I figured something like that would have to be the case. There's no way you can treat modal issues with a bunch of thin wood planks poking out from the walls, and a bit of insulation behind it. It seems there's a LOT of stuff that the "paper" isn't saying.... Hmmmm...I did a bit more digging and apparently, panel absorbers are used behind some sections instead of the porous absorption to treat modal issues
I'm not surprised!But I am surprised by how few rooms have been built with the design.
When folks plan to spend a lot of money building their studio, they usually do the research, like you are doing, and come to the same conclusions you are arriving at: this is not a viable method for treating a control room.But curiously, it has no actual acoustic measurements of the final outcome.... I wonder why?... and some more detailed pics of the construction process
If you look around the forum, most members here are not scared to show their results... They do REW tests, and happily post the graphs that show how their rooms REALLY work. As a studio designer, I'm also not scared to show the results I get from rooms I have designed (either completely or partly). You can see that on many threads here on the forum (Steve's thread, Studio Three Productions, and many others). When you have a design concept that works, and has been proven to work, then why would you NOT want to show the results? It makes you wonder why there's no published final results on either the Mk1 or Mk2 versions....
It can be done, yes! But don't forget that your room size sets the limit for what you can achieve: the dimensions put limits on room response. There's no way you can make a broom closet sound like a concert hall!Providing I can design my room to work for both my live/tracking purposes and mixing (mixing's still secondary)
OK, so that''s two extremes, but you get the point. The bigger a room is, the better it can sound, and the less treatment it will need to get there.Well, yes, that "calculator" does indeed give you a set of wood plank sizes... but there is no indication at all of how it PERFORMS!! In other words, no details of what the diffusion and scattering coefficients are, nor the lobing, nor the power spectrum, nor the spatial, timing, or phase changes, nor what the cut-off frequencies or cut-off angles are... nor anything at all, in fact! In fat, all that calculator does is to generate a random sequence of numbers that you can use to make different plank sizes, but with no regard to acoustic results whatsoever. On the other hand, if you use a generator for a Schroeder diffuser, or a Skyline diffuser, based on QRD or PRD principles, then you DO get all of that information, so you do know how it will work (QRDude, for example, does that, even though it is very simple).I built the design on a trial of AFMG Reflex and it does seem to have good diffusion and scattering. I used this online calculator to generate the slat depth .
Also, something I should have mentioned before but it slipped my mind: if you leave air gaps between the wood planks, then it is NOT a diffuser! Sorry: it just isn't. It will scatter, yes, but it will NOT diffuse. No way. Anybody who claims the contrary does not understand how diffusion works. The wells MUST have a solid bottom, and be sealed air-tight to function at all. In order for diffusion to work, the incoming wave does two things: first, it bounces off the bottom of the well and gets sent back out at a different angle and with a different timing and phase (think about it.. it HAS to do that), and second it sets up resonance in the well if the incoming wave happens to be in the correct frequency range, because it is a sealed well. If there is no bottom to the well, just empty air, then NEITHER of those can happen! Hence, it is not a diffuser. It is just a "scatterer". It would only work as a diffuser for the case where the planks are stuck tightly to each other, sealed, with no air gaps. In that case, it is something like a Schroeder diffuser (1D), but it still would not work like a true Schroeder diffuser, because it does not follow a mathematically sound numeric sequence that produces smooth diffusion and flat power spectrum! It produces RANDOM diffusion in that case, which is NOT desirable, because it is not even, smooth, balanced, or "diffuse". They can call it whatever they like, but it simply is not a diffuser if the wells have no bottom. Wood planks separated by air spaces are not diffusers. Plain and simple.
If you want to understand this yourself, then get the book "Acoustic Absorbers and Diffusers: Theory, Design and Application" by Cox and D'Antonio. It is THE definitive book on the subject. Highly recommended. These two guys basically created the entire industry when they defined the theory of what diffusion is, building on the original work of Manfred Schroeder. The math can get a little heavy in places, but the descriptions and examples are crystal clear.
I'm not sure that they want to!It would be very beneficial if the Author did test it in a lab. I'm not sure of the cost of those though!
Getting it tested might reveal that the emperor has no clothes... Looks good to me! That should work just fine, and would be good for low frequencies in generalLooking at what's available in my area I'm probably going to use this: Superglass Superwall 36. It is a glass wool and has a density of around 20kg/m3, giving approx 9000 Rayls for GFR,
Yep. Although such a thin air gap doesn't really make much difference. You could get slightly better performance by re-arranging that, as 50mm up front, 15mm air gap, then 100mm up against the wall. Not a huge change, but worthwhile. Same materials in a better relationship.9000 Rayls with a 150mm depth and 15mm air gap has pretty good good absorption
That's correct, yes. That is what I'm saying: a "diffuse" reflection by itself guarantees nothing. Firstly, it isn't really diffuse (see below) and secondly any specular reflection that arrives within that window (which is nominally 20ms, but can be longer... it varies with frequency, and from person to person.. probably more like 30 ms) will cause psycho-acoustic effects, such as messing up your ability to accurately determine directionality, and messing up your perception of frequency response. (Those two are actually opposite sides of the same coin: they go together, because of the way your ear and brain work).Hmm... I hadn't thought about the Haas time here. I was under the impression that a diffuse reflection was sufficiently reduced in intensity to negate this.
Are you saying that even if a reflection is reduced by 20db or even 30db below the direct sound it wouldn't be sufficient if within 20ms?
The entire point of the 20db/20ms thing is that it is the ITDG (or ISDG if you prefer) that lasts for 20ms. That's pat of the RFZ spec: According to that, during the first 20 ms there must be NO reflections at all, at any level, then AFTER that delay the diffuse sound field is supposed to arrive, at least 20 dB down. Which is why it is impossible to implement a true RFZ design in a small room: the rear wall has to be at least 10 feet behind the mix position, implying that the room has to be at least 14 feet long, but that applies to the surface of the acoustic treatment on the rear wall, and the location of the soffits on the front wall, so for realistic speakers, soffits, and rear wall treatment, the room needs to be at least 20 feet long (6m).
Plus, there's another issue: Notice the the "diffuse field" is supposed to arrive after that 20ms delay... but in a small room, there is no diffuse field! A room has to be very large before there can be a true statistical diffuse reverberant field. In acoustics, "diffuse reverberant field" means a sound field where, for any location in the room, there is an equal probability of receiving sounds coming from all directions at the same level. So the chance of that -20dB signal hitting your ears should be the same for sounds arriving from the rear of the room, or the front, or the floor, or the ceiling, or the side wall, or any other direction. But with a typical small control room, that is not possible: the sound will reach your ears from a specific direction first, that you can easily identify: the initial reflections after the ITDG will come from behind you, after bouncing off the rear wall, and BEFORE they can hit the front wall, side wall, ceiling, floor, etc. It takes a long time to establish a true diffuse reverberant field, since sound needs to bounce around through many, many reflections, all over the place, before the field can be even and smooth in all directions.
In other words, it is impossible to have a true diffuse reverberant field in a small room, and therefore it is impossible to have a true RFZ in a small room. It has to be large. Very large. In a small room, you only get a true diffuse reverberant field about an octave above the Schroeder frequency for the room.
In other words, even though your room is a decent size, it still will not have a true reverberant field in it. Very few control rooms do, so don't feel sad about that! Your situation is better than most...
So, the best you an do is to design the room so that first sounds arriving from the rear wall are as diffuse as possible, which implies NO specular reflections at all, and true diffusion (not just scattering) that is as smooth, even, and balanced as possible. That's why the rear of your room needs to be as absorptive as you can make it, especially for low frequencies since they are never going to be diffuse, no matter what you do, and also you have the issue of modes, and SBIR related to the rear wall.
This is why I would not put such large areas of solid, hard, reflective surfaces at the rear of the room.
SBIR from the rear wall is the biggest single problem in most small rooms. Period. That first phase-cancellation null is going to be at a very low frequency, and it defines the acoustic "signature" of the entire spectrum, since this is a comb-filter issue, and it starts very, very low. A hard, solid, flat surface on the rear wall will create a huge SBIR problem. There are two ways to attack that: 1) Deep absorption. Very deep (hangers plus other stuff has a decent effect), and: 2) large broken/angled geometric surfaces, to help "break up" the wave a bit. There's nothing else you can do: you cannot diffuse low frequency sound, because the diffuser that you'd need would be larger than the entire room, and would have huge wells, many feet deep, and many feet wide. You can't use a resonator to absorb it because SBIR is not a resonant issue in the first place. You can't diffract it, because any device large enough to do that would be bigger than the room. You can only absorb it to a certain extent, and do some low-level "scattering" by putting very large, solid, heavy objects in the way, with large geometric shapes (for example: a "poly-slat" device covers the entire rear wall, from corner to corner and even then is only about one quarter wavelength of the lowest issues...).Can you explain a bit more about how it would affect SBIR?
Helmholtz resonators have zero effect on SBIR. It is not a resonant problem, so there is nothing to "resonate". SBIR is purely phase cancellation, so resonant devices have no effect on it. It does not respond to panel traps, membrane traps, slot walls, perf panel, or any other form of resonant device, since they are all based on there being some type of "ringing" or resonance. With SBIR, there is none.If this diffuser allows low bass frequencies to pass through it into the 200mm of insulation behind it, and also has a variable helmholtz effect. This surely would be as effective, if not more effective, against low frequencies than just 200mm of insulation alone?
Also, 200mm is nothing at all for SBIR. Typical frequencies are way down in the 20, 30, 40, 50 Hz range, where wavelengths are many METERS long. For example, if you have an SBIR issue at 45 Hz, the wavelength is 7.6m. You need a thickness of at least 7% of the wavelength to get a useful effect for normally-incident sound, so 532mm would be just enough to have some effect. If you look at Steve's room, there's 510mm of depth to his rear acoustic treatment. In the case I mentioned, the front face of the rear wall treatment (what you see) is 989mm from the rear corner. Even the poly-slat walls are 265mm deep at the thickest part of the curve. Rear wall treatment has to be DEEP. VERY deep.
So no, a few thin vertical planks with 200mm of insulation behind is not going to do much for rear-wall SBIR.
... and that's what I was talking about! My point exactly.... by using those ineffective devices across the entire rear wall, you leave no place for REAL acoustic treatment, and certainly none for the variable devices, that you need..I meant because the entire rear wall was treated with the PRN air transparent diffusers then there wasn't any room left for variable-acoustic devices,
True, but that doesn't mean that you can't make them variable in some way...and the front wall has the flush mount baffles,
I can think of at least three ways you could do that, simply... 
And the ceiling? You are completely neglecting the single most important surface in the room for tracking most instruments. Control room ceilings need to be mostly absorptive, but musical instruments general sound better when the ceiling is diffusely reflective... or even partly specular...so only the side walls were left for these devices.
It got a lot of interest, due to its quirkiness, yes, but once again, how many rooms were actually built like that in the end? And where are the acoustic test results that show that it works as advertised? 7 years is a long time for people to test this out, and build a whole bunch of rooms... it if really works... It is one thing to produce nice computer-generated projections of how the things work, but it's another thing entirely to actually test one in real-life. Speaking from experience, I can tell you that most rooms don't actually perform the way that the mathematical models predict. There are just too many variables to be able to model them completely beforehand: it's far easier and faster and cheaper to just do basic prediction, build the room, then analyze it ad treat it for the way it ACTUALLY turned out, rather than the way it should have turned out. So I have little confidence that the MR rooms that were built actually did end up as predicted. Not to mention the HUGE expense of building one....The original concept from 11 years ago got quite a bit more of a look at by the community.
I'm not a big fan of the Newell concept of non-environment rooms, and certainly not of true LEDE rooms either! From that point of view, I agree with John Brandt: It is a huge waste of space, for practically no benefit, to build a gigantic non-symmetrical outer shell, then a symmetrical inner shell. I very much doubt that the guys at GS are actually building true LEDE and NER rooms. What they build mostly is much closer to RFZ, in reality. And what some of then refer to as LEDE rooms are NOT true LEDE rooms either! Most contemporary designs abandoned that approach a couple of decades ago. A true Don and Chip Davis LEDE room is unpleasant to work in, and fatiguing. It sounds unnatural. There is nothing like it in nature, nor in real life experience. The human brain is not accosted to it. Yes, it works as advertised, and yes, you can produce good mixes in one, but it's not a nice place to work, since your brain has no points of reference. The entire front-end of the room is totally dead, and the entire rear end is totally reflective: the only place in nature that sounds vaguely close to that would be if you stand just outside the mouth of a very shallow cave, just a couple of meters deep, and listen to music coming from in front of you.... not a common experience!It seems over at Gearslutz they have a lot of people who want to use LEDE and Newell designs, no one really does much else these days.
On the other hand, if you look around at the most successful rooms built over the past couple of decades, RFZ shines through as being the best.
On the other hand, nobody here on this forum wants to sell you anything! John strictly forbids that. No acoustic products can be promoted or offered here by their manufacturers or reps. The only time you might see a positive mention of a product here is by people who have actually bought and used that product in their own rooms, but have no desire or intention to sell it to you. No advertising is allowed here: nobody is out to sell you anything. And neither do we hide the "secrets" of how we design and build rooms: it's all out in the open, freely shown, freely discussed. And is also proven to work, very well, with a strong, clear track record, and demonstrated, measured, published results. No secrets.Also most of the guys who know their stuff over there are professional designers/sell products so they tend to have their own ideas and not want to use someone else's, or they keep their designs close to their chest.
So who do you trust more? The guy who wont tell you how to do it, and wants to sell you something? Or the guys who are happy to show you how to do it yourself, for free, and walk you through it, for free, and will only charge you something if you decide that you don't want to spend the time learning and designing yourself, preferring to hire someone else to do it for you... Which makes more sense? Which do you think is more trustworthy?
Honestly, from my point of view, your room is too small to use numeric based diffusion when you are mixing. Probably OK for tracking, but not for mixing. So anything you do on their with diffusion, you need to be able to cover-up or disable in some way for mixing.I am interested in testing the effect of the diffuser design in my room.
Not trying to be obnoxious, but how on Earth would you test your devices???I'm thinking of building 1 or 2 smaller modules using his method taking measurements.
Do you happen to have an anechoic chamber, and half a million dollars worth of test gear at your disposal? If not, then you can't test them. You would have no idea if the devices you built would even be working at all, nor if they are producing a flat power spectrum, or lobing, or frequency, phase, or timing distortion. You might think that you can just listen to the devices and see how they "sound" to your ears, but you can't. The issues are not usually audible (unless the device is terribly bad!), but the psycho-acoustic effects are very real, and would cause you to not produce good mixes, and have strange "sounds" in your instruments when you track, that you can't really identify, but just notice that things sound "off". It would be especially noticeable from large instruments, that radiate sound from their entire body, such as guitars, violins, drums, brass, woodwinds, etc. Since each part of the radiated sound would hit a different part of the diffuser, it would come back at you with a different power level, different phase, different frequency, and different timing, but not diffusely: your room is not large enough to allow the field from a diffuser to fully integrate and merge into an even, smooth field. So you would not be able to detect if your devices are working, or not working, yet, you'd notice that some of your recordings just sound a bit "odd", and be unable to figure out why they sound like that...You can't test diffusers yourself. You need equipment, training, and an anechoic chamber.
Yes but no!It's obviously not laboratory accurate but it would be interesting to test the concept,
See above. You are right in that it would not be a laboratory test, and therefore not accurate, so I don't see the reason to bother!I'd LOVE to do that, absolutely! But I doubt that you can create the conditions that we would need to even be able to test them. Testing absorbers is pretty simple. Testing Helmholtz resonators is easy too. So is testing membrane traps, and panel traps, and perf-panel traps, and slot walls... Finding reflections in a room is also fairly easy, and so is figuring out modal response, and SBIR.... but diffusion is an entirely different subject. You need motorized mics that move across a curved frame around the diffuser while they make hundreds of measurements, or many dozens of mics set up in a curve around the device, and you need a place where you can do that without the room itself interfering. The you need the equipment, and software, and expertise to analyses all of that, and graph it, and make sense of it...When I get to my measurements stage I'd love to have your input Stuart, and maybe guide me in the best way to test this device (assuming you're interested in the results yourself and have some free time).
I've been looking over some of John's posts from the past and rethinking my rear wall,
First, if you tune a device to "40-100Hz" then most likely it is not a Helmholtz resonator! That's a HUGE range of frequencies: more than one octave! Helmholtz resonators are high-Q devices, covering just a few hertz of bandwidth. You can detune them yes, and cover a broader range, but the then Q is really low, and the device is ineffective. Modal issues are also high Q, so they need high Q devices to deal with them, of you plan to attack them with resonance. You would need an array of several devices, each tuned to one modal issue... but then you also need a large surface area and large volume for each frequency... (rule of thumb says that you need about 1% of room volume to successfully treat a modal issue. Let's say you have 20 issues that need dealing with... are you willing to give up 20% of your entire room volume to do that?)Lower rear corners, deep slat helmholtz tuned to 40-100hz. Then measure the effect, if it's good, place the same device in the top rear corners too.
Second, by putting the devices in the corners, you are taking up the prime locations where porous absorption is most effective....
I would not go with this plan.
You said you had looked at many of John's rooms: how many of them did you see with huge diffusers in the upper and lower rear corners?
There's a reason why nobody builds rooms like that...
That's upside-down and back-to-front! Super chunks reach maximum efficiency and performance in the top and bottom rear corners of the room. You could leave out the middle section of a superchunk and not greatly damage the performance. But leaving out the top and bottom is like leaving out the entire thing!Middle (vertically) rear corners superchunk at listening height, for reflections.
This part I do like. I would make it 500mm and use hangers, but I do like the concept of the split poly.Middle of rear wall, 200mm thick absorption panel.
In front of the absorption a full height polycylindrical absorber that is cut down the middle and swings on hinges.
When open the rear absorption panel is exposed and the "inside" of the poly "doors" exposes more absorption.
Closing the poly covers the absorption to add more liveliness to the room.
The concept is good.Look for "flexible plywood". It's a special type of plywood, manufactured so that it bends very easily in one direction without cracking. Often used by carpenters to make curved furniture. IT can take a pretty tight curve, very easily:I've thought about how I will physically contruct this. Here's my idea:
- Stuart -
