(DIY) Subwoofer Setup using REW

mattkhan

Distinguished Member
BASIC INFO

What is RoomEQ Wizard (aka REW)?

From the help

REW (Room EQ Wizard) is a Java application for measuring room responses and countering room modal resonances. It includes tools for generating test signals; measuring SPL; measuring frequency and impulse responses; generating phase, group delay and spectral decay plots, waterfalls and energy-time curves; generating real time analyser (RTA) plots; calculating reverberation times; displaying equaliser responses and automatically adjusting the settings of parametric equalisers to counter the effects of room modes and adjust responses to match a target.

Who is this thread for?
Anyone who wants to get this most out of their subwoofer through the use of objective data to learn about what they listening to and how that relates to what they like.

How do I use this thread?
This thread will contain 2 things
  • any and all discussion about REW that people want to have
  • a FAQ about using REW to setup a subwoofer
The Qs in the FAQ will always be in this first post and the Qs will evolve over time. Each answer from this point will be a separate post with links to/from the Q. If links to a section within a post (an anchor) are possible on AVF then do let me know :smashin:

Why should I care about REW?
See here

Where do I get REW from & who else can help me use it?
See here

GETTING STARTED

Is there a step by step guide available?

AustinJerry maintains a guide over on AVS which can be found here. This gives a blow by blow account, with pictures, on how to get started.

What do I need to get started?

See here

What connections do I need to make to use REW?
Refer to this HTS post for full details & the various options for getting ready to measure.

How do I configure REW to use a physical loopback connection (to provide a timing reference)?
A physical loopback provides a means to measure absolute time/phase. See here for configuration details.

How do I configure REW to use an acoustic loopback connection?
REW 5.15 beta 3 has implemented an "acoustic loopback" feature. This sends a high frequency reference signal to a speaker which then acts as the timing reference. This feature can be used to determine relative timing/phase between drivers. Further details can be found in this HTS post

What is the difference between relative phase and absolute phase?
Practically speaking, nothing. Measurements with accurate absolute or relative phase can be summed/compared without issues.

What level (in decibels) should a sweep play at?
See here

DIALLING IN THE SUBS

Is there an alternative to doing this manually?

Yes. Multi Sub Optimiser (MSO) is a powerful free tool that can optimise your setup for you. MSO lives at What Is Multi-Sub Optimizer? and has a thread on AVS at Optimizing subwoofers and integration with mains: multi sub optimizer - AVS Forum | Home Theater Discussions And Reviews

This requires either data with accurate phase data, i.e. requires REW 5.15 beta3 or later for access to the acoustic timing reference or use of a physical loopback.

Approximating a Linkwitz Transform using Shelving Filters and PEQ
See here

Why should I (time) align multiple subwoofers (drivers)?
See here

When using an impulse response to align 2 speakers, what frequency range should I use in the sweep?
See here

How to time align 2 (or more) drivers using REW?
See here

ROOM EQ

How do I work out which room modes I can easily treat with EQ?

See here

Is there an example of working through the whole process?
It spans 2 posts starting here

How do I use REW to calculate PEQ filter(s) that address a single modal peak?
See here

SOUND QUALITY & COMPRESSION TESTING

How do I measure distortion using REW?

See here

What can I do with the information in the distortion graphs?
See here

What effect does the room have on distortion measurements?
See here

How do I measure max useable output?
See here

UNDERSTANDING MEASUREMENTS

What do the "window" controls do?

See here
 
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mattkhan

Distinguished Member
NB: I think I need to do this in a few posts as the editor is starting to grind with loads of pics in it

FWIW another way to do the 1st bit is via close mic measurements of the sub, tbh if you have a good feel for the transfer function of your room then I don't think you need to bother but ymmv...

NB: these are the measurements I have to hand, not current setup, so just take as an illustration of one approach to this

0. setup (primarily for cuboid rooms)
- apart from the actual connection setup, I add my room size to the EQ window so click this
upload_2014-4-8_23-15-19-png.475186

- enter your room size & click "find resonances" (NB: all bets are off if your room is not a regular shape)
upload_2014-4-8_23-16-47-png.475187


1. work out which modes are easily treated with DSP on paper
- 1st modes are a function of a single room dimension, these are the axial modes which are formed by a standing wave between 2 surfaces
- a common room layout will have seating positions across the width of the room like so

upload_2014-4-8_23-21-52-png.475191


- in this layout, the length & height axial modes will be excited in basically the same way across the 3 listening positions but the width mode will vary dramatically
- you can play with this in the room sim, here's mine (red = length axial, green = width axial, blue = height axial)

upload_2014-4-8_23-24-34-png.475192


- the 3 lines are the 3 positions shown in the floor plan, note how they peak in the same way on the red and blue modes and vary massive in between
- on paper, the 1st mode looks a good bet for DSP, the 2nd one not really, the 3rd one maybe (reasons to be seen!)

2. confirm response via measurements
- get the mic at the MLP, sweep to 300Hz
- go to SPL & Phase tab, click controls, click "Show Model Frequencies"

upload_2014-4-8_23-18-35-png.475190


- look at the chart, you can reasonably expect to see a clear alignment of a peak with a mode
upload_2014-4-8_23-13-47-png.475183


- repeat measurements (NB: I don't have any to hand that would be useful so you have to take this bit on trust) at any other listening positions for 2 reasons;
a) confirm how these correlate to the room sim
b) build your own understanding of the space acoustically
- this paper from harman might be interesting background reading
- this spreadsheet also by harman is a simple visualisation of how standing waves form in a room, it gives a view like this which shows the relative strength of the standing mode across the dimension (if you drag a listener across the rew room sim in 1 dimension you will see the response change as per the view below)

upload_2014-4-8_23-35-44-png.475193


3. decide whether to apply low end boost or not
- this depends on what you're aiming for but if you look at my raw response then you can see
a) a clear peak at 41Hz
b) I am down ~22dB in an octave (~40Hz -> ~20Hz) rather than a traditional sealed sub roll off of 12dB/octave
- if we ignore that peak for a moment and aim for a section that looks flatter then we do see roughly a 12dB drop

upload_2014-4-8_23-41-10-png.475194


- we now have to decide what to do next.... options include
a) boost the low end, perhaps cut the peak too
b) raise the sub level as a whole & cut more aggressively across the board
c) just cut the peak and accept what the system gives us with no EQ
- there might be others approaches, the right one depends on at least the following
a) your amp (does it have the power on tap)
b) your sub (can it handle the boost)
c) what you're aiming for (music? LFE?)
- in my case, I go with option a) (though I would consider option b in a PC only situation)

4. applying low end boost to meet the cut of the 1st mode
- the way I did this when I had an DSP was to raise the low end so it "meets" the cut applied to the main mode
- the boost is done via an LS12, the cut via PEQ
- I would do this in 2 steps so you can check each one works as expected (and because REW can't suggest PEQ on top of suggested LS filters)
- first the LS12, in this case quite a large boost (I don't boost this much these days) shown by the blue line
- note that the corner frequency of the LS12 still means there is a lot of boost higher up the frequency range

upload_2014-4-8_23-48-48-png.475195


- compare against the outcome, you can see the ~13dB has been applied

upload_2014-4-8_23-51-25-png.475196
 
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mattkhan

Distinguished Member
5. cutting the target modes
- now you have the LS in place, you can ask REW for filters so go to the EQ screen
- change the upper EQ limit so it doesn't suggest filters into the acoustic XO range (you can measure this but a rough rule of thumb will be 60Hz for an 80Hz XO)
- set the EQ type to DCX2496 when using the inuke (though note some have seen the Q value suggested by REW to not match the inuke, I found REW q=10 needed inuke Q=5 to match....)

upload_2014-4-9_0-1-44-png.475198


- if you were to measure it then you would measure a main on its own then the SW on its own but with bass management on then look for how they roll off
- the point being that this is why you're using auto eq so leave auto eq to sort out the responses through the XO
- anyway get REW to suggest filters, apply them to the inuke and remeasure to confirm
- first suggested

upload_2014-4-9_0-4-32-png.475200


- then predicted vs measured, to show this click the overlays button

upload_2014-4-9_0-6-16-png.475202


- select the predicted SPL tab and then select the before and after measurements (NB: the before measurement is the one you had selected when you clicked the EQ button and got it to calculate filters)

upload_2014-4-9_0-5-42-png.475201


- if the 2 measurements don't largely agree then something is wrong and you need to repeat til they do broadly agree
- mine are close enough albeit some mid bass oddities

6. how anal are you?
- depending on your level of OCD, you might now go and repeat across multiple listening positions and then perhaps average the results before EQing again
- I will leave that as an exercise for the reader :)

7. run auto eq
- if you have decent extension and reasonably flat response then you are in good shape for your auto eq of choice to fine tune the results and integrate with the mains so now is the time to run that auto eq

8. verify auto eq
- just repeat the measurement process for L, SW, L+SW separately to check everything looks sane
- there is a common problem around crossover dips due to bad distances being calculated by one shot auto eq routines (google Subwoofer Distance Tweak Instructions for details)
- I can post how to check this via impulse responses another time :)
 
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mattkhan

Distinguished Member
How do I use REW to calculate PEQ filter(s) that address a single modal peak?

The use case here is for applying targeted PEQ before running some auto EQ routine (to give that routine an easier job to do).

1) take measurements as usual
2) decide exactly which mode (singular) you want to tackle
3) open the EQ window
4) set the Equaliser to whichever device you're using (or generic)
5) set target level to whatever level you want to flatten the peak to (119dB in the example given, the absolute level is irrelevant here)
6) set match range to the area consumed by the peak you want to flatten (30-50Hz in th example given)
7) click "Match Response to Target"
8) review the waterfall view to check impact on ringing
9) tweak gain/q/freq of filter(s) as necessary (though REW is generally v good at this)

upload_2015-3-7_22-55-49.png


Return to the FAQ
 
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MemX

Well-known Member
Ooh, this is a good thread! :thumbsup:

Subscribed so I can come back when I have finally downloaded REW and have time to play with it :)
 

mattkhan

Distinguished Member
I think I will make the first post into a FAQ style and link that to any particular posts that give the detail. Subjects I can think of include

- equipment choices (pros/cons)
- time alignment of multi subs (how to)
- sub mains integration (SPL method, phase alignment, band limited impulse method)
- real world examples from different rooms (maybe @Jamesvicky @markymiles @KelvinS1965 could contribute a post or two summarising their setup?)

Anything else?
 

markymiles

Distinguished Member
Good idea Matt. There are obviously lots of guides for the complete novice over on HTS for setting up REW. Might be worth linking to them as I think you may find some people a little lost from the beginning. You're assuming people are quite familiar with the program.

I'll post a few graphs when I get a minute.

As you have the knowledge maybe a little description of PEQ, what is Q, different filter types, etc.
 
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markymiles

Distinguished Member
Well as you asked here's my journey. As matt helped me it's not dissimilar to his methodology and results.

Two subs, not perfectly equidistant from the mlp, with the best combined response I could get. Matt will no doubt get to this with his time aligning two subs bit. Having a USB mic I am unable to do the time aligning properly. But suffice to say it made a big difference setting a delay to the nearest sub and more than the measured distance.

Here's my best combined response:

qgwk.jpg


I didn't add a bottom end LS12 filter at this stage and let REW suggest filters to get rid of the peak. Setting the target level is important here otherwise REW came back with lots of filters. I set it at 82 db I think which gave only two filters:

09ut.jpg


And the result with the two filters:

ezdb.jpg


I was tempted to leave this alone and let audyssey take it from here. I didn't think I needed a LS12 filter as Matt suggests and just applied a little 3db, Q4, 20hz boost.

This resulted in this:

9vxh.jpg


Happy with that, not sure exactly how accurate the below 20 hz bit is. Just for info I'll show what audyssey did with it:

6cw5.jpg
 

hoppaz

Well-known Member
Can this be made a sticky at the top of the diy forum Mods?

Excellent thread Matt thanks for taking the time to do this.

Thumbs up to Markymiles too
 

Graham N

Well-known Member
Well I got my UCA202 last night and tried to set it up and give it a go. I pretty much failed at the first attempt to calibrate it and gave in and watched a film instead. The problem I had was when it said loop r input to r output it only showed a meter reading on the out level meter. It didn't matter whether I selected left or right on the input channel box. If I looped the L input to either L or R output both left and right meters worked. I don't know if this is normal or the unit is faulty.

I managed to get one sine wave to run but it said something about only being 37.5db. I don't know whether to persevere with this or just let an antimode do its best until I get my amp back and then let Audyssey do it's thing,

Graham
 

mattkhan

Distinguished Member
Well I got my UCA202 last night and tried to set it up and give it a go. I pretty much failed at the first attempt to calibrate it and gave in and watched a film instead. The problem I had was when it said loop r input to r output it only showed a meter reading on the out level meter. It didn't matter whether I selected left or right on the input channel box. If I looped the L input to either L or R output both left and right meters worked. I don't know if this is normal or the unit is faulty.

I managed to get one sine wave to run but it said something about only being 37.5db. I don't know whether to persevere with this or just let an antimode do its best until I get my amp back and then let Audyssey do it's thing,

Graham
if you describe your connections & post some pics of the preferences screen then we could try to debug the problem
 

IronGiant

Moderator
Can this be made a sticky at the top of the diy forum Mods?

Excellent thread Matt thanks for taking the time to do this.

Thumbs up to Markymiles too
I meant to do that, but I was exhausted after converting all the images. :)

Not that I'm begging to be loved or anything ;)

Edit: stickied
 

Graham N

Well-known Member
Well I have got my DIY subs up and running but still can't get my head around REW. I also don't know if my UCA202 is working as it should. I bridged the right input and output to do the calibration and I got nothing on the right or left meter bar. If I bridge the left input and output I get BOTH left and right meters working. I managed to get one sine wave coming through the right sub but don't know whether that is a calibration file or an actual test. I don't like wasting too much of others peoples time when I can't get my head around it at all so I may give up. It is taking me longer to connect up and run the tests than it did to build the subs.:facepalm:
I don't think I am destined to get these subs working at their best. My Onkyo 3009 with its multi EQ XT32 has gone in for repair two days before the subs were finished. My old Onkyo 905 I borrowed from my son doesn't have this. I was going to connect both subs to my Antimode 8033C that I was using until I got the 3009 but I have mislaid the 9V AC power supply. I posted a request in the sub forum for a picture of the power supply to help me identify it. So if anyone reads this that has one I would be grateful for a picture.

Pictures below of the bridged connections and associated REW preference screen shots. It won't accept the .mdat file and I have messed with it and can't get it looking like it was. I have just added a screen shot of it instead.

thanks for any help.

Graham.

PS is there a simple program I can use instead of REW before I give up
 

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mattkhan

Distinguished Member
Well I have got my DIY subs up and running but still can't get my head around REW. I also don't know if my UCA202 is working as it should. I bridged the right input and output to do the calibration and I got nothing on the right or left meter bar. If I bridge the left input and output I get BOTH left and right meters working. I managed to get one sine wave coming through the right sub but don't know whether that is a calibration file or an actual test.
You might have done this already but I would take things step by step to demonstrate that everything is working as expected, this means checking the soundcard works for playback and recording without using REW then checking that you can still do the same with REW and only then adding in the loopback. There are ~20 pages of step by step instructions in the guide from avs which you can find here. A fair bit of that talks about hdmi connections and usb mics (not relevant to you) but the windows audio config is still the same.

Try that and see how you get on. Just remember to get it working in windows alone first before you try REW.
 

Graham N

Well-known Member
Hi Matt, I seriously am almost at a point where I have spent almost as much time trying to get this working as I did at making the subs. Probably only stuck with it this long due to wasting £30 on the UCA202.

I looked at the link and managed to set up the playback part as per instructions. But it only lists set up info for a USB mike as far as I can tell. If I select the built in mike I get the following task bars. GENERAL:CUSTOM:LEVELS:MICROPHONE ENHANCEMENTS:ADVANCED but in the one for the UCA202 I only get GENERAL and ADVANCED. There are no settings for me to do anything with. I wonder if it is because the 202 is listed as line in and line out and not actually a specific mike input.

I think I will connect something stereo through the 202 to see if I can anything in and out

Thanks for persevering

Graham
 

Graham N

Well-known Member
I have connected my iphone to my Litttle dot 1+ and out to some headphones and confirmed correct operation. I then introduced the UCA202 in between the iphone and Little Dot with secondary headphones plugged into the jack on the 202. Got no sound but did get the level meter on the mike input on the laptop showing a signal. I then bridged the 202 ins to outs and still nothing.

Then DUH, switched the monitor off/on button to on and wallah,sound from both sets of headphones with the volume control on the 202 only controlling the secondary phones. Removed the links and connected properly and now have sound with monitor switch set to on.

Now need to take a breath and look to the next step

Graham
 

Graham N

Well-known Member
Matt, what is the sequence after running the loopback calibration. Do I leave the loop in to do the sine sweep or do I connect the SPL meter and one sub now instead, or something else. I am only getting one line on the graph not two as in the example. And when do I add the calibration file for the meter?

Regards

Graham
 

Graham N

Well-known Member
BTW the issue with two bars or no bars showing up was because I had to select two channel for the mike in the basic set up you suggested, it was defaulted to one channel.
 

mattkhan

Distinguished Member
Matt, what is the sequence after running the loopback calibration. Do I leave the loop in to do the sine sweep or do I connect the SPL meter and one sub now instead, or something else. I am only getting one line on the graph not two as in the example. And when do I add the calibration file for the meter?

Regards

Graham
by loopback calibration, do you mean the soundcard calibration (as per this bit of the help)? If so then yes you change the connections after completing the soundcard calibration.

Lets say you intend to use the L channel for measurement, when you calibrate for the soundcard then you connect the L output to the L input only.

When you complete that then you can set the soundcard cal file in the preferences, connect the L output to the AVR and the L input to the mic/spl meter (& connect the R output to the R input to provide the timing reference). You then set the meter cal file, check c weighting & you're ready to measure.
 

Graham N

Well-known Member
by loopback calibration, do you mean the soundcard calibration (as per this bit of the help)? If so then yes you change the connections after completing the soundcard calibration.

Lets say you intend to use the L channel for measurement, when you calibrate for the soundcard then you connect the L output to the L input only.

When you complete that then you can set the soundcard cal file in the preferences, connect the L output to the AVR and the L input to the mic/spl meter (& connect the R output to the R input to provide the timing reference). You then set the meter cal file, check c weighting & you're ready to measure.

Yes, prior to running the sine wave. So are you saying that after running the calibration with the loop between the right input and output that I leave the loop in place and then connect the SPL meter to the left input and connect the left output to the AVR or sub amp input? I thought I did the loop for calibration and then used the same in/out for measuring.

And this is when I apply the cal file for my specific meter and should then be good to go?

Graham
 

mattkhan

Distinguished Member
Yes, prior to running the sine wave. So are you saying that after running the calibration with the loop between the right input and output that I leave the loop in place and then connect the SPL meter to the left input and connect the left output to the AVR or sub amp input? I thought I did the loop for calibration and then used the same in/out for measuring.

And this is when I apply the cal file for my specific meter and should then be good to go?

Graham
No. Lets assume you intend to measure with

L = actual measurement
R = timing reference

when you calibrate the soundcard, you will connect L out to L in (nothing connected to R) and measure. This gives you a soundcard calibration file which you set in the preferences screen.

Now you want to measure so you;

* remove the L out to L in loopback
* connect an R out to R in loopback
* connect L out to the AVR
* connect L in to the SPL meter
* load the mic cal file
* set c weighting

make sense?
 

Graham N

Well-known Member
No. Lets assume you intend to measure with

L = actual measurement
R = timing reference

when you calibrate the soundcard, you will connect L out to L in (nothing connected to R) and measure. This gives you a soundcard calibration file which you set in the preferences screen.

I calibrated using R to R as recommended

Now you want to measure so you;

* remove the L out to L in loopback So I remove R out to R in loopback
* connect an R out to R in loopback Connect L out to L in loopback
* connect L out to the AVR Connect R out to the inuke (only checking subs for now)
* connect L in to the SPL meter Connect R out to the SPL meter
* load the mic cal file Load the mic cal file
* set c weighting Set c weighting

make sense?
 

Graham N

Well-known Member
Also now I am getting somewhere even small steps, I am taking more time to read the help files rather than just to try jumping straight in.
 

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