Tackling room resonances

[The_Doorman]

I'm all set up to start mixing songs in my new studio (room). You can see a couple of pictures at www.doormanmusic.com/studio. Using the excellent book "Mixing secrets for the small studio" of Mike Senior I first started treating the room a bit. In every corner I put a bass trap/absorber of 104 x 64 x 10 cm made of Rockwool 221. I put pieces of DAP-Audio ASM-03 acoustic foam (50 x 50 x 10 cm) behind every Genelec 8020 speaker and 1 at each reflection point. Only 1, maybe a bit too little?

So, while testing both the Genelec's and an Avantone Mixcube with the LFSineTones audio file mentioned in the book all seems well until frequencies of 92, 111, 147, 165, 185, 233 and 262Hz kick in. Especially the latter five are really louder.

What could I do additionally in treating the room? I mounted the bass traps halfway in each corner and considering a low ceiling at 2,2m with beams it's difficult to mount more. Does placing more acoustic foam help? Any helpful suggestions are really appreciated!

[Hugh Robjohns]

More bass trapping is really the only way. Placing bass traps in the tri-corners where two walls meet the ceiling is the most efficient and effective location, bu running theme full height of the wall-wall corners is the next best option.

Bass has long wavelengths so the absorbers need to be deep. An inch o two of foam won't help...

H

[Bob Bickerton]

If you have the budget and are serious about it, you could have your room analysed by an acoustician and have a bespoke treatment plan designed.

If you're handy, you could then make and hang acoustic panels to implement the design.

Bob

[James Perrett]

Looking at your pictures I see lots of bare walls - you need more guitars on them

If you can't have more guitars then maybe put some tall bookshelves along the back wall to break up the reflections. I'd also follow Hugh's recommendation for more bass trapping - there are plenty of spaces for it.

[The_Doorman]

I'm a bit at a loss here... I bought two Auralex LENRD bass traps and decided to run some tests using REW (Room EQ wizard) and micing the output of my Genelec speakers at the mixing position. Placing the traps in two of any of the 4 wall-wall-ceiling corners did not improve anything in the spectrum of 30-300 Hz. Even worse, dismounting the previously placed bass traps that you could see in the pictures (Rockwool 221=55 kg/m3, 4"), also did not make a big difference! You can see the latter plots (for the left and right speaker, respectively) at www.doormanmusic.com/studio. I also uploaded a picture of the lay-out of my studio where you can see the dimensions, my mixing position and the only wall, which is concrete, indicated. The other three walls are drywall consisting of double layers of Rockwool 211=45 kg/m3 with plasterboard at the exterior.

I already invested a couple of hundreds but feel I'm not making any progress here. Could the beams protruding from the ceiling be the main culprit? Should I confine acoustic treatment more to the mixing position?, as in this example: http://www.soundonsound.com/techniques/studio-sos-michael-harvey

Again, your help is very much appreciated!

[Hugh Robjohns]

I'm a bit at a loss here... I bought two Auralex LENRD bass traps and decided to run some tests using REW (Room EQ wizard) and micing the output of my Genelec speakers at the mixing position. Placing the traps in two of any of the 4 wall-wall-ceiling corners did not improve anything in the spectrum of 30-300 Hz. Even worse, dismounting the previously placed bass traps that you could see in the pictures (Rockwool 221=55 kg/m3, 4"), also did not make a big difference!

I'm not really surprised. Effective bass trapping is a real challenge and it takes a lot of big bass traps to have a worthwhile effect. A couple of small foam wedges won't do anything useful at all. Most panels sold as 'bass traps' are nothing of the sort -- they're midband or broadband absorbers at best.

Here's an example of a professionally treated room to give you an idea of what's typically needed. The top red trace shows the RT measurement from the bare room, while the bottom blue trace is with most of the standard acoustic panels installed -- big improvement but still a wayward low bass. The purple trace is with the large white bass-trap panels installed as you can see in the second photo (there were more of those across the back wall too)

[James Perrett]

In my last studio I had modular bass traps covering almost the whole back wall as well as treatment over most of the rest of the room. In my current studio I have floor to ceiling corner traps in 3 corners (will be 4 when I get round to finishing it) and also between the wall and ceiling along the whole wall behind the speakers.

[The_Doorman]

OK, thanks. Considering a current tight budget (earlier, I had to spend 15k at making the basement waterproof) what would be my best bet (to get a reasonable bass reduction)? In order of importance would it be (based on your suggestions)?:

1) e.g. Primacoustic Cumulus Tri Corner Bass Traps in each of the 4 tri-corners
or:
2) Primacoustic Maxtraps in the wall-wall positions replacing the current Rockwool 221 panels

I mention Primacoustic with regard to availability in the Netherlands (GIK, Realtraps would also have to be imported).

Regarding budget I could realize option 1 but option 2, for now, only at two places. So, in front or in the back of the mixing position?

I could then glue the DAP foam onto the Rockwool 221 panels and place them at the reflection points.

[James Perrett]

The best way to do this on a budget is to forget about buying commercial products and build your own panels from Rockwool slabs in a wood frame covered by Cara fabric.

[The_Doorman]

Do own 'Recording secrets'and 'Mixing secrets' but did not know about The Studio SOS book (found it after googling your final sentence!). This can be really helpful and indeed a starting point to construct the traps myself.

[The_Doorman]

OK, here's what I did so far:

1) Rotating the mixing position 90 degrees so that it's now along the length of the room and at equal distances from left and right walls gave a huge improvement in bass resonances / modal ringing. Mixing position is at 28% of the length of the room. Not near 38% but at a maximum aesthetically acceptable position
2) I now placed the black Rockwool 221 traps on top of each other in the back wall corners, extending from top to almost the ceiling (but the tricorner is shielded by several ceiling beams when viewed from the mixing position - see pictures at www.doormanmusic.com/studio.
3).... and placed loft insulation rolls according to several suggestions amongst which http://www.soundonsound.com/techniques/studio-sos-stourbridge-community-centre in the front corners. These are PE wrapped mineral wool rolls, brand Knauf Expert with Rd value 4,55 (don't know exact density). They fitted perfectly from floor to ceiling and gave a notable improvement when looking at the waterfall plots (see my URL).

The current waterfall graphs are consistent with a resonance at 65-70Hz (using Mike Senior's LFSineTones audio file) trembling the desk and an audible peak at ~98Hz.
My questions:
1. what do you think of the current waterfall plots?
2. when can bass trapping be considered good enough for decent mixing results, considering this studio set-up?
3. what could I do more to improve it?

The back wall (where, btw, I will mount guitars as usable diffusers) is concrete and at more than 5 m distance. The other walls are plasterboard. Loft insulation in the front corners gave a better effect than in the back corners.
4. are the corners near the mixing position more important to treat regarding bass build-up, irrespective of the composition of the wall?
5. I can assume that the windows at the front will transmit the bass?

Your help and feedback is again greatly appreciated!

[Tim Gillett]

Dont know if it's been covered but the speakers' interaction with a desk can add a nasty peak in the region you mentioned. Is this a possible issue?

[Dr Huge Longjohns]

You could put some more rolls along the floor to wall junction under the window for starters.
What are your speakers sitting on? You can get all sorts of funny business going on if they're on hollow boxes or something?

[The_Doorman]

Last week I got even better results. In the end the rolls are at the back and the panels at the front. Also moved the monitoring position slightly. Now I'm left with ringing at 60Hz according to the waterfall graph. I'm gonna live with that.

I've got two rolls left so I will put them at the floor to wall junction like you said. The desk resonance is pretty much gone, it turned out to be loose items trembling. My speakers are on styrofoam boxes completely filled with sand, so they're pretty solid.

[TNGator]

The best way to do this on a budget is to forget about buying commercial products and build your own panels from Rockwool slabs in a wood frame covered by Cara fabric.

guys I know this discussion is quite old but Im trying to sort out my room and as such am going through the previous posts and queries relating to room treatment etc. I found a build supplier here in Dublin near my home who has rockwool in easy to use slabs in a pack. Sounds easier to use than a roll of the stuff. But does the rockwool have to be of a certain grade or thickness etc. Builders sell this for the purpose of insulating a house. They're not in the home studio business. Can any rockwool work?
Thanks
Xave

[Eddy Deegan]

... does the rockwool have to be of a certain grade or thickness etc. Builders sell this for the purpose of insulating a house. They're not in the home studio business. Can any rockwool work?

Not all rockwool is equal. You need to find the right rockwool density for audio use. I can't reel off the right specs from the top of my head but my understanding is that you can get the correct grade from a builders merchant, though you may need to have them order it or hunt around a bit.

Hopefully someone more knowledgable than I can give you the info you need, else I'll dig it out from my notes later when I get home.

[Drew Stephenson]

Not sure if you use the same specification over there but what you're after is RW3, 45 - 60kg/m3 is the density you want to be looking for.
Or at least I hope it is because it's on my shopping list...

[TNGator]

Not sure if you use the same specification over there but what you're after is RW3, 45 - 60kg/m3 is the density you want to be looking for.
Or at least I hope it is because it's on my shopping list...

Tá. You know in hindsight my question ws a bit silly in that there probably isn't a great selection. It might be a case of you'll take what you're given. But thanks Bro... At least I can keep an eye out for those specs.

[James Perrett]

Rockwool RW3 or Rocksil RS60 are the most popular ones. For some purposes you can go for lower density like Rockwool RWA45 and for others you might want a higher density like RS100 but for panels the 60kg/m3 density seems to be the best compromise. If you can mount them so that they are spaced slightly away from the wall they become effective down to a slightly lower frequency.

[Sam Spoons]

Or for corner traps, a stack of triangular pieces filling the corner with a 12"-18" front face are even more effective ('cos the cut edges are more absorbent than the treated faces and 'cos the effective depth is greater).

[Mike Stranks]

Or for corner traps, a stack of triangular pieces filling the corner with a 12"-18" front face are even more effective ('cos the cut edges are more absorbent than the treated faces and 'cos the effective depth is greater).

Yup! As taught to me by Studio Support Gnome!

[Wonks]

If you struggle to get rockwool of a suitable density, glass fiber is far more widely used in the US for bass and broadband traps than in the UK. Similar issues with loose fibers causing irritation and similar remedies utilised, but the absorption performance is comparable. (US spelling of 'fibre' used).

[Sam Spoons]

Or for corner traps, a stack of triangular pieces filling the corner with a 12"-18" front face are even more effective ('cos the cut edges are more absorbent than the treated faces and 'cos the effective depth is greater).

Yup! As taught to me by Studio Support Gnome!

Me too, SSC's, or to give them their full title "Studiotips Super Chunks".

Glass fibre is not as kind to your body as Rockwool mineral fibre (it's more likely to cause irritation and so on) but no reason why it should be less effective AFAIK.

[Eddy Deegan]

what you're after is RW3, 45 - 60kg/m3 is the density you want to be looking for. Or at least I hope it is because it's on my shopping list...

for panels the 60kg/m3 density seems to be the best compromise. If you can mount them so that they are spaced slightly away from the wall they become effective down to a slightly lower frequency.

Checking my notes, Max was of similar opinion - 60kg/m3 was the magic number, at least in my case. Of the five bass traps in the plan he formulated for me, 3 are spaced from the wall and 2 are thick enough (due to a good window indent depth) to not need it.

[Martin Walker]

+1 for 60Kg/m3

After installing half a dozen RealTraps after reviewing them for SOS years back, I still needed more trapping, so I bought some 45Kg/m3 rockwool that I assembled into 4' by 2' by 1' megachunks, sprayed with the recommended dilute PVA adhesive (to stop the fibres shedding), and then simply wrapped them in butter muslin.

They made a very real difference, but have sagged a bit since. Mine were all floor-mounted, so if you're considering wall-mounted traps then 60Kg/m3 makes a lot more sense.

Martin