Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 592 - AVS Forum | Home Theater Discussions And Reviews
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post #17731 of 19247 Old 02-20-2016, 04:03 PM
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Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measuremen...

I read the guide and that answered a few of my questions (1&2) but not 3 & 4. Is there some sort of measurement that is ideal? Also, would a mini dsp fix my "problem" areas? Assuming that is the whole point to this measuring then what unit is recommended? Being new to this I am just trying to figure it out. This is a whole new arena that I didn't know existed!

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post #17732 of 19247 Old 02-20-2016, 07:54 PM
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Quote:
Originally Posted by Claybe View Post
Also, would a mini dsp fix my "problem" areas? Assuming that is the whole point to this measuring then what unit is recommended?
You want to fix your room acoustically as much as possible before considering any type of unit.

This means
  1. positioning sub woofers optimally
  2. placing absorption in the right places to minimize reflections
  3. adding bass traps to reduce low frequency ringing (aka bass overhang)

REW can help you do all of that without having to buy additional electronics.
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post #17733 of 19247 Old 02-20-2016, 07:56 PM
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Quote:
Originally Posted by Claybe View Post
4. What is a "good" measurement supposed to look like?
If you flip through this thread you'll see plenty of good (and bad!) measurements. Frankly, I am amazed at what some people have achieved but they have been at this for quite some time.
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post #17734 of 19247 Old 02-20-2016, 08:02 PM
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Well I am in a temporary space for my theater as my basement flooded and I am waiting to see about fixing it. So I will wait until I have my final theater to implement any room treatments.
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post #17735 of 19247 Old 02-20-2016, 09:06 PM
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Quote:
Originally Posted by Claybe View Post
Well I am in a temporary space for my theater as my basement flooded and I am waiting to see about fixing it. So I will wait until I have my final theater to implement any room treatments.
You asked what a "good measurement" looks like. Of course there is no one answer. But here are some characteristics that you might find in a good-sounding room:

- A reasonably-flat response curve from 20Hz up to 15-20Khz. By reasonably-flat, I mean variations no more than +/- 5dB.
- A general downward slope from left to right, with the left side of the response curve (low end) 5-10dB higher than the far right side (high frequencies).
- Bass resonance under control as per the guidelines contained in the REW guide.
- Room reflections under control, also as per the guide.

Looking at the response curve you posted, several significant issues stand out:

- A steep roll-off below 40Hz
- Severe choppiness in the 80-200Hz range (a 30dB drop)
- A significant roll-off in the high end starting at 7Khz.

What to do to fix response issues?

- Do nothing until you are in your permanent room.
- Explore various speaker locations to smooth out the frequency response.
- Check the response of the sub and the main speakers to understand whether the low and high frequency roll-offs are because of speaker design, or room conditions.
- Consider an AVR with automated room correction.
- Consider carefully selected and placed room treatments.
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post #17736 of 19247 Old 02-21-2016, 07:29 AM
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Thank you AustinJerry! That is an extremely helpful post! I am in the market for a new AVR. Can you recommend some with room correction?
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post #17737 of 19247 Old 02-21-2016, 07:36 AM
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Quote:
Originally Posted by Claybe View Post
Thank you AustinJerry! That is an extremely helpful post! I am in the market for a new AVR. Can you recommend some with room correction?
Onkyo AVR's come with a proprietary room correction that is not well-regarded, IMO. Denon and Marantz AVR's come with Audyssey room correction, which produces very good results. There are several flavors of Audyssey, "MultEQ XT32" being the best. And then there is Emotiva's XMC-1, which features Dirac Live room correction, which is also an excellent room correction technology. There are other products as well, but purchase costs start to escalate.
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post #17738 of 19247 Old 02-21-2016, 07:49 AM
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Thanks again! I have an Elite Pioneer AVR and used the advanced Correction but I guess it didn't do its job! I have been looking at the marantz AVR and the minidsp products as well. Most helpful!
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post #17739 of 19247 Old 02-21-2016, 07:57 AM
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Also, can you explain what "a steep roll-off below 40hz" means and what can be done about it? I have 2 18s and feel like this shouldn't be a problem, but then again I don't know what it exactly means either!
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post #17740 of 19247 Old 02-21-2016, 08:37 AM
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Quote:
Originally Posted by Claybe View Post
Also, can you explain what "a steep roll-off below 40hz" means and what can be done about it? I have 2 18s and feel like this shouldn't be a problem, but then again I don't know what it exactly means either!
If you look at your response curve, the level at 40Hz is 100dB. At 30Hz, the output drops to 83dB, and at 15Hz, output is at 75dB. This is a loss of 25dB in a range that should be relatively flay, especially if you two 18in subs. The response should look more like this:



Either the correction on the Pioneer is doing something strange, or the subs are not positioned for best response. Experiment to see if the low end can be improved--moving the subs around is likely going to produce the most change.
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post #17741 of 19247 Old 02-21-2016, 10:50 AM
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Hey guys, I've been a busy man, here are couple of measurements. Its a 10 inch sub with 2 passive 8 inch radiators. Its rated 500W RMS but it seems it loves to rattle at low frequencies.
Frequency response graphs show measurements from four different positions in the room (unsmoothed). No EQ of any sort. There is also waterfall for each of those.
So, question is which position to choose? The one with flattest frequency response? Or one with the least messy waterfall?
And about waterfall graphs...there are two issues, one is up to about 27 Hz and other is around 35 to 45 Hz. And they show up on all graphs though with different strengths. What are those? Room modes or things that rattle? Because things in my room rattle. Subwoofer too. Planning to get a real one but for now I experiment with this one. So I wonder if those two issues can be treated?

Thank you.
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post #17742 of 19247 Old 02-21-2016, 11:23 AM
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Looks good, I think you are headed in the right direction and obviously have seen an improvement in getting to where you are for sure.

I'm a perfectionist, but why not add some owens corning 703 4" panels wrapped in fabric to help with the ringing around 200Hz? I'd do this to the side walls and entire ceiling and try to have a reflection free zone around the mlp using OC 703 4" (or glue pieces together for thicker layers).

I'd also add as many bass traps as possible using the same 4" panels glued together in 8" pieces. I have one that is 16"x8'x4' and it made a huge difference in fixing some ringing. Only took a few hours to wrap and glue pieces to fabric and assemble the trap in four parts (each part is 8"x24"x48").

Quote:
Originally Posted by Tyrindor View Post
Thanks, I'm new to this whole REW thing and I've been trying my best to learn how to get the most out of my system. Spent about 20 grand overall on audio so I feel like I should learn how to properly calibrate it. I re-ran audyssey with some tweaks, I used PEQ/Phase control on the subs afterwards to reduce peaks and nulls. This was recommended by SVS to always reset PEQ and Phase controls before running Audyssey and then adjust them for fine tuning afterwards.

I reclined the home theater seating which allowed me to put the mic closer to where my ears actually are. Here are the results. There's a slightly bigger null at 60hz and 105hz, but overall no more than ~8dB variance across the entire 15hz to 7khz sweep and the issues above 300hz are gone. This seems pretty dang good to me, but I honestly don't know how to read any of these charts minus the first one.

Do these tell you what you need to know? Do you see any problems?

Greatly appreciated.

Premise, a FREE home automation program. Open-source Z-Wave Premise Module found here.
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post #17743 of 19247 Old 02-21-2016, 11:23 AM
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Originally Posted by donktard View Post
Hey guys, I've been a busy man, here are couple of measurements. Its a 10 inch sub with 2 passive 8 inch radiators. Its rated 500W RMS but it seems it loves to rattle at low frequencies.
Frequency response graphs show measurements from four different positions in the room (unsmoothed). No EQ of any sort. There is also waterfall for each of those.
So, question is which position to choose? The one with flattest frequency response? Or one with the least messy waterfall?
And about waterfall graphs...there are two issues, one is up to about 27 Hz and other is around 35 to 45 Hz. And they show up on all graphs though with different strengths. What are those? Room modes or things that rattle? Because things in my room rattle. Subwoofer too. Planning to get a real one but for now I experiment with this one. So I wonder if those two issues can be treated?

Thank you.
I don't think rattles are affecting the waterfalls. What you are looking at is room resonances. It's difficult to recommend the best position for two reasons, first because the graphs are hard to read (the font is too small), and second because there isn't really that much difference.

It is interesting that the sub response "dies" at 20 Hz, i.e. not much output at lower frequencies. A more typical response would go much lower, as in this measurement:

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post #17744 of 19247 Old 02-21-2016, 12:24 PM
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Originally Posted by donktard View Post
Its a 10 inch sub with 2 passive 8 inch radiators. Its rated 500W RMS but it seems it loves to rattle at low frequencies.
One of my subs rattled a bit. I found that it was the power cord which I had coiled near it to avoid accidental unplugging. I moved it a bit farther from the sub and voila! no more (well, a lot less) rattling.
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post #17745 of 19247 Old 02-21-2016, 12:29 PM
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Quote:
Originally Posted by AustinJerry View Post
I don't think rattles are affecting the waterfalls. What you are looking at is room resonances. It's difficult to recommend the best position for two reasons, first because the graphs are hard to read (the font is too small), and second because there isn't really that much difference.

It is interesting that the sub response "dies" at 20 Hz, i.e. not much output at lower frequencies. A more typical response would go much lower, as in this measurement:
Yeah I have high resolution monitor and image downscale messed things up. I won't repost it since it all looks pretty close.
Well sub isn't ported so I assume that contributes to rolloff below 20 Hz and it was a pretty poor choice to begin with. Planning to get some nice ID sub and post graphs then.
Placed it behind couch right now, because ringing is smaller then and when i place it in positions with lot more ringing I can localize it.

Can I do anything about 20 Hz issue in a typical living room? I assume bass trap for that one would have to be too huge given 1/4 wavelength of a frequency.
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post #17746 of 19247 Old 02-21-2016, 12:51 PM
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Originally Posted by artur9 View Post
One of my subs rattled a bit. I found that it was the power cord which I had coiled near it to avoid accidental unplugging. I moved it a bit farther from the sub and voila! no more (well, a lot less) rattling.
Nope, when I play sub signal for SPL calibration pretty much something inside whole construction rattles. When reproducing low frequencies also. And if i push it too hard it just gets legs and walks across the floor. Not much headroom or weight in that thing really.
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post #17747 of 19247 Old 02-21-2016, 01:27 PM
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Originally Posted by donktard View Post
Yeah I have high resolution monitor and image downscale messed things up. I won't repost it since it all looks pretty close.
Well sub isn't ported so I assume that contributes to rolloff below 20 Hz and it was a pretty poor choice to begin with. Planning to get some nice ID sub and post graphs then.
Placed it behind couch right now, because ringing is smaller then and when i place it in positions with lot more ringing I can localize it.

Can I do anything about 20 Hz issue in a typical living room? I assume bass trap for that one would have to be too huge given 1/4 wavelength of a frequency.
Trying to tame resonances below 40Hz is very difficult. However, IMO it is not that necessary. Resonances are particularly noticeable when playing music content, i.e. you don't want the upright bass to sound bloated or tubby. But music content rarely extends to 40Hz and below, so the only thing operating down there are movie sound effects. And I challenge you to hear a difference with an explosion, whether there is resonance or not. My advice would be to concentrate in the 50-300Hz range for controlling resonance, where it can make a significant difference, and where reasonably-sized room treatments can be effective.
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post #17748 of 19247 Old 02-21-2016, 01:37 PM
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I am trying to measure my subs and am getting no sound from them. Also, sometimes when I start the generator it shuts my AVR off??? I am using a HDMI connection and the cinema setting that is suggested for measuring the subs. Thoughts?
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post #17749 of 19247 Old 02-21-2016, 04:55 PM
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Quote:
Originally Posted by Claybe View Post
I am trying to measure my subs and am getting no sound from them. Also, sometimes when I start the generator it shuts my AVR off??? I am using a HDMI connection and the cinema setting that is suggested for measuring the subs. Thoughts?
To measure the subs, output the REW test signal to HDMI1 and HDMI2 at the same time, make sure your mains are set to small, and disconnect the mains signal. Or output the REW signal to HDMI4 (the LFE channel).

No idea why your AVR would shut down.
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post #17750 of 19247 Old 02-21-2016, 06:15 PM
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Quote:
Originally Posted by AustinJerry View Post
Trying to tame resonances below 40Hz is very difficult. However, IMO it is not that necessary. Resonances are particularly noticeable when playing music content, i.e. you don't want the upright bass to sound bloated or tubby. But music content rarely extends to 40Hz and below, so the only thing operating down there are movie sound effects. And I challenge you to hear a difference with an explosion, whether there is resonance or not. My advice would be to concentrate in the 50-300Hz range for controlling resonance, where it can make a significant difference, and where reasonably-sized room treatments can be effective.
Well, waterfall shows that everything between 50-300 Hz decays in less then 300 ms, although I did put some treatment to tame that area it looked good even before that.
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post #17751 of 19247 Old 02-21-2016, 06:24 PM
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Quote:
Originally Posted by AustinJerry View Post
To measure the subs, output the REW test signal to HDMI1 and HDMI2 at the same time, make sure your mains are set to small, and disconnect the mains signal. Or output the REW signal to HDMI4 (the LFE channel).



No idea why your AVR would shut down.

I don't have the option for HDMI 1 or 2. I think the laptop I am using is causing some problems. There is output via the HDMI but I don't think it is right. Should I try this with the stereo outlet?
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post #17752 of 19247 Old 02-21-2016, 06:56 PM
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Originally Posted by Claybe View Post
I don't have the option for HDMI 1 or 2. I think the laptop I am using is causing some problems. There is output via the HDMI but I don't think it is right. Should I try this with the stereo outlet?
Well, unless you describe the HDMI problems, we can't offer any advice.

You can also use REW by outputting the signal by plugging into the 3.5mm headphone jack with a cable that has two RCA connectors on the other end. This is described in the guide. Send the REW sweep to both the left and right channels, which will output to the left and right main speakers and the subs at the same time. If you want to isolate the subs, unplug the left and right speakers.
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post #17753 of 19247 Old 02-22-2016, 06:05 AM
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Quote:
Originally Posted by 3ll3d00d View Post
So, once I measure response like this I simply average the responses?
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post #17754 of 19247 Old 02-22-2016, 06:11 AM
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So, once I measure response like this I simply average the responses?
no, you sum them using trace arithmetic
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post #17755 of 19247 Old 02-22-2016, 06:55 AM
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no, you sum them using trace arithmetic
I see. Thank you.
Another question. I actually dont have adequate cables to connect all with above mentioned method, so I was thinking, instead of buying them...can i simply have sub hooked to AVR and rerun Audyssey each time I move sub to set timing/distances?
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post #17756 of 19247 Old 02-23-2016, 11:27 AM
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Sorry for the novice question, when using tone generator with RTA option for finding best sub location(s) what exactly am I looking for in the graph as I move the sub(s) around the room. Is it the same thing as if I were taking a sub only FR sweep, the smoothest flat response?

2nd question: after finding the optimal position for sub 1 using RTA, do I turn the first placed sub off and repeat the procedure for the 2nd sub or have both subs receiving a signal (on) as I try and locate the best spot for the second sub? Thanks guys and sorry for the very basic question. Thanks to Markus for posting the RTA panel and generator settings for this application.

Cheers Jeffrey
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During my sub measurements all over the room I have noticed a few things. Ringing of room modes is usually proportional to SPL, for example: 30 Hz, 90 dB SPL, ringing to 300 ms at 70 dB. Or: 30 Hz, 80dB SPL, 58 dB ringing to 300 ms. So, higher the SPL, louder the ringing at that room mode. However, at very few positions I have noticed there is actually less ringing for same SPL (e.g. 90 dB, but only 60db ring). Would anyone care to determine a cause for this behavior?
Mic was at fixed position all the time.
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post #17758 of 19247 Old 02-23-2016, 02:28 PM
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Quote:
Originally Posted by donktard View Post
During my sub measurements all over the room I have noticed a few things. Ringing of room modes is usually proportional to SPL, for example: 30 Hz, 90 dB SPL, ringing to 300 ms at 70 dB. Or: 30 Hz, 80dB SPL, 58 dB ringing to 300 ms. So, higher the SPL, louder the ringing at that room mode. However, at very few positions I have noticed there is actually less ringing for same SPL (e.g. 90 dB, but only 60db ring). Would anyone care to determine a cause for this behavior?
Mic was at fixed position all the time.
Something is moving. You say the mic was at a fixed position. Are you moving the sub around trying to find the best spot for it? If you place the sub in a null, then of course it's output, and therefore the ringing, will be lower. One of the strategies for sub placement is to locate it in a null.
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post #17759 of 19247 Old 02-23-2016, 05:34 PM
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Quote:
Originally Posted by AustinJerry View Post
Something is moving. You say the mic was at a fixed position. Are you moving the sub around trying to find the best spot for it? If you place the sub in a null, then of course it's output, and therefore the ringing, will be lower. One of the strategies for sub placement is to locate it in a null.
Yes, I was moving the sub, and most of the time SPL of ringing correlates very closely with SPL of that specific frequency. But in few rare cases I had same SPL of that frequency, but different SPLs of ringing. For example, with subwoofer in one spot and measurement of exactly 90 db i had 65 db of ringing. While with sub in other spot and 90 db SPL i had 55 dB ringing.
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post #17760 of 19247 Old 02-23-2016, 05:47 PM
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Originally Posted by donktard View Post
Yes, I was moving the sub, and most of the time SPL of ringing correlates very closely with SPL of that specific frequency. But in few rare cases I had same SPL of that frequency, but different SPLs of ringing. For example, with subwoofer in one spot and measurement of exactly 90 db i had 65 db of ringing. While with sub in other spot and 90 db SPL i had 55 dB ringing.
As I said in my previous post, the sub was probably situated in a room null.
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