John Sayers' Recording Studio Design Forum Archive

Hi all,
First, forgive my english...it's not my native language
This forum become huge pile of informations, and sometimes it's hard to find correct key word to find the answer...
I'm researching about flush mount and really want to fully understand how to make it right.

1. I have question about speaker placement on the front wall of soffit mount.
Where should I place the speakers (horizontally)? in the center of the baffle/front wall? how to determine this? is there any calculation or formula involved?
Is it relate to where the spot of the mix position? so the meeting point of both speakers (60°) not fall in the half length of the room? 2. If I go with heavy stand (brick stand) for the speakers, do I still need decoupling mechanism under the speakers?
I understand, that the speakers should not transform vibration to rest of the structure especially front wall, but when the speakers not touching the front wall (there's a gap) and the stand is very rigid and massive, will it still vibrate the rest of the structure? Or the purpose of the decoupler is in order to the speakers not to move? I'm so sorry, I'm so stupid to figure out...

3. Relate to #2, if I go with heavy stand, do I still need the bass hangers? since I think the space below is reduced.

Hope I you guys understand my question.

Thank you very very much...

Hi there JM, and Welcome!

Where should I place the speakers (horizontally)? in the center of the baffle/front wall? how to determine this? is there any calculation or formula involved?

The center is not the best place, as it can lead to "focusing" or "lobing" of some frequencies. It's better to have it off-center. I have read that the ideal location is about 2/5 of the width of the soffit, but that often isn't possible, as it would put the speaker very close to one edge. So offset it as much as you can while still leaving a good margin.

Is it relate to where the spot of the mix position? so the meeting point of both speakers (60°) not fall in the half length of the room?

No, not really. First, forge the "60° equilateral triangle" that you see in so many places. That only works if the room is big and the speakers permit it. For most home studios it's NOT a good layout. The best layout is to start by placing your mix position at somewhere between 33% and 43% of the room length (in other words, somewhere around 38%, give or take 5% either way). Then position the speakers in the soffits so that they are NOT directly lined up with the corners of the room, and roughly as far apart from each other as the distance from the mix position (your ears) to the front wall, or preferably a bit more: So if, for example, the distance form the from wall to your ears is 180cm, then try to keep the speakers at least 180 cm apart. At the same time as you are doing that, angle the speakers so that they are both aiming at a point about 25 to 50 cm behind your head. If the angle is not 30°, that's fine. As long as it is somewhere in the range 25° to 35°, that's great. You can even go as much as 45°, but that's the limit. I try to not go more than about 40°, maximum, but 25 to 35 is good for most rooms.

So play around with those parameters until you get something that works: mix position 33% to 43% of room depth, speaker location about 20% to 40% of room width, and about 2/5 of the width of the soffit, speaker separation as large as possible, but at least the same as the distance from front wall to mix position, and speaker angle in the range 25° to 35°, aimed at a spot around 25cm to 50cm behind your head. For most rooms, that should give you a pretty decent geometric layout. If you do it correctly, you'll find that the axis of each speaker is pointing roughly at the tips of your ear lobe, or maybe a bit further out (a few cm, max).

2. If I go with heavy stand (brick stand) for the speakers, do I still need decoupling mechanism under the speakers?

It's better, yes. If that's what you plan to do, then consider using Sorbothane pads to decouple the speakers from the stand.

will it still vibrate the rest of the structure?

It is possible, yes. Unlikely, but possible.

3. Relate to #2, if I go with heavy stand, do I still need the bass hangers? since I think the space below is reduced.

That's one reason why I don't use brick stands inside soffits: It takes up all the space where you need bass trapping (hangers)! In my soffit designs, I use a very rigidly framed "shelf" that the speaker sits on (with a floating suspension system), and that shelf just runs across the inside the soffit, from side to side and front to back. There is a large slot in the shelf, to allow cooling airflow up past the rear of the speaker, and the framing under the shelf provides the support for hanging the hangers.

Hope I you guys understand my question.

They are all very good questions! It shows that you have been thinking about this carefully, which is a good sign!

- Stuart -

Stuart,

Sorry for late responds.
Thank you very very much, I was thinking to send you a PM before I create this thread, and lucky me!! you are the one reply this thread.
And wow ...in very details!!! Thank you again Stuart!!

They are all very good questions! It shows that you have been thinking about this carefully, which is a good sign!

Thank you for very kind words...I read alot about soffit/flush mount especially in this forum and GS, I get the general concept but some design, construction technique and details posted on forums make me want to know better. And maybe I'm too dumb FYI, I ,very often, skipped math subjects when in schools...

The center is not the best place, as it can lead to "focusing" or "lobing" of some frequencies. It's better to have it off-center. I have read that the ideal location is about 2/5 of the width of the soffit, but that often isn't possible, as it would put the speaker very close to one edge. So offset it as much as you can while still leaving a good margin.

Noted!
The soffit you are referencing is the baffle/wall right?
How big/wide the soffit wall is the next question? Trying to clearing my head.
How deep should the cavity of the wall? is there any

John and your design seems trying to utilize for bass trapping whatever space available under and above soffit, and I also saw other design (what I see ) is full of rigid front wall from floor to ceiling, like Thomas Jouanjean's room (maybe this why it's called flush mount method, and John's design & yours called "soffit mount"?)
let's assume the back wall already treated with deep porous trap, is it not enough to break the modes?
When below and upper part of the front wall is soft wall (for bass trap), Is it not going to make energy able to wrapped around?

The best layout is to start by placing your mix position at somewhere between 33% and 43% of the room length (in other words, somewhere around 38%, give or take 5% either way). Then position the speakers in the soffits so that they are NOT directly lined up with the corners of the room, and roughly as far apart from each other as the distance from the mix position (your ears) to the front wall, or preferably a bit more:

Would you please elaborate more a bit, Stuart (the red bold) is it mean the speakers not in the geometric plane of the room?

I tried to play around with your information you gave, as I adding the front wall and my window is on the green wall, is the room length/deep change?
where I should locate the 38% point? from the inner wall? or the new front wall?
Will it create triple leaf effect? from this CR to live room? Assume live room inner wall is behind the CR front inner wall
Sorry to back to basic again, Stuart...

Thank you very much

The soffit you are referencing is the baffle/wall right?

I know this question is directed at Stuart, but I'm confident I can answer it. Yes, he is referring to the baffle/wall.

How big/wide the soffit wall is the next question? Trying to clearing my head.

As big as possible.

How deep should the cavity of the wall? is there any

Enough to accommodate the depth of your speaker in a speaker enclosure and some ventilation/insulation behind it.

let's assume the back wall already treated with deep porous trap, is it not enough to break the modes?

It's not about "breaking modes". You actually want more modal activity, not less. You basically cannot get enough bass trapping. So no, the rear wall is not enough.

When below and upper part of the front wall is soft wall (for bass trap), Is it not going to make energy able to wrapped around?

The idea is for it to be an infinite baffle, There doesn't need to be much open "soft as you call it" space.

Would you please elaborate more a bit, Stuart (the red bold) is it mean the speakers not in the geometric plane of the room?

He means that your speakers should not be positioned on the 45 degree line in relation to the corner.

as I adding the front wall and my window is on the green wall, is the room length/deep change?

If I understand you correctly, then yes, that portion of your wall does create a room depth change, but I wouldn't freak out about it. It won't change enough to worry about.

where I should locate the 38% point? from the inner wall? or the new front wall?

The inner wall.

Will it create triple leaf effect? from this CR to live room? Assume live room inner wall is behind the CR front inner wall

No. Just make sure you only have single pane glass. One for CR and one for live room.

Greg