Room Treatment Advice Needed

[Pensacola Hi-Fi]

I am working on a home theater room (7.2) and close to the treatment stage. Looking for advice as I dont believe I have any local shops that can come in and give me pointers.

Notes/questions:

The room is 16' x 16' with a build out on the right side for a fireplace.

One sub is in the corner and thinking about placing another behind the screen.

AT screen with speakers hidden

I am putting soffits (blue) around 3 if not all 4 walls. Wanting to make them bass traps - should that be done all the way around?

All my corners will have either a sub, door or counter so corner bass traps are out.

Going to line the L side with OC 703 and at least 2 of the 3 sides of the fireplace build out.

Any back wall and front state treatment suggestions?

Thanks in advance for any help.

 

[TheWarrior]

Due to the square room, you really need corner absorption floor to ceiling. You must have horrible bass resonances! I think GIK Acoustics sells some corner traps that don't consume a whole wall. Perhaps even just a portion? Corner loading your subs may help, or it could hurt. Listen to familiar content and position them, INCHES make a difference!

Soffits should be no less than 6", especially if there's no corner absorbers. Do them in stages and listen/measure (if you can) at each of the seating locations. Acoustically dead rooms are the supposed 'ideal' but they are very uncomfortable to sit in. Unless you are mastering soundtracks, people tend to prefer some reflections!

You probably need some 4" absorbers on the back wall, and keep your seat(s) well on the back half of the room. That is to prevent the sound from your front speakers, bouncing off the back wall and arriving near the same time as the direct sound. That will affect speech intelligibility as well as your sense of envelopment. Your surround sound locations should blend seamlessly. I think some of the Star Wars movies (and others) have one of the THX 360 deg. sound pan intros that make excellent calibration tools!

Don't go diving in to side wall absorption until you can identify a problem. The 'first reflection' issue came from recording studios. Your domestic living space is not a recording studio. Nor should you want it to be!

 

[Pensacola Hi-Fi]

What software do you recommend for measuring?

 

[TheWarrior]

REW

Its free!

 

[highfigh]

Some kind of pressure dampening system is best for low frequencies- drywall on hat channel, mass loading, limp membrane for broad-band and Helmholtz Resonators can be tuned to offset problem frequencies. Lots of info about those and since you build the theater, you can control where they go to a greater extent than someone who is trying to treat a room that doesn't allow it easily. Don't forget that the ceiling is a good place to use treatments when the walls make it difficult.

I disagree about leaving the side walls alone- any time sound has a secondary path to the listener that's close to the SPL of the direct sound, it should be treated as hostile. Use 1ms/ft as your speed of sound and you'll be close enough for a small room. Measure the path length from the speaker and use a mirror to find the first reflection points- if you can see the speaker from the seating area, the wall should be made somewhat absorptive and the area to be treated is defined by the places where you can see the speakers. The fact that I didn't write 'speaker' as a singular means that you need to treat for left AND right speakers. I have a spot on each side that are causing reflections to be distracting when the SPL is high enough to make the reflected sound audible. One is coming from the side of a kitchen cabinet and the other is coming from a window- if I put something in front of those areas, the sound stops. In my case, the one to the right made dialog sound like it was coming from my cell phone, so I moved it and the sound remained.

Strong first reflections cause phantom sounds to occur, when the volume is above a certain level- below that, the direct sound will mask the reflected. It's not just the walls, either- ceilings and floors are additional areas that should be treated if you want to eliminate most or all of the problems.

 

[SRL Acoustics]

Given that all your corners are used up, I would go with your idea of soffit bass trap on all four walls. I think I would shift your couch towards the front about a foot and use a large diffuser on a steel stand on the back wall. You will be shocked at the difference this will make. I have a customer in Florida I can put you in touch with if you wish...

 

[SRL Acoustics]

Here are some pics of what I would propose. The depth is 10.5", and is a high prime design. This will benefit the entire audio range including the bass region. To have a truly effective result in your room using absorption, you would literally have to fill the room completely to gain enough sabines to solve it. This is of course impractical, so for the volume considered, the large diffuser is a great solution for part of your treatment. Here is what it looks like uncovered, and covered with Guilford of Maine grill cloth.

 

[highfigh]

How would you treat a room wood lath & plaster ceiling, terrazzo floor and walls that are plaster on brick that's on poured concrete walls? I checked RT60 and some frequencies are in the 6 second range. Very even decay with no flutter echo.

Yeah, that's where they want to have a home theater. Oh boy. At least they're open to the idea of treating it.

 

[SRL Acoustics]

Can you give a layout with dimensions?

 

[highfigh]

Can you give a layout with dimensions?

The larger part of the space is 21'D x 31'W x 9'-6"H, the rear is centered on the larger area and is 13'D x 19'W x 9'-6". Between the two spaces is a drop in the ceiling (covers the I-Beam) that is 15"H x 25-1/2"D and the width of the opening is 2' narrower, acting as a pilaster. Along the wall/floor and wall/ceiling is a cove with the smaller radius at the bottom. The front wall has a doorway at the right end and the left has a matching seating area that's being made into a shelving unit at the top for AV equipment and media storage- the seat will stay and new Walnut/glass doors will be made to match the others. The right wall in the larger section has a fireplace that extends into the room about 24" and has wooden paneling above the hearth.

The room is so live that I want to prevent as many bad experiences as possible and the AVR I plan to use can be set up to limit the maximum output level- excessive level isn't necessary, they won't use it at that level, they have four kids under 12 years of age and it will sound bad (kind of like the saying about teaching a pig to sing). They want to maintain the look of the room, as much as possible, but since the walls have a small moulding applied to it that I want to mimic as a way to frame the treatment panels, I think I can do something good with this room. The area above the fireplace would reflect sound, but it would do something to diffuse it and I'm going to stand firm in my locations for treatment materials. The ceiling is fair game, too- I mentioned creating coffers with wood that's laid flat, then trimmed with moulding that matches the rest that I want to install around the panels on the walls. In addition, the left and front walls only have a single frame of moulding (not sure why) and the front wall is where the projection screen will mount- I have recommended making smaller framed areas, to match the back wall- it looks odd with two that are so different. If I can find fabric that works well for a 4K screen, I'll place treatments behind it. I wouldn't be able to take up enough space to install the diffusion panels but might be able to use something on the sides if they aren't too thick.

We also discussed some kind of curtain behind the drop in the ceiling, for the times when movie and music sound quality is most important.

I'm installing the projector at the center, where the ceiling and the face of the drop for the beam meet and I'd like to install a strip of absorption there, too.