# Effect of soffit in a HT



## raZorTT (Jan 17, 2008)

Hi guys,

I'm in the process (slow) of building a HT and am trying to plan the soffits.

I'm tossing up whether to frame the soffits and then cover them with gyprock/sheetrock OR frame them and cover them with fabric.

Do you guys think it will affect the acoustics with the more solid construction? 

I was thinking that if I go went down the fabric path I could potentially put small bass traps in the corner of the wall and ceiling

What do you guys think?

Cheers,

Simon


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## bpape (Sep 14, 2006)

Hi Simon

Welcome to the forum. In either case, you'll want to build the soffiting AFTER the room is drywalled if you're going to use it for any kind of treatment, lighting/hvac without poking holes in the room, running cables, etc. 

If you frame, fill with insulation, and cover with a thin layer of drywall, it will perform as minimally efficient bass absorber from about 50Hz to around 150hz. If you do just framing, insulation, and cloth, it will act more broadband and be a bit more efficient depending on the thickness and amount of surface area of the insulation. 

Which way to go? Really depends on what's happening in the rest of the room and how the rest of the acoustical map looks.

Bryan


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## raZorTT (Jan 17, 2008)

Thanks for the welcome Bryan 

I guess I need to go into a bit more detail  sorry about that. Hopefully this isn't going to be too long!

The room dimensions are 4.7m (15.4ft) wide, 6.0m (19.6ft) long and 3.0m (9.8ft) high. Even though the room is going to be my HT I had to compromise and put in 4 thin and tall (~500mm\20inch wide, 2m\6.5ft high) windows on one side.

All of the walls have insulation inside and I have used a thicker gyprock/drywall. Not quite room in a room or green glue but that was all I could do unfortunately. The room has been drywalled and plastered. 

For other treatments I was planning to cover the wall behind the screen (building the screen off the theater wall) and up to the L & R speakers on the side walls from floor to ceiling. We don't have linacoustic here in Australia so I have been trying to find something equivalent. So far i'm probably looking at 50mm/2inch thick CSR supertel http://www.bradfordinsulation.com.au/Products/Commerical/HVAC/Supertel.aspx 

Along the sidewalls i'd also like to cover up to ear level, but am not sure how the windows will affect things. Do you think it would be better to cover the one wall completely and on the other side, cover the bits that aren't windows? Or would it be better to mirror the coverage of the window side on the complete wall?

Will some thick curtains, to handle light transmission, help with any absorption? or not really?

I was planning on putting bass traps (Superchunk? the triangle pieces stacked up) in the corners of the screen and side walls 

With that essay out of the way, back to the soffit. I am planning to put downlights in the soffit along the sides walls, the rear wall and some above the screen. Also i'm going to put in a light tray for a rope light. I'm not really for or against a particular construction, just if one has benefits then i'd like to go down that path.

Thanks for making it this far. I'd really appreciate your thoughts. :jump:

Cheers,

Simon


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## bpape (Sep 14, 2006)

Curtains can help for general reflections if they're relatively thick (and will need to be for good light control) and are made of an absorbant material. You want to keep symmetry left to right in front of you. You could likley get away with mixing it with curtains on the one side. I'd likely use 1" on the side walls.

With that particular setup, I'd probably shoot for the rear soffit to be pretty much just frame and absorption covered in cloth. Sides can be drywall filled with insulation.

Bryan


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## raZorTT (Jan 17, 2008)

Thanks Bryan,

Ok so I'll aim to do something along the lines of the attached image. the red is 2" thick and the green 1" thick.

Cheers,

Simon


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## bpape (Sep 14, 2006)

Don't forget the chunk style absorbers in the front corners. I'd also probably go ahead and make the left wall solid instead of strips to better match the other side with the curtains.

Also, the last 2 panels on the sides in the rear, I'd face those with something like FSK to add a little more midbass control back there and keep it from getting too dead in the highs.

Bryan


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## salvasol (Oct 31, 2006)

Here is another idea for  Blocking a window  ... this helped the Prof. with light control and accoustics :yes:


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## raZorTT (Jan 17, 2008)

bpape said:


> Also, the last 2 panels on the sides in the rear, I'd face those with something like FSK to add a little more midbass control back there and keep it from getting too dead in the highs.
> Bryan


Is FSK the perforated paper that is sometimes on the back of the insulation? So have it facing into the room instead of against the wall??

Cheers,

Simon


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## raZorTT (Jan 17, 2008)

salvasol said:


> Here is another idea for  Blocking a window  ... this helped the Prof. with light control and accoustics :yes:


HMMMM.. now you've got me thinking onder:

That would be the best solution. I wonder if I can get approval to plug them up raying:. 

I had always wanted to bulid fabric frame panels to put on the walls, but had kind of given up on the idea due to needing to put in curtains to block out the windows.

Would the best thing to do be to make a plug that is like a wall? so attach insulation to gyprock/sheetrock, and then have a fabric panel with 1" thick absorption material over the top? Or would I be better off with the 1" thick strips on the wall like in the above image and plugging the windows like Prof. ?

Probably the first option?

Cheers,

Simon


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## bpape (Sep 14, 2006)

Either can work just fine. If you build a plug, make sure it's filled with insulation to damp the cavity you're forming or it will resonate.

FSK is a little heavier than what you're thinking, It's like a heavy kraft paper on one side, a foil on the other, and a fiber mesh in the middle. You'll see it sometimes already bonded to things like pipe insulation.

Bryan


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## raZorTT (Jan 17, 2008)

Thanks guys!!

This is sort of off topic, but how do people measure the effect of treatments in their room?

Is it fairly specific equiptment? or is there a DIY piece of equiptment that people can get their hands on?

Cheers,

Simon


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## bpape (Sep 14, 2006)

If you have something like a Radio Shack SPL meter, you can download Room EQ Wizard here on this site (free download) and run it on a PC tied to your system. You'll need a bi-directional sound card (capable of record and playback simultaneously) also.

Just remember when measuring, that you're interested not only in frequency response, but also impulse response and decay times.

Bryan


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## raZorTT (Jan 17, 2008)

thanks Bryan I'll check out the local electronics stores :bigsmile:


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## Prof. (Oct 20, 2006)

Hi Simon,
I've been off line for a few days, so I'm just catching up..

I used the Supertel insulation in my theatre for acoustic panels and bass traps and it works well..:T

Bradfords have a BPF Supertel (black paper face)..which I think is similar to the FSK.. that I used for the rear window plug..
The window plug has 4 inch thick Supertel fitted..one 2 inch panel of plain Supertel and one 2" thick panel of BPF Supertel..

Also you can get an SPL meter for Dick Smiths fairly cheaply..

EDIT..I should also mention that you only need to use the faced Supertel for any panel on the rear wall..nowhere else..


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## raZorTT (Jan 17, 2008)

Sorry Prof. 

Have been sick over the past week..

Where did you source the supertel from? a hardware store or someone more specialised?

Cheers,

Simon


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## raZorTT (Jan 17, 2008)

bpape said:


> Hi Simon
> 
> Welcome to the forum. In either case, you'll want to build the soffiting AFTER the room is drywalled if you're going to use it for any kind of treatment, lighting/hvac without poking holes in the room, running cables, etc.
> 
> ...


Hi Bryan,

I was looking to get an idea of what is happening in the room before I start framing the soffits etc. I've gotten the radio shack SPL meter and the SB live external to hook everything up.

I've gone through the REW help file and don't think i'll have any issues calibrating everything. However, 
I haven't been able to find a guide on what things I need to test? Is it as simple as using the measurement button and picking a bunch of different frequencies? Do I need to just test the sub by itself? or Include the mains? Should the center and surrounds be part of it as well?

Have you seen in your travels a post or guide that steps beginners though?

Cheers,
Simon


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## bpape (Sep 14, 2006)

Hey Simon

There are some pretty good tutorials here on the Shack. 

You'll just run a sweep. You can then have it generate impulse response, frequency response, and decay time/waterfalls. There is also the RTA function that's very helpful in tweaking sub/seating locations.

Bryan


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## raZorTT (Jan 17, 2008)

Thanks Bryan,

So should I just use the mains and sub? or hook the center and surround speakers up aswell?

Cheers,
Simon


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## bpape (Sep 14, 2006)

You'll want to take several measurements. Obviously the one that matters most is the mains and sub. 

You'll want one with just the sub so you can work on positioning. 1 with just mains running full range so we can see where there may be overlap around the xover frequency, and 1 with all 3.

Bryan


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## raZorTT (Jan 17, 2008)

Thanks Bryan!


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