Help needed understanding REW measurements - Page 2 - Home Theater Forum and Systems -

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post #11 of 15 Old 08-05-12, 02:52 AM Thread Starter
Join Date: Dec 2011
Posts: 16
Re: Help needed understanding REW measurements

Well, studying Mix/Rec-Engineer. Room will be mainly used for mixes of music material but I also screw beats togehter in ther

Thanks for the replys guys.

Standing out the rooms modes/resonate frequencies was kind and a help for the paper I have to turn in.

I read about windowing, even grasp bits of the FFT, which I am certainly not able to hold a speech on or anything.
Guess I ll need some plays to read up about the IR and the blackman harris spectrogram. REW manual could cap that for me...

Anyway on to your questions Barleywater:

The stereo field axis 1,99 cm measured from HF-Tweeter to another.
Distance to rear wall has been corrected since the pic taken.
Its 21 cm to the front- and 34 to sidewalls.

Distance to Meassuring Mic 185 cm from both HF tweeters. (See pic for setup)

Been changing the speakers placement staring @ 1m from front wall but thid had huge proximity effect resulting bass boosts. Think the setup is kinda right but feels like a wide stereo image with almost collapsing grasp. There tends to be whole in the center of the stereo field but I ve has the monitors in another environment with greater stereo field. Which feels weird though.

The overall sound could've been described as "Live" before treatments, it is now but much improved under the ceilings absorber.
Theres concav formed stucco in the walls ceilings area, which I suspect to be causing echo's or at least not smoove decaying.

Used the Audix TM-1 Meassurement Mic

It only comes with a calibration file at a premium price which I havnt got. Is there a way to extract one myself?

What do you mean with dynamic range compression? As a further room treatment such as EQing the room or in general mixing situation.
I'd realy like to understand the Blackman HArris spectrogem better so I could bring it in my thesys.

Now what can you tell me about the Initial Time Delay Gap? Is this info given in .mdat file?
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post #12 of 15 Old 08-05-12, 10:53 AM Thread Starter
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Re: Help needed understanding REW measurements

Enrgy Time Curve shows earliest reflections at 13 ms. The standard of 10 ms ITD has been met.
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post #13 of 15 Old 08-05-12, 02:18 PM
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Re: Help needed understanding REW measurements

ETC and Impulse Response do indicate a strong reflection around 13ms, but it is not the first reflection.

It is likely back wall.

Zoom in closer in to t=0 and picture reveals many early reflections: Left and Right speakers each have strong reflection at about 7ms. Lots of important activity 3-5ms. Getting closer back in time to the Big Bang very strong reflection at 1.3ms and even stronger at 700u (0.7ms). Left and right reflections are not equal in intensity, arrive with differing times, and have different frequency responses. This leads to poor imaging. Monitors should be standing upright, or upside down as well for improved imaging. When on side timing cues from tweeter and woofers are smeared horizontally, and acoustical mixing of tweeter with woofer produce lobes. When speaker is horizontal so are spread of lobes, contributing to imaging issues as well.

Help needed understanding REW measurements-floddern-post8-etc-zoom-l-r.jpg

Despite wall treatments, side walls are contributing very strong early reflections, once again, image problems, EQ problems. Often overlooked is sound from reflections inside speaker box that escape back through driver. Ported monitors are trouble all the way around. Sealed or open baffle speakers are much easier to control.

For reference here is ETC of one of my speakers measured at 107cm. Room is a fair sized, carpeted living room with no special treatments. I usually listen to them set up much like yours:

Help needed understanding REW measurements-myref-107cm-etc.jpg

All reflection caused peaks are orders of magnitude smaller, and the sound is very good.

Going super near field improves direct/reflected ratio. Standing monitors upright helps imaging. Hole in middle suggests placing monitors a little closer together.

DRC, in this case is Digital Room Correction, such as Sourceforge DRC (very hard to use), Audiolense, Acourate, Dirac Live, and Audyssey; and any other similar approach.

Calibrating microphone: No telling how flat is really is without calibration data. Manufacturer generic specification must be held at arms length. Up front cost is no guarantee. Doing calibration yourself realistically requires access to a calibrated microphone.

What model of monitor are these?

I would like to see measurements of each monitor placed in middle of space. Place microphone at 20-22cm and 2-3cm below axis of tweeter. Aim monitor at back wall (couch end). Measure 10-22050Hz at 44.1kHz sample rate, or 10-24kHz at 48kHz sample rate. Please post mdat.


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post #14 of 15 Old 08-08-12, 05:39 AM Thread Starter
Join Date: Dec 2011
Posts: 16
Re: Help needed understanding REW measurements

Lets see if I have this right: capsule 20 cm off axis from HF-Tweeter (left, right matters?)

and 2 too 3 cm below. At center of room or center of stereo axis?

This may take up to a weel because I lend the mic to a student that has picked a similar topic.

The monitors are Gennaro Acoustics, there used to be an HP but it appears he's gotten out of business.
Anyway he has good rep. in germany and has ~mainly sold his units to studios in the sync or radio play buisiness. (Which is a drcrnt market since its sold on CD's, former MC, LP)

He has few Full- Mid- Nearfields in his portfolio.
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post #15 of 15 Old 08-08-12, 09:06 AM
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Re: Help needed understanding REW measurements

Yes, 20cm from face of speaker, 2cm to 3cm below axis of tweeter. Center of room, speaker aimed at back wall (couch).

This allows observation of quasi anechoic response. All sounds from nearest surfaces will be sidewalls, floor, and ceiling, and impulse response before these reflected sounds mix in are good representation of speakers real performance above about 100-200Hz. This includes diffraction externally of sound from box edges, sound of box panels, and sound from back of woofer that bounces off inside of box and penetrates woofer to color sound. If both speakers are measured from exact same spot and microphone placement, results also indicate how closely matched the speakers are, which also impacts stereo image.

Please use full range sweep as I described, it will tell me more about room behavior's extended response.


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