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Discussion Starter #1
Hi everyone. I have what is probably a very basic question about REW, so my apologies. I have searched and read a great deal but haven't found anything that sheds a direct light on what I am asking.

I am in the process of a new home theater build and want to use REW not to equalize speakers but to guide me on acoustic treatment decisions. I am setting up the room for an Atmos system with 4 overheads and 2 subs in addition to my 2 pairs of full range speakers (front left and right and rear left and right). I run a phantom centre channel. My 4 overheads are Tannoy Di5 DC (-3dB at 90 Hz), and the 2 subs are ACI Titan II (-3dB at 20 Hz) crossed with my 4 mains at 65 Hz. So my setup is a 4.2.4 system. The room is difficult - 3.6m x 3.5m with 2.2m ceilings, and all walls, ceilings and floors are either reinforced concrete or concrete block (I live in Switzerland). I can get away with a maximum of 12cm treatment on the rear wall and up to 6cm on the other walls. Roof can have 20cm of treatment. I expect I will likely go with VPR panels in the back corners based on what I am seeing elsewhere in terms of bass absorption in shallow treatment spaces.

My noobie question is about how I should be going about using REW to guide my acoustic treatment choices. I've never used the program before so how I strategize about using it for my situation is slowly coming together from the various guides and threads. I feel quite clear on its use to determine subwoofer placement and there are loads of guides/threads on that. But another very important concern for me in my space is decay time of low frequencies and minimizing the low frequency modes I expect in my room. For this consideration I am thinking I need to be running REW measurements with all 8 of my speakers running (as well as both subs) and examining the sub-300 Hz areas on waterfall plots. But most of what I read about usage of REW seems to relate to people running the program for subwoofer placement optimization (which I also want/need to do and plan on doing first), or for equalizing speakers one at a time or a pair at a time. I don't find much about simultaneously running 8 speakers and when I see mention for 7.1 setups the detail seems vague and not directed at whether it is the appropriate thing to do to measure whole room decay times and assess modes.

So...without being certain but based on what I have read, my plan of attack for my situation at this point is:

  1. Install speakers in final locations - apart from the subs which are broadly movable and whose final placement will be based on REW testing, the other 8 speakers are constrained to be in very specific locations due to the room geometry.
  2. Install listening couch (there is no other large furniture)
  3. Install Umik-1 microphone in MLP
  4. Connect Umik-1 to laptop, and laptop to Oppo 105 via HDMI
  5. Connect Oppo to 8 channels of amplification for speakers and to 2 subs
  6. Do a series of measurement sweeps using only subs to optimize their position then place in final positions
  7. Do a series of measurements with ALL 8 speakers and both subs looking primarily at waterfall plots to address the room issues in the sub-300 Hz region
  8. Proceed in a stepwise fashion adding acoustic treatments, repeating waterfalls with all speakers carrying a sine sweep signal to optimize the room acoustics for the sub-300 Hz region
  9. After low end modes treated as best as possible, shift focus to treating reflection points and making decisions about use and placement of PRD diffuser(s). At this stage I could see shifting away from sending signal to ALL speakers and only sending to one speaker at a time or specific pairs of speakers.

So my question is - is this the right approach to using REW for my situation?

Thanks - sorry if it is a completely idiotic question and if it is feel free to link me to a thread elsewhere that sheds light.

Best wishes,

Dave M
 

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But another very important concern for me in my space is decay time of low frequencies and minimizing the low frequency modes I expect in my room. For this consideration I am thinking I need to be running REW measurements with all 8 of my speakers running (as well as both subs) and examining the sub-300 Hz areas on waterfall plots.
No, there is no need to run all the speakers at once. Most of your bass will be coming from your subs, so most important is to measure with your subs playing. There is more general information in the Links and Guides thread, the REW 101 step by step setup guide is aimed at using REW with UMIK and HDMI.
 

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Your approach will work fine (with the exception John noted). When you finally get to #9 you might start posting questions in our Home Acoustics Forum, where the folks there can help on what REW graphs to analyze, how to read them, and what treatments to apply.

P.S. Welcome to the Forum!

Regards,
Wayne
 

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Discussion Starter #4
Thanks Wayne and John, very helpful.

So John even if 4 of my speakers (all apart from the overheads) are full range and crossed over to my subs at 65 Hz I don't need them on when trying to figure out acoustic treatments for the sub-300 Hz range? To be honest that surprises me a bit....I would have thought those 4 speakers would be adding a good deal of sound to the room in that range.

But thanks again - I am a complete newbie to using the application and setting up the room.

Best wishes,

Dave M
 

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Full range speakers with a low crossover setting will be making a contribution of course, but you still don't need them all playing at the same time because it would be unusual for most source material to have the same content in all channels. For multichannel material the LFE channel will get the bulk of low frequency content, for stereo material there will often be monophonic bass in L and R so it is worthwhile to play those together with the sub. Otherwise check speaker+sub pairings individually.
 

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Discussion Starter #6
Sorry for the delay - was away over the holiday weekend. Just wanted to say thanks to John for the additional information. I will be getting to the testing stage after building a door for the space - currently it is just an opening into my concrete block lined echo chamber. I plan on getting the door built in and installing a microphone stand above the couch as well as any additional furniture that I know will need to sit in a specific final location.

Once I have the main fixtures installed I will proceed along the lines of what I proposed, shooting first to establish best positioning of my two subwoofers. I may come back here looking for a bit more guidance down the road...

Thanks again,

Dave M
 
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