Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 229 - AVS Forum
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post #6841 of 12042 Old 11-13-2013, 08:46 PM
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Quote:
Originally Posted by AustinJerry View Post

I just clicked the "Apply Default Settings" button in REW, and it sets the 99 and 59 values.  I really didn't give this much thought.  Clearly, adjusting these values changes the way the spectrogram looks, but I'm not sure what the relationship between these values and the measurement level is.  Perhaps someone could explain it?

The scale matches the amplitude of the signal. In controls I set, "match top of scale to peak", and then adjust the "scale range" as necessary.
This way the top of the scale always matches the highest amplitude of the signal being measured and you can set your noise floor as desired.

If you are updating the manual, I would suggest 40dB scale, since that seems to match most literature I have been reading. Jim mentioned previously that he only considers above -35dB.

I would like to see the waterfall settings changed so that the top of the scale matches the peak of the signal with a set scale range also, but not sure how this can be easily described for newcomers, or if everyone feels it's even prudent.
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post #6842 of 12042 Old 11-13-2013, 09:01 PM
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Quote:
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LOL, that was quick. I deleted my post a few seconds after posting when I zoomed in on the graph and realized I could 'just' see the impulse with the graph at full size.


BTW Jerry,

your Guide states the values for posting Spectrograms and mentions using the 'default values' for the graphs listing a db scale range of 99db for top and 59db for bottom. Could you double check this? In mine, the default appears to be 91db and 51db. Setting it to 99 and 59 removes all red from the graph with an 85db measurement. Are you guys measuring at 90-95db?



Max

I just clicked the "Apply Default Settings" button in REW, and it sets the 99 and 59 values.  I really didn't give this much thought.  Clearly, adjusting these values changes the way the spectrogram looks, but I'm not sure what the relationship between these values and the measurement level is.  Perhaps someone could explain it?
The spectrogram shows something similar to the waterfall except it does so using the colors as intensity.

If the top of the SPL scale is 99db and the measurement is at 85db, no part of the graph would show red (unless there's a significant peak). If the measurement SPL is not standardized though, the decay results on Spectrograms with the 99/59db settings differs. For instance, I looked at an 85db measurement with the 91/51db settings that resulted in REW. It showed red regions (like everyone's Spectro's) and decayed in about 350-375ms. Using the same measurement and setting it to 99/59db removed all the red and the decay below 30Hz was all under 300ms. Standardizing the scale requires standardizing the measurement levels to produce comparability in graphs.


Max
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post #6843 of 12042 Old 11-13-2013, 09:12 PM
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I am completely confused now.

 

Here is my measurement:

 

The measurement peak is 97.44dB.  So what settings do I use in the spectrogram for this measurement?

 

I don't know why this hasn't been discussed before.  It means we all have been producing incorrect spectrograms, which isn't good.

 

 

Clearly very different results:

 

 

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post #6844 of 12042 Old 11-13-2013, 09:12 PM
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Quote:
Originally Posted by djbluemax1 View Post

Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by djbluemax1 View Post

LOL, that was quick. I deleted my post a few seconds after posting when I zoomed in on the graph and realized I could 'just' see the impulse with the graph at full size.


BTW Jerry,

your Guide states the values for posting Spectrograms and mentions using the 'default values' for the graphs listing a db scale range of 99db for top and 59db for bottom. Could you double check this? In mine, the default appears to be 91db and 51db. Setting it to 99 and 59 removes all red from the graph with an 85db measurement. Are you guys measuring at 90-95db?



Max

I just clicked the "Apply Default Settings" button in REW, and it sets the 99 and 59 values.  I really didn't give this much thought.  Clearly, adjusting these values changes the way the spectrogram looks, but I'm not sure what the relationship between these values and the measurement level is.  Perhaps someone could explain it?
The spectrogram shows something similar to the waterfall except it does so using the colors as intensity.

If the top of the SPL scale is 99db and the measurement is at 85db, no part of the graph would show red (unless there's a significant peak). If the measurement SPL is not standardized though, the decay results on Spectrograms with the 99/59db settings differs. For instance, I looked at an 85db measurement with the 91/51db settings that resulted in REW. It showed red regions (like everyone's Spectro's) and decayed in about 350-375ms. Using the same measurement and setting it to 99/59db removed all the red and the decay below 30Hz was all under 300ms. Standardizing the scale requires standardizing the measurement levels to produce comparability in graphs.


Max

P.S.
Ah, I see, there's a setting in the Spectro Controls for "Match Top Of Scale To Peak". This setting is ON by default. When On, it matches the scale to the measured peak.
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I think I may have developed some significant decay improvements.


You haven't.


The top graphs have peaks @ 100dB and the bottom graphs only peak around 87dB. Adjust your bottom graphs to reveal an extra 13dB and the waterfalls will look all but identical!

Rather than looking at the waterfalls, I presume the spectrogram differences is what he was purporting. If the graphs posted relate to each waterfall (i.e. top waterfall goes with top spectrogram and so on), then the Sub EQ cuts appear to have had a nice impact on his bass decay above 30Hz:

Compare Peak EQ cuts:




With Sub EQ cuts:




Appears to be a noticeable improvement imho.

@jlpowell84: I've been meaning to ask you this for a while but would you mind using the "large" preview option when posting graphs? It makes it a lot easier to review your plots.
As you can see, one of these graphs has a scale to 100db, the other is to 96db, Stuart's last Spectro was 92db

Jerry,
I guess we can just leave it to REW with the 'Match Scale To Peak' setting ON, as the Spectro's in your last round of measurements testing the Scopus traps vary between 95db, 96 db and 97db since it's On by default and sets the scale automatically.
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post #6845 of 12042 Old 11-13-2013, 09:17 PM
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We need to get correct guidelines for spectrograms nailed down quickly.

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post #6846 of 12042 Old 11-13-2013, 10:00 PM
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Quote:
Originally Posted by AustinJerry View Post

We need to get correct guidelines for spectrograms nailed down quickly.
From all the Spectros posted so far, I think leaving REW to its default 'Match Scale To Peak' works quite well. It produces decent Spectros from measurements at different levels (considering people measure at different levels).

I tried measurements at 95db, but I don't think everyone wants to run measurements that high. I suppose if we could come to some kind of consensus on a calibrated measurement SPL (90db?), we could then set the scale accordingly.


Max
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post #6847 of 12042 Old 11-13-2013, 10:05 PM
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I don't think we will ever agree on a standard measurement level. So if what we have been using is good enough, I am in no hurry to change things. I just don't want some measurement troll challenging my graphs.
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post #6848 of 12042 Old 11-13-2013, 10:38 PM
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And I would certainly LOVE to have these parameters in big letters on my notepad so I can post graphs correctly smile.gif

I am going to run back through these posts today because my two spectrogram graphs above all I did is hit generate and take a snapshot. I'm sure I will discover why one was at 100db and the other 96db smile.gif
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post #6849 of 12042 Old 11-13-2013, 10:44 PM
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With match levels set as default, we only need to agree on the noise floor (scale range). But good luck with that, everyone has a different opinion on how far below max amplitude we should be worried about.

This provides a set of measurement standards, one of which is the noise floor for decay. It mentions -40dB (graph C1).
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post #6850 of 12042 Old 11-13-2013, 11:18 PM
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Quote:
Originally Posted by Alan P View Post

Direct center of chair seat at ear level...this is where I take all my measurements because it's where my head usually is. smile.gif

Good. Did you also measure single speakers? When measuring more than one speaker at the same time you'll get interference effects at higher frequencies. Everything else you see in your measurements is quite normal and the result of sound waves interacting with the room.
Did you read Jerry's guide?

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post #6851 of 12042 Old 11-13-2013, 11:39 PM
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So match scale to peak on spectro's then? Auto...
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post #6852 of 12042 Old 11-14-2013, 02:48 AM
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It looks like you're cutting off the initial impulse in your graphs


Max

Isn't the initial impulse at T=0? I know in usually have the left limit at -.03ms, but does it really make a difference?
LOL, that was quick. I deleted my post a few seconds after posting when I zoomed in on the graph and realized I could 'just' see the impulse with the graph at full size.

BTW Jerry,
your Guide states the values for posting Spectrograms and mentions using the 'default values' for the graphs listing a db scale range of 99db for top and 59db for bottom. Could you double check this? In mine, the default appears to be 91db and 51db. Setting it to 99 and 59 removes all red from the graph with an 85db measurement. Are you guys measuring at 90-95db?


Max

 

My defaults are the same as yours, Max.

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post #6853 of 12042 Old 11-14-2013, 02:50 AM
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LOL, that was quick. I deleted my post a few seconds after posting when I zoomed in on the graph and realized I could 'just' see the impulse with the graph at full size.

BTW Jerry,
your Guide states the values for posting Spectrograms and mentions using the 'default values' for the graphs listing a db scale range of 99db for top and 59db for bottom. Could you double check this? In mine, the default appears to be 91db and 51db. Setting it to 99 and 59 removes all red from the graph with an 85db measurement. Are you guys measuring at 90-95db?


Max

 

I just clicked the "Apply Default Settings" button in REW, and it sets the 99 and 59 values.  I really didn't give this much thought.  Clearly, adjusting these values changes the way the spectrogram looks, but I'm not sure what the relationship between these values and the measurement level is.  Perhaps someone could explain it?

 

When I click Apply Defaults it defaults to 91 and 51. I haven’t updated yet though to the latest version of REW on my Mac. Perhaps I should...

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post #6854 of 12042 Old 11-14-2013, 02:55 AM
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Originally Posted by AustinJerry View Post

I don't think we will ever agree on a standard measurement level. So if what we have been using is good enough, I am in no hurry to change things. I just don't want some measurement troll challenging my graphs.

 

Agreed. It will be impossible to get everyone to measure to an agreed level. I want to use 90dB, someone else wants to use 80dB etc... the REW defaults seem to work fine for most cases.

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post #6855 of 12042 Old 11-14-2013, 05:48 AM
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Originally Posted by Audionut11 View Post

With match levels set as default, we only need to agree on the noise floor (scale range). But good luck with that, everyone has a different opinion on how far below max amplitude we should be worried about.

This provides a set of measurement standards, one of which is the noise floor for decay. It mentions -40dB (graph C1).
A 40db range seems to be REW's default as well.

So REW's default settings of a 40db range and 'Match Scale To Peak' seem to provide decent graphs, but here's the kicker. As we've noticed, viewing the same graph with a different top and bottom range shows different decay, even with the same 40db range.

Doesn't that mean that graphs with significant peaks (raising the top end and thus, range of the scale) will produce different results than a more even graph without huge peaks?

Perhaps we can just request that folks always post a Waterfall with a Spectrogram? Although the Spectrogram 'appears' a little easier to read, it's the consistency of the results that I'm wondering about. At least with the waterfalls, as long as there's at least a 40db range from the top of the measurement (the mountain, not the window) to the bottom, we can see if it's running into the noise floor down low, and if the measurements should be redone at higher SPLs. The results though, are more consistently read.


Max
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post #6856 of 12042 Old 11-14-2013, 05:57 AM
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Jim, help me interpret what we are seeing here.  Any issues?



Is this smoothed in any way as it looks really good with a decay of 30dB within the first 1mS, very impressed? Something for me to aim for when I fix my floor reflections.

I look forward to reading Jim's comments.
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post #6857 of 12042 Old 11-14-2013, 06:07 AM
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post #6858 of 12042 Old 11-14-2013, 06:14 AM
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And I would certainly LOVE to have these parameters in big letters on my notepad so I can post graphs correctly smile.gif

I am going to run back through these posts today because my two spectrogram graphs above all I did is hit generate and take a snapshot. I'm sure I will discover why one was at 100db and the other 96db smile.gif

As we now understand, if you allow REW to set the scale based on the measurement's max level, the differences in your two spectrograms are explained by different measurement levels. As Max noted, REW applies -40dB to determine the lower limit. Measuring down 40dB has been mentioned as the guideline for waterfalls as well.

Unless someone has an issue, I think we now have an agreement on how to configure the spectrogram. I'll double-check the Guide to make sure the wording is clear.
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post #6859 of 12042 Old 11-14-2013, 06:27 AM
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No smoothing.

Wow! Having looked at your setup I am surprised that you appear to have no significant floor reflections. Either good design/layout or luck. smile.gif

What is your floor carpeted with?
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post #6860 of 12042 Old 11-14-2013, 06:38 AM
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Wow! Having looked at your setup I am surprised that you appear to have no significant floor reflections. Either good design/layout or luck. smile.gif

What is your floor carpeted with?

Typical wall-to-wall carpet with an enhanced pad. In the product literature for my PSB Synchrony One speakers, a point is made that Paul Barton designed the three-woofer array to minimize floor bounce. Perhaps it is working.

And, of course, some luck as well!
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post #6861 of 12042 Old 11-14-2013, 07:50 AM
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Typical wall-to-wall carpet with an enhanced pad. In the product literature for my PSB Synchrony One speakers, a point is made that Paul Barton designed the three-woofer array to minimize floor bounce. Perhaps it is working.

And, of course, some luck as well!

Design or luck it is working very well.
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post #6862 of 12042 Old 11-14-2013, 08:32 AM
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Quote:
Originally Posted by AustinJerry View Post

Jim, help me interpret what we are seeing here.  Any issues?



Lets briefly try to sum up what the first 2.5ms apply to:

Speaker diffraction
Floor bounce
Nearby objects (such as coffee tables and furniture)

And dont apply to:

Walls (too far away)
Ceiling (in most cases)


Whats interesting, among other things, at looking at the first 2.5ms is it bypasses the vast majority of your room treatment. What is good or bad in terms of the graph and its objectives I am no expert on. One reason I brought up the issue was I wanted to see what others are getting to improve my understanding. It would be nice if the first spike was 20db down, but I don't think that is realistic. But just looking at yours and mine, a -5db spike out at 1ms is probably not so great.

Lets keep in mind that 1ms represents only a 13.5" deviation from the direct response, so we are looking at very close reflections here.

Another angle to consider is under what conditions we are taking the measurement. In other words, are we sure the mic stand is not playing a part? The listening chair?

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Typical wall-to-wall carpet with an enhanced pad. In the product literature for my PSB Synchrony One speakers, a point is made that Paul Barton designed the three-woofer array to minimize floor bounce. Perhaps it is working.

And, of course, some luck as well!

Speaking of which....I have floor bounce issues - a 5 db or so 25 Hz or so extended trough in frequency response - with the Mythos, which sometimes occurs in the 150-250 Hz range. The dip is also documented in at least one review I've seen, where they suggested turning up the built-in bass trim < 100 Hz to compensate (something I don't do to keep the overall speaker level-matched).

Sometimes moving the speakers does enough to make the bounce small enough to tweak with the Audyssey Pro Curve Editor, but is there a specific treatment one can do with floorstanding speakers that might help in this range (e.g. something beyond standard wall to wall carpeting)? Or is strictly a matter of placement?

If this is OT to the REW/treatment accessing plots I'll post elsewhere..but since floor bounce was raised...

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post #6864 of 12042 Old 11-14-2013, 10:15 AM
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Speaking of which....I have floor bounce issues - a 5 db or so 25 Hz or so extended trough in frequency response - with the Mythos, which sometimes occurs in the 150-250 Hz range. The dip is also documented in at least one review I've seen, where they suggested turning up the built-in bass trim < 100 Hz to compensate (something I don't do to keep the overall speaker level-matched).

Sometimes moving the speakers does enough to make the bounce small enough to tweak with the Audyssey Pro Curve Editor, but is there a specific treatment one can do with floorstanding speakers that might help in this range (e.g. something beyond standard wall to wall carpeting)? Or is strictly a matter of placement?

If this is OT to the REW/treatment accessing plots I'll post elsewhere..but since floor bounce was raised...



The black curve (red = now) is where I once was and my null at 225hz was primarily a floor bounce issue. Honestly, this issue was one of the most troublesome and time consuming problems to fix of ALL my room issues. In my case, optimizing speaker placement alone wasn't enough to deal with it. IMO, thick carpet and pads dont do much in the 150-250hz range.

Since one cant usually put thick absorbers on the floor to deal with floor bounce, we have to be clever. Footstools with open bottoms that can be filled with absorbent is one trick. Blocking/redirecting the bounce with the right piece of furniture can be another (although you must be careful that such furniture doesnt create a new bounce of its own).

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post #6865 of 12042 Old 11-14-2013, 10:43 AM
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Jim, how did you identify the dip as a floor bounce issue?  Temporarily lay down a panel in front of the speaker?  If yes, then if I put an absorber on the floor in front of a speaker and don't see any difference in the ETC, can I assume I don't have a floor bounce issue?

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post #6866 of 12042 Old 11-14-2013, 10:51 AM
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Quote:
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Jim, how did you identify the dip as a floor bounce issue?  Temporarily lay down a panel in front of the speaker?  If yes, then if I put an absorber on the floor in front of a speaker and don't see any difference in the ETC, can I assume I don't have a floor bounce issue?

Yes.

For the ETC, I used slicing to see the difference more clearly although it did show on a full range ETC in my case.

Do you see a FR difference when you put a absorber in the floor bounce region? I did.

But as I sorta implied, my issue was primarily, but not exclusive to floor bounce. There are room mode and SBIR contributions as well.

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The black curve (red = now) is where I once was and my null at 225hz was primarily a floor bounce issue. Honestly, this issue was one of the most troublesome and time consuming problems to fix of ALL my room issues. In my case, optimizing speaker placement alone wasn't enough to deal with it. IMO, thick carpet and pads dont do much in the 150-250hz range.

Since one cant usually put thick absorbers on the floor to deal with floor bounce, we have to be clever. Footstools with open bottoms that can be filled with absorbent is one trick. Blocking/redirecting the bounce with the right piece of furniture can be another (although you must be careful that such furniture doesnt create a new bounce of its own).

On my charts, it looks like someone took a meaty bite out of the FR; depending on placement, that "bite" can shift in the region (and can sometimes vary by speaker), as well as the intensity (typically LT 10 db, but more than 2-3 db). My issue is that when I had my speaker further back toward the wall, the dip actually seemed a little better. But moving them out a bit to help with bass decay and even out imaging can make it worse. Sometime moving a few inches wider or narrow helps, since I'm probably getting some redirection from a dining room chair or the A/V case, but it's difficult to ID how to optimize without creating other issues. Although I know it's a last resort, if I can get in the neighborhood of the +/- 3 db adjustment I can do to individual speakers on the Audyssey Pro Target Editor, I'll be happy. Assuming that it works, of course, which it sometimes doesn't quite so well.

I may try the footstool/absorption route, if I can systematically ID where it's the worst.

Stuart

 

Denon 4311 with XT32 and Audyssey Pro

Oppo 93 and 103

Panasonic VT50

Sherwood R-972 with its version of the Trinnov Optimizer

MiniDSP 10x10 HD

PSB Imagine T2, Center, and Surrounds (as of 5/2014); HSU ULS-15 subs (2)

 

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post #6868 of 12042 Old 11-14-2013, 11:26 AM
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On my charts, it looks like someone took a meaty bite out of the FR; depending on placement, that "bite" can shift in the region (and can sometimes vary by speaker), as well as the intensity (typically LT 10 db, but more than 2-3 db). My issue is that when I had my speaker further back toward the wall, the dip actually seemed a little better. But moving them out a bit to help with bass decay and even out imaging can make it worse. Sometime moving a few inches wider or narrow helps, since I'm probably getting some redirection from a dining room chair or the A/V case, but it's difficult to ID how to optimize without creating other issues. Although I know it's a last resort, if I can get in the neighborhood of the +/- 3 db adjustment I can do to individual speakers on the Audyssey Pro Target Editor, I'll be happy. Assuming that it works, of course, which it sometimes doesn't quite so well.

I may try the footstool/absorption route, if I can systematically ID where it's the worst.

First, try to determine if absorption is the answer, or at least helps the issue.

You, like me, probably have several contributors, some helping, some hurting. I too got mild to moderate fluctuations in the null region as I moved either the speaker or the LP. And also like you, some things that made it better made other things worse. This is why it took me 7 months to get it basically to my liking.

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post #6869 of 12042 Old 11-14-2013, 11:39 AM
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Do you see a FR difference when you put a absorber in the floor bounce region? I did.

 

I'm just curious how much attenuation you've seen in your FR as a result of the various treatments you've applied?  AFAIK, nobody seems to have a complete set of measurements of their room (FR, waterfalls, ETC's, decay plots etc.) before and after treatments.  I've got a lot going on in my FR above the crossover and I'm wondering how much (if any) difference I should expect from 18-24" of pink fluffy on the front wall?  I seem to recall Jerry and Keith mentioning previously that they didn't see as much difference in their FR as a result of the treatments they added but when I look at the peak you were able to attenuate then I start to wonder what is reasonable to expect?

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post #6870 of 12042 Old 11-14-2013, 11:49 AM
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I'm just curious how much attenuation you've seen in your FR as a result of the various treatments you've applied?  AFAIK, nobody seems to have a complete set of measurements of their room (FR, waterfalls, ETC's, decay plots etc.) before and after treatments.  I've got a lot going on in my FR above the crossover and I'm wondering how much (if any) difference I should expect from 18-24" of pink fluffy on the front wall?  I seem to recall Jerry and Keith mentioning previously that they didn't see as much difference in their FR as a result of the treatments they added but when I look at the peak you were able to attenuate then I start to wonder what is reasonable to expect?

That is a huge and encompassing question.

If you click on the "my room" link on my signature, that is most significant documentation I can offer to what I have done and how it affected my measurement data. I don't think it would be fair or easy to recreate it all here in this thread.

In all fairness to Jerry and Keith, you get big differences when you apply big changes. 4" fiberglass with air gaps in 24" x 48" panels just isnt ever going to move things like 18"-24" of pink fluffy in a 72" x 96" panel will (my side panels). So ones expectations must be weighed according to what you are willing and able to put in place.



(1/24th oct smoothing)

This is my earliest FR measurement (green) vs now. This isnt quite fair because I had different speakers at that time as well. But my room was only sparsely treated in that green graph.

IMO, this is a dramatic difference, and shows that major changes are achievable.

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