Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 46

Quote:

Originally Posted by djbluemax1 

Keith, you're a good candidate for a membrane bass trap. Unlike resistive traps which require a depth of about 1/4 wavelength (several feet thick in the 20-30Hz region), membrane bass traps can be constructed so they're only inches thick, and they go flat against a wall. You can paint them or cover them with drapes or wall hangings etc.

Google membrane traps. They can be constructed using plywood as the membrane. I'm not sure you have room to try Helmholtz resonators.



Max

Thanks Max... I will google....

WRT to room for things, I am approaching the situation where there will be no space in the room for me. :) I could have the best sounding room that nobody can ever listen in... LOL. 

EDIT: cover them with drapes... now there is an idea. I currently have a window in back of the room. The window is recessed in the usual way and is covered with thick drapes ATM. I could stand a huge membrane trap on the window ledge and then simply pull the drapes shut. There is also a blind (permanently closed) on the window itself, so nobody would have to suffer the trauma of looking at the back of a membrane trap when sitting in the yard.... hmmmm.... 

Quote:

Originally Posted by kbarnes701 

 

Speculating here, but above 1kHz you don't need the absorption to be as effective do you, due to the very small wavelengths?  Isn't this why a 242 is effective at the higher end but nt as effective as a 244 at the lower end? I would welcome enlightenment as I am not even sure what the coefficient of absorption means (as is probably obvious).

The COA is simply a measure of how effective the trap is at a particular frequency, and is a useful measurement when comparing different solutions, either from the same manufacturer, or across different manufacturers.  Once we have identified the source of the unwanted reflections, and the frequency of the reflections, we will be able to make a more educated decision WRT which treatment is likely to be the most effective.

The GIK site probably has the same COA chart for the 242 treatments, but when I was searching for it, I couldn't find it.  If you happen to locate it, please share it here.

Quote:

Originally Posted by djbluemax1 

Keith, you're a good candidate for a membrane bass trap. Unlike resistive traps which require a depth of about 1/4 wavelength (several feet thick in the 20-30Hz region), membrane bass traps can be constructed so they're only inches thick, and they go flat against a wall. You can paint them or cover them with drapes or wall hangings etc.

Google membrane traps. They can be constructed using plywood as the membrane. I'm not sure you have room to try Helmholtz resonators.



Max

I believe the GIK Scopus trap falls into this category.  They have three models, each targeted for a specific low frequency range.  Trouble is, we don't know how many of the traps would be required to tame the problem.  Once again, my recommendation would be to share the measurement data with the GIK expert and seek his advice.

Quote:

Originally Posted by AustinJerry 

Quote:

Originally Posted by kbarnes701 

 

Speculating here, but above 1kHz you don't need the absorption to be as effective do you, due to the very small wavelengths?  Isn't this why a 242 is effective at the higher end but nt as effective as a 244 at the lower end? I would welcome enlightenment as I am not even sure what the coefficient of absorption means (as is probably obvious).

 

The COA is simply a measure of how effective the trap is at a particular frequency, and is a useful measurement when comparing different solutions, either from the same manufacturer, or across different manufacturers.  Once we have identified the source of the unwanted reflections, and the frequency of the reflections, we will be able to make a more educated decision WRT which treatment is likely to be the most effective.

 

The GIK site probably has the same COA chart for the 242 treatments, but when I was searching for it, I couldn't find it.  If you happen to locate it, please share it here.

OK - thanks Jerry. I am very doubtful that 244s on those doors will be acceptable whatever the tests reveal though ;)

Quote:

Originally Posted by AustinJerry 

Quote:

Originally Posted by djbluemax1 

Keith, you're a good candidate for a membrane bass trap. Unlike resistive traps which require a depth of about 1/4 wavelength (several feet thick in the 20-30Hz region), membrane bass traps can be constructed so they're only inches thick, and they go flat against a wall. You can paint them or cover them with drapes or wall hangings etc.

Google membrane traps. They can be constructed using plywood as the membrane. I'm not sure you have room to try Helmholtz resonators.



Max

 

I believe the GIK Scopus trap falls into this category.  They have three models, each targeted for a specific low frequency range.  Trouble is, we don't know how many of the traps would be required to tame the problem.  Once again, my recommendation would be to share the measurement data with the GIK expert and seek his advice.

Yes, this I will do once I am confident in my measuring technique. They already have a 3D model of my room so it will be east to check it against the measurement and make a recommendation.

TOW, when I measured my FL, FR and C yesterday I did it with Audyssey ON as I mentioned. Over the weekend I will be taking more measurements including with Audyssey OFF. Question - when measuring the front LCR alone (no subs) should I set the speakers to Large for the test? I am currently measuring them with the 100Hz XO I use for listening. Which is the correct procedure?

Quote:

Originally Posted by kbarnes701 

 

OK - thanks Jerry. I am very doubtful that 244s on those doors will be acceptable whatever the tests reveal though ;)

The GIK panels can be mounted on a tripod-like stand that you could move out of the way when not in use....

Quote:

Originally Posted by sdurani 

Quote:

Originally Posted by kbarnes701 

The paper is concerned with stereo reproduction which is the least of my concerns, my room being for movies only, and the room sizes they use are very different to my room, so I will need to be somewhat circumspect in my interpretation of the 'targets' - but I understand those caveats and am prepared to try to accommodate them.

While the paper does indeed deal with a single pair of speakers, I applied some of that thinking to each pair of speakers in my system (fronts, sides, rears). The paper also got me to pay more attention to left/right symmetry. Rather than addressing individual reflections, the paper makes a good case for using band limited and smoothed ETC measurements to improve left vs right consistency across speaker pairs. Once you start listening carefully, an unbalanced soundstage (and surround field) can become distracting.

Understood. Thanks again. I re-read the paper over a cup of coffee this afternoon and there is a lot of stuff in it that I found useful, even though I need to be aware of the differences in their room, their objectives and mine.

Quote:

Originally Posted by cuzed2 

Quote:

Originally Posted by AustinJerry 

I believe the GIK Scopus trap falls into this category.  They have three models, each targeted for a specific low frequency range.  Trouble is, we don't know how many of the traps would be required to tame the problem.  Once again, my recommendation would be to share the measurement data with the GIK expert and seek his advice.

Ethan Winner (REAL TRAPS) also has a discussion or "how to" on membrane traps.
I actually made one for my back wall.

Oooh - that sounds good. If mine were behind the drapes, I could get away with 'less than perfection' of construction, so I could probably get away with DIY. I shall look at Ethan's site now... thanks.

Quote:

Originally Posted by AustinJerry 

Quote:

Originally Posted by kbarnes701 

 

OK - thanks Jerry. I am very doubtful that 244s on those doors will be acceptable whatever the tests reveal though ;)

 

The GIK panels can be mounted on a tripod-like stand that you could move out of the way when not in use....

Good thinking Batman....

Quote:

Originally Posted by cuzed2 

Keith,

For some practical photos of my "panel/membrane trap" build; feel free to check my thread
http://www.avsforum.com/t/896895/cuzneddy-cinema-project-begins/1320
Begins with post 1350 (pg45), and ends about post 1375 with some before/after REW graphs...

Excellent - thanks. I am heading over there right now.

Quote:

Originally Posted by kbarnes701 

TOW, when I measured my FL, FR and C yesterday I did it with Audyssey ON as I mentioned. Over the weekend I will be taking more measurements including with Audyssey OFF. Question - when measuring the front LCR alone (no subs) should I set the speakers to Large for the test? I am currently measuring them with the 100Hz XO I use for listening. Which is the correct procedure?

Great question!  I never even thought of setting them to Large.  I'm very interested to hear everyone's take on this as I'm really in the weeds at the moment reading other threads about waterfalls and ETC's...probably should just wait for Jason to report back in as there seems to be a lot of opinions out there on "best practices"!

Quote:

Originally Posted by jkasanic 

Quote:

Originally Posted by kbarnes701 

TOW, when I measured my FL, FR and C yesterday I did it with Audyssey ON as I mentioned. Over the weekend I will be taking more measurements including with Audyssey OFF. Question - when measuring the front LCR alone (no subs) should I set the speakers to Large for the test? I am currently measuring them with the 100Hz XO I use for listening. Which is the correct procedure?

 

Great question!  I never even thought of setting them to Large.  I'm very interested to hear everyone's take on this as I'm really in the weeds at the moment reading other threads about waterfalls and ETC's...probably should just wait for Jason to report back in as there seems to be a lot of opinions out there on "best practices"!

I don't think there is a right or wrong answer to Keith's question.  As with all REW measurements, it depends on what your objective is, and how you interpret the results.

So, for example, if you are measuring to determine early reflections (i.e. for ETC graphs), then you want to isolate each speaker, and have the subs off.  Similarly, if you are trying to measure whether a speaker is placed properly, you would isolate that speaker for measurement.

But, if you are looking for overall bass response, you would probably measure L+R+Sub(s).  Measuring just one speaker+sub(s) provides less important information, IMO.

Edit:  No that I have re-read your post, Keith, I see the question is Large vs. Small.   IMO, you would run the measurements exactly as you would normally run the speaker, i.e. Small with 100Hz crossover.  ICBW, BTWID.

Quote:

Originally Posted by AustinJerry 

Edit:  No that I have re-read your post, Keith, I see the question is Large vs. Small.   IMO, you would run the measurements exactly as you would normally run the speaker, i.e. Small with 100Hz crossover.  ICBW, BTWID.

Quote:

Originally Posted by IgorZep 

Quote:

Originally Posted by kbarnes701 

Over the weekend I will be taking more measurements including with Audyssey OFF. Question - when measuring the front LCR alone (no subs) should I set the speakers to Large for the test? I am currently measuring them with the 100Hz XO I use for listening. Which is the correct procedure?

As Jerry said, there is no definitive right or wrong answer and all depends on what you want to achieve or learn from the measurements. If you are measuring individual speaker with Audyssey OFF then you probably want to learn the whole range of the speaker output, so, you can choose the best speaker location, probably for direct or pure audio listening modes, or to make less work to Audyssey, etc. For all this it would be good to measure it full range as Large (or just choose Pure Audio) with no XO. If you want to learn how the speaker interacts with subwoofer with bass management enabled - you would measure with XO set as you are using it for listening. Usually you start with no XO, and learn/understand/solve individual speaker problems and then come to the configuration closer to your real listening. But it can well be the reverse, depends on what is more important to you at the moment and how deep you are ready to go.

Thanks Igor, Jerry. That all makes sense to me.

If anyone else normally uses a Mac, I can confirm that Beta 13 seems to work as expected with OS-X. I installed it on my desktop Mac today and it is very easy to configure the Mac to work with it. I cannot make any measurements from the desktop Mac (different room) but I have loaded yesterday's .mdat file and it translates properly to OS-X, also as expected. I will continue to use Windows to take the measurements because my Mac laptop does not have HDMI. But I will view and manipulate the .mdat graphs on my desktop Mac from now on as I find it much better having 2 or 3 times the screen real estate.  I rigorously compared all the graphs on the Mac with the graphs displayed on the Windows laptop and they are all identical in every way (also as expected). If my Mac laptop had HDMI I would be confident using it for measuring too. 

WRT to my post earlier about ringing noticeable in the waterfall at 20-30Hz, I mentioned this in the Submersive thread and member Bill Fitzmaurice made what I thought was a very salient point:

"You may be a victim of Graphitis Nervosa: You see it on a graph and then endlessly kvetch about it, even though it's exceedingly unlikely you can actually hear it. Ringing at 80-100Hz, very audible. Ringing at 20Hz... hey, you can barely hear the first impulse at 20Hz, let alone any ringing. And, shy of the above mentioned method, not likely you can do anything about it."

The point about 20Hz being near inaudible anyway had, up to this point, escaped me. I think he is right on the money with the Graphitis Nervosa remark, in my case ;)

Quote:

Originally Posted by kbarnes701 

WRT to my post earlier about ringing noticeable in the waterfall at 20-30Hz, I mentioned this in the Submersive thread and member Bill Fitzmaurice made what I thought was a very salient point:

 

"You may be a victim of Graphitis Nervosa: You see it on a graph and then endlessly kvetch about it, even though it's exceedingly unlikely you can actually hear it. Ringing at 80-100Hz, very audible. Ringing at 20Hz... hey, you can barely hear the first impulse at 20Hz, let alone any ringing. And, shy of the above mentioned method, not likely you can do anything about it."

 

The point about 20Hz being near inaudible anyway had, up to this point, escaped me. I think he is right on the money with the Graphitis Nervosa remark, in my case ;)

Top o' the morning, Keith!  There is a lot of wisdom in that quote.  On occasion, I have been known to relax for a moment and notice how really nice my system sounds, regardless of that 5dB dip around 90Hz.  Moments like that are priceless and make it all worthwhile!

Quote:

Originally Posted by AustinJerry 

Quote:

Originally Posted by kbarnes701 

WRT to my post earlier about ringing noticeable in the waterfall at 20-30Hz, I mentioned this in the Submersive thread and member Bill Fitzmaurice made what I thought was a very salient point:

 

"You may be a victim of Graphitis Nervosa: You see it on a graph and then endlessly kvetch about it, even though it's exceedingly unlikely you can actually hear it. Ringing at 80-100Hz, very audible. Ringing at 20Hz... hey, you can barely hear the first impulse at 20Hz, let alone any ringing. And, shy of the above mentioned method, not likely you can do anything about it."

 

The point about 20Hz being near inaudible anyway had, up to this point, escaped me. I think he is right on the money with the Graphitis Nervosa remark, in my case ;)

 

Top o' the morning, Keith!  There is a lot of wisdom in that quote.  On occasion, I have been known to relax for a moment and notice how really nice my system sounds, regardless of that 5dB dip around 90Hz.  Moments like that are priceless and make it all worthwhile!

G'day to you too, Jerry. Yes, I am fretting less about that very low frequency ringing as seen on my waterfall since contemplating Bill's answer. I don't know why it didn’t occur to me - 20Hz is getting close to inaudible at all but the highest SPLs - so when it is 40dB down....

I ran a full set of measurements today with Audyssey on and off, with my Subs in Pgm1 and Pgm2 (the latter applies a 3dB boost from about 40Hz down), with my trims as set by Audyssey and as set by me (3dB hot). About 24 measurements in all I think.

What is interesting wrt to the bass end is the difference between these 4 states:

1. Audyssey on, Pgm1 engaged, 'flat' bass trims
2. Audyssey on, Pgm 1 engaged, trims 3dB hot
3. Audyssey on, Pgm 2 engaged, 'flat' bass trims
4. Audyssey on, Pgm 2 engaged, trims 3dB hot

I will post the waterfalls shortly, but I want to do some more work on a couple of things first. What is interesting is that the ringing at 20-30Hz shows significantly less, as you might expect, with Pgm1 engaged, 'flat' trims. Less energy to start with equals less overhanging energy to get rid off. Of the 4 combinations above, I have decided ATM to use No 2. This is the best compromise as seen from the waterfalls. I had been using No 4, but I have long since suspected that, in my room, it is just a bit too much, and I had to turn off Dynamic EQ to make it acceptable. I am now using No 2 with DEQ ON again. I may, over the course of listening for a few days, reduce the trims to 'Audyssey flat' and see if I am happy with what will then be No 1 above.

It is very interesting to see the waterfalls graphing it like this - and REW is a total delight to use. I am still bowled over by the way I can take a single series of measurements and then examine the data in so many different ways.

Next week, I am going to buy some pink fluffy stuff to use as temporary absorption to see if I can improve the ETCs I posted the other day. If so, then I will be ordering a few GIK 242s for use on the side wall and where the double doors are (using your idea of having them on stands there). I am now not all that convinced I need a pair of 244s on the back wall, behind the drapes) as I doubt they will help with the bass ringing, and given that I have improved that by tweakery anyway.

I looked at the GIK Scopus (membrane) traps but the best they do offers good absorption centred at 40Hz, and I don't really have an issue at 40Hz - they won't really do much for 20-30Hz. 

I'll buy a roll of pink fluffy stuff, and then when I have done experimenting with it, it can go down in the attic to add to the insulation already there - waste no, want not ;)

Oh yes, final thoughts from the latest measurements. I am not seeing as flat a response as I was seeing from my OM measurements. Initially I believed I was but I was not comparing like with like exactly.

Here is the graph at 1/6th smoothing:

I am not disappointed with it especially - if we ignore the deliberate mid-range compensation dip, it doesn’t look too bad. This is Pgm1 on the SubM with Audyssey on of course, hence the roll-off in the upper treble (movie curve). That dip centred at 77Hz is a stubborn dip that I have been wrestling with for some time without much success. I may attempt some more distance tweakery or attempt to flatten it somewhat with the Pro Target Curve Editor. Pulling it up 3dB should help a lot.  Might be easier to pull down the peak that precedes it. Currently my Pro setup is not applying any TCE edits that I have made. Or a bit of both of course. Another job for next week. If I could do that then it would be pretty flat and then it may sound better with the subs a little hot, or even with Pgm2 engaged.

This is essentially the same graph but with the subs 3dB hot in the trims:

Just for interest, this is the same graph as above but showing the impact of switching the SubMs to Pgm2:

^ I am not surprised that the frequency response graph looks somewhat different in REW than in OM.  But, as you say, it is still a good looking curve, with the exception of some work needing to be done around 75Hz.  I don't recall, did you plug your room dimensions into the Standing Wave Calculator to see exactly where the room modes are?  Recall that there is some freedom in the lateral placement of your left and right speakers across the front wall (as far as I can see in the picture you provided).  You might be able to move those speakers into a null to alleviate the 75Hz dip (just thinking out loud).

I'm playing around later today with ETC, based on the guidelines in Nyal Melor's Acoustic Measuring Standards white paper, which I found quite interesting.

Quote:

Originally Posted by AustinJerry 

^ I am not surprised that the frequency response graph looks somewhat different in REW than in OM.  

Is that because of the difference between the mics or something else?

Yes, that is a pesky little devil, proving very stubborn to being moved. Hehe - sounds like my terrier. I will try using the TCE as described. IIRC I had some success with rthat before but currently the TCE adjustments are not loaded in Pro (I forget why).

I didn't try the SWC yet, but it is on my list. The photo is deceptive - the lens is so wide (16mm) that it 'stretches' the room, so what looks like a 3ft gap is actually less than a foot. There may be some small latitude there though - I will investigate - thanks.

Yes, me too. One has to remember the caveats - that the paper is essentially for stereo systems, but it does have a lot of good stuff in it IMO. And it also has 'targets' which, personally, I find very helpful.

Quote:

Originally Posted by kbarnes701 

Quote:

Originally Posted by AustinJerry 

^ I am not surprised that the frequency response graph looks somewhat different in REW than in OM.  

 

Is that because of the difference between the mics or something else?

 

 

 

I guess my question is, are the OM and REW frequency response curves actually different, or do they just look different because of variances in the vertical scale, smoothing, etc.?  If there are actual differences, e.g. the dip at 75Hz is deeper, then it must be a difference in the microphones.  The UMM-6 has the custom calibration file, which could account for some difference.  And, of course, there is always the variability between measurements.  I could set up REW and measure something today that I measured earlier in the week, and the measurements will look slightly different--call it my variability as a measurer.

Quote:

Originally Posted by AustinJerry 

Quote:

Originally Posted by kbarnes701 

Quote:

Originally Posted by AustinJerry 

^ I am not surprised that the frequency response graph looks somewhat different in REW than in OM.  

 

Is that because of the difference between the mics or something else?

 

 

 

 

I guess my question is, are the OM and REW frequency response curves actually different, or do they just look different because of variances in the vertical scale, smoothing, etc.?  If there are actual differences, e.g. the dip at 75Hz is deeper, then it must be a difference in the microphones.  The UMM-6 has the custom calibration file, which could account for some difference.  And, of course, there is always the variability between measurements.  I could set up REW and measure something today that I measured earlier in the week, and the measurements will look slightly different--call it my variability as a measurer.

Ah right, OK... the graphs aren't all that easy to compare in fact - the OM graphs are more 'compressed' vertically even when using the same 5dB resolution, so yes, they do look different. I will try to dig out an old OM graph with 1/24th smoothing that shows the same thing as a REW graph and compare them side by side. I'm not at all concerned - REW is about 1000 times better than OM IMO and I am a very happy bunny since this thread set me on the right path.

(I'd be even happier if Jason came back.... you there, J??)

Remember, just cause the lines look different, it's still the same room and the same equipment that has sounded so good to you.  Don't let the graphs fool you into thinking your system took a turn for the worse overnight!