After several months of using my room I thought it would be a good time for an update about the next steps in the design.
The first thing is that I am enjoying using the room and in the main producing mixes that are balanced. The Neumann KH310 monitors are so forgiving (not flattering, just very able) that everything can sound good, so you can quickly get used to the tonality of a track even though it's slightly off, so referencing is of course very important. However it’s a nice space to work in and I’m sure it’ll look great once I finish.
All along my plan had been to get the room up and running following the basic principles I understood, with general bass trapping in the form of hangers across the rear wall and under the soffits, and an absorbent ceiling (as it's quite low). From there I was going to revise the design and implement any further treatment and possibly digital tuning once all that treatment steps have been exhausted.
Current status:
Reverb time
Left and right SPL
Left and right individual readings overlay (left is green, right is brown)
Waterfall
I'd been lucky enough to get a grant from the Arts Council in the UK to 'improve my creative practice' and part of that was furthering my knowledge of acoustics. Unfortunately this money had to be spent this year, and as Stuart is busy catching up with other projects from when he was unwell, I ended up contacting two acoustics consultants to get their views on next steps for my room.
This was a really interesting exercise so I thought I'd share on this forum the outcomes of my conversations. I contacted two because I was interested if they would have different proposals and as you’ll see there are some areas that both agreed on, and others where they have quite different opinions.
I shared my latest REW readings and room dimensions with consultant 1 and explained how the space is constructed. I asked for advice on further flattening the response and the reverb time dip. Summary of consultant 1 views of issues:
1. Axial modes at 62, 106 and 153Hz that correlate with the dimensions of the room (5.5m x 3.25m x 2.25m)
2. Shape - he said that because my room has parallel walls that the low frequency peaks will be too sharp to deal with precisely with tuned traps, and at best the shape of the peak will be from a triangle to more of a W, as tuned traps have a bell curve response
3. Too much absorption in the mid band
4. The HVAC design, having some exposed foil ducting between inner and outer room, would potentially influence LF performance
5. He noted that there is a 600-650Hz dip which he has seen before with these Neumann monitors - likely around a crossover point
6. The ‘bass trap’ that I currently have in the position of a cloud (which is an a GIK acoustics 244 panel I had in the loft
https://gikacoustics.co.uk/product/gik- ... echnology/) was also something he’d noted issues in the 500-600Hz area before. The recommendation was to remove this and see if it had an impact.
7. Soffit mounts – he thought these were a bad idea and was concerned they’d introduced a range of problems:
a. insufficiently rigid monitor support (as the speakers could be potentially energising the whole soffit wall construction) – to get this right for soffit mounting he recommended concrete block and cement was needed
b. potential causing the 490Hz dip (or possibly rear wall trapping, or both)
c. speakers not being able to operate in free field as they’d been designed to
The main recommendations were to:
1. Remove the soffit mount wall and construct speaker stands out of MDF entirely filled with sand
2. Build a fake wall to give the look of the soffit wall, if desired
3. Add 4 hard panels to the ceiling angled to reflect the sound towards the centre of the room. This is to add some reverberation back to the room
4. Remove the hangers at the rear wall and replace with tuned traps to deal with the axial modes identified. Designs for these were provided. I explained that the graphs showed the hangers had reduced RT in the lower frequencies and that I was concerned taking them out completely would bring some of this back. However I guess the tuned traps would by design take out the most offending reverberations/ringing, and being bell shaped they’d also reduce surrounding frequencies so the net result could be the same as the hangers.
The second consultant was a one hour video call consultation where we discussed the following:
1. From my measurements he identified a major peak at 53Hz (40% energy) that needed a tuned trap to absorb at the rear wall (or two tuned traps side by side). He suggested my hangers could be halved in length so they hang above the tuned traps. Whilst he referred me to a website to design the trap sizing (and drilled hole spacing across the front) we discussed that it needed to be built out of two layers of MDF, air tight into the room, with the back of the trap actually at the back of the room, and the sides, top and bottom of trap caulked to room surfaces.
2. We then discussed the issue of parallel versus splayed walls and he was of the opinion that parallel are better because they’re easier to model and design around
3. The soffit walls – consultant 2 was also not a fan of soffit walls and he also recommended solid stands build from MDF and sand filled. He recommended a fabric ‘wall’ built to mimic the soffit wall and the whole space behind filled with absorption
4. His design philosophy is 100% absorption behind and around the monitors, and this could mean less general absorption at the back of the room. He also spends a lot of time modelling the speaker positioning and said the height can make a huge difference to phase issues.
I had a bit of a ‘aha’ moment when speaking to consultant 2 around the sharp 100Hz dip, because this dip wasn't there before treatment went in. He told me this was likely a phase issue, because as standing waves and frequencies are absorbed, the interactions between the remaining frequencies bouncing around cause phase interactions which move up and down the frequency range as treatment is introduced. He advised using the room modeller in REW to see whether changing the amount of absorption on the ceiling etc would affect the 100Hz null.
This is absolutely what happened, as can be seen in this overlay graph - it's great when theory clicks and is reflected in practice:
This graph also demonstrates that the hangers have turned the 62Hz peak into a dip (so I guess that's a phase issue too), and resolved quite an issue around 73Hz, but that before the hangers 140Hz was fine and now there's a dip!
Summary of these interactions:
• Both consultants share the same opinion about soffit mounting and would recommend removing it. Consultant 1 did note that this would be an unpopular proposal with me (after the effort gone in to construction) so suggested I do other things first and review their impact.
• Both also propose tuned traps, although at different frequencies.
• They have different opinions about room design: splayed or non splayed walls. I should imagine this difference of opinion is endemic across studio designers! Either way it's irrelevant as I'm not rebuilding. For what it's worth I'm of the opinion that splayed walls are a bad idea in a control room.
What am I going to do?
A bit at a time, and nothing major in a hurry as the room is usable!! I think I’m going to explore various sizing options for tuned traps at the back, across the floor level, and then hopefully I could leave the hangers hanging part way down. Alongside this I will see if I can figure out how to use the REW room modeller.
Any thoughts?