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Discussion Starter · #1 ·
Hi everyone. I've posted a few questions in the past, but it's been a while. I'm finally getting around to finishing the other half of my basement and this includes the dedicated theater. I thought I had most things thought out, but now that I'm actually in-progress my head is spinning trying to narrow down what order things need to be done and how/why!

My questions now concern soffits. I see soffits in most builds, but my main question is why? Are they for accoustics, to house lights and hide wires, or just for looks? So, do I need them other than for looks?

Next, does the size of them matter?

I see some done with plywood and then covered in drywall. Why? Is that necessary or better than plain drywall? Should only the face be plywood and the bottom be both or vice versa?

Sorry if this stuff is covered somewhere, but going through all the build threads is very exhausting and I'm not having much luck with direct searches.

Give me a crash course on soffits!

Any help is appreciated!
Thanks,
Shane
 

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Hi everyone. I've posted a few questions in the past, but it's been a while. I'm finally getting around to finishing the other half of my basement and this includes the dedicated theater. I thought I had most things thought out, but now that I'm actually in-progress my head is spinning trying to narrow down what order things need to be done and how/why!

My questions now concern soffits. I see soffits in most builds, but my main question is why? Are they for accoustics, to house lights and hide wires, or just for looks? So, do I need them other than for looks?
Soffits can be used for all those things as a matter of fact. I personally use my soffits for bass absorbtion, housing the perimeter lights, running wires from the AV closet to the front of the room, and enclosing HVAC lines. I also like the look and it gave me the structure to add a star ceiling.

Next, does the size of them matter?
Not really - the only one it matters for would be for acoustical and how much you wanted them to absorb.

I see some done with plywood and then covered in drywall. Why? Is that necessary or better than plain drywall? Should only the face be plywood and the bottom be both or vice versa?

Sorry if this stuff is covered somewhere, but going through all the build threads is very exhausting and I'm not having much luck with direct searches.

Give me a crash course on soffits!

Any help is appreciated!
Thanks,
Shane
I think this comes down to whether they are false soffits or not. If there are HVAC lines you need to enclose, you will generally see the plywood / drywall combination to have the 2 layers to muffle the sound.

Otherwise, they are built as a "false" soffit with just the framing and then the drywall to enclose it.

I actually did both in my space - I enclosed an HVAC line with the 2 layers and then extended the false soffit from the edge of that.
 

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My questions now concern soffits. I see soffits in most builds, but my main question is why? Are they for accoustics, to house lights and hide wires, or just for looks? So, do I need them other than for looks?
They can be used for all of the above..They can also help to break up any standing waves where walls and ceiling meet..
But they are not entirely necessary and for the most part are there for aesthetic reasons..
Soffits with downlights and or string lights add a nice appeal to any theatre..

Next, does the size of them matter?
Size of the soffits will generally be determined by the size of your room..If you have a smallish room, you wouldn't necessarily have large wide soffits..Likewise..small soffits in a large room would look out of place..

I see some done with plywood and then covered in drywall. Why? Is that necessary or better than plain drywall? Should only the face be plywood and the bottom be both or vice versa?
The type of installations you're referring to have been done that way for acoustic reasons..Whether you need to do that will depend on the acoustics in your room and whether any special treatment is needed..
I made my soffits from just plain MDF and loosely filled them with insulation..They also have downlights fitted with LED string lighting around the perimeter..and all my power, audio and video feeds run through them as well..
 

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I don't see a lot done this way. But the most interesting ones to me are the ones filled with sound absorbing material and faced with an acoustically transparent cloth. It seems lime a great wag to get some solid bass absorption.
 

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Discussion Starter · #5 ·
Thanks for all the info so far. I also see soffits put up at different times. Looks like some people build them after their walls/ceilings are drywalled and painted and others do it before drywall. Any difference?
 

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I have to put mine up before drywalling because they are covering up ducts and pipes and stuff. I'm also using the plywood method you mentioned, not for soundproofing specifically, but because it allows for a "frameless soffit." Using a wood layer eliminates the need for vertical framing members, allowing the soffit to be framed tighter around the ducts, etc.
 

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Does the construction above also helps for bass absorption? I need to use a soffit in my HT build for at least one side (pipe 125 mm - 5 inch) and the back side (pipe 100 mm - 4 inch) to hide and muffle the ventilation pipe. For symmetry, I'd do a soffit on al four sides. Maybe 60 cm width (2 feet) and it will be 20 cm height (8 inch).

Ceiling is suspended from a I-joist ceiling construction. I got midrange and high frequency absorption covered. Another possibility than the design above (I think) is to first finish the ceiling (decoupled, double layer, green glue...) and then add the soffit construction, but this way, the soffit would need to be finished with acoustic open material (fabric) in order to be a bass trap while avoiding triple leaf principle. Is this the wrong approach and should I stick to the layout above?
 

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Does the construction above also helps for bass absorption? I need to use a soffit in my HT build for at least one side (pipe 125 mm - 5 inch) and the back side (pipe 100 mm - 4 inch) to hide and muffle the ventilation pipe. For symmetry, I'd do a soffit on al four sides. Maybe 60 cm width (2 feet) and it will be 20 cm height (8 inch).

Ceiling is suspended from a I-joist ceiling construction. I got midrange and high frequency absorption covered. Another possibility than the design above (I think) is to first finish the ceiling (decoupled, double layer, green glue...) and then add the soffit construction, but this way, the soffit would need to be finished with acoustic open material (fabric) in order to be a bass trap while avoiding triple leaf principle. Is this the wrong approach and should I stick to the layout above?
Erwin,

I ended up using my false soffits as bass absorbers. Per Bryan's suggestion, I filled them with pink fluffy after putting in 703 to support it (as well as some thin OSB strips) and faced them with MLV (mass loaded vinyl). The MLV I selected allowed for absorption from 20 Hz to 200 Hz. It seems to have helped in my case, although i do appear to have a bit of a spike around 30 Hz.
 

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Thanks.

Very smart to use MLV in that position.

I have planned a large area of diffusion panels (DIY, I buy them as flat packs ready to assemble) in the center of the ceiling (60% of the width). It worked out that the soffits can be minimal (not wider than 10"). I intend to have done acoustic measurements as soon as the diffusers are up and use the results to determine what to put between the mini-soffits and the diffusers. Maybe broadband absorption (8" thick), maybe specific bass trapping.
 
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