Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 60

 

LOL - thanks Jerry. It's good to hear all that. Yes, I did redo the sub distances. The sound is just awesome. Better than anyone I know (here in the UK) has and better than, I’d guess, 99% of everyone on the planet.

 

But do have a play with the REW EQ tab - the potential there is just awesomely awesome. Legendary even ;)

 

Treatment come in every colour you can imagine. Jerry and I favour GIK - check out their website for all sorts of useful info. Realtraps look good too but are more expensive. Start with the corners - that's where you can make really big differences. Then, gradually, over time, sneak some more in once Mrs Stuart has gotten used to the corner ones.... ;)

Here is my recent tale of frustration.  My current sub layout (4xULS-15's), is to have two subs on the front wall at the 1/4 and 3/4 marks, and two subs next to eachother on the back wall at the 1/2 mark (and only 2 feet behind the MLP).

 

I decided that I might get better response by relocating the two rear subs to spots on the side walls, across from eachother.  I spent the better part of a day relocating the subs, hiding the cables, running a fresh sub gain match, running a fresh Pro calibration, and then taking the REW measurements.  The results were terrible.  Exhausted and discouraged, I went to bed.  Didn't sleep well, and got up at 6am to back out the changes and return the subs to their original spots.  I wasted at least 10-12 hours for absolutely nothing.

 

So, I made a promise to myself.  What I have now is probably about as good as it is going to get in my present room, and I won't ever try moving the subs again!

 

So, where am I today?  Here are the measurements:

 

Left, Right, Center Audyssey on

 

 

Low frequencies:

 

 

 

Reflections:

 

 

As you can see, each graph shows that there is room for improvement.  But am done for now, because IMO I have reached the point of diminishing returns.

 

I agree with Keith.  GIK products are reasonably priced, and they have a good reputation in the audio industry.  I believe I mentioned earlier that I went to their web site and clicked on a link requesting guidance from their consulting staff.  I sent some pictures along with the REW measurements, and had a very useful dialog with Brian Pape, their lead consultant.

 

Please confirm what I am looking at.  Is the left speaker measurement with the speaker set to "small"?  If yes, then it includes the subwoofer as well, which is fine.  However, the left speaker response is showing a steep roll-off below 100Hz, yet the sub is relatively flat below 100Hz.  Maybe the left speaker is set to "large"?

 

Are these measurements after an Audyssey calibration?

 

A separate measurement of the sub is OK, but it is usually done when looking for the best spot to place the sub.  If you are interested in overall bass response, then the combined measurement of sub+main provides the most useful picture.

 

The average of the measurements is not useful.  More useful would be a measurement of the left+right+sub, all playing at the same time (left and right set to small, of course), from 15-20,000Hz.  An average is usually used when you measure the same speaker over several measurment locations.

 

I did exactly the same. Brian was very helpful.

Jerry,

Thanks. The speaker is set to "small" but I will check it again tonight; there's a known bug with the player I have defaulting to stereo mode and cancelling the sub output. I will make sure this is not happening. In any case, go ahead and scrap the measurement. I will make new measurements with the information you just gave me. (I actually tested each speaker earlier today and it took several hours. I'm very happy I don't have to do this and that I didn't post).

I don't have Audyssyey or any other room correcton installed in my system, except Anti-Mode for the sub, which I will put in bypass mode when I make the measurements. I do have an AVR with YPAO that I'm not using, which might be helpful later.

I have HDMI with 5.1 output. How do I configure REW to play Left/Right at the same time?

Edit: found answer in post 132
Edited by Pres2play - 3/3/13 at 11:49pm

Sorry, I keep forgetting that you have a somewhat unconventional setup.  Looking forward to seeming the new measurements.

Anyone in San Jose,CA have REW and wouldn't mine showing me how everything works before I buy all the stuff thanks.

Jerry, the above instructions in post 2 recommends testing L and R speakers separately. Perhaps this pertains to ETC test only?

 

I sympathise with you on that Jerry. It is incredibly frustrating to spend all that time for no worthwhile result. BTDT.  I think your conclusion is the right one - at some point, unless we have a large, dedicated room with numerous placement options etc, we have to accept that we have done the best we can. I am also at or very close to that stage.  Unless I decide to try the Parametric EQ route ;)  Just play with the EQ in REW and see!  Cheap to try - the Behringer is very inexpensive. But  would need someone like Jason to hold my hand through the learning curve, so...

 

I'm not sure what Jason meant by that advice.  However, my thinking is like this:  when you are sitting in your MLP and hearing bass frequencies, you are listening to the combined contribution of all of your speakers plus the subs.  So it makes sense to me, when assessing bass response, to start out measuring left+right+subs with the AVR in stereo mode.  (Since the surrounds are not likely to add a significant contribution, ommitting them doesn't skew the results that much.)  Center+subs is also a useful measurment.

 

There is nothing wrong with measuring individual speakers, like left+subs, but IMO this measurment is used to understand how each speaker contributes to the overall response.  Measuring the combined response still tells the full story.

 

Your opinion may differ.

+1. Ultimately we don't listen to left+subs, or right+subs, but a sound stage. As long as the L/R are more or less tracking similar FR patterns in a basic FR test, and one is happy with the imaging, I don't see the point in focusing on individual speakers only. Subs only are an exception, for placement purposes, if you've got placement flexibility.

Note that for us 8-channel HDMI users, selecting Left and Right speakers (channels 1 & 2), and selecting the appropriate option for "Multi CH In", gets us to the same place as Stereo, for two-channel listening. At least I hope so after what I went through on Saturday .

Stuart et all,

Maybe it was Jason or I read it somewhere else, but here goes.

Measure L + sub and R + sub separately and overlay the two graphs. See if the two curves are within +/- 2 dB to each other throughout the whole frequency range. If not there might be some timbre-matching issues and it's time for a little troubleshooting with the help of changing speaker placement. Does this make sense?

Keith - I just remote logged into my home laptop and regenerated the Waterfall. Same post-Audyssey data source, same 600 ms and default waterfall setting of 1/48 smoothing, except that I reset my range from the previous 40 to 90 db, to 50 to 100 db, and regenerated the plot. That assumes that the approximately 55 db reading I got, after calibrating to 80 db the UMM-6 mic+REW with the Radio Shack SPL meter, is accurate in determining my room's noise floor (I think it was actually about 57 db, but regardless it's compatible with other settings we've seen for the USB mics).

Does this look right? It certainly looks 'better', doesn't it? I mean, I can't be "done", can I?


Edited by sdrucker - 3/4/13 at 4:17pm

That was Jason, in his post #2 on the first page of the thread.

Whether we agree collectively that there's a need for separate speaker measurement AFTER any test of timbre, FR, or image matching is a judgment call. YMMV IOW.
Edited by sdrucker - 3/4/13 at 11:42am

 

Yes - that is why it is important to measure LF and RF separately - purely for evaluation of how they correspond to each other. While it is true we never listen to just LF+Sub or RF+ Sub, how RF and LF work individually is important for the system imaging, for how reflections are caused and dealt with etc. I think measuring LF+Sub, RF+Sub and C+Sub are important measurements and only take a few moments to take anyway. Stuart makes these points of course in his post above. There is additional info relevant to this, IIRC,  in Nyall Mellor's paper, linked to in this thread somewhere. 

 

The serious ringing is all below 20Hz. Even there, you are 30 or more dB down. As it is all but impossible to hear the initial impulse at 20Hz, even at 85dB, I'd say it was unlikely you'd hear much of the ringing, at 30-35dB lower. Also, be aware that you cannot control this with treatments - it is too low in frequency and would need treatments several feet thick. So you can buy some more subs and try to control the room with that, and/or you can experiment with room placement of the subs to see if you can minimise those modal interactions that way. Or you can say "if I can't bloody well hear the problem, I can just ignore it". Depends on how developed your OCD is :)  

 

I doubt if you're 'done' yet :)  I think you can only achieve 'done' status when you have wasted an entire weekend, as Jerry and I have recently ;)  And even then, it is questionable how long 'done' lasts in the real world. I suspect it lasts 'until the next time'. 

 

BTW, although I am sounding like some kind of expert in this post, it is all an illusion, so I wouldn’t take much notice of what I say unless it is corroborated by a genuinely credible source, such as Sanjay. What we need is for someone who is a real expert to start a thread.... oh... er... right... ;)

Hey, there are people that think I'm some sort of expert on the Mythos ST with Audyssey, so I know where you're coming from . Being an articulate voice of one (or two) will get you pseudo-guru status, at least until Feri dispels your illusion .

After reading all the follies you've engaged yourself in, I have a hard time imagining I'm "done" with the room or my speaker/MLP configuration room either.

But what you're saying is my naive interpretation too...if the noise floor measurement is accurate, unless I want to go chasing < 20 Hz issues and get ridiculously thick (and not acceptable to WAF LOL) treatments, and I can't go the Jerry route of moving subs to odd side wall places of my room due to the logistics (i.e. moving a piano and putting cable under carpets), that's it for the moment except for "minor" tweaks to my crossover splice, or some hammering of some peaks with the Curve Editor. Although I suppose I can move onto ETC and do string tests .....

OTOH, look on the bright side. I'll eventually add front heights, and it's very likely we'll have to move the MLP closer to the center of the room to fit the crib (the joys of condo living)*, and at any rate, within a year or so we're moving to a bigger place. Then the fun starts all over again!

* I've been bugging my wife to get rid of the glass living room table and allow me to move the sofa/MLP into the center of the room for a while (and concurrently improve the viewing distance to 55" VT50 as well optimize surrounds better), so the new baby is an excuse/catalyst. However, then I might be facing more room nulls as I move away from near-field sub placement. I suppose I can do a pre-Audyssey L/R+sub and Center/sub run in the "proposed" MLP to see if it creates a whole new set of issues. Alternate crib placement is on the side of the living room, but that's less than optimal unless we add thermal windows to the living room. Good thing we have about six months to worry about this...

** Jason's been MIA for five weeks by my count.....I think we've been orphaned....fortunately we're 'learning by example', in large part due to you & Jerry, with some chiming in from the likes of Sanjay and at least one "devil's advocate"...you know whom you are.....
Edited by sdrucker - 3/4/13 at 12:20pm

Hey, changing the lower limit to 50Hz does make a difference:

 

 

This one almost looks respectable.  Of course, changing the lower limit didn't actually affect the sound, it just made me think it's better...

 

As far as being "done", I certainly am toast right about now.

@ Stuart,

 

"Crib reflections" can be serious!  You need treatments.

LOL!

I can just see hanging blue or pink colored bass traps or absorption material on the crib...somehow Lisa might go for that!

But in all seriousness, the side placement would be out of the listening angle from the mains....at least no worse than the 30" or so tall A/V rack, or the old TV stand I moved next to it for having more DVD & BluRay storage.

It's either the living room or our 15-year-old gets a roommate in the short term. That's city living for you until we move....
Edited by sdrucker - 3/4/13 at 12:37pm

Hey Jerry, why not move on to spectrograms? Waterfalls are becoming boring, spectrograms look nice and colorful. And they show what is going on from an "aerial" view before and after the sweep and everything in between. No wonder JohnM's avatar is a spectrogram and not a waterfall.

Have had no such intentions, ever. LOL We're just talkin' here, eh?!...

Well, finally, here are a couple of graphs. Please refer to drawing for microphone positioning. Looks like you were right again, Jerry. The best listening spot (or least offensive) appears to be position 4, which is about 2.5 feet from the back wall. This is all with no eq and Anti-Mode in bypass.




position 1 (red) vs 4 (blue)


position 2 (green) vs 4 (blue)


position 3 (purple) vs 4 (blue)

 

I'm game, Feri.  Here is a first attempt:

 

 

Since I know nothing about these, are the axes set proprely?  What does the graph tell us?  Is there a link that explains spectrographs?

 

I would get a stool and sit there for serious listening! 

Thanks Jerry, looks nice, eh? Well, actually a spectrogram is another 3D graph where the x-axis is frequency, the y-axis is time, and the z-axis is amplitude - which can not be presented on a 2D graph - so its substituded by color codes.

It shows from bottom to top how the sweep signal "builds-up" (look for the negative milliseconds) till it reaches 0 (the peak amplitude of the sweep) and the most important part is above 0, that is the decay time vs. frequency plot shown with different colors. The "color legend' is the vertical color bar on the right side, the more red the higher the amplitude (93 dB in your case), the more blue the less (53 dB in your case).

On your spectrogram we can see you've got the longest decay time at 60 Hz and again below 20 Hz.

There must be some more explanations in REW Help files, I suppose.

To Stuart's point about disappearing down the never-ending rabbit hole. In an attempt to understand more of the problem I recently mentioned in my post to Jerry, tomorrow I am doing the following measurements:

 

 

 

 

That's 54 separate measurements. The objective is to try to learn more about what is happening at the XO splice with different variables - one with my Submersives in Pgm 1, another with them in Pgm 2, another with the subs 'flat' as set by Audyssey, another with the subs 3dB 'hot' as I used to run them and so on. And all with Audyssey on and off so I can see what impact Audyssey is having. I may be gone some time :)

Edited by kbarnes701 - 3/4/13 at 1:41pm

Actually it's our second; Our first is now 15. Long story about the "why" part, but it ultimately came down to "now or never", for both biological and practical family reasons (and also, not wanting to leave our son as an "island" unto himself down the road). But yes, I think you're right that it does change your life. The irony is for the longest time, we'd planned on only being a one child family, but sometimes your priorities change where you rethink. Call it another version of "mid-life crisis" ...even if it's not the norm to go from thinking about empty nesting to rebooting to our mid-30s:).

I must be one of the few people that would use family expansion as a direct excuse for improving a HT room . So maybe I won't completely forget about the 20 Hz LOL:D At least until mid-September (current due date)...