John Sayers' Recording Studio Design Forum Archive

Hey, I posted this same thing in the 12 page long thread titled "Soffit Mounting" originally posted by Ethan Winer but I did not get a response so I wanted to start a new thread with my questions here. Not that you need my permission, but moderators, feel free to delete my post in the other thread.


Based on John's soffit design:

What I want to know is what is the point of hangers instead of just filling the cavity with insulation? Seems like an extra complication when enough insulation will absorb anything that the hangers would.

Also, what is the point of building a box around the speaker? I remember Barefoot commenting in old threads about soffit mounting that there is no reason to build a box around a speaker, and in fact, that a regular stand is fine - as long as the stand and speaker are decoupled from the front wall. Seems like another unnecessary complication.

Also, I don't see a point either for separating the sections of the soffit cavity inter upper or lower parts or having any specific compartments..or leaving a gap at the bottom of the soffit wall.

I've read this entire thread and many others and don't understand why a speaker on a stand with a left to right, floor to ceiling wall in front of it with a properly cut hole for the speaker, cavity filled with a bunch of insulation, wouldn't be as good as any other soffit design.. at least for a passive speaker that doesn't need to have any kind of air circulation to keep its amps cool.

OH, and here is a question. I am putting the mains up above the sight path of the nearfields, and I need to angle my soffit down so that the speakers point at my head of course. I was thinking a cool design would be to just continue the angle of the soffit wall all the way down to the floor. In this design, I end up with less cavity volume on the bottom of course. As opposed to angling the soffits where the speakers are and then straightening it out about half way down. (so that the bottom part of the soffit is at a 90 degree angle to the floor) this way I of course end up with more cavity space on bottom. Anyone have an opinion on if my first idea is an acceptable design and will work as well as the second way?

What I want to know is what is the point of hangers instead of just filling the cavity with insulation? Seems like an extra complication when enough insulation will absorb anything that the hangers would.

There doesn't seem to be much research available on hangers, but it appears that they work along the lines of waveguides, which simple absorption does not do.

Also, what is the point of building a box around the speaker?

Good question! Wish I knew thew answer....

Also, I don't see a point either for separating the sections of the soffit cavity inter upper or lower parts or having any specific compartments..or leaving a gap at the bottom of the soffit wall.

The gap at the bottom is to provide a way for room sound to get to the hangers. Without that gap, the hangers wouldn't be doing much!

The divider shelf is to separate the two sections: the section for the hangers, which is exposed to the room through the gap at the bottom, and the section for the speaker itself, which is not.

I've read this entire thread and many others and don't understand why a speaker on a stand with a left to right, floor to ceiling wall in front of it with a properly cut hole for the speaker, cavity filled with a bunch of insulation, wouldn't be as good as any other soffit design..

That would work fine, as far as being an infinite baffle for the speaker itself, but makes poor use of the space occupied by the soffit. John's design uses the entire section below the speaker as a large and very effective bass trap. If you don't need bass trapping in your room, then you could leave that part out. But it's unlikely that you won't need bass trapping!

I am putting the mains up above the sight path of the nearfields, and I need to angle my soffit down so that the speakers point at my head of course.

That's fine, as long as the tilt angle is kept to less than 10°, and preferably less than 7°.

I was thinking a cool design would be to just continue the angle of the soffit wall all the way down to the floor.

That's fine too, except that you lose all the space at the bottom, since it would be getting very narrow down there.

Anyone have an opinion on if my first idea is an acceptable design and will work as well as the second way?

As a pure infinite baffle, that would work, but it doesn't make good use of the space. You do need bass trapping, and lots of it, especially if the room is small. And the best place to put bass trapping in a small room is exact where the soffit is, so it makes sense to put the divider shelf in the middle, and use the entire bottom section for bass trapping.


- Stuart -

"The divider shelf is to separate the two sections: the section for the hangers, which is exposed to the room through the gap at the bottom, and the section for the speaker itself, which is not."

AH, I get it. See, I was thinking the absorbtion in the lower half of the soffit cabinet was just acting as more sound dampening for the speaker inside of the entire cavity. BUT, it's for a bass trap for the room! Which is why the shelf is needed for the speaker because it goes across the entire horozontal middle part of the cavity, and I assume you should seal it with caulk, so that it's ISOLATES the lower cavity from the upper cavity so that the speaker sound doesn't go out the Port. Right?

"That's fine, as long as the tilt angle is kept to less than 10°, and preferably less than 7°."

Unfortunately my design is currently using a soffit tilt angle of 13 degrees. I need to be about no more than 6.5 feet from the soffit because otherwise I am underneath ductwork at a height of 6'5". And I need to fit a pair of nearfields in there as well, so it presents a challenge to keep them out of the way of eachother unless I put the mains at a height that requires at least a 12 degree angle so that they can safely be above the nearfields. But maybe I can work it out.

However, I have seen John use a soffit tilt angle of 12.5 degrees in one of his example designs on his site. So, he obviously thought it was acceptable, but we wouldn't know if that was his first choice of angles unless we knew the circumstances. What are your references for thinking it shouldn't be more than 10 degrees? Even on the Genelec monitor placement guide (cant find the link right now) it shows a speaker above the listener at 15 degrees, but it wasn't soffit mounted.. And they didn't show it being titled down though

Anyway, thanks Stuart. I need your help with my overall design..can you go take a peak at my post in the design forum titled "Tonealive's control room design"? I have more specific info on the soffit and the room that might help you understand the overall situation even better.

Also, what is the point of building a box around the speaker?

Tonealive, it's to hold the speaker rigid, in fact the whole design is to make the whole structure rigid so it becomes an extension to the original speaker box.

Yes - I often use 12 degrees lean forward so as to get the soffit speaker above the nearfields.

here's an example of a 12 degree lean.



regarding taking the angle all the way down here's Masterphonics.

John Sayers wrote:

Also, what is the point of building a box around the speaker?

Tonealive, it's to hold the speaker rigid, in fact the whole design is to make the whole structure rigid so it becomes an extension to the original speaker box.

aHA. So the soffit is not just an extension of the baffle but the whole box.

Thanks so much, I understand the need for the various components now.

John Sayers wrote:Yes - I often use 12 degrees lean forward so as to get the soffit speaker above the nearfields.

Great.. that solves a couple problems with the monitor placements for me.

Thanks again!

Tonealive

John, what are those speakers in the Masterphonics studio.

Eric - they are Westlake/Eastlake monitors. They use JBL drivers coupled with their own timber horn design. They were used extensively in all the Tom Hidely designed rooms.

Hi, one more clarification: John, your soffit design says the box around the speaker is supposed to be a "tight fit". But you said earlier in this thread that the point is to make it rigid. So is there supposed to be a gap between the speaker and the box around it, or is it supposed to touch it on all sides? If a gap, how big?

Also, if I am soffit mounting passive speakers, do I need to leave vent space in that box, or would it be better in that case to be closed off?

If I screwed the speaker right into the shelf it sits on, is that just as good as building a box around it? Also, I thought I heard before that the speaker was actually supposed to sit on something that decoupled it from the stand it sits on..

the box around the speaker is supposed to be a "tight fit". But you said earlier in this thread that the point is to make it rigid.

It looks like John is busy on one of his projects right now, so I'll take a shot at that for you, and John can correct things later if I get it wrong.

The way I understand John's "rigid" comment, is that the entire soffit, and especially the front panel (baffle) must be very massive, solid, and rigid. The basic theory behind soffits is that the front panel it acts as an "infinite baffle", or an infinitely large extension of the speaker cabinet itself. Of course, "infinite" only in the sense of "very large with respect to the longest wavelengths". To do that, the panel cannot move, vibrate, oscillate, resonate, absorb, or do anything else but just "be there", in order to direct the low frequency sound in the same direction as the high frequencies: straight forwards, into the room. If the panel were to move, or vibrate, then it would be adding it's own tune to the sound, "coloring" it in some way.

So the way I understand John's comment is that the entire soffit must be built with that purpose: Keep the front panel as rigid as possible.

On the other hand, you also do not want the speaker cabinet vibrating around and banging up against the internal structure that holds it in place: Hence, it should be held tightly by whatever is keeping it there. John uses a box, but I've also seen Barefoot (I think it was him) suggest using broad canvas tie-downs with ratchets to hold the speaker tightly: you do not want it moving either.

BUT! Here's the thing: You also do not want the speaker transmitting its vibrations into the structure of the soffit! So it has to be held tightly, yes, but also decoupled from the soffit panel, and from its own supporting structure. It would be neat if you could just sort of levitate it in mid air, without it touching anything, but also without it being able to move.... But there are no magical incantations that seem to work for that, so the solution is to isolate the speaker and box from the support in some way or other. And also to leave a small gap between the front of the speaker and the soffit itself: Maybe a mm or so. The speaker cabinet itself should not touch the actual front panel of the soffit, if possible, so as to not be able to transmit any energy into the panel. Of course, if the panel is hugely massive, then it probably doesn't matter, but better to be safe than sorry.

So, to summarize, the idea is to decouple the speaker from its support but also hold it firmly in place, and also to have a very massive, very rigid front panel on the soffit. Simple, right? (siple on paper: not so simple in practice...)

Also, if I am soffit mounting passive speakers, do I need to leave vent space in that box,

Passive speakers still need cooling: you are pumping at least a hundred, maybe a couple of hundred watts of electrical power into the speaker coils, and only getting less than one single watt of acoustical power out the front. So guess where all the rest goes: heat. It is dissipated as heat, mostly in the coils of the drivers. So even though they need less cooling than an active speaker, you probably still need some cooling, if you hope to use your speakers for a long time. I would still provide some ventilation.

If I screwed the speaker right into the shelf it sits on, is that just as good as building a box around it?

Nope...

I heard before that the speaker was actually supposed to sit on something that decoupled it from the stand it sits on..

Yep...

Look around the forum: Somewhere Barefoot posted a neat design with an exploded translucent view, so you can see how all the parts fit together, and the concepts behind his design. His design is different from John's, but achieves the same end purpose, just in a different way.


- Stuart -

Awesome, that answers my questions

About the concept of leaving ventilation for the speaker.. I decided to do a design where I took the tilt angle of the soffit all the way down to the floor. I still packed the whole thing with insulation, no hangers. So do you think I should cut the one foot tall slot along the base of the soffit face so that I can use the cavity as a bass absorber, or is that too much opening to to have considering that the entire soffit cavity is functioning like the upper section of John's soffit in his design.

One more. You said that the soffit panel shouldn't absorb. I was planning on attaching some insulation the the back side of the face to keep the panel from resonating. Sounds like a good idea..you meant something different right?

So do you think I should cut the one foot tall slot along the base of the soffit face so that I can use the cavity as a bass absorber, or is that too much opening to to have considering that the entire soffit cavity is functioning like the upper section of John's soffit in his design.

John's design divides the cavity in two, with the top section being for speaker, and the bottom being for bass trapping. There is a shelf-divider in between, to separate the spaces. So if you have that divider in place, then yes, you sure can use the lower section as bass trapping, and if hangers don't fit, then just stuffing that bottom section it full of absorption with a 1 foot gap at the lower end of the front panel would be a reasonable substitute.

You said that the soffit panel shouldn't absorb. I was planning on attaching some insulation the the back side of the face to keep the panel from resonating. Sounds like a good idea..you meant something different right?

Yup! I meant the FRONT side of the panel, the side facing the room: the panel itself should not be absorbent. But you sure do need absorption in the cavity inside the soffit itself, where the speaker is! The purpose is to damp the resonance in there, and since it is mostly low frequencies going on in there, you an throw in as much absorption as will fit! All your absorption off-cuts and waste from the rest of the room can go in there, along with old clothes, dirty washing, discarded carpets, a sofa or two, etc.... Seriously, the cavity inside the soffit can be your "trash can" for bits of absorption: fill it to the brim, if you want. The point I was trying to make is that the soffit panel itself (the "baffle") needs to be solid, rigid, massive, hard, thick, etc.

- Stuart -

John Sayers wrote:
regarding taking the angle all the way down here's Masterphonics.

masterphonics_1.jpg

In this case is the seperate cavity for bass trapping underneath the speaker section still present? I can't see the gap in that picture.

The reason there is no desk reflection absorption underneath the speaker soffit is the fact the whole soffit section is tilted?