Significant impact of ceiling treatment

[Andrew_Stoneman (AJS)]

Thanks to my friend’s CNC router, we converted some redundant 1220x600 50mm Rockwool absorbing panels into abfusers - basically by cutting slots into the 5mm back panels

Additionally, I created a ‘problem’ bass issue with a firmware update to my SOtM streamer; it sounded much better, bar some boom around 30hz +/-

Surprisingly, Adding two abfusers to the walls either side of my seat fixed most of the bass issue - I’d thought that I’d probably need to move my seat and/or the speakers

I then tried the third panel on the floor, between the speakers and (using a long mirror) central to the tweeters’ line of first reflection. This was beneficial, but things improved significantly as I slid the panel away from me towards the speakers

Proof of concept done, I mounted the panel on the ceiling…

Excellent result. I hadn’t realised how noisy the ceiling actually is; the initial impression is one of feeling a bit squashed down, but as your ear adjusts, it opens up the soundstage and instrument separation

Since the ceiling is generally the largest uninterrupted surface in many rooms, it makes sense to break it up, I’ve found

[Swisstrips]

The ceiling is a sorta “free” space and very often overlooked. If one is able to address it with treatments (as we do with the side walls and corners) it can have profound (positive) results. Adding a few more ceiling treatments, you may find the overall sound improves again.

[Andrew_Stoneman (AJS)]

That’s my point, exactly

I’ve been experimenting with room treatment (absorbers and diffusers) and room correction since the early noughties (TacT RSC 2.0 and 2.2x and a succession of Lyngdorf amps)

I actually built the absorber panels (that we converted to abfusers) back in 2007, but I retired them from my current room a few years ago as they were killing the soundstage by over-damping

I’ve been meaning to try the abfusers for many years; my friend recently retiring provided the opportunity to do the CNC work, but I was concerned that I’d just over-damp again

My other problem was the 6m RSJ and split height ceiling - that isn’t even centrally placed
… and if it worked on the floor, would it also work on the ceiling - and how would I get it there?!

The floors are concrete and are as hard as diamond to drill and the RSJ is covered in plasterboard

In the end I rigged ball chain to the wood frame of the plasterboard, and so far it’s stayed up!

To your point, namely adding more panels, at this stage I don’t think I need to

If I do, my instinct and previous experience suggests similar slotted panels, but without any Rockwool filling, would work

In conclusion though - ceilings are over (under?) looked in home HiFi. I know studios routinely do it and it’s been on my to-do list for many years
Now I’m very pleased I’ve tried it and it works extremely well

I’ll close by adding that it has had a disproportionate impact in my room I.e. the single 1200x600 ceiling panel changes the sound almost as much as 4x similar panels on the side and rear walls, the two large diffusers on the front wall and two more to the left of where I sit

Remarkable!

[Arjan_H]

Reflections from ceiling and floor are best treated. They are bad for the stereo image because from these it is hard to distinguish where the source is (left or right speaker). Reflections from the side walls make the image just a bit bigger, which doesn’t have to be a bad thing.
It surprises me that a diffuser can absorb a 30Hz standing wave. Probably there is more going on!

[Andrew_Stoneman (AJS)]

My room has a natural +ve 30hz mode where I sit which, to a fair extent, Room Perfect (RP) on my Lyngdorf '3400 can control. The recent update to the SoTM firmware gave a significant boost in that general area; I can’t specifically measure it with REW or fix it with the '3400 since the boost is coming from the source, and both RP and REW work downstream from the SoTM i.e. in/from the amp itself. I’m guessing it’s in the 30hz region due to that room mode, and how it sounded of course

The effect of the abfusers has not been to absorb the boost, it’s just helped to tame it. In fact it’s the best of both worlds for me; I keep the slam and heft of the low bass boost, but it sounds terrific as the former unpleasant, boomy component has gone and a lot of bass detail and texture has been revealed

Notably for this thread, this bass-taming effect actually came when I installed the abfusers on the walls to my left and right, and before the floor/ceiling addition. I also found it interesting that they’re not over the first reflection points, but closer to my seat and the back wall. However, I’ve experienced that type/degree of change with wall panels before…

What the ceiling abfuser did (and again, not on the first reflection point but this time further away from my seat) was remove a ‘glare’ that I’d not previously noticed, and I do mean glare! In hindsight, this was the ceiling reflection. Fixing the glare makes the soundstage and separation of instruments much better - it’s been a significant upgrade

I was really rather shocked/surprised by the extent of the effect and (during the on-floor testing phase) had to repeatedly remove, play, replace, play etc etc many of my reference tracks - just to prove to myself that I wasn’t imagining it. I also tried flipping it over, so the slots were on the ground and the solid, reflective back was up - this gave an obvious lift of high frequencies, as you’d expect, but also reinforced that the panel was in the most impactful position - and that glare thing was both real and a negative influence

I subsequently used my tape measure as a plumb line to mark the corresponding ceiling position, and up it went…

[Arjan_H]

Very nice! It shows that acoustics matter a lot.
I had the same experience with two bass absorbers (diaphragma’s on a closed box). They don’t really take low frequency away, only the decay gets shorter and definition gets a lot better, also above the low frequencies. Probably there has been taken away the masking effect of long low frequency decays as well.