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PostPosted: Tue Feb 12, 2019 10:35 pm 
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Location: Albany, NY
Yeah. It's amazing how well it retains heat, but sound it doesn't do anything.

I'll be super curious once I get everything in and set up how things sound outside. Luckily I'm on a corner oversized lot, so I have some good distance (for a city block anyway) from my neighbors.

Got my initial quote from GIK today. Looking at at least 2k for decent treatment, 3k for great.

Redoing the floor by pulling up the carpet and laying down rubber acoustic matting and then covering with wood is about 2k based on some pricing estimates and such from sites.

Unsure what adding the 16mm of drywall with green glue on the walls and rehanging the ceiling with sound isolation clips would cost.

Stuff adds up quick! And this is only for very basic level stuff.


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PostPosted: Fri Feb 15, 2019 8:23 pm 
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vutall wrote:
Yeah. It's amazing how well it retains heat, but sound it doesn't do anything.

I'll be super curious once I get everything in and set up how things sound outside. Luckily I'm on a corner oversized lot, so I have some good distance (for a city block anyway) from my neighbors.

Got my initial quote from GIK today. Looking at at least 2k for decent treatment, 3k for great.

Redoing the floor by pulling up the carpet and laying down rubber acoustic matting and then covering with wood is about 2k based on some pricing estimates and such from sites.

Unsure what adding the 16mm of drywall with green glue on the walls and rehanging the ceiling with sound isolation clips would cost.

Stuff adds up quick! And this is only for very basic level stuff.


Hi Vutall,

Studio costs can easily build up! Sound isolation and aircon being the biggest money sinks.

You are limited quite alot by not having the support for room in room, (without replacing the floor joists of course).

You can decouple to a certain degree with resilient devices though.
Resilient bars across the ceiling and walls and 2 layers of plasterboard with green glue will likely be the best bang for your buck in your situation. You could get 45dB-ish of isolation with the wall in this scenario.
Your floor will be a weak link. Second floor rooms will be hit the worst. Most of the noise will be flanking through the structure via the floor joists. There's no easy way around this.

You could spend half (or more) of your budget fixing the floor first, or consider resiliently lining every room on the second floor (ceiling and walls).

If I were you and have family in the house you don't want to disturb, I would give my wife/kids the attic and persuade my wife to let me have $20 - 25000 to build an outbuilding studio in the garden. Let her know it will increase the house value for when/if you move as you could market it as an airconditioned home office / home theater so you should recoup some costs.

Dan


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PostPosted: Sat Feb 16, 2019 5:52 am 
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That's not a bad idea Dan.

We certainly have the space for it in our yard. We also were thinking of tearing down the above ground pool, so maybe it could go in the same space.

Thanks for the heads up!


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PostPosted: Sat Feb 16, 2019 6:55 am 
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Cool :thu:

If you go ahead with an outbuilding, definitely get more advice from this forum, you'll need it! :wink:

You'll need to design the building from the ground up as a studio, so make sure you don't just go getting a builder in to build a "shell" first, because everything from dimensions to electrical outlets needs careful consideration and often cannot be built with the "standard" construction methods.

I'm in the middle of my own garden outbuilding studio so if you want to you can have a look through my build thread for ideas:
viewtopic.php?f=10&t=21269

Mine's been 2 years since I was at your stage though. If you have more time/money for contractors you could probably get it done quicker; maybe a year from design to completion.

Dan


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PostPosted: Mon Feb 18, 2019 1:01 pm 
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Thanks for the link, I've looked through it and like it!

If you don't mind me asking, what's your current running total of expenses so I can get an estimate?


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PostPosted: Tue Feb 19, 2019 10:21 am 
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I'm looking at £10 - £12K for the complete cost. I've done all the work myself and with family help. Only have now got contractors to connect electrics and A/C as these are legal requirements.
I'm about £5k in so far.

Dan


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PostPosted: Tue Feb 19, 2019 8:44 pm 
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That's pretty great! Not as bad as I thought, but still pretty pricey.

So, here is the layout and suggested panels from GIK. After shipping and such, looking just about $3,000 US.

Right side of the picture (What I call the rear of the room) is where I will have my desk and monitors.

Just wanted to double check with you all before I pull the trigger that this all looks good. GIK had one of their specialists work it all up for me, but I always like to double check with others too!

Finally, instead of tearing the carpet out right now, what about throwing down some of that cheap plastic office chair mats? It would give me a reflective surface instead of an absorbing one, and would be a good temporary platform to work on until I decide if I want to actually build out this room or build an outbuilding. At least in theory. Any ideas there?

Products used:
(rear wall)
2x Soffit Bass Trap, Range Limited. -one in each corner
2x Monster Bass Trap, Range Limited -one next to each Soffit


(Middle of wall)
2x 244 Bass Trap -One on each wall, Landscape orientation

(Rear Ceiling)
5x 242 Acoustic Panels

(Front Ceiling)
10x GridFusors

(Front Wall)
1x Soffit Bass Trap, Range Limited. -in corner
2x Monster Bass Trap, Scatter Plate -next to soffit


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PostPosted: Thu Feb 21, 2019 6:47 pm 
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vutall wrote:
That's pretty great! Not as bad as I thought, but still pretty pricey.

So, here is the layout and suggested panels from GIK. After shipping and such, looking just about $3,000 US.

Right side of the picture (What I call the rear of the room) is where I will have my desk and monitors.

Just wanted to double check with you all before I pull the trigger that this all looks good. GIK had one of their specialists work it all up for me, but I always like to double check with others too!

Finally, instead of tearing the carpet out right now, what about throwing down some of that cheap plastic office chair mats? It would give me a reflective surface instead of an absorbing one, and would be a good temporary platform to work on until I decide if I want to actually build out this room or build an outbuilding. At least in theory. Any ideas there?

Products used:
(rear wall)
2x Soffit Bass Trap, Range Limited. -one in each corner
2x Monster Bass Trap, Range Limited -one next to each Soffit


(Middle of wall)
2x 244 Bass Trap -One on each wall, Landscape orientation

(Rear Ceiling)
5x 242 Acoustic Panels

(Front Ceiling)
10x GridFusors

(Front Wall)
1x Soffit Bass Trap, Range Limited. -in corner
2x Monster Bass Trap, Scatter Plate -next to soffit


Hi Vutall,

I'm have a look more closely this evening, but at first glance I wouldn't think it's great to be honest. I think those "gridfusors" are hugely expensive for what they are and, being polystyrene, won't work well for diffussion, as well as being too close to your head to be useful.

Dan


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PostPosted: Fri Feb 22, 2019 2:30 am 
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are hugely expensive for what they are and, being polystyrene, won't work well for diffussion, as well as being too close to your head to be useful.
:thu:
Exactly. Numeric sequence diffusers need to be at least ten feet (3m) away from your head, and perhaps more if they are tuned low. How far away would those be from your head?

I'm wondering what the target decay time is for that room? That should be one of the factors that you are aiming to get under control. What are you aiming for there, and what will the treatment that you show in that image actually produce?

Considering the size of the room, I'm not fully convinced that the proposed treatment is going to get the acoustic response under control. It's a start, but likely not all that you will need. I have nothing against GIK: in fact, I like them, they do sell good products, and Glen is a respected member of this forum. But do take into account that if there's a company that sells only bananas, oranges and apples, it's unlikely that they'll advise you to eat eggs and lettuce as well, even if that's what you really need in your diet... I think you get the point. Companies promote their own products, obviously. If you need eggs in your diet but the grocer only sells bananas, oranges and apples, would he tell you to NOT buy his apples, and go somewhere else to buy eggs?


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PostPosted: Fri Feb 22, 2019 11:09 pm 
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The ceilings of the room are just a little under 8f high. When I'm at the console mixing the diffusors would be more than 10ft away due to angles.
OK, that's good, but what frequency ranges are those devices tuned for? D'Antonio and Cox (the guys who wrote the book on this type of diffuser, and did all the research to figure out how they work), suggest that ten feet is the minimum distance, but you might also need more distance if the device is tuned low. In different papers, they suggest at least three times the wavelength of the lowest scattering frequency (which is an octave below the tuned cutoff frequency), or seven times the low cutoff frequency. Those work out to be very similar, actually, but in both cases the distance is related to the tuning.

Here's why:
Attachment:
QRD-Diffusion-lobing--pattern-graph-SML-ENH.PNG


That's the typical type of sound field pattern you get from this type of diffuser. As you can see, close up to the diffuser, there is severe "lobing", where the phase, level, and direction of the sound field is broken up into discreet parts that you can hear as you move your ear around: the diffusion is NOT even at close distances. It needs quite a distance before the parts of that pattern merge together again into a true diffuse field. If your ears are too close to the device, then you are not hearing smooth diffusion sound. One ear might well be hearing something different than the other ear, and just moving your head a bit side-to-side or front-to-back could move one or both ears into a different region of the pattern. For mixing, you need to have a clear, smooth, diffuse, low-level sound field that arrives at your ears no less than about 20ms after the direct sound from the speakers already reached your ears. During that 20ms gap, there should be NO sound arriving at your ears, or as little as possible. Then the diffuse field arrives after about 20ms, and it arrives smoothly, evenly.

That's the issue here. That's part of the reason for the "minimum 10 feet" rule: because if it is ten feet behind you, then the "there-and-back" distance to your ears is 10+10feet=20 feet, which works out to about 20ms of time delay (sound travels roughly one foot every millisecond). In other words, the sound came out the speakers, hit your ears, carried on past your ears for at least 10ms, hit the diffuser, then came back again for another 10ms, and therefore your ears hear it 20ms after they heard the direct sound. If you are closer than ten feet, then the sound arrives too soon, and that potentially messes up your psycho-acoustic perception of the direct sound. And in addition to the above, if the wavelengths of the diffuse sound or scattered sound are very long, then even at ten feet they have not had enough distance to merge and smooth out, so your ears might be in "lobes" of different intensities, phases, and timing, which once again can potentially affect your perception of the direct sound field.

Quote:
Tracking vocals/non drum instruments, they would only be a few feet from the performers.
That probably isn't too much of an issue, and can even be beneficial. By carefully placing your instruments and mics, you can possibly take advantage of the not-fully-diffuse sound field, and in any case, for musicians, they don't need the "20ms delay" in any case! They are performing in a more live space, and do not need the strict control that you need for mixing in a control room.

Quote:
As far as target decay time goes, I honestly have no idea. I really don't know what I'm doing to be honest and was leaving the suggestions and science to the professionals haha.
The decay time refers to how sound dies away after the speaker or instrument stops producing it. In other words, if the speaker is playing a song, and you suddenly turn it off, how long after you flip the switch can you still hear the sound bouncing around in the room? There are tables and specifications and recommendations for that, for different situations. and that's where you are going to have a problem: you have one single room that you are trying to use for two very different acoustic purposes. The decay time for a control room absolutely needs to be in the range 150ms to about 350ms, depending on the size of the room, but for most home studios, a good goal is around 200 ms (there are equations for calculating the exact time, based on room dimensions). But for the musicians, and for tracking, you need a much longer decay time: maybe 500ms to even as high as 1800 ms, depending on genre, instruments, musicians, etc.

So, you have a major conflict on your hands! In order to mix well, you need 200 ms, but in order to track/rehearse/jam well, you need maybe 800 ms. You can't mix properly in a room with long decay times, because the room itself masks some of the sounds that you need to hear, and you can't play well in a room with a short decay time, because it sounds dull, lifeless, uninteresting...

That's the issue.

The guys at GIK have tried to divide your room into two areas to help a bit with this: one area is more live, reflective, diffuse, for performing, and the other area is a bit drier, but is is still only one room, and the two "ends" of the room are still connected.

What I would suggest, is that you consider building some variable acoustic devices, so you can change the response of the entire room to meet different situations. In other words, you have panels on the walls that you can flip, slide, or rotate to expose different types of treatment to the room: when you expose the absorptive part, that brings down the overall decay time and makes the room more "dry". When you expose the diffuse part to the room, that improves the decay time a little and adds some soft character to the room. And when you expose the purely reflective parts to the room you get a larger increase in decay times, and more specular reflections bouncing around. So you can adjust the response to be any way you want it.

Quote:
Need the rear half of the room to sound good for mixing, and the front half of the room to sound good for tracking.
I think you have that backwards! The front of the room is where the speakers are: it's the wall in FRONT of you as you sit at your mixing desk, mixing. In other words the wall that is closest to your head. The rear of the room is the part behind you as you are seated at the mixing desk. The rear wall is the one that is furthest away from your head as you are seated at the desk, mixing.

But anyway, the issue still remains: if you divide the room into two acoustic "zones", that doesn't solve the problem. As you are seated at the desk, trying to mix, you will still hear the longer uneven decay times form the rear end of the room, and they will potentially affect your ability to correctly perceive the direct sound from the speakers. And when your musicians are playing at the back of the room, the won't be getting the long decay time they need because that would have to come from the furthers wall (the front wall), but there won't be any reflections from that end of the room, because it is too dead! That's your dilemma. By trying to treat the room to do both things at once, you end up with a room that is lousy for both! It isn't good for mixing, because the far end is too live and uneven, and it isn't good for playing, because the far end is too dead and lifeless...

The solution is variable treatment. Eggs, not apples. :)

Quote:
unsure when my storage container with all my gear will get here. Hard to do a REQ reading without my stuff
As soon as it arrives, set up a minimal system in that room: just the speakers against the front wall, and the mic at the mix position, and your DAW on a small desk roughly where the real desk will go. Do your initial tests like that, in the empty room. It will sound terrible and look really bad on the graphs, but that's the entire point! It shows you all the ugly defects in the room, in all their terrifying splendor! :)

- Stuart -


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PostPosted: Sat Feb 23, 2019 3:23 am 
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It's certainly a lot to take in. I'll definitely get some recordings and data to post up here when I can.

In all honesty, the room itself is going to be used for mixing 90% of the time anyway, as Ill be using my synths and stuff without need of using mics. Most micing ill be doing is my wife for her classical/music theater stuff and some voice over narration/audiobooks she wants to do. Live music will be rare as I have to go find people who want to be recorded :P

I used front and rear as if the entrance to the room (behind me when sitting at the console) was the front and where my monitors (in front of me when sitting at the console) are as the rear of the room mostly for orientation purposes when looking at the diagram, but yeah, I probably should switch those terms around :D

Having panels I can switch out isn't a bad idea. But, wouldn't replacing the diffusers with the panels make the room over-treated?

It's a long room, a little over 15ft long, so no matter how I treat the portion behind me I'm going to have a long delay as sound returns to me since it's going to be at least a distance of 10ft. The only way to fix that (I'm assuming) would be to reposition my mixing desk and then that would effectively mean I had no space to track.


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PostPosted: Sat Feb 23, 2019 7:48 am 
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In all honesty, the room itself is going to be used for mixing 90% of the time anyway,
Then it would probably be a good idea to set it up for mixing! Maybe have some reflective panels that can be opened, slid, or rotated in front of the absorption, if you need longer decay times for music, but they would normally be in the "absorption" position.

Quote:
Ill be using my synths and stuff without need of using mics. Most micing ill be doing is my wife for her classical/music theater stuff and some voice over narration/audiobooks she wants to do.
It is quite feasible to track vocals in a control room environment. Vocals and some instruments usually sound very good when recorded in the control room, with typical control room decay times.

Quote:
But, wouldn't replacing the diffusers with the panels make the room over-treated?
Not necessarily. I would ask the guys at GIK what there estimate is for the decay times in the room, at the mix position, with that treatment. The ceiling in a control room usually needs a lot of treatment, and most of that is usually bass trapping, or at least some form of absorption, to reduce flutter echo and control modes in the vertical direction.

Have you checked your room ratio and other information in detail? Use one of these Room Ratio calculators for that:

http://www.bobgolds.com/Mode/RoomModes.htm

http://amroc.andymel.eu/

Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful, especially the Bob Golds one: it calculates how much absorption you would need to make that room meet the specs for a critical listening room of that size.

Quote:
It's a long room, a little over 15ft long,
Excellent! Although "long" is relative... Acoustically, it's not that long. The wavelength of a 20 Hz tone (the lowest that human can hear), is about 56 feet, so that wavelength would not even fit into your room: thus, you have no room modes at such low frequencies. Going up the scale a bit, a 6-string bass can get down to about 33 Hz, so the wavelength there is about 34 feet: still doesn't fit. Going higher still, a kick drum fundamental is often around 80 Hz, where the wavelength is about 14 feet, so you that would be the longest wave that would actually "fit" into your room. So "long" is relative....

But longer is better! In general, you want a long room, such that the diffuse field is delayed as long as possible. I did mention that 20ms is the SHORTEST gap that is useful: 30 ms is better. This is sometimes called the "Haas time" and refers to a psycho-acoustic effect known as the "precedence effect" or the "Haas effect", named after the scientist who discovered and explained it. It's rather complex, and is related to the way our ears and brains work to perceive sound, but basically if a sound and a reflection of that same sound arrive within the "Haas time" (ie, less than about 20ms), then your ear and brain cannot differentiate between the direct sound and the reflection: they are too close in time for you to perceive them as two separate sounds. Instead, your ear and brain try to interpret that as though it were a spatial reference clue: your brain ends up thinking that the sound came from a different direction from where it actually came, and that the frequency response was actually different from what it really was. It's not a bad effect, if you are just listening to music for pleasure, because it adds to the "spaciousness" or "airiness" of the music: the music seems to "surround" you more, and can be quite pleasant. Which is why concert halls tend to emphasize such "early reflections" for the audience, as it makes the music sound better, more enveloping, warmer, mellower nicer. But that's no good for a control room! In a control room, you do NOT want the music to sound "better" or "wider" or "more surrounding"! Not at all. You want it to sound exactly like it really is, nothing added, nothing removed. You want to hear ONLY the direct sound from the speakers as you sit and mix. You do not want the room to change that in any way: You want to hear the truth, with no "coloration". Therefore, you do NOT want to have any reflections at all arriving at your ears inside the Haas time, because your brain misinterprets them, fooling you into hearing things that are not really there. So you'd think that it would be better to have no reflections at all, ever! Just let the sound go past, and never come back.... Well, that doesn't sound good either. A totally dead room like that, which just "sucks up" all the sound is not so pleasant. There are such rooms, and they are called "anechoic chambers", because they kill all sounds, all echos, all reflections: nothing comes back from the walls, floor, and ceiling. Very silent. Very dead. And very unpleasant to work in for long. It just does not sound natural: Your brain WANTS some acoustic clues about the size of the room, in order to correctly interpret what it is hearing. Therefore, the current best control room designs do return that diffuse field after about 20ms, or maybe 30 ms, or maybe even 50 ms in a large room, and that gives your brain all the clues it needs to figure out the room that it is in, and correctly interpret the acoustic "signature". As long as the "gap" is at least 20ms long, and up to about 50ms, your brain is happy: the room sounds natural, neutral, open, neither too dead nor too live, and you get to hear only the pure, clean, unmodified sound exactly as it came out the speakers, not colored in any way by the room, or by these subtle psych-acoustic effects.

So, to summarize: the direct sounds comes out your speakers, hits your ears, then carries on past you, where it eventually hits the rear wall, rear side walls, rear ceiling, and is reflected back to your ears. So for every sound that comes out the speaker, you hear the direct sound, then silence, then the reflected field coming back from the rear wall. That "silence" is sometimes called the "initial time delay gap" or ITDG, and the sound that follows it 20ms later, is often referred to as "terminating" the ITDG: it ends the silence. Of course, the "silence" is not really silent at all, since other sounds that left the speaker earlier are already getting back to your ears, but your ears and brain are really smart, and can figure it all out... as long as there's a 20ms gap for EACH sound.

Now, you might think that you could just put a big piece of wood across the back of the entire room, 10 feet behind your head, and you'd have a wonderful "termination" to the ITDG. You would, but it would be way too strong! It would be overpowering: the reflection would be nearly as strong as the direct sound, and it would be "specular", coming back at you from a very specific direction... and that would once again mess up your ability to perceive the real sound from the speakers. Those powerful reflections arriving after 20 ms would tend to mask similar direct sounds just arriving at your ears from the speakers, once again messing with your perception.

So, the sound field that comes back at you from behind 20ms (or more) after the direct sound, also has to be at least 20 dB lower than than the direct sound, and it has to be diffuse, not specular. In most control rooms, that is achieved with a combination of acoustically absorptive surfaces (to reduce the level by 20 dB), acoustically reflective surfaces (to send a little bit of the sound directly back, but not much) and acoustically diffusive surfaces, to break up the sound into a diffuse field.

So, the basic goal is that there is an ITDG of 20ms or more, then you get the diffuse sound coming back, 20 dB lower in level, then the diffuse field dies away slowly, until you can't hear it any more after the full decay time for the room. So if the decay time for your room was 250 ms, then you would hear: DIRECT SOUND! [silent itdg 20ms] .... TERMINATIOnnnnnnnnn..and..difusse---field---d.ec..ay....ing------slo--w----ly---for--230ms----more----.....

Now, if your room is bigger, then the ITDG can be longer: 30ms is good too! And you can also have a slightly lower level, such as maybe 25 dB down, especially if he room is large, ... as long as you still have an overall decay time that isn't too short for the size of the room.

The problem comes for small rooms, where there just isn't enough space to the rear wall to have a 20ms ITDG... Small rooms are a problem. You have to get very creative to deal with that, and get good results.

So, anyway: your room, at 15 feet long, is a decent size. Your head will be about one-third of that distance away from the front wall (about 5 feet), and therefore there will be about 10 feet between your head and the rear wall, which is fine for the 20ms ITDG.

Quote:
so no matter how I treat the portion behind me I'm going to have a long delay as sound returns to me since it's going to be at least a distance of 10ft.
And that's a GOOD thing! Longer is better. Provided that it doesn't get VERY long.... 15 feet is about the minimum length to be able to get this effect easily. Longer would be better, but 15 feet is OK.

Quote:
The only way to fix that (I'm assuming) would be to reposition my mixing desk and then that would effectively mean I had no space to track.
There's a theoretical ideal position for your head in the room, that supposedly minimizes modal issues: it places your head at spot where the modal issues are least intense. That spot is 38% of the room length. However! That's just the THEORETICAL "best" point: in reality, many engineers prefer a spot a little closer to the front wall, at maybe 35-30% of room length. So that's where your head will be, and your desk will be set up in front of that spot, at a comfortable location where you can reach everything easily.

There's a lot of "rules of thumb" for setting up a room, but it helps to understand WHY those rules are there.

But of course, rules can be broken too! :) It is possible to set up a room that defies some of the rules, and still get success. Studio designers often have to do that, for various reasons. But for first-time studio builders, it's better to follow those "rules", or at least use them as guidelines, to set up the layout correctly.


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PostPosted: Sat Feb 23, 2019 9:24 am 
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Thanks for the detailed write up! Lots of things to think about here! Appreciate learning the science a bit too.

Edit:

I am having a little trouble understanding the calculator, could you interpret them for me? Here are the results:

Computed Information:
Room Dimensions: Length=15.67 ft, Width=11.83 ft, Height=7.42 ft
Room Ratio: 1 : 1.59 : 2.11
R. Walker BBC 1996:
- 1.1w / h < l / h < ((4.5w / h) - 4): Pass
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Pass
Nearest Known Ratio:
- "7) M. M. Louden: 1971: 3rd best ratio" 1 : 1.5 : 2.1
RT60 (IEC/AEC N 12-A standard): 230 ms
- ±50ms from 200Hz to 3.5kHz = 180 to 280ms
- ±100ms above 3.5kHz = 130 to 330ms
- <+300ms at 63hz = 530ms
- 300<RT60<600ms
RT60 (ITU/EBU Control Room Recommended): 182 ms
- ±50ms from 200Hz to 4kHz = 132 to 232ms
- <+300ms at 63hz = 482ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 369 sabins
Volume: 1375 ft^3
Surface Area Total: 776 ft^2
Surface Area Floor: 185 ft^2
Surface Area Ceiling+Floor: 370 ft^2
Surface Area Front Wall: 87 ft^2
Surface Area Front and Rear Wall: 174 ft^2
Surface Area Left Wall: 116 ft^2
Surface Area Left and Right Wall: 232 ft^2
Surface Area 4 Walls: 406 ft^2
Surface Area 4 Walls + floor: 591 ft^2
(sabins - front wall - carpet) / Left+Right+Rear wall: 30 %
(sabins - front wall) / Left+Right+Rear wall: 88 %
Schroeder Fc: 129hz
Frequency Regions:
- No modal boost: 1hz to 36hz
- Room Modes dominate: 36hz to 129hz
- Diffraction and Diffusion dominate: 129hz to 516hz
- Specular reflections and ray accoustics prevail: 516hz to 20000hz
Count (36-230hz) : Axials=13, Tangentials=54, Obliques=72
Count (36-100hz) : Axials=5, Tangentials=4, Obliques=1
Critical Distance (direct = reverberant field): 12.20ft


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PostPosted: Sat Feb 23, 2019 1:43 pm 
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Location: Santiago, Chile
Quote:
I am having a little trouble understanding the calculator, could you interpret them for me?
Sure!

The parts towards the bottom are fairly self-explanatory, about the surface areas of various parts of the room, and the volume, so I won't comment in detail on those, but the other parts are interesting.

Quote:
Room Ratio: 1 : 1.59 : 2.11

The "Room Ratio" tells you what the relative relationship is between the dimensions, where the height is considered to be 1 "unit". So your room is 2.11 times longer than it is high, and 1.59 times wider than it is high. Useful information, because there are "good" ratios and "bad" ratios....

Quote:
R. Walker BBC 1996:

Refers to a study released by the BBC in 1996, that lays out how they determined if a room would be any good as a control room, by looking at the relationship between room dimensions. They came up with many ways of looking at it, and in the end narrowed it down to three "critical" tests, which are:...

Quote:
- 1.1w / h < l / h < ((4.5w / h) - 4): Pass
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Pass
The first one tests that the "length times 1.2 divided by height" is less than "4.5 times the width divided by the height, less 4", as that was found to represent a good acoustic relationship: your room passes that test.
The second one tests that both the length and the width are less than three times the height. Because very long narrow rooms, and very short fat rooms are both bad: your room passes that test.
The final test is all about modal response: It checks that, for example, the width is not the same as the height, and the length is not exactly twice the width, and similar things. Those types of direct relationships always spell trouble, in terms of modal response. The calculator does that by checking if any of the dimensions is within 5% of any other dimension, or of a multiple of that dimension. So if your room is ten feet wide, it must be either less that 9.5 feet long, or more than 10.5 feet long. Etc. It checks all three dimensions in relation to each other, because if they are too close then you are going to have low frequency modes that are not spread around evenly, and in fact are prety much on top of each other: a bad situation. your room passes that test.

So your room passes all three BBC critical tests!! :thu: Your room would be approved by the BBC as a potential control room.

Quote:
Nearest Known Ratio:
- "7) M. M. Louden: 1971: 3rd best ratio" 1 : 1.5 : 2.1
Remember I said there were good ratios and bad ratios? Once again, this is all about room modes. Some very smart scientists have identified many good ratios over the years, and those are recognized with the name of the scientist, and which one it is on his list. It turns out that your ratio is close to one of the ratios identified by Louden, and in fact it is is third best ratio. That also turns out to be #7 on the list of really good ratios, as determined by the late, great Eric Desart, a very highly respected acoustician, among the best in the world, who unfortunately passed away a little more than a year ago. He was a member of this forum, and is still missed by many of us. So your ratio is close to Eric's number 7, which is Louden's 3rd best. It's a good ratio.

Quote:
RT60 (IEC/AEC N 12-A standard): 230 ms
According to the IEC and AEC standard (N-12 A), the correct decay time for your room, is 230 ms. That's one of several methods for calculating decay times. But it is also broken down further as:

Quote:
- ±50ms from 200Hz to 3.5kHz = 180 to 280ms
- ±100ms above 3.5kHz = 130 to 330ms
- <+300ms at 63hz = 530ms
- 300<RT60<600ms
Meaning that the decay times for all frequencies between 200 Hz and 3.5 kHz should be in the range 180 ms to 280 ms, but that adjacent frequency bands should not differ by more than 50 ms. This is not a characteristic of your room as it is: it is a goal that you have to aim for. Build that in to your acoustic design. You have to provide the right treatment to obtain that goal.
For frequencies higher than 3.5 kHz, the decay time can vary through a larger range, 130 ms to 330 ms, but adjacent bands must not differ by more than 100 ms.
For lower frequencies, you can go up 530 ms at 63 Hz, but once again, adjacent bands not more than 300 ms apart.

Quote:
RT60 (ITU/EBU Control Room Recommended): 182 ms
- ±50ms from 200Hz to 4kHz = 132 to 232ms
- <+300ms at 63hz = 482ms
- 200<RT60<400ms

On the other hand, if you use ITU/EBU specification for control rooms (rather than the IEC/AEC one), then the decay time for your room should be 182ms, in the range 132 to 232 for frequencies between 200 Hz and 4 kHz, etc.

Two different ways of figuring decay times, but both tell you simialr things: you need about 200 ms decay time across the entire spectrum, with adjacent bands not varying by more than 50ms, but the top and bottom ends are a bit more relaxed and you can go out to about 500 ms in the low end, and 400 ms in the high end.

Quote:
Absorbtion to achieve ITU RT60: 369 sabins
If you decide that you want to achieve what the ITU calculations tell you, then you would need to have a total of 369 sabins of absorption in your room. The "sabin" is the unit that measures acoustic absorption (like the mile measures distance, and the second measures time). One sabin is defined as the same absorption that you would get from having an empty hole in your wall that measures one square foot. In other words, sound goes out that hole and never comes back. So one sabin is one square foot of perfect absorption. Thus, you would need 369 square feet of porous absorber in your room, if you wanted to get a decay time of 182 ms, as calculated for your room using the ITU/EBU method.

Short summary: you need about 350 square feet of absorber in your room, to get it under control. It needs to be spread around fairly evenly, but concentrated where it is needed most, and with varying thickness and coefficients of absorption, as needed for each location.

Quote:
Schroeder Fc: 129hz
A very useful but little-understood characteristic, named after the great acoustician Manfred Schroeder. That number tells you something very important. Below that frequency, room modes are the dominant acoustic feature of your room (assuming that you treated it with 360 sabins of absorption), and above that frequency the sound field is more even and smooth, with diffraction and diffusion being the dominant characteristics. It's complex to explain, but basically it tells you that most of your acoustic problems in that room will be below 129 Hz, so you will need major bass trapping that concentrates on that frequency range. You will need less and less absorption as you go higher up the spectrum, and more and more absorption/diffusion in the mid range, up to about 500 Hz, then diffusion/reflection above that. So your absorbers need to be selective, able to absorb/not absorb some frequencies, depending on where they are in the room.

Quote:
Count (36-230hz) : Axials=13, Tangentials=54, Obliques=72
Count (36-100hz) : Axials=5, Tangentials=4, Obliques=1
This is all about room modes. Below 100 Hz you have a total of only ten modes, of which 5 are axial, 4 are tangential, and 1 is oblique. If you look at a larger frequency range, up to 230 Hz, then there's 139 modes in that range, of which 13 are axial, 54 are tangential, and 72 are oblique. That tells you that axial modes are your biggest problem below 100 Hz, and that tangentials and obliques are more problematic above 100 Hz, but since they are lower level than axials, you still need to be worried about the axials mainly.

Quote:
Critical Distance (direct = reverberant field): 12.20ft
If you were to set up your sound system to play pink noise at constant volume, then hold your sound level meter right in front of the speaker and start walking backwards, obviously the sound level would decrease as you move away from the speaker, because you are in the direct field from the speaker. But as you move further and further away, you start getting less and less direct sound, and more and more diffuse sound, a you get further in the reverberant field. At some point, you will see that the level on your meter does not drop any more as you move further away: it stays constant, no matter how far away you go, because you are full in the reverberant field now, not the direct field. If you start walking back towards the speaker, the spot were the level rises by 3dB on your meter is the "critical distance": it defines the point where the direct field and the reverberant field are equal. Beyond that, you are in the "far field" and get no direct sound. Closer than that and you are in the "near field", getting more direct sound than reverberant sound.

In your case, with the room treated for ITU/EBU, your critical distance would be at 12.2 feet away from the speakers. Beyond that, it is all reverberate sound, and it overwhelms the direct sound.

Cliff notes summary: Your room is a good candidate for a control room, and has the potential to be excellent acoustically, if you treat it in the manner needed to get the response suggest by the ITU/EBU specifications, which implies about 350 ft2 of absorption, suitably placed around the room, with the spaces between the absorbers being left reflective, or perhaps diffusive in some manner where possible, and the characteristics of each absorber being chosen such that it absorbs the problematic frequencies at each location, while not absorbing frequencies that don't need absorbing.

Whew!

- Stuart -

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PostPosted: Sat Feb 23, 2019 5:04 pm 
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Joined: Wed Feb 06, 2019 1:11 pm
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Location: Albany, NY
That is a lot to take in. I was right in a lot of my guests, but a lot of the finer points/details I had no clue about, so thank you so much for filling me in!

Also, I'm going to shoot you a private message, so when you get a chance please check those!


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