John Sayers' Recording Studio Design Forum Archive

Each soffit, as compared to each speaker. So if the woofer is 12", then the baffle on the soffit that holds the speaker should be about 3 feet wide. Ideally, of course. Not always possible in real life. If the woofer is 8", then a two foot wide baffle would be the minimum.

Think of it this way; the entire purpose of the soffit is to get rid of the artifacts caused by having a small speaker baffle inside the room. If your soffit only makes it a bit bigger, then you didn't accomplish a lot. 3x width means 3x the wavelength for the highest edge diffraction and baffle step response mid-point. All of that moves down the scale correspondingly.


- Stuart -

Soundman2020 wrote:Each soffit, as compared to each speaker. So if the woofer is 12", then the baffle on the soffit that holds the speaker should be about 3 feet wide. Ideally, of course. Not always possible in real life. If the woofer is 8", then a two foot wide baffle would be the minimum.

Think of it this way; the entire purpose of the soffit is to get rid of the artifacts caused by having a small speaker baffle inside the room. If your soffit only makes it a bit bigger, then you didn't accomplish a lot. 3x width means 3x the wavelength for the highest edge diffraction and baffle step response mid-point. All of that moves down the scale correspondingly.


- Stuart -

Ahhh I see, sorry I misunderstood and thought you meant the entire speaker cabinet rather than just the size of the drivers! Haha *phew*

So if each monitor has 2x10” LF drivers then each soffit should be at least 60” wide? Or do I just use 1 of the drives which would be 30”? I’m guessing the former

So if each monitor has 2x10” LF drivers then each soffit should be at least 60” wide? Or do I just use 1 of the drives which would be 30”? I’m guessing the former

Probably 60", yes, but it depends on the speaker. For example, some Adam speakers and some of their competitors from Eve use a pair of smallish woofers at opposite ends of a long box: in that case, the effective size of the woofer is much larger than each individual woofer, and larger than the sum of both: more like the distance between their centers, but that's just a very rough estimate. If you have two or more smallish drivers pumping out the same sound, then the effect is more complex to calculate: not just summing the individual sizes. It all depends on how they work together. But in your case, 60" is probably a good estimate. Go bigger if you can: bigger is better! And try to keep the speaker offset a bit, away from the center of the baffle.

- Stuart -

Soundman2020 wrote:

So if each monitor has 2x10” LF drivers then each soffit should be at least 60” wide? Or do I just use 1 of the drives which would be 30”? I’m guessing the former

Probably 60", yes, but it depends on the speaker. For example, some Adam speakers and some of their competitors from Eve use a pair of smallish woofers at opposite ends of a long box: in that case, the effective size of the woofer is much larger than each individual woofer, and larger than the sum of both: more like the distance between their centers, but that's just a very rough estimate. If you have two or more smallish drivers pumping out the same sound, then the effect is more complex to calculate: not just summing the individual sizes. It all depends on how they work together. But in your case, 60" is probably a good estimate. Go bigger if you can: bigger is better! And try to keep the speaker offset a bit, away from the center of the baffle.

- Stuart -

Just wrote a really detailed reply and then lost it all! Never mind here's a summary...

Okay thats cool, so how about something like this?

I couldn't get a true RFZ with angled walls alone in my previous design so I thought I'd experiment since I should ideally change my baffles anyway. I made the room bigger (11' H x 19' 8" W x 24' L) and with this new design I should be in the clear from early reflections over 3' directly behind my head. I added a cupboard for the monitor amps and computer etc on the sides which may or may not stay. (just so you know they are doors and not weird angled aliens sprouting out of the walls)

What I need to know now is how do I avoid creating a 3 leaf system? I ask because from what I've seen RFZ rooms usually angle the inner solid walls rather than the acoustic walls and then the space created by the angled walls is utilised in the adjoining rooms, such as the tracking rooms or iso booths. Can I use this space for trapping with part of the wall solid and reflective (but not sealed) and maintain a rectangular shell?

More details and questions to come but I hope that makes sense for now?

Another question:

I've been measuring the length of my room from the rear wall to the window on the front wall, which is actually sticking out from the inner wall into the room and forms part of the middle section between the speaker baffles. Is this correct or should I measure it to the corners which are actually behind the acoustic wall?

I've been measuring the length of my room from the rear wall to the window on the front wall, which is actually sticking out from the inner wall into the room and forms part of the middle section between the speaker baffles. Is this correct or should I measure it to the corners which are actually behind the acoustic wall?

What "acoustic wall" are we talking about here? There's only one wall at the front of your room: the hard, solid, massive, rigid surface of the inner-leaf that you see when you stand in the middle of the empty room. That's the wall you should be using for all of your ratio calculations. There's only one wall there: It has an inner-leaf (on your side: the side facing the room) and an outer-leaf (the "other" side, facing into the adjacent room). The thing that is the "outer leaf" for your room, is also the inner-leaf for the adjacent room. But it's the inner-leaf from YOUR point of view that matters: What you see as you stand inside the empty room, before installing any treatment, furniture, or gear.

- Stuart -

Soundman2020 wrote:

I've been measuring the length of my room from the rear wall to the window on the front wall, which is actually sticking out from the inner wall into the room and forms part of the middle section between the speaker baffles. Is this correct or should I measure it to the corners which are actually behind the acoustic wall?

What "acoustic wall" are we talking about here? There's only one wall at the front of your room: the hard, solid, massive, rigid surface of the inner-leaf that you see when you stand in the middle of the empty room. That's the wall you should be using for all of your ratio calculations. There's only one wall there: It has an inner-leaf (on your side: the side facing the room) and an outer-leaf (the "other" side, facing into the adjacent room). The thing that is the "outer leaf" for your room, is also the inner-leaf for the adjacent room. But it's the inner-leaf from YOUR point of view that matters: What you see as you stand inside the empty room, before installing any treatment, furniture, or gear.

- Stuart -

Thank-you Stuart. What I mean is, there is the wall behind the speaker soffit which is the front wall, but I'm talking about where the window is (looking into the live room) it needs to protrude out into the room to become flush with the edge of the speaker soffit. So that will bring the front wall in about 6" but only the middle of that wall (where the window is). So should I measure to the window or the rest of the wall surrounding the protruding window?

Hopefully this will make it a little clearer as to what I'm going on about!

Green = Wall
Red = Window

Should I measure the length of my room from the red or the green?

I would like to know which is correct so that I can be sure that the measurements I am putting into modal calculators are accurate as well as for the purpose of marking out my starting point for my listening position.

Thanks a lot

Should I measure the length of my room from the red or the green?

As I said: the walls. In other words, the green in your diagram. The window will have a minor effect, since it is only a small part of the total surface area of that wall. Also, there's not a hug difference between the two: just a couple of inches. Therefore there won't be a huge difference in the overall result either.

so that I can be sure that the measurements I am putting into modal calculators are accurate as well as for the purpose of marking out my starting point for my listening position.

There's no need to go too crazy with either of those. Modes are important, yes, but certainly not the MOST important aspect of your room. They are just one of many aspects that you should take into account. Ditto mix position: yes, you can try to nail the theoretical 38% spot to sub-millimeter precision, but you'll still need to adjust that to accommodate many other decisions along the way. And a listening test at some point along the way might modify it even more. As will REW tests.

Yes, these things are important, and it's good to think about them and get good dimensions and locations, but rest assured, they will all change many times between now and the moment you declare the studio "finished", and start your first real session.

- Stuart -

Soundman2020 wrote:

Should I measure the length of my room from the red or the green?

As I said: the walls. In other words, the green in your diagram. The window will have a minor effect, since it is only a small part of the total surface area of that wall. Also, there's not a hug difference between the two: just a couple of inches. Therefore there won't be a huge difference in the overall result either.

so that I can be sure that the measurements I am putting into modal calculators are accurate as well as for the purpose of marking out my starting point for my listening position.

There's no need to go too crazy with either of those. Modes are important, yes, but certainly not the MOST important aspect of your room. They are just one of many aspects that you should take into account. Ditto mix position: yes, you can try to nail the theoretical 38% spot to sub-millimeter precision, but you'll still need to adjust that to accommodate many other decisions along the way. And a listening test at some point along the way might modify it even more. As will REW tests.

Yes, these things are important, and it's good to think about them and get good dimensions and locations, but rest assured, they will all change many times between now and the moment you declare the studio "finished", and start your first real session.

- Stuart -

Thank-you Stuart. Yes, as I'm sure you're aware trying to juggle the 38% rule with the 3x width of the driver for the soffit rule while maintaining a good ratio, correct RFZ angles, big enough window and still having enough space is all the fun of the fayre!

Okay then so my next question: should the area marked in green be enclosed and air tight from the rest of the room or should it be open to the rest of the space? I know in John's designs there are ports for ventilation and hangers are often installed under the speakers which means the area is not completely sealed. But there are other designs such as those of Tom Hidley and Newell where the baffle and the middle section are completely sealed off from the rest of the room with a very heavy rigid face. The idea being to keep all the sound out in the room and to stop it from getting in behind the speakers.

I guess my first question is, what are the pros and cons of each? And most importantly how does one refrain from building a third leaf in either situation?

I'm also wondering about the side walls.

As I'll be building the whole control room inside out, how likely is it that i'll need to add treatment to the side walls or will the insulation be thick enough as is?

Perhaps that is a very difficult question to answer without being able to measure the room, but I'm just trying to gauge how thick those side walls will be so that I can plan the room with that in mind.

I do see john's plans simply use the inside out walls with slats over the insulation without further treatment added.

thanks so much

I'm not sure if you are following his thread, or if you have even seen it, but this thread might be very useful for you, in understanding the process for control room treatment:

http://www.johnlsayers.com/phpBB2/viewt ... 68&start=0



- Stuart -

trying to juggle the 38% rule with the 3x width of the driver for the soffit rule while maintaining a good ratio, correct RFZ angles, big enough window and still having enough space is all the fun of the fayre!

Yup! But there's one item you might not be aware of: The "equilateral triangle" thing is not strictly true. You do NOT need to have the angle of the speaker acoustic axis set to 30°. If you have to adjust that to make things fit better, then so be it. If you have to have 28° or 34° or whatever, that's fine. John has even done rooms at 45°, quite successfully. I try to stay in the range 25° to 35°, but if you are careful, and understand the consequences, then you can go outside that a bit, if you need to.

should the area marked in green be enclosed and air tight from the rest of the room

No. No need for that.

I know in John's designs there are ports for ventilation and hangers are often installed under the speakers which means the area is not completely sealed.

Correct. If you don't have ventilation for your speakers, they will likely overheat and fry!

But there are other designs such as those of Tom Hidley and Newell where the baffle and the middle section are completely sealed off from the rest of the room with a very heavy rigid face.

Well, regardless of what else you do, the front baffle MUTS be very heavy and rigid! That's a requirement.

The basic principle here is that you are trying to turn the front of your room into an "infinite baffle". Your speakers already have a front baffle (the front face of the cabinet), but that is very small, compared to the low frequencies that it is able to produce. Since low frequency waves that are longer then the smallest dimension of the box will "wrap around" to the other side, while higher frequencies will not, and will b project straight forward, clearly there are several problems with that: power imbalance, edge diffraction, skewed frequency response, etc. If you could somehow put the speaker in a baffle that was larger than the longest wavelength, then you solve all of those issues. Technically, the ideal baffle is "infinite": Much larger than several wavelengths of the lowest frequency. Obviously, not possible in any real-world studio. So you make the baffle as large as you can. The larger you can make it, the better. However, that baffle must also be sufficiently massive and sufficiently rigid such that sound waves cannot cause it to vibrate itself, as that would negate some of the benefits. So it goes without saying that the baffle must be as dense and rigid as you can make it, in addition to being as large as you can make it.

The idea being to keep all the sound out in the room and to stop it from getting in behind the speakers.

There is no need to stop the sound getting behind the speakers. There is only a need to stop it wrapping around the speakers front baffle. That's not the same thing, although it might sound like it. As long as the baffle is large enough, it doesn't matter if some sound "gets behind it", provided that there is sufficient damping and geometry back there to deal with it.

Yes, in theory, the ideal perfect baffle would be a solid concrete wall, meters thick, meters wide, and meters high, with the speaker embedded in it. But the difference between that "ideal" and what can actually be achieved with a good soffit design, is minimal. There's no need to go beyond what is necessary to get things under control.

And most importantly how does one refrain from building a third leaf in either situation?

There is no third leaf: Think about where the sound source is actually located when you soffit-mount a speaker, with respect to the two leaves surrounding your room...

As I'll be building the whole control room inside out, how likely is it that i'll need to add treatment to the side walls or will the insulation be thick enough as is?

There are basically two methods for "tuning" a room: Start with it way too live, and add treatment progressively until it is sufficiently balanced (not dead, not live). Or start with it way too dead, and add treatment to liven it up, until it is sufficiently balanced (not dead, not live). There are arguments both ways for which is better, but if you build your room inside out, then by definition you are building it "too dead". You will need to liven it up. Take a look at the link I gave above. That room is built inside out, and "too dead", on purpose, because that's the way I prefer to do it. And you can see the process of getting that under control, adding life back into the room.


- Stuart -

Thank-you Stuart, I have briefly read that thread before yes but need to get around to reading it in full. Loads of great information in there and most of it will probably go over my head at this stage! But hopefully I am gradually learning bit by bit.

Soundman2020 wrote:Yup! But there's one item you might not be aware of: The "equilateral triangle" thing is not strictly true. You do NOT need to have the angle of the speaker acoustic axis set to 30°. If you have to adjust that to make things fit better, then so be it. If you have to have 28° or 34° or whatever, that's fine. John has even done rooms at 45°, quite successfully. I try to stay in the range 25° to 35°, but if you are careful, and understand the consequences, then you can go outside that a bit, if you need to.

Yes, I have played around a little with different angles, I quite like the idea of a wider spread such as using 25 degrees, but would need to make it work with the rest of my angles.

Correct. If you don't have ventilation for your speakers, they will likely overheat and fry!

Is the ventilation also a way of avoiding a third leaf? More on this below...

Think about where the sound source is actually located when you soffit-mount a speaker, with respect to the two leaves surrounding your room...

Though this is obvious to you, this has my head scratching. I have my outer wall that goes all the way round all of the rooms within the studio. Leaf 1. Then I have the inner walls for each room. Leaf 2. Then the soffits which should be rigid and heavy within the inner walls of the CR. Leaf 3? Or is the fact that those soffit walls are not sealed air tight mean that they do not form a third leaf? Please see crudely drawn diagram!

There are basically two methods for "tuning" a room: Start with it way too live, and add treatment progressively until it is sufficiently balanced (not dead, not live). Or start with it way too dead, and add treatment to liven it up, until it is sufficiently balanced (not dead, not live). There are arguments both ways for which is better, but if you build your room inside out, then by definition you are building it "too dead". You will need to liven it up. Take a look at the link I gave above. That room is built inside out, and "too dead", on purpose, because that's the way I prefer to do it. And you can see the process of getting that under control, adding life back into the room.

I am with you on that one, definitely makes more sense to me to start dead and bring it back to life a little. I guess my question was will I likely need to add more absorption or trapping to the side walls when I start tuning the room? I only want to know so that I can have an idea of how thick those walls might end up when treated.

Thanks for your constant support Stuart, I know you're very busy!

Next post will be about the my concrete slab plan...

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!

Then I have the inner walls for each room. Leaf 2. Then the soffits which should be rigid and heavy within the inner walls of the CR. Leaf 3?

Your isolation system is isolating with respect to the sound source, which is the speaker, not the room. Where is the speaker, with regard to your isolation system? Answer: it is between your Leaf 2 and your imaginary leaf 3... With soffits, the speakers are NOT in the room: they are in the soffits. The front baffle of the soffit is basically a "wall" yes, but the noise-making part of the speaker is BEHIND that wall. Between the speaker and the next room, you only have two leaves!

Sure, the mid and high frequencies are projected into the room, but the lows are inside the soffit: they emanate from all sides of the speaker cabinet itself, not just from the front, so those lows only "see" two leaves between them and the next room. The highs and mids would potentially see the soffit as a third leaf, but they are going the wrong way! Away from the soffit, not towards it. Sure, they do come back again, as a pseudo-reverberant field, but that's after they have hit the side and back walls, and the ceiling, and floor, and been reduced in level by 20 dB (optimally), and also diffused so that once they get back to the "3rd leaf" again, they arrive as a randomly incident, low level signal, and they are hitting a very massive, rigid, thick, heavy baffle... In theory, that's a 3rd leaf for them, but in practice, it's not very relevant.

Also, the lows that are projected into the room by the soffit, are not really outside your "third leaf", since your third leaf is not a leaf at all: As far as the sound waves are concerned, that "leaf" is actually the speaker itself, not a leaf! It is, after all, the new front baffle of the speaker! That's the entire purpose of having a soffit: to extend the baffle, blah blah blah, infinite baffle, blah blah blah... so what you are considering to be the third leaf between the sound source and the next room, is actually not a 3rd leaf: it IS the sound source. It is now part of the speaker, and is not a wall, as far as the speaker is concerned.

Try to see this issue form the point of view of the speaker, not your point of view sitting in the room. The room isolates with respect to the sound source, and that is the speaker, of which the soffit baffle is a part. See it as a system, not as individual parts. Speaker = original small speaker cabinet PLUS soffit, acting together as one single much bigger speaker. If you think of the soffit as being part of the speaker, then it "disappears" as a third leaf: it isn't.

OK, to complicate matters: If you had another loud sound source inside the room (eg, drum kit), then yes, I guess you could say that the speaker baffle would act something like a third leaf with respect to that sound source, but even then it is not an issue: the baffle is extremely massive, and there's a very large air gap between it and your "leaf #2", so any MSM resonance there would be at a frequency that is very low, likely outside the audible range. Even as a 3-leaf system, the F- and F+ frequencies would be low enough that it's just not an issue.

I guess my question was will I likely need to add more absorption or trapping to the side walls when I start tuning the room? I only want to know so that I can have an idea of how thick those walls might end up when treated.

You might need additional absorption in teh side walls, depending on your speakers ("Q", or dispersion, or polar pattern if you prefer), the angles, positions, possible sub, etc. Lots of things come into play there. But even so, it would be unusual to need more than about 6" of absorption at your first reflection points, and since you already have 3 1/2" (assuming 2x4 studs), you'd only need another 2 1/2" beyond that. Even allowing for frames, decorative molding, etc., you'd probably fine considering 3" additional depth at the first reflection points. Perhaps less.

Thanks for your constant support Stuart, I know you're very busy!

- Stuart -