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PostPosted: Thu Aug 31, 2017 1:46 am 
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Location: Eureka, CA USA
Hello, first time poster here, but I would be at a loss without the wealth of information I've acquired studying this forum over the last year or so. Many thanks to all involved.

In my converted garage studio (18' 2" length, 10' 6" width, 8' 3" height) I am nearly finished building soffits per John's design as posted in many places in this forum (That is to say all that remains to be done is installing the bezel and acoustic hangers in the cavity below) Mounted in the soffits are Focal Alpha 65 powered monitors (6.5" woofer drivers, frequency response 40hz to 20khz). Built into these monitors is a low shelf knob labeled FO = 250 that is variable +/- 6db. The Focal Alpha 65 has a 9.9" baffle width, so according to the equation that's been posted in this forum to determine the appropriate baffle step compensation for any given speaker, (F = 4560/width of baffle), the correct FO for the shelf is 460.6 hz, which would then be attenuated 6db to correctly compensate for the infamous baffle step problem. Enter confusion. Why wouldn't the speaker designer build in the circuit at 460 hz? Perhaps they are targeting an average, or best guess, frequency range that would apply to a broad range of rooms when used in free field monitoring regarding proximity to walls, and are not considering the speaker may experience any kind of boundary that resembles an infinite baffle.

Well, trying to be as studious as possible, I contacted Focal directly by e-mail and asked whether my guess as to why the FO was at 250 was indeed the case. The response ignited a spark -- though perhaps just in wishful thinking -- that the built-in shelf knob at 250 would be sufficient for my soffit mounted Focals. The Focal rep responded with the following message and image:

"Hi Marc,

Thanks for contacting us. I don’t have the exact details of the low-shelving curve.

But according to this graphic, at -6dB looks like the corner frequency is close-ish to 450 so I think it will work just fine.

I know of 1 studio that did this with the Solo6 and it did work quite good. Just have to have enough room behind the back plate to allow for cooling!"

Attachment:
image001.jpg


I returned his message and asked if this was a graphic of the actual shelving built into the Alpha 65 (It also has High Shelf controls) and he replied saying that it is, indeed, and that this graphic is straight from the Alpha 65 manual (I bought the speakers second hand so I don't have this literature, unfortunately). I should also mention that I researched the FO of the shelf on the Solo6 speaker he mentioned and it is 150hz. I plugged its width dimensions into the equation and the result was even further off that of my speakers.

Perhaps my knowledge of the details of low shelving is the problem. Honestly, I get a little confused with all these terms FO, corner frequency, etc. It could be that the equation (F=4560/width) supplies a number that is not the same as "FO" in which case, maybe this graph is showing exactly what I need to get the job done correctly.

I'd like to understand how shelves work if my understanding is confused. However, I guess my primary concern and related question really comes down to this: Based on the above posted graphic of the shelf curve of the Alpha 65, will this shelf curve suffice for soffit mounting the Alpha 65s? I'd certainly love to not have to fuss with an external parametric! Thank you for any determinations y'all might come to with my little quandary here!


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PostPosted: Thu Aug 31, 2017 12:40 pm 
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Hi there "marcjeffares", and Welcome! :)

Quote:
I am nearly finished building soffits per John's design as posted in many places in this forum...
Photos! Diagrams! Details! :)

There's a saying around here: "Pics, or it didn't happen!"...

Quote:
Mounted in the soffits are ...
Mounted how? Using the "rigid tightly clamped" method, or the "floated" method?

Quote:
... Focal Alpha 65 powered monitors (6.5" woofer drivers, frequency response 40hz to 20khz)...
Since those have slightly curved side panels, I'm guessing that you did the "floated" method, right? It would be hard to build an enclosure box that would clamp those rigidly and tightly.

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Built into these monitors is a low shelf knob labeled FO = 250 that is variable +/- 6db.
:thu:

Quote:
The Focal Alpha 65 has a 9.9" baffle width, so according to the equation that's been posted in this forum to determine the appropriate baffle step compensation for any given speaker, (F = 4560/width of baffle), the correct FO for the shelf is 460.6 hz, which would then be attenuated 6db
Well, not really. Yes, the baffle step would occur at 460 Hz for that speaker, but that's the CENTER POINT of the entire power imbalance curve. The curve covers about two octaves either side of that, give or take, depending on the speaker design. To be more accurate, if you consider this to be a treble rise, not a bass roll-off, and the speaker to be a point source, then the rise in level starts at the frequency where the wavelength is 8 times the width of the front baffle on the speaker, and ends at the frequency where the wavelength is twice the width of the front baffle. So, for a speaker baffle 9.9" wide, the curve starts to rise at (wavelength = 8x9.9 = 49.5"), therefore frequency = aprox. 274 Hz. It then increases gently by 6 dB until (wavelength = 2x9.9 = 19.8"), therefore frequency = aprox. 685 Hz. 460 Hz is the point in the middle, where the rise is 3 dB.

However, all of that is theoretical, and assumes that the speaker acts like a point source, or small spherical source (in which case it's hard to imagine how it might also have a flat front baffle!), and the actual range and curve could be different for different shapes. Flat faces and angled corners, for example, introduce spikes and dips in that curve, so it's not a nice smooth constant curve at all.

Quote:
Built into these monitors is a low shelf knob labeled FO = 250 that is variable +/- 6db.
That might refer to the point where the rise starts, not the mid point. Although why they would do that is strange, and does not match the graph they gave you! One explanation might be that the front baffle of the speaker is not a circle with a diameter of 9,9", but rather a rectangle, and in thereon there's also another (smaller) baffle step associated with the vertical dimension, so they might be averaging those out. Not sure, but possible.

Quote:
Perhaps they are targeting an average, or best guess, frequency range that would apply to a broad range of rooms
The baffle step issue is related to the speaker cabinet, not the room. The room places additional loading on the speaker, yes, and the room is also not a perfect 4 pi space, and the baffle is not truly infinite anyway. So the way all of that affects the baffle step is more in the sense of intensity, not so much frequency. So instead of needing a 6 dB cut, you might only need 4 dB cut, for example.

Quote:
used in free field monitoring regarding proximity to walls,
It's very unlikely you'd find true free-field acoustics in a small room!

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if my understanding is confused. However, I guess my primary concern and related question really comes down to this: Based on the above posted graphic of the shelf curve of the Alpha 65, will this shelf curve suffice for soffit mounting the Alpha 65s?
It's actually far more complex than you think, and in reality you are probably over-thinking the bass roll-off issue anyway (if that makes sense... it sort of sound contradictory...).

OK, here's the issue: It's a small room, so the room itself will load your speakers acoustically, in addition to the baffle step. So the actual response of your speakers in that room would NEVER be flat, no matter what you do to treat the room. There will always be bumps and dips in the REAL response of your speaker in your room. The response won't ever look like it does in the manual, since that test was done in a perfectly controlled anechoic free-field environment, which your room is not. When tested like that, the speaker really does show that response curve, but that's not real life. As soon as you put the speaker in a room, the room affects that curve in multiple ways, and it will not be flat.

The baffle step issue is just one of the many ways that the room will mess with your speakers response. There will be modal issues that produce a net bass increase across much of the low end, but there will also be specific peaks and dips in that at the modal frequencies, and there will also be dips caused by SBIR from the rear wall, and the side walls, and the ceiling, and the floor, plus comb filtering resulting from the combinations of these phase issues (since they repeat for all harmonics, all the way up the spectrum), plus mid-range "roughness" caused by your desk, DAW, or console, plus a few other nasties. Even the soffit itself won't cause the smooth, even 6 dB curve that you expect, rising nice and evenly from 274Hz to 685Hz: That curve will suffer from it's own artifacts, lobing, focusing, phase cancellations, and comb filtering. Theory is nice, but how does it work in practice? :)

Not to mention that your soffit itself is not a true "infinite baffle", and does have a defined width, so it will have a new baffle step response of its own....

So the single control on the back of your speaker is woefully inadequate for dealing with all of that. The best you can do is ti set it to -4dB for the first attempt, measure the room response with REW, and decide if it might be better to set it to -6, or maybe -2, or perhaps even back to zero...

Quote:
I'd certainly love to not have to fuss with an external parametric
:) Ahh, well then, you are doomed to uneven response in your room... :)

You might want to take a look at this thread, updated yesterday: viewtopic.php?f=3&t=20964 Pay special attention to the last couple of posts on that thread, but do read from the beginning...

Also take a look at this thread, to see what can be accomplished in a well designed room with great speakers, great treatment, and great digital tuning: viewtopic.php?f=2&t=20471 ...

Or this one too: viewtopic.php?f=1&t=20895 (new update coming soon on that one...)

Quote:
Thank you for any determinations y'all might come to with my little quandary here!
I would suggest that, instead of getting yourself bogged down in theory, just test the empty room using REW, build your soffits, put the speakers in, and do REW tests again, several times, with different settings on your roll-off control, then treat the room properly, as well as it possibly can be treated, and perhaps ask me about digital tuning, if you really want to get the room as good as it can be.


- Stuart -

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PostPosted: Fri Sep 01, 2017 3:02 am 
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Thank you, Stuart! I've learned a lot from you specifically on this forum. At one point, I went and read the entire saga of your first post regarding your studio build. It was particularly intriguing to watch the conversation about the degree tilt of monitors unravel! Following that conversation, and other related posts, along with the added construction complexity, convinced me to avoid tilting my soffits, which was really a welcome sigh of relief as my construction (and acoustic-science related) skills are minimal at best. Once I realized that tilting the speakers wouldn't physically remove my ears from the floor to ceiling mid-point, the light bulb above my head exploded. This is just one example of the help and power to make educated decisions that I've so gratefully received here in this magical mystery-land of a forum. Ladies and gentlemen, we are floating in cyberspace!

With apologies for lameness, I must admit that I don't currently have a way to take digital photographs and transform them into tendrils of the worldwide web. I never did buy a digital camera and my cell phone is so old that it is probably slowly giving me cancer. Of course, I could remedy this problem fairly inexpensively, but every dollar that evaporates from my bank account for another purpose is just one less piece of Owens Corning 703 or whatnot. Even this poor excuse doesn't excuse me from not posting diagrams of my build. I have just not taken the time to attain and learn the necessary software. These woeful inadequacies have been a big part of why I've stuck to just reading the forum and trying to answer all my questions that way. It isn't my intention to waste anyone's time. I was just getting really stuck understanding the specifics of the baffle step and outside-the-forum research proved almost entirely worthless in this capacity. I guess I was trying to limit my post to just that one baffle-step related question regarding the built-in shelf of the speaker so as to not be a source of frustration by my lack of visual detail. But, of course, limiting the world of acoustics to one specific is futile, as I know by now, so mark that as another "woeful inadequacy", I suppose :blah: Oh, this strange and wonderful world of sound! It baffles, excites, overjoys, crushes the heart, and elates the soul all at once, right?

Regarding the mounting of the speakers within the soffit, prepare yourself: your palm will undoubtedly fly to your forehead uncontrollably. The tragic comedy that has been my speaker selection, speaking of speakers, speaks to my sometimes contradictory behavior. I spend hours thinking, planning, reading, researching, and then I will overlook a hugely important detail moments before I slam my finger down on the Ebay "Buy It Now" button. If you're still with me, here we go: it's worth a chuckle, anyway.

Already having largely (not to mention prematurely, I now realize) constructed the soffits inspired by the rigid method (that is to say the box that would house the speaker was the only real framing left undone as I saved money for speakers and tried to decide on a model that would fit my modest budget) I finally got it together to buy the speakers. I compared a lot of speakers for specifications and dimensions, etc., and I decided on the Focal Alpha 65s. But somehow I never noticed that the sides were curved! I just never saw the slight curve in the pictures I saw online and never read about it anywhere in the specs. The spec sheet just had the dimensions of a rectangular cube, so that's what I assumed was going on. When they arrived at my door, I opened the box up. Nope. They were curved, and I was crestfallen.

To make a long story (yawn) somewhat short, not willing to deconstruct and start anew my soffit build, and terrified of the mental-health related medical bills that might stack up were I to succumb to deconstruction and rebuilding, I ended up (gulp) improvising. With the framing, shelf, etc. already in place assuming a rigid design, I decided that instead of building a box I would very tightly clamp down the speakers with canvas ratchet tie towns. It seemed to work surprisingly well, as the speaker is held quite tightly in place. I may or may not be delusional, but I decided that I could live with my mistake if need be. So, that's how they are mounted. I realize it isn't ideal, but as I've gathered (or at least inasmuch as my interpretation allows) from your comments on other posts, properly floating a speaker is quite complex and I'm not very confident in my ability (or a this point, I really must admit, patience) to pull it off.

Sidebar: It just occurred to me that it was very misleading of me, and indeed inappropriate, to infer in my original post that my soffit was built per John's design, as with my improvised alteration included, it is decidedly NOT relatable to John's design. I'm sorry for that oversight.

As far as the baffle step debacle, thank you very much for your valuable information regarding the behavior of the low shelf filter. I think for the first time I now understand how that 460 number derived from the F=4560/ width equation operates. To give myself a little credit, I had planned on doing extensive REW tests before I sealed those Focal puppies away for good in the soffits, as you suggested. I really just wasn't sure if I should even be messing with the built in shelf filter if it was at the wrong FO, and that perhaps my time and testing would be best spent with an external parametric set with the (I now understand to be center-point) frequency of the shelf at 460 hz. The answer, I'm assuming, is test extensively for all of the above scenarios! Try the built in shelf at all settings, as WELL as an external parametric. I look very much forward to reading the posts that you've suggested and will do so with vigor and renewed purpose. It's great to have a personal recommendation of specific threads to read as it is sometimes a head spinning process for me to hunt through the sea of acoustic wayfaring to find posts that relate to questions I have.

So, with more research to do, and MUCH room testing to do, I go forth with gratitude. I look forward to perhaps posting the results of my testing for the forum's help in interpreting and ensuing treatment plans.

Thanks so very much!


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PostPosted: Fri Sep 01, 2017 4:01 am 
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I have just not taken the time to attain and learn the necessary software.
Pencil and paper is pretty easy to learn! :) Of course, you'd then have to solve the "no camera" problem to get it to us...

How about your computer: most computers come with built-in cameras these days... Especially notebooks...

Quote:
It baffles, excites, overjoys, crushes the heart, and elates the soul all at once, right?
Very true! And it also costs twice as much as you ever thought it might, even in your worst nightmare...

Quote:
I saved money for speakers and tried to decide on a model that would fit my modest budget) I finally got it together to buy the speakers. I compared a lot of speakers for specifications and dimensions, etc., and I decided on the Focal Alpha 65s.
Those are pretty decent speakers, actually! :thu: Not great in the very low end, of course, but if you need that, then adding a sub (or better: two subs) would do the trick.

Quote:
But somehow I never noticed that the sides were curved!
So you met Murphy and encountered his law? :) It happens....

Quote:
With the framing, shelf, etc. already in place assuming a rigid design, I decided that instead of building a box I would very tightly clamp down the speakers with canvas ratchet tie towns.
Actually, Barefoot once recommended that method! I have used it in a couple of studios, but still with a box around the speakers. I don't do it that way any more, since floating works out much better, but it is an option. However, do leave yourself some form of access, to check the tightness of the straps. It might need tweaking over time, as the fabric stretches, or the mountings loosen, or the wood warps... or all three!

Quote:
as I've gathered (or at least inasmuch as my interpretation allows) from your comments on other posts, properly floating a speaker is quite complex
It is complex, yes, but several of my customers have done it on their own, carefully following the instructions. The hardest part is calculating the correct dimensions and locations of the rubber pads that surround the speaker, but once that is done, the rest is just careful, accurate carpentry.

Quote:
it was very misleading of me, and indeed inappropriate, to infer in my original post that my soffit was built per John's design, as with my improvised alteration included, it is decidedly NOT relatable to John's design.
Photos! It would be REALLY good to see how you did that, as now would be the time to correct any oversights!

You don't have any friends that have cameras? Not even one? Buy him a beer, and get him to take a bunch of shots for you, all over the studio, and upload them to your computer. It's REALLY hard to get a good grasp of where your room is right now in the process, without seeing pictures. I don't care if it is a hug mess in there, and very disorganized: what I'm interested in seeing is how it is built.
Quote:
The answer, I'm assuming, is test extensively for all of the above scenarios!
For adjusting the builtin controls, two or three tests will be more than enough. But if you want to take it further, with digital tuning, that can take a few more... for Studio 3 (one of the links above) we did very literally hundreds of tests, over many months, to get it that good. I think there were well over three hundred tests, by the time we finished.

Quote:
Try the built in shelf at all settings, as WELL as an external parametric.
When you read those threads, you'll see why the external parametric option is a really good "final touch", and can be used... ONLY AFTER the room is fully treated, acoustically. Trying to use it before, is going to get you tied in knots, and will make it worse, not better. Even though you might manage to get the frequency response curve flatter, and think you achieved something fantastic, in reality you will have screwed up something else, even worse, without realizing it... then you'll never be able to understand why your room curve looks so nice, yet the room doesn't sound good, and your mixes don't translate... :)

So, FIRST treat the room acoustically as well as possible, to get the parameters that you absolutely MUST have in order to be able to even THINK about using electronic tuning...

Quote:
I look very much forward to reading the posts that you've suggested
:thu:

Quote:
it is sometimes a head spinning process for me to hunt through the sea of acoustic wayfaring to find posts that relate to questions I have.
Try using the "search" feature of the forum. I realize it's not that great, and doesn't give you much control or many options, but it can help.

Quote:
I had planned on doing extensive REW tests
You could do one right now, exactly as the room is, and post the results! Here's how to use it:
viewtopic.php?f=3&t=21122


- Stuart -

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PostPosted: Sat Sep 02, 2017 1:44 am 
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I've read the recommended threads and am inspired! I think I'm ready to bite the bullet and find a way to get pictures up along with a full disclosure of all the painful pitfalls and room design inadequacies. There are a few which I could use good advice in dealing with. Also, I will soon get REW tests online according to the instructions on the posted link. It's a bit nerve wracking to expose what has been a solitary sojourn into design and construction! But that's what this place is for, right? :D No one should have to go through this kind of psychological torment alone, I suppose. Haha.

Shall I start a new thread when I am ready to post the above described? Or is it fine to just continue here on this one? Thank you!


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PostPosted: Sat Sep 02, 2017 10:37 am 
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find a way to get pictures up along with a full disclosure of all the painful pitfalls and room design inadequacies.
:thu:

Quote:
It's a bit nerve wracking to expose what has been a solitary sojourn into design and construction!
You are not alone! That's what the forum is all about. Many members have arrived here looking for help, and posted photos of humble studios that the poured many months of blood, sweat tears, and cash into. People here aren't all that interested in what a home studio looks like: this is not an interior decorating forum! It's a studio design forum, and what matters here isn't how your place looks, but how it sounds! Pro studios need to look great and sound great, but home studios mostly need to sound great. If you can get it to look cool as well, that's an extra, but acoustics comes first.

You may well have done some stuff wrong acoustically, and we'll help you fix that, but if you did some stuff wrong aesthetically, I'm not the right guy to help you improve on that.

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But that's what this place is for, right?
:thu: :yahoo:

Quote:
Shall I start a new thread when I am ready to post the above described? Or is it fine to just continue here on this one?
Just carry on right here. It's better to keep all your posts together in one thread, so you can find them all in the future.

- Stuart -

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PostPosted: Wed Sep 20, 2017 8:59 am 
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Hello again. I’ve finally taken digital photos of my project! I borrowed a friend’s phone. So, I figure I may as well “start over” with my post to include all relevant information (like I should have done in the first place!) So, here it goes.

The now fully constructed (except for any sound-treatment related construction) studio’s main purpose is a mixing room, but also must function as a rehearsal space for a five piece band (drums, two electric guitars, bass and keys); however, this secondary use is very much subordinate to the primary use as a mixing room. It is a “room within a room” construction located in a detached single-car garage on a concrete slab. The walls and ceiling are 2x4 timber framed. Two layers of 5/8 inch gypsum with 30 pound roofing felt sandwiched between make up the walls' and ceiling's surface area. All relevant seams have been caulked with Green Glue acoustic caulk.

I realize roofing felt is a sub-par material to help with decoupling the two pieces of gypsum (thought I have read, perhaps erroneously, that it is a workable substitute for mass loaded vinyl), and that it might have been better to use different thicknesses for the two gypsum layers, but as my budget for the entire studio was about $3500 (which I have already surpassed, of course) and I got a big discount on a pallet of 5/8” drywall, (the roofing felt was free!), that’s what I used. Fortunately, highly effective soundproofing wasn’t a major concern for me, and now that the construction is done, I’m satisfied that it is “soundproof enough” for my purposes (a drum kit being played in the studio is barely audible within 50 feet of the outside structure, which with respect to the distance of my nearest neighbors is ok. I live on the very edge of a residential to industrial area)

On to the studio’s dimensions. Once they are all listed, I’ll do my best to explain the peculiarities. Length: 18’ 2 9/16” Height: 8’ 4 5/8” for a length of 13’ 11 7/16” and then a height of 7’10 1/8” for the remaining 4’3 1/8” of room length. Width: 10’ 4 7/8” at the tall end, to 10 ‘ 7 13/16” at the short end.

And now for those peculiarities — some of which are the focus of questions I’d like to ask the forum. I’ll list these questions, and all others, at the end of the post, for organization’s sake, and for now just continue with information:

Peculiarity #1: The original structure has a pitched roof (9.5 ft on the high end to 8 ft on the low end over a distance of 19.5 ft. These numbers are approximate, as I’ve misplaced where I had the original dimensions of the inside of the existing structure). To make matters worse, the concrete slab is sloped so that it is one inch higher at the short end of the structure than it is at the tall end. During the planning stage, I wrestled with whether or not to attempt to follow the pitch of the roof with my build, but ultimately decided against it. Not only would my limited construction skills (I’ve done the whole thing by myself except the occasional help with heavy lifting, etc.) make that difficult, my research on this forum and elsewhere seemed to add up to “not worth it.” So, I decided to make the ceiling as tall as I could for as long as I could, and then make a “step down” for the last 4’3 1/8” of the length of the room. Here is what this “step-down” looks:

Attachment:
studio picture 13.jpg


Peculiarity # 2: The varying width has a twofold explanation. One: the outside structure, though solidly built and in fine condition, was not built particularly square. Two: I am just not a very good carpenter and I have nearly inadequate tools. I tried to keep things as square as I could, especially given that the external structure wasn’t square, but I was still bound by its realities and wanted to have as big an inner room as possible. I fell short far from perfect. (For anyone following this thread, you’ll notice that my being a bit of a hack is a commonality.)

The other peculiarities, or more accurately — problems — were a result of design flaws, arrived at through my attempts to solve certain other problems through the process. Two of the main four questions I have deal with these “me created” problems and the way in which I handled the ventilation for the studio.

I live on the north coast of California (only about 80 miles south of the Oregon border), a very temperate climate (it very rarely freezes and very rarely reaches 80 degrees F). So, my ventilation needs are probably not as extreme as other folks contend with. I am concerned mostly with just exchanging air within the room. I did some research and it seems that a 10” duct, and a 10” duct boost fan (which I have located outside the external structure in an attached tin shack), will work fine for my needs.

Having read somewhere that ducts should have at least a couple 90 degree turns in them to help with sound isolation, I went about installing flexible insulated ducting in the studio. The places to install the duct collars through the studio wall, and leading to the outside structure, was predestined because there were already vents cut into the existing structure — one at the southeast corner, and one at the northwest corner, both of which are located at the ends of the room lengthwise.

A quick aside: I should mention at this point that I do not own the garage in which the studio is built. I rent the garage (and the house it belongs to) from a good friend of mine who has graciously allowed me to build this studio but has asked that I minimize impact to the original structure. Soo…I didn’t want to cut different vent locations in to the existing structure, and didn’t have the room to spare to run ducts elsewhere to the inside from the outside. So, I installed the ducts where the outside vents were located, installing them into cavities surrounded in gypsum on the inside — two layers of 5/8 with roofing felt sandwiched within, like the rest of the walls. The intake, located in the right corner of the rear wall of the studio (as you face the front wall from the listening position) looks like this on the inside where the rectangular figure represents the wall that is straddling the corner (please excuse the incredibly poor hand drawings —they are pretty terrible — but hopefully, they are sufficient to give you an idea):

The dotted line is supposed to represent a flexible 10” duct curling inside the cavity from each duct opening:

Attachment:
studio picture 15.jpg


Here is a couple of photos of what it looks like on the outside:

Attachment:
studio picture 7.jpg


Attachment:
studio picture 9.jpg


It’s my understanding that symmetry isn’t as important on the rear wall of a mixing room, so I’m hoping I can get away without adding a similar corner straddling wall on the adjacent corner of the rear wall, and instead use that corner for bass treatment, as that seems more important than maintaining symmetry in the rear of the room. I’d welcome any ideas for how to minimize whatever impact that irregular corner may have on the response of the rear wall.

The next problem concerns the location of the outtake duct. It’s a long story as to why the actual duct opening ended up where it is. Aside from what I already explained about where it had to be located based on the existing conditions of the outside structure, its current, and unfortunately practically unchangeable location (the various layers of the soffit wall are glued together) , is, as you will see from the photo below, far from ideal. I had planned on using a different pair of speakers, and there were other considerations that have changed since I built the ventilation in. It doesn’t really matter now how it happened. It happened. And I would like to take the most reasonable action in fixing the problem, or at least minimize its negative impact. Here it is in all its palm-to-forehead-inducing glory:

Attachment:
studio picture 3.jpg


And here is a diagram showing the internal framing of the ventilations soffit and how it interacts with the speaker soffit. They are separate entities:

Attachment:
studio picture 16.jpg


As you can see, the speakers are installed tweeter facing down, as that seemed to place the speakers at a better practical height. The tweeter is 4 feet off the ground. Either orientation of the woofer seemed to be ok for the the ceiling-to-floor distance, but having the woofer higher up seems like it would help to minimize problems interacting with the as yet not installed mixing desk. Having the woofer underneath the tweeter seems like it would be difficult to keep the woofer from being obstructed by the desk and/or gear to the listening position. Unfortunately, this speaker orientation puts the speaker on a more direct vertical plane as the duct and might augment whatever problems the duct would create in the first place. I have a few thoughts on how to deal with the problem—some of which (I hope not all!) might be completely hare-brained. Hopefully, you have some light to shine on the best solution, or perhaps why I should take a sledgehammer to the whole thing.

Solution one: Install variable-depth slat resonators (one on each wall) that would serve as a sort of splayed wall to deal with reflections, as well as cover the duct hole and eliminate whatever, I assume, acoustic nightmare would occur having a giant hole in the soffit on one side of one speaker but not the other speaker. That slat resonator could be about 45 inches on its face (any longer and it would cover up a light switch, plus the door is only a few inches back from that light switch, anyway), creating a 53 degree angle to the speaker. It would be six feet tall. The 2’ 4 5/8” remaining space of room height could be divided between floor and ceiling and used for superchunks. It would look like this, only in real life instead of a 5 year old’s drawing:

Attachment:
studio picture 17.jpg


Solution two: Install splayed walls with an opening at the top and bottom. Behind these walls would be acoustic hangers.

Solution three: Cut an identical hole into the soffit wall on the right side of the right speaker. This doesn’t seem like a great solution, because on the left side the hole is the mouth of a duct that goes through 3 turns to the outside, while on the right it would just lead to a cavity (that though equal in volume to the cavity housing the coiled up duct) is stuffed with insulation. In this scenario, I would forgo splayed walls and just use absorption at the reflection points.

Solution four: The duct hole isn’t as big of a problem as I think and I should just go about installing absorption at both side wall reflection points as I had originally planned.

At this point, I should provide some information about the speaker soffits. They are framed with 2x4s in a very piecemeal, but I hope effective fashion. That is to say, the framing is connected to the studio walls via 2x4 blocks holding it out from, and also connecting it to, the wall. It’s kind of hard to explain. I wish I had taken pictures of the framing as I did it. Now that its done, it’s pretty impossible to get a good picture of what’s going on with it. I’ve tried and I can’t seem to draw it to make it translate at all. Probably because my drawing skills are awful. Sigh. I'm no construction, or acoustic, expert (obviously!) but the soffit framing seems quite sturdy to me. The speakers are strapped down onto the framing of the soffits themselves— like they were sitting on a window frame in a conventionally framed wall of a house (which is pretty much how I treated the speakers -- as the windows -- in the framing of a wall in a house) with blocks of 2x4 attached to the back of the bottom horizontal frame of the “window” and providing a platform for the speaker to sit on. The speakers are strapped down with ratchet tie downs, as I mentioned in my previous post, to the framing and attached blocks. The soffit walls are made of two layers of 5/8” gypsum, except for the middle third which substitutes the outermost layer of gypsum for a 5/8” layer of plywood to provide as nailing for the final layer of 3/4” thick 3 1/2” wide planks of spruce and ceder timbers. In the end, I ended up extending the height of those planks to go further than the nailing beneath, and just screwed into where I knew studs were, which worked fine. All layers are screwed and glued together except the planks, which are just screwed. I wanted to be able to re-use them someday down the line if I ever tear this place down and build another. It's a long story, but the wood has sentimental value to me, and is also, though not of amazing quality, not super cheap to have to buy again someday.

Reading through what I’ve just written regarding the soffits, I realize it’s pretty convoluted. Perhaps embarrassingly so. But, in some ways, it’s a moot point because at this stage I just don’t have the budget (or probably sanity) to redo the soffits. I’m pretty much stuck with what they are. That said, I (wishfully) think I’ve executed the concept pretty well considering my many shortcomings. I think the most important elements of mass and rigidity are present. Also, to my knowledge, the angles are correct, etc. So, hopefully, I’ve done an “okay enough” job!

Here is a close up of the “flush mount” of the speakers. Big surprise, it isn’t perfect! I it recessed maybe 1/8 inch. I guess this is due to the slight imperfections of all the materials used as compared to my measurements (which were also probably not perfect!). I’m thinking I can take a hand sander and feather out those edges so that they smoothly blend into the rest of the wall. It was very difficult to get that sucker seated in there that well. The speaker doesn’t actually touch the soffit wall. There is a tiny gap (it’s really hard to see in the pictures. The only way to see it is to be in the dark and shine a light through one side o the soffit wall) between the speakers and the wall. It’s only about 1 or 2 mm.

Attachment:
.jpg


And, here is a front shot of the soffits. The space between, I plan on filling with 703 or whatever material I end up getting.

Attachment:
Soffit front view.jpg


This is a shot of the cavity underneath the soffit to be used for hangers. The piece of plywood with the 4" hole you see on the right of the cavity is just the divider that separates the lower cavity from the speaker cavity. I stuffed the speaker cavity with insulation last night and haven't screwed the divider back into place yet so it is just leaning against the wall.

Attachment:
studio picture 6.jpg


Well, that’s about it for my pictorial. I hope it’s been helpful to have images along with full disclosure of all my mistakes along the way! I will be running REW tests on the room, I hope, later this week. I realize that some of the questions and concerns I have will possibly be better answered once that data is posted, but in the meantime, I’m sure you have some much valued advice based on these pictures and explanations alone. In conclusion, I will just list the main questions and concerns I have:

1. How can I minimize the impact of the ceiling height “stepping down”?
2. How can I minimize the impact of the air intake duct’s gypsum wall straddling the rear right corner of the room, and is it ok to not match it for symmetry in the rear left corner?
3. What is the best way to fix the problem created by the duct hole’s proximity to the speaker on the soffit wall

I have other questions regarding types and locations of treatment, but I realize that most of those questions are dependent upon the REW results, so I’ll save those for my next post. Thanks so much for reading the long saga of my mistake-riddled, humble attempts! This has been, and continues to be, one of the most challenging things I’ve ever done! I’m extremely thankful for any and all help that you so graciously provide . . .


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PostPosted: Mon Oct 02, 2017 4:26 am 
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Location: Eureka, CA USA
Hi, there. Well, I've completed the first round of baseline testing for the empty room. Hopefully, I've followed all the instructions adequately as explained in the link that Stuart included in his first reply to the original post. Please find the link below to view the results.

I've labeled each measurement to relay the necessary Left/Right information, as well as what the shelf adjustment control was set at on the Focal 65s for each measurement. I hope these are grouped and labeled logically so as to be easily understood. Just to make sure, I'll explain my labeling: the first "L", "R", or "LR" indicates Left, Right, or Left and Right, speakers. The number following those letters in parentheses indicates the numerical value (in db) of each of the four settings of the low shelf eq knob on the Focals: (0) = Flat; and then (-2) through (-6) is the negative db value of each setting. Following those indications, all the measurements have "BL" included, which is just an abbreviation for "Baseline" and then the words "Empty Room" follow on each measurement. Hope that clears up my labeling process. Here's the link to the dropbox file

https://www.dropbox.com/s/ffaeo6rstay7b ... .mdat?dl=0

My initial question regarding these tests, is, based on the measurements, which shelf setting on the Focals seem to be doing the best job in the room? I realize there must be all kinds of chaos going on in my empty room here! But as a starting point, it would be best to know what shelf setting to decide on, so that I can permanently seal in the speakers (i.e. hang the hangers in the below cavity, etc) I am a total newbie to REW, so I really have no idea how to interpret what I'm seeing here, but I had fun performing the tests and look forward to having a better understanding of the results.

Thanks so much!


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PostPosted: Mon Oct 02, 2017 9:57 am 
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Quote:
I've followed all the instructions adequately as explained in the link that Stuart included in his first reply to the original post.
It certainly looks like it! :thu: Congrats on the thorough calibration, and the very useful multiple sets of bass roll-off settings.

Quote:
I'll explain my labeling:
Nice! I like your system :)
Quote:
which shelf setting on the Focals seem to be doing the best job in the room?
I would go for -2 at present. That might change later, as you get treatment in, but for now -2 looks to be the best. It's curious, though: with the -2 setting, the low end didn't actually go down at all: the mids and highs went UP! That's strange. I didn't realize Focal had implemented their EQ like that. I mean, it' the same result in the end, but it does increase the overall level like that for the -2 setting. The others behave normally ( -4 and -6 act as expected). You didn't accidentally adjust anything in your signal chain, between the "0" and "-2" tests did you, by any chance?

Quote:
I realize there must be all kinds of chaos going on in my empty room here!
Yep! It looks pretty darn ugly in there! Must sound something like a chainsaw massacre inside a concrete pipe... :) But that's the entire point: it shows the room in it's true, raw, state, which helps greatly to plan the treatment.

Quote:
I am a total newbie to REW,
Not any more! :) You did the calibration and the testing correctly an accurately. Now you can install your first treatment devices, and test again, then compare the tests to see if they are working as expected, then add the next devices, and repeat...

- Stuart -

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PostPosted: Mon Oct 02, 2017 10:48 am 
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Location: Eureka, CA USA
Thanks for the reply, Stuart!

Great to hear that my calibration, etc., was correct. As far as I know, there shouldn't have been any change between the 0 and -2 tests. I did notice that the change seemed to be less drastic on the low end than with the other settings.

As far as the first treatment devices go, do you have any suggestions for the side wall first reflection point treatment, considering the air duct problem pictured in my previous post? I'd like to get a solid plan figured out for what to do on the sidewalls, as I expect that might involve construction of a slat wall and I'd like to get the more complicated stuff done first if possible (just helps with my morale, I guess :)

Also, any thoughts on the "stepped down" ceiling and how that might be best addressed?

Thank you!


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PostPosted: Wed Oct 04, 2017 7:21 am 
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Marc,

The best advice that I can give you is to download Sketchup and learn how to use it. The learning curve isn't that difficult and there are a lot of instructional videos available on youtube. https://www.sketchup.com/ the free version does everything you need it to. If you look at my studio and speaker design thread you will see everything I did along the way and had a chance to visualize it much better and to show others what I was doing so they could tell me how wrong I was (I turned out to be right though :D )

Everything that I built I did in Sketchup first.

If you want to see some examples you can check this thread out http://www.johnlsayers.com/phpBB2/viewtopic.php?f=12&t=16933

I also had to deal with some of those uneven places. In my control room, I just made a block of 703 in the corner to make it invisible to higher frequencies. The lower frequency wavelengths are large enough that they won't be affected by the corner.

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