John Sayers' Recording Studio Design Forum Archive

hello forum,

long time reader, first time poster. i'm coming up on the end of doing a full build out on a mix room in montreal. my partner actually consulted here a few times here last year w stuart when we were first getting started on the plans. we're now relatively far along. most of the "brute construction" is now done and we're getting on to our treatment.

to give some context: the studio is primarily designed to be a mixing facility, for both music and film. there is a small iso booth for reamps, overdubs and vocals. there is also an entry vestibule/soundlock used to get superior isolation from the existing studio adjacent to us. we've done a full floating floor using neoprene mounts. the room shape features an RFZ wall splay designed to reflect all side wall first reflections towards the back of the room where a large absorptive pad has been built to soak them up. we also have two 9'x4' roxul superchunk traps in our corners for bass frequencies.

i'm trying to get some opinions about soffits. we're building these soon and would like to understand the procedure in as much detail as possible. i've already referred to several posts here on the forum, and are considering a hybrid design that will rely heavily on john and thomas barefoot's specifications:


http://www.johnlsayers.com/phpBB2/viewt ... 6&start=75

http://johnlsayers.com/phpBB2/viewtopic.php?f=12&t=718

i just have a few questions i wanted to clear up before proceeding so as to get the best results possible.

here is picture of our room. it's 19.5' deep by 24.5' at it's widest:



please let me know if you need any other pertinent details on the design thus far.

we currently have a pair of adam A8X's that we will be mounting. however we will be following thomas barefoot's design to as to be able to retrofit with a monitor upgrade in the near future. for this reason, the plaans you see have a larger and smaller box where the left and right channels will be.

we've also included space in the design to include a centre channel when we upgrade to a surround rig for film mixing. there is some debate as to whether this is wise or if we should only build the center soffit wall when we upgrade down the line.

my questions today are the following

1. has anyone soffit mounted A8X's and know how they behave "in the wall"?

2. i'm curious to hear anyone's advice or successes using barefoot's retrofittable design ( http://johnlsayers.com/phpBB2/viewtopic.php?f=12&t=718 ). it seems like it should work well. are there any pitfalls to watch out for? considerations to plan for initially?

3. we're looking at upgrading toward Adam S3A's or S3V's or Focal Twins. what success has anyone had with flush-mounting these? would they fit well into the "larger box" that TB plans for in his design?

4. i notice in john's designs that he builds a tight fitting box around the speaker. barefoot sits it on a shelf snugly strapped in. opinions on which is preferable?

5. any advice on soffit mounting the centre channel down the line? we've discussed placing it outside the wall on a stand further forward, with time delay to compensate. we haven't come across much in the way of surround sound soffit designs and would love any input on how best to do this.

6. john's design calls for acoustical hangers below the speaker shelf. as i understand it, these are fibreboard (mdf?) wrapped with rigid insulation (owens 703?). how far spaced out should these be? would be able to get away with stuffing this area with roxul as an alternate design for bass trapping? or would this be insufficient?

7. our console is 39" high and we also wanted to place ns10's on the meter bridge (8.5" high). this would put our speaker shelf 47.5" high with the tweeter at 60" high. our room is only 109" high, so this puts us above the 38-42% height that Gullfo recommends. i'd also prefer to not have to fuss with angling the speaker if possible. if push the ns10's toward the middle enough to lower the soffit mounted Adam's, would this help? or do we open up another can of worms with the ns10's blocking the centre channel and narrowing in image?

8. before we install the centre channel, what would be best to put in that cavity? i am thinking loose insulation fronted with rigid insulation.

9. john recommends a 2" rigid insulation pad below the speaker to catch reflections off of the console whereas thomas' bezel extends in all directions outward from the speaker, flush to its surface. john has a rigid layer behind his insulation pad. is there any great contradiction here? if our bezel only goes to the sides and above the speaker with insulation below, will this compromise it's performance?

thank you all in advance for your generosity of time and knowledge in answering any of these questions. all the best.

p.s. if anyone is having difficulty viewing the embedded image, it can be seen here:

http://imgur.com/wl48Ds6

Hi there "deliv_lalime". Welcome! Please read the forum rules for posting (click here). You seem to be missing a couple of things!

we currently have a pair of adam A8X's that we will be mounting.

Nice! Good choice.

we've also included space in the design to include a centre channel when we upgrade to a surround rig for film mixing. there is some debate as to whether this is wise or if we should only build the center soffit wall when we upgrade down the line.

I would do it now, for sure. A 5.1 room is a whole different animal than a 2.0 room, so if you plan to go 5.1 in the future, build the room as 5.1 now. You can still use it as 2.0 in the meantime. But converting a 2.0 room to 5.1 is a big deal, and might mean tearing down and re-doing large parts of it.

1. has anyone soffit mounted A8X's and know how they behave "in the wall"?

I have a couple of clients who have done A7's and A7X's successfully, and one "in progress" design for A8X's. There should be no problems doing that, as most of the Adam range lends itself quite well to soffit mounting.

2. i'm curious to hear anyone's advice or successes using barefoot's retrofittable design ... it seems like it should work well. are there any pitfalls to watch out for? considerations to plan for initially?

I used that concept, heavily modified, for a studio that is nearing completion right now, and it looks like it is working fine. Basically, my modification creates a sort of "drawer" that slides in place and is held to the back with long threaded rod and nuts. To change the speaker, undo the nuts, slide out the drawer, fit the new speaker, slide it back in, tighten nuts... Done!

3. we're looking at upgrading toward Adam S3A's or S3V's or Focal Twins. what success has anyone had with flush-mounting these? would they fit well into the "larger box" that TB plans for in his design?

Make the box big enough right now for any possible future speakers that you might consider. For the one I did, the current speakers are Genelec 1032's, with the possibility of going up to the Adam S5X-H, which is a monster.

4. i notice in john's designs that he builds a tight fitting box around the speaker. barefoot sits it on a shelf snugly strapped in. opinions on which is preferable?

Two different design concepts. Either will work, if done correctly. John's philosophy is to hold the speaker very rigidly in place so it cannot move at all. Barefoot decouples it form the structure.

5. any advice on soffit mounting the centre channel down the line? we've discussed placing it outside the wall on a stand further forward, with time delay to compensate. we haven't come across much in the way of surround sound soffit designs and would love any input on how best to do this.

If your L and R mains are soffited, then your C should be too, so that they sound essentially the same. ITU and EBU specs do allow time correction for speakers that are not on the circle (or for all the other speakers that are on the circle, as the case may be), but do not recommend it. The rear surrounds are a bit different, and can go on stands, but I still prefer to soffit mount them where possible. That does require some strange room geometry, though, in some cases...

6. john's design calls for acoustical hangers below the speaker shelf. as i understand it, these are fibreboard (mdf?) wrapped with rigid insulation (owens 703?). how far spaced out should these be? would be able to get away with stuffing this area with roxul as an alternate design for bass trapping? or would this be insufficient?

It is Homasote, not MDF. It's a very soft fiberboard, the type you use for making bulletin boards for push-pins. And it is wrapped with fluffy fiberglass or mineral wool, not 703. 703 is used to line the cavity around where the hangers hang, but the wrapping is the fluffy type.

we also wanted to place ns10's on the meter bridge (8.5" high).

It's never a good idea to have speakers on the meter bridge, for several reasons: vibration can lead lead to early-early sound (arriving at yoru ears BEFORE the direct sound from the speakers...!), and the reflections off the console surface really mess up the mid range, and also create heavy comb-filtering. Yeah, I know; you see it done like that "all the time" in pictures of studios. But just because other people do things wrong and don't care doesn't mean that we have to as well!

this would put our speaker shelf 47.5" high with the tweeter at 60" high.

Way too high for A7's That places the acoustic axis at about 58"-and-abit. The speakers should be set up such that the acoustic axis is at 1.2m above the floor (47-1/4"). If you go too high, then you are off-axis, and even though the A7s have good off-axis response, it's still not ideal. If you have to raise the speakers, then you also have to tilt them down, which implies a whole lot of other issues that you need to consider.

if push the ns10's toward the middle enough to lower the soffit mounted Adam's, would this help?

Yup! But not on the meter bridge: put them on heavy, rigid stands just behind the desk.

8. before we install the centre channel, what would be best to put in that cavity? i am thinking loose insulation fronted with rigid insulation.

Exactly the same as for the L and R soffits...

9. john recommends a 2" rigid insulation pad below the speaker to catch reflections off of the console whereas thomas' bezel extends in all directions outward from the speaker, flush to its surface. john has a rigid layer behind his insulation pad. is there any great contradiction here?

No contradiction: there is still a hard surface behind the insulation, so the soffit surface is continuous. It is 2" back, yes, but far enough away from the acoustic axis as to not be a problem. You wouldn't want to do that right next to the side of the woofer, for example, but that far below is fine. The depth of that surface is much less than the wavelengths that are in play at that distance.

p.s. if anyone is having difficulty viewing the embedded image, it can be seen here:

That's one of the items mentioned in the link I gave you up top!


- Stuart -



- Stuart -

hi stuart!

deliv_lalime is so formal, please call me patrick

thank you so much for the time taken answering my post. i can't tell you how much it is appreciated to the people on the ground here exerting themselves building this.

my apologies for missing a few of the forum rules. i've read through them thoroughly. please find attached here my properly embedded image from my first post as well as updated location. i'll also make an effort to fill in a few of the blanks i might have left out describing our build thus far. do let me know if i miss anything else.

first off, detailing our existing construction: we are building within an existing complex which houses a full-service recording studio & then a separate mastering suite on the same floor as us, as well as a record label office and technician's atelier on other floors. as such isolation was a primary concern (we are directly adjacent to the larger studio's minimally-constructed iso B, which is the only separation between us and their main tracking room). to achieve this we built a floating floor supported by neoprene mounts (the manufacturer and a local acoustician consulted extensively on the design, and i am reasonably confident that we aced this).

our walls and ceilings are a triple layer of 5/8" firecode gyp, sealed with acoustical caulking, affixed to steel studs. the floor itself is a double layer of OSB, topped with a plywood plan finish. though they are not properly represented in the drawing here, each door in the build is doubled, using solid-core doors, rubber gaskets and custom-milled thresholds.

we have begun treatment and already constructed two corner bass traps, each a superchunk design, 48" on the hypotenuse, made from roxul safe and sound, fronted with 2" of owns 703. there is also an 11' wide pad at the back of the room, 56" high and 14" deep, made from 12" of safe and sound, fronted with 2" of owns 703.

in front of the pad we've built a 10" stage to accommodate a couch and coffee table for clients watching films on the projection screen, giving them a comfortable viewing angle above the engineer's head. the stage doubles as additional bass trapping, as it is filled with roxul SNS.

which brings me to the current stage of the build, the soffits. thank you again for all of your answers. they bring much reassurance that we are on the right track here. what you say about the sayers and barefoot being totally different designs clarifies much. here are my follow-up questions. as always, our gratitude for your time in this.

1. as we wish to "future-proof" against a likely monitor upgrade in the near future, we will be pursuing the barefoot design, borrowing a few points from john's. how extensively should we pursue decoupling the speaker shelf framing from the rest of the room? neoprene mounts/pads at the floor? spring connectors for the walls?

2. when filling in cavities with "loose insulation" as john's diagrams indicate to do, what should be used? would roxul safe and sound do the job? and how loose is "loose"? torn up to improve air passage? or will there be sufficient ventilation for the active monitors through bats laid in as they come when bought?

3. pursuing the barefoot decoupling concept, we are still borrowing from john's design on some fronts. we will be placing acoustical hangers below the speaker shelves. is this wise? we will also be leaving the 10" open bass port at the bottom of the front wall? does this opening defeat the purpose of the decoupling?

4. how many hangers should we use below each speaker shelf? as many as can be fit? and i am assuming that the dimensions of these should be whatever will comfortable fit with clearance inside of the cavity below the shelf. is this correct?

5. as you recommend we will be building the centre channel wall as well from the outset. budget will likely prohibit us from actually installing a speaker here and so we will fill the cavity with insulation and cover where the bezel would go with recessed plywood covered with rigid insulation. does this seem workable?

6. my only remain concern with this design is reflections from the left and right channels hitting the centre wall and then hitting the splay wall and coming back toward the mix position. is this a major concern or do our wall angles seem good enough to push it all towards the back of the room?

7. thank you for the advice about placing the ns10's on stands behind the console. we will definitely pursue this. all the same, how much should be concerned about these and other objects (computer monitor) being in the projection field of the monitors? even if they are not direct obstacles between the engineer and monitor, are there workarounds for the potential reflections that might come off of the sides of the ns10's?

8. lastly, how many hangers should we plan on attaching below the speaker shelf? as many as size will permit? and as to their dimensions, i assume we should make them as large as the dimensions of the cavity will permit. am i correct in this?

as always, thank you so much for your consultation here.

best regards,

patrick

Wow! Lots of questions! That's good, actually. Obviously you are thinking things through carefully.

please find attached here my properly embedded image from my first post as well as updated location

to achieve this we built a floating floor supported by neoprene mounts (the manufacturer and a local acoustician consulted extensively on the design, and i am reasonably confident that we aced this).

I hope you did! And I sure don't want to rain on your parade, but floating a floor properly is a lot harder than most people think. Here's a very interesting thread about what it takes:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

our walls and ceilings are a triple layer of 5/8" firecode gyp, sealed with acoustical caulking, affixed to steel studs.

That's just the inner leaf, right? What about the outer leaf?

we have begun treatment and already constructed two corner bass traps, each a superchunk design, 48" on the hypotenuse, made from roxul safe and sound, fronted with 2" of owns 703. there is also an 11' wide pad at the back of the room, 56" high and 14" deep, made from 12" of safe and sound, fronted with 2" of owns 703.

Excellent! That should do a decent job of bass trapping at the rear, and controlling reflections. You might even need a little reflective or diffusive surface back there, so that the rear of the room doesn't sound too lifeless in the highs. But do a REW test first, to see if you need that.

1. as we wish to "future-proof" against a likely monitor upgrade in the near future, we will be pursuing the barefoot design, borrowing a few points from john's. how extensively should we pursue decoupling the speaker shelf framing from the rest of the room? neoprene mounts/pads at the floor? spring connectors for the walls?

You don't need to decouple twice: Once is enough. In fact, decoupling twice can also act like a 3-leaf system if you don't do it correctly. So just decouple at the speaker itself, with Sorbothane pads between the speaker and the box it sits in.

2. when filling in cavities with "loose insulation" as john's diagrams indicate to do, what should be used? would roxul safe and sound do the job? and how loose is "loose"? torn up to improve air passage?

Any old insulation is fine! Use it as your garbage can for insulation: all the off cuts, bits and pieces, leftovers, etc. Just dump them in. Or if you don't have any waste insulation, then just fill it with large pieces, standing up or laying flat, but not forced in under pressure.

or will there be sufficient ventilation for the active monitors through bats laid in as they come when bought?

Before you put the insulation in, make a sort of "chimney" inside the soffit, above the speaker, using chicken wire. Just form it into a shape that will allow a clear passage for air to flow up, then dump your isulation in around it.

3. pursuing the barefoot decoupling concept, we are still borrowing from john's design on some fronts. we will be placing acoustical hangers below the speaker shelves. is this wise?

Yes! Excellent. You very likely need that extra bass trapping at the front, so that's great.

we will also be leaving the 10" open bass port at the bottom of the front wall? does this opening defeat the purpose of the decoupling?

Not at all! You need that opening to allow the sound in to the hangers, and also to allow the cooling air to enter through the slot behind the speaker. It does not affect the decoupling at all, if you do it the way I suggested, with Sorbothan pads around the speaker.

4. how many hangers should we use below each speaker shelf? as many as can be fit? and i am assuming that the dimensions of these should be whatever will comfortable fit with clearance inside of the cavity below the shelf. is this correct?

Right, as many as can fit easily without touching each other or the sides of the soffit. They must hang freely, with about an inch or so between them, minimum. If you do it right, then when they are all in place if you start one of them swinging by hand, then the others should also swing a tiny bit in sympathy.

5. as you recommend we will be building the centre channel wall as well from the outset. budget will likely prohibit us from actually installing a speaker here and so we will fill the cavity with insulation and cover where the bezel would go with recessed plywood covered with rigid insulation. does this seem workable?

Perfect!

6. my only remain concern with this design is reflections from the left and right channels hitting the centre wall and then hitting the splay wall and coming back toward the mix position. is this a major concern or do our wall angles seem good enough to push it all towards the back of the room?

That's why you need to ray-trace very carefully, to make sure that no reflections get to your head. Search the forum for "ray trace" to find out more about that. It is very important to do this correctly!

7. thank you for the advice about placing the ns10's on stands behind the console. we will definitely pursue this. all the same, how much should be concerned about these and other objects (computer monitor) being in the projection field of the monitors? even if they are not direct obstacles between the engineer and monitor, are there workarounds for the potential reflections that might come off of the sides of the ns10's?

Make sure that the path from the tweeters to your ears is totally unobstructed, with nothing at all close to that path that could cause high frequency reflections, which act rather like beams of light. The woofers should be mostly free from obstructions, but if there is something small partly in the way, that probably won't do any harm.

Here too you should ray-trace reflections form the backs of your video monitors and NS-10s, to make sure that there won't be any objectionable reflections, and adjust the angles of those things as needed.

Hope that helps!


- Stuart -

hi stuart, thank you so much as always for getting back to us! your information is very reassuring. my contractor and i had a good laugh at the ingenuity of the chicken wire chimney. we will definitely enjoy building that. also thanks for reccomending us to sorbothane. i just had a really nice chat with their rep over in kent, OH.

only two quick questions and i think we're good to go on this.

1. i am assuming that the strap featured in barefoot's design is nixed as it would defeat the purpose of the sorbo pads, yes? am i missing out on some functionality that the strap added to the design?

2. how far out from the speaker should the bezel extend? is there some ratio of baffle size as compared to speaker size we should be observing? in john's design the timber finish goes almost all the way to the top of the wall. however his example features a speaker placed much higher up the wall than ours. we will be placing 16" speakers at a height of 40" on a 109" wall.

thanks as always, stuart! you are a huge encouragement to us. i look forward to showing you the room some day should travel ever bring you up this way from santiago.

best,

patrick

1. i am assuming that the strap featured in barefoot's design is nixed as it would defeat the purpose of the sorbo pads, yes? am i missing out on some functionality that the strap added to the design?

There isn't much tension on the strap, and it is flexible, so it should not transfer much energy from the speaker to the frame: It will transfer some, yes, but since the frame is already very rigid and massive, and it will mostly be higher frequencies that get transferred, so I wouldn't worry about it too much. The other point here is that if the speaker is inside a box and there is Sorbothane between them to decouple, then adding the straps to the outside of the box to keep it in place does not affect the decoupling at all...

2. how far out from the speaker should the bezel extend? is there some ratio of baffle size as compared to speaker size we should be observing? in john's design the timber finish goes almost all the way to the top of the wall. however his example features a speaker placed much higher up the wall than ours. we will be placing 16" speakers at a height of 40" on a 109" wall.

Ahhhh! Now that's the 60 million dollar question, isn't it! ?

Technically, the bezel or soffit panel around the speaker is known as an "infinite baffle", and that gives you an idea of how big it should be in theory: infinite! However, that really means "infinite with regard to the wavelengths in question".

Obviously, a truly infinite size baffle is impossible, and even one that is very large with respect to all audible wavelengths is also impossible, considering that the wavelength of 20 Hz is about 17 meters! It would be rather difficult to have a baffle 34 meters wide and 34 meters high with your speaker in the middle...

Many years ago, some speaker manufacturers would actually bury their speakers in the ground, pointing upwards at the sky with the front surface level with the ground, and take their test measurements like that. That's about as "infinite" as you can get, in the real world.

OK, so let's look at the theory here in more detail, to find out exactly what it is we are trying to accomplish, to then come up with a sensible size. What is the actual purpose of the soffit?

It works like this:

Sounds don't all behave the same. Higher frequencies tend to propagate more like beams of light, or rays, projecting straight out from the speaker in a sort of tight cone and gong forwards, without spreading out much to the sides. Low frequencies, on the other hand, act more like a balloon that is being inflated around the speaker, spreading out in all directions. Part of the reason that so much design work goes into tweeter horns, is to try to get the high frequencies to spread out wider and more evenly, and so much work goes into woofers to try to get the sound to NOT spread out so wide, so that the highs and lows match more reasonably (there are other reasons too, such as the major impedance mismatch between speaker cone and air, etc.)

In a perfect speaker, all of the sound, at all frequencies, would seem to come out the front of the speaker as a flat planar wave that just moves across the room. The only real-world speakers that come close to accomplishing this, are large electrostatic panels, and that's exactly how they work: the entire front panel (several feet high and wide) is a membrane that moves back and for all at once. And they sound fantastic! But they are expensive, complicated, and not able to produce very high levels of sound, so you don't see them too often these days. Unfortunately.

Another problem with such speakers is that they won't fit in your car to take them home from the store, and they won't even fit on the shelf in the store! They are huge.

So, since manufacturers cannot actually make a perfect speaker, they are stuck with just making "really good" speakers that try to sound much bigger than they really are. And that gets back to the problem of how sound propagates differently for different frequencies.

OK, so if highs go straight forwards but lows don't then obviously there is a power mismatch between the two. If you have, for example, 1 watt of high frequencies and 1 watt of low frequencies, well ALL of that 1 watt is going straight at your head for the highs, but only HALF of it is going towards you for the lows: the other half is spreading out behind the speaker, going AWAY from you. In technical terms, there is a difference of 6 dB in the sound power radiated forwards for highs, and all around for lows. The lows are said to be radiating into "full space" (a sphere all around the speaker), and the highs are radiating into "half space" (half a sphere, in front of the speaker).

The main reason this happens is because of the "baffle", the technical name for the front panel of the speaker: Just by being there, it forces all of the highs to go straight towards you, while the lows go all around. The

size

of the baffle determines where the changeover happens. The basic issue is that sound waves are only affected by objects that are substantially larger than their own wavelength, so waves that are smaller than the shortest dimension of the baffle tend to go forwards (since the baffle is bigger than the are, and prevents them from going backwards), but waves that are larger than the dimensions of the baffle don't even see it: they just "wrap around" behind it, as though it was not even there.

This whole effect is called the "baffle step response", because if you look at a graph of power vs. frequency, you'll see a "step" in the middle of the curve, at the point where the size of the waves is comparable to the size of the baffle. If you really ant to get technical about this, the mid point of that "step" occurs at the frequency f = 4560 / Wb, where "Wb" is the width of the baffle in inches. You probably don't need to know that, though. And if you are

To "fix" this power imbalance between lows and highs, manufacturers include a "baffle step correction" circuit inside the speaker, usually as part of the cross-over network, so that the speaker increases the power for low frequencies. In fact, it has to produce twice as much power for the frequencies that are lower than the baffle step, as compared to frequencies above the baffle step.

All of this problem is totally eliminated by putting the speaker inside a soffit, flush with the front surface. In effect, the soffit face is just a much larger baffle that moves the baffle step point to a much lower frequency, since it acts as an infinite baffle for waves that are smaller than the shortest dimension of the soffit. That's why professional speakers have a "bass roll-off" control on the back that reduces the power for low frequencies by 6 dB, so ti is the same as the power for high frequencies. In reality, what that control does is to turn off the "baffle step compensation" that is built into the speaker, since you don't need it any more if the speaker is very close to a wall, or soffit mounted.

OK, so getting back to your basic question: how big does the baffle have to be? Obviously, if you made a baffle just one inch bigger than the speaker, then you haven't accomplished much! And if you make it 100 feet bigger, then you have accomplished everything, and more! Basically, start by looking at the lowest "cut-off" frequency for your speaker. There's no point in making the baffle big enough to deal with frequencies that it doesn't even produce. So for example, if your speaker works down 80 Hz, then it only produces waves up to 14 feet long, so a soffit 14 feet wide would be fine. However, you don't actually need to cover a full wavelength: In fact, a quarter wave is fine, so you could get by with a soffit 3'6" wide, for a cutoff of 80 Hz. If your speaker goes down to 50 Hz then a soffit 5'8" wide would be good, theoretically.

Those are still pretty big for typical home studios, but that's what theory says. On the other hand, soffits normally blend into the side walls and the front wall, which makes them appear bigger than they really are, acoustically: that combination of "soffit plus walls" can even act somewhat like a very large horn, which is good as it helps with the impedance matching, to a certain extent.

So there's your answer: make the soffit as big as you can in all directions, within reason, and hopefully about a quarter wavelength of the lowest frequency that your speakers produce.

But! There's another issue here: the speaker should NOT go in the exact center of the soffit: if you do that, then it creates symmetrical "lobing" patterns, focusing some frequencies more strongly than others in certain directions. You should offset the speaker so that it is a different distance from each edge of the soffit. Normally that happens automatically in the vertical plane: the speaker is closer to the bottom edge of the panel than the top. But you also need to do the same left-to-right. Ideally, try to get the speaker to a location at about 2/5 of the width of the panel, but if you can't get it that far over, then any amount is better than no amount! It normally turns out that moving the speaker so far off center means that it won't fit inside the soffit any more: the back edge will be hitting the side wall, or the front wall, depending on which way you moved it. So just move it as far as you reasonably can off center.

That's just one of the hundreds of compromises that you have to make, when designing a studio!

If you REALLY want to get muddled up in the theory of all this, and confuse yourself even more, then here's a little program I found many years ago that helps predict the baffle step response effect for speaker designers, and also calculates the parameters of the baffle step correction circuit that would be needed for any give speaker shape/size.... :

i look forward to showing you the room some day should travel ever bring you up this way from santiago.

Cool! I do get up to Canada every couple of years, so next time I'm there I'd love to drop in and take a look. Thanks for the invitation!


- Stuart -

stuart, thanks so much as always for the very thorough and thoughtful response. after what i thought was much careful checking and measurement in our sketchup plan, we went to start building in the room and found the cavity to be much too small for everything we had hoped to accomodate (decoupled shelves, acoustical hangers, ventilation for active monitors).

and so back to the drawing board it was. i completely revamped the plan, adjusting the speaker placement and angle to give more room in behind. i've also left what seems like nothing up to "we'll figure it out as we build it". it seems as though we should be able to make this work given the space we have.

that said, my partner is nervous about installing these soffits. though we have heard much about how great they can sound, we've also heard some horror stories about how they perform when installed badly. as such it would be really helpful to get one last review on the plans as they stand. i'm attaching here our sketchup file as well as screen caps with labels of all the pertinent details.

i'll also try to go through as many of the details as possible here to hopefully get your best assessment of how well we might expect this to work.

as i mentioned previously, we are implementing a hybrid design, using many of the details from john's soffit design over top of thomas barefoot's adaptation using a decoupled shelf to allow for speaker replacement in the future. we mill likely be mounting A8X's, S3X-H's or Focal Twins to start with and upgrade down the line.

the front soffit wall is a 2x4 frame recessed 1" from the surface of the speaker. below the speaker shelf it will hold 2" of roxul RHT 40 backed with 1" of MDF to deal with reflections off the back of the console. in behind the mdf will be another layer of RHT 40 facing the inside of the soffit cavity.

above the speaker shelf, the 1" MDF bezel will be mounted flush with the front surface of the speaker. as per your reccomendation, we will be building the bezel as large as possible so that it will go right to the edge of each soffit wall (L/C/R). the speaker center, as per your recommendation, is decentered and sitting at ~20% of the way from the intersection with the center wall. the final dimensions of the bezel will be determined by the actuall speaker which is installed, but the lateral width will be 7-13" on the inside edge of the L/R channels, and 13-18" on the outside. it will extend all the way from the top of the speaker (roughly 50-55" up the wall) to the top vent 6" from the 109" ceiling.

the pad backed with MDF below the speaker will extend from the bottom of the shelf all the way to 10" from the floor at which point there will be a cloth covered opening allowing for a bass port.

beneath the shelves will be acoustical hangers made of 1/2" homasote wrapped in 1" soft insulation. these will be roughly 2.5" thick each and hung at 1" intervals perpendicular to the soffit wall, the entire length of each shelf.

the inside of the cavity is covered from floor to ceiling with 2" of Roxul RHT 40, and will be stuffed before ceiling with "pink stuff" insulation.

our shelves sit at a height of 39", flush with the top of our console. elevating the speakers 1.5" above the height of the console will be the load-calibrated sorbathane pads you steered us to. on top of the shelf, a 30" high open-sided box will be built and wrapped in chicken-wire. the top and bottom of the box will have vent holes 2.5" x 10" vent holes cut that are connected to a chicken-wire chimney going toward the 4" vent at the top of the soffit wall.

the speaker will sit on the sorbathane hemispheric pads inside of this box, loosely strapped to the shelf. the empty space remaining in the box will be filled with loose insulation, with the back portion blocked off with chicken wire to preserve venilation space.

the speaker walls are a 22.5 degree angle in relation to the back wall. all three speakers are 91" from the projection axis. this works out to roughly 40% of the way back in our 210" deep room. the splayed walls adjoing the soffit walls are 65 degrees in relation to the back wall. careful ray tracing seems to suggest that we will have no reflections at mix position, with everything being pushed back toward the rear absorptive pad i described in a previous post.

the soffit cavity is 111 3/4" wide by 35" at it's deepest and 20" at it's shallowest.

i think i've covered most of everything here. please do let me know if you think we've gotten anything wrong here or if there is something we could do "more right". i hope i've been as clear as i've hoped to be through here; do let me know if anything at all requires clearing up.

thank you so much as always for your expertise, stuart. it is most appreciated ))

+++++++++++++++

link to .skp file:

http://www.sendspace.com/file/aietbl

Wow! I just noticed that I hadn't ever replied to this thread! I hope it's not too late...

and so back to the drawing board it was. i completely revamped the plan, adjusting the speaker placement and angle to give more room in behind. i've also left what seems like nothing up to "we'll figure it out as we build it". it seems as though we should be able to make this work given the space we have.

From what I can see, it looks good. You seem to have your angles, distances and sizes all worked out neatly.

that said, my partner is nervous about installing these soffits. though we have heard much about how great they can sound, we've also heard some horror stories about how they perform when installed badly. as such it would be really helpful to get one last review on the plans as they stand. i'm attaching here our sketchup file as well as screen caps with labels of all the pertinent details.

The plan looks fine to me. At least as far as the soffits themselves go. What I don't see is the rest of the room, and how that relates to the soffits. That is also important.

As I mentioned before, probably the most important issue with soffits is that they must be built very solid, rigid, and massive, and the speakers must either be fully decoupled from the front baffle (Barefoot style), or absolutely rigidly held in place (Sayers style). As long as you do that, and adjust the settings correctly, then you should be fine. Of course, you also need to design and treat the rest of the room properly too...

we mill likely be mounting A8X's, S3X-H's or Focal Twins to start with and upgrade down the line

The A8X's should be great for that.

above the speaker shelf, the 1" MDF bezel will be mounted flush with the front surface of the speaker. as per your reccomendation, we will be building the bezel as large as possible so that it will go right to the edge of each soffit wall (L/C/R). the speaker center, as per your recommendation, is decentered and sitting at ~20% of the way from the intersection with the center wall. the final dimensions of the bezel will be determined by the actuall speaker which is installed, but the lateral width will be 7-13" on the inside edge of the L/R channels, and 13-18" on the outside. it will extend all the way from the top of the speaker (roughly 50-55" up the wall) to the top vent 6" from the 109" ceiling.

That sounds great. So far so good.

Our shelves sit at a height of 39", Are you sure that is correct? That implies that the acoustic center of the speakers you use will be 8-1/4" inches above the shelf, and that includes the Sorbothane pad. That sounds too little to me. The would be a rather small speaker. Are you sure you checked those dimensions correctly?

i think i've covered most of everything here. please do let me know if you think we've gotten anything wrong here or if there is something we could do "more right". i hope i've been as clear as i've hoped to be through here; do let me know if anything at all requires clearing up.

With the exception of the shelf height, everything else sounds fine. I'd suggest you double-check the height issue. The acoustic axis of the speaker must be 1.2m above the floor, which is 47-1/4". The acoustic axis is somewhere between the woofer and tweeter, and is different for every speaker. Most manufacturers publish that information in the manuals, or will give it to you if you ask.

- Stuart -

Hi guys

I hope it's okay to bump this excellent thread about soffit mounting speakers even though there hasn't been any postings in years. Reading up on the subject and deciding what might work best for me.

deliv_lalime wrote:i completely revamped the plan, adjusting the speaker placement and angle to give more room in behind. i've also left what seems like nothing up to "we'll figure it out as we build it". it seems as though we should be able to make this work given the space we have.

[...]

i'll also try to go through as many of the details as possible here to hopefully get your best assessment of how well we might expect this to work.

So Patrick, may I ask how the studio build went?

Did you successfully soffit mount the speakers, and did you eventually upgrade them to bigger models?

Fingers crossed it all worked out great for you guys!


All the best
Fred