# Did I "deaden" my room too much by adding this superchunk? .mdat inside...



## jlird808 (Nov 2, 2010)

I have 10.5 foot ceilings and put a 23" x 23" x 30" superchunk in one corner. While it did wonders for the lows and low mids I fear I may have killed too much of the highs/upper-mids.










Out of habit, I bought/used an acoustically transparent fabric, flannel to be exact (it was on sale)! I know the typical rule is to use a "breathable" fabric on RFZ panels but in corner traps, you run the risk of deadening the room by letting the low AND mids/highs thru. 

It's hard for me to tell by just listening at this point. I fear that I've "gotten used to it". I do notice a subtle roll-off of the highs that wasn't there before. But I'm not sure how bad it is and if it warrants recovering or covering over with a reflective fabric.

So I did some REW testing but nothing really showed up in the Freq Response graph. I only really know how to read FR and waterfalls though  I guess this is my opportunity to get into IR and RT60, spec analysis, etc.

Would somebody be able to look at this .mdat? Is there another way to analyze this besides an FR?

http://dl.dropbox.com/u/66773128/0309_0224_pre_post chunk.rar

There's two dates of tests. The first (2/24) is before the superchunk. The 2nd (3/7) was after. In the meantime, I'll be researching RT60 and IR tests.

Any help would be totally appreciated...:clap: If anything.....a good link to RT60 and IR stuff...

THANKS!!!!


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## EarlK (Jan 1, 2010)

> I looked at your files & I believe your question is a bit off-base ( fwiw ).

> Of real importance is the @ 12db hole ( shaped like a "V" ) centered at 11K . It will certainly be audible .

> Since this 11K notch only exists in all of your newest captures , you need to ask yourself what has created the new notch .

> Apart from adding the super-chunk , what have you changed in the system ( between the old & new ) measurements ?

> I doubt that the explanation ( for the notch ) is attributable to your newly built, corner based super-chunk .

:sn:

PS 1 : Your old "ETC"s were much much cleaner ( see below ) .

PS 2 : If you have any ( VST based ) EQ placed inline with your soundcards output ( and is therefore showing up in your new captures ) turn it off & remeasure .


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## jlird808 (Nov 2, 2010)

Thanks for the reply!! 

I didn't change anything else to my knowledge. I HAD to move the mic between tests (to build the superchunk for one reason). Though I try to get as close as I can, its probly impossible to be perfect obviously. I'm not sure what else, I've moved my monitors slightly so many times, not sure if I did that between these two tests and just forgot 

I do have an inline EQ (Patchmix for my EMU 1212m card) but the settings/filters have stayed the same. That I DO KNOW as I'm very meticulous about that. Besides, I dont have any EQ filters setup above around 200-300hz.

EQ changes so much in the upper freq just by slight movements of the mic. I think that's why I "didn't bother" with that V probably when I first saw it. A slight move of the mic (which would be my head in real world) and the V is gone. I basically just setup an RFZ with 3" ceiling cloud (12" from ceiling) and 3" panels (off the wall about 1") and had kinda "given up" measuring/treating above that 200-300hz mark. Any thoughts on this?

Regarding the ETC, should the "spikes" be equidistant or something? Is that what I'm looking for? Haven't got a chance to read up on it yet (I'm at work lol). I did find this though:

http://www.hometheatershack.com/for...suring-interpreting-impulse-response-etc.html

I will measure more when I get home today, see if the V is still there. COULD mic placement be the SOLE cause?

THANKS AGAIN!!!:R:R:clap::clap:


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## EarlK (Jan 1, 2010)

> EQ changes so much in the upper freq just by slight movements of the mic. I think that's why I "didn't bother" with that V probably when I first saw it. A slight move of the mic (which would be my head in real world) and the V is gone.



> If it was me, I'd still want to identify the source of your 11K notch ( it's symmetry, "looks like", super-strong, out-of phase HF bounce ) .



> I basically just setup an RFZ with 3" ceiling cloud (12" from ceiling) and 3" panels (off the wall about 1") and had kinda "given up" measuring/treating above that 200-300hz mark. Any thoughts on this?


> I'm not a "project-room" acoustics consultant / "GS" has plenty of those who love to talk about clouds & super-chunks ( as you well know ) .



> Regarding the ETC, should the "spikes" be equidistant or something? Is that what I'm looking for? Haven't got a chance to read up on it yet (I'm at work lol). I did find this though:


> Unless SAC chimes in ( he's the ETC man-about-town ) , you'll most likely need to take this back to the appropriate forum at "GS" / to get a reasonable answer .

> FWIW ( to these eyes ), your Feb. ETCs look to be a much better baseline than what you now have ( though I'm not convinced the addition of the Super-Chunk would add that much energy back into the room / I tend to think you have a mis-applied DSP filter or something is amiss within "Patchmix" / such as an input bleeding into your output ) . 

> The sources for the tall "spikes" standing above the pack ( so to speak ) should be identified and properly dealt with .

> Running another SoundCard calibration would help illuminate my "electronic-cause", speculations .

:sn:

> PS : Here's some reading for you about reasonable criteria to shoot for when viewing ETCs .


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## SAC (Dec 3, 2009)

Its hard to say what exactly is going on as the two sets of measurements cannot be easily compared.

We can observe differences, but it is difficult to determine which are a result of room changes and which are the result of mic and speaker position changes.

Our ability to comment on the room is also further restricted as we do not see what the ‘native’ response is in the room without treatment. Thus, we cannot tell if the treatment that has been applied was necessary or done optimally. …an issue that is important in a small room where we want to preserve as much specular energy as we can while managing it in a productive manner. So, we are almost necessarily limited to noting what issues remain despite treatment.

So let’s step through a few observations – being careful to avoid jumping to actual judgments of room behavior due to the lack of 1:1 correspondence.

One particularly curious note is the presence of low level high Q resonances that increase with time! Cue Twilight Zone theme…

And contrary to my earlier admonition that we cannot definitively determine many aspects, one that we can is the presence of a 60 Hz electrical issue that is evident in the waterfall.

Overlaying the 2 sets of ETC measurements shows a significant difference, which cannot easily be explained by the corner traps and most likely is attributable to a repositioning of the speakers and mic between measurements.

In fact, in the later set of measurements, it looks like the entire room response was damped with the exception of the prominent sparse early arriving reflections In other words, that the low level reflections have diminished in gain while the higher gain sparse reflections have not – something the corner traps simply cannot do, especially considering that specular energy is not incident on the traps. It is quite curious that the prominent sparse reflections remain at about the same levels while the associated lower level reflections are significantly reduced!

Another concern is the assignment of T=0 to the initial arrival of the impulse response.

The Preferences->Analysis panel is set correctly but there remains a problem in that sound does not propagate in zero time. Something is amiss in the hardware loopback configuration. Perhaps more significantly, it means that you must determine the vector resolution of the early arriving high gain sparse ‘spikes’ by using the blocking method, as you cannot accurately determine the total time of flight and thus cannot calculate the actual corresponding distance.

Another issue that we can determine from the measurements is a big one and you won’t like it – but neither will you like the practical impact of the problem that is created.

One thing that is apparent in both sets of measurements is the very significant very early arrivals (0-~0.4ms as well as the sparse reflection at ~1.45ms) which is almost certainly due to speaker mounting and reflections off the work surface. This NEEDS to be addressed as it is a serious detriment to the response. Get the speakers properly mounted on stands (whose base does NOT protrude beyond the edge of the speaker cabinet!) located further behind the work surface. And tilt the work surface to minimize the upward reflection of any reflections. This can be done relatively easily by simply moving the desk out when you are actively working and pushing it back when not in use. I would recommend marking the floor in order to facilitate the proper reproducible positioning of the desk.

Additionally, you might realize a further benefit from the corner traps by adding a 6+mil barrier to the front beneath the cloth face. This will reflect any incident specular energy above ~600 Hz which may be useful to help ‘flesh out’ the early arriving low energy density. But before going to the trouble, you might measure with the barrier applied to the outer surface to first to determine if it would add any detrimental energy returns...and the additional returns will be dependent upon the amount of mid or high energy sourced from the speakers…but it’s hard to tell from the angles of the speakers in the picture.

The next observations are dangerous in the sense that I do not know what the response of the system is with9out treatment. We only see how the system behaves in the room with the presence of some treatment, so the actual nature and source of the issues in not easily determined without more investigation. (May seriously suggest, if it is not TOO outrageous a chore, to make measurements at least without absorbent panels. Then we can make definitive determinations…)

Since those reading this come from many application points of view, let me quickly walk through a few considerations applicable to all, and not merely to this specific environment.

I am assuming that the primary use of this space is for recording and production work – recording, critical listening and mixing of an electronic (as opposed to an acoustic) source (the keyboard).

Thus the early reflections in the ISD up to the first significant energy return from the rear of the room, should be reduced with the surgical use of absorption by a minimum of about 15 dB. This will insure an analytical – effectively anechoic - arrival of the very early signal rendering the localization in the mix and the imaging to be very precise and tightly defined. In other words, you will hear exactly what is being recorded and reproduced in the speakers, prior to the augmentation of the sound by the room. Your goal is to optimize what is recorded independent of the contribution by the space.

Thus you will want to identify the vector paths of the few sparse early arriving reflections in what is the ISD region from ~1.5-7ms prior to the first significant energy return. And seeing as how the early arriving soundfield in the ISD is very sparse, you would do well to also identify the points of incidence corresponding to the few reflections whose gain is just below the 15 dB threshold and to mitigate them as well. If they were part of a more spatially and temporally well mixed set of reflections I would not worry, but their sparseness is a potential problem. 

In this particular instance a few such sparse reflections persist and should be addressed.

Also, the later arriving soundfield from ~7-30+ms. is characterized by many sparse reflections whose gain is up to twice that of their neighboring reflections. You will want to smooth the slope of the decaying soundfield by lowering the gain of the sparse reflections, while simultaneously increasing the spatial and temporal density of the soundfield. In other words, you want to make the response look more like a thick dense mat of reflections of similar gain levels without individual spikes exceeding the average gain level of the surrounding spikes – and the soundfield should decay in an orderly manner.

Were this a casual listening room and if one preferred a larger but less well defined localization and imaging, a higher degree of diffuse early reflections would be acceptable up to a level of 10 dB below the direct signal. But it should be stressed that such a soundfield would necessarily be temporally and spatially diffuse and without any exceptional higher gain reflection(s). Any higher gain reflections would need to be treated through the surgical application of absorption.

In either case, aside from identifying and addressing the very early high gain sparse early reflections with absorption, the remaining later arriving soundfield would benefit from the use of some diffusion in order to remediate the isolated sparse relative high gain reflections and would reduce their gain and create a more uniformly spatially and temporally dense early and later arriving soundfields. 

And in this case there are quite a few sparse relatively high gain reflections that would benefit from diffusion which would both reduce their gain while increasing the temporal and spatial density of the soundfield.

But it’s hard to tell the specific effects of any existing treatment without good /consistent before and after measurements that would allow us to note the specific effect existing treatment has had on actual reflections, as well as how possible adjustments of existing treatments may be made, or how the addition of additional new treatments can most optimally be utilized to create the optimal environment through the preservation and ‘re-purposing’ of existing energy.

When we talk we can delve into other factors about which I cannot make an informed comment without additional information.


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## jlird808 (Nov 2, 2010)

Ok lots for me to process...and I cant process it all at the moment unfortunately (at work again ). 

But just a few things:

What is ISD?

Is there a specific degree that I should tilt my desk to at least to? Im lookin at pics of my desktop and thinking that I could put some blocks, etc underneath the back legs. Just wanna make sure I tilt it enough without going overboard as its also my computer/work desk.

Also, I did retest for about half an hour when I came home yesterday. Unfortunately, I live above a cafe and they had a bluegrass shindig going on so I couldnt do much. But yes, the V was gone. I recalibrated my soundcard also and it looked decent. I'll probably test more tonite and submit some more files. Sometime within the next couple weeks I may remove the side and rear panels at least and test the room WITHOUT. I cant see myself taking down my cloud or that super chunk though...lol who knows I may surprise myself.

Another concern I have is that my 1212m PCI card sometimes picks up some faint "computer noise" and I wonder if its related to these digital issues u guys are referring to. Its VERY faint, so u have to get up close to hear it, but I can hear it when I open a web browser, change web pages, open a Word doc, etc. Ive tried changing PCI slots but to no avail. I actually heard it with my last PCI card interface as well so....maybe it's cabling or my PCI slots? Ugh...I'd hate to get a new motherboard and then find out it's cabling. I'm going to send an email to EMU when I got home too...see if they have any ideas.

I have a lot more questions, but I need to wrap this up. Probably send another message later tonite.

THANKS SAC & EarlK!!!! :bigsmile::bigsmile::bigsmile:


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## jlird808 (Nov 2, 2010)

Hey, what about this? Instead of tilting my desk, what If I built an angled "box" or "cover" (maybe out of wood or scrap 705) that fit OVER the MIDI keyboard and the main FLAT desk area? I would build it with an angle that would reflect sound down below my ears, as you mentioned. I could then put it on to do intense mixing/critical listening and take it off when recording with the keyboard.

_Get the speakers properly mounted on stands (whose base does NOT protrude beyond the edge of the speaker cabinet!) located further behind the work surface. And tilt the work surface to minimize the upward reflection of any reflections. This can be done relatively easily by simply moving the desk out when you are actively working and pushing it back when not in use._

A couple things here:

Why the speakers further back? The closer they get to the wall, won't the low freqs get crazier? I've been trying to get them as far off that back wall as possible with my limited space...thought that was ideal.

And what are the issues with the base of a speaker stand protruding beyond the edge of the cabinet? Totally curious....

THANKS!!!


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## SAC (Dec 3, 2009)

An absorbent 'shield' can indeed be used if it is workable in the space.
You will want to verify its effectiveness with measurements of course.

Discontinuities in surfaces, including shelf edges, gaps, the edge of speaker baffles, etc., created diffractive sources. Points of secondary transmission and act just like additional small signal sources, and radiate energy just as if they were additional reflections. That is also why you normally see speaker baffles rounded over, so as to minimize the degree of change. Just be warned that to totally mitigate such behavior, a low radius curve is required, with the small radius curves being effective for correspondingly higher frequencies with correspondingly shorter wavelengths.

Quoting from Peter D'Antonio: 
_"...Floor, ceiling, and sidewall reflections are cause for acoustic distortion. The floor bounce can produce low frequency problems, which are difficult to deal with since it is difficult to provide any passive absorption or diffusion on the floor. However, this is one area where that large obstacle with many knobs on it can actually be beneficial in diffusing these floor reflections. Just when you felt secure in using near field monitors, I have the unfortunate task of informing you that console reflections may create comb filtering at a level equal to or greater than room effects caused by the interaction of mid/far field loudspeakers."_

Below are two very simple illustrations regarding the speaker on the bridge versus on a stand approach to minimize early work surface reflections. And in reference to your concern, we are not trying to get them closer to the wall, we are trying to get then further behind the work surface so as to moderate the reflections and the reflection angles off the work surface.


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## jlird808 (Nov 2, 2010)

Ah I see now.

Just wondering, if I build the "shield" out of 705, does it even need to be angled? Since its absorbing and not reflecting, couldn't I actually just lay a panel (wrapped) across the top of my desk lol?


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## SAC (Dec 3, 2009)

You could do that as an alternative to tilting the surface if it does not need to be in use. You will want to examine all of 'the nearby configuration' for the sources of the very early reflections...be they diffraction relative to the speaker mount, etc.

One way to track this down is to iteratively use the blocking method - realizing that you will most likely block multiple points of origination simultaneously, as diffractive sources can be sourced from many locations and early reflections can come off any of the surfaces on and near the work surface.

And of course I would recommend following up any change with an ETC to determine the effectiveness of each change.


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## jlird808 (Nov 2, 2010)

Actually I meant that the "shield" wouldn't even necessarily have to be angled...though now that I think about it, it would probably still be ideal.

Is the blocking method putting absorbent panels at all points of an RFZ and then testing? Also, what are "difractive sources"? Are those shelves, table edges, etc....surfaces that change and cause disruptions in audio?


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