Here's the initial setup:
I intend to build a custom mixing desk on wheels that I can push in between my speaker baffles, when not mixing. That will be useful when teaching guitar and recording, then I can just wheel it out (with some markers for the correct locations) for critical listening.
So at the moment I have no desk in.
empty room.jpg
Here's those charts I promised:
Frequency Response:
SPL Low End LR.png
Looking at the low end to begin with:
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On checking the calculations again, the null at 72-74Hz is not likely to do with side wall reflections as the distance is too short.
Expected first reflections nulls:
Side walls: 165Hz
Floor: 145Hz
Ceiling: 125Hz
Looking at the theoretical modal response in the room, puts a strong ceiling - floor axial mode at 67.25Hz. Although a little off, this can be explained by my inside out ceiling. The lowest points of my ceiling (The ceiling joists) would have it's axial mode around 73Hz.
The peak at 65Hz seems to be caused by the 2nd length mode.
If these modes are not sufficiently treated by the broadband absorption in the room, I will consider membrane and Helmholtz traps tuned to these frequencies.
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Lots of the usual comb filtering. But nothing too major I can see at the moment. Although with so many reflections there is too much noise to analyse much at this point.
Waterfall:
Waterfall LR.png
Because the decay rate is so long, I've extended the waterfall time range to 2 seconds.
I see strong modes at 65-67Hz (two axials close together) and 95-97Hz (a few tangential and axials bunched together), causing major ringing. Again we see the huge null in the mid 70Hz region.
You can see that due to the lack of a sub, there's not much happening at all below the 60Hz region, which lines up with the speaker specs. I plan to add a sub (or two) eventually.
Spectogram:
Spectogram LR.jpg
Does anyone think this looks a lot like a comb??
Decay Rate:
Decay Rate.jpg
Large dip at 125Hzish.
Two theories:
1)
Ceiling bounce.
2)
Plasterboard absorption. Plasterboard on wooden studs has a very high absorption coefficient at 125Hz (approaching 0.3!). So because 5 surfaces in my room are plasterboard on wooden studs, this has a massive effect at this frequency, with each reflection absorbing some energy.
Of course I need to bring the decay rate of the whole spectrum right down, for my multipurpose room. So expect lots of fibreglass and added variable acoustic devices.
Here you can see the frequency response of the two speakers separately:
SPL LR Separate.jpg
There's not too much variation there, so I'm pretty happy.
Initial treatment plan:
- Flush (soffit) mount the speakers.
- Add "soffit wings" at first reflection points. - Take new REW measurements.
- Fill ceiling with 1 layer of 100mm fibreglass and 1 layer of 50mm fibreglass. - Take new REW measurements.
- Add 500mm depth of treatments to rear wall. Mainly consisting of acoustic hangers. - Take new REW measurements.