John Sayers' Recording Studio Design Forum Archive

It seems there are some contradictions at work here?

Not contradictions, really. More of "ignorance", I'd say.

Taking your points in reverse order:

it seems there should be a significant difference depending on whether you mount them in boxes with only a few mm of space rather than a space big enough for adjustable shelves etc.

Right! The entire point of soffit mounting is to convert the small front baffle of the actual original speaker cabinet into a very large front baffle, with a lot of area around it. In fact, technically the term is "infinite baffle", since the optimum design would make the baffle infinitely large with respect to the sound waves that it must deal with. In practice, that isn't possible of course, but the idea is still to make it as large as possible, exactly as you say.

I've never seen a soffit with "adjustable shelves", although there are designs that allow you to replace the speaker with another model of a different size. However, when properly implemented, those designs still do have a large amount of area around the speaker on all sides. Without that large area, there is no point to soffit mounting.

There are other important points that should be taken into account, such as making sure that the speaker is offset from the center of the baffle, to prevent symmetrical artifacts forming around it and creating intense patterns of comb filtering. So there's a trade-off here between the need to have as much area as possible around the speaker, and also to not have the speaker in the center. A good rule of thumb is to have it offset to about 2/5 of the width and around 1/4 of the height of the baffle. But just like the infamous "38% rule", those are not absolute perfect positions, written in stone: just good starting points.

Then there's the support of the monitors. The kind of framing I see so often implemented really contradicts the typical emphasis on heavy dense stands that are fully decoupled from the room.

Welllll.... yes and no... Sort of! Heavy dense stands are meant for speakers that are NOT soffit mounted, but are free-standing in the room. The same concept applies to soffit mounting, but there's a difference:

With a stand, the only support the speaker has is from below. With a soffit, it is supported from all sides: top, bottom, left, right and also from behind. So it is already being held in place far more rigidly, since it has framing on all sides.

Also, there are two different basic approaches for designing soffits. The first is to hold the speaker and baffle in place so rigidly that the cannot move at all. This is what John normally does with his designs. The soffit is a very massive, very rigid, very solid frame where the speaker cabinet itself is held tightly by a box that it just fits in to, and the entire structure is attached very firmly to the floor, with no decoupling. This works due to the sheer mass and high rigidity of the soffit. The other concept is to decouple the speaker from the framing, with suitably dimensioned (and carefully calculated!) rubber strips around it, so that it can vibrate freely without transmitting that to the structure. In this design, there is a small gap between the speaker and the infinite baffle, so that the speaker can move freely without touching the baffle. There is even one design (by Barefoot) where the baffle and the speaker are on two separate, independent frames that don't touch.

Both designs work when done properly, but it is important to not confuse the two.

The thing that bugs me most with flush mounting is that on one hand such importance is placed on a hard, flush, uninterrupted baffle.. but then others recommend use of 3-6" of absorption which makes the front baffle neither flush nor hard.

Yup! That's a problem, for sure. I'm not sure where it comes from, but there seems to be some place that is recommending exactly that, which makes no sense at all. If your speaker is surrounded by soft absorption, then you DO NOT have a soffit mount! There might be reasons why some people would want to do that, but it is NOT soffit mounting, and will NOT produce the same benefits as a true soffit mount.

The entire purpose of soffit-mounting is to remove the speaker from the room. Any time that a speaker is close to walls, ceiling or floor, then that creates artifacts where the sound waves "bouce" off the walls and return to interact with the direct sound. This creates things like SBIR cancellations, comb-filtering, early reflection issues, phasing, and a bunch of other undesirable problems. Soffit mounting eliminates all of those, since the speaker is no longer in the room, technically. The correct name for soffit mounting is "flush mounting", since the front of the speaker is flush with the wall, thus removing the speaker from the room. But if the speaker is NOT flush with the wall, then it is NOT a soffit mount, and those artifacts will still be there. The speaker itself must be surrounded by a hard, flat, rigid, massive surface: that is the most basic definition of what soffit mounting is.

The only "exception" to that is what John often does: A few inches below the speaker he has a box on the front of the soffit with insulation in it, that absorbs the strong reflections from the front of the desk and the console. That is important in rooms that have large consoles or desks with large vertical surfaces facing the speakers: those surfaces are a big problem, since they reflect a lot of loud sound directly back to the lower part of the soffit, where it bounces back once again into the room (causing artifacts), and can even create standing waves at some frequencies. So if you have a large console or a desk with speakers, then it's a very good idea to do that. It does not affect the "infinite baffle" principle much, since there is still a hard, solid, rigid surface just behind that absorption, which is only a couple of inches behind the rest of the baffle, and is far enough from the speaker as to not affect things too drastically. This is a bit of a trade off, but those early, very strong reflections are far more important than the slight effect of not having the baffle perfectly flat.

So yeah, it can be confusing when you see these things, and you are right that some of them are just plain illogical and silly, but some of them do have a purpose as well.

Probably the best thing you can do is to post the design you are thinking of for your soffits, so that we can take a look at it and suggest ways to improve it, if necessary.

- Stuart -

Soundman2020 wrote:

The thing that bugs me most with flush mounting is that on one hand such importance is placed on a hard, flush, uninterrupted baffle.. but then others recommend use of 3-6" of absorption which makes the front baffle neither flush nor hard.

Yup! That's a problem, for sure. I'm not sure where it comes from, but there seems to be some place that is recommending exactly that, which makes no sense at all.

Excerpt from Genelec's site:

"The following should be considered when flush-mounting any monitor:
•For the benefits listed above the wall construction should be solid and consisting of heavy mass material. However this can lead to reverberation time problems at low frequencies
•If the wall is totally solid and reflective then some lower midrange boost may occur, so make the wall slightly absorptive around the 200 to 500 Hz region - use 10 to 20 cm thick rock wool or foam plastic glued onto the front wall surface
•The flush mounting details around the enclosure should be as smooth as possible; otherwise the cabinet edge diffraction benefits will be wasted."

I keep thinking about this, but is there really any point in attempting to enclose the rear panel of the mounting box if you're already making it a few inches longer for cabling plus cutting big ventilation ports in it? I'm having a hard time seeing how this would serve a purpose and am tempted to just leave mine open. I already have a tight fit around the sides and top.

is there really any point in attempting to enclose the rear panel of the mounting box

For acoustics and cooling: No, no reason at all. But for structural integrity there's a good reason: that's the only piece that keeps the box square. That might or might not be an issue, depending on the overall design.

- Stuart -

How can I sofit mount if I cant have the box all the way to the floor as described from John Sayers?

How can I sofit mount if I cant have the box all the way to the floor as described from John Sayers?

John's soffits do not go all the way to the floor. There's a gap of at least 12 inches at the bottom, to allow sound to enter the area where the hangers are.

But regardless of that, your design is not feasible, and not usable for the main speakers at the mix position. Many large control rooms do mount speakers high up like that, but they are meant to cover the rear of the room, where the client couch is.

The issues with your design are multiple. First and most important, the speakers are tilted way too far down. The absolute maximum angle that any speaker manufacturer recommends is 15° down-tilt, but even that is excessive. Most recommend no more than 10°, and there is research that suggest the limit should be 7°. Personally, I wouldn't even go that far: I've never designed any room with more than 5° of tilt to the speakers.

Why?

Firstly, because our ears are not designed for that! Our auditory system depends on very subtle phase and timing differences caused by the pinnae, in order to determine directionality. Sending the sound from way up high at a very large angle, messes that up an alters the sense of directionality of a sound source. So your engineers will not be able to accurately determine panning locations of mics and instruments with the setup you show. To them, the sound would appear to be coming from a different direction than where ti is really set on the sound stage.

Then there's the issue of first reflections: With the speakers mounted so high, at such a steep angle, there will be major, abundant, strong reflections off the console and desk surfaces, into the engineers ears, at all frequencies across the spectrum. So not only will the engineer be unable to to determine direction properly, he also won't be able to determine frequency and tone well, since he'll have huge comb filtering issues from those reflections, and he won't be able to hear reverb tails and other subtle hints, as they will be drowned out by the reflections from the console. Those reflections will be well inside the Haas time window, so there will be the smearing effect from that too.

Then there's the issue of head movement: As the engineer moves his head forwards or backwards just a little while he is operating the console, he'll be moving his ears very large distances across the speaker axes: There's only one very tiny point where his ears will be on-axis, and at all other points he will be off axis, and very much so. No speaker has good off-axis response at the angles that you would be subjecting him to. Just by sliding his chair forward a few inches to reach the top of the console, he'd be about 30° off axis, and therefore in a very non-linear area of the speaker polar pattern. You'd have to nail his chair to the floor and set up a rigid neck brace to keep his head in the right place!

Then there's the issue of the baffle area around the speakers in your design: it does not increase the area very much. Below the speaker, in fact, you have practically no additional area at all, and side to side the area changes: at the top of the speakers, it is also minimal.

There are many other issues that I don't have time to go into, but those are the biggies. I'd suggest that you change your design to something more conventional, and more useable: Keep the angle under 7°, and keep the speakers at ear height.


- Stuart -

Thanks Stuart

I think we will just have to go with near field monitors on stands as the window area is almost built.
So when we see speakers high up in a studio does this mean it is mainly for the clients?

So when we see speakers high up in a studio does this mean it is mainly for the clients?

Pretty much. And also for "checking the mix" on those big wonderful boomy things that sound so cool when turned up to 11. But they generally aren't used for making mix decisions. At least, they aren't used by smart engineers who understand how human hearing works!

I think we will just have to go with near field monitors on stands as the window area is almost built.

So if you have glass behind the speakers, where are you going to put the front wall absorption that helps to deal with SBIR, comb filtering, and other reflection issues coming off that glass? With speakers on stands, treatment at all first reflection points is a given. If you happen to have glass at that point, then you have a problem... You have to decide if the view is more important than the mix... Some places do actually prefer the view, which I've never understood: If someone goes to all the trouble and expense of building a great control room, whose very purpose is critical listening as accurately as possible so the engineer can mix well, then why would they want to throw that all out and basically trash the room, just to keep a nice piece of glass in place? For me, the decisions is easy: forget the glass and build the room to do what it is supposed to do.

That's not to say that you can't use glass in control rooms: You certainly can! but it has to be carefully designed and positioned so it does not interfere with the primary purpose of the room, which is to mix, not to look good...


- Stuart -

How about if there were some removable insulated panels that went in for critical listening that deal with the glass issue?

And this is without acoustic absorption infill panels.

I guess when critical listening is required then the panels can be inserted and when not ion use just sit below behind the desk.

What do you think? It is possible right?

Anyone?

I think this will work.

I guess when critical listening is required then the panels can be inserted and when not ion use just sit below behind the desk.

You could do that, I suppose. It should work, acoustically.

- Stuart -

Thanks. It would be great to use for critical mixing tasks and removed will be great for when we track and connect with the talent.

A. Should the particular soffit components (the ones that have the structure to hold the speaker) be sealed away from the rest of the extension which would be filled with absorbent materials or hangers?

It does not need to be sealed, and indeed it cannot be sealed due to the need for ventilation, but it is still a good idea to have a massive, rigid partition between the two sections.

I also usually angle the two sections differently, to provide better RFZ and to avoid lobing and resonant artifacts as much as possible, as well as to save space.

It is noted that the box above the speaker should be loosely fitted with insulation. As i understand, the whole idea is for the air to enter from the bottom freely, heat up at the speaker and go up through the top with resistance, so it loses energy on the insulation, right?

No. The air does not ever move through the insulation. The air path is totally free and clear of any insulation. The air is drawn in at the bottom, moves up between the hangers, up past the rear of the speaker, up through the back of the soffit, and out through the top or front.

But i have seen people on this forum designing pathways for the air to move freely from the dedicated ports in the speaker box..

What "dedicated ports in the speaker box"?

The speaker enclosure box that surrounds the actual original speaker cabinet has large wide slots in the bottom and top, just above and below the rear panel of the speaker. There is also a deep gap between the rear panel of the speaker and the rear panel of the enclosure box. There has to be, to allow free circulation of air. Their are usually also additional holes in that back panel, to allow for the connection of the power cable and signal cables.

In the end i see photos with fully insulated soffits and them being fully covered with a wooden panel thats has no exit hole for air at all..

There are still exit paths for the air there... you just can't see them! They are probably concealed behind the cloud, or they go out through the top of the soffit, not the front.

- Stuart -