Bass traps and diffusers

[RoadrunnerOZ]

Pretty well a lot of the ideas in correction of speakers and rooms have been around for more than 50 years - I’ve seen some of the best and the worst having been involved in design, build, equipment installation, wiring and commissioning of well over 30 studios (plus countless home studio setups when I was managing a hi-tech audio and keyboard store). Unfortunately some people think if you throw egg cartons or money at a wall it’ll fix it - either that or forget the wall and fix it in the box. If a room has issues it’s best to correct these as much as possible - then all you need to compensate for is your DAW Interface/Monitor setup.
Some nasty sounding areas in studios have often turned out to be very useful. I was helping build a studio in 1977 and there was a problem with sound ringing from a steel stair beam with hardwood stairs feeding into the live room even though the under-stair area was behind a wall with a door acces for storage. So I fit heavy plasterboard double layered under the stair beam to kill the ringing and seal it off and added isolation to the door Turned out this tiny wedge 12 foot tall at the big end was e perfect reverb or delay with a speaker at the thin end of the wedge and several mics spaced along the length. We also used it to re-record or double snares, record guitar amps etc. We only had the EMT plate and one other reverb then.
In another studio I built I had enclosed the outdoor balcony with soundproof floor over the decking, walls and ceiling and vacuum double glazed windows and doors and added a small bathroom - we called the whole new area a “lounge” so as not to exceed the 100sqM studio area allowed for Cottage industry - over 100 sqM you paid commercial rates on the property at 4 times the cost (big money on 42 acres). Turns out the shower room was perfect for vocals - no reverb needed, or if the door left open a natural reverb for the lounge live room.
Built a reverb unit from a 450mm diameter concrete pipe, speaker at one end and a 57 on a pulley/wire to change reverb time

 

[Spencerleehorton]

To my mind if I can’t really hear any difference between soundID being on or off that tells me my room is pretty close to where it needs to be.
I can still hear that there are bottom end differences but it’s very small differences.
I did boost my bottom end on my Adam a7x so might put them back to normal and retest and listen.
But ill do that once ive built a fee more traps and put them on the bottom of the front wall.

 

[RoadrunnerOZ]

That under desk absorption should help damp the longitudinal effects from the top rear of the room to the bottom front - 68.6Hz

 

[kags]

To my mind if I can’t really hear any difference between soundID being on or off that tells me my room is pretty close to where it needs to be.
I can still hear that there are bottom end

Right on! No room is perfect- especially small-ish rooms, but you’re very close and should be super-stoked to work in the room! My personal room has a ring at 40-ish, but the room sounds so good to me that I don’t feel like it changes my decisions and my clients are happy with my work. I always check mixes/masters on headphones vs speakers for many reasons, low end being one of them.

 

[Spencerleehorton]

I suppose the next question would be what is the best way to test the drum room now?
Obviously I’m not going to be listening to monitors in there I’m just going to be recording drums, guitars and possibly vocals.
Setup one monitor in there and test with monitor in centre of room or by each wall?
Or just take several measurements where each drum/cab/mic will be?

 

[kags]

I suppose the next question would be what is the best way to test the drum room now?
Obviously I’m not going to be listening to monitors in there I’m just going to be recording drums, guitars and possibly vocals.
Setup one monitor in there and test with monitor in centre of room or by each wall?
Or just take several measurements where each drum/cab/mic will be?

Measurements don’t matter for the live room. You have to just set up and try it. You could use a speaker on a stool to simulate a vocalist. Play acapella vocals or acoustic guitar through the speaker at a performance volume and mic the speaker. Try it in a few locations and listen to how different parts of the room sound.

Drums are a different story, but basically you’ll have to set up and play in the room. You could set up just kick and snare and move the kit around till you find what sounds good in the room. Even without testing with mics, if the drums sound good to the drummer, they should record well.

I don’t know anyone who measures anything except maybe RT in a live room. The rest is taste and best measured by ear. Diffusers, polycylindrical reflectors, space couplers, and standard absorbers are all effective but there are no real rules.

Avoid “reflection filter” type devices that go around mics - they make any mic sound awful.

 

[RoadrunnerOZ]

It’s all about what the room is going to sound like to the mics used to record a drum kit. You need to ensure you control the top end really well in a room like this and because it’s square you’re going to have corner to corner to corner issues at around 114Hz and 156Hz from walls and ceiling laterally and vertically plus then the diagonals at 72Hz, 81Hz and 92Hz approx. You want the room to sound natural and not ring too much - overtreatment will kill a live room. A quick test is to set up a kit then hit each drum and cymbal, stopping them immediately and listening to the post-hit sound of the room. If a kit sounds good in a room it should sound good to the mics.

 

[Spencerleehorton]

Ok so if I’m going to treat the 3x3m room probably just some corner traps and a couple on the ceiling over the kit?

 

[Spencerleehorton]

The kit sounds pretty good in there at the moment just wondered whether there was a good way of analysing the room to get better results?
It needs redecorating so I’ll empty and paint then go from there

 

[RoadrunnerOZ]

Same applies to acoustic guitar and vocals - if they sound good to the ear the mic will like

Ok so if I’m going to treat the 3x3m room probably just some corner traps and a couple on the ceiling over the kit?

If treating walls maybe only one of any two opposed faces is needed. Ceiling over the kit yes. If the kit’s in a corner you might treat the two walls directly behind the drummer from the corner outwards from the floor up to above mic height.
To analyse just set up a kit, mic it up and record it going around the kit with time spaced hits on each element of the kit - like sound-checking drums for a live gig - then look and listen for any unnatural peaks on the recording that equate to room dimension generated frequencies. These will tend to ring on after the drum hit for each drum.

 

[Spencerleehorton]

So am I right in thinking that some absorber traps over the kit on the ceiling will help and on the walls I really should be looking at diffusers?

 

[Electrobumps]

This waterfall looks very good- even the 80 Hz area is below 200 ms I imagine the room is very comfortable to mix in. You may have found a resonance between your desk and the front wall at 120 Hz that any thick absorber would mitigate. Excellent results.

The waterfall looks good, but what about the spectrogram. I had a similar situation where the waterfall looked good. But the spectrogram was showing a lot of energies in the low mids. My first mixes in that room I ended up scooping way to much low mids. I’m curious to know your thoughts on this.

 

[Electrobumps]

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Just wait for AI to take over speaker tuning… erm…

I’m fine with it to make my monitoring sound better. It’s when they start mixing!

 

[RoadrunnerOZ]

So am I right in thinking that some absorber traps over the kit on the ceiling will help and on the walls I really should be looking at diffusers?

You will need some absorption on the walls (and ceiling) first to knock back a ringing room - then you can look at diffusion if needed

 

[RoadrunnerOZ]

Diffusion in a small room needs to be looked at for the higher frequencies after the LF’s are brought under control - LF diffusion involves very deep diffusers and can make a room that is too regular, like a square base or 2:1, sound worse without absorption.

 

[Spencerleehorton]

as space is at a premium in the drum room im thinking i'll build 4 x 50cm x 100cm x 10cm traps with the left over 30kg/m3 rockwool for the corners, two in each corner, floor to ceiling.
i'll then build another two for the ceiling over the kit which i sit against the back wall and face the main door, with the kit pretty much in the middle of the room.
the other door is on the left wall along with the window which i could put another panel over as this might cause some reflections right?
i'll draw a diagram so it makes more sense.
the pink objects are the panels to be clear

 

[RoadrunnerOZ]

Is the drum room floor 3 x 3?

 

[RoadrunnerOZ]

I’m assuming the back wall is at the drummers back and would look at covering more of that wall to get rid of short reflections back into the mics.

 

[Spencerleehorton]

Yes drum room is 3x3m, should have used a square really!!!
And yes the kit is setup so drummers back is to the back wall.

 

[RoadrunnerOZ]

So this means your mics will all be mainly pointing inwards towards that wall when you mic up - to avoid cancellations from direct reflections off the wall, it should be treated for the span of the kit and mics including overheads.
The tri corner reflections floor to ceiling, and vertical corner to corner reflections along wall faces and across room are dealt with by your floor to ceiling corner traps.
However your lateral corners (top L across to top R) on each wall top are untreated and will reflect from same corners at wall bottoms down the wall faces (156Hz) as well as diagonal across the room bottoms (95Hz) plus top to floor to top across the room etc - you just need to see how much is going on after you put in the first traps. You may need horizontal top corner traps as well if there are ringing issues.