Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 451 - AVS | Home Theater Discussions And Reviews
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post #13501 of 14645 Old 02-08-2015, 08:14 AM
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Quote:
Originally Posted by Brian Fineberg View Post
Could you elaborate?
Remember (as per the guide) that reflections are supposed to be -20dB down before 20ms. You have at least 3 reflections that are much higher than that.

That one at 5ms is really much much too high.

Last edited by artur9; 02-08-2015 at 08:15 AM. Reason: beaten by jim yet again!
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post #13502 of 14645 Old 02-08-2015, 08:32 AM
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Quote:
Originally Posted by artur9 View Post
Remember (as per the guide) that reflections are supposed to be -20dB down before 20ms. You have at least 3 reflections that are much higher than that.

That one at 5ms is really much much too high.
Oh. I thought it was as long as it is -20 before 20ms it's ok. I didn't realize it shouldn't be over -20 at all.

I'm wondering what that reflection can be. Since my ceiling is infinished but stuffed with pink stuff. And there are no walls to speak of haha
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post #13503 of 14645 Old 02-08-2015, 08:52 AM
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Quote:
Originally Posted by Brian Fineberg View Post
Could you elaborate?
Not Jim, but the general guideline is to look at reflections that occur within the first 20ms that have not decayed to -20dB. So this would mean the rather significant reflection at 5ms is an issue, as well as the very early reflection below 1ms. I am not sure what the third issue is, but I am sure Jim will explain.

So, place the horizontal cursor at -20dB and see which reflections are above the line. How do the left and right speaker ETC's look?

Edit: Both Jim and Artur have identified the third reflection.
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post #13504 of 14645 Old 02-08-2015, 08:54 AM
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Quote:
Originally Posted by Brian Fineberg View Post
Oh. I thought it was as long as it is -20 before 20ms it's ok. I didn't realize it shouldn't be over -20 at all.

I'm wondering what that reflection can be. Since my ceiling is infinished but stuffed with pink stuff. And there are no walls to speak of haha
Use the "blocking method" to determine which direction the reflections are coming from. Once you know the direction, it should become easier to identify the actual reflecting surface.
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post #13505 of 14645 Old 02-08-2015, 08:56 AM
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Quote:
Originally Posted by AustinJerry View Post
Use the "blocking method" to determine which direction the reflections are coming from. Once you know the direction, it should become easier to identify the actual reflecting surface.
Is the blocking method in the guide?

Last edited by Brian Fineberg; 02-08-2015 at 09:01 AM.
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post #13506 of 14645 Old 02-08-2015, 08:57 AM
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Quote:
Originally Posted by Brian Fineberg View Post
Is the blocking method in the guide?
I think so. If not, I have a diagram illustrating it.
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post #13507 of 14645 Old 02-08-2015, 09:03 AM
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Quote:
Originally Posted by AustinJerry View Post
I think so. If not, I have a diagram illustrating it.
Could you pm it to me? Very appreciative!

On that note again I'm not too too concerned about these reflections as the theater will be built soon. This is alll in an a finished area. For a temp setup. But would like the best sound I can get. And it sounds pretty darn good right now. Good to know it can get better.

The clap test is pretty good as well
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post #13508 of 14645 Old 02-08-2015, 09:15 AM
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post #13509 of 14645 Old 02-08-2015, 09:38 AM
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Awesome thanks!
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post #13510 of 14645 Old 02-08-2015, 05:46 PM - Thread Starter
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Quote:
Originally Posted by mtbdudex View Post
^^^ From post#2
Jason - can you correct the typo above?
It reads "not more than 450hz for modal frequencies", should read "not more than 450ms for modal frequencies, those frequencies below Fs "
Hi Mike,

Thanks for the heads up.

I've updated the post and fixed some formatting errors as well.

Sorry for the delay,

--Jason

Thanks to EVERYONE that Helps Make These Threads so Awesome!

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post #13511 of 14645 Old 02-09-2015, 07:54 AM
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New REW user with problematic room

Hi all,
I am finally getting ready to tackle the sound issue in our small dedicated home theater. The room is rectangular, with the framed projector screen on the narrow wall (only possible way to fit the necessary seating).


After watching the Home Theater Geeks podcast episode 177 and 178 we decided to try and do something to our room. I spent the week end experimenting with makeshift foam absorbers and speaker placement and found a placement which works for Music and sounds really great. It is however, not possible to use that placement for Movies since the speakers end up four feet in front of the screen.


I reset the room (i.e original speaker placement and no absorbers), bought a UMIK-1 from minidsp and followed the excellent guide. I made a number of measurements and it looks like my room is really awful compared to the examples.


Since the room is narrow (2,78 meters, approx 112") and "longish" (4,75 meters, 16 feet) and we have a wall to wall screen. The speakers ends up Close to the side walls. I Think this causes some of the very many reflections seen in the attached ETC graphs.


We are considering replacing the screen fabric with AT fabric from Dream Screens. But if we can make do with what we have by tweaking placement and applying treatments this is of interest.


Where do I go from here? My first instinct was to recreate the placement I employed this weekend and measure the response in that setting. But that is changing quite a few parameters I thought it would be good to ask first.


Our AVR is an Onkyo TX-NR636 which we use in an 5.1.2 setup for Atmos.
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post #13512 of 14645 Old 02-09-2015, 08:23 AM
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Yes, I see a few reflections in your ETC measurements.

If reducing the unwanted reflections is your objective, then I don't think re-arranging your speaker placement is the correct approach. You need to go through a lengthy exercise to identify and remove the reflections one-by-one. First, you will need wall treatments that are effective in removing the reflections. Foam absorbers are not necessarily the most effective treatments. I suggest visiting several of the web sites that specialize in acoustic treatments (GIK Acoustics, ATS Acoustics, Realtraps) to familiarize yourself with their products. Both the GIK and the Realtraps web sites have some very good articles that would be worthwhile reading as well. Perhaps one of the companies has a representative in your country where you can purchase their products.

Once you have one or more effective treatment panels, place them temporarily in the likely spots causing reflections (i.e. the first reflection points), re-measure using REW, and observe whether the treatment has been effective in reducing one or more reflections. Don't forget the back wall and the ceiling--both are sources of reflections as well as side walls.

And keep in mind that reducing reflections is a lengthy process, but the rewards in the form of improved audio quality makes is very worthwhile.
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post #13513 of 14645 Old 02-09-2015, 10:02 AM
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Quote:
Originally Posted by Saril View Post
If I perform a manual calibration, per Jerry's guide, and both the UMIK-1 and SPL meter agree at 80db, shouldn't they also agree at the noise floor? What I'm seeing is the REW SPL meter showing around 42 dbc and the SPL meter showing close to 50 dbc. Same situation if I just use the sensitivity constant.

REW has current update. I'm wondering if my CSLabs microphone is defective. Thanks for any help.
Anybody? Am I wrong in expecting a CSL UMIK-1 and handheld SPL (Mastech MS6700) that agree at 80 dBc to also agree at 50 dBc???
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post #13514 of 14645 Old 02-09-2015, 03:28 PM
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Quote:
Originally Posted by jjazdk View Post
Look at the level Jerry, the mic should not have self noise in the order of 57dB SPL spikes!



The spikes and noise floor will of course scale with the sense factor, that should be obvious.

But, your spikes are very high in level, there is definitely something wrong.

Attached is the spectrum from my fairly noisy livingroom (big aquarium pump + a noisy HTPC). Look at my spikes at 1kHz and above, their level is a LOT lower than yours. My mic is from the Dayton OmniMic V2 kit, and I have checked that the calibration is correct.

Well, here's another RTA done using an external test tone to calibrate the mic level (instead of sens factor) that I think corresponds to the noise floor typical for USB mics:


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Last edited by jkasanic; 02-10-2015 at 08:46 AM.
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post #13515 of 14645 Old 02-09-2015, 03:37 PM
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post #13516 of 14645 Old 02-09-2015, 07:49 PM
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Quote:
Originally Posted by AustinJerry View Post
Attachment not visible.
Sorry, will repost in the am.
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post #13517 of 14645 Old 02-09-2015, 11:02 PM
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No, they will not agree at the noise floor, unless they have the same inherent self noise, which is not likely.


Quote:
Originally Posted by Saril View Post
Quote:
Originally Posted by Saril View Post
If I perform a manual calibration, per Jerry's guide, and both the UMIK-1 and SPL meter agree at 80db, shouldn't they also agree at the noise floor? What I'm seeing is the REW SPL meter showing around 42 dbc and the SPL meter showing close to 50 dbc. Same situation if I just use the sensitivity constant.

REW has current update. I'm wondering if my CSLabs microphone is defective. Thanks for any help.
Anybody? Am I wrong in expecting a CSL UMIK-1 and handheld SPL (Mastech MS6700) that agree at 80 dBc to also agree at 50 dBc???
Saril likes this.
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post #13518 of 14645 Old 02-10-2015, 06:26 AM
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I have performed some more testing (first was here Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs).


Is this the improvement I Think it is? I have tried the blocking method, but I Think my absorptive material isn't quite up to the task. I can't find that first big spike which is less than 2 ft.


Also am I Reading the waterfall diagram correctly is that I have no alarming problems with my bass response in MLP (for an largely untreated room)?
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post #13519 of 14645 Old 02-10-2015, 06:33 AM
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There are still quite a few undesirable reflections before 20ms. For the improvements you were able to accomplish, can you hear the difference?

Can you post an un-smoothed frequency response graph for the low frequencies, 15-300Hz, please?
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post #13520 of 14645 Old 02-10-2015, 08:46 AM
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Quote:
Originally Posted by AustinJerry View Post
Attachment not visible.

I updated my previous post
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post #13521 of 14645 Old 02-10-2015, 09:27 AM
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Quote:
Originally Posted by jjazdk View Post
No, they will not agree at the noise floor, unless they have the same inherent self noise, which is not likely.
Thanks for your comment - makes sense. I will do more testing with test tones and determine where I go from there, e.g., 1K Hz at 75 dBc, 1K Hz at 60 dBc, 40 Hz at 60 dBc, handheld SPL vs. UMIK-1,etc.
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post #13522 of 14645 Old 02-10-2015, 12:27 PM
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Quote:
Originally Posted by jkasanic View Post
Well, here's another RTA done using an external test tone to calibrate the mic level (instead of sens factor) that I think corresponds to the noise floor typical for USB mics
Here is one from the UMIK on my desk, the 120 Hz spike is from the fan on my PC. Overall level 49 dB.

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post #13523 of 14645 Old 02-10-2015, 12:41 PM
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Originally Posted by JohnPM View Post
Here is one from the UMIK on my desk, the 120 Hz spike is from the fan on my PC. Overall level 49 dB.

Attachment 538041
There seems to be a noticeable difference between the UMIK-1 and the UMM-6. Here's a link to an RTA that Jerry posted of his UMM-6 when we first noticed this issue:


Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs

Several posts before this one you can see posts from Alan P and myself with subwoofer only measurements. Mine do appear to be about 10dB higher than his but I guess the ultimate question is how is this impacting my measurements if at all?
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post #13524 of 14645 Old 02-10-2015, 05:59 PM
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Quote:
Originally Posted by fredl View Post
Also am I Reading the waterfall diagram correctly is that I have no alarming problems with my bass response in MLP (for an largely untreated room)?
The decay seems nice but it is very uneven. Can you move your subs around (you have 2?) to try and even it out?

Also, you may not have been playing it loud enough. You want it 40dB over the nice floor (usually 40-50) and your measurements look to be around 75dB on average.
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post #13525 of 14645 Old 02-15-2015, 02:28 PM
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So I intended to put my subwoofer in MLP today and move the mic, but it actually was easy enough to move the 100 lb HSU sub. I have 6 possible positions around the front stage, since I do not want to sacrifice rear space with a primary sub (it is a kids play and yoga area). Let me know if there is anything I need to change with my graphs.

Theater layout and subwoofer positions
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Position A (Right 23 in from front)
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Between A and B (Right 40 in from front)
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Position B (Right 65 in from front)
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Position C (Left 11 in from front)
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Between C and D (Left 25 in from front)
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Position D (Left 38 in from front)
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Position E (Left of center speaker)
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Position F (Right of center speaker)
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So, some issues I ran into:
- Both Left and Right of center are right in front of a projector screen and had some recurrent dips, even after correcting subwoofer level (concrete floor is not completely level). I have no idea what this was, but I could hear some type of 'resonance' during the measurements
- While moving the sub to F-Right of Center, the volume turned up by 10% (9 o'clock to 10 o'clock) and not recognized until after moving the sub.

Questions:
1. Am I correct in assuming that my best sub positions for MLP is Between C-D (left front), followed by between A-B?
2. My original listening position position is A. In theory, would bass traps be able to remove some of the peak at 40 Hz?
3. Are my curves from A-B and C-D good, or would I need to do anything else with the sound? I know that waterfalls would likely help, but I wanted to get the placement first.

Any advice is greatly appreciated.
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post #13526 of 14645 Old 02-15-2015, 03:02 PM
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Quote:
Originally Posted by markus767 View Post
Just in case any of you is interested in using REW and PEQ for room correction, here's a short tutorial:
https://mehlau.net/audio/room-correction-peq/
I did both (sweep and RTA) just for fun. Kept the mic in one position (mine ) and, as expected, the suggested filters were quite similar:

RTA:

Filter 1: ON PK Fc 38.7 Hz Gain -11.2 dB Q 4.43
Filter 2: ON PK Fc 60.8 Hz Gain -7.7 dB Q 8.96
Filter 3: ON PK Fc 65.8 Hz Gain -8.1 dB Q 14.91
Filter 4: ON PK Fc 96.0 Hz Gain -2.8 dB Q 30.88
Filter 5: ON PK Fc 126 Hz Gain -6.3 dB Q 13.64
Filter 6: ON PK Fc 139 Hz Gain -5.0 dB Q 8.83
Filter 7: ON PK Fc 157 Hz Gain -3.4 dB Q 8.37

Sweep:

Filter 1: ON PK Fc 38.6 Hz Gain -10.9 dB Q 4.78
Filter 2: ON PK Fc 60.7 Hz Gain -7.9 dB Q 8.88
Filter 3: ON PK Fc 65.9 Hz Gain -8.4 dB Q 15.72
Filter 4: ON PK Fc 95.5 Hz Gain -2.9 dB Q 42.26
Filter 5: ON PK Fc 126 Hz Gain -6.8 dB Q 14.91
Filter 6: ON PK Fc 138 Hz Gain -4.9 dB Q 9.37
Filter 7: ON PK Fc 158 Hz Gain -3.4 dB Q 8.89

I think the pink noise is slightly less annoying, but that may just be because I've done a lot of sweeps.
The disadvantage is that you can't use the RTA reading for waterfalls or anything else.

Michael

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post #13527 of 14645 Old 02-15-2015, 04:33 PM
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Quote:
Originally Posted by Spazdoc View Post
So I intended to put my subwoofer in MLP today and move the mic, but it actually was easy enough to move the 100 lb HSU sub. I have 6 possible positions around the front stage, since I do not want to sacrifice rear space with a primary sub (it is a kids play and yoga area). Let me know if there is anything I need to change with my graphs.


Any advice is greatly appreciated.
TBH, I don't see any of the positions resulting in what I would call smooth bass. Have you considered adding additional subs? This is typical of what you should be aiming for:

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post #13528 of 14645 Old 02-15-2015, 06:31 PM
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Quote:
Originally Posted by AustinJerry View Post
TBH, I don't see any of the positions resulting in what I would call smooth bass. Have you considered adding additional subs? This is typical of what you should be aiming for:




That's what I'm talking bout!


Sent using Tapatalk since the mobile version is still
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post #13529 of 14645 Old 02-15-2015, 09:28 PM
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Quote:
Originally Posted by AustinJerry View Post
TBH, I don't see any of the positions resulting in what I would call smooth bass. Have you considered adding additional subs? This is typical of what you should be aiming for:

That is quite an impressive curve with 4 subs. Was this after Audyssey?

I am currently trying to optimize my single-sub setup, with a plan for a second VTF-15H eventually. These are obviously pre-Audyssey and acoustic treatment.
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post #13530 of 14645 Old 02-16-2015, 02:41 AM
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Quote:
Originally Posted by LastButNotLeast View Post
I did both (sweep and RTA) just for fun. Kept the mic in one position (mine ) and, as expected, the suggested filters were quite similar:

RTA:

Filter 1: ON PK Fc 38.7 Hz Gain -11.2 dB Q 4.43
Filter 2: ON PK Fc 60.8 Hz Gain -7.7 dB Q 8.96
Filter 3: ON PK Fc 65.8 Hz Gain -8.1 dB Q 14.91
Filter 4: ON PK Fc 96.0 Hz Gain -2.8 dB Q 30.88
Filter 5: ON PK Fc 126 Hz Gain -6.3 dB Q 13.64
Filter 6: ON PK Fc 139 Hz Gain -5.0 dB Q 8.83
Filter 7: ON PK Fc 157 Hz Gain -3.4 dB Q 8.37

Sweep:

Filter 1: ON PK Fc 38.6 Hz Gain -10.9 dB Q 4.78
Filter 2: ON PK Fc 60.7 Hz Gain -7.9 dB Q 8.88
Filter 3: ON PK Fc 65.9 Hz Gain -8.4 dB Q 15.72
Filter 4: ON PK Fc 95.5 Hz Gain -2.9 dB Q 42.26
Filter 5: ON PK Fc 126 Hz Gain -6.8 dB Q 14.91
Filter 6: ON PK Fc 138 Hz Gain -4.9 dB Q 9.37
Filter 7: ON PK Fc 158 Hz Gain -3.4 dB Q 8.89

I think the pink noise is slightly less annoying, but that may just be because I've done a lot of sweeps.
The disadvantage is that you can't use the RTA reading for waterfalls or anything else.

Michael
Yes, if you leave the mic in one position the results will be virtually identical but the important part of the method described in the link above is that the mic is moved through the listening area. That's the beef

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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