# My first graph.



## spaceape (Feb 6, 2012)

I just did my first graph and were wondering how bad it all looked.










Cross-spectrum calibrated Dayton EMM-6 microphone
TASCAM 122 MKII
2x SVS SB12-NSD
Denon AVR-4311 (with MultEQ Pro)

Speaker crossovers at 60Hz and LPF of LFE at 120Hz

I also have a Behringer FBQ1000 connected too the loop between my AVR and the two subs. So i can possibly try and fix some of the peaks and nulls.


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## flatfinger (Jul 27, 2011)

spaceape said:


> I just did my first graph and were wondering how bad it all looked.
> 
> 
> 
> ...


The below 100hz looks great . How far back is the mic ??? The troughs in the 100-200hz range look like 1/4 wave boundary effects . Nice response really .

http://www.soundonsound.com/sos/1995_articles/dec95/boundaryeffect.html


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## spaceape (Feb 6, 2012)

flatfinger said:


> The below 100hz looks great . How far back is the mic ??? The troughs in the 100-200hz range look like 1/4 wave boundary effects . Nice response really .
> 
> http://www.soundonsound.com/sos/1995_articles/dec95/boundaryeffect.html


The mic is at the sweetspot in the middle of my couch 9-10 feet from the speakers at the front wall which is were the subs stand also. The speakers are only around 1 foot away from the front wall and my couch 1 foot away from the back wall. My room is very small but i have a reasonable amount of broadband absorption.

My room dimensions:










http://www.blu-ray.com/community/gallery.php?member=spaceape

The full graph:










And with smoothing:










My mid and high frequencies are a mess it looks like but it might just be the way those frequencies operate. :dontknow:


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## hjones4841 (Jan 21, 2009)

It is rare to see a FR curve that looks 'pretty' in the mids and highs unless a lot of smoothing is applied.


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## spaceape (Feb 6, 2012)

hjones4841 said:


> It is rare to see a FR curve that looks 'pretty' in the mids and highs unless a lot of smoothing is applied.


Okay cool. 

Do you think the dip at around the 100hz mark can be attributed too the crossovers or something else. I've tried too level it out before with the BFD but i never had any luck.


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## flatfinger (Jul 27, 2011)

spaceape said:


> Okay cool.
> 
> Do you think the dip at around the 100hz mark can be attributed too the crossovers or something else. I've tried too level it out before with the BFD but i never had any luck.


You said that the speaker boxes were one foot from the wall ...... Mine are a little closer and I have a boundary effect suck out at around 112-120 hz... The fact that you can boost that frequency to no avail actually confirms it .. It's also called the allison effect or the 1/4 wave effect ...

Here's anothe link for you ...http://www.genelecusa.com/learning-center/publications/magazine-articles/

from the second one down ;
( Monitor placement in small rooms )



> The wall behind the loudspeaker can cause cancellations — Two
> signals with the same level but in anti-phase (180 degrees out of phase) can cancel
> each other out, resulting in silence.


From http://www.acs.psu.edu/drussell/Demos/reflect/reflect.html



> => at a fixed (hard) boundary, the displacement remains zero and the reflected wave changes its polarity (undergoes a 180o phase change)













It's also interesting to consider rear facing ports on a reflex design speaker ; a whole other can of worms:yikes: !!!

Cheers


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## spaceape (Feb 6, 2012)

flatfinger said:


> You said that the speaker boxes were one foot from the wall ...... Mine are a little closer and I have a boundary effect suck out at around 112-120 hz... The fact that you can boost that frequency to no avail actually confirms it .. It's also called the allison effect or the 1/4 wave effect ...
> 
> Here's anothe link for you ...http://www.genelecusa.com/learning-center/publications/magazine-articles/
> 
> ...


Hey thanks a lot for your help. I just read through it. I will try if i can't squeezes in some more absorption between the front wall and the speakers. Not sure how much i can do with the distance from the wall 50cm is properly my maximum before i start falling over it all. :heehee:

Front left and right = 40 cm (maybe a few cm less)
Center = 30 cm
Sub left = 27 cm
Sub right = 23 cm
Sofa from rear wall = 41cm

I haven't played around with my subs phase yet. Not really sure how too do this correctly. onder: All my B&Ws are rear ported but my SVS subs are sealed.


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## flatfinger (Jul 27, 2011)

The problem is that the lower the frequency , the more/thicker materials are needed to be effective. I've also read that it's actually more effective to have a gap behind in/and between the wall and your treatments; Treatments slow the sound waves down and the velocity is dissipated as heat !! Evidentally making a round trip all the way through , doing the bounce and then making another trip through the treatment will lower the strength of the wave more than having the treatments flush on the wall!


Also , I found this in a forum somewhere and am unable to cite and credit the individual ( Sorry who ever you are !) But here's another reason not to get too freaked out if the lower spectrum on your graphs isn't perfect ....




> The response of an audio system in a room does not have to be absolutely flat on the screen. According to revised Fletcher model the human ear can detect the changes in energy output below 300Hz only in the bandwiths about 100Hz wide. This means that a peak or valley below 300Hz should not be broader than 100Hz in total. But how deep or high? In idealized conditions (headphones or anechoic chambers) a listener can hardly detect the peak or valley smaller than +/-2dB. The lower the frequency the lower the sensitivity of the ear. Therefore peaks and valleys not exceeding 100Hz width and 2dB height or depth will make no real difference comparing to the ruler flat response. Music is not static unlike pink noise signals so the irregularities will remain unnoticed.


Cheers


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## MysticDan (Nov 13, 2011)

when you do this measure, you first measure with the left speaker, and next use the right speaker?
if yes, this graphics is for what side?


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## spaceape (Feb 6, 2012)

flatfinger said:


> The problem is that the lower the frequency , the more/thicker materials are needed to be effective. I've also read that it's actually more effective to have a gap behind in/and between the wall and your treatments; Treatments slow the sound waves down and the velocity is dissipated as heat !! Evidentally making a round trip all the way through , doing the bounce and then making another trip through the treatment will lower the strength of the wave more than having the treatments flush on the wall!
> 
> 
> Also , I found this in a forum somewhere and am unable to cite and credit the individual ( Sorry who ever you are !) But here's another reason not to get too freaked out if the lower spectrum on your graphs isn't perfect ....
> ...


So the ones i should be concentrating on would be my subs or both front speakers and subs? I already have a foot of owens corner 705 type insulation and an Auralex Subdude under each sub. I also have a 4" 2'x 4' panel behind each of the fronts and two 4" 24"x 32" behind the center speaker. The speakers all have foam plugs inserted.

I was thinking of maybe placing another one (making it 8") behind each of the fronts. Or i could try it on the wall behind the subs.


MysticDan said:


> when you do this measure, you first measure with the left speaker, and next use the right speaker?
> if yes, this graphics is for what side?


I can disable all but the front left, right and the subs from inside the AVR menu. If i want more than this i'll need too remove the banana plugs from the back of the speaker terminals. 

My measurements were initially only meant too help eq'ing my subs and later getting a better picture on how the speakers, listening position and acoustic treatment were doing it's job and were the weak spots would be. 

With Auddesey Pro i am able too design some graphs but not really doing much manual equalizing. The mic measurements are also limited and very low resolution. This is why i ended up getting a proper mic and subwoofer equalizer thinking this area would be were i would need the most eq. Also not many external digital/hdmi connected eqs that i know of. So i stuck with analog for the time being.

The measurements i did above were with all the speakers active in the AVR.


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## Barleywater (Dec 11, 2011)

First I would have extensively measured room prior to treatment.

Second I would work extensively with Audyssey, confirm with multiple measurements using REW, and by extensive listening.

Look at posts of THX UltraII: First Measurement and tutorial for good Time Alignement, Group Delay and Phase: Post #25

First Measurement goes on for 21 pages. About 13 pages in a very educational back and forth ensues. John spends a lot of time teaching Sander hands on for measurement and alignment.

Sander demonstrates his learning by posting tutorial, and finally gets around to using his Audyssey setup, and rapidly finds that overall, based on measurements of results with REW, that Audyssey does a very good job. And also finds that little can be modified with Audyssey settings before they become disengaged, or then measure no better than best manually derived settings that take hours to achieve.


Auddyssey is DSP classifiable as digital room correction, it is multiple point measurement based system that has proven effective for avoiding havoc encountered with single point measurements done at normal listening distances. Lots of work has gone into this. Lots of effort has gone into convincing AVR manufactures to build it into their products.

I've been engaged as avid audio enthusiast, focused primarily on stereo music playback with fully active speaker setups. Early on I adopted use of digital crossovers and became quite adept at setup. Numerous iterations of adjusting settings, measuring, and analyzing may be done to get very good results. Alternately basis measurements are used as system model, and analysis involves more time on simulation for picking trial settings. Either way, after much practice, a raw system still takes me several hours to setup using these techniques.

Years ago I started studying DIY digital room correction, and was highly skeptical of limited measurement based results on the web. Some looked too good to be true, others looked at though much hadn't been accomplished. The process still required multiple trials, and many disclaimers about horrible results if measurements and settings choices were poor. So I stayed away.

As my comprehension of technical papers on basis of room correction techniques grew I revisited the topic and began exploring. Fundamental concepts include that for every EQ there is an opposite EQ, and the two effects cancel each other out. This principle holds in both the time domain and in the frequency domain. This is impulse response inversion. The simple case is minimum phase filter, such at EQ filters available for manual adjustments. A much more complex class of mixed phase filters exist. A branch of these filters involves multiple time delay taps. Solving for even simple mixed phase filters really requires a computer and appropriate software.

It is possible, even in highly reflective room to equalize at least one listening position (measurement point) to flat or nearly any desired target. Results at all other points in room may likely be horrible. As room becomes less reflective, temporal aberration decreases, and a single point correction tends to become acceptable over a wider area.

Using impulse response inversion, and indeed appropriate measurement point(s), I can set up basic crossover points for multiple driver speaker, and equalize is to nearly perfectly flat, or nearly any desired curve in a few minutes. Then additional measurements and equalization at listening position is relatively short and sweet, such as may readily be accomplished with REW EQ.



So yes, in theater setup, what may otherwise be relatively large, empty, and reflective room is helped by liberal use of absorbers and diffusers. Many a movie theater has heavy floor to ceiling pleated drapes covering brick and cinder block walls, and hung acoustic tile ceilings.

Fire up your measurement rig, and see what you find. Please post some results.

Regards,

Andrew


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## spaceape (Feb 6, 2012)

Barleywater said:


> First I would have extensively measured room prior to treatment.
> 
> Second I would work extensively with Audyssey, confirm with multiple measurements using REW, and by extensive listening.
> 
> ...


Wow Thanks so much Andrew. I' ll start reading through all of that. It's very hot inside today so that makes it hard too concentrate but i'll try. Im also not a 100% done in the room yet so i would rather wait so as not having too do the eq part again a week from now. But extensive measurements and fixing some of my worse frequency responds i can do.

Looking at what you just wrote it becomes evident i still have a lot too learn. :sweat:


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## spaceape (Feb 6, 2012)

I took a couple 4" panels that i had laying behind my sofa and moved them unto the front wall behind the front left and right speakers combining them with the 4" i already had (8" panel in all).

I also tried a couple of different crossovers (both lf and hf).

My old weaker 4" treatment. Hf crossover of 60Hz and lf of 120Hz:



















8" hf at 60Hz and lf of 120Hz:


















8" hf 80Hz lf 120Hz


















8" hf 60 lf 80Hz


















8" hf 80Hz lf 80Hz


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## spaceape (Feb 6, 2012)

The graph with the 60Hz HF crossover and 80Hz LF seems the one with the overall flattest frequency responds am i right? 

Strangely the old 4" absorption actually had better low frequency responds it looks like.. At least under 100hz.


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## spaceape (Feb 6, 2012)

I did some moving around of the absorption panels again but no crossover tweaking.

Took one of the 4" panels behind of my front speakers left and right and moved them behind the subwoofers. So they're now just next too each other four 4" panels in a row:



















Then i tried taking two 5" panels from the bottom sides of my sofa and placing them behind the front left and right (15cm in all):



















Then i took two more 2" panels from the side of the room and placed them were i just took two identical ones (too the sides of the sofa):


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## spaceape (Feb 6, 2012)

Front l+r and subs moved away from the front wall around 4":



















Maybe get some foam just too try and level out the mids and highs?


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## Barleywater (Dec 11, 2011)

Last pic in post #3 with 1/12 octave smoothing is most informative. Looks like THX curve. For speaker and microphone placement as pictured and described, result is actually pretty good looking.

How do Left and Right speakers measure independently? How is stereo imaging? Where are subs placed? What are you using for main speakers?


Speaker in corner v speaker along wall likely causing imbalance both with frequency response and with stereo image.


Use of REW overlays is great way to compare results.

Posting an mdat file of saved results would be more informative.

Regards,

Andrew


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## spaceape (Feb 6, 2012)

Barleywater said:


> Last pic in post #3 with 1/12 octave smoothing is most informative. Looks like THX curve. For speaker and microphone placement as pictured and described, result is actually pretty good looking.
> 
> How do Left and Right speakers measure independently? How is stereo imaging? Where are subs placed? What are you using for main speakers?
> 
> ...


Hi Andrew. :wave:

THX curve? How should that look?

Too measure left and right independently i would need too take out the wire from one or the other binding post. My room and speakers are so cramped in so that is not an easy thing too do many times over. Please tell me why this is necessary and how too measure it properly.

Not sure about the stereo image as im always watching movies with surrounds and lots of bass but will try and listen more closely when watching tv. The overall sound is maybe a little sharp in the very top.

The subs are placed on the front wall right next to/inside of the front left and right. My setup is as follows:

Speakers: B&W CMC2, 2x CM9, 2x CM5, 2x SVS SB12-NSD, 3x Clark TST209 Bluray Player: Denon DBP-4010UD AV Reciever/Amp: Denon AVR-4311 (w/ MultEQ Pro), Dayton SA240-B 240W.

http://www.blu-ray.com/community/gallery.php?member=spaceape

Not sure if i got the last thing you said but im guessing you are saying too close too a wall and corner is a bad thing and will cause imbalance. I've done all i could trying too alleviate that but my room is very small and not much freedom too move stuff around.


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## Barleywater (Dec 11, 2011)

Approximately THX curve has 10dB drop starting around 1kHz and ending in high frequencies. You've got a downward slope starting much earlier. 

Seams that between soundcard, REW, and AVR should be way to route signal to speakers independently.

Differences in left and right speakers responses are visual cues for disturbances to stereo image.

Nice gear.

Regards,

Andrew


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## spaceape (Feb 6, 2012)

Barleywater said:


> Approximately THX curve has 10dB drop starting around 1kHz and ending in high frequencies. You've got a downward slope starting much earlier.
> 
> Seams that between soundcard, REW, and AVR should be way to route signal to speakers independently.
> 
> ...


Aha. :nerd:

Maybe just disabling all i can in the AVR (center+surrounds and disabling/enabling subs for either stereo or 2.2) and then taking either the left or the right RCA out of the AUX input on the AVR? (other inputs that are better for using REW?)

This should allow me too get a better picture of each part of the speaker system. Is this what you are taking about Andrew? 

Sorry im Danish so i just need too understand this correctly.


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## Barleywater (Dec 11, 2011)

> This should allow me too get a better picture of each part of the speaker system. Is this what you are taking about Andrew?


Yes.


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## spaceape (Feb 6, 2012)

> NOTE: Something that you should remember to do when you are setting up your BFD is add a foot to the value you enter for sub distance in your pre/pro or receiver set up. The 1 msec DSP processing delay in the BFD would account for approximately a foot in distance.


From the BFD guides.

I have a question though. Should i still add another foot too the distance after running a Auddesey calibration (BFD connected too the AVR)? Is this note only for people without automatic calibration tools like Auddesey?


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## Barleywater (Dec 11, 2011)

I sense the context is for measuring distance to sub and speaker with tape measure. With BFD connected, Audyssey and with REW total propagation time through air, electronics and software are measured.

Short answer: don't add the extra foot unless you are measuring physical distance.

Regards,

Andrew


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## spaceape (Feb 6, 2012)

Barleywater said:


> I sense the context is for measuring distance to sub and speaker with tape measure. With BFD connected, Audyssey and with REW total propagation time through air, electronics and software are measured.
> 
> Short answer: don't add the extra foot unless you are measuring physical distance.
> 
> ...


Yeah you're properly right Andrew.  Thank you will try that.

Btw. My latest graphs but. Just messing around at the moment hehe.  http://forum.blu-ray.com/showpost.php?p=6364870&postcount=2144

There seems too be a dip at the 45Hz-70Hz region without Auddesey enabled which is why i got worried it could possibly be the distance settings ( is that used if Auddesey is off?) or my speaker/"satellite" crossover of 60Hz.


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