Bass traps and diffusers

[Spencerleehorton]

Behind mix position

I’ve finished 10 panels now and the mix position doesn’t seem to have the null anymore, if anything it’s can hear more bottom end now, bottom end seems to have more clarity and when I move away from mix position it seems more even everywhere, rather than dips and boosts.
Next stage is getting the last two finished and attached to the ceiling.
Then move everything so I can get two more between the speakers on the front wall then two either side of the mix position.
Than I will start measuring with the ECM8000 and REW.

 

[Spencerleehorton]

Also looking for some advice on what to do panel wise for my 3m x 3m drum room?

 

[Spencerleehorton]

Very crude drawing of drum room

 

[Spencerleehorton]

I guess it’s just the same, treat the corners and put up some panels mid level of the room and put in some on the ceiling, as the room is small I’ll only be able to get away with 4” thick panels but pretty sure this will have some effect

 

[kags]

So my question would be this:
My problem with mixing seemed to be I was adding too much bass in general to the mix which would I think mean that there was a low end null within the mix position, does the data that room sim outputs so far support this?

Unfortunately we always sit in the null between the side walls. This ensures symmetry at the expense of living with the modal issue. If you have 8 foot ceilings, your head, while seated, is in the floor-ceiling null. 8 foot rooms are the most unforgiving places to work.

These nulls plus SBIR create problems in small rooms below 100Hz that are difficult to treat without taking up a lot of space.

I’ve found that integrating a sub (or two) can help smooth out modal issues in small rooms. You can add a sub in the REW sim and move it around to see how it affects the overall response. I set my subs at 70 Hz or lower to avoid localization, but for this to work well, you do need mains with flat response down to at least 50 and hopefully lower.

 

[kags]

View attachment 119551
Very crude drawing of drum room

The drum room is more about your personal prefs. I like to make the ceiling non reflective so overhead mics don’t get reflections from ceiling. Wall treatment is totally subjective. Placement of the kit in the room is critical, too. I tend to put the stool near a wall or corner to get the most low-freq help from the boundaries. I also like space couplers in small drum rooms. I’ve been playing with making space DIY couplers With cut PVC pipes. The dimensions are not critical. I use 3” pipe and cut 3” lengths and glue them together and paint the whole thing.

 

[kags]

I guess it’s just the same, treat the corners and put up some panels mid level of the room and put in some on the ceiling, as the room is small I’ll only be able to get away with 4” thick panels but pretty sure this will have some effect

You really want to kill reflections that will cause interference at the mics, so 4” will be fine.

 

[Spencerleehorton]

This seems to make sense

http://arqen.com/acoustics-101/spea... deep dips in,by the speaker-boundary effect.

 

[Spencerleehorton]

ive moved everything round within room sim in REW and the best placement seems to be with max absorbtion with the speakers as close to the wall as possible.

obviously i need to experiment now with several different placement of the panels and test the room and use my ears.

hopefully the test data will match what my ears are telling me.

 

[john12ax7]

Arqen also has some nice resources for room treatment and DIY diffuser designs.

For a mix room I found it most beneficial to make the entire back wall one large and very deep absorber. I built large 4x8 foot absorbers and then experimented with spacing from the wall to get the best measurement response.

For a drum room, if the ceiling is low probably better to make the whole ceiling absorptive, or at least above the drums. Then digitally alter the perceived size. The walls experiment and see what sounds good. Maybe one part of the room reflective and the other absorptive? Though the room is kind of small so not sure that's viable. Perhaps just build movable panels and move them around until you get something you like.

 

[john12ax7]

The REW stimulator is useful but your 0.9 coefficients are too optimistic. The assumption in the simulator is that the entire wall is covered and has that coefficient.

This is another useful tool. You can see that achieving high coefficients under 100 Hz can be challenging. And even then you would need to cover the entire wall at that depth for it to be valid in the simulator.
http://www.acousticmodelling.com/8layers/porous.php

 

[john12ax7]

Btw, which diffusers were you planning on building? The Arqen one seems fairly straightforward though I haven't built it.

For recording spaces I like having large movable gobo type units. Have a deep absorber on one side and then a diffuser on the other. Then you just roll them around and position as needed to get the result you want.

 

[Spencerleehorton]

I have made 12 absorbers which are 100cm x 60cm and are 8” deep with 30kg m3 rockwool inside with cotton covers (dust sheet) I will make about the same for the drum room at 4” thick

 

[RoadrunnerOZ]

I have made 12 absorbers which are 100cm x 60cm and are 8” deep with 30kg m3 rockwool inside with cotton covers (dust sheet) I will make about the same for the drum room at 4” thick

I would suggest for the drum room to use from 96 - 168kg/m3 compressed glass fibre instead of the 30kg. I have built many studios and have used the 168kg under floating floor bearers with rubber blocks as frame support for floating floors and the 96 and 130kg for wall and ceiling lining and also surfacing.
The absorption works best when the fibre board is against a high mass surface - in one studio I just recently completed the absorptive material - 50mm thick - is glued to back-boards which are then screwed to the brick walls, the compressed glass boards come with cloth covering on one side but for exposed surfaces they can be framed with decorative cloth cover. For mobile panels I have used 50mm compressed glass boards glued either side of 19mm particle board which is rubber suspension mounted in the outer frame on casters. The particle board being “free” soaks up a lot of the LF energy.
The boards I use here are Noisestop and Partition HD panels by Fletcher, Quietel by Bradford Insulation and I’m sure you would have plenty of sources where you are.
The big problem with blanket batt style Rockwool is it’s not rigid and doesn’t hold form, it also sheds particles and is not very dense. The compressed board is resin bonded, rigid, resin bonded on the glue face and cloth coated on the other side for the outward face - it can be cut with a box cutter and a straight edge. Being uniform thickness it also can be glued to surfaces easily leaving a presentation surface (if you like black) or you can cloth cover it.
Glass or rock fibre particles floating around a room isn’t good for the lungs so all cut edges should be sealed - I use a rubber semi-gel glue spread with a spatula along the edges or brushing resin.

 

[Brian Roth]

FWIW, this thread caused me to find some Owens-Corning 700 series data sheets in my files:

https://groupdiy.com/threads/owens-corning-700-series-fiberglas™-spec-sheets.86166/
I am not an acoustics expert, but have seen/used various combinations in "stacks" for room treatments, gobos, etc. Medium density 703 seems to have been a mainstay.

IIRC, one "stackup" designed by a reputable acoustical engineering firm 40-ish years ago had 2" of 701 facing into the room, then behind it 2" of 703, then 1" of 705 against the wall surface. I may be totally off on the exact thicknesses for each layer after four decades! But I do recall the sheets in the stack.

Bri

 

[RoadrunnerOZ]

I’d be looking at the 707 for drum rooms - 96Kg/m3

 

[Brian Roth]

Again, I don't claim to be an acoustics expert....but I was told that the "stack" of differing densities provided a semi-wide band of absorption. This was 1980's thinking, when some folks (not me lol) would spec multi-foot deep piles of typical "fluffy" insulation.

Bri

 

[Brian Roth]

I’d be looking at the 707 for drum rooms - 96Kg/m3

OK, I guess .....but that sounds like 705 from the spec sheets I found/posted:

704: 4.2 pcf (67 kg/m3)
705: 6.0 pcf (96 kg/m3)
707: 7.0 pcf (112 kg/m3)

Bri

 

[Spencerleehorton]

All my rockwool is wrapped in celofane/ plastic film so no fibres will get airborne and won’t smell.

 

[Spencerleehorton]

I have only one pack of 30kg m3 to make the final panels for the drum room so that will have to do for time being.
They are 120x60x10 and I have 8 of them so will double them up to make 4 panels and will buy some denser stuff when building the next set of panels.
Probably just use them for the ceiling above the drum kit.