Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 35

 

I have done extensive measurements in my listening room, without Audyssey, with a "standard" Audyssey calibration, and with a Pro Audyssey calibration.  In every case, the measurements for the calibrated environment show significant improvements over the non-calibrated environment.  The differences between the "standard" and the Pro calibrations have been subtle.

Can you measure any one of your front speakers from more than one listening position (e.g., left, middle, right seats on your couch) with Audyssey OFF? It would be interesting to find out why Audyssey isn't correcting the dip (maybe it doesn't see it in other locations and doesn't want to boost a dip at the MLP only to create peaks in other seats).

Question regarding using the Audyssey Pro mic, for REW measurements and to pre=install locate an in ceiling sub. Since I have the Pro kit and the calibration file, does the former work as well as any other mic, listed in the thread, or is there a limit on the low end? Regarding the later, any advice on placing a sub-say 14"Velo in the MLP and putting the Audyssey or other mic on a boom pole, then measuring along the 15 foot high ceiling, to locate the best install site , for the 250lb. Wisdom STS sub. Any other ideas on methodology to easily locate the best in ceiling sub location. Volume of the room is huge.

Thank you very much
Fury

 

Sure, this would be relatively easy to do, now that we have streamlined REW kits.  I will post them as soon as I have them.

 

I have the Pro kit as well, but have never tried to use its microphone with REW.  The mic needs phantom power.  Have you tried plugging the Audyssey mic amp into REW to see if it works?  And then there is the case of a missing calibration file, which would make the measurements suspect.  It sounds like you can't afford a false installation, so if you are going to trust REW for such a critical placement, I would purchase a USB mic that is known to produce good results.

 

Just curious, why the ceiling location?  Do you have reports from others who have had successful results with this unusual placement?  I did a quick search on "sub in ceiling" and got quite a few hits, so I guess you have company.  Very interesting.

Too bad. There are a lot of these microphones out there. And this is the one I could use to start practicing with REW for free (and I am not alone with this...).

I just ran through that a few minutes ago. It didn't really tell me anything I couldn't figure out myself but it gave me a good template for publishing graphs. It's was a good idea to establish some guidelines about this.
Reading some post here helped me to identify/understand my ASIO problem/misunderstanding (I don't know if your PDF could help with that or not, we won't know but it doesn't matter now).


I think I see a workaround here:

Connect the USB mic to a PC, apply the calibration in real-time with a PC software, output the corrected signal from the PC to the V.AUX L input on the AVR (where calibrated microphones meant to be connected on my AVR, but this could vary from AVR to AVR and may not available at all on some...).

But I assumed that the digital (optical) V.AUX is also acceptable. If we are limited to the analog V.AUX L then we need a calibration for our DAC (analog PC output). And I guess that's the case since that optical input also has Optical 4 label despite it's located in the "V.AUX" block.

And I don't know about such a software but I guess REW could easily expanded with support for this.

---

Anyway...
Here is the result of my first REW trial with an uncalibrated Audyssey mic (so, ignore the absolute sound pressure level, the AVR's Master Volume was set to 0db and REW was set to -15db, the noise floor was low).


Edited by janos666 - 2/5/13 at 11:59am

Hi janos666, I don't think you really need a precision calibrated mic just to practice with REW. Now that you have successfully set up your gear with HDMI and 8 channel support just plug in your Audyssey mic "as is" and start to play. Why not? smile.gif

Hi Jerry,

Thanks for the reply. The ONLY reason that the in ceiling location is required is, She, who must be obeyed. Now, this a living/Great room, untreated and there is plenty of attic space for the 5X3X1.5 foot sub. The thing is 103db efficient and can handle 5K watts, per manufacturer. I lament the loss of my treated meridian suite, but I must say that the Wisdom Sage L75i's and the sc-1, quickly setup and the Oppo105 Analogs are an amazing system, in that context, especially. U R right, can't cut 20X15inch ceiling holes, let alone move the sub across joists to get the best location. Any advice on selection of best placement, in this application?

Thank you very much

Fury

I have and it works fine. It has too much gain however so you need to dial it down on the mic input of the PC.
For low frequency and overall analysis is actually fine.
We have subs in the ceiling of our theater. It will allow you to have a sub "in the middle of the room" so to say. Here is a construction shot of a pair of them:



If you had to put them on the floor they would be right in front of the door which obviously is not practical. This is especially useful if you use Fluid Dynamics modelling (see the last section in this article: http://www.madronadigital.com/Library/BassOptimization.html) as you give many possibilities to the optimization path to find the optimal number and position of subs.

@srgtfury and Amirm,

 

Very interesting information on the ceiling sub placement.  However, it certainly poses some interesting challenges with respect to finding the right placement.  Conducting a "sub crawl" across the ceiling would be a real project!  

Thanks Jerry. Yeah, according to the REW Help file we are good to go between -12 and -30 dB. The only case that comes to mind is when we are going to look into how Audyssey's DynamicEQ peforms, probably best done with the MV on the AVR set to 0 dB (no effect of DEQ) and then decrease it by increments allowing REW to draw the relevant graphs. Just thinkin' out loud! Whaddaya think?

 

Agreed.

Actually thought about taking the 14" Velo and down-firing and suspended a few to five feet above floor level, bridged across a couple of ladders and moving the rig around the area. Not sure if that or using a mic on a boom pole is a better/good idea. Any advice?

Hi Amirm, cool setup. was your, measured result, what the calcs., predicted, as regards the in-ceiling installation portion of the project?

Thank you very much

Fury

I did. I already editied the post you quoted from to attach some waterfall graphs from my fist REW measurements.

My current point on the learning curve is that I understand what the graphs present but I have no idea what would be the optimal solution for the problem.

And it's very strange that I can see something at 20Hz with middle sized floor standing speekers. They emit something which I guess isn't really a 20Hz sinus wave but it's audible too.

Janos,

 

i couldn't tell very much from the Waterfall graphs.  A waterfall is used normally to represent resonances at low frequencies, so a waterfall that extends all the way to 20kHz is essentially meaningless.  Also, the area of interest in the waterfall is where the resonances decay into the noise floor.  It is difficult to understand from your graphs where the noise floor is, which is usually around 40dB in a quiet listening room.

 

It would be more useful if you could post several frequency response graphs for us to look at, say one from 20-20,000Hz with 1/6 smoothing, and one from 20-300Hz with no smoothing.  Thanks.

Edited by AustinJerry - 2/5/13 at 4:10pm

@ Jerry: I know you wanted to say the noise floor is around 40 dB and not 40 Hz, eh?!

@János: As Jerry says, ...but hey, have you read Jerry's excellent Step-by-Step Guide yet? It's worth to "do it"!! A wealth of information can be found there made in a form that is really easy to follow.

@ Et all: would it be appropriate to ask posters to include a couple of photos of their room setup whenever graphs are submitted?

Let's discuss!

 

Thanks for the correction, Feri.  WRT providing pictures, it couldn't hurt.

Not at all.
I don't know about you Jerry, but I'm a visual type-a guy, so IMHO a couple of pictures accompanied with charts and graphs may not only not hurt, but would be a great way to evaluate (to a certain extent) what is going on in the room when seeing the poster's speaker setup. Let's consider the importance of photos that may lead to first-hand comments on a "yes-yes" or "no-no" basis. Lookin' forward, as always!

Not a bad idea - as it gives other posters (and the "gurus") guidance about the challenges we face in combining "audio nirvana" with the realities of daily living in our HT space . Not just physical/logistical, but with WAF. Especially when WAF keeps us from having the optimal MLP for our room.

As long as nobody laughs...

Actually, If the WAF measures > 69db, the MLP takes on a whole new meaning...YES!!!!

Thank you very much

Fury

Hi Fury. Thanks for the kind words. I don't recall the specific deviations for our project. But Keith (Yates) says that is usually between 1 and 2 db which is darn good.

noob question: How would I use Jerry's guide to record and submit frequency response measurements to a vendor to obtain room acoustic advice to purchase their products? i.e. what numbers?

 

You need to do a set of measurements using the full frequency spectrum of 15Hz-20KHz and then submit the .mdat file to the vendor. They can then analyse your data file any way they like using REW at their end.

I would also add a journal on measurement circumstances (mic placements namely) and setup including some photographs of the in-room speaker setup and the room itself to show "what is the situation". Still they may have questions.

Hope this helps.

 

Good idea. I used one of the freely available room modelling/design programs (like Google Sketchup) to make a 3D model of my room and uploaded that to GIK to get their suggestions for my room. You were right - they still had questions :)  I can heartily recommend GIK for ready-made treatments - they are reasonably priced, do a good job and are supported by independent lab measurements wrt to their effectiveness. Their chief designer was happy to spend considerable time in helping me and in suggesting different ways to move forward. At no time was there any sales pressure from them either. If I was starting over with treatments, I would probably DIY them now.

My mic will be here tomorrow, YEAH! I get to spend all weekend annoying the wife and dogs with sweeps!

Our dogs love mic sweeps...but they also like sleeping by the subwoofers, so go figure.

Is anyone else experiencing low sensitivity with the mic? I am.

What level did you set in the Windows Audio Recording device screen?

 

Edit:  What mic are you using?

He has the UMM-6.