Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 376 - AVS Forum
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Audio Theory, Setup, and Chat > Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs
3ll3d00d's Avatar 3ll3d00d 04:57 PM 08-27-2014
Quote:
Originally Posted by HDgaming42 View Post
But where does it lie?

The only thing that agrees with my AVR is this RTA method, which makes no sense as it is using the same tone generator in REW that doesn't agree with my AVR...
A possible answer, based on your earlier frequency response, is the variation in levels across the range. You have 10dB from 45 to 30Hz for example. Perhaps you should eq first and then revisit to avoid chasing ghosts.

HDgaming42's Avatar HDgaming42 05:27 PM 08-27-2014
Quote:
Originally Posted by 3ll3d00d View Post
A possible answer, based on your earlier frequency response, is the variation in levels across the range. You have 10dB from 45 to 30Hz for example. Perhaps you should eq first and then revisit to avoid chasing ghosts.
An astute observation. Thank you for taking the time to go back and peruse the mountain of data I've collected to offer this explanation.

Judging by how a non-averaged RTA was entirely unworkable, I suspect, like you're suggesting, the disparities I have in the bottom end are what is responsible for the variation I see between calibration methods.

I will stick with the AVR settings for now and continue down the (long twisting) path toward home theater nirvana.

As for the Mackie monitors, if I never intend on running them at reference levels (the room is a shoe box, and that would likely deafen or kill the occupants) could I get away with simply leaving them at "normal"? From the numbers you (re)provided, this seems reasonable to me...
Bluescale's Avatar Bluescale 05:54 PM 08-27-2014
I have a question about room treatments. As I mentioned previously, I didn't get around to canceling my order for the mineral wool boards. I have a case of 6 Roxul Rockboard 80, and another case of 6 Roxul Rockboard 60 on their way now. The 80 is 8 lb/ft3 (equivalent to OC 705), and the 60 is 6 lb/ft3 (equivalent to OC 730). I was planning to create two 6" thick bass traps using the Rockboard 80. Do you guys have a recommendation of what I should do with the 60? Should I build 2 less dense bass traps, or should I build some broadband absorbers? If I go for broadband absorbers, should I go for six 2" thick or three 4" thick panels.

Also, the back wall near where the sub is set up rattles quite a bit when things dig really deep (think the skadoosh scene in Kung-Fu Panda). Will placing an absorber back there help with the rattling?
HDgaming42's Avatar HDgaming42 08:11 PM 08-27-2014
Quote:
Originally Posted by 3ll3d00d View Post
FWIW there's some good info on what the levels really should be in this thread - http://yabb.jriver.com/interact/inde...topic=77124.20 - and why narrow band pink noise is a bit of a fudge to allow for deficiencies in the measurement chain. In particular note the comments from bobkatz (aka http://www.digido.com)
Slowly making my way through this thread. What an excellent resource! I can see why Markus advocates the RTA method:

Quote:
Im with Bob on the sub/LFE setup. I never ever trust pinknoise and RMS meters for the sub and LFE (even narrow band LFE noise) which is why I use sweeps, and individual tones from 20hz to 200hz with FFT analysis to check for funky cross over problems and room modes before i even think about level matching. Almost all common household rooms will have problem room mode frequencies in the 30-100hz range (standing waves and nulls) which makes RMS pink noise useless because your going to have upto 10db room mode peaks and 10db holes between 20-300hz or so. The meter wont be able to distinguish a room mode peak or a null or a crossover problem. Only careful measurement with proper instruments can properly set LFE/sub crossover and levels if you want the most accurate result.
I believe this addresses my situation exactly. Thanks 3ll3d00d!
Audionut11's Avatar Audionut11 08:57 PM 08-27-2014
Quote:
As for the Mackie monitors, if I never intend on running them at reference levels (the room is a shoe box, and that would likely deafen or kill the occupants).
Reference level is reference level. Headphones, shoebox, stadium, doesn't matter. The only difference is the power requirements required to produce that level.
markus767's Avatar markus767 12:05 AM 08-28-2014
Quote:
Originally Posted by Audionut11 View Post
Reference level is reference level. Headphones, shoebox, stadium, doesn't matter. The only difference is the power requirements required to produce that level.
Unfortunately the perceived loudness of "reference level" is different in different sized rooms. The premise that the steady state response would directly translate to perceived loudness is flawed.
markus767's Avatar markus767 12:13 AM 08-28-2014
Quote:
Originally Posted by HDgaming42 View Post
Does this look (attached) correct? I was able to match up 60Hz, but 30Hz is out of wack...
You just have found out that the room distorts the magnitude response of a speaker by a great deal. Run Audyssey and you'll notice that the response will be much smoother afterwards.
markus767's Avatar markus767 12:19 AM 08-28-2014
Quote:
Originally Posted by HDgaming42 View Post
If the RTA method is bulletproof then great, I guess we're done. I just don't understand why both test tone CDs (two sets of pink noise) and REW both want my sub lower than the AVR and the RTA method...
They average the response of different frequency ranges. Your response is VERY uneven at low frequencies.

If the RTA method shows large deviations between the bands like in your room then you need to optimize speaker setup and room acoustics.
markus767's Avatar markus767 12:29 AM 08-28-2014
Quote:
Originally Posted by Bluescale View Post
I have a question about room treatments. As I mentioned previously, I didn't get around to canceling my order for the mineral wool boards. I have a case of 6 Roxul Rockboard 80, and another case of 6 Roxul Rockboard 60 on their way now. The 80 is 8 lb/ft3 (equivalent to OC 705), and the 60 is 6 lb/ft3 (equivalent to OC 730). I was planning to create two 6" thick bass traps using the Rockboard 80. Do you guys have a recommendation of what I should do with the 60? Should I build 2 less dense bass traps, or should I build some broadband absorbers? If I go for broadband absorbers, should I go for six 2" thick or three 4" thick panels.
Make them as thick and broadband as possible. Reducing low frequency energy from the room will improve the perceived sound quality more than killing first reflections like many recommend. It's harder to do than higher frequency absorption and it's even harder to measure but it reduces deterimental effect caused by upward masking. You'll hear more detail in higer frequencies.

Quote:
Originally Posted by Bluescale View Post
Also, the back wall near where the sub is set up rattles quite a bit when things dig really deep (think the skadoosh scene in Kung-Fu Panda). Will placing an absorber back there help with the rattling?
Probably not. You'll have to find what is rattling and dampen it.
Bluescale's Avatar Bluescale 01:09 AM 08-28-2014
Quote:
Originally Posted by markus767 View Post
Make them as thick and broadband as possible.
For the Rockboard 60, Are two 6" panels better than three 4" panels, even through they cover less surface area in the room?
markus767's Avatar markus767 01:12 AM 08-28-2014
^
What's the flow resistivity of Rockboard 60?
3ll3d00d's Avatar 3ll3d00d 03:25 AM 08-28-2014
Quote:
Originally Posted by HDgaming42 View Post
As for the Mackie monitors, if I never intend on running them at reference levels (the room is a shoe box, and that would likely deafen or kill the occupants) could I get away with simply leaving them at "normal"? From the numbers you (re)provided, this seems reasonable to me...
generally speaking audyssey will get you pretty close, doing this yourself is more about fine tuning (like setting levels yourself using an RTA) and/or problem resolution (e.g. in case you have noise floor issues).
Bluescale's Avatar Bluescale 08:25 AM 08-28-2014
Quote:
Originally Posted by markus767 View Post
^
What's the flow resistivity of Rockboard 60?
I couldn't find that data. I found absorption co-efficiencies at various frequencies:

Acoustical Performance:
ASTM C 423
CO-EFFICIENTS AT FREQUENCIES
Thickness 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz NRC
1.0” 0.08 0.33 0.78 1.03 1.02 1.04 0.80
1.5” 0.17 0.62 1.00 1.05 1.01 1.01 0.90
2.0” 0.32 0.81 1.06 1.02 0.99 1.04 0.95
3.0” 0.78 0.89 1.04 0.98 1.01 1.02 1.00

The package I'm getting contains six 2" boards.
markus767's Avatar markus767 09:13 AM 08-28-2014
^
Without flow resistivity values not much can be said. Try straddling the wall corners with it for a first test.
RUR's Avatar RUR 09:38 AM 08-28-2014
The most useful source for GFR I know of is this thread @ Gearslutz. It's spotty, at best, but FWIW Rockboard 40 shows as 5.2 x 10^4 (post #22). If RW3 60 and RW4 80 = Rockboard (this site shows as Rockwool Slab), GFR for each is shown in post #49.

Wish there were a more concise and known-accurate source for GFR, but I know of none - for Rockwool at least.
Bluescale's Avatar Bluescale 10:22 AM 08-28-2014
Thanks, RUR. I stumbled across that same thread earlier this morning trying to find an answer to Markus' question. I'm not comfortable using the Rockboard information because, as Andre points out, manufacturer to manufacturer, and even region to region differences can be significant.

I've sent an email off to Roxul asking for the airflow resistance and resistivity. Let's see if they get back to me with anything useful, and in a timely manner. If not, I'll do what Markus suggested - stick it in the corner, and measure.
artur9's Avatar artur9 11:58 AM 08-28-2014
Quote:
Originally Posted by Bluescale View Post
stick it in the corner, and measure.
A room has more corners than you think. There are the wall-wall corners, wall-floor corners and wall-ceiling corners.

You may want to experiment with wall-wall vs wall-floor corners. The best corners for traps are the ones where wall+floor+ceiling come together. Hence the tri-corner trap that one can buy.
Bluescale's Avatar Bluescale 12:38 PM 08-28-2014
Alas...

Quote:
Good day,

Thanks for the inquiry into ROXUL.

We have not done airflow resistivity testing on ROCKBOARD 60 or ROCKBOARD 80. We have tested the product’s acoustical performance to ASTM C423. This is a test for noise reduction coefficient. The information can be found on the attached technical data sheets.

My apologies that we cannot provide any airflow resistance data for you. That being said, ROCKBOARD 60 and 80 are often used successfully in acoustical panel applications.

Please let me know if you have any other questions.
http://www.roxul.com/files/RX-NA_EN/...OCKBOARD60.pdf
http://www.roxul.com/files/RX-NA_EN/...OCKBOARD80.pdf
Bluescale's Avatar Bluescale 12:43 PM 08-28-2014
Quote:
Originally Posted by artur9 View Post
A room has more corners than you think. There are the wall-wall corners, wall-floor corners and wall-ceiling corners.

You may want to experiment with wall-wall vs wall-floor corners. The best corners for traps are the ones where wall+floor+ceiling come together. Hence the tri-corner trap that one can buy.
Don't I know it!

And my room has more corners than most, because of the odd nooks and crannies and angles (I can think of 13 places where three boundaries meet). My theory is that one of the reasons I have less reflection issues than I would expect is because the room is so non-symmetrical, it's operating as a bit of a diffusor.
AustinJerry's Avatar AustinJerry 12:58 PM 08-28-2014
A way to pick the most effective place for bass trap placement is to play a bass frequency test tone and walk around the room with an SPL. Those corners showing the highest readings are the best spots for the traps.
Bluescale's Avatar Bluescale 03:43 PM 08-28-2014
Quote:
Originally Posted by AustinJerry View Post
A way to pick the most effective place for bass trap placement is to play a bass frequency test tone and walk around the room with an SPL. Those corners showing the highest readings are the best spots for the traps.
Is there a preferably tone to play, or is it a good idea to play a sweep (say 10-200 hz), and see which corner has the most overall energy?
jim19611961's Avatar jim19611961 05:14 PM 08-28-2014
Quote:
Originally Posted by AustinJerry View Post
Thanks, Jim. I got too tied up to create one myself. Better from you anyway.
John replied at HTS.

Might take a look since you are having the same symptoms as I am. You might want to participate as well to help John see the problem.
AustinJerry's Avatar AustinJerry 06:15 PM 08-28-2014
I'll try and run some tests tomorrow. Testing for understanding, you want me to take several consecutive measurements, being careful to not alter anything, and simply varying sweep length from 128 to 1M?
jim19611961's Avatar jim19611961 06:31 PM 08-28-2014
Quote:
Originally Posted by AustinJerry View Post
I'll try and run some tests tomorrow. Testing for understanding, you want me to take several consecutive measurements, being careful to not alter anything, and simply varying sweep length from 128 to 1M?
Yep. And save the data.

Edit: Then go to the HTS thread and look at your IR in the fashion John presented them. See if you IR's match up like John's, or are all over the place like mine.
markus767's Avatar markus767 09:37 AM 08-29-2014
Jim,

Just did a quick test and my IRs look exactly the same regardless of test signal length. I've tested this with an external USB interface and with the built in speakers/mic of my laptop.
jim19611961's Avatar jim19611961 10:10 AM 08-29-2014
Quote:
Originally Posted by markus767 View Post
Jim,

Just did a quick test and my IRs look exactly the same regardless of test signal length. I've tested this with an external USB interface and with the built in speakers/mic of my laptop.
Thanks. Additional input is always welcome for problem solving. But I am really at a loss to what is wrong.

I wonder if it could be my USB path?

Computer -> 15ft usb cable -> Usb Hub

From the Usb Hub one output goes to my DAC on my stereo system via another 15ft Usb cable, a second output on the Usb Hub goes to my Usb mic via another 10ft Usb cable.

It is done this way because my measuring computer is a desktop in the next room about 20feet away.

Does that sound problematic?
Saril's Avatar Saril 10:22 AM 08-29-2014
Quote:
Originally Posted by Alan P View Post


Takes me about 15 minutes at most. That being said, I've had good results from just a 3 point calibration (1 - MLP / 2 - 3" left of MLP / 3 - 3" right of MLP)...takes about 5 minutes.

With all the time you've wasted trying to set your levels manually with REW you probably could have run full 8-point Audyssey a dozen times!

And, yes, I trust the levels set by Audyssey....and have verified them many, many times with an analog SPL meter and REWs SPL meter. I've ran Audyssey so many times in the last year, I've lost count.

The only thing I do is bump up the sub trim from where Audyssey sets them....my preference is hotter than most though at +8db.
Alan (or anyone) - have you ever measured a noise floor lower than 50 dB C/Slow using the UMIK-1 and REW? I am reading around 40 - 43 dB C/Slow with my UMIK-1 and SPL reads about 10 dB higher. Thanks for any insight with this.
markus767's Avatar markus767 10:26 AM 08-29-2014
Quote:
Originally Posted by jim19611961 View Post
Thanks. Additional input is always welcome for problem solving. But I am really at a loss to what is wrong.

I wonder if it is my USB path?

Computer -> 15ft usb cable -> Usb Hub

From the Usb Hub one output goes to my DAC on my stereo system via another 15ft Usb cable, a second output on the Usb Hub goes to my Usb mic via another 10ft Usb cable.

It is done this way because my measuring computer is a desktop in the next room about 20feet away.

Does that sound problematic?
John is probably right - he usually is I would look at the signal path in detail. Remove as many variables as possible. Can you do computer USB out > DAC > computer analog in?
jim19611961's Avatar jim19611961 10:31 AM 08-29-2014
Quote:
Originally Posted by markus767 View Post
John is probably right - he usually is I would look at the signal path in detail. Remove as many variables as possible. Can you do computer USB out > DAC > computer analog in?
I agree John knows what he is doing. I am not questioning his expertise.

It would be difficult to do the path suggested. What would it accomplish if I could?
jim19611961's Avatar jim19611961 10:45 AM 08-29-2014
I tried making two separate paths:

Computer Usb1 -> DAC
Computer Usb2 -> Hub -> Mic

Same results
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