Treatment for (slightly) odd shaped mix room

All about acoustics. This is your new home if you already have a studio or other acoustic space, but it isn't working out for you, sounds bad, and you need to fix it...
civvie
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Treatment for (slightly) odd shaped mix room

#46

Postby civvie » Mon, 2020-Sep-28, 19:58

Thanks Eric and Jennifer for checking in.

I've made some progress with mixed results :?

I've built the superchunks, put a broadband absorber between them, and hard backed my existing cloud.

Superchunks
90cm wide 60cm deep, 40kg/m3 rockwool.
20200926_182913.jpg


Broadband Absorber
90cm wide 20cm deep (10cm 40kg/m3 rockwool and 10cm airgap)
18mm plywood frame. Floor to ceiling.
20200928_155526.jpg

20200928_213602.jpg


Hard Backed Cloud
10cm 60kg/m3 Rockwool and 10cm airgap, 18mm ply backing

I did the Superchunks first and measured after that with a nice improvement in the low end, very happy.

Baseline
Baseline.jpg

Baseline sg.jpg

After Superchunk
Superchunk.jpg

Superchunk sg.jpg


Then I hard backed the existing cloud and put in the broadband absorber between the superchunks and measured again - not so good this time. The low end seemed to get worse! I have no idea why. :(
SC+FrBB+HBC.jpg

SC+FrBB+HBC sg.jpg


As you can see the low end seemed to get a bit worse than the previous measurement, I have no idea why...

Here is the mdat with all three measurements included.
All to date Sep28.mdat
(27.07 MiB) Downloaded 851 times
All to date Sep28.mdat
(27.07 MiB) Downloaded 851 times


I'm going to keep reading to try and work out where I've gone wrong here. Any input greatly appreciated!



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endorka
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Treatment for (slightly) odd shaped mix room

#47

Postby endorka » Tue, 2020-Sep-29, 04:50

The superchunks really do make a big difference. Impressive.

Did you take a measurement with superchunks and broadband absorber but without the hard back on the cloud?

Cheers,
Jennifer



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Treatment for (slightly) odd shaped mix room

#48

Postby civvie » Tue, 2020-Sep-29, 06:31

endorka wrote:Source of the post Did you take a measurement with superchunks and broadband absorber but without the hard back on the cloud?


Unfortunately not :(
I built both in one day and measured at the end. I assumed hard backing the cloud would mostly help with first reflections of higher frequencies and not do much to the bass, but of course, I could be wrong.

One thing that has come to mind is that both the cloud and the front wall absorber are quite solid and don't have any air ports in them, as in the only open area is the front side (with the rockwool across it). I've seen designs where the sides are open, but I don't know the theory on this....



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endorka
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Treatment for (slightly) odd shaped mix room

#49

Postby endorka » Tue, 2020-Sep-29, 07:55

civvie wrote:I built both in one day and measured at the end. I assumed hard backing the cloud would mostly help with first reflections of higher frequencies and not do much to the bass, but of course, I could be wrong.


I think the contrary might be true. Without the hard backing the cloud will deal fine with the highs via absorbption. The hard backing is there to reflect the lows away from the mix position.

Your cloud may well be working as it should be. Have you looked at the impulse charts? They are amazing!

Caveat: I've never built and tested a hard backed cloud myself, so take my advice with a pinch of salt.

One thing that has come to mind is that both the cloud and the front wall absorber are quite solid and don't have any air ports in them, as in the only open area is the front side (with the rockwool across it). I've seen designs where the sides are open, but I don't know the theory on this....


I would have thought the hard back would be a feature of the cloud (see above).

On the other hand I was quite surprised you added a hard back to the broadband absorber. It seems unnecessary and potentially harmful in a manner we discussed earlier in this thread with respect to SBIR. Namely the possibility of a better isolated wall there reflecting more bass back into the room. The wall there is only a single sheet of plasterboard so if the backing material is 18mm thick you've probably more than doubled the mass of the wall behind the broadband absorber. According to mass law this would give 5dB or more attenuation. That has to go somewhere, right?

The main increase in the waterfall with the hard backed cloud is at ~30Hz. There is some increase too around ~60Hz. These correspond to the primary and secondary length modes of the room respectively, which would seem to correspond to the above.

It's just a guess but could be confirmed or ruled out by removing the central broadband absorber and doing another measurement. You'd then have measures for superchunks + cloud, which could be useful in other ways too.

Cheers,
Jennifer



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Treatment for (slightly) odd shaped mix room

#50

Postby civvie » Wed, 2020-Sep-30, 07:57

endorka wrote:Source of the post I think the contrary might be true. Without the hard backing the cloud will deal fine with the highs via absorbption. The hard backing is there to reflect the lows away from the mix position.

Your cloud may well be working as it should be. Have you looked at the impulse charts? They are amazing!


Ahh right, interesting. I thought of low end as less directional and less influenced by fancy hard angles, but I guess it must still have an effect. I've seen hard backed clouds as a consistent feature of Stuart's designs so I thought I probably couldn't go too wrong... Might require a re-think and re-test. (Taking the hard back off that cloud would be HARD work damn it, got very busy with a nail gun up there... :shock:)

endorka wrote:Source of the post Have you looked at the impulse charts? They are amazing!


Ahh really!? I'm not great at interpreting this data... Is the impulse great in the Baseline test too? So maybe no need for hard backing at all with the cloud?

endorka wrote:Source of the post On the other hand I was quite surprised you added a hard back to the broadband absorber.


Oh I've misscomunitcated, there is no hard back on the front wall absorber. It is an 18mm ply frame like in the picture in my last post, with an open back but fastened firmly to the front wall. The air ports I'm reffering to would be like this (not my panel, just one I found online):
c897c46d0a91cb682f0ae2b3bf4daaa8.jpg


Though I'm not sure if this is to help acoustic properties or just simply to reduce the weight :?:

I guess I need to remove the front wall absorder and retest. Acoustics aint easy but I shall persevere!



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Treatment for (slightly) odd shaped mix room

#51

Postby civvie » Wed, 2020-Sep-30, 11:27

I just readjusted the angle of the cloud to be a lot steeper and re-measured, but it hasn't made a lot of difference.
cloud more angled.mdat
(9.02 MiB) Downloaded 869 times
cloud more angled.mdat
(9.02 MiB) Downloaded 869 times

This leads me to think the issue is somehow related to the front absorber...



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endorka
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Treatment for (slightly) odd shaped mix room

#52

Postby endorka » Thu, 2020-Oct-01, 20:23

That would certainly be my next line of enquiry. I've had a look at the file but I'm out of my theoretical depth with respect to these hard back clouds so don't have much to offer I'm afraid. In your shoes I'd be taking panels out of the room and placing them back in one at a time to find the culprit.

In addition to the measures you already have it might be illuminating to try:

superchunk + front wall absorber

If that doesn't shed sufficient light on the subject, try also:

superchunk + cloud

Dragging these things about in reality ain't like Sketchup, that's for sure!

Cheers!
Jennifer



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Treatment for (slightly) odd shaped mix room

#53

Postby Soundman2020 » Mon, 2020-Oct-26, 21:51

Lot's of testing today using a slightly simplified walking test method in two different speaker positions.


Sorry to be coming back in to the thread so late! (Got a lot on my plate right now...) But others have been taking good care of you in the meantime... :thu:

Anyway, I downloaded the REW files, and I'm taking a quick look at them right now. But just one quick comment here first:

But the big drawback that I immeadiately noticed was the loss of definition in the mids.
Don't worry too much about what you see in the mids and highs, since you are planning to flush-mount (soffit mount) your speakers. It's the low end that needs your attention most: the soffits themselves will do a lot to clean up things across the spectrum, but the lows are the big problem...

No idea how to explain this loss of mids but it really ruins this corner position.
With soffit mounting, the speakers are not in the corners! They are rather far out of the corners, actually. The main purpose of the "walking mic" test is to find the position with the smoothest low-end, which is the most important aspect of the acoustic response of the room, by far. Part of that is to help identify which issues are SBIR and which are modal. Modal issues do not change in frequency as you move the mic: they only change in amplitude. SBIR changes frequency, with lesser changes in amplitude. The combination of those two is a pretty good indicator of the overall room response, and the Walking Mic test helps find them both, and locate the "least offensive" spot for the mix position. The low end defines the entire frequency response of the complete spectrum, so getting the best spot for that, already goes a low way to cleaning up the rest. You might not be able to see that on the initial tests, but it's the end modal response that sets the stage for all of the rest. It "shapes" the frequency response for the full spectrum.

One final test which is interesting is another full L / R / L+R measurement from the exact mic position from the "Symmetrical Baseline" test, but with the speakers moved to the corner position.
What sticks out more obviously from this one, is the lack of low-end symmetry:
civvie--LR-corners.png
That might be due to the angled front wall, and will be somewhat attenuated by well designed soffits.

I thought this might illuminate which issues are SBIR and which issue are modal.
Not so much: :) It's the walking mic test that is most useful for that.

There's a lot of data here and I'd love it if anyone had the time to take a look at it
I'll take a look at that, and try to respond shortly, but... :
At the moment my initial position still sounds the best to me, I'm guessing because of the flatter mid response.
Don't rely too much on your ears at this stage! REW can reveal a whole bunch of issues that you can't hear consciously, but that do have a large effect on your overall perception of sound (eg, directionality, sound stage, stereo image, focus, etc.) In other words, you can't actually detect what the problems are with your ears by just listening, even though you can "sense" that something isn't right, because the effects you are listening for are actually CAUSED by your own ears! Psycho-acoustics is the science of how we humans perceive sound, as opposed to how the sound actually is. The interactions between sound wave patterns, your ears, your head, and the room, cause your brain to interpret sounds in a certain way, which isn't necessarily the way the sound really is. That's where REW comes in: it shows you how the sound really is, then you can understand how your brain misinterprets that sound. That's why you can't hear it: because by the time it gets to your conscious brain, your ears themselves and he "unconscious" pre-processing that your brain does first, has already modified what it is going to tell you. Thus, it is impossible to identify what the problem is just by listening, except to say that it "sounds off": So, for example, you might notice that the sound stage is too wide, or not wide enough, but be unable to figure out WHY just by listening, but REW will show you the early reflection that is causing you to "sense" that, and it will give you enough info to determine exactly where that reflection is coming from. Your ears cannot do that, because they don't have the ability to even hear early reflections directly! But a mic does.....

:)

You'll use your ears a lot more once the initial problems are taken care of, after the soffits and initial treatment are in place, but you can't trust them too much this early in the game.

- Stuart -



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Treatment for (slightly) odd shaped mix room

#54

Postby Soundman2020 » Tue, 2020-Oct-27, 01:18

However I still prefer the mids and the imaging with the speakers more forward away from the wall, I found a spot today that sounds best to me, so I am now thinking about flush mounting the speakers in this position.
Don't forget to take into account that simply building the soffits, changes the room response, and the speaker response! The final setup, with the speakers mounted in the soffits, will not sound much like what you are hearing with the speakers on stands at the location you found here.

When designing soffits, the first parameter to take into account is the mix position, not the speaker position. The mix position is determined from the low frequency response, which is a combination of modal issues and SBIR issues. The mix position determines where the "axis intercept" point will be, and places a limit on the possible toe-in angles and possible speaker locations. The dimensions of the speaker itself (particularly the depth) places further limitations on the location of the speaker. The the framing for the soffit places even more limitations on where the speaker can be located. It quickly becomes a "juggling act", as you compromise one thing to optimize another, but you'll find that there isn't actually much of a range of options for speaker location, in most rooms. They have to be placed somewhere within a not-very-large st of locations. If you start by putting the speakers at the spot you like most, you will very likely end up with the listening position in a non-optimal location, acoustically.

I still can't find what materials to make the hangers from in the UK. I can't find a supplier of Homasote or anything similar so far, any suggestions?
Can you get Enermax panels where you are? They should work. Or "Sundeala"? That's another option. What you are loking for is any type of SOFT fiber-board, such as is used for the backing behind dart boards, or office bulletin boards ("thumb tack" boards, "notice boards"). The density is around 400 kg/m3, so much lighter than ply or OSB. Those are closer to 600 kg/m3.

First things first - I've solved the phase 9.5k dip issue! - And it's been a big lesson in using REW and being PRECISE with MIC PLACEMENT!
What you are seeing is the interference patterns between the left and right speakers. AT THE MIC LOCATION, but ou would never actually hear that in the real world... because your ears are NOT at the mic position! There's only one mic, but you have two ears, spread apart by several inches. So your ears are not where the mic is. This is the reason why you only use one speaker at a time when looking at the upper mids and highs, rather than both at once, since you can't tell if you are looking at non-existent interference patterns, or actual room acoustic problems. So, for the high end, only look at one speaker at a time. For the low end, use both speakers, since you really are interested in how they work in combination, and the wavelengths are much longer, so there's no problem with interference patterns.

I'm a bit confused as to what I should do between my baffles. ... Straight hard panel:
That's the one that gets my vote!

Here's a rough placement for the hangers. How's this look?
You seem to have both superchunks and hangers in there: You don't need both. The superchunks ar taking up valuable space where you could have much larger hangers. Also, you are not allowing for the framing structure of the soffit, which will take up a lot of space inside. It has to be very robust: rigid, solid,... I would suggest going with just hangers, along with thick absorption on the wall surfaces (inside the soffit), as well as the floor and ceiling (also in side the soffit). That way, you can make the hangers as big as possible, and optimize their angles.


I think the contrary might be true. Without the hard backing the cloud will deal fine with the highs via absorbption. The hard backing is there to reflect the lows away from the mix position.
:thu: It can also have a small effect on modal issues, if it is large enough and massive enough.

I've seen hard backed clouds as a consistent feature of Stuart's designs so I thought I probably couldn't go too wrong...
:thu: :)

The air ports I'm reffering to would be like this (not my panel, just one I found online):
That's the right idea. Or instead of holes, you could do slots. The idea is to expose as much additional area of the insulation as possible to the room, to improve performance. The holes/slots are also rumored to produce minor diffusion....

- Stuart -



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Treatment for (slightly) odd shaped mix room

#55

Postby civvie » Wed, 2020-Dec-30, 14:07

Hi all,

Sorry for the delay, I've just had nothing to report as have been working :roll:
Back into the build now and hope to have it all done over the next few weeks.

Thanks for the reply Stuart, I'll address a few of your points below:

Soundman2020 wrote:Source of the post Don't forget to take into account that simply building the soffits, changes the room response, and the speaker response!


Yes very true. However, the design I'm using is a fully decoupled method outlined by Thomas Barefoot here: http://www.johnlsayers.com/phpBB2/viewt ... f=12&t=718

I'll have a 12" gap below and at least a 12" gap above. Behind are the superchunks and as many hangers as I can fit.
In this case is it not true that the room volume stays the same and my 'soffits' are just like huge speaker enclosures?

Soundman2020 wrote:Source of the post Can you get Enermax panels where you are? They should work. Or "Sundeala"? That's another option. What you are looking for is any type of SOFT fiber-board, such as is used for the backing behind dart boards, or office bulletin boards ("thumb tack" boards, "notice boards"). The density is around 400 kg/m3, so much lighter than ply or OSB. Those are closer to 600 kg/m3.


I found this stuff which seems ideal: https://www.builderdepot.co.uk/12mm-ivo ... pack-of-95
It's very fibrous and very much like homosote.
Much cheaper than sundela too ;)

Soundman2020 wrote:Source of the post You seem to have both superchunks and hangers in there: You don't need both.


Ah, alas the superchunks are already built... but the measurements are great, big improvement! Hopefully the hangers will improve even more.

Soundman2020 wrote:Source of the post I'm a bit confused as to what I should do between my baffles. ... Straight hard panel:
That's the one that gets my vote!


:thu: I'll leave a gap - measure - then plug it up and measure again - for science!

Soundman2020 wrote:Source of the post It can also have a small effect on modal issues, if it is large enough and massive enough.


That must have been the case with mine, as it is indeed massive. I've removed the backing now and the bass measurements are better again, so it's staying off!

I'll be back soon with more pics and measurements.

Thanks all!



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Treatment for (slightly) odd shaped mix room

#56

Postby Soundman2020 » Wed, 2021-Jun-30, 20:16

In this case is it not true that the room volume stays the same and my 'soffits' are just like huge speaker enclosures?
That's true, yes... but ANY large object in the room will change the acoustic response. It isn't just about the air volume in the room, but rather about surfaces, reflection, absorption, and things like that. Even just you, standing in the room, will change the acoustic response: Your body absorbs some sounds, reflects other sounds, diffuses yet other sounds, etc.

I found this stuff which seems ideal: https://www.builderdepot.co.uk/12mm-ivo ... pack-of-95 It's very fibrous and very much like homosote.
That looks like it should work just fine. As long as it is reasonably rigid: This is what gives the hanger its shape, and keeps the insulation in place.

I'll be back soon with more pics and measurements.
Got any update on that? We'd love to see how your place is coming along.

- Stuart -




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