. This would suggest I go buy more bass trapping I presume?

Yes, but it might not make a huge difference, depending on how the rest of the room is set up. Yo only showed us the treatment at the front: we also need to see the treatment on the wall behind you. That's the critical wall. You need major bass trapping on that. If you have nothing there at present, then large absorbers in the corners would be good, plus six inches thickness of insulation across all the rest of the wall.

4. If I buy more bass trapping for the rear corners .. what do I do with the rear right? there is no corner to speak of....

Fit it in as best you can, sort of where the corner would be if the right side wall continued all the way back. Or put one horizontally in the wall/ceiling corner. Or both!

5. Is my bass trapping effective enough by leaving the rockwool in the packs? Does the wool have to be loose to have more effect?

It is having some effect, certainly: the graphs would be a lot worse if it wasn't there. Compressing insulation can reduce the effectiveness, especially at low frequencies, depending on how much it is compressed. You could try with one uncompressed roll, to see how that changes, and then decide.

- Stuart -