Help analysing my REW data - drum room/mix-space

[Noisebomber]

Hi there,

I've recently completed my drum room/mix space build (original construction thread here: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20546).
I'm stoked with the results so far and have achieved a fantastic level of sound proofing. I'm a multi-instrumentalist song writer and intend to use the space to record
my work.

The space was comically reverberant to start with and I immediately treated the room with some acoustic panels (as per design in the "25 min, $25 acoustic panel" thread)
as well as placing 4 twice as think versions around the corners as some preliminary bass traps. I may have gone overboard with the panels as now my room is super dead and I expect
to be removing some of them.

I ran a REW test last week using a DBX RTA M as per instructions (60 degree angled up pointed forward from listening position). The only part I haven't followed was the use of a proper SPL meter (I used an iPhone app, sorry I know that's a no no but wanted to see if I managed to calibrate ok before purchasing a proper SPL meter, I expect a scolding and will re-do tests if you think these files are flawed).

REW file is here: https://www.dropbox.com/s/cus6wl17zr430 ... .mdat?dl=0
Files are labelled left/right speakers, both speakers with clipping (the dual test had a clip warning appear after it had run, for the next test I reduced mic gain a little) & both speakers.


Room dimensions-

L: 530cm
W: 460cm
Height room centre: 245cm
Height room sides: 204cm

Here's some photos. The drums were covered up with blankets during test. I've yet to hang the bass trap near the door (didn't think about door position during build!) so have
just been placing it there when I'm working.

I would like to further improve the acoustics for mixing and get some advice on suitable diffusion to liven the space up a little, or if I should just pull some of the acoustic panels off.

[Soundman2020]

Hi there "Noisebomber"...

I've recently completed my drum room/mix space build...

That's sort of a self-contradiction! That's like saying "I've recently completed my waterless swimming pool" The reason I say that is because the acoustic needs of a control room are vastly different than the acoustic needs for a drum room. Control rooms needs acoustics as described in BS.1116-3: totally neutral in both frequency response and time-domain response. But drums need a lively room, with character. Playing drums in a control room leaves them sounding life-less, dull, muffled. And trying to mix in a drum room leaves the mix sounding just plain ugly.

OK, so the solution is variable acoustics: devices that can be changed in some way (opened, closed, slid, flipped, rotated, rolled, covered, uncovered, etc.) in order to change teh acoustic response of the room from "neutral" to "live". It is possible, yes. I have designed a couple of rooms like that, with decent results.

I may have gone overboard with the panels as now my room is super dead and I expect to be removing some of them.

Actually, you have not gone anywhere near far enough! Removing panels would be a big mistake. Your REW data reveals that there are major modal issues going on, as well as what looks like SBIR issues, and large amplitude early reflections, among several other things.

Your room is only dead in the high end, not in the low end, and even then it's not that dead... for a control room that size, it's a little low, yes, bur not terrible.

However, for drums, yes, it is "ugly dead". And that's where you'll need to design variable acoustic devices. It is impossible to have a room for both drums and mixing using only fixed acoustics. Some people try to tune their rooms "in the middle", part way between sounding good for drums and sounding good for mixing, and the result is that it sounds no good for either!

OK, the issue with what you have done so far, and the reason it sounds too dead, is because heavy, deep porous absorption ("bass trapping") is critically necessary to get the low end under control, but it also sucks out the highs completely, long before you have enough in the room to actually deal with the lows. Fortunately, there's a simple solution: Tune your traps! It is simple to add "stuff" to your bass traps that will reflect the highs back into the room while still allowing the lows to get through and be absorbed. One way to do that is by adding plastic sheeting across the front of some of your traps. Plastic sheeting is technically a "foil", and it reflects back part of the spectrum, based on it's density (thickness). So by choosing the correct thickness of plastic, you can control what range of frequencies you want to reflect, and what range you want to absorb, and by varying the coverage (what percentage of the face of the bass trap has plastic on it, vs. what percentage does not), you can control the amount of absorption/reflection. For example, if you wanted to reflect back everything above about 1 kHz, then you could put 6mil plastic on your bass traps, but if you did that and it was then too bright, you could cut off broad strips from that plastic, so you were only covering 50% of the surface... or 25%, or 75%, or whatever: You can get a lot of control like this.

Another approach is to attach broad wood slats to the front of your bass traps. Here too, you can control the frequency range you reflect by varying the size of the slats, and the amount by varying the percent coverage. Slats will go down to lower frequencies than plastic.

So, to fix your room, you are going to need much bigger, much deeper, bass traps, such as the "suprchunk" style bass traps, in your room corners. As many corners as you can (there are twelve corners....) And you will also need to cover many of them with at least some plastic, in order to NOT kill the highs.

Files are labelled left/right speakers, both speakers with clipping (the dual test had a clip warning appear after it had run, for the next test I reduced mic gain a little) & both speakers.

You reduce the level by about 7 dB, but then you did not repeat the tests for the left and right speakers individually! So now you have the crazy situation where both speakers together are showing up QUIETER then one speaker by itself...

Here's some photos.

Your bass traps are definitely not big enough, and are in the wrong place. The most effective point for bass traps is in the tri-corners, where two walls and the ceiling meet, and where two walls and the floor meet. Your bass traps don't go from ceiling to floor, so they don't get into the tri-corners.

Also, you will need to have thick absorption across the entire rear wall (at least, when you are using the room for mixing).

It's a reasonably sized room, so it can actually be quite good. But it will need more and better treatment, and you will also need to lay it out better. Your speakers seem to be too close together at present, and your mix position seems to be too close to the front wall, from what I can see in the photos. Also, your equipment layout is not symmetrical, and I strongly suspect that some of the reflections I'm seeing are coming from that.

- Stuart -

[Noisebomber]

Thanks Stuart,

Ok, I have some work to do!

I was originally planning to do superchunks but due to room design, it will have to be something movable for the front right door corner so door can be opened/closed
and something that fits around the HVAC unit on the same wall, opposite corner without obstructing the HVAC outlet.

I will just have to get creative and figure out a superchunk design that can work with these 2 corners.

Will the fact they're not 100% the same as the other 2 corners be a major issue? There isn't really much I can do about it but I want to ensure it's likely to improve my
low end situation.

Also regarding my screw up with the REW levels, do you think I should conduct a new test with space as is before I start superchunks or are the current files going to be adequate
for comparison?

Thanks heaps for helping me with this.

Kris

[Noisebomber]

if you wanted to reflect back everything above about 1 kHz, then you could put 6mil plastic on your bass traps

PS: Just want to double check you mean 6mm thick plastic here?

I'm having trouble finding anything this thick, with the thickest I've found being 3mm.

The only plastic this thick I can find is acrylic perspex type stuff.

[Soundman2020]

Just want to double check you mean 6mm thick plastic here?

No, I mean 6 mil plastic. "mil" is construction industry abbreviation for "thousandths of an inch". So 6 mil = 6/1000". Google it!

https://www.google.cl/search?site=&sour ... il+plastic

I'm having trouble finding anything this thick, with the thickest I've found being 3mm.

I did mention that "plastic sheeting is technically a "foil", ...". I don't think you'd call 3mm thick a "foil"!

6 mil plastic is the type that builders use as a vapor barrier inside walls and ceilings, foundations, drop cloth, construction curtains, etc. You can find it in pretty much any building supply store, on rolls.

- Stuart -

[Noisebomber]

Thanks for clarifying, that makes more sense and I can source stuff this thick easy.

I find it bizarre to learn people use the first 3 letters of the metric term 'millimetre' (which is a thousandth of a meter) to describe 1 thousandth of an imperial measurement.

[Soundman2020]

I find it bizarre to learn people use the first 3 letters of the metric term 'millimetre' (which is a thousandth of a meter) to describe 1 thousandth of an imperial measurement.

Very true! But there's not a lot that is logical about the entire imperial system anyway... ! Metric is so much simpler... but unfortunately the imperial terms seem to have stuck, even in countries that are totally metric. Chile, (where I live) is 100% metric, and has been for many decades... except where it isn't! In the local equivalent of Home Dept, I still buy lumber that is marked as "2x4", even though it is ALSO marked as 38mm x 89mm... and yet it comes in 3m lengths, not feet! Then I'd by 4" framing nails for it, but the drywall to put on it measures 122cm x 244cm, which is actually 4' by 8', yet plywood comes in sheets that are 120cm by 240cm... go figure! I'd paint it with paint that comes by the gallon, but I'd use metric sized brushes or rollers to apply it, and the coverage would be specified in the weirdest of all: square meters per gallon! Ugh! I'd then put in 1/2" copper pipe for plumbing, but 20mm conduit right next to that for electrical wiring, while for the plumbing pipe I'd use 1/2" to 3/4" copper adapters that are 30mm long, and to attach them I'd buy solder by the meter or the gram, yet gas canisters for my blowtorch are marked in ounces....

Nuts!


- Stuart -