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MercedesBerater

When to REW

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I am building a home theatre. I am trying to decide when to REW. I am wondering if I should go forward with my own acoustic panels at all first reflection points and bass traps in corners THEN perform a REW diagnosis on the room and where I need further help (minor tweaks, hopefully)

OR- should I do REW first and treat based on those results? (Disclaimer- I am researching how to read and interpret these REW graphs - I'm getting ideas on what they mean, but it doesn't help me decide location of panels- is that still a guessing game?)

Any advice would be great.

Room will be 75:25 home theatre:music

Second subwoofer added when room is complete & prior to any panels & REW.

Construction is moving along and I'm getting into the color planning & treatments stage

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I'd recommend taking microphone measurements now (upsweeps) using REW, even if you're just using the microphone in your laptop/computer.  Place the microphone at your notional listening position and record the upsweep(s), then move your microphone around to another listening position and repeat.  Then you can look at the RT60 plots to see how much absorption you need as a function of frequency (including bass traps).

 

Diffusion panels are difficult to overdo, but I find that most folks neglect these type of panels.  Recommend using diffusion around your front and side walls close to your front and center speakers, back wall, as well as halfway back from your listening position.  Think about the ceiling if you have a ceiling less than 8 feet high.

 

Chris

Edited by Chris A

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Room dimensions are 16'W x 26'L x 7'8"H

Follow up question- I'm doing double 5/8" drywall with GG for walls, ceiling has 1 layer of 5/8" glued & screwed to subfloor I between floor joists then furring strips perp to floor joists with double 5/8" drywall with GG.

Walls are staggered stud construction with top and bottom plate 2x6 only common joint.

Will the measurements be adversely affected (or negligibly) if I do the REW before finishing the exterior of the staggered stud walls?

I planned on finishing the interior & leaving exterior of walls naked for some time in case I need to pull more wire or add outlets easy.

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Will the measurements be adversely affected (or negligibly) if I do the REW before finishing the exterior of the staggered stud walls?

 

As you go up in frequency from 70 Hz (nominal bass trap fundamental frequency), the measurements will become more sensitive to finished surfaces - but note that you're typically worried about frequencies below 1 kHz, so my guess is that taking measurements now between these two frequencies will give you an idea of what you'll need. 

 

For frequencies below 70 Hz (or 35 Hz if you're looking at using double-length bass traps along a wall-ceiling or wall-floor interface, and especially corners of the room where the effectiveness of the traps are maximized), building in a little "give" in the facing sheet rock or plaster will actually control room resonances better than using any kind of traps.  I'd recommend stiff front corners but more compliant wall surfaces as you go toward the back of the room.

 

Chris

Edited by Chris A

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No reason to put up panels and double bass traps without using REW to see what the problem is first.  Hard to fix what you don't know.  Some of the bass problems can be fixed with the decor.  I have all soft seating in my area, carpeted, ect.

 

One thing for sure if you are doing this from the ground up is to separated the heating/air conditioning.  This will keep down noise in the rest of the house.

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A/c is being isolated as much as possible.

Ok- measurements now to see where to put $ first... Then run REW again to see if it's diminishing returns & if $ permits going further.

I still don't comprehend how a REW graph will help me decide where to place panels?

Or is it almost always at 1st reflection points?

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You could alway wait till everything else is done and start with a more accurate reading and go from there.  I don't use bass trap and have pretty a pretty good room response without panels and large bass trap.  I use Omnimic for sub EQ and the room.  It is a lot easier to get up and running.  It is more expensive also.

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I still don't comprehend how a REW graph will help me decide where to place panels? Or is it almost always at 1st reflection points?

 

You've got part of the answer - for higher frequencies (well above 1 kHz), you're trying to break up the secondary sound arrivals into a diffuse, random pattern.  For midrange early reflections, you typically absorb these using absorption panels and soft materials/curtains.  For frequencies below about 200 Hz, bass traps absorb these - which are typically dependent on the room's modes. 

 

An easy way to remember how to deploy panels is to place one diffusion panel, one absorption panel, and one empty space of bare wall, then repeat again.  Diffusion panels work well at high frequency first reflection points to scatter these higher frequencies much like reflected light. 

 

REW will tell you how much absorption panels and bass traps to use (total).  You can use REW to help with higher frequency treatments, but this is a bit more advanced.  Suffice it to say that placing these diffusion panels at the first reflection points (walls and ceiling) halfway back to the listening position will go a long way toward controlling these frequencies.

 

Bass traps inhabit the corners and wall-floor-ceiling intersections. 

Edited by Chris A

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Buy quality panels and buy a lot.  It makes a huge difference.  I just bought 80 sq. feet of panels for a 400 sq ft room a few months back and it will change everything for the better.  I still need to run REW again just to see how much it changed on paper, but none the less, it is a world of difference to my ears.

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I was thinking of making floor to ceiling cloth wall sections with absorptive material behind- and frame it out like a picture frame. That way it looks more architectural & aesthetically pleasing / upscale Vs some panels hung everywhere. Better WAF ;)

And for diffusion I'm planning on front and rear wall similar to WakeJunkies stone walls. With stone wall columns In between the acoustic floor/ceiling panels. I think the stone should give enough irregularity for diffusion & the added benefit of more mass for bass management not leaking through walls.

But before I start stonework I was hoping to get an idea of where everything needs to go.

Building the room & getting speakers was easy! The acoustics is what's boggling my mind.

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For floors to ceiling acoustic wall sections I was looking into johns manville whispertone wall board 2" (49"x121"x2" to keep one continuous piece wrapped in cloth- don't want a pieced together lines under the cloth! Eek!)

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REW measurements will help you decide where the acoustic panels will be most effective, if you do before and after readings while positioning them, following the good advice in the above posts. Doing the treatments you describe, even without measurements, will be randomly beneficial to your listening room. The Whispertone wallboard specs are similar to the material used under the fabric covered walls of commercial movie theaters. You are starting out with the right ideas.

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Thanks for input. I have a client that has a recording studio who offered to come take room measurements with his exotic studio toys. Can't hurt to let him work some magic. But I'd still like to not be too far off - so his measurements can really perfect the room.

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Measurements don't really tell you anything unless you know what you're looking for, and I think that's the basis of the confusion you describe.

I've been measuring rooms for several years now and never has anything been straightforward obvious. In other words, the measurement isn't going to tell you that the panel needs to move one inch up and two inches left. You're going to have to apply your intuition to the problem and then find a test that can invalidate the assumption. This ends up being an iterative process that takes a long time until you've built up the experience.

All that said, I would start by identifying the problems you know will exist in your room. Modal response, flutter echo, ITD's, decay rates, etc....then identify solutions you're willing to tackle. Each treatment option does different things, so you gotta learn how to measure when they're being effective. The hard part is that there is always so much "noise" in the measurements; not actual noise floor, but so much information that it's hard to focus on one thing accurately. Slowly as improvements are made, you'll notice the information gets easier to interpret.

I know this is more philosophical in nature, and probably not very helpful, but it's just the nature of making useful measurements. Trying to get an arbitrary flat frequency response at a single mic location is very misleading and not really the goal. Although a good room will tend to have a flatter response. (correlation versus causation)

So practically speaking, I would start by learning how to identify different types of room issues in your measurements. Move the mic around and note what changes and what stays the same. And don't forget to use your ears while you're at it. The goal is to fix what you hear, so don't worry about measurements that look bad.

Practically speaking, you could just start posting measurements and people can help describe what is there. Just be sure to note the mic position and measurement settings since it has a huge impact on what you see.

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I do think that is good advice. It helps alleviate my concern that I'm just not "getting it". I couldn't wrap my head around how a waterfall plot could help me position a panel correctly. Every article I read seemed to gloss over that important part. Basically it's trial and error with measurements showing what changed to determine if it had a good/bad effect.

Very much appreciate that post DrWho!

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Looking at the ETC plot, you 'could' calculate where each reflection is coming from...but you'll need to move the mic around a bit to isolate which reflective surface (or combination of surfaces) it's coming from. It might help to start outdoors with a single wall to see what this looks like.

Then you can put the mic in that location and use a proper time window to understand the tonal balance at the reflection point, which will determine the size you need for the acoustic panel (depth and spacing of diffuser or thickness of absorption, etc...)

However, if you know the polar response of your speaker, then you pretty much know what all the early reflections are doing. Once you get into the later periods where there are multiple reflections, then you start to do statistical trends so you don't have to think about 100 paths at once.

Btw, are your walls already built? I get the impression this is a room within another room? I'm just wondering if you have any option to splay your walls so they're not parallel. One inch per foot is a good rule of thumb, but you don't need to go the whole length of the room either.

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Walls are done. Yes room within a room. Drywall is underway now. Doing it all myself... Slowly but surely. 70 hr work weeks don't leave much time

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Did you say what kind of speakers you are using?

 

If you're done, how did the room come out, and what did you do?

Edited by garyrc

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