Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 786 - AVS Forum | Home Theater Discussions And Reviews
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post #23551 of 23561 Old 09-12-2017, 06:42 PM
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Quote:
Originally Posted by sam_adams View Post
The room is too small for these long wavelengths to combine constructively or destructively. The wavelengths are at odd fractional lengths compared to the room dimensions.



This is the area where you will see peaks or nulls in the response of a sweep—especially from subwoofers. The soundwaves combine constructively or destructively to create sharp peaks and nulls in the response. This is the area where basstraps—thick ones—are most effective. If you look back through some recent postings in the thread from members who have posted their .mdat files, you might still be able to download them and look at the responses to get a sense of what is happening in this area.



Diffusion is what creates the sense of 'openness' or 'space' in a room. Diffusion allows the sound to spread out without diminishing in intensity. If you overtreat a room with absorbers, the room has a tendency to 'feel' small or confined even when there is no music playing—like walking into an overfilled clothes closet. Diffusion can broaden the sweetspot and is what makes certain passages, like the guitar solo in Steely Dan's "Reelin' In The Years", fill the space between the speakers and gives you the illusion that the guitar is right there in front of your face.



This is the area where sound waves tend to reflect off of surfaces in a fashion more like light waves do. This is the area where you will get those annoying flutter echoes that bounce back-and-forth between walls. Depending on the wall surface, they may sound metallic or sometimes wooden in nature.

Keep in mind that the areas defined in those computed results are not sharply defined. The effects tend to blend together in transition zones between the areas.

When treating a room the goal should be to minimize the modal response of the room in the low frequency bass region—tame the boom. Preserving the 'openness' of the room while taming early reflections and flutter echoes is accomplished by using a mix of diffusion and absorption. Many times it is recommended to combine absorbing panels with diffusing panels to reach this balance.

However, most home listening rooms are too small to effectively employ 1D or 2D quadratic diffuser panels or other diffusion methods because their effect is not fully developed unless they are positioned at a minimum of six feet from the MLP. They often tend to be very expensive even for DIYers to construct, as well. Sometimes using small absorbing panels spaced over a broad area with some space between them can accomplish the same thing. (I'm going to have to find for that paper I read so I can post that. Like Mozart, too may PDFs.)

In a small room it may sometimes better to employ an absorbing panel with a Binary Amplitude Grating over the surface of the absorbing medium. These Binary Amplitude Diffuser (BAD) panels have the benefit of absorption with diffusion built in and the BAD grating develops its diffusion effect at closer distances—sometimes as little as three feet and in two dimensions—which is perfect for a room ten to fifteen feet wide.

This can be a real process—and expensive to boot. The thing to do is measure and evaluate your results. Research the alternatives.


Many thanks for the comprehensive reply. Your knowledge in this area is truly impressive. I have discussed the room in some detail with GIK acoustics as well and their recommendation was thick bass traps on rear wall of room and 244 panels on side walls. I have taken some measurements with REW but more for FR at MLP nothing beyond that. My understanding is limited in other areas it can help in. Leaning towards the recommendation from GIK.


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post #23552 of 23561 Old 09-21-2017, 04:43 PM
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Following Jerry's guide for time aligning my 4 identical subs using a minidsp2x4 HD with a Marantz AV8802A with XT32, I did a 1 position audyssey calibration for each sub. I get a different distance every time I do it. They only vary slightly, within .10m. My question, is that just normal giving the way low bass has longer wavelengths than higher frequencies and should I be concerned about it? I actually did 3 1 position measurments for each sub and averaged them for each sub, but that is very time consuming. Just wondering if I was doing it correct or am I being too critical about it and just stick with the first measurment for each sub? Thanks.

Display: LG 65" OLED C7P + OPPO UDP-203 4K UHD Blu-ray Player
Processor : Marantz AV8802a (XT32)
Amps: (3) Marantz MA700's + (8) Marantz MA500's
Speakers: L,R,SR,SL,SBR,SBL - B&W 685s2's + Center - B&W HTM61s2 + Front & Rear Heights - B&W 686s2's
Subs: (4) SVS PC-2000's via MiniDSP2x4 HD
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post #23553 of 23561 Old 09-21-2017, 06:44 PM
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Quote:
Originally Posted by MBrown2020 View Post
Following Jerry's guide for time aligning my 4 identical subs using a minidsp2x4 HD with a Marantz AV8802A with XT32, I did a 1 position audyssey calibration for each sub. I get a different distance every time I do it. They only vary slightly, within .10m. My question, is that just normal giving the way low bass has longer wavelengths than higher frequencies and should I be concerned about it? I actually did 3 1 position measurments for each sub and averaged them for each sub, but that is very time consuming. Just wondering if I was doing it correct or am I being too critical about it and just stick with the first measurment for each sub? Thanks.
I don’t ever recall doing multiple 1-position calibrations, so I can’t say whether I would have received differing distance results. However, the difference you are seeing is insignificant, and certainly not audible. Once you use the distance calculations to set the delays in the 2x4, what does the combined bass response look like? And are you connecting all four subs to a single output on the 8802A?
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post #23554 of 23561 Old Yesterday, 01:13 PM
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Quote:
Originally Posted by AustinJerry View Post
I don’t ever recall doing multiple 1-position calibrations, so I can’t say whether I would have received differing distance results. However, the difference you are seeing is insignificant, and certainly not audible. Once you use the distance calculations to set the delays in the 2x4, what does the combined bass response look like? And are you connecting all four subs to a single output on the 8802A?
Yes, all 4 subs are connected to the 2x4HD and connected to sub out 1 on 8802. My combined response is good, I was just wondering why it varied. None of the other 11 speakers vary in distance like the subs.
Attached Images
File Type: jpg subs.jpg (54.6 KB, 18 views)

Display: LG 65" OLED C7P + OPPO UDP-203 4K UHD Blu-ray Player
Processor : Marantz AV8802a (XT32)
Amps: (3) Marantz MA700's + (8) Marantz MA500's
Speakers: L,R,SR,SL,SBR,SBL - B&W 685s2's + Center - B&W HTM61s2 + Front & Rear Heights - B&W 686s2's
Subs: (4) SVS PC-2000's via MiniDSP2x4 HD
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post #23555 of 23561 Old Yesterday, 02:06 PM
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First, thanks for the thread and the guides. This has been helpful and allowed me to slow down and start thinking about what I am doing.

I got my hands on a lot of cheap rigid fiberglass (1" thick) and have family in this weekend who are much handier than I am. So, even though I'm still in the planning stages, I wanted to start putting together panels that I can use later. Does anyone have any general advice on where to start? For example, would I be ok if I did ~6" thick traps for the corners (allowing for spacing between the wall and panel) together with several relatively small (1'x1'x1"?) panels for absorption but with many grouped near each other (think of replacing a 4'x2' panel with a very cheap diffisor)?

I have followed the recommended guides for REW to get initial output, and I have placed in the Google Drive location linked below. This contains all graphs (hopefully clearly labelled) touched upon in the pdf guide and formatted/measured accordingly in addition to room dimensions and pictures of the layout. (Note that it is set up along the diagonal based on another forum's recommendation which, at least to date, has sounded better than previous attempts.)

I'm more than happy to post pictures, files, etc here if it's easier, but with so many, I didn't know where to start.
https: // drive.google.com/open?id=0Byzh6qKm0nboM1hOOWlyUG5LQUk

*I cannot post links it turns out since that requires 5 posts. If 'editing' the link like this is frowned upon, let me know, and I'll remove it.

Thanks again, and I look forward to any comments.
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post #23556 of 23561 Old Yesterday, 02:17 PM
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Originally Posted by mark3141 View Post
First, thanks for the thread and the guides. This has been helpful and allowed me to slow down and start thinking about what I am doing.

I got my hands on a lot of cheap rigid fiberglass (1" thick) and have family in this weekend who are much handier than I am. So, even though I'm still in the planning stages, I wanted to start putting together panels that I can use later. Does anyone have any general advice on where to start? For example, would I be ok if I did ~6" thick traps for the corners (allowing for spacing between the wall and panel) together with several relatively small (1'x1'x1"?) panels for absorption but with many grouped near each other (think of replacing a 4'x2' panel with a very cheap diffisor)?

I have followed the recommended guides for REW to get initial output, and I have placed in the Google Drive location linked below. This contains all graphs (hopefully clearly labelled) touched upon in the pdf guide and formatted/measured accordingly in addition to room dimensions and pictures of the layout. (Note that it is set up along the diagonal based on another forum's recommendation which, at least to date, has sounded better than previous attempts.)

I'm more than happy to post pictures, files, etc here if it's easier, but with so many, I didn't know where to start.
https: // drive.google.com/open?id=0Byzh6qKm0nboM1hOOWlyUG5LQUk

*I cannot post links it turns out since that requires 5 posts. If 'editing' the link like this is frowned upon, let me know, and I'll remove it.

Thanks again, and I look forward to any comments.
Regarding DIY treatments, there are a number of threads here on AVS that will provide guidance on building effective panels. You will probably get better advice in one of those threads. Regarding where to place the treatments, that’s where REW measurements will be useful.

BTW, I doubt that anything only 1” thick will be very effective as a treatment.
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post #23557 of 23561 Old Yesterday, 02:30 PM
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I'll do a little more digging on appropriate designs. There's so much conflicting information scattered among so many resources, it's hard to know what to trust.

As I'm working on that, any feedback on where to start treatments based on my measurements would be appreciated.

By the way, are you still in Austin? I'm a Texan but now live in Maryland. I spent almost ten years there and went to UT so consider it home. I don't go back there frequently, but when I do, I'm always amazed at how crowded it's become.
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post #23558 of 23561 Old Yesterday, 05:06 PM
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When measuring subs only is it best to disconnect the center and use HDMI 3 or can one use HDMI 4?

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post #23559 of 23561 Old Yesterday, 05:40 PM
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When measuring subs only is it best to disconnect the center and use HDMI 3 or can one use HDMI 4?
Couple of differences. First of all, when measuring using HDMI3, the crossover for the center channel is still in effect. This means the sub’s response will fall off above the crossover. This is not necessarily a bad thing, depending on what you are trying to measure. If you want to see how high the sub’s response will go, raise the center’s crossover to its highest allowed value (typically 250 Hz).

When measuring using HDMI4, the center crossover is no longer in effect, but the LPF for the LFE channel comes into play (typically 120Hz). In addition, when measuring using HDMI4, the output is increased by 10dB, so be aware that the measurement curve will be higher.
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post #23560 of 23561 Old Yesterday, 05:50 PM
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Originally Posted by AustinJerry View Post
Couple of differences. First of all, when measuring using HDMI3, the crossover for the center channel is still in effect. This means the sub’s response will fall off above the crossover. This is not necessarily a bad thing, depending on what you are trying to measure. If you want to see how high the sub’s response will go, raise the center’s crossover to its highest allowed value (typically 250 Hz).

When measuring using HDMI4, the center crossover is no longer in effect, but the LPF for the LFE channel comes into play (typically 120Hz). In addition, when measuring using HDMI4, the output is increased by 10dB, so be aware that the measurement curve will be higher.
Thank you, that 10db threw me when i had everything running and measuring.

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Denon AVR-X4300H/Turd Sony- 7.4.4
Polk Rti A9 LCR, Volt6 Surrounds and Heights
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post #23561 of 23561 Old Yesterday, 08:36 PM
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Originally Posted by mark3141 View Post
I'll do a little more digging on appropriate designs. There's so much conflicting information scattered among so many resources, it's hard to know what to trust.

As I'm working on that, any feedback on where to start treatments based on my measurements would be appreciated.

By the way, are you still in Austin? I'm a Texan but now live in Maryland. I spent almost ten years there and went to UT so consider it home. I don't go back there frequently, but when I do, I'm always amazed at how crowded it's become.
Looks like you have a blank canvas there, Mark. The response curves for the left and right speakers have huge dips in the 60Hz range. This suggests that the speakers may not be placed properly. The first step, before any treatments, would be to experiment with speaker placement to find the smoothest response. I don't see any sub measurements. One or more subs will do wonders in the 20-100Hz range. The ETC measurements show significant reflections, caused no doubt by the bare walls. Once you have finalized the speaker placement, you can use the techniques described in the guide to determine where the reflections are originating. Then place an effective treatment there and re-measure to see if the reflection has been addressed.

I see you included several averaged measurements. Forget these--they provide no useful information. And the distortion graphs don't tell you anything this early in the game.
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