# Help needed understanding REW measurements



## floddern (Dec 29, 2011)

Hi Peeps,

I Writing a report about my room treatment here and having with results of SOME meassurements.
Brief info:
The room has been treatet, these are a final measurements.

I ve no idea about the Impule response diagram, are the results OK, bad? Wheres the ITD-Gap?


OK, I ve updated the pictures. waterfalldiagram, IR, RT60, EDT and the spectrogram.

ALL are in the order LR , L , R

Hope this help the overview.


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## floddern (Dec 29, 2011)

*Re: Little Help needed w/ final REW measurements*

About the treatment. Well everything has different names ang i d have to look it up so pictures say more than words.

Foam above desk 14 cm thick, 2 square meters.
Foam rear wall 24 cm thick, 2, 5 square meters.


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## floddern (Dec 29, 2011)

*Re: Little Help needed w/ final REW measurements*

Pictures of my Room. Front and Rear.


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## floddern (Dec 29, 2011)

*Re: Little Help needed w/ final REW measurements*

IR = LR,L,R


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## floddern (Dec 29, 2011)

*Re: Little Help needed w/ final REW measurements*

RT 60


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## floddern (Dec 29, 2011)

*Re: Little Help needed w/ final REW measurements*

Early Decay Time (EDT)


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## floddern (Dec 29, 2011)

*Re: Little Help needed w/ final REW measurements*

Spectrogram LR, L,R


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## floddern (Dec 29, 2011)

https://skydrive.live.com/?cid=497c9a62a9d516ca#cid=497C9A62A9D516CA&id=497C9A62A9D516CA%21205


.mdat file excuse german writings


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## crom0123 (Feb 14, 2012)

Hi floddern,

Overall your room's frequency response is good.
Some work is needed in the low frequency range 20-150Hz:
-tame the room modes that appear at ~27,36,67,112,137Hz
-fill the big 20db gap you got between 80-100Hz
There are a couple of solutions for that:
1.moving the speakers/listener position-the cheapest solution
2.bass traps-the most effective solution (pricey+lot of work)
3.EQ (please see the BFD section of this forum)

Cheers,
crom


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## Barleywater (Dec 11, 2011)

Thanks for posting mdat. Your cloud service is workable.

Basic soundcard cal is perfectly done. I don't see any microphone calibration. What are you using for measurement microphone?

Before coloring your impressions with my observations and analysis, what are your they? How is sound stage/image? How is extended listening session? How does familiar music sound here compared to listening to on other systems?

I see keyboard, so you do composition in space? Are you doing mixing here? 

What was measurement microphone location? Is preferred listening at desk or on couch? It would be good to see measurements from both locations.

In pictures I see the that space is at a premium.

Also that left and right monitors are not same distance from front wall. This has impact on frequency response easily up to 1kHz, small monitors tend to be omnidirectional to here. This in turn impacts imaging. How smoothly does voice pan from side to side? Do male and female differ?

Frequency response of full measurement is not at all surprising. Windowing for complete measurement shows limits to treatment. Yes, even with extreme smoothing, and gating to a few milliseconds response is not flat.

Here is spectrogram with Blackman-Harris 4 windowing of 12ms:









Continuous horizontal banding below 1kHz shows energy reflecting in single group and may be interpreted as primary modal behavior. The transition to flame like vertical banding above shows higher order modes with complex standing wave behavior. Horizontal band at t=0 may be interpreted as color coded frequency response of monitor. This spectrogram is derived from right speaker data.

Shortening window to 3ms increases resolution but limits results to above 300Hz:









Here it is seen that direct sound of monitor is much flatter, but that spectral balance isn't maintained, even for fairly early reflections.

Various equalization techniques may yield improvements. For playback/mixing DRC techniques may work quite well.

Regards,

Andrew


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## floddern (Dec 29, 2011)

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
http://www.thomann.de/gb/audix_tm_1.htm

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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## floddern (Dec 29, 2011)

Enrgy Time Curve shows earliest reflections at 13 ms. The standard of 10 ms ITD has been met.


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## Barleywater (Dec 11, 2011)

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.









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:












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.

Regards,

Andrew


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## floddern (Dec 29, 2011)

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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## Barleywater (Dec 11, 2011)

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.

Regards,

Andrew


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