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Soffit Layout inquiry Studio Monitors
Old 5th September 2011
  #1
Gear Maniac
 

Soffit Layout inquiry

Hello everyone. I have some questions regarding what the Pro's use for guiding their design of the front of a CR, when using Soffit mounted monitors. Here goes.

I've wondered about this for a few years now.

Having spent a great deal of time delinating various Soffit geometries in Sketchup,
it seems to be, at least for me, a very convuluted process involving the juggling of a host of elements. Although there are a few starting points set in stone, there are so many variables, I'm not sure which should take precidence and which do not matter.
But the 2 most confusing elements for me, is the monitoring position APEX point, in relationship to the front of the room, and the monitoring triangle ANGLE. Yea, there are other variables such as the Soffit vertical angle etc. but as a STARTING POINT, I
ultimately use the 38% rule of thumb as I know of no other tangible point to start from.
And then I use an equalateral triangle as a "default" geometry layout.

But here is the problem

Regarding the 38% "starting point", in determining the apex of an equalateral triangle for the engineering position in a CR, exactly how would this relate to Soffit mounted monitors, as you can't really have a "starting point" as the geometry for soffit mounts are set in stone, once you determine the spacial requirements for the monitor boxes/support mechanics, and the soffit faces. And once I complete the layout, the 38% has morphed into an arbitrary distance due to framing, monitor depths etc. And this bothers me.



Which brings up another question.

Given the fact that the "equilateral triangle" does NOT have to be equilateral, this makes the geometry decision hierarchy very flexible, but at the same time, can create confusion as to where the monitors should actually be, This confusion stems from not understanding the CRITERIA that Pro Studio designers use. And this is precisely what I'm asking.

1. When actually laying out the Soffit geometry for a control room, exactly what data are you using to manipulate the geometry itself?

2. What are the important/non important issues.

3. Do you have a decision hierarchy that you sequence the various decision by?

4. What takes precedence? ie..do you layout the soffit first, and then design a room around that according to target acoustical values, or Vice Versa? In other words, do you start from an monitoring apex and work outward, or do you layout the room and fit the monitoring geometry within it?

5. Either way, where is your starting point?

I have grappled with these conundrums long enough. I'm really trying to find out if there is a "common" set of criteria or STANDARDS that ALL designers use, or is this really more of a arbitrary set of decisions that are different per designer/project?

Over time, I've kinda learned my own set of decision sequences, but I'm really curious about this.

I know this may be proprietary knowledge, and if so, well, ok. But if it is, that would suggest all designers have their OWN set of criteria targets. Which tells me something.

Anyway, thanks for any insight.
fitZ
Old 5th September 2011
  #2
Gear Addict
 

Fitz,

The starting point is always (for me) the triangulation of the monitors with a 60 deg splay. However the triangulation point is typically NOT the operators location but a point 18" up to 32" behind. This depends on the horizontal directivity of the speaker, the L/W/H of the room, sitelines, gear, etc...the whole "picture".

If possible, raising the speaker up sufficiently to angle them down 3-5 deg improves mid/hi coverage at rear client location.
Old 5th September 2011
  #3
Gear Maniac
 

Quote:
The starting point is always (for me) the triangulation of the monitors with a 60 deg splay. However the triangulation point is typically NOT the operators location but a point 18" up to 32" behind. This depends on the horizontal directivity of the speaker, the L/W/H of the room, sitelines, gear, etc...the whole "picture".

If possible, raising the speaker up sufficiently to angle them down 3-5 deg improves mid/hi coverage at rear client location.
Excellent. This is what I thought. And I do use EXACTLY what you said.

As an example.




Maybe not for everyone, but for me. However, here is another question. Regarding a window. At times, the window seems to govern the distance between monitors, and sequentially, then, if I use a equilateral triangle, the distance between monitors equals the distance to the apex point. HOWEVER, here is what I'm wondering.

IF this is how YOU do it, then the apex point becomes a an arbitrary distance from the front of the room, no? And even with this information you use, you STILL must have a starting point, FRONT TO BACK along the long axis of the room to figure out the soffit depths, and then, that only allows so much room between monitors for a window. And that's where the problem lies...at least for me. If I keep the apex point along the long axis, in order to widen the window, I must change the angle of the triangle. And sometimes, there is a narrow range of angles I can use, but what would tell me the best configuration? For instance, normally, the angle from the center of the room axis to the monitor axis is 30 degrees. But using a wide window would place the monitor along an arch, say from 35 degrees to 45 degrees max. So, is there any kind of "rule" or guideline as to "best practice" of the monitor axis angle. It would appear, the available space for the FACE of the soffit would govern this, as I like to make the soffit face as wide as practical, and still have the monitor's vertical axis CENTERED on the soffit face. Does that make sense?

But all things considered, what you said about the "whole ball of wax" is pretty much how I do it too. I was just wondering if there was something wrong with this approach. Pretty much to me, this makes most of the elements pretty arbitrary, even the vertical angle. Which I normally make about 6-7 degrees. Never seen any rule for this either. Anyway, thanks for posting your "guidelines.heh
Old 6th September 2011
  #4
Gear Addict
 

Nice work Fitz,

Properly flush mounting mains is one of the least arbitrary aspects of studio design. It takes TONS of commitment as it works or it doesn't.

I'm not sure you're fully factoring the on verses off-axis response of a given speaker. Also the orientation of the woofer(s) is a huge factor that can solve window/siteline issues (...also brings into play boundary emphasis properties, as a positive or detriment).

In a small room, I'll triangulate on-axis to the operator being ~38% front/back. In a room with ~20' length or greater, the operator remains in same location but the specific speakers and their properties are used to triangulate the monitors for as even coverage as possible spatially.

As for the down angle, 6-7 deg should be workable. You can induce phasing between mid/hi's depending on the speaker design. Case in point, I have a client in Chicago and we're refitting their mains. The original design used beautiful PMC mains but at a 14 deg down angle...a total sonic nightmare. We've pulled those out to be free-standing in the "B" room (which I designed around the PMC's) and are soon to load a 2-way compression driver/horn type main speaker with a vertical directivity capable of dealing with that down angle.

It is about the speaker/room relationship as a system.
Old 6th September 2011
  #5
Gear Maniac
 

Quote:
Properly flush mounting mains is one of the least arbitrary aspects of studio

design
OK, that makes sense. But there are aspects that "appear" to be arbitrary. This is why I'm trying to learn from the pro's.

And please, understand that I've never claimed to be a pro at this. I do this online on Amateur forums to help other Home Recording enthusiasts.

That being said, I hope you don't mind if I ask for a little more enlightenment.

Quote:
It takes TONS of commitment as it works or it doesn't.
Alright, this is where I need some clarification. Could you please DEFINE what "works" IS? You must have some rational measurement criteria of this, which , as it would appear to be a very narrow performance window and there must be a fine line between "works" and "not works". It's not as if you hear sound when it works, and nothing if it doesn't work. So what tells you your design has succeeded?


Quote:
Also the orientation of the woofer(s) is a huge factor that can solve

window/siteline issues
I'm not sure if I understand this, but I THINK I DO.
As an example, I asked Francis Manzella about the orientation of the woofer in the monitors his company manufactures. The only thing he expressed was the actual monitor AXIS to the engineering position APEX point is along the vertical axis of the Mid/tweeters, equidistant. But didn't comment on my question regarding which side of the box the woofer should be on...the window side or the sidewall side. And if this is what you are talking about, then yes, this can make a difference as to window width. With a caveat. ONLY if the width of the room is wide enough. But then, other factors come into play.

Like, the 38% point. IF, you have the room to widen the window, it changes the 38% distance from the front wall. So that seems "arbitrary". And depending on how LONG the room is, this affects the actual distance from the Apex to the soffit face as well.

Geeeeezus, Under some circumstances, I don't see how anyone could actually constrain the soffit design to be anything other than that which it HAS TO BE..and still keep the equalateral triangle and the 38% intact. Even if you have room to increase the window size, if you do, then one or the other aspects has to change...no? This is what I'm talking about. Not to mention...the actual width of the soffit. Due to a given room size, this pretty much defines exactly the MAXIMUM width the soffit face can be too.

But just to illustrate your point, s this what you are talking about?

Here is a Sketchup showing the Monitors with the Woofer on the inside(closest to window)


And here is one with the woofer on the outside(closest to sideall boundary


If I keep the Soffit face the same, then there is no difference in the possible width of the window.

And herein is my "usual" problem. As you know, most HR enthusiasts are using existing rooms. There is no room for expansion. So, as I usually keep the closest monitor box edge about 1" off the front wall, there is NOTHING I can do to alter the soffit face geometry to increase the window size. And this whole ball of wax, is governed by the 38% rule of thumb. I can't move the soffit face towards the mixing position, as this actually makes the possible window width even smaller. Which brings up the next question.

When room size limitations/38%/monitor size- force the soffit face to be at a certain

distance from the engineering Apex, this in effect becomes an ARBITRARY distance.

If I move the soffit face forward arbitrarily, due to monitor box size limitations, then again, this becomes an arbitrary distance. So, my question is.......

Given an equilateral triangle/38% starting point, is there some kind of "rule of thumb" as to the MINIMUM distance from the engineering APEX to the face of the soffit, along the 30 degree monitor axis?? I mean, at what point does this distance become either critical or ...what you call..."doesn't work"...if it even "works" at all given certain limitations.

Well crap. I'm outta time and still have a gazillion questions. Ok, well thanks for any new information. I'll be back.

ps. I sure envy people who have projects either from the gound up or at least a big enough building to lay this stuff out correctly.Working with bedroom sized projects sucks.heh
Old 6th September 2011
  #6
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Northward's Avatar
Starting point is the size of the room - and by that I mean the outer shell dimensions.

We have in-house equations that were put together based on our specific room model needs (all inter-dependent via their common parameters) that tell us rather fast what can be done in there and what is the expected optimal geometry and thus, optimal speaker placement.

From there it's all cascading really.

If time allows, I'll write more
Attached Thumbnails
Soffit Layout inquiry-tool-flush-mount-geo.jpg  
Old 6th September 2011
  #7
Gear Maniac
 

You know, something finally occurred to me.

The room LENGTH/WIDTH RATIO, has a hell of a lot to do with this. Is there some kind of default "ratio" that works better than others. And I'm not talking room modes here. I'm referring to a ratio that allows everything required for a set of soffits to WORK.

Hmmmm, I'll have to do a Sketchup to illustrate this question maybe.
Old 6th September 2011
  #8
Gear Maniac
 

HOLLY MOLY! Look who's here.heh Hello Thomas, you stuck that in so quick I didn't see it before I asked about "ratios". hahahahahahahahaha!


Well, that's what I thought. Man, I don't have time to respond right now. I'll be back tonight. BTW, thanks for chiming in here. You know me. Never a dull moment.
Old 6th September 2011
  #9
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gullfo's Avatar
 

Quote:
Originally Posted by Northward View Post
We have in-house equations that were put together based on our specific room model needs (all inter-dependent via their common parameters) that tell us rather fast what can be done in there and what is the expected optimal geometry and thus, optimal speaker placement.
Hey Thomas, looks like someone spilled ink on the spreadsheet, maybe you could post the spreadsheet heh

FitZ - it definitely is a number of things like room size and listening triangle, window/view angles, LF trapping, etc as well as equipment etc which shape the spacing and monitor layout. Fran mentioned that the Griffin monitors are configured for the room they're going into so placement of the mid-HF array and LF drivers all depends on the configuration, stereo vs. 5.1 etc and I think you'll find this true as well for many studios where (for eg.) Augsperger speakers were/are custom built.

on design i pretty much start with the same overall criteria as Jeff per post #2 and i have a proprietary spreadsheet which "tells me things" about the space but then the modeling in 3D against "all the stuff" usually forces me to adjust some things. also, consider that while the window between the monitors has impact you can also use space under the monitors as well for windows since they can extend the soffit with minimal negative effect. this results in that "peaked" or "raised center" windows you see frequently.
Old 7th September 2011
  #10
Gear Addict
 

Fitz,

I suspect that your knowledge and understanding is stronger than you give yourself credit for in this complex arena!

Let me ask you a question (as much to lob the topic into the general discussion as anything else)...do you prefer a hard monitor wall facade or an absorptive one? If absorptive, how so (material and thickness)? You have a keen eye and have truly devoured most designer's sites. To me the answer of this question points to great advancements in flush-mount practices in the past ~15 years from those ~30yrs ago. Of course the correct answer also has the factor that seems to drive you crazy, "it depends".
Old 7th September 2011
  #11
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Northward's Avatar
Quote:
Originally Posted by gullfo View Post
Hey Thomas, looks like someone spilled ink on the spreadsheet, maybe you could post the spreadsheet heh
Yup. I think the cat did it.

Jeff, Glenn, will you be at AES NYC?
Old 7th September 2011
  #12
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audiothings's Avatar
 

Quote:
are soon to load a 2-way compression driver/horn type main speaker with a vertical directivity capable of dealing with that down angle.
which ones, may i ask? Meyer makes a very interesting pair... Then there are RAs, Kino****as, Auggies, GedLees... any others?

I built a giant pair based on AudioKarma's Econowaves... A whole new world! Now I want to take the design one step further and rebuild my room around them!
Old 7th September 2011
  #13
Gear Addict
 

Sure Audiothings (gladly), they are AudioKinesis. Designer Duke LeJuene is actually a protege of Dr. Geddes. Fantastic speakers. He custom tweaked the box and crossover for this application. I'll post an update when they're installed. AudioKinesis - sound that moves you

Thomas, unfortunately I am not attending AES this year.

Fun thread!
Old 7th September 2011
  #14
Gear Maniac
 

Quote:
I suspect that your knowledge and understanding is stronger than you give yourself credit for in this complex arena!
Wow. Thank you. Unfortunately, I don't have the educational underpinnings to give me the confidence to back up my opinions in this regard.

Quote:
...do you prefer a hard monitor wall facade or an absorptive one?
If you are talking about the area between the two soffit faces, well.......it depends on who I'm listening to at any given moment.heh


Jeff, I'm an amateur who deals with other amateurs online, who very seldom listen to me and rarily end up building what they are asking about in the first place. The only studio I've personally been involved with is my own. So, that should tell you something. However, to answer your question, this is precisely why I started this thread. I don't HAVE a preference. Throughout my entire exposure to this field, I've only endeavored to learn WHY, certain things are designed as they are, and the consequence of that endeavor has been...wait till tomorrow. A new opinion will expose itself soon that will completely negate what I've managed to build myself based on yesterdays opinions.heh

What I'm trying to say is, I've never had the responsibility for the sonic performance of another persons studio. And frankly, over the last 10 years, I've learned that I'm completely out of my league when it comes to scientifically predicting a CR performance. In reality, here is the deal. Jeff, plain and simple, I'm a DETAILER and fabricator.. I like "details" and I like fabrication. I spent 20 years in a store fixture manufacturing company. The first 5 as a Union journeyman millworker, and the rest as as a Pro Cad detailer Their main client was Macys. I personally detailed most of the fixturing throughout their three Flagships stores. And during my tenure as the senior CAD drafter, I learned TONS of things about fabrication and machining, materials, techniques, and products related to Store fixturing. In fact, I LOVE detailing. So naturally, this interest carried over into my interest in Studio design.


However, the problem is....I also am a musician. Spent 30 years as a pro guitarist. So, naturally, recording entered the picture, and once it did, I was hooked. Over time, I wanted to learn how to build a studio. Well, at the time, except for Mix magazine, there wasn't much resource material available regarding the theoretical side of studio design. UNTIL, I came across Everest's Master Handbook of Acoustics. Lord, I wish I had never seen it.heh From that day forward, I've endeavored to learn all I can. Unfortunately, I also discovered...OPINION and advances in knowledge do not always agree. So, here I am today...STILL trying to sort out which one rules the nest.

Ok, back to your question. Actually, to me, from my limited experience, for a HOME RECORDING STUDIO, very seldom do people have enough room for a live room, so there is no need for a window. And since these rooms are usually very small, the front wall is barely wide enough for soffits in the first place. However, from my perspective, small rooms need all the absorption they can get. So, for my CR, I bought 4" thick 703. Since I also am using the same at the early reflection points on the sidewalls/ceiling, which in effect means the whole front of my CR is absorbitive, except for the soffit faces. Here is "my" design....


And here is the current reality.

I haven't actually installed the absorption yet. That's because it's number 46 on my "honey do" list. heh However, I DO have 4 sheets of 4"x4'X10' and 3 sheets of 3"X4'X10. Lord knows if I'll ever get it installed the way things are going in the world at the moment...sheezus.




So, in summary, I've never had to actually take a stand on this issue. Except in my own little world, and for me, it was a no brainer.

HOWEVER, in view of what I've learned in the last 20 years or so, it would appear this is one of the "schools of thought", that have evolved over time. It would also appear that unless you have been involved with "pro" studio clients, with deep enough pockets to build a studio whereby the CR is large enough to "express" your thoughts, and then enough savy to prove your concept "works"...well, it's all academic.

Furthermore, when you say "facade", this implys a wall whereby the soffits are within a much wider front, whereby there is an extra area between the soffits and the sidewalls, which may even be angled more than the soffits themself, or even be part of the soffit face, but much wider than is usually available to HR enthusiasts. And there definetly would be a window. In that case...if I were given the responsibility...I'd probably use STEEL. Or at least Chemetal/Stylmark as a finish over concrete/mass, or something to that effect.heh Which is one of my "proprietary" uses of materials. That's because I like it. Hahahahahahaha!


Now, if you are talking about the soffit faces themself..well, if they were absorption, that would come from the old "dead end" school of thought, no? I would think things have evolved away from that. Same with diffusion. So, what does that leave? A hard facade with a designers preference of finish, no?

I hope that answered your question.

I also have more questions. But later. Gotta go make some money on ebay.
Old 7th September 2011
  #15
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gullfo's Avatar
 

at least it looks like you have the LF trapping in the truck solved heh

Thomas - i won't be at the AES conference.
Old 7th September 2011
  #16
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johndykstra's Avatar
 

Hey fitz.

Similar boats we are in yeah?

From what I have gathered via the same avenues as yourself... in my novice opinion, when looking at your current soffits, you are leaving yourself with a lot of possibilities for diffraction...the main reason you soffit in the first place. You have several layers of sheathing that don't quite make it to the walls or ceiling, and the junction at the front window seems incomplete. Essentially, you have succeeded in making the baffle of the speaker larger than it would be were it free standing, but by not completely tying the soffits to the structure, you are still getting the diffractive properties of a free standing speaker to some degree. It makes me wonder if we are not thinking this through in a similar fashion.

For my eventual control room, I plan to do much what I think I see in your room. That's to say, I plan to make the soffits "movable" and fine tune their placement as well as my chair's. Once this location is achieved, I'm going to uninstall the temporary sheathing of the soffit structure, and tie the framing into the room. I understand that while testing, my movable soffits will not be performing exactly as they should, however, I think they should give a "close enough" glimpse as to how the soffits themselves effect the space modally, while at the same time, greatly reducing the SBIR (diffraction) without having to go at it blindly...building it permanent from the start.

What I do not know in regards to my "plan":

Is this free standing soffit structure going to resonate too much during it's tweaking stage because it isn't tied in? If it IS... is this an anomaly I will be able to ignore on the graphs and still be able to get some useful data towards an ideal placement?

Perhaps more importantly...is all of this tweak-ability worth it? Am I over thinking? I mean... soffit mounting is in an effort to reduce boundary effects of free standing speakers. The are going to DO that regardless of their placement. We aim to have the axis of the speakers converge to a point between ~1'-2.5' behind our head. We aim to have a listening "zone" that allows you to move freely around your work surface... so ~3'-5' side to side and ~2' front and back. Seems to me, that if you move a measurement mic around within that mixing zone you are going to get wildly different readings at this stage of treatment (none).

Perhaps the best thing we can do, is before anything else assess the modal activity of the empty space. Move a mic around your planned listening zone and make sure you aren't in a null who's frequency is lower than you will have the ability to treat.

I'm really just thinking aloud here... hope you don't mind
Old 7th September 2011
  #17
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Quote:
Originally Posted by johndykstra View Post
Perhaps more importantly...is all of this tweak-ability worth it? Am I over thinking? I mean... soffit mounting is in an effort to reduce boundary effects of free standing speakers. The are going to DO that regardless of their placement. We aim to have the axis of the speakers converge to a point between ~1'-2.5' behind our head. We aim to have a listening "zone" that allows you to move freely around your work surface... so ~3'-5' side to side and ~2' front and back. Seems to me, that if you move a measurement mic around within that mixing zone you are going to get wildly different readings at this stage of treatment (none).

Perhaps the best thing we can do, is before anything else assess the modal activity of the empty space. Move a mic around your planned listening zone and make sure you aren't in a null who's frequency is lower than you will have the ability to treat.

I'm really just thinking aloud here... hope you don't mind
tidying up my thoughts a touch. I guess what I'm driving at above, and the highlighted portions in particular; is that in typical room set ups much effort is given to choosing a speaker placement. This is in effort to minimize the effects the room's boundaries have on the low end diffraction around the cabinet to the front wall etc... we are eliminating this with soffits. So really, our focus when building soffits, should be really only that they aim at an area of the room with minimal modal nulls... and at the very least avoid very low frequencies, as these will be very difficult to treat. The rest should take care of itself (sbir) or be treated with the rest of the room's plan.
Old 8th September 2011
  #18
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Northward's Avatar
We keep the elevation and angle in main speakers to a maximum of 5° because it influences our perception of some important frequencies, due to the HRTF.

Between -5 and +5° though, the variation is negligible to non existent. More, we feel it is problematic and it's likely you'll have a problem, even with speakers with adapted directivity.

As usual, YMMV.

Quote:
2 ELEVATION CUES
In general, the elevation characteristics in human hearing can be modelled with delayed elements to simulate the ear's concha. Fig. 1 illustrates different lengths of the reflected' path as the elevation
angle of incidence changes. The reflected path decreases in distance with increment of elevation angle. When the reflected path is combined with the direct path, a notch in the signal frequency spectrum is observed that increases with frequency as elevation increases. Batteau [1] used two delay elements summed with the direct sound to model the reflection caused by the pinna. This model was psycho-acoustically verified in [2] to be able to produce elevated perception. Experiments on the localisation in the median plane have been conducted by modifying the spectral content of the stimuli used. The localisation of l/3-octave noise stimuli on the median plane has found to be primarily determined by the stimulus frequency and is independent of the location of the source [3]. The result suggested that spectral maxima (peaks) determined the location of sound on the median plane. The presence of maxima also suggested that minima (notches) in the spectra could be utilised as localisation cues. The study by Hebrank and Wright [5] on median plane localisation, hypothesised that frontal elevation cue is a notch created by interference with reflection off the concha of the ear. This notch increases approximately from 6 kHz to 13 kHz as elevation increases from _30° to +30°. The importance of spectral notches for sound localisation has also been emphasised by many authors [7]-[8]. Fig. 2 shows the HRTF of the KEMAR subject obtained from MIT, Media Labs[9], at an azimuth angle of 0° for a range of elevation from _50° to 230°. Note that elevation angle larger than 90° is used to refer to elevation angle orientated toward the rear of the subject. The variation of the spectral features (shown in Fig.2) such as notches and peaks are in agreement with previous researches. An increase in the centre frequency from about 6 kHz to 12 kHz of the first notch, Nl is observed for the HRTFs when elevation increases from below the subject to vertically above the subject in both front and rear hemisphere respectively. A second notch, N2 is observed at higher frequency from about 10kHz to 11kHz that also varies increasingly with elevation. However, the feature of the second notch is less obvious for higher elevation above the subject. In between these two notches can be considered as a peak in the frequency response that also varies increasingly with frequency. A third notch, N3 is also present between 15kHz to 16kHz. Similarly, this notch is not obvious for elevated perception above the horizontal plane


Source: ELEVATED SPEAKER PROJECTION FOR DIGITAL HOME ENTERTAINMENT SYSTEM by Woon-Seng G.an, See-Ee Tan, Meng-Hwa Er and Yong-Kim Chong
Digital Signal Processing Laboratory, Nanyang Technological University, Singapore - 2001.

Old 8th September 2011
  #19
Gear Maniac
 

Guys, I didn't intend on this thread to dive into "my" interpretation of Soffit mounting monitors. But Jeff asked me a question, and I only have my CR to relate to. Hence my posting stuff about it. Furthermore, the REAL reason I started this thread is ....

Soon, I may have to move. The current economy is forcing me to re-evaluate my current ability to stay in this house. Fortunately, I've been offered a very good situation that will allow me to not only
keep my studio interest alive, but incorporate my equipment with a mentors studio as well as my shop, with the intent that I design and build a new HR studio in his home.As he really wants me to make this a working studio, I decided to delve into some aspects a little deeper than I ever have. This is due to the fact, that my mentor is a soon to be credentialed Physicist, and Mathamatics instructor at a local college.Hence my posting this thread. He is looking forward to tackling what I've never been
able to do. And that's interpret all the equation stuff related to this field. And frankly he has a top notch setup, and the bucks to do it..at least in a HR environment.

However, in that light, let me address Johns observations of the current state of my little CR soffits

Quote:
I'm really just thinking aloud here... hope you don't mind
Are you kidding? Mind? HELL NO!! I'm open to ANY input whatsoever!!
Especially since you're building a HOME studio CR.

Quote:
Similar boats we are in yeah?
You betcha. And that's why I think other HR enthusiasts may gain an insight into various aspects of this subject by opening a dialog about them.

Quote:
in my novice opinion, when looking at your current soffits, you are leaving yourself with a lot of possibilities for diffraction...the main reason you soffit in the first place.
hmmmm, didn't you see my "design" Sketchup. Well, the diffraction thing is EXACTLY why I chose to fill in the area between the monitors with 4" 703. The sketchup doesn't show it, nor does the picture because I haven't actually installed it yet. And with early reflection absorption on the opposite sides of the soffits and a cloud of the same, well, in essence, I guess this becomes a "dead front end"..except for the soffit faces.

Frankly, I sat in a friends CR a few years ago with a similar set up. I loved it. Everything was crystal clear. So, since my room is so small, I decided this was the best way to go. Oh, and the glass sliding door is "supposed" to be covered with 2 layers of 3/4" MDF before putting up the absorption panels. Maybe these details will illustrate what I "was" planning on doing. However, this may never happen considering what I said above. Anyway, I hope this makes sense. The bottom line was, in my limited understanding of acoustics, my "belly" told me that diffraction would occur at both vertical edges of the soffit face, so by putting absorption there, I figured this would keep the "diffracted" reflection from occurring.

To better illustrate my intent, here is a few jpgs of a 1.5"=12" model I originally built to visualize how I would have to cut the 703 panels to extract the most from my supply.The absorption is really 1/2" thick acoustic ceiling tile panels, that I used to scale the model from. In the model, 1/2"=4" thick 703


Note the "superchunks" at the junction of the sidewalls/ceiling. Since this is the only location I have to incorporate "superchunks", other than the rear wall "closet'(see mor on that later), and the doors at each side of this closet require the superchunks to "recede" into panels above the door, this pretty much dictated the design. Anyway, here is what it was "supposed" to eventually look like.


And here is the original Sketchup showing some framing.



Here was one of the "superchunk" fabric frames I fabricated. Still hanging in the garage. Damn, where does the time go?


And yea, I'm an old fart.

Well, so much for explaining my original intent. Does that make sense..in regards to the "diffraction" thing? Or was it a brainfart? Either way, it may not even happen now. Hence this thread to find out the real deal.

Ok, back on track.
Quote:
Between -5 and +5° though, the variation is negligible to non existent.
Quote:
2 ELEVATION CUES
Hmmm, I wonder why these guys used speaker's "high above" then.

Guys, I just came across this interesting article. But something conflicts with what Thomas just posted. Just curious.

http://www.nytimes.com/2011/09/06/sc...1&pagewanted=2

From the article.
Quote:
Statistics showed that speakers directly ahead, combined with speakers 55 degrees to either side of the listener, provided the most attractive soundstage. The “wide” speakers mimicked the reflection from the side walls of the concert hall by causing the sound to arrive at the listener’s ears milliseconds after the sound from the front. Sound from other angles did not have as great an effect.
Next, the team asked listeners what combination of speakers gave the best impression of “depth of stage.” Here again, statistics showed a clear preference for speakers in front of listeners and high above them. This sound — also slightly delayed — gave the ear and the human brain a sense of where the different instruments were on a bandstand.
I don't know if this has any bearing on future CR design, but it seems to me, IF, research has shown that this system of DSP manipulation of signals so they are time delayed to imitate "early reflections" so the soundfield in a small room will sound like a concert hall...works, then EVENTUALLY, a studio that deals with high end projects, must have the ability to MONITOR in 11.1
After all, 5.1 is common place now. Right? With computer power increasing
exponentially...future home theater systems may become 11.1. ?????

Just a thought. Maybe a brain fart. Any thoughts though?
Old 8th September 2011
  #20
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Northward's Avatar
Quote:
Originally Posted by fitZ View Post

Guys, I just came across this interesting article. But something conflicts with what Thomas just posted. Just curious.
Oh, I don't think they're conflicting. They're just not looking at the same thing, although it is the same area of work indeed. The point of the little piece of the study I posted is more to show that speaker elevation does play a big role in perception of certain important presence frequencies due to HRTF - so we should think twice before placing speakers too high, in particular in rooms where the mains are supposed to be the speakers you mix on, and not just to impress clients . No more, no less

RE: the high above bit. This can also be room dependent - in good rooms, stereo is enough to really feel surrounded by sound, and they usually show excellent depth and somehow elevation perception. In some lesser rooms it's all very 2D / flat. This has a lot to do with a good management of dispersion etc.
Old 9th September 2011
  #21
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Quote:
Originally Posted by fitZ View Post
Does that make sense..in regards to the "diffraction" thing?
Yes.

And no.

I get your reasoning, and you may very well be correct. My question is:

Is absorbent placed in front of the gaps around your soffit sufficient to hinder LF diffraction? It would seem "better safe than sorry" to me to cinch up the sheathing all the way to the walls/ceiling/floor.

Beautiful work BTW. On all of it. You're an inspiration. I hope all goes well with the house and the studio... sounds like an exciting opportunity with the human calculator.

On a side note... why does this thing always tell me I am misspelling "soffit"? I'm pretty sure that's how you spell it no?
Old 9th September 2011
  #22
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Quote:
Originally Posted by johndykstra View Post
On a side note... why does this thing always tell me I am misspelling "soffit"? I'm pretty sure that's how you spell it no?
you need to add it to your dictionary since while that is how you spell, not all dictionaries include it - especially English ones... French (FR and CA) generally do have it... annoying to be sure.
Old 12th September 2011
  #23
Gear Maniac
 

Quote:
Yes.

And no.

I get your reasoning, and you may very well be correct. My question is:

Is absorbent placed in front of the gaps around your soffit sufficient to hinder LF diffraction? .
Well, what's the alternative? A solid panel? How would that help diffraction? It would "seem" to me(note-belly speaking here) that would simply reflect the "diffracted" component, which correct me if I'm wrong, but would now be out of phase with the direct sound...no?

Which is something I've wondered about too. If ...at the edge of the soffit face, the expanding hemispheric "wavefront "meets the boundary between soffits, or the sidewall boundary's for that matter, if this is a simple reflection, or diffraction. In the case of "my" soffits, I INTENTIONALLY allowed this area to be "recessed" for the 703, vs a boundary with the face that meets the edge of the soffit face. If that makes sense? In fact, this is exactly what I'm trying to learn about. What happens at that edge? With a boundary, it would seem no diffraction really occurs, since there is no corner to "wrap around". With a recessed area, this edge now acts like a speaker enclosure...no? So that's why I put absorption there. So there is neither a simple reflection or diffracted component reflection...or something to that effect. And actually, it's not JUST my "belly" telling me this.

Eric Desart once told me that "diffraction" occurs at the edges of Superchunks. Which baffles me, because I was under the impression the "diffraction" occurs at the edges of objects like speaker boxes, walls, furniture etc....when it "wraps around" said edges. I don't understand why it would be considered "diffraction", when there is no edge to "wrap around". like at a soffit edge. Hmmm, maybe I'm just confusing things. Wouldn't be the first time either.


So, can anyone explain "what happens" there? And what is it that is negative...if anything. In fact, if there IS something negative, then why do I see so many CR's with soffits, that have a solid boundary between soffits. Not only that, but since I am planning on using 4" 703 with a 2" airgap...wouldn't this qualify as a "bass trap". I mean, even Mr. Lachot used a very deep area above the Studio window at Manifold. Granted..it is WAY deeper than mine, but wouldn't this perform as a bass trap regardless?

See, in my limited understanding of acoustics..all I have to work with is my belly. That's why this thread exists.

Oh, and btw, thanks for all the insight so far. But I still don't understand the definition of "works"heh
Old 12th September 2011
  #24
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good questions. I know what my belly says, but I don't trust my belly.

My belly says it's best to have as gradual angles as possible, while still being practical. A soffit's sheathing that doesn't meet the boundaries is probably the least gradual, as the sheathing itself is a 90 degree corner, plus the depth of the soffit mounting to the boundary wall. Now let's say you extend the soffit sheathing all the way to the ceiling. Yes it's a 90 degree interface, but you don't have the diffraction around the backside, you only have the reflection that is the ceiling... you would have this regardless.

The "gradual angles as possible isn't really my belly talking... it's my belly remembering Andre from my thread. Start at this post

https://www.gearslutz.com/board/5869490-post80.html

and continue to see how we were working around the diffraction of my front window sill
Old 13th September 2011
  #25
Gear Maniac
 

Quote:
good questions.
Thanks, but none of them are really getting answers.
Quote:
I know what my belly says, but I don't trust my belly.
Me either. That's why I'm asking the questions. Otherwise, I'd just go ahead and trust my belly and acoustics be damned.heh

Quote:
My belly says it's best to have as gradual angles as possible, while still being practical.
Hmmm, you lost me on that one. Gradual angles as possible? Well, in the horizontal plane, the angle of the soffit is usually defaulted at 30 degrees in relationship to the front wall, no? And the vertical is a somewhat "arbitrarally" defined angle, depending on any one designers preference's and viewpoints, no? In that regard, I don't understand your statement.


Quote:
A soffit's sheathing that doesn't meet the boundaries is probably the least gradual
Why would anyone build a soffit that the face doesn't meet the floor, walls, and ceiling? That would appear to defeat the purpose, no? And I still don't get what you mean by "gradual" as the term suggests something that is changing from one state to another..like speed, color, temperature..etc.

Quote:
Now let's say you extend the soffit sheathing all the way to the ceiling. Yes it's a 90 degree interface,
Ok, unless the soffit face is angled vertically. Like mine. Which would actually create an angle more than 90degrees. And then you have some CR's with an upward angled ceiling as well. Which may or may not even have a bearing on anything..except perhaps the angle of the reflected wave...er...pressure front..or something to that effect.heh

Quote:
but you don't have the diffraction around the backside, you only have the reflection that is the ceiling... you would have this regardless.
Are you trying to show me the difference between a soffit interface that would create diffraction and one that would create reflection? If so, it makes sense. On the other hand, it seems to conflict with what Eric told me. Or maybe this isn't what you're trying to do in the first place.

God, don'tcha just love acoutstics?heh

Quote:
it's my belly remembering Andre from my thread. Start at this post
I couldn't find Andres reply

Anyway, just trying to learn. Maybe this is becoming academic anyway. I'm starting to get the feeling that it's all in the eye of the beholder.heh
Old 13th September 2011
  #26
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i'm not sure it's simply the eye of the beholder, the soffit sizing is determined by space available, space needed for treatment of the room, and the best tradeoffs for getting the monitor response right. this may include building trapping in-behind the soffit face and leaving openings - and maybe adding some absorption on the face to reduce reflections or adding hard surfaces to add reflections. however, if the absorption behind the soffit is sufficient, then the "diffraction" around it into that space is not a problem but rather a design consideration in balancing the increased LF response with the need to balance the decay rate on the LF... getting sufficient size to the soffit so the diffraction occurs low enough not to become a problem is a challenge in a small space but properly defining the center and side walls and well as ceiling, and sometimes the floor too, all play into how "big" the soffit is acoustically. graduating the treatments from LF to HF in terms of absorption and diffusion is part of making the RFZ work without being dead or otherwise imbalanced. my 2¢
Old 14th September 2011
  #27
Gear Maniac
 

Quote:
i'm not sure it's simply the eye of the beholder
Neither am I.

But given your .02, I wonder. IF, the same room parameters, same defined performance target and same budget for a given CR design project, were commisioned to 10 different designers, it would be interesting to see how each designer delienates his solution, and how similar the designs were to each other. It would seem they would have to be somewhat similar, to meet a given set of performance criteria.

That is, unless...and this is what I've asked about many times...each designer has his OWN interpretation of what constitutes...proof of performance. I believe there's been many opinions given on this forum in that regard too. And if I'm not mistaken.. a few scoffs as well.heh

Oh well. I'll let this thread die now. I'm getting tired of trying to extract answers to my questions. Thanks everyone for what you DID supply.
Old 14th September 2011
  #28
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i 'd agree you would likely end up with at least 10 designs but in theory they should reach a reasonable set of performance levels which are consistent with published standards, the owner requirements, and each other and ultimately be a good working environment.
it might be fun to have a "room design challenge" where you (or someone) posts a decently detailed SU file (of a reasonable common room people might have in their home not some complex thing..) + a document explaining what your requirements are and see if some folks decide to play... output should be either 3D model in SU or PDFs and explanation of expected performance. may be a good way to get some ideas on say a 10x15x8 room (just under minimum) or perhaps something like 8x13x17 (a bit over minimum) etc possible ending up with ideas people could use...
Old 15th September 2011
  #29
Gear Maniac
 

Quote:
but in theory they should reach a reasonable set of performance levels which are consistent with published standards, the owner requirements, and each other and ultimately be a good working environment.
Hey Glenn. That's cool. Unfortunately, and this is precisely what I've tried to pin down for years, what constitutes the following

And this is where my opinion that the "eye of the beholder" speaks loud and clear.

Can you "define"....

1. "reasonable set of performance levels" ie..do these "levels" change if a room gets larger? Are "performance levels" something that all studio designers agree on?
2. "the owner requirements" ie..what should the owner provide in the way of "requirements"?
3. "published standards" As in ISO etc? For non Pro design enthusiasts, these are very expensive to obtain, no?
4. "a good working environment"...ie..in what way?

Glenn, thanks for chiming in here. Yea, I think this would be cool, but I highly doubt if any of the Pro's have the time or inclination to participate, and NON pro's like me don't have these criteria defined...and that's the point I've been trying to make. IF, these criteria ARE defined then this forum should have a sticky that everyone can use as a "starting point"..much like the 38% thing..no? I mean, I think this is what I've been trying to learn all this time. THE DECISION HIARCHY. There must be some sequence of decisions that ALL designers use, either proprietary, or sonic acoustical with regards to a given space, equipment, budget etc. I mean...


Either this design "process" is a BLACK BOX that data is thrown in, tossed around, and one piece of the puzzle is extrapolated at a time, or there is a DELIBERATE and sequenced series of question/answer decision making at play. And if so, then does each designer use a proprietary sequence, or is there a common denominator sequence of decisions that all designers use? At least for defining the acoustical performance parameters of a given space. This is precisely what I'm trying to find out. Sure, all designers have their pallet of finishes/materials and things of that nature. But there must be a narrow range of solutions to any given space, depending IF there is a common definition of "performance levels"...or something to that effect.heh

Ok, well, if you 're open to it, maybe I'll start working on a Sketchup with a common room size, and go from there. Maybe.heh

Anyway Glenn, thanks for your contribution to my education.

Oh, btw, you mentioned something about a soffit with a perimeter that allows diffraction to occur, with absorption behind the soffit face. In my mind, I picture that as a soffit face with NO connection to adjacent boundaries, which means there must be an area between the soffit face and the boundaries that absorption occurs. That's something I've NEVER seen. Care to show me anything you have regarding this? I'm curious how wide this "open" area between the soffit face and boundaries would be determined and why.


Later.

ps...I might not let this thread die after all..but we'll see.
fitZ
Old 15th September 2011
  #30
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i think from a disconnected arrangement, i would build in a series of cavities / wave guides which provide some broad tuning for problem frequencies and space for air cavities on the slats and membrane absorbers. i'd leave around 12" (300mm) or so for air gaps but probably alter the exact opening based on the tuning desired and if any calculations indicated air flow needs to go up or down. thus all the space behind the "walls" would be absorptive and targeting the LF decay needed to get to a good balance. "good" is defined by my idea of good and whatever the customer thinks is good but referencing ISO and EBU "standards" to make sure it's reasonably close.

i have followed you for years in your pursuit of a common standard/basis that everyone can adhere to and agree to but it does not seem to be the nature of the art even when the science behind it is improving every year and folks are no doubt trying to leverage it wherever it makes sense to do so in practice.

in this quick sketch the cloth separating the panel areas would be the openings into the trapping.
Attached Thumbnails
Soffit Layout inquiry-example-disconnected-soffits.jpg   Soffit Layout inquiry-example-disconnect-soffits-framed-1.jpg   Soffit Layout inquiry-example-disconnect-soffits-framed-2.jpg  
Attached Files
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