# Advice on REW graph



## nasp (Feb 12, 2010)

This is my first post, so hello to everyone. I need to get some advice on some measurements of my studio that I took with REW. It is already treated with a couple of bass traps, wedges as well as some hidden mattresses  but I always thought that something is wrong especially with the bass. (though as I can see now from the measurements the highs are also problematic). I calibrated my RME fireface 800 soundcard and took some measurements at around SPL 70 with a blue baby bottle condenser mic. I am attaching a few measurements I made (although the are very similar). 

I can see many gaps in the bass and high frequencies. So, is my room far from a good production and mixing environment? Will I need a couple of more bass traps and wedges to have a more flat measurement or is the problem bigger?

All help is appreciated. Thanks. Spy


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## Wayne A. Pflughaupt (Apr 13, 2006)

Welcome to the Forum, Spy!

I see you calibrated your sound card, which is good, but after that your measurements are only as accurate as the mic used to take them. Very few mics are ruler flat, so a calibration file is needed for the mic as well, to remove its shortcomings from the measurements.




> (though as I can see now from the measurements the highs are also problematic).


I guess you’re referring to the “raggedness” aka comb filtering? That’s fairly typical in a room that’s not totally dead. Your mattresses and other treatments have paid off; that’s some of the best (least) comb filtering I’ve ever seen posted on this Forum.




> I can see many gaps in the bass and high frequencies.


I assume you know that picture-perfect in-room response is virtually impossible to achieve. The only real problem you have is below ~150 Hz. Above that point, your response is relatively flat, audibly-speaking. The only upper-frequency problem I see is a broad dip centered around 8.5 kHz. But not knowing the disposition of the mic – that could very well account for it.

Regards,
Wayne


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## nasp (Feb 12, 2010)

Hello Wayne,
thank you for your lengthy reply. I have tried calibrating the microphone but haven't managed to do it. Are there any other instructions apart from the notes included in REW?

I am really glad that the room has relatively flat response! So, if the microphone has comparatively flat response, do you think I mainly need to deal with the bass frequencies at 65-150HZ and highs at 8.5KHZ and leave it at that or do you think I should try to improve it even more?

Thanks

Spy


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## nasp (Feb 12, 2010)

Hi Wayne again,

I found this thread where brucek ( a member) said: "We provide the cal files for the ECM8000 microphone and also the Galaxy and Radio Shack SPL meters on the download page. Any other mics have to have a calibration file that you create with Notepad. You require a calibration file from the manufacturer or in a pinch, a calibration graph for the microphonebefore you can create one."

I will request a calibration file or graph from bluemic for the baby bottle but then how do I create one in notepad? Can a calibration file be created from the following graph of the baby bottle?

Thanks
Spy


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## nasp (Feb 12, 2010)




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## nasp (Feb 12, 2010)

Hi again 

I have downloaded a calibration file for the ECM8000 mic and I have made a calibration file for the baby bottle using the ECM8000 as a template and using the baby bottle's above graph. Can you please let me know if this is accurate enough?

Thank you 
Spy

View attachment Baby bottle calibration.cal


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## Wayne A. Pflughaupt (Apr 13, 2006)

Yes, the file looks good. Here's a post on making the files, but it looks like you already have the right idea.

Regards,
Wayne


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## cyberbri (Apr 27, 2006)

It looks like you could raise your sub level about 5-10dB. You should do graphs at 15-500Hz to get a better view of that area. You have a very large peak at around 50Hz and it drops off below that, at least from these graphs, which makes me think you might have somewhat of a low end sub like a lower end Velodyne or something (assuming it's a subwoofer and not powered monitors or something). But other than that peak, the bass response looks pretty flat. You could probably experiment with sub placement and phase / sub distance settings to get the sub to blend a little better with the mains. If you could eq that 50Hz peak out (and raise the level), you would have a very nice bass response. (the 50Hz peak could be throwing off the sub calibration, skewing it so the level is set much lower)

I agree that it looks like very nice in-room response. Under 1KHz looks to be about 5dB~ hotter than above 1KHz. I'm not sure if that's the mic or the actual response. If you are mixing music with that kind of response, your end results could end up a bit hot on the high end, and/or a bit low on the mid-low end. Just speculating because you would be compensating for those differences in the mix itself to get it to sound better. But looking at the mic's chart, that could be mostly due to the mic's characteristics. If you could program REW to compensate for that and flatten that response out, you might find that your in-room response is very very flat. Except for the bass. If those are monitors and no sub involved, you could move them closer to the wall to increase the response (although it might not stay as flat), or work with whatever eq/bass boost you might have on the monitors or in the software you're using.


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## nasp (Feb 12, 2010)

Thanks Wayne and Bri for your replies.

I don't have any sub woofer connected. Only a pair of active dynaudio BM6A monitors. I'll load the baby bottle calibration file I created and ran REW again and will post the results. Thanks Spy


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## DanTheMan (Oct 12, 2009)

I don't think you can really get a useful graph with a cardioid patterned mic. I've not seen any measurement mics made this way. Maybe I'm wrong as I'm no pro, but that's my understanding. Listen to Wayne or Bruce over me any day of the week. A small capsule omni should work much better as far as I know. There are cal files for the behringer and the Dayton emm6 or get one from cross spectrum labs for a more perfect calibration and get very accurate results for little outlay. 

Personally I like to see a 5db scale as it shows more detail, but it won't look as pretty. 15 is a bit large, but that may be the norm around here--I really can never remember what the "standard" is. It also would seem that you have alot of dispersion from your loudspeakers in about the 3 to 10kHz region judging by its comb filtering, or your dampening is better at killing the bass. Can you tell me a bit about the speakers? 2-way, 3-way, dome, sealed, ob, etc...

Thanks for posting!

Dan


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## nasp (Feb 12, 2010)

Hi Dan, 
Thanks for replying. The speakers I used to take the measurement are 2 way active nearfield speakers, DynAudio BM6A. I placed the mic at ear position about 2-3 feet away from the speakers (exactly between the speakers where I sit) and took the measurement. If I load the calibration file for the baby bottle mic, will the measurement still not be accurate?

Thanks
Spy


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## glaufman (Nov 25, 2007)

Hi Spy, welcome to the Shack! As for your cal file for your mic, you have some pretty precise entries, I wonder how you got them so precise from the graph you showed. Normally I would think that graph isn't precise enough for truly accurate measurements, did you get a file with the actual data from somewhere (MFR? calibration house?)
For bass frequencies, I wouldn't think the polar plot of your mic would be an issue... it's possible you don't want to trust higher frequencies, but that's where I'm not sure...


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## Wayne A. Pflughaupt (Apr 13, 2006)

nasp said:


> If I load the calibration file for the baby bottle mic, will the measurement still not be accurate?


Dan raises a good point about the mic being cardioid. Can’t say that I’ve ever seen one used for in-room measurements. Perhaps this is because an omni is more akin to the way our ears hear than a cardioid. :huh:

As for as your measurements being accurate with the calibration file you made, I expect that basic frequency response measurements should be at least as good as what you could get using an off-the-shelf measurement mic like the ECM8000 and our generic calibration file. The only problem I can see is that being cardioid, the mic will reject off-axis reflections a lot better than the usual omni capsule found in regular measurement mics. This could very well be why the comb filtering in your graph looks so “good” – i.e. minimal.

So – if frequency response is what you’re mainly interested in, you should be able to get reasonably accurate measurements with the mic you have w/ your calibration file. If you’re interested in seeing the effects of any acoustical treatments that you might add or subtract to the room, I’d suggest getting a more traditional measurement mic that will pick up the room reflections better.

Regards,
Wayne


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## nasp (Feb 12, 2010)

Thanks a lot for your answers. Really appreciate it! :T The reason I am taking the measurements is for mainly checking the frequency response of the room. The room is mainly used for mixing so I want it to be as accurate as I can get it for now(I am buying some more acoustic treatment, mainly bass traps) and to be able to know that I can trust what is coming out of the monitors and what I am really hearing. If in the end, I can use the baby bottle with the calibration file and can get a measurement that really reflects the rooms frequency response, then it would be great. If not, then maybe I should just purchase one of the mics that there is already a calibration file on the website. What do you think? Should buy one or do I really not need it?

Thanks a lot
Spy


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## DanTheMan (Oct 12, 2009)

nasp said:


> Hi Dan,
> Thanks for replying. The speakers I used to take the measurement are 2 way active nearfield speakers, DynAudio BM6A. I placed the mic at ear position about 2-3 feet away from the speakers (exactly between the speakers where I sit) and took the measurement. If I load the calibration file for the baby bottle mic, will the measurement still not be accurate?
> 
> Thanks
> Spy


Nice speaker! Just heard them the other day and thought they sounded great. Maybe my favorite monitor. It was between them and the top of the line JBLs with each having their own strengths and weaknesses. The cost was similar as well.









For nearfield measurements like that you may want to set the gate at 3 msecs(or maybe up to 6 msec) or so to see what your ear will get prior to reflection. Of course if they are sitting on a table, close to a wall or something, you'll still get reflections in there. The bass response will drop off the graph, but that comb filtering might drop out of there as well. At that close of a distance that will be a better representation of what your ear will actually hear first and thus use for localization. You'll also notice that with a cardioid that your response varies a lot with distance and angle. I'm not sure how you would get a good measurement from that but it may be possible. I would just think that an omni would be much better. Got any friends with overhead omni mics?

Dan

edit: addendum, a 3msec gate will only give you a resolution of 333Hz, 6msec resolution 167 Hz and so on.


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## nasp (Feb 12, 2010)

yeap, i think they are great monitors!:bigsmile: I today received a reply from bluemic ( the manufacturer of the baby bottle):



> Sorry,
> 
> I do not have a frequency response chart to give you other than the one in the manual. Our mics were not designed to be used for calibration. I suggest using a mic designed for this purpose.
> 
> ...


After all your comments and the message from bluemic I think its probably wise to just buy one of the recommended mics like the ECM8000 or Galaxy CM140 and take a proper measurement. I will also take a measurement using the baby bottle and the cal file I have made and then post the results. Fingers crossed, after I install the new acoustic treatment in a couples of days the frequency response of the room using a more appropriate mic will be much better.raying:


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## DanTheMan (Oct 12, 2009)

Look at Cross spectrum labs if you want a great cal file of your exact mic or order the Dayton equivalent of the Behringer--it's generally better at mid to treble frequencies while the Behringer is generally better under 100Hz. With a good cal file, they'll be equal. If you have trouble entering the .cal file into the computer, use MS Notepad and save the whole thing as "yourmiccal.cal" (with the quotation marks) and you can use that as your cal file in REW. The format is frequency, space, db level. Like this for data points 5-20Hz but continue all the way to 25,000Hz in real life:

5.00 -10.0
6.30 -09.0
10.0 -06.9
20.0 -03.2

etc..

Data points just made up for brevity.
With that and a calibrated sound card, you'll be rocking a serious measuring rig!

Good luck and keep us informed. , you could even post a link to your music!

Dan


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## nasp (Feb 12, 2010)

Today I have installed some new acoustic treatment :jump: :jump: I still haven't bought a mic which is recommended for measurement purposes. I'll run REW tonight though with the cal file I made and will post the results.


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## DanTheMan (Oct 12, 2009)

I missed this reply. How did you make out? Any new graphs?

Dan


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## nasp (Feb 12, 2010)

I'll post some graphs tonight! I have taken some measurements with the cal file of the baby bottle but I have been waiting to get one of the recommended mics. I haven't had the chance though. So I'll take some measurements and post them first thing when I get back home tonight with the baby bottle.


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## DanTheMan (Oct 12, 2009)

Cool. Can't wait!

Dan


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## nasp (Feb 12, 2010)

Hey guys. Here's the new measurements:




































The absorption and bass traps had great effect. I made another more accurate (I think) calibration file for the the baby bottle. You can see its curve on the graph. I tried to get the cal file to match the mic's frequency response as that found in the manual. I realize you cannot get very reliable measurements with such a mic. I'll get a mic made for measurement purposes when funds permit and make some new measurements. If anyone needs the cal file I made for any reason please let me know.

So, the first two graphs I took were at 72 SPL. I had the mic at the sweet spot where I sit, at ear level, facing on one direction. The last two graphs also at 72 SPL I had the mic facing towards the speakers (as if I had it in front of me singing). Anyhow, regardless of whatever I did all graphs look similar. 

I am still worried about the bass sector though. What do you guys generally think? Is it acceptable or do I need some more bass traps. maybe some traps that go very low down to 50 Hz? Do the 90-100 HZ and 50-60HZ look problematic?

Thanks

Spy


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## cyberbri (Apr 27, 2006)

Putting the speakers closer to a wall will reinforce that bass. I don't think bass traps will bring up that giant valley between 60 and 120Hz.


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I am still worried about the bass sector though. What do you guys generally think? Is it acceptable or do I need some more bass traps. maybe some traps that go very low down to 50 Hz? Do the 90-100 HZ and 50-60HZ look problematic?


It would be easier to decipher your graphs if you'd change the vertical axis to 45-105 dB, but I'll bet the 56-60 Hz problem is that the speakers are producing less bass down there. It would be easier to make a judgement on that if you extended the graph down to 20 Hz.

Regards,
Wayne


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## glaufman (Nov 25, 2007)

cyberbri said:


> Putting the speakers closer to a wall will reinforce that bass.


But it'll also (probably) produce more peaks and valleys.
I'm always in favor of more bass traps, but to be effective to more than a couple dB at 50Hz, they'd either be big or tuned. Sometimes the trick is putting them in the proper place, which might mean some experimentation to figure out where (geographically) the problem is.
And +1 to what Wayne said


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## nasp (Feb 12, 2010)

The BM6As manual says that the speakers go down to 40Hz. I'll try and move the speakers more towards the corners of the room and take some new measurements. To be honest, I just placed the bass traps in the 4 corners of the room , from ceiling to floor. I haven't experimented much. The speakers currently are 2 - 2 1/2 feet away from the corners so I'll try and move them around 1- 1 1/2 and see how it sounds. I'll also get the vertical axis before saving the graphs to 45-105 dB and I'll post the new results.

Thanks for all your help

Spy


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## glaufman (Nov 25, 2007)

Keep in mind there are actually 12 corners in your room (assuming it's rectangular)... don't forget the wall-floor and wall-ceiling corners...
What are the dimensions of the room?


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## cyberbri (Apr 27, 2006)

glaufman,

I agree, but I think some peaks and dips are better than a huge valley for a full octave between 70 and 140Hz. I don't think bass traps in the room are going to fix that. It probably needs to be placement/positioning within the room to get some of that response back first and foremost.


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## glaufman (Nov 25, 2007)

Perhaps, but that'll depend on exactly what peaks/dips the corner placement shows... if it starts booming somewhere, I wouldn't consider that having gained anything... and won't eliminate the valley entirely...
I'd rather ID why it's there and try to tame it with moving or adding to the traps.


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## DanTheMan (Oct 12, 2009)

What type of bass traps are you using?


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## nasp (Feb 12, 2010)

I am using 8 Auralex LENRD bass traps + 2 acoustic solutions bass traps ( from a UK based company). 

I have read online that there is a formula you can use to get the correct length between the wall and the speakers. It's the height of the room times 0.618. Have you ever heard of this formula? I found that my speakers are placed approximately the correct distance. Around 30 cm shorter actually than what it needs to be.


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## DanTheMan (Oct 12, 2009)

I'm going to say something that is contrary to popular practice: placing foam in corners isn't going to do a lot for bass problems. In corners there is a lot of pressure and not much particle velocity. IOW, nothing much to absorb there. Absorbers are better placed 1/4 wavelength of the offending frequency from the boundary in theory, but this tends to place them in the middle of the room. Mechanical dissipation is a far better solution for boundary placement. Read text and view simulations:
http://www.isvr.soton.ac.uk/SPCG/Tutorial/Tutorial/Tutorial_files/Web-standing-rooms.htm
Bass is a tricky phenomenon.

Dan


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## DanTheMan (Oct 12, 2009)

nasp said:


> I have read online that there is a formula you can use to get the correct length between the wall and the speakers. It's the height of the room times 0.618. Have you ever heard of this formula? I found that my speakers are placed approximately the correct distance. Around 30 cm shorter actually than what it needs to be.


Yea, the old "Golden Ratio." I wish that worked and it does have some reasoning behind it in a theoretical room at a theoretical listening position, with a theoretically perfect speaker, etc..., but other than that it is just experiment until you're happy armed with actual facts. Acoustics is just far to complicated for that amount of reductionism. I'm sure you can find people online who'd say that formula changed their life blah, blah, blah and there's chance that it did. Grant it, there's an exceedingly small chance it made much genuine improvement, but it just doesn't mean there's any real reason for it. IOW, an ordinary room may not and probably doesn't measure any better overall. Too much luck, chance, and wishful thinking involved for me.

Of course there is plenty that can be done with the application of real knowledge.

Dan


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## glaufman (Nov 25, 2007)

The idea is to take the likely problem areas due to one dimension and not reinforce them with additional problems in the same area due to another dimension. In that respect, the theory is sound. Sorry for the pun. In practice, sometimes it works and sometimes it doesn't. Why? Because there's a lot more going on. Your walls aren't perfectly square. They're not even perfectly straight. They're not even perfectly flat. Etc.

That being said, there are a handful of times that measurements have shown me something, I decided on a whim to apply one rule or another, and found that something fixed. Not every time, but enough to not discount trying.

Acoustics is one area where no matter how much you simulate, something will be different in the real world. So experiment and see what works. But make sure some of the "golden rules" are part of your experiments so you can see for yourself.

And I've seen enough experiments to see that corner traps work. But as with all acoustic things, they work at certain frequencies and not at others. And with certain materials, and not with others.


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## nasp (Feb 12, 2010)

I'll try and move the speakers a bit closer to the corners and run REW and post the results. 

The WHOLE wall behind the speakers is also a wardrobe (about 2 feet width) so the bass traps are placed in the corner outside the wardrobe and not inside it. I'll try and put the bass traps inside the wardrobe and take some more measurements and post the results as well. I just thought that by placing the bass traps outside the wardrobe, the back of the speakers will be facing exactly towards the bass traps and there will be better absorption.


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## glaufman (Nov 25, 2007)

Corners are seldom good places for getting smooth response from speakers... how close to the corners are you talking about moving them?


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## DanTheMan (Oct 12, 2009)

Oh, one more question: How does it sound now? 
and a couple more: what exactly are you trying to do with the foam bass absorbers? The bass shown doesn't seem like it's overwhelming. Are you just looking for a nice "dead end"?

Why not see what happens if you pull them into an area where you have a lot of particle movement?
here's a wavelength calculator: http://mehlau.net/audio/calculator/ just divide that value by 4 and place the bass absorber that far from the corner or wall and see what happens. Keep the patterns in mind from the other site I linked. If I'm crazy, you'll know it then. One other thing is that most foams are pretty broad band absorbers. 

Dan


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