Need help validate REW based setup. Sounds wrong :(

[pratul]

Hello folks: I just got my pre-processor (Anthem-AVM70) and am trying to set it up using REW but not very happy with the way it sounds. My setup and what I have done till now is below:
Pre-processor: Anthem AVM 70
Amps: Anthem MCA 5, 3
Subwoofers: M&K MX5000M2 x2 (front corners)
LCR Speakers: M&K S-250THX
SL & SR Speakers: M&K SS-250THX
BSL & BSR Speakers: M&K S-150THX
Front crossover (L&R): 120hz
Center crossover: 80Hz
Surround Crossover: 80Hz

• I have adjusted the distance of the subs to get the flattest response I could get for from the Subs.
• I have adjust the sub distances to get the flattest response from the Subs and fronts (L&R)
• I have adjusted the crossover frequencies to get the best response from all speakers.

The bass is great, the surround effects are good, the dialogs are clear but there is something missing. I can't figure out what. It just doesn't sound right.

I am hoping you can take a look at the attached REW file and tell me if I have done something wrong. This is my first time playing with REW.

Thank you for your help!

 

[pratul]

Also, this file is from the REW sessions I used to pick the right crossover frequencies for all the speakers.

 

[sam_adams]

Strictly from a procedural perspective, you didn't load the cal file for your ARC mic:

If the cal file for the mic wasn't in the box, you can get it here by inputting the mic serial number. Scroll down to the bottom of the page.

Also, when measuring the subwoofwers, don't use the LFE channel (channel 4 on HDMI) as this channel has its own crossover frequency setting and slope. Additionally, the output will be +10dB above the bass managed level. Better to measure the subs individually or together using one of the speaker channels—with the speaker disconnected—to get a better sense of the crossover response. The center channel will combine the bass managed response from the left and right channels.

When measuring the left and right channels, don't measure them together. Measure them separately. That way you will avoid comb filtering of the response and you won't get odd impulse responses, caused by slight timing differences between the speakers.:

The bass response has a large hole around 60Hz.

Changing the timing/distance or crossover frequency won't help this as it's probably caused by a room mode. You need to move the subwoofer(s) around the room to fix that. Getting the position(s) with the best response means that the room correction won't have to apply as much correction to smooth out the response. Dips are fixed by position and peaks are fixed by EQ. You can input your room dimensions into any one of these simulators:

AMROC

Bob Golds

Hunecke

or use the REW simulator

to get a sense of the room modes that you would be dealing with. Remember that the results are a best guess and not absolute.

The center channel (as well as the other channels) seems to have a great deal of reflections:

Try measuring with the sub turned off to see if the level of the impulse between 3ms and 10ms drops or disappears. This will give you a better perspective on the reflections from the center channel. Mic positioning in relation to the MLP and any furnishings might be effecting this. You may need to think about some treatments if it doesn't change much.

 

[pratul]

Thank you for the detailed reply and pointing out the things I missed. Responses to your feedback are below:

• you didn't load the cal file for your ARC mic: Yes. The mics Anthem is shipping now don't have a cal file. I am getting another one that will have one.
• Better to measure the subs individually or together using one of the speaker channels: Thanks! I will try that later today.
• When measuring the left and right channels, don't measure them together. Measure them separately. That way you will avoid comb filtering of the response and you won't get, caused by slight timing differences between the speakers: I initially measured them separately and using the "alignment tool" adjusted the distances to get the best response. I will include them separately and together when I measure again tonight.
• The bass response has a large hole around 60Hz: Yes, I tried placing the subs at the front corners, at 1/3 positions, one in the front and one in the back (both diagonal corners) and moving the subs forward/backwards and left/right by a foot each time but can't seem to get rid of the drop at 60hz. The current position (front corners) gave the flattest response I could get. I will look at the room simulators and try once more.
• The center channel (as well as the other channels) seems to have a great deal of reflections: I didn't know about this feature of REW. Which graph are you looking at and how do you read them? Are there any youtube videos you would recommend? What do you do to get rid of / reduce the reflections? Move the speakers around?

Lastly, my theater room is 33' long and 13' 8" wide with ceiling 8' 5" high. The lower half of the entire room is covered with 1" thick acoustic insulation behind acoustic fabric.

Once again thanks for your help!

 

[pratul]

@sam_adams : Just to be clear.. when you say "Try measuring without the sub turned off to see if the level of the impulse between 3ms and 10ms drops or disappears." you mean measure the center channel with the subs turned on. Correct? Thanks for your help!

 

[sam_adams]

@sam_adams : Just to be clear.. when you say "Try measuring without the sub turned off to see if the level of the impulse between 3ms and 10ms drops or disappears." you mean measure the center channel with the subs turned on. Correct? Thanks for your help!

That was a typo. I meant to say, "with the sub turned off". I did an edit to fix it so as not to confuse others. But after a little fiddling with the Filtered Impulse Response graph, the energy is way above the sub's range.

The graphs above—and below—are from the Impulse Response window:

Any peak above the -20dB line would be audible and might cause a perceived change in the imaging of the speaker(s). Those reflections could be coming from a room surface or some furniture in the room. They could also be from the fixture holding the mic.

The bass hole around 60Hz is probably a combination of room modes between 51Hz and 68Hz from the length and height of the room with some contribution from some tangential modes between 53Hz and 69Hz. Here's a little 3D representation of your room's modes over on the AMROC room mode simulator. Your MLP might be right in the middle of, or close to, the intersection of those modes. Try moving the mic measurement point forward or back, or left or right, from the MLP to get a better sense of the mode distribution. Once again, our good friend, Bob Golds, has some advice.

 

[pratul]

That is a lot of good info! Thanks for sharing. Will review it tomorrow when I get some time.
BTW: I took a few more measurements moving the subs around this evening. I "think" I have improved it a "little".
I still need to adjust the distances to see if that will help any. Will do that tomorrow. In the file named "Compare-mar3rd.mdat, I have the measurements from today as measurement #1 and the second one is from before. Thanks again for your help.

 

[pratul]

@sam_adams I ran measurements on all the speakers like you described and tried to move the subs around to get rid of the dip at around 60hz but can't find the right location for the sub. The response from the right sub is great but the left sub is the one creating the dip. I have tried moving it to every location I can think of, including the back of the room, the dip moves but doesn't go away. Right now it is at around 50 hz. One thing I didn't try was move it right next to or on top of the sub on the right side. Will that help? I looked at the room simulators you had suggested. 52-65 hz have a pressure nodes at the front corners. I seem to be getting the best measurements with subs there but the left sub continues to show a dip at those frequencies. I tried swapping the subs but the issue remain on the left side of the room.
I also ran the measurements for all the front speakers without the sub as you had suggested to look at the impulse responses. If I am reading the graphs right, the left is the best while the center is the worst. I think it is most likely from the reflection from the ceiling. the 6 ms delayed reflection could be that. Would you agree? I will try to add a panel on the ceiling and see if that helps.
Lastly, I tried to match the distances for the subs and the FL&FR speakers using the delays REW was reporting. I tried to get them as close as I could. I tried to use the "Alignment tool" to align the subs with the front speakers using the method described in the video titled "REW Home Theater Subwoofer And Main Speaker Time Alignment And New House Curve Method" (Sorry can't post a link yet.) Basically selected measurement 3 and 7 for the compare and aligned phase slopes at 120hz.

Could use your help with placement of the left sub and interpreting the measurements from the front speakers. What else would you suggest I do?

Thanks again for your help!