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PostPosted: Mon May 28, 2018 8:42 pm 
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Soundman2020 wrote:
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Though this is obvious to you, this has my head scratching.
It's actually not that obvious at all! And it does need some head scratching at first... until you change your point of view, and get that "Eureka" moment... :) It fools a lot of people, I think, so don't feel bad by any means!


Thank-you Stuart for that excellent information, you've answered questions I've been pondering for a very long time! I now understand that under the right circumstances there are exceptions to rules. Very much like music theory itself!

The exciting news is that we're almost ready to pour the new concrete slab. There is an existing slab there which is in a very sorry state and during the development of this project (with the unforeseen necessity to take down the existing building in order to safely cut down trees) we've decided we can make the CR a little wider and so we would need to pour concrete anyway.

Now that all of the footings have been dug out we will be preparing the foundations for this new slab and I am designing the scheme for the cable troughs under the floor. Before I share that I just wanted to show my plan for the new slab(s) so you guys can correct me if it's wrong.

There's two options,
option 1:
as seen in this google image, is to do independent slabs for each inner and outer wall, completely isolated slabs not touching each other with an expansion seal in the gap.
Attachment:
teaserbox_38074297.jpg



Option 2:
Here is a very rushed basic diagram of an idea I had, would this work?

I've chosen to show the intersection of the hallway walls and the CR wall next to the hallway as it's the most complicated part:
The outer walls will be built upon concrete blocks (sorry, not labelled on diagram!), in-between the blocks there will be concrete for the floor. The CR walls will be built on a floating slab that will float on rockwool insulation and ply. I have seen designs using "pucks" or isolating springs etc, but would they really be necessary in my design?

While I'm at it, I realised that I wasn't sure how to face the inside of the most outer wall (marked with "???") should I leave it open to the insulation or can I face it with sheetrock?

Attachment:
Screen Shot 2018-05-28 at 02.50.08.png


So those are the two options, I'm interested to know if one is better than the other or if they're just two ways of achieving the same thing bringing about the same results?


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PostPosted: Thu Jun 07, 2018 6:20 am 
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I've been scavenging all sorts of goodies for the build - lots of massive windows and frames, some of them will be usable others will come in handy in the non recording parts of the studio such as the lounge or bathroom. I also went and picked up 6 incredibly heavy fire doors - complete with handles, locks, keys, automatic door stoppers and 3.5" solid glass circular windows in each (see pic) I got the lot for £100 which was too good to turn down.

I've also secured a great deal on 25 rolls of isover space saver loft insulation. it's 10kg/m3 which will be nice and light for filling cavities or making traps. It's a little thick at 150mm but 25 bags at £5 per bag I thought it was worth getting.

I also have a local framer who is going to build the frames to my exact spec and erect them for me. He's incredibly skilled and very very competitive in terms of price.

first things first, I need to finalise my plans and then pour the slab. I almost have half a studio just sitting in the drive way, can't wait to put it altogether :yahoo:


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PostPosted: Sun Jun 10, 2018 10:27 pm 
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Yet another control room floor plan update.

H 10'10" x W 19'5" x L 23'8"
It meets the Bonello criterion, it's on the edge of the bolt area, listening position is at 37.5%

Soffits are 4'10" at the bottom, tapering out to almost 6' at the top, Speakers are offset in soffits and angled 30 degrees, intersecting about 1' behind head. They will also be angled vertically 5 degrees with the tweeters at about 47" above floor.

For the front wall window I'm going back to 3 panes of glass in a wrap around formation as I need the 2 outer panes to form part of the soffits for the speakers otherwise the soffits will be far too small. (Unless I can simply just 'cut' into the soffits for 1 single larger piece of glass? But then the soffits would not be continuous) This gives me a nice big window as well as nice big soffits.

The side walls next to the soffits are angled 33 degrees from the speakers, and the area behind them will be full of hangers as well as housing some rack gear with doors in front. These areas will be ventilated as will the soffits.

The side walls next to those will have windows so that I can see in to the adjoining room and hallway. This is also a handy way to allow natural light in as those areas will also have windows to the outside world. These walls/windows are angled 3.6 degrees which is enough to keep reflections away from the listener and will also allow me to get a bit more absorption into the side walls.

As the ceiling is vaulted and will be around 13' at its peak this area will be full of hangers which will hang down to make the visible ceiling around 8'. That gives me hangers as long as 4' in the centre. They will all be angled towards the front wall in a tapered fashion.

The soffits running along the rear and sides will house the ventilation ducting as well as low frequency absorption and some lighting. All of the side walls will probably end up being covered in some slats in a 1d binary amplitude diffuser pattern, as well as part of the rear wall just to add some life back into the room but still allowing most of the air into the broadband absorption.

The rear wall can have over 3' of space for hangers plus a large diffuser if needed, and there will still be over 11' of distance to the listening position. (over 14' to the actual solid wall)

I've marked on the floor plan the RFZ created by the angled walls, but that is only rough as it doesn't take in to account the reflections from the board, credenza and obviously the ceiling, but it measures around 4.5' behind the head and around 4' to the sides and in front.

Please let me know what you think, and please rip it apart and tell me if there's anything a miss!


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PostPosted: Wed Jun 13, 2018 4:49 am 
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Picked up the fluffy insulation today, when we arrived the lady had even more than she realised so I ended up with over 30 rolls for £125. I thought we were going to have to make 3 or 4 trips to get it, but my dad decided to fit it all on the trailer and in the car in one go - luckily it was only 10 mins down the road. I'm itchy.


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PostPosted: Thu Jun 14, 2018 11:24 am 
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Not bad at all for 125! Lucky man!


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PostPosted: Thu Jun 14, 2018 6:54 pm 
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Soundman2020 wrote:
Not bad at all for 125! Lucky man!


- Stuart -


Thankyou Stuart! I do indeed feel very blessed. But how about my ideas and design? Any obvious problems with what I’ve come up with?


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PostPosted: Sun Jun 17, 2018 9:23 am 
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Hi guys, I could really do with some advice if any of you have a few moments spare.

I've attached 3 different floor plans for my control room, each one has its own concept. Now I realise that the finer acoustic details cannot be properly worked out at this stage before the room is built or tested, however I gotta start somewhere. so these are concepts only. The idea is to create a room with enough space that I have options later on, but I'd like your opinions on what direction might be the best one to take.

Common to all designs are:

-the listening position (37.5% of room length)
-speakers angled at 30 degrees
-broadband hangers on the rear wall
-broadband hangers on ceiling
-2' soffits for silencers around the perimeter of the ceiling/top of walls also full of insulation

Here's what sets each apart from the other:

A
- based on a John Sayers design (to the best of my knowledge)
- slat side walls angled at 6 degrees
- diffusion on rear wall

B
- based on a hybrid of traditional RFZ and non environment
- front wall and speaker soffits angled around 5 degrees vertically
- angled cloud for more deflection
- front side walls angled at 33 degrees, face can be absorptive or reflective or both
- rear side walls angled at 3.6 degrees, face can be absorptive or reflective or both
- optional diffusion on rear wall if needed

C
- based on non environment concept
- non angled side walls with hangers behind fabric wall
- no diffusion on the rear
- fully reflective front wall

The first picture shows the reflection free zone of A & B (C is mostly absorptive so nothing is shown). This is where I'm a little unsure -by ray tracing I have roughly come up with the RFZ for each marked in grey. Is the criteria for a RFZ simply that any early reflections being deflected off of any surface must reach the listener no sooner than 20ms after the direct sound and attenuated by -20? And as long as that happens the RFZ is effective?

The reason I ask is because I see most guys in the forum building their studios somewhat like my 'A' design with fairly shallow angled slat side walls. But as you can see from the ray tracing, the listening position is completely out of the RFZ (which is in front of the listening position and mainly useless) Now I could place absorptive panels in the first reflection points, but then I don't see the advantage of angling the walls other than to prevent flutter... and in that case absorption would deal with that anyway, and so I don't see the advantage of doing this over plan 'C'; but I see most people just using slat walls... which would suggest reflection as well as absorption and a little diffusion, but surely they would also create problematic reflections straight into the listener's ears? OR is it that I have not taken in to account that the majority of those reflections (outside of the grey area) would reach the listener later than 20ms. Have I understood that correctly? Or does this layout (A) simply not work? one way the listener could get into the grey RFZ is if the mixing desk was not so large, then the listening position could be moved forward.

Now as you can see in plan 'B' the front side walls are angled such that all of the reflections (in the 2D plane at this stage) completely miss the listening position and create a really large RFZ. This design makes a lot more sense to my simple brain. My question is, would this design be hugely advantageous over design 'A' ?

Finally, C - I like the idea of the non environment room for mixing, and it seems as though it would offer the biggest sweet spot of the lot. But what I don't like about the idea is those times when the control room might be used for composing or doing vocal takes the room would be a little lifeless and uninspiring. I fear that clients might not feel completely comfortable in such a room for long periods, and that is concerning to me.

I'm also not clear as to what the pros and cons are for absorption vs deflection when it comes to creating a RFZ? I suppose deflection keeps some energy in the room whereas absorption kills it a little more. But is that the only consideration? Would first reflections still exist in a non environment room at certain lower frequencies?

Thanks for any answers you can give me!


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PostPosted: Sun Jun 17, 2018 11:16 am 
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Quote:
- front wall and speaker soffits angled around 5 degrees vertically
I really wouldn't do that, to be very honest. There are very good reasons for not tilting your front wall. To start with, that implies raising your speakers up higher so that they still aim at your head, which means that you have them above the horizon. The higher you have them, the more off they are. Your ears are designed to produce the flattest, best response for things ON the horizon: that's where the lions, tigers, and other nasty things are, so your brain does best with sounds from those angles. For sounds significantly above the horizon, your perception of frequency is shifted, since the sound waves are hitting your pinna at a different angle. Above 15°, all bets are off, but even at 5° there's a noticeable decrease. Since one of the most basic purposes of having a control room is to get the best possible accuracy you can for frequency, it makes sense to do everything you can to keep the PERCEPTION of that frequency accurate as well. Second, with the speakers up high facing down, your head is only ever on-axis to the speakers at one specific spot. If you move your head forwards, then your ears are below axis, and if you move your head back then your ears are above axis. Speaker response is smoothest and cleanest on-axis. Same rule applies as above. Third, if the speaker is up high pointing down, that puts a lot more reflections of the desk and console directly in your face: can you say "comb-filtering"? It also makes the lower-mid range very uneven and messy. Fourth, it0s really hard to do! Just building a compound structure that is angled in both dimensions is a tough one. It's bad enough with angling in just ONE dimension: two makes it more than twice as hard. Fifth: gravity. If you tilt your speakers down, the soffit baffle is not standing vertically: it is leaning over. It is HEAVY! Putting it in place and keeping it there is an extra problem. So is the speaker mount: the speaker wants to slide out of its mountings, especially under vibration.

Etc.

So I would discard that as an option. Yes, some people do that: Wes Lachot, for example, often does rooms with tilted front walls. I have done it too (Studio Three, for example). It can work, sure. But it's not as easy as it looks, and you need to work extra hard in the design, and again in the construction, to get it right. Studio Three has an angle of 4.23°... Accuracy is tough!

Keep your walls, soffits, and speakers vertical. Life is hard enough already without making it unnecessarily harder.

Quote:
- angled cloud for more deflection
Yes :thu: Once again, studio three has an angled cloud. In fact, the cloud is split into several sections, and hung at two different angles. The front part is steeper. Frank's room will have a split cloud with only one angle, but it will be angled. I pretty much always angle clouds, unless the ceiling is VERY low. But even then, I angle part of the cloud...
Quote:
-the listening position (37.5% of room length)
Good, but it doesn't have to be! If moving it a couple of points further forward or backward would help, then do it!

Quote:
-speakers angled at 30 degrees
Same here: Good, but it doesn't have to be! If changing that a couple of degrees either way would improve things, then do it. These numbers (38%, 30°, etc.) are not written in stone: they are just starting points, and you can adjust them a little, as needed.

Quote:
-broadband hangers on the rear wall
Yes!

Quote:
- diffusion on rear wall
Yes!

Both of those are needed, and your room seems to be big enough to allow for good diffusion.

To give yourself a but more floor space at the back, you can make the hanger section a bit shallower in the middle, but keep it deep in the corners.

Quote:
- front side walls angled at 33 degrees,
That's rather steep! Why so much? I seldom need to angle those "wings" that steeply.

Quote:
face can be absorptive or reflective or both
Both: reflective at head height and a couple of feet each way, absorptive near the ceiling and floor.

Quote:
- rear side walls angled at 3.6 degrees,
Why? Waste of space....

Quote:
optional diffusion on rear wall if needed
It will be...


Quote:
The first picture shows the reflection free zone of A & B (C is mostly absorptive so nothing is shown).
It should be shown! You will still have reflections, and there will still be a zone that has none...

NER rooms done like "C" will be very dead: that will need a lot of reflective/diffusive surfaces to liven it up again, and meet the decay time specs (BS.1116-3). There's nothing wrong with doing it that way, but then you will need to tune it carefully. I think I already showed you Frank's thread, but if not, here the link again: viewtopic.php?f=2&t=21368

Quote:
Is the criteria for a RFZ simply that any early reflections being deflected off of any surface must reach the listener no sooner than 20ms after the direct sound and attenuated by -20? And as long as that happens the RFZ is effective?
Those are two different pars of the RFZ concept. The first part is that NO first-order reflections arrive at your head. Ever. Nothing. ALL first order reflections are re-directed to the rear of the room, where they are both diffused and absorbed, to create the "diffuse field". That diffuse field must not get back to your ears until at least 20m2 after the direct sound got there, and when it does it should be about 20 dB lower than the direct sound, sustained for a short time if possible, and then decay smoothly and evenly at the correct rate for the room size, with all frequency bands decaying at the same rate, +/- 0.05s

Quote:
The reason I ask is because I see most guys in the forum building their studios somewhat like my 'A' design with fairly shallow angled slat side walls.
I guess we are looking at things from the opposite perspective, but I would consider "A" to have steeply angled sidewalls! Steep with reference to the angel of the soffit. With that layout, you have a very sharp "knee" where the soffit meets the side wall, and I prefer to avoid that by using a shallower angle. Jut enough to get the RFZ decent.

Quote:
But as you can see from the ray tracing, the listening position is completely out of the RFZ
That's becuase your side walls are angled way too much (from my perspective: too little from yours).

Quote:
but I see most people just using slat walls... which would suggest reflection as well as absorption and a little diffusion, but surely they would also create problematic reflections straight into the listener's ears?
Only if you get the angle wrong! :)

Quote:
OR is it that I have not taken in to account that the majority of those reflections (outside of the grey area) would reach the listener later than 20ms.
Do the math: as a very rough rule of thumb, 1 foot = 1 ms. So measure the DIFFERENCE in distance between the direct sound and the reflected sound: if that difference is LESS than 20 feet, then you have a problem... And even if it is greater than 20 feet, if this is a first reflection, then you are already breaking rule #1: no first-order reflections at the mix position....


Quote:
Now as you can see in plan 'B' the front side walls are angled such that all of the reflections
Yes, that's a better angle, but STILL too steep for y lickings. It still protrudes too far into the soffit, and the room. Reduce the angle further, make your soffit face wider. The wings don't need to be very big to achieve proper RFZ.

Quote:
But what I don't like about the idea is those times when the control room might be used for composing or doing vocal takes the room would be a little lifeless and uninspiring.
Right! :thu: Check that against BS.1116-3 and EBU Tech-3276, for decay times... This is one reason why I'm not a big fan of NER.

Quote:
I fear that clients might not feel completely comfortable in such a room for long periods, and that is concerning to me.
:thu: Spot on.

Quote:
I'm also not clear as to what the pros and cons are for absorption vs deflection when it comes to creating a RFZ? I suppose deflection keeps some energy in the room whereas absorption kills it a little more.
Correct. After all, you spent a lot of money to produce those precis, accurate sound waves, so why kill them as soon as you can? It sounds unnatural, anyway. So keep the energy in the room, but away from your head, then diffuse it and only attenuate it slightly, so that it is outside the Haas criteria. Then it sounds natural, smooth, and your ears can properly determine directionality and perceive correct frequency response. This is why i AM a big fan of RFZ.
Quote:
Would first reflections still exist in a non environment room at certain lower frequencies?
Supposedly not, but in reality yes.

- Stuart -

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PostPosted: Tue Jun 19, 2018 10:35 pm 
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Thanks Stuart! while responding to your response I realised one thing I had not accounted for is the speaker coverage angle! So I think I need to understand that better before continuing to design my RFZ.

I have been ray tracing as if there is a full 180 degree coverage angle when in fact that may not be the case; there may only be a 60, 80 or 90 degree coverage angle. Despite having requested this information from Quested, I have not received a reply and cannot find this info published in any of their specs sheets on the web. Now that I think about it, I (think) understand how John's designs work in regards to the side walls... the maximum angle from the speaker coverage dictates where the first side wall reflection will be and therefore an angle of 6 degrees, or 12 degrees should be sufficient in most cases. I suppose what it comes down to is how large do you want your RFZ to be...

The speakers I have consist of 2 10" LF drivers, 1 soft dome MF and 1 soft dome HF. Considering that they are soft dome drivers I imagine the dispersion will be quite substantial so in your experience what would be a good guess as to the speaker coverage angle? 80 degrees?


Soundman2020 wrote:
Quote:
- front wall and speaker soffits angled around 5 degrees vertically
I really wouldn't do that, to be very honest. There are very good reasons for not tilting your front wall. To start with, that implies raising your speakers up higher so that they still aim at your head, which means that you have them above the horizon. The higher you have them, the more off they are. Your ears are designed to produce the flattest, best response for things ON the horizon: that's where the lions, tigers, and other nasty things are, so your brain does best with sounds from those angles. For sounds significantly above the horizon, your perception of frequency is shifted, since the sound waves are hitting your pinna at a different angle. Above 15°, all bets are off, but even at 5° there's a noticeable decrease. Since one of the most basic purposes of having a control room is to get the best possible accuracy you can for frequency, it makes sense to do everything you can to keep the PERCEPTION of that frequency accurate as well. Second, with the speakers up high facing down, your head is only ever on-axis to the speakers at one specific spot. If you move your head forwards, then your ears are below axis, and if you move your head back then your ears are above axis. Speaker response is smoothest and cleanest on-axis. Same rule applies as above. Third, if the speaker is up high pointing down, that puts a lot more reflections of the desk and console directly in your face: can you say "comb-filtering"? It also makes the lower-mid range very uneven and messy. Fourth, it0s really hard to do! Just building a compound structure that is angled in both dimensions is a tough one. It's bad enough with angling in just ONE dimension: two makes it more than twice as hard. Fifth: gravity. If you tilt your speakers down, the soffit baffle is not standing vertically: it is leaning over. It is HEAVY! Putting it in place and keeping it there is an extra problem. So is the speaker mount: the speaker wants to slide out of its mountings, especially under vibration.


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PostPosted: Wed Jun 20, 2018 3:52 am 
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Quote:
I have been ray tracing as if there is a full 180 degree coverage angle when in fact that may not be the case; there may only be a 60, 80 or 90 degree coverage angle. Despite having requested this information from Quested, I have not received a reply and cannot find this info published in any of their specs sheets on the web. Now that I think about it, I (think) understand how John's designs work in regards to the side walls...
Right, but speaker dispersion is not a hard-edged "cone". It's a very blurry, soft edge, and it is different vertically and horizontally. Higher frequencies are projected straight out, more or less like rays, in a fairly tight "cone", maybe 40° wide (20 either side of the axis). Lower frequencies spread out more, perhaps 50° or 60° or so. Still lower frequencies spread even wider: say 80° or 90° As you go further down, the spread gets larger and larger: 120°, 150°, 180°. At the point where the wavelength equals the width of the speaker cabinet, the sound starts to wrap around completely, and below that, you get basically 360° dispersion. But even then, the spread isn't smooth and even: there can be interference patterns created by the speaker itself that cause coverage to change quite drastically at different directions and frequencies.

Now for the kicker: the same applies to the reflections off the RFZ surfaces! A high frequency wave will reflect rather tightly, as a "specular" reflections, somewhat like a ray of light, whereas a low frequency wave will sort of "mush" around and "reflect" broadly, at larger angles, blurrily. The larger the reflecting surface, the better focus and specularity you get. (sort of...)

Therefore, you need to consider reflections across a rather broad range of frequencies with your ray tracing. At least out to 60° or so each side of the axis.

Quote:
The speakers I have consist of 2 10" LF drivers, 1 soft dome MF and 1 soft dome HF. Considering that they are soft dome drivers I imagine the dispersion will be quite substantial so in your experience what would be a good guess as to the speaker coverage angle? 80 degrees?
80 degrees at what frequency? :) It's not that easy.

Look for a dispersion diagram for your speaker: If the manufacturer doesn't want to give you one, and you also cannot find one on-line in a review or lab test comparison, that's probably a sign that you should look for a different speaker.

There are several ways of presenting the data, but a set of polar patterns is a good one, and easy to understand: Something like this:
Attachment:
EV.SX-100-SPEAKER-POLAR-PATTERNpolar-ev_sx100+.gif

That shows the dispersion for a series of different frequencies, as viewed from above (looking down from the ceiling, on top of the speaker).

Another option is the polar intensity diagram, showing how the intensity changes by frequency at various angles off-axis:
Attachment:
Adam-a5x-polar-dispersion-pattern.jpg

Harder to read, and not much use, to be honest

Yet another is a simple "spread" diagram:
Attachment:
SRM450_EYE_DispersionDetail.gif

But that's just marketing hype; No real use at all for studio design (and neither would I recommend an SRM-450 as a studio monitor! :) )


Another method is the "relative frequency response" graph:
Attachment:
speaker-Q-directivity-dispersion-relative-frequency-plot.jpg


A far more useful and complete, but harder to read, method is the full "directivity plot" or "isobar plot":

Attachment:
speaker-Q-directivity-isobar-dispersion-plot.jpg


That one contains all the info you need to see exactly how the speaker produces the sound field. The one above shows a really lousy speaker, with major issues. The one below shows a much better speaker:
Attachment:
kh120_ver_directivity_510--2.gif

That happens to be for the Neumann KH-120 speaker, which is an excellent, excellent monitor, and has great response across the board, but even so you can see some issues around the cross-over frequency, at roughly 2 kHz. Nothing to worry about, of course, but still visible with this plot.


Your speaker manufacturer must be able to supply SOME type of directivity information! If not, that's not a good sign.

Quote:
the maximum angle from the speaker coverage dictates where the first side wall reflection will be and therefore an angle of 6 degrees, or 12 degrees should be sufficient in most cases.
Nope! :)

Quote:
I suppose what it comes down to is how large do you want your RFZ to be...
That, and how good you want it to be, and how low you want it to extend, in frequency...


- Stuart -


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PostPosted: Wed Jun 20, 2018 4:10 am 
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Soundman2020 wrote:
Quote:
I have been ray tracing as if there is a full 180 degree coverage angle when in fact that may not be the case; there may only be a 60, 80 or 90 degree coverage angle. Despite having requested this information from Quested, I have not received a reply and cannot find this info published in any of their specs sheets on the web. Now that I think about it, I (think) understand how John's designs work in regards to the side walls...
Right, but speaker dispersion is not a hard-edged "cone". It's a very blurry, soft edge, and it is different vertically and horizontally. Higher frequencies are projected straight out, more or less like rays, in a fairly tight "cone", maybe 40° wide (20 either side of the axis). Lower frequencies spread out more, perhaps 50° or 60° or so. Still lower frequencies spread even wider: say 80° or 90° As you go further down, the spread gets larger and larger: 120°, 150°, 180°. At the point where the wavelength equals the width of the speaker cabinet, the sound starts to wrap around completely, and below that, you get basically 360° dispersion. But even then, the spread isn't smooth and even: there can be interference patterns created by the speaker itself that cause coverage to change quite drastically at different directions and frequencies.

Now for the kicker: the same applies to the reflections off the RFZ surfaces! A high frequency wave will reflect rather tightly, as a "specular" reflections, somewhat like a ray of light, whereas a low frequency wave will sort of "mush" around and "reflect" broadly, at larger angles, blurrily. The larger the reflecting surface, the better focus and specularity you get. (sort of...)

Therefore, you need to consider reflections across a rather broad range of frequencies with your ray tracing. At least out to 60° or so each side of the axis.

Quote:
The speakers I have consist of 2 10" LF drivers, 1 soft dome MF and 1 soft dome HF. Considering that they are soft dome drivers I imagine the dispersion will be quite substantial so in your experience what would be a good guess as to the speaker coverage angle? 80 degrees?
80 degrees at what frequency? :) It's not that easy.

Look for a dispersion diagram for your speaker: If the manufacturer doesn't want to give you one, and you also cannot find one on-line in a review or lab test comparison, that's probably a sign that you should look for a different speaker.

There are several ways of presenting the data, but a set of polar patterns is a good one, and easy to understand: Something like this:
Attachment:
EV.SX-100-SPEAKER-POLAR-PATTERNpolar-ev_sx100+.gif

That shows the dispersion for a series of different frequencies, as viewed from above (looking down from the ceiling, on top of the speaker).

Another option is the polar intensity diagram, showing how the intensity changes by frequency at various angles off-axis:
Attachment:
Adam-a5x-polar-dispersion-pattern.jpg

Harder to read, and not much use, to be honest

Yet another is a simple "spread" diagram:
Attachment:
SRM450_EYE_DispersionDetail.gif

But that's just marketing hype; No real use at all for studio design (and neither would I recommend an SRM-450 as a studio monitor! :) )


Another method is the "relative frequency response" graph:
Attachment:
speaker-Q-directivity-dispersion-relative-frequency-plot.jpg


A far more useful and complete, but harder to read, method is the full "directivity plot" or "isobar plot":

Attachment:
speaker-Q-directivity-isobar-dispersion-plot.jpg


That one contains all the info you need to see exactly how the speaker produces the sound field. The one above shows a really lousy speaker, with major issues. The one below shows a much better speaker:
Attachment:
kh120_ver_directivity_510--2.gif

That happens to be for the Neumann KH-120 speaker, which is an excellent, excellent monitor, and has great response across the board, but even so you can see some issues around the cross-over frequency, at roughly 2 kHz. Nothing to worry about, of course, but still visible with this plot.


Your speaker manufacturer must be able to supply SOME type of directivity information! If not, that's not a good sign.

Quote:
the maximum angle from the speaker coverage dictates where the first side wall reflection will be and therefore an angle of 6 degrees, or 12 degrees should be sufficient in most cases.
Nope! :)

Quote:
I suppose what it comes down to is how large do you want your RFZ to be...
That, and how good you want it to be, and how low you want it to extend, in frequency...


- Stuart -


Thanks Stuart, those charts are great to see, very interesting how complicated it can get. I knew that dispersion would get bigger and bigger the lower down the frequency response you go, but surely there's little you can do about that in a medium sized room apart from try to attenuate with absorption? but for a RFZ are we not mainly concerned about more directional rays from upper mids and high frequencies? LF will seem to always have an omni-presence.

If we do need to deflect LF as well, then surely we would need to have much bigger angles that would require rooms much larger than the ones typically found on this forum?

Roger Quested himself has replied to my e-mails, but he hasn't given me specifics yet though I have asked for them, I suspect he's a very busy man. I shall await his reply. in the mean time he simply said 'soft domes have very wide dispersion' which is rather vague.


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PostPosted: Thu Jun 21, 2018 11:18 pm 
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Soundman2020 wrote:
Quote:
- front wall and speaker soffits angled around 5 degrees vertically
I really wouldn't do that, to be very honest. There are very good reasons for not tilting your front wall. To start with, that implies raising your speakers up higher so that they still aim at your head, which means that you have them above the horizon. The higher you have them, the more off they are. Your ears are designed to produce the flattest, best response for things ON the horizon: that's where the lions, tigers, and other nasty things are, so your brain does best with sounds from those angles. For sounds significantly above the horizon, your perception of frequency is shifted, since the sound waves are hitting your pinna at a different angle. Above 15°, all bets are off, but even at 5° there's a noticeable decrease. Since one of the most basic purposes of having a control room is to get the best possible accuracy you can for frequency, it makes sense to do everything you can to keep the PERCEPTION of that frequency accurate as well. Second, with the speakers up high facing down, your head is only ever on-axis to the speakers at one specific spot. If you move your head forwards, then your ears are below axis, and if you move your head back then your ears are above axis. Speaker response is smoothest and cleanest on-axis. Same rule applies as above. Third, if the speaker is up high pointing down, that puts a lot more reflections of the desk and console directly in your face: can you say "comb-filtering"? It also makes the lower-mid range very uneven and messy. Fourth, it0s really hard to do! Just building a compound structure that is angled in both dimensions is a tough one. It's bad enough with angling in just ONE dimension: two makes it more than twice as hard. Fifth: gravity. If you tilt your speakers down, the soffit baffle is not standing vertically: it is leaning over. It is HEAVY! Putting it in place and keeping it there is an extra problem. So is the speaker mount: the speaker wants to slide out of its mountings, especially under vibration.

Etc.

So I would discard that as an option. Yes, some people do that: Wes Lachot, for example, often does rooms with tilted front walls. I have done it too (Studio Three, for example). It can work, sure. But it's not as easy as it looks, and you need to work extra hard in the design, and again in the construction, to get it right. Studio Three has an angle of 4.23°... Accuracy is tough!

Keep your walls, soffits, and speakers vertical. Life is hard enough already without making it unnecessarily harder.

I completely agree with you, it would be a lot harder to do. There's a couple of reasons why I would need to angle them if I went with this design though:

It would make my soffits larger since they would taper out at the top (see dotted line in design) otherwise I would be under the minimum recommended width without that angle. This way the top of the soffit would be about 6' and the bottom would be about 4' 10" the middle point would be over 5'

Although not drawn in the design, I will also have a couple pairs of near fields. The idea with angling the mains is so that the near fields do not block the mains as much as they would without the angle.

I remember reading in this forum (perhaps even written by yourself) that if one is to angle the soffits then 5 degrees is about the maximum you can do before it starts to make a real big difference, though I agree ideally they should not be tilted at all.


Quote:
- diffusion on rear wall Yes!

Both of those are needed, and your room seems to be big enough to allow for good diffusion.


So the next thing then is how about diffusion behind the client couch? How do I make sure it sounds okay for the clients with diffusion right behind their heads?

Quote:
- front side walls angled at 33 degrees,That's rather steep! Why so much? I seldom need to angle those "wings" that steeply.
so this is in relation to the soffits, the angle as measured from the side wall would be 27 degrees. The idea is to make the RFZ as large as possible with the space that I've been given, a shallower angle would reduce the size of it.

Quote:
- rear side walls angled at 3.6 degrees Why? Waste of space.... [\quote]

Yes perhaps, but there will be windows there. Granted they don't necessarily need to be angled, and I could always angle them vertically instead, so that reflections go towards the floor or ceiling, but I would also get a little more absorption on that wall if I angle it


Quote:
I guess we are looking at things from the opposite perspective, but I would consider "A" to have steeply angled sidewalls! Steep with reference to the angel of the soffit. With that layout, you have a very sharp "knee" where the soffit meets the side wall, and I prefer to avoid that by using a shallower angle. Jut enough to get the RFZ decent.


I guess I have been looking at designs where the width is narrow, and so people have to make do with what they're given, hence a lot of studios seem to have that very sharp knee, being effective RFZ for a dispersion of 30 or so degrees either side.

Quote:
Yes, that's a better angle, but STILL too steep for y lickings. It still protrudes too far into the soffit, and the room. Reduce the angle further, make your soffit face wider. The wings don't need to be very big to achieve proper RFZ.
I guess it depends on how big I would like that RFZ to be. From the ray tracing I've been doing, If I reduce them, the angle changes and makes the RFZ smaller. Now I could use absorptive side panels, but then I don't see any benefit in having soffit wings at all. Though they do protrude into the soffits at the bottom, because the soffits would be angled, at the top the soffits are very wide indeed. The other reason is it would allow me to fit some rack gear behind doors which would justify losing that space, and also provide a little isolation for slightly noisy rack gear.

I can come up with an amended design following your recommendations, but in the mean time after clarifying a few things would design 'B' work well for the basis of a control room that (with the right testing and treatment) could meet spec and allow for an honest mixing environment in your opinion?


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PostPosted: Fri Jun 22, 2018 5:01 am 
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Quote:
So the next thing then is how about diffusion behind the client couch? How do I make sure it sounds okay for the clients with diffusion right behind their heads?
1) Keep the couch far enough in front of the diffuser that it won't have too much of an effect (in other words, good distance between couch and diffuser: move the couch forward a few feet)
2) Tune it high enough that it doesn't have too much of an effect (remember the "3 times lowest scatter wavelength" rule...)
3) Keep the diffusion high, slightly above the ear height of the folks seated on the couch.
4) Use a diffuser design that gives a smoother response at closer distances. Fractal-based designs are good for that.

Of course, you'll need to compromise on some of those, probably, due to room size restrictions and practicalities, but take into account that the guys on the couch are not really doing critical listening: they are there to be blown away by the bass, and by your mixing skills. They don't really need as much pure acoustic clarity and precision as you do, at the mix position. If the producer is sitting back there and has a comment on the sound, then invite him to take a few steps forward and listen again where you are. But with your size room, and good treatment, that's unlikely. I reckon your room will sound pretty darn good.

Quote:
so this is in relation to the soffits, the angle as measured from the side wall would be 27 degrees. The idea is to make the RFZ as large as possible with the space that I've been given, a shallower angle would reduce the size of it.
No it wouldn't.- Think it through.... You seem to be not seeing the forest, only the trees... :) Don't be afraid to change sizes and angles all over the place!
Quote:
It would make my soffits larger since they would taper out at the top
And how would that help to make them wider where they NEED to be wider, which is where the actual drivers are? I think if you check, you'll find that you are making them NARROWER at that point by tilting them down... unless you star the tilt very low, and make the tilt angle very large... which has the drawback of REDUCING space for treatment under the speaker...

Quote:
Yes perhaps, but there will be windows there. Granted they don't necessarily need to be angled, and I could always angle them vertically instead, so that reflections go towards the floor or ceiling,
Why do you want to angle your rear windows?
Quote:
but I would also get a little more absorption on that wall if I angle it
Why do you think you need thick absorption on the side walls, so far back in the room?

Quote:
I guess I have been looking at designs where the width is narrow, and so people have to make do with what they're given, hence a lot of studios seem to have that very sharp knee, being effective RFZ for a dispersion of 30 or so degrees either side
Take a look at Studio Three, and tell me about the "sharp knee"... :) Also, take a look at Franks' thread, and tell me about the sharp knee... :) Studio Three is a large room, Franks is a small room. In both cases, there is no sharp knee. It IS possible to do that, if you are prepared to be flexible and keep on trying all kinds of tricks, until you optimize each part as much as it can, with the best compromises all over.

Quote:
I guess it depends on how big I would like that RFZ to be.
To a certain extent, yes, but not as much as you seem to be thinking.
Quote:
From the ray tracing I've been doing, If I reduce them, the angle changes and makes the RFZ smaller.
Then you are not doing something right! My guess would be that you are always starting the wing at the same point, never changing that.... try again with different starting points for the wing.

Quote:
Now I could use absorptive side panels,
Nope. I would avoid that. Use absorption above and below the central panel of the wing, by all means, if you need to, but not at speaker height.

Quote:
at the top the soffits are very wide indeed.
Why? Why do you think that's a good thing, when there is no sound source up at the top of the soffits? The sound source is way down low in the soffit....

Quote:
The other reason is it would allow me to fit some rack gear behind doors which would justify losing that space,
How much extra rack space do you need? How much rack gear do you plan to have in there? There's lots of space in the desk, in the desk wings, and in the gondola behind the mix position: Will you need more than that? And even if you do need more rack space, to me it seems like there would still be plenty of room for that in the sides of the soffits, and maybe even in the wings. What's the total amount of RU that you need?

Quote:
and also provide a little isolation for slightly noisy rack gear.
Desk wings, with silencers?

Quote:
I can come up with an amended design following your recommendations, but in the mean time after clarifying a few things would design 'B' work well for the basis of a control room that (with the right testing and treatment) could meet spec and allow for an honest mixing environment in your opinion?
"B" is a good starting point, but I would re-do the wings as outlined above: Make them smaller, shallower angle, shifted over. Improve your RFZ like that, make your soffit baffles larger, gives you some rack space too, and does not require tilted soffits, with all the complications they create, for very little benefit.


- Stuart -

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PostPosted: Sat Jun 23, 2018 9:39 am 
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Soundman2020 wrote:
Quote:
So the next thing then is how about diffusion behind the client couch? How do I make sure it sounds okay for the clients with diffusion right behind their heads?
1) Keep the couch far enough in front of the diffuser that it won't have too much of an effect (in other words, good distance between couch and diffuser: move the couch forward a few feet)
2) Tune it high enough that it doesn't have too much of an effect (remember the "3 times lowest scatter wavelength" rule...)
3) Keep the diffusion high, slightly above the ear height of the folks seated on the couch.
4) Use a diffuser design that gives a smoother response at closer distances. Fractal-based designs are good for that.

Of course, you'll need to compromise on some of those, probably, due to room size restrictions and practicalities, but take into account that the guys on the couch are not really doing critical listening: they are there to be blown away by the bass, and by your mixing skills. They don't really need as much pure acoustic clarity and precision as you do, at the mix position. If the producer is sitting back there and has a comment on the sound, then invite him to take a few steps forward and listen again where you are. But with your size room, and good treatment, that's unlikely. I reckon your room will sound pretty darn good.

Quote:
so this is in relation to the soffits, the angle as measured from the side wall would be 27 degrees. The idea is to make the RFZ as large as possible with the space that I've been given, a shallower angle would reduce the size of it.
No it wouldn't.- Think it through.... You seem to be not seeing the forest, only the trees... :) Don't be afraid to change sizes and angles all over the place!
Quote:
It would make my soffits larger since they would taper out at the top
And how would that help to make them wider where they NEED to be wider, which is where the actual drivers are? I think if you check, you'll find that you are making them NARROWER at that point by tilting them down... unless you star the tilt very low, and make the tilt angle very large... which has the drawback of REDUCING space for treatment under the speaker...

Quote:
Yes perhaps, but there will be windows there. Granted they don't necessarily need to be angled, and I could always angle them vertically instead, so that reflections go towards the floor or ceiling,
Why do you want to angle your rear windows?
Quote:
but I would also get a little more absorption on that wall if I angle it
Why do you think you need thick absorption on the side walls, so far back in the room?

Quote:
I guess I have been looking at designs where the width is narrow, and so people have to make do with what they're given, hence a lot of studios seem to have that very sharp knee, being effective RFZ for a dispersion of 30 or so degrees either side
Take a look at Studio Three, and tell me about the "sharp knee"... :) Also, take a look at Franks' thread, and tell me about the sharp knee... :) Studio Three is a large room, Franks is a small room. In both cases, there is no sharp knee. It IS possible to do that, if you are prepared to be flexible and keep on trying all kinds of tricks, until you optimize each part as much as it can, with the best compromises all over.

Quote:
I guess it depends on how big I would like that RFZ to be.
To a certain extent, yes, but not as much as you seem to be thinking.
Quote:
From the ray tracing I've been doing, If I reduce them, the angle changes and makes the RFZ smaller.
Then you are not doing something right! My guess would be that you are always starting the wing at the same point, never changing that.... try again with different starting points for the wing.

Quote:
Now I could use absorptive side panels,
Nope. I would avoid that. Use absorption above and below the central panel of the wing, by all means, if you need to, but not at speaker height.

Quote:
at the top the soffits are very wide indeed.
Why? Why do you think that's a good thing, when there is no sound source up at the top of the soffits? The sound source is way down low in the soffit....

Quote:
The other reason is it would allow me to fit some rack gear behind doors which would justify losing that space,
How much extra rack space do you need? How much rack gear do you plan to have in there? There's lots of space in the desk, in the desk wings, and in the gondola behind the mix position: Will you need more than that? And even if you do need more rack space, to me it seems like there would still be plenty of room for that in the sides of the soffits, and maybe even in the wings. What's the total amount of RU that you need?

Quote:
and also provide a little isolation for slightly noisy rack gear.
Desk wings, with silencers?

Quote:
I can come up with an amended design following your recommendations, but in the mean time after clarifying a few things would design 'B' work well for the basis of a control room that (with the right testing and treatment) could meet spec and allow for an honest mixing environment in your opinion?
"B" is a good starting point, but I would re-do the wings as outlined above: Make them smaller, shallower angle, shifted over. Improve your RFZ like that, make your soffit baffles larger, gives you some rack space too, and does not require tilted soffits, with all the complications they create, for very little benefit.


- Stuart -


Thank-you Stuart. Yes I have had a good look at Studio 3 but can't remember seeing a floor plan? I would love to see one if you have it?

Okay, I have had a real good play around with the angles and of all the ones I tried, this seems to be what I like best. I tried moving my listening position forward, moving the speakers forward, different speaker angles, making the wings shorter, narrower, longer, wider, tried different angles etc etc.

What I found was by making the side wings shorter, the RFZ became shorter but wider, and by making the wings longer, the RFZ became narrower but longer. I found that an angle of 25 degrees (in relation to the side walls) is a nice length and a nice width. You can see in my second diagram the extremes of the first reflections where the room angles change, (dotted lines are the reflections) it makes the RFZ 5 1/2' long at the tip, and about 8' wide. Of course, that's NOT taking into account the reflections from the credenza or the desk it self.

I've also angled the rear treatment in at 12 degrees but leaving a flat part in the middle for the diffuser, and moved the couch out about 2 1/2' The treatment in the corners would be over a meter thick, or rather a meter of hangers.

I got rid of the tilt of the soffits and now they are a straight up 5' wide, with the speakers offset. The speakers fire to a 'point' which is 16" behind the head. Now, according to Quested they recommend that the listener is between 80cm - 100cm in from the tip of the triangle, do you think I should adjust my design to accommodate this based on their advice?

The other thing I am slightly worried about is the front window. It's now going to be stuck out further from the rest of the wall, the framing comes out into the room to meet the edges of the speaker soffits. It means the length of the room where the window is is now close to 22' which is close to the average height of my ceiling (10' 10"). So I have a couple of questions:

1. should I even care? especially since the ceiling is actually vaulted, going from 8' 10" - 12' 10", 10' 10" just being the average, so does it even matter anyway?

2. If it does matter then theres a second length dimension that would work well which is 23' 1", so do the soffits need to have a nice smooth transition to the middle where the window is or I could I just have a cut out where the window would be? As in, carry the angle on towards the middle of the front wall, but cut into it in order to reveal the window which is further back than the soffits? As long as the soffits are still the same width.

Also, now that the side walls and side windows are straight, is there any chance of flutter occurring? Especially if I decide to use slats? Or would the slats eliminate flutter? How about the window? I know that the speakers will be firing off axis to the side walls, so there won't be direct flutter from them, but how about from other sources or secondary reflections?


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