Thoughts on my first REW attempts

[distoga]

I've measured my 7 bed layer of my 7.1.6 (Denon X8500H) 3 times. Without Audessey, Flat, and Ref(erence). I'll note that I need to investigate why Flat and Reference are killing highs on my RSL, RSR and Center (odd...) but without Audyssey active the speakers don't have the drop out above 10k.

Room is heavily treated with FR703. (It's below a garage so all 6 surfaces are 12" concrete). 4" ceiling (false ceiling covered in stretched cotton fabric), 4" most of the back wall, 1" side walls up to ear level, and 2" front wall. There are also 2'x2'x9' triangle bass traps in the front corners behind an AT screen. It's taken a 6 second flutter to about 140ms with all this treatment.

Speakers are LCR RBH 661se, surround 44se, rear 61se, and 2 subs Rythmik 15" sealed subs in boxes I built and placed next to L and R. All speakers set to small with crossovers at 80hz.

My questions are:

1. The mic was kept in the same location for all speaker location tests. What can be gained from doing this and using multiple speakers vs a single speaker and multiple mic locations? fyi, I didn't move it yet because I wanted tests to be reproducible as I learned REW. I do plan to go back and test multiple mic positions for each L, C and R (and others if it would be useful) but I thought that all speakers might be a good start?
2. Are these good or bad results? I've looked around and seen some much worse but I've also seen a lot better but it's hard to know where I'm fitting.
3. Is it normal for speakers to be so jagged (?comb?) like these as these graphs show, even near close hz ranges?
4. Any thoughts on what can cause the drop in 100-300hz and some ideas on where to look to fix it?
5. I'm not sure why when testing just LFE the db is far higher than with speakers, I think it's because when running with other speakers the avr is bass managing it so really only the LFE test itself is showing the true possible output of the LFE?
6. Other comments on graphs or suggestions on what I should be looking at adjusting for speaker angles, room treatment, audyssey adjustments, sub PEQ, etc?

I have mdat files for each of these three graphs if there's an interest in reviewing them but they're a little large to include here at about 23MB each and I haven't hit the 10 post requirement to link to google drive.

Tests taken with a umik-1, Linux, pulseaudio set to hdmi output, 7.1 and AVR at multichannel pcm so I can control 7.1 channels tests individually


Thanks!

 

[sam_adams]

I haven't hit the 10 post requirement to link to google drive.

Try adding the link without the 'http://' part and use dashes for the '.' i.e.: www-google-com.

 

[distoga]

https_://drive_google_com/file/d/1K90BmxbDI5yja7TQJ36wMJhJyZXPUdL4/view?usp=sharing
https_://drive_google_com/file/d/1LmeKNY88cYVJZms0LUx5JWJdyFicY_GZ/view?usp=sharing
https_://drive_google_com/file/d/1eeyOLp2XBjm8F23H5IToRgE6_AUZfOT2/view?usp=sharing

 

[sam_adams]

Here's the working links for your measurements:

Audyssey Flat:

https://drive.google.com/file/d/1K90BmxbDI5yja7TQJ36wMJhJyZXPUdL4/view?usp=sharing

Audyssey Reference:

https://drive.google.com/file/d/1eeyOLp2XBjm8F23H5IToRgE6_AUZfOT2/view?usp=sharing

No Audyssey:

https://drive.google.com/file/d/1LmeKNY88cYVJZms0LUx5JWJdyFicY_GZ/view?usp=sharing

You are running version 5.19 of REW. You should consider updating to the latest release candidate, 5.20RC5, as @John Mulcahy has done a great job of adding more tools to REW since 5.19 was released.

I've measured my 7 bed layer of my 7.1.6 (Denon X8500H) 3 times. Without Audessey, Flat, and Ref(erence). I'll note that I need to investigate why Flat and Reference are killing highs on my RSL, RSR and Center (odd...) but without Audyssey active the speakers don't have the drop out above 10k.

Room is heavily treated with FR703. (It's below a garage so all 6 surfaces are 12" concrete). 4" ceiling (false ceiling covered in stretched cotton fabric), 4" most of the back wall, 1" side walls up to ear level, and 2" front wall. There are also 2'x2'x9' triangle bass traps in the front corners behind an AT screen. It's taken a 6 second flutter to about 140ms with all this treatment.

Speakers are LCR RBH 661se, surround 44se, rear 61se, and 2 subs Rythmik 15" sealed subs in boxes I built and placed next to L and R. All speakers set to small with crossovers at 80hz.

There's still some close reflections within the first 5ms that are above -20dB. That could be the back of the chair or something close to the mic. When you're measuring, you want the mic to placed as close to the position that your head will be at. If the surface of the couch or chair is highly reflective such as leather, try draping a blanket over the back to absorb some of the reflections.

Even with all the treatments you've applied, there is still quite a bit of variability on the T20 and T30 times:

Ideally you would like to have the variability down to +/- 20% over the 300 Hz to 3 KHz range which will have the greatest effect on dialog intelligibility.

1. The mic was kept in the same location for all speaker location tests. What can be gained from doing this and using multiple speakers vs a single speaker and multiple mic locations? fyi, I didn't move it yet because I wanted tests to be reproducible as I learned REW. I do plan to go back and test multiple mic positions for each L, C and R (and others if it would be useful) but I thought that all speakers might be a good start?

If you are only concerrned about the Main Listening Position (MLP), placing the mic in one position to do your measurements is fine. Measuring from multiple positions is a good way to determine how the low frequencies and modes in the room would be perceived by listeners at those other positions.

2. Are these good or bad results? I've looked around and seen some much worse but I've also seen a lot better but it's hard to know where I'm fitting.

There are no good or bad results, per se, the measurements reveal how the room and how you have treated it effect the perceived sound quality. When doing your sweeps, you don't have to start every measurement from the single digits. Your subs are -30 dB at 10 Hz so there is little to be gained measuring any lower than that. In fact, with the response that far down, you will be measuring the LF noise in the room and not the speakers. When doing your measurements, try to measure at a reasonable listening level of around 75dB at your MLP. Audyssey will do its calibration at that level and it's probably more comfortable and less of a hazard to your ears if you're not measuring at 95 dB.

Additionally, when measuring the subs, you really don't have to measure out to 20 KHz as, again, the response is so far down you'll only be measuring noise. 500 Hz is good enough. Don't apply any smoothing to your sub measurements.

When analyzing your measurements, keep in mind that smoothing your graphs hides a multitude of sins. Over-smoothing can give the impression that things are okay when they are really not. Our eye-brain system is really good a picking up on patterns, so you should look at as many measurements from other members—here and on other forums—to train yourself into recognizing the patterns in the responses before applying any smoothing to measurements.

3. Is it normal for speakers to be so jagged (comb?) like these as these graphs show, even near close hz ranges?

Even in the best of treated rooms there are always reflections from surfaces, diffraction from the corners of cabinets, and environmental noise that will show up in your measurements. Remember that the mic is much more sensitive than your ears and will pickup things that you can't possible hear. Keep in mind that the ear/brain system of hearing integrates out a lot of the things you see in these measurements.

4. Any thoughts on what can cause the drop in 100-300hz and some ideas on where to look to fix it?

This could be a timing issue with the mains. If you can't move the subs around you can adjust the distance settings in your AVR to change the timing to see if you can fill in the low spots.

There is a drop in the response at around 56 Hz to 58 Hz that is probably a room mode:

That might be hard to fix if you can't move the subs around.

5. I'm not sure why when testing just LFE the db is far higher than with speakers, I think it's because when running with other speakers the avr is bass managing it so really only the LFE test itself is showing the true possible output of the LFE?

The LFE (Low Frequency Effects) channel is a separate channel that has a higher output, +10 dB, and a separate crossover frequency, 120 Hz, than the bass management settings for the main speakers. You can use the LFE channel to test with when choosing positions for the subwoofers to reduce the effects of room modes on the bass response.

6. Other comments on graphs or suggestions on what I should be looking at adjusting for speaker angles, room treatment, audyssey adjustments, sub PEQ, etc?

You're doing okay so far. Like shooting free throws, muscle memory takes about 15,000 shots to develop proficiency—same goes for the brain. Just develop a system when doing your measurements and check yourself often. If you see something that doesn't look right, ask yourself, "Am I doing this right?" Treatments can be discussed over in the Room and Acoustics forum. Audyssey is over in the Auto-EQ Platforms forums.

 

[distoga]

Thanks for the review, that was extremely helpful and I'll continue on with your suggestions. I spent all last night reading more about the differences and pieces of each REW graph and the purposes of them. I had used REW about 10 years ago but not very in-depth as I'm trying to now. I have a few follow up questions if you had more time to answer. Again thank you for your time and help.

1. In the first impulse graph, I understand the purpose of the top peaks and how to read those now, but I can't find anything that explains what it means when the graph line goes down to 100 and bottom out on the graph. Does that mean there is absolutely 0 energy at those particular times or what does it mean if anything?
2. How should I be reading the step graphs, like the one you posted? The only thing I found, which I couldn't understand the meaning of (yet), was "The step response shows the output which would result if the input signal jumped to a fixed level and stayed there. It is the integral of the impulse response. If there is an offset in the measurement input chain the step response will show an overall rise or fall as time progresses, rather than tending back to zero. " I also could not find out how you generated the sine wave on the step graph or what that sine wave means.
3. Here are my expected room modes. Nothing is calculated at 56hz-58hz. Could the fact that the subs are about 18" from front front/length wall change a room mode result or is it more likely the specific location of the mic create the lower energy at that location due to reflections? http_://i261_photobucket_com/albums/ii57/distoga/modecalc.png
4. In my first post about the 100hz-300hz dip, you mentioned to adjust the bass timing. This is trial and error I believe but do you recommend attempting to keep both sub delays/distance the same or purposely keep them different? Also could you explain why the sub placement can effect the mains when the crossover is set to 80hz as I would have thought the subs aren't outputting any energy in that range. Would toeing in/out the mains or adjusting their delay/distance be the right thing?
5. I typically listen at -8 to -15db AVR volume when the room is calibrated at 75db, but there are some movies or demo's I run louder, including up to a 75db reference). I began to use use 35db earmuffs when I did testing years ago because I found even a 75db tone would bother me if I did enough of them. Since I wear the earmuffs, should I still stick to a 75db test sweep or should I turn my receiver down to -15db (60db reference)? My thought was since a 75db reference level allowed for 105 speaker and 115 lfe peaks I should attempt to run REW at a higher db to watch for issues that might occur near peaks. I was eventually going to run REW at the 75db reference and at 60db reference and see how graphs would be different, maybe notice if my AVR or speakers had any issue with reproducing at my peaks..

 

[distoga]

I tried RC5 tonight but never could get it to output audio from my Linux laptop. .19 works so I'm not sure what's going on yet. I switched to my wife's windows laptop and hit another block where asio4all would change which channel/speaker it was outputting audio to. 1.1 would sometimes to go SL, R, SBR, LFE, it was pure random. Simplly exiting a measure window and going back in, without changing the output device, would end up with a different channel being used. I'll also have to figure that one out because a quick google didn't find anyone else reporting that oddity.

I put some blankets over the two rows of leather couches to help with reflections. In the end, I switched back to java and just doing R/L testing. I played around with delay (distance) in my AVR and found that changing the subs from 11.6' and 11.2' to 1.6 and 1.2 removed the drop out. I also tried 0's and tried random combination of 1,2,3,4,8,10,11,14,15,18,20 for each as well. I'm not sure if I should keep trying random delay combinations for my subs or mess with the the subs PEQs next. Impulse looked a little better I think, and rt60 a little better but would you say they could still use some improvement? I could add more acoustic treatment but when you speak you already can tell it's getting a little dead.

https_//drive_google_com/file/d/1mzHfITOQlJudtqqAZJpcwZHTFHqU0xe0/view?usp=sharing

 

[jmorris644]

Thanks you for starting this thread. I am about to begin my journey and my room is quite similar. I too have the room under the garage with 8" concrete walls. The ceiling is spancrete and the walls are all poured 8" concrete surrounded by 4" of Styrofoam and then sheetrock. I have yet do do any treatments as I just finished construction. My screen is AT and my speakers are Klipsch. I too have 2 subs but they are 12". I have a friend that builds professional recording studios so he is currently determining the acoustic treatments necessary for the room.

You mentioned that your room is treated with a lot of FR703. That is just the fabric, correct? Does the fabric cover any acoustic material?

I currently set my system up using Audessy solely as I am waiting to get my treatments. Is there any advantage to doing any measurements prior to and after treatments with REW? I am also considering adding a device that can take the output of REW and apply it in real-time when watching video.

 

[serko70]

Your SR (from 70Hz onwards) and SL (from 200 Hz) are out of phase with the rest of the speakers (see attached). This is causing the dip between 100-300Hz. Since I checked phase overlays from noaud measurements, this can't be filter related. They might have faulty crossovers. SBR SBL and C all seem fine.

 

[serko70]

The sharp drop around 59 hz Sam has pointed out is speaker boundary interference. I am guessing your front speakers are 125-130 cm away from the front wall which is causing that dip. Your speakers lower bas limit is 50 Hz which has 1/4 wavelength of 150 cm. So if you can move your front speakers 25-30 cm further away from the front wall (I know easier said than done!) this dip will fall below the speakers bass capacity and disappear.