Standard REW graph settings?

[Bugal1998]

Hi all,

Are there industry or ASR community standards for the microphone position (MLP or spatially averaged), stereo vs mono left or right sweep, dB range, smoothing, and other relevant settings for various REW graphs when measuring a room? And is there a standard best practice ‘group of graphs‘ that are used to understand baseline room and speaker performance?

If not, perhaps we could document some standardized best practices here as an ASR resource.

Thanks in advance, and apologies if my search missed an obvious thread or resource!

 

[ozzy9832001]

50dB range, smoothing depends what you are looking at and for what purpose, left and right separate. Single sweep is the only way to get information like decay, phase and other timing info. MMM for EQ (1/6 smoothing) or average of measurements.

MMM for EQ @ 1/6 is my opinion and what I use, but I think the rest are pretty standardized. I think some use a 55dB graph, but I find 50dB is enough.

 

[Bugal1998]

50dB range, smoothing depends what you are looking at and for what purpose, left and right separate. Single sweep is the only way to get information like decay, phase and other timing info. MMM for EQ (1/6 smoothing) or average of measurements.

MMM for EQ @ 1/6 is my opinion and what I use, but I think the rest are pretty standardized. I think some use a 55dB graph, but I find 50dB is enough.

Great start, thank you!

Any thoughts on the various waterfall and decay settings?

 

[ozzy9832001]

Great start, thank you!

Any thoughts on the various waterfall and decay settings?

Usually 1/12 unless I'm looking for something very, very specific. Generally, I'm looking for overall, but if something is making a funny noise, I'll smooth with better resolution.

 

[Curvature]

MMM

OP, for MMM, this is done in RTA with the window set to rectangular, averages to forever, no smoothing.

Then capture the trace and apply whatever smoothing you like. I usually go with variable or psychoacoustic.

There's some technique with the microphone movement. It's not very critical apart from ensuring that you smoothly, slowly move the microphone and change height as you do so, not staying in the same horizontal plane.

Edit: Typo.

 

[Curvature]

I should also mention: MMM is to understand response across an area. Single point measurements are accurate for, as in the name, one point, and provide precise amplitude and phase information. So it depends on what you want the measurement to show you. Generally, corrections made at a single point will have some impact to the response in the volume around it, i.e., the error of the measured response and your correction will increase the further you move away from that point.

If making corrections, all of your filters should be individually audible, otherwise it's not a useful exercise.

Understanding minimum vs. excess phase and the interaction of different wavelengths in small rooms will help designing filters and diagnosing problems. Learning this side of things, including human hearing, is a far more involved and impactful process than making measurements.

 

[sam_adams]

Are there industry or ASR community standards for the microphone position (MLP or spatially averaged), stereo vs mono left or right sweep, dB range, smoothing, and other relevant settings for various REW graphs when measuring a room? And is there a standard best practice ‘group of graphs‘ that are used to understand baseline room and speaker performance?

Simply post your measurement .mdat file to a filesharing service, Google Drive or Microsoft OneDrive, that will allow us to download and evaluate your measurements. Always use a timing reference when making your measurements, too.

 

[Bugal1998]

Understanding minimum vs. excess phase and the interaction of different wavelengths in small rooms will help designing filters and diagnosing problems. Learning this side of things, including human hearing, is a far more involved and impactful process than making measurements.

Excess phase is a topic where I need to invest a bit more time.

Simply post your measurement .mdat file to a filesharing service, Google Drive or Microsoft OneDrive, that will allow us to download and evaluate your measurements.

Will do!

 

[Bugal1998]

@sam_adams Here is a link to a series of REW sweeps I made tonight. If anyone who cares to analyze the results has trouble accessing the file, please let me know.

I forgot to turn the HVAC blower off, so this is a worse case scenario for low frequency noise in the room. I used the Mini-DSP UMIK-1, and it's showing a:

• Dip around 200hz and a rise around 500hz
• Peak around 10hz

None of which is present in the Trinnov graphs or Omni-mic measurements. I may play around with filling in the dip to see if it sounds better, but the room sounds very good as-is... Improvement is always welcomed!

Edit: The measurement notes identify the measurement position (Center is middle of the head, and the other positions are at the left and right ears as noted). No MMM at this time.

 

[sam_adams]

The frequency response in the transition region from 100Hz to 200Hz indicates that there might be an issue with the speaker placement in relation to the wall(s) behind them that may be an SBIR issue. Possible mitigation would be to place an absorbing panel behind the speakers.

The filtered impulse response indicates that most of the early reflections are reasonably under control, but you may want to retest by covering the seating position with an absorbing covering like a blanket and if you are using a boom stand for the mic, covering the stand and the boom arm with some type of absorber like a bath towel to see if the peaks under the first 20ms are reduced.

The RT60 plot indicates that you need to do a little work to reduce the variability in the band from 500Hz to 10KHz to get it closer to 350ms. Approach this area carefully since over-treating will suck the perception of spaciousness out of the room.

The modal area waterfall plot looks good with minimal signs of ringing.

The impulse plots for the speaker timings are about as good as it will get. Keep in mind that impulse timing separations under 650µs are 'inside your head' and are of no real consequence.

 

[Rednaxela]

dB range

Perhaps have a look at the short discussion with the author of REW, starting here. Though most of the time workable enough, strictly speaking dB range is only one half of the story.

 

[Bugal1998]

@sam_adams

Thanks for taking a look! A couple of comments and observations:

SBIR Dip: The dip potentially caused by SBIR didn’t show in other measurements (in fact they showed a peak) and I manually reduced that area to resolve excess ’chestiness’ in certain tracks; the current response sounds better to my ears, so I’m not sure if the dip is real or not. There’s also absorption built into the wall behind the speakers already, but I should validate the speaker-absorption position using a mirror. More investigation needed.

Early reflections: I may try covering the boom and chair with absorption next time; it certainly sounds very good as-is (clear and spacious).

RT 60: The room acoustics were calculated/designed with the addition of a second row of seats (moveable to accommodate 2-channel and movie listening configurations), however, I only have the front-row installed. There is also some absorption that surrounds a future center channel that hasn’t been installed. I suspect a second row of seating and the center channel absorption will eventually bring the remaining frequency decays in-line. In the meantime, the longer decay compounded by the wider dispersion of the JBL M2 over that same range creates audible brightness, so I’ve adjusted the in-room response in the offending range slightly downward to regain a neutral tonality.

Ringing: Considering the effort that went into the low-frequency room acoustics (floating walls and ceilings, full wall bass absorption front and rear, back half of the room with a functional bass riser, etc.) I would have been disappointed if there were ringing issues. The HVAC blower is no doubt raising the noise floor in that region.

Impulse response: I’m curious what Trinnov is doing here to help; I may remeasure without Trinnov corrections to see what it’s contributions are.

Thank you again for the analysis!

I still think there‘s value in documenting some basic community best practices here, so I may take a pass at documenting them.

 

[Thomas_A]

@sam_adams

Thanks for taking a look! A couple of comments and observations:

SBIR Dip: The dip potentially caused by SBIR didn’t show in other measurements (in fact they showed a peak) and I manually reduced that area to resolve excess ’chestiness’ in certain tracks; the current response sounds better to my ears, so I’m not sure if the dip is real or not. There’s also absorption built into the wall behind the speakers already, but I should validate the speaker-absorption position using a mirror. More investigation needed.

Early reflections: I may try covering the boom and chair with absorption next time; it certainly sounds very good as-is (clear and spacious).

RT 60: The room acoustics were calculated/designed with the addition of a second row of seats (moveable to accommodate 2-channel and movie listening configurations), however, I only have the front-row installed. There is also some absorption that surrounds a future center channel that hasn’t been installed. I suspect a second row of seating and the center channel absorption will eventually bring the remaining frequency decays in-line. In the meantime, the longer decay compounded by the wider dispersion of the JBL M2 over that same range creates audible brightness, so I’ve adjusted the in-room response in the offending range slightly downward to regain a neutral tonality.

Ringing: Considering the effort that went into the low-frequency room acoustics (floating walls and ceilings, full wall bass absorption front and rear, back half of the room with a functional bass riser, etc.) I would have been disappointed if there were ringing issues. The HVAC blower is no doubt raising the noise floor in that region.

Impulse response: I’m curious what Trinnov is doing here to help; I may remeasure without Trinnov corrections to see what it’s contributions are.

Thank you again for the analysis!

I still think there‘s value in documenting some basic community best practices here, so I may take a pass at documenting them.

About the early reflections, there is a strong reflection at around 2 ms which could be floor reflection.

 

[ozzy9832001]

Looking at the wavelet, it looks like you have something going on around 140hz and a lot of reflected energy from 300hz to about 500hz.

Your group delay is also very, very choppy.

I'd be interested in seeing a measurement before Trinnov manipulates it.

I may be blind, but did you post what your room dimensions, how far you are from the speakers and how far the speakers are from the front/side walls?

 

[ozzy9832001]

SBIR Dip: The dip potentially caused by SBIR didn’t show in other measurements (in fact they showed a peak) and I manually reduced that area to resolve excess ’chestiness’ in certain tracks; the current response sounds better to my ears, so I’m not sure if the dip is real or not. There’s also absorption built into the wall behind the speakers already, but I should validate the speaker-absorption position using a mirror. More investigation needed.

The dip at ~140hz is probably ceiling, assuming an 8' ceiling height. For most people sitting at a desk, this would probably be a peak, but if you are sitting on a couch it may show as a dip.

Early reflections: I may try covering the boom and chair with absorption next time; it certainly sounds very good as-is (clear and spacious).

The 2ms reflection is happening from a surface that is causing the sound to 2 delayed by 2ms (or roughly 2 ft). My assumption, without any actual layout information would be front wall or sidewall.

RT 60: The room acoustics were calculated/designed with the addition of a second row of seats (moveable to accommodate 2-channel and movie listening configurations), however, I only have the front-row installed. There is also some absorption that surrounds a future center channel that hasn’t been installed. I suspect a second row of seating and the center channel absorption will eventually bring the remaining frequency decays in-line. In the meantime, the longer decay compounded by the wider dispersion of the JBL M2 over that same range creates audible brightness, so I’ve adjusted the in-room response in the offending range slightly downward to regain a neutral tonality.

Your decay times are long and audible. The interesting thing about them is they are actually quite uniform. Usually the bass region is significantly worse. Though with all the treatment you've done I honestly would expect them to be a bit lower (this is more to taste, however).

Impulse response: I’m curious what Trinnov is doing here to help; I may remeasure without Trinnov corrections to see what it’s contributions are.

I would be as well, because it looks like it's doing something in the time domain, but can't tell if it's helpful or not.

That's why I think posted measurements with it off would be very helpful.

 

[Bugal1998]

About the early reflections, there is a strong reflection at around 2 ms which could be floor reflection.

Most likely. In blind testing I have always preferred to leave the floor reflections untouched.

 

[Bugal1998]

I may be blind, but did you post what your room dimensions, how far you are from the speakers and how far the speakers are from the front/side walls?

Nope. Not blind.

I didn't post them here because the intention of the thread was to create an ASR 'community template' for newer REW users, and not to analyze my room; but hey, there's educational value in that as well (for me and other ASR users)... So why not?

Let me check speaker location measurements and followup

 

[ozzy9832001]

Nope. Not blind.

I didn't post them here because the intention of the thread was to create an ASR 'community template' for newer REW users, and not to analyze my room; but hey, there's educational value in that as well (for me and other ASR users)... So why not?

Let me check speaker location measurements and followup

I feel the biggest issue for new REW users is learning how to read the graphs and extrapolate correct information from it. Since multiple issues can be present at a time.

 

[Bugal1998]

I may be blind, but did you post what your room dimensions, how far you are from the speakers and how far the speakers are from the front/side walls?

Room length finished space: 24'
Room length to structure: 28'7"
Room width: 19'2"
Ceiling height: 8'5"
Speaker stage height: 6"

Distance between speakers center-to-center: 10'2"

Listening distance from speakers (to ears): 12'3"
Listening distance from front wall (to ears): 14'7"
Ear height below ceiling: 4'7"

Middle of speakers to sidewall: 4'5"
Front of speaker to wall behind speaker: 3'3"


Middle of woofer to main floor: ~2'7"
Middle of HF driver to main floor: ~4'

Middle of woofer to ceiling: ~5'9"
Middle of HF driver to ceiling: ~4'5"

 

[Bugal1998]

Usually the bass region is significantly worse. Though with all the treatment you've done I honestly would expect them to be a bit lower (this is more to taste, however).

Structural factors, choices to increase sound isolation (especially at low frequencies), and some cosmetic decisions all increased bass reverbation times.

The floor and three out of four wall structures are concrete.

Concrete board and 5/8 concrete brick veneer and morter was added to a large portion of the side walls. A portion of the sidewall has 1/4 plywood and 3/4" pine board.

The ceiling has 3/4"plywood and 2 layers of 5/8" plywood.

Each of those factors work to increase bass decay times.