Should I add yet more absorption panels or diffusors to an already treated room?

dkulmacz

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I'm designing some improvement to my home studio/music room and looking for some advice on how to finish up.

Basic room is 10' by 12' by 8' with an open closet on the back wall. Speakers are two Kali IN-8 monitors and an SVS SB-1000, all placed up against the 10' wall, controlled with a MiniDSP 2x4 HD providing crossover and EQ. It's got a bit of absorption treatment already, all made from soft rockwool in fabric casings: floor-to-ceiling 'superchunks' in the front corners, a couple small superchunk wedges on the back and side floors against the walls, 6" thick panels at the first reflection points on side walls from the hip molding up, and a 3" thick ceiling cloud. I'm currently in process of making two more 6" deep panels that I'm mounting diagonally across the side wall-to-ceiling corners, covering about half the length of the room. I've attached a diagram showing the setup, FYI.

54014


I have two spots left available to add a final bit of treatment.... on the side walls, behind the listening position past the room's halfway point (shown by red stars in the picture). My question.... should I just add another two panels of 6" thick DIY rockwool absorbers (15" by 45"), or add two DIY cylindrical diffusers?

The diffusers would be made from sections of a 28" diameter heavy cardboard tube, typically used as concrete molds. I'd start with a 4 foot length of tube, cut it into 120 degree sections, and attach them to an appropriately sized piece of MDF board. I'd probably paint them, or cover them in thin cloth strictly for looks, and could theoretically also fill them with rockwool. Then mount them on the walls. In the end, they'd be about 22" wide, maybe 5" deep, and extend from the ceiling wedge downward. I've considered using the third piece to make a "portable" diffuser of similar dimensions that I could stand up somewhere as needed (probably mainly directly behind the listening position, perhaps in the closet behind the curtains). Making the diffusers will be more expensive and more difficult, but not by all that much.

I did a bit of analysis on cylindrical diffusors of these dimensions with a program that simulates diffusors in a room (can't remember the name), and they seemed to produce acceptable diffusion patterns (all things considered). I've also investigated making other types of diffusers (skyline, fractal, quadratic residue) but they all looked a bit too expensive and difficult to be worth the effort. The cylindrical seemed a good compromise to add some diffusion where none currently exists.

I'd appreciate any advice on whether you think diffusion will make a noticeable and positive impact compared to more absorption, and justify the cost and effort.

EDIT: Here's a pic showing the expected size and location of the diffusers......
54015
 
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kevinzoe

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Hi. Nice attention to detail - kudos. Based on my room construction and acoustical treatment experience (novice level but somewhat knowledgeable) here are the things I'd ask you to think about . . .
> Acoustical Measurements - have you taken any for frequency response and/or reverb decay (RT30/60, ETC) measurements? Without them you're kinda shooting in the dark I'm afraid.
> Diffusion - the "dangers" that I've experienced with polyfusers(hemifusers) is that there will always be one spot on its curved surface that directs a reflection right back to your ear(s) which may not be attenuated much like a proper diffusor - I see polys as redirectors of reflections as they do nothing to change the reflections scattering or phase impacts like Skylines/QRDs. So, to prevent this "danger" try putting one poly horizontal at ear level so it redirects vertically and thus away from your ear(s). You can have vertical oriented polys below and above it of course. If you do wish to buy/make a diffusor instead of the horizontally placed polyfuser, then choose a 2D one like a Skyline so that only about 50% of reflections are horizontal back towards your listening position (e.g. fewer reflections means attenuated compared to 100%)
> Bass Traps - in small rooms where space is limited it might be better to try diaphragmatic membrane based traps that aren't very deep rather than loads of fibreglass based traps that need to be quite thick for lower frequencies.
> DSP will be your friend - do you use it? But you need measurements (see earlier suggestion) to indicate where and how much is needed for parametric EQ typically.

Hope this helps somewhat . . .
 

dkulmacz

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Hi. Nice attention to detail - kudos. Based on my room construction and acoustical treatment experience (novice level but somewhat knowledgeable) here are the things I'd ask you to think about . . .
> Acoustical Measurements - have you taken any for frequency response and/or reverb decay (RT30/60, ETC) measurements? Without them you're kinda shooting in the dark I'm afraid.
> Diffusion - the "dangers" that I've experienced with polyfusers(hemifusers) is that there will always be one spot on its curved surface that directs a reflection right back to your ear(s) which may not be attenuated much like a proper diffusor - I see polys as redirectors of reflections as they do nothing to change the reflections scattering or phase impacts like Skylines/QRDs. So, to prevent this "danger" try putting one poly horizontal at ear level so it redirects vertically and thus away from your ear(s). You can have vertical oriented polys below and above it of course. If you do wish to buy/make a diffusor instead of the horizontally placed polyfuser, then choose a 2D one like a Skyline so that only about 50% of reflections are horizontal back towards your listening position (e.g. fewer reflections means attenuated compared to 100%)
> Bass Traps - in small rooms where space is limited it might be better to try diaphragmatic membrane based traps that aren't very deep rather than loads of fibreglass based traps that need to be quite thick for lower frequencies.
> DSP will be your friend - do you use it? But you need measurements (see earlier suggestion) to indicate where and how much is needed for parametric EQ typically.

Hope this helps somewhat . . .

Thanks for the feedback!
  • Yes.... I've attached the most recent REW profile of the room and system. I have estimates of the metrics you mention, but don't really know what to do with them. I believe the reverb decay is pretty OK considering the size of the room, but aside from that, nothing.
  • Thanks for the details on diffusers; I landed on conical for practical reasons, i.e., cheap and easy. I've looked into various other options like skyline and quadratic, and they're just too much effort to make DIY and too expensive to buy. And they likely produce a diffuser that's just too heavy to be practical. I've limited my choices to conical, soft absorber, or nothing. Unfortunately a horizontally-mounted cylindrical diffuser would have to be too small to be effective (vertical can be 4' long; a horizontal one could only be about 2' wide [using 28" diameter tube]).
  • I considered including a membrane bass trap in the back of each cylindrical diffuser; I didn't think the results would be worth the effort and expense. I also considered making a tuned Helmholz resonator to address a particular room mode at 109Hz.... I even created a detailed design and bought all the materials needed to make it, but abandoned the idea. In the end, the largest design I could manage in the room would have been simultaneously too small to make much difference, and too heavy to be manageable. Plus I didn't really want to spend a month drilling hundreds of precisely located differently sized holes in an MDF board.
  • I use a MiniDSP 2x4HD for both room EQ and monitor/sub crossover. It's actually giving me pretty good results (see attached file). I've considered trying to use the FIR filters, but have concluded from reading that the 2048 taps available in the 2x4 HD aren't sufficient to be very useful. I may inquire in the proper sub as to whether it might be enough to address one single phase issue, though, but haven't gotten around to it.
Thanks again!
 

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kevinzoe

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hi
> I don't own REW or MiniDSP so any screen captured images of your measurements would be helpful . . .
> have you installed your conical shaped reflectors (diffusors?) yet and if so any benefit heard?
> FIR filter taps should be way more than the 2048 you have available on your MiniDSP in my opinion. This is based on me having and using Audiolense XO software and seeing what ~2000, ~4000, ~10000 taps provide which is not enough for bass and low midrange frequency correction. I use ~32000 taps currently. If you haven't seen/tried Audiolense for FIR filters for freq response and time domain correction, then I recommend it, albeit with a bit of a steep learning curve. It's end user forum is found here:
> Audiolense will handle your crossover too in addition to doing digital room correction for freq and time and is likely a more comprehensive product than miniDSP or so I've read on the forums . . .
> Just a suggestion but can you place the speakers 33% of the room's length away from the front wall behind them and your listening chair 33% out from the back wall (in other words divide the room in thirds)? I've had good luck using 33% - 38% spots for speaker location and/or chair location.
 
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dkulmacz

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> Just a suggestion but can you place the speakers 33% of the room's length away from the front wall behind them and your listening chair 33% out from the back wall (in other words divide the room in thirds)? I've had good luck using 33% - 38% spots for speaker location and/or chair location.
Technically "yes" I could do this, but it would be too disruptive to the room; it's both a listening space and a music room with guitars, basses, and various synths taking up space, and this type of setup would make that difficult/impossible to maintain. But thanks for the suggestion.
 
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