Designing My Soffit Mounts

#1

Greetings all,

This is my first post here but I've been lurking for a few months now. I'm so thankful that forums like this & John Sayers exist as I've learnt so much! Big ups to Stuart!

I've decided to build some soffit mounts in my small bedroom for my Mackie HR824 (mk1) speakers.

I plan on eventually treating the whole bedroom (you'll notice the murphy bed at the rear wall that I built specifically for this purpose) but I figured soffits was a good place to start (I can do a REW test straight after and that will determine what I do next).

The room is 390 x 221 x 290. Here are some pics from the Sketchup model I made:

(The door by the bed is the entrance door & the door with the windows around it is the balcony door)

From my months of lurking on here & JS I've gathered the following:

- Listening position should be around 35-40% of the room length
- Speaker angle can be anywhere between 25-40° (sometimes even slightly outside that window)
- Speakers should be roughly 55% of the room width apart
- Speakers be pointed towards around 12-16 inches behind the head (i.e. pointed at the ears, not the eyes)
- The soffit baffle width should be 3-5x the width of the speaker woofer
- The speaker should be positioned around 3/5 of the way down the width of the baffle
- A proper RFZ should have 1st reflections no closer than a foot to the listening position

(Please correct me if any of these are wrong!)

With these in mind, I whipped up the following basic soffit shape (for now I only have questions regarding the design from above):

I wanted to achieve the best possible RFZ, given that the soffit wings can't extend further than the balcony door. The numbers you see above produce the following 1st reflections:

And here are the rays closest to my listening position:

As you can see, the problematic reflections are caused by the parallel walls (they're around 6" away from the listening position i.e. well within a foot).
Unfortunately the balcony door opens inwards & towards the speakers so I'm unable to extend the soffit wing so its partly on the door.
So my first question is, could they be remedied by absorbers placed right where the soffit wings end (the left one would be attached to the balcony door), like so:

I tried decreasing the angle (i.e. moving the speakers back) to offset the parallel wall reflections, but the more I do that the closer the reflections from the soffit wings become (resulting in not one but two problematic 1st reflections, one of which I can't remedy with an absorber). Here's a quick example of what that looks like:

What do you guys think? Any suggestions you guys could give me would be immensely appreciated!

#2

Greetings,

Before going to all the trouble to build this, you do realize you won't have very good isolation, especially with the doors and windows in the equation. The first step would be to improve that situation which will, of course, make your room smaller (completely changing your calculations).

All the best,

Paul

#3

SoWhat wrote:Source of the post Before going to all the trouble to build this, you do realize you won't have very good isolation, especially with the doors and windows in the equation. The first step would be to improve that situation which will, of course, make your room smaller (completely changing your calculations).

I don't think I need to soundproof the room honestly. I'll only be using the room for producing/mixing/mastering and I live in a fairly quiet area w/ no immediate neighbours. Plus I may be changing location in a year or two so I don't want to sink too much money into this

#4

Hi Snailboyaway

On first look this looks remarkably similar to what I did for my Mackie HR824 mk1 a few years ago. I had a room about the same width and soffit mounted the monitors. I didn’t go for soffit wings and instead had around a 1m wide soffit face each side.

At the first reflection points left and right I used 600mm x 1200mm absorbers mounted horizontally and also the same mounted on the ceiling.

I had a load of treatment on the back wall and down the wall to ceiling corner intersections and I was really pleased with the results. If you find my my build thread on here you can see the response charts for what I achieved in that room with some digital tuning.

My situation was similar in that I knew it was a temporary room but this definitely worked well.

What I would say is that you need to be careful about how you manage the sound that comes from the rear of these speakers - I think I made a mistake in completely closing off my soffits on all sides, it might have been better to have an open side. With mine i ended up with bass coming out of my amp vents and because they had a certain size I wonder if they turned into a kind of tuned port...?

Anyways, there’s a build thread on the John Sayers forum with my designs in if you fancy looking it up, but otherwise good luck!

Cheers
Gareth

#5

Hi Gareth!

On first look this looks remarkably similar to what I did for my Mackie HR824 mk1 a few years ago. I had a room about the same width and soffit mounted the monitors (...) there’s a build thread on the John Sayers forum with my designs in if you fancy looking it up, but otherwise good luck!

Can't thank u enough for pointing me to this thread! Will be extremely helpful (esp the housing box stuff - was dreading having to figure that out).
For anyone who's interested, here's the thread in question: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=20895

What I would say is that you need to be careful about how you manage the sound that comes from the rear of these speakers - I think I made a mistake in completely closing off my soffits on all sides, it might have been better to have an open side. With mine i ended up with bass coming out of my amp vents and because they had a certain size I wonder if they turned into a kind of tuned port...?

Ah good to know!

I didn’t go for soffit wings and instead had around a 1m wide soffit face each side. At the first reflection points left and right I used 600mm x 1200mm absorbers mounted horizontally

Yeah someone on JS suggested doing the same thing so I've gone ahead and done that.
Here's the left soffit (just base & king studs, no inner studs, baffle, panels etc yet):

I had a few Qs regarding your design, Gareth (altho if anyone else knows the answer please chime in

)

1.) The plywood sheet just under the speaker - I realise it's part of John's original design and I've yet to see a soffit build without it, but is it necessary considering I have a small, backless desk w/ v little reflections? Is it's existence as a baffle extension essential for the soffit to work properly? When Stuart says the speaker should be offset around 1/4 of the height of the baffle, does that include the inset plywood sheet?
I wonder if it would be better if the whole lower cavity was fully exposed to the room, rather than being partly covered by this sheet
(The bit I'm referring to: http://www.johnlsayers.com/phpBB2/downl ... p?id=70040)

2.) I've seen some soffit designs with acoustic hangars at the bottom and top of the soffits, but others (like yours) have the space around & above the speaker completely filled with rockwool. Why not use hangers in both bass traps, if hangers are better than superchunks?

3.) Is there a reason why you don't have a plate at the top of your wooden frame?

4.) Am I meant to attach the soffits to the surrounding walls? Or should they be loose?

Thanks again for the help!

#6

Hi
I’ll do my best to answer your questions as far as I know, but hopefully someone else can fact check this too...

1.) The plywood sheet just under the speaker - I realise it's part of John's original design and I've yet to see a soffit build without it, but is it necessary considering I have a small, backless desk w/ v little reflections? Is it's existence as a baffle extension essential for the soffit to work properly? When Stuart says the speaker should be offset around 1/4 of the height of the baffle, does that include the inset plywood sheet?
I wonder if it would be better if the whole lower cavity was fully exposed to the room, rather than being partly covered by this sheet
(The bit I'm referring to: http://www.johnlsayers.com/phpBB2/downl ... p?id=70040)

I think you’re referring to the plywood that sits parallel to the soffit front underneath the speaker. In my case, based on many articles on the John Sayers forum, this was set back from the soffit front by about 100mm and then covered with rock wool and then a fabric front. The aim of this is to absorb any reflections from the back of the furniture/desk etc and therefore it is not part of the soffit front itself, which has to be level with the front of the speaker.
I’m sure you could just have this open to the hangers and it would work fine.

2.) I've seen some soffit designs with acoustic hangars at the bottom and top of the soffits, but others (like yours) have the space around & above the speaker completely filled with rockwool. Why not use hangers in both bass traps, if hangers are better than superchunks?

I think it’s fairly standard to fill the space around the speaker boxes with loose Rockwool, as for above, in my case it was far easier just to put rockwool in there rather than more hangers, particularly because on the right hand side I had an air duct and the power distribution board up there too. If you have the space I dare say hangers would be good.

3.) Is there a reason why you don't have a plate at the top of your wooden frame?

I’m not sure what you mean, sorry.

4.) Am I meant to attach the soffits to the surrounding walls? Or should they be loose?

I did attach them, because I assumed it’s best for this to be as sturdy and strong as possible. I figured if it was not attached but touching the walls then the soffit structure could vibrate and make a noise as it bounced off the walls. Maybe not, but this hopefully helps explain my thinking.

I hope this helps!
Gareth

#7

Thanks for the reply Gareth! Rly appreciate the help

I think you’re referring to the plywood that sits parallel to the soffit front underneath the speaker. In my case, based on many articles on the John Sayers forum, this was set back from the soffit front by about 100mm and then covered with rock wool and then a fabric front. The aim of this is to absorb any reflections from the back of the furniture/desk etc and therefore it is not part of the soffit front itself, which has to be level with the front of the speaker.
I’m sure you could just have this open to the hangers and it would work fine.

So gullfo on JS told me (and I think Stuart mentions it elsewhere) that it basically acts as an extension of the baffle (despite it being inset) & he recommends that I use it. Will probably play it safe as I've yet to come across a soffit design that doesn't have one (though that's probably because they all use big, reflective mixing desks)

I think it’s fairly standard to fill the space around the speaker boxes with loose Rockwool, as for above, in my case it was far easier just to put rockwool in there rather than more hangers, particularly because on the right hand side I had an air duct and the power distribution board up there too. If you have the space I dare say hangers would be good.

Yeah I might go for it as hangers are apparently preferable to superchunks, and small rooms need as much bass trapping as poss

I’m not sure what you mean, sorry.

My bad, I meant that there's nothing connecting the timber at the very top of your frame (a base plate like you have at the bottom):

Just wondering if there was a particular reason for this?

I did attach them, because I assumed it’s best for this to be as sturdy and strong as possible. I figured if it was not attached but touching the walls then the soffit structure could vibrate and make a noise as it bounced off the walls.

Yeah, this was my thinking too!

#8

Hi
Ah the top, I see. I think I just decided it wasn’t worth it as all the strength was needed for the bits around the monitors, and I had secured the wooden frame above and below the monitors to the walls.

It may have been sheer laziness too!

Good luck with your plans. Did you use Stuart’s raytracing tool or something else? I need to further work on my design.

Thanks
Gareth

#9

Ah the top, I see. I think I just decided it wasn’t worth it as all the strength was needed for the bits around the monitors, and I had secured the wooden frame above and below the monitors to the walls.

It may have been sheer laziness too!

Fair enough!

Good luck with your plans. Did you use Stuart’s raytracing tool or something else? I need to further work on my design.

Thanks!
So I used amray (https://amcoustics.com/tools/amray) for a general view of all the 1st reflections (the pics w/ all the blue lines - very rough as you have to trace lines over a top-down 2d export of your design), made a note of all the ones closest to the head then went into Sketchup and calculated the closest reflections w/ the protractor tool

#10

Great thanks! Will check out amray

Gareth

#11

Currently waiting for the timber to arrive, but here's the finished(?) design for the framing:

Is there anything that anyone here would do differently?

Gonna use screws & glue to connect most of the timber together (brackets for certain joints) and also for connecting to the walls, ceiling & floor.
I guess I should also use caulk for filling the gaps right?

For air circulation, is it fine to have the air go in through the bottom hangers, up through speaker port, through a hole in the upper shelf to the top hangers, then out the opening at the ceiling, like in my design?
Or is there a particular reason why some people go for the 'hole in the baffle' route?
Here's an example of someone doing it my way:

Also, as you can see in the pics, I've sealed off the speaker sections from the tall middle section with a sheet of plywood - should I do this with the upper/lower hanger sections as well or is it fine to have them exposed to the middle part?

#12

Hi
Nice sketch up work.

I agree caulking is a good plan. I didn’t use glue as I knew mine had to come apart again in the future - something to consider.

I think your idea of venting out the top past the hangers is a good plan. I found that an awful lot of bass came out my vent due to the way the Mackies are designed with that passive radiator on the back. It’s a great design in allowing the speaker to produce low frequencies but it means those frequencies come out the back.

I would urge caution around sealing the middle section off with the vertical pieces of wood you’ve described for the same reason. It might be better to allow the sound from the back to escape into the middle section which you fill with loose insulation. Maybe start like this and see how you go, as fitting the vertical wood later wouldn’t be too hard.

What are you covering the front of middle part with? Will it be material or solid?

Cheers
Gareth

#13

I agree caulking is a good plan. I didn’t use glue as I knew mine had to come apart again in the future - something to consider.

Good point! Will maybe just use screws + caulk then

I would urge caution around sealing the middle section off with the vertical pieces of wood you’ve described for the same reason. It might be better to allow the sound from the back to escape into the middle section which you fill with loose insulation. Maybe start like this and see how you go, as fitting the vertical wood later wouldn’t be too hard.

I guess I figured the point of a soffit was to have an extension of both the front baffle and the speaker box, and that the module containing the speaker needs to be sealed off as much as possible for the soffit to be effective.
But then like you said, the speaker isn't really designed that way and maybe the middle section needs to have lots of holes for the sound to escape (both the speaker and the housing box are hardly sealed are they).
So yeah I'll follow your advice and do an REW test before putting the sheet on, as it might not be necessary. Thanks!

What are you covering the front of middle part with? Will it be material or solid?

So I'd planned to attach a baffle to the middle section (same height) and use fabric on the top and bottom, like so:

I figured this was ideal as it functions as an extension of the side baffles
(I also have a 2nd monitor that I'd like to attach to the baffle)

Btw the baffle will be 48mm thick

#14

Hi
That looks good to me and that's a seriously thick baffle.

Gareth

#15

Just a question as this is not my specialist topic (even though we all need to understand all the topics). Bass radiates from the woofers outwards in all directions. The bottom edge of the baffle is much nearer the centre of each of the woofers than are the sides or top. Will this shortest distance be the defining limit of an infinite baffle? What distance do these woofers need for an infinite baffle?

For me, these are questions I should be studying. For snailboyawayyy it can serve as a check that you know and are confident that you are doing it right.

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