Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 118 - AVS Forum | Home Theater Discussions And Reviews
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Old 06-13-2013, 12:50 PM
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Originally Posted by Roger Dressler View Post

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Originally Posted by jkasanic View Post

I was working under the premise of trying to make the room the best I could BEFORE adding any EQ but when dealing with LF this appears to be hit or miss in terms of the value equation (cost and practicality vs. benefit achieved).  How low should I be worried about if my sub plays flat to around 18Hz?  Does the criteria change if I have the ability to go lower in my setup in the future (i.e. sub upgrade)? 
As no one answered, I have just a comment. IMHO, the area of concern for bass treatment stops below the lowest room mode. It may still be very deep for a decent size room, 35 Hz or lower, but that's still an octave higher than the range you are contemplating.

Being that is the case, your treatment options are not limited to bass traps. Multi-sub mode cancellation per Welti can yield much more effective results than absorption.

 

Roger, thanks for the specific response.  If you consider my room modes below, does that mean you would not attempt to tame the peak at 30Hz through absorption but rather through the addition of multiple subs placed to cancel out this particular gain?

 

 

Here is the FR of only my sub (1/24th smoothing applied to make comparison easier):

 

Green is with the sub in the middle front wall (under C speaker), red is right front corner loaded and purple is the same as green but with MultEQ XT32 applied.

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Old 06-13-2013, 12:59 PM
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im really concerned that you are attempting to imply a later-arriving diffusive sound-field is in any way comparable to active surround speakers providing a delayed copy of the direct signal.

again, you provided zero clarity on how these "additional surround sound speakers" can provide a more ""diffuse" a signal in a more sophisticated way than any physical diffusor could.".. can you finally expand on this? im interested to know how a single surround speaker can provide a more sophisticated diffusive signal.

I see it the other way around. A diffusor and/or a Haas kicker works only on the entirety of the recorded signal which consists of the direct sound plus the reverberation of the recorded space. Surround speakers on the other hand can deliver any combination of recorded direct sound and reverberation. Furthermore, those components can be processed - delayed, made less coherent (more "diffuse"), filtered, convoluted, really anything.
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and it appears the context of the primary requirements for the model has been lost and we are now attempting to apply an "FX" to the room.

Is any room interaction really anything different from adding an effect on top of the recorded signal?
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sure you can. a porous material in close proximity to the well openings of a RPG is a quick way to turn the diffuser into an absorber.

Flipping a switch on my surround speakers sounds more practical to me.

Markus

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Old 06-13-2013, 01:07 PM
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Originally Posted by jkasanic View Post

Roger, thanks for the specific response.  If you consider my room modes below, does that mean you would not attempt to tame the peak at 30Hz through absorption but rather through the addition of multiple subs placed to cancel out this particular gain?

Not Roger but it really depends on how long the mode decays. In my opinion long modal decay is as bad as frequency response peaks. The reason is probably upward masking of higher frequency sounds.
Experiment with sub location and try to reduce modal decay. The frequency response suggests that the peak isn't caused by only one mode.
A second sub can do wonders. Reducing modal decay by passive means is usually hard to achieve.

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Old 06-13-2013, 01:46 PM
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Originally Posted by markus767 View Post

I see it the other way around. A diffusor and/or a Haas kicker works only on the entirety of the recorded signal which consists of the direct sound plus the reverberation of the recorded space. Surround speakers on the other hand can deliver any combination of recorded direct sound and reverberation. Furthermore, those components can be processed - delayed, made less coherent (more "diffuse"), filtered, convoluted, really anything.

again you fail to understand the context of the discussion and the model at hand and instead wish to turn this into a discussion of using the room itself as an "FX" generator - tell me more about why i would want processing, delays, filters, "really anything" from surround sound speakers when listening in a neutral/accurate 2ch reproduction room? for pleasurable listening, anything goes. but you've wandered quite far off context at this point.

and you still fail to recognize the resultant polar lobing issues that develop as a result of the multiple sources.

a third time you fail to even remotely explain how a surround sound speaker can "diffuse" a signal in a more sophisticated way than "any physical diffusor could".

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Is any room interaction really anything different from adding an effect on top of the recorded signal?

absolutely and im quite astounded you're even making such a claim. nevermind the directional components of returns from the room, but their sparse/diffuse nature as well. how are you providing a diffusive sound-field from a surround speaker? how are you providing lateral sparse reflections from the sidewalls by "adding an effect on top of the recorded signal"? how many surround sound speakers must you have to account for all of the room contributions? how is the speaker able to modify the signal once it has left the speaker (eg, room interactions)?

you have failed to provide ETCs or polars of these active surround speakers that can "diffuse" a signal in a more sophisticated way than "any physical diffusor could".
are you really apt to imply that reproducing a diffusive signal (eg, reverb) actually implies the sound-field emitted from said speaker is actually diffuse??
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Old 06-13-2013, 01:55 PM
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Not Roger but it really depends on how long the mode decays. In my opinion long modal decay is as bad as frequency response peaks. The reason is probably upward masking of higher frequency sounds.
Experiment with sub location and try to reduce modal decay. The frequency response suggests that the peak isn't caused by only one mode.
A second sub can do wonders. Reducing modal decay by passive means is usually hard to achieve.

 

Can you please expand a little on the bolded section?  What is it about the FR plot that suggests this?  I do have two axial modes between 30 and 40 Hz so is this a contributor as well?

 

Here is the corresponding Bass Decay for the sub placement on the mid front wall under the C speaker:

 

 

Note the ringing needs approx. 500ms to drop below a noise floor of 50 dB.  If I decrease the noise floor to 40 dB (as there is some speculation as to what we should be using with the UMM-6 USB mics but it seems 50 is the accepted level) that extends the ringing at 30Hz out to 650ms.

 

Here's the corresponding bass decay plot which shows the same issue around 30Hz:

 

 

I did some extensive experimentation on my single sub placement.  The only better location than the mid front wall location was exactly mid room (more nearfield to MLP) but this is not a feasible permanent location.  I'm more inclined to go the dual sub route but hadn't really considered doing it before adding treatments.  I guess there could be more merit to doing it in this order and then seeing what issues remain in the LF?

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Old 06-13-2013, 02:07 PM
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absolutely and im quite astounded you're even making such a claim.

Sorry but I fail - again smile.gif - to understand how anybody can think of room contribution as "neutral".

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Old 06-13-2013, 02:08 PM
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Originally Posted by jkasanic View Post

...

A good option if there is only one seat you care about is to add a parametric EQ. You could dial out that 30Hz resonance pretty easily. It will also remove the modal ringing.

If you have multiple seats that are important it's unlikely that EQ + one sub is going to give you good results. Likely you'll need to do 2 to do some room mode cancellation. My rule of thumb is 2 subs is good for one row of seats, for multiple rows you need 4.

BTW treating 30Hz passively is difficult.

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Old 06-13-2013, 02:09 PM
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Originally Posted by jkasanic View Post

Can you please expand a little on the bolded section?  What is it about the FR plot that suggests this?  I do have two axial modes between 30 and 40 Hz so is this a contributor as well?

Note the ringing needs approx. 500ms to drop below a noise floor of 50 dB.  If I decrease the noise floor to 40 dB (as there is some speculation as to what we should be using with the UMM-6 USB mics but it seems 50 is the accepted level) that extends the ringing at 30Hz out to 650ms.

I did some extensive experimentation on my single sub placement.  The only better location than the mid front wall location was exactly mid room (more nearfield to MLP) but this is not a feasible permanent location.  I'm more inclined to go the dual sub route but hadn't really considered doing it before adding treatments.  I guess there could be more merit to doing it in this order and then seeing what issues remain in the LF?

Id probably agree. If you were going to go dual sub, do it before treating.

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Old 06-13-2013, 02:11 PM
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Having a quasi RFZ myself, I can say that at -6db even, its not something I really hear, but notice if its absent.
I have a similar effect when listening to 2-channel music in surround, the additional speakers are dialed in so that they're only noticeable by their absence (when I switch to 2-speaker playback). BTW, I brought this up because you had earlier said "But there is another approach that gives some of the benefits without acoustic bouncing being involved."
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If the ultimate goal is better sound, then adhering to LEDE / RFZ may not be as important as just getting to something you personally like.
Just get something I personally like? Y'know that happens to be the name of the acoustical model I chose to work towards. I tried to pick a simpler name, like "my room", but that was already taken.
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We are not talking about a control/mix room where accuracy is vital.
Considering how vital accuracy is in control/mix rooms, which of the various studio models has been found to be the most accurate? There must be some sort of consensus after all these decades.

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Old 06-13-2013, 02:12 PM
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Originally Posted by jkasanic View Post

I'm more inclined to go the dual sub route but hadn't really considered doing it before adding treatments.  I guess there could be more merit to doing it in this order and then seeing what issues remain in the LF?

Get a second sub then think about room treatments.
Could you post the IR or the .mdat of your measurement?

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Old 06-13-2013, 02:18 PM
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Originally Posted by Nyal Mellor View Post

A good option if there is only one seat you care about is to add a parametric EQ. You could dial out that 30Hz resonance pretty easily. It will also remove the modal ringing.

He has XT32 which will take care of that.
By the way, I don't agree that applying EQ will always and in each and every case take care of modal ringing. This works only if the response is minimum phase. And even if the transfer function of that single point in space is minimum phase, how do the points next to it behave?

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Old 06-13-2013, 02:26 PM
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Considering how vital accuracy is in control/mix rooms, which of the various studio models has been found to be the most accurate? There must be some sort of consensus after all these decades.

There is none because there's not much real science happening in that area.

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Old 06-13-2013, 03:08 PM
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Considering how vital accuracy is in control/mix rooms, which of the various studio models has been found to be the most accurate? There must be some sort of consensus after all these decades.

most accurate? that doesn't make any sense at all. the goal is translation via the decisions made in an accurate/neutral acoustical space.
if you want to turn your room into an FX generator, then by all means that is your choice. but such statements are only exposing that which is not understood.

speaking of which, what speech mix rooms allow high-gain early sidewall reflections due to "increased speech intelligibility"?
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Old 06-13-2013, 03:38 PM
 
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Considering how vital accuracy is in control/mix rooms, which of the various studio models has been found to be the most accurate? There must be some sort of consensus after all these decades.
I don't think you are allowed to ask that question. Folks assume if pros use something it must be accurate. After all, they are pros, right/? Right.... smile.gif

BTW, earlier the Blackbird studio was yet again put forward as some kind of proof point of greatness in this regard. This is the picture people fall in love with:

BlackbirdStudio.jpg

That was the staged set up for the marketing picture. Here is the reality of it being used in this lovely performance by Dawn Langstroth. Notice where she is singing with makeshift Plexiglas, foam absorber and such in front of her. Notice others sitting on the floor, other barriers in place.. Anything but "taming' the first reflections:

Reports are that said diffusers are now covered with curtains!
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Old 06-13-2013, 03:43 PM
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the poor salesman doesn't understand the difference between tracking/recording and mixing/mastering.

the best thing he has to distract about is the producer's decision to have her sing and record the vocals in such a fashion? and just what does this have anything to do with the reproduction process?
he needs to at least learn the basic concepts here; after all he is in the professional audio business. one should know recording is entirely subjective. what's next, it's going to be implied that someone recording drums in a stairwell must also be mixing/mastering in the stairwell? "Anything but "taming' the first reflections" in the stairwell!

the room is dual purpose and can be arranged to record or mix in. what a concept! and the video he linked to is in the recording stage, not the final mixing/mastering stage. this should be obvious?
although im surprised he didn't speak up about those mysterious "wooden partitions". during a previous thread where blackbird was mentioned, he brought up the wooden partitions and mistakenly wasn'e even aware of what a GOBO is and how they are utilized in the recording process.

although it is nice to see broadband diffusers vs the baby microdiffusers installed in his company's showroom.
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Old 06-13-2013, 04:11 PM
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Quote:
Originally Posted by markus767 View Post

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Considering how vital accuracy is in control/mix rooms, which of the various studio models has been found to be the most accurate? There must be some sort of consensus after all these decades.
There is none because there's not much real science happening in that area.
"That area" = studio design? I was asking because all those designs, as different as they are, can't all be equally 'accurate'. That would render the term meaningless.

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Old 06-13-2013, 05:14 PM
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He has XT32 which will take care of that.
By the way, I don't agree that applying EQ will always and in each and every case take care of modal ringing. This works only if the response is minimum phase. And even if the transfer function of that single point in space is minimum phase, how do the points next to it behave?

Yes XT32 does take care of the frequency domain issues though interestingly in my experience it does not take care of the room mode ringing as well as parametric EQ - see this case study: Audyssey vs parametric EQ.

It also has the issue of correcting to an arbitrary target curve above the room's transition frequency which is not room correction in my book it is speaker correction. I do not believe one can arbitrarily correct to a pre-defined target curve without knowledge of the power response of the speaker in question.

In my experience modal ringing can nearly always be dealt with via EQ but obviously if your frequency response varies significantly from place to place (and you care about that because you are in a multi seat HT) then EQ by itself is not the only solution you need. Room mode resonances are always minimum phase. The only area you have to watch for is if a room mode frequency is close to a non-minimum phase area caused by a reflection.

As Toole said in our white paper:
I try to be careful to say at low frequencies (subwoofer region below 80 Hz) small rooms behave as minimum phase systems (as it applies to equalizing resonances).’ When pushed I go on to say that this is mostly true for resonant peaks that stand above the average spectrum level, but as that level recedes below the average spectrum level, we clearly have a "signal to noise" (minimum phase‐to‐non‐minimum phase) problem, because there are obviously non‐minimum‐phase activities in the region ‐ interference dips being an example. This is relevant because the best evidence of an audible resonance is a highly visible peak, which, if attenuated to the average spectrum level (i.e. flat) results in a severe attenuation of ringing ‐ which is the desired situation.

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Old 06-13-2013, 05:48 PM
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Now whether bass trapping will suck the mids and highs out of you room depends on application. Behind your speakers, no. No mids highs BEHIND the speakers anyway.
True, but low frequencies wrap around the speaker, so the front wall is a good possible location for bass traps since they won't suck out mids and highs from that direction. Even more so if there is a false wall to hide the treatments, like Joe (jkasanic) has.

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Old 06-13-2013, 06:19 PM
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If you consider my room modes below, does that mean you would not attempt to tame the peak at 30Hz through absorption but rather through the addition of multiple subs placed to cancel out this particular gain?
Joe, if placing your sub at the midpoint of room width took care of a modal problem around 40Hz:



Then placing another sub at the midpoint of room length might take care of a modal problem around...



I say "might" because your room has openings. Before buying another sub, I would move the existing sub there to confirm that you can address your 30Hz problem with placement alone. When you measure, your 40Hz problem will re-appear, but that's temporary.

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Old 06-13-2013, 06:24 PM
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are there any toole/olive studies out there regarding LEDE/RFZ/NE rooms? what rooms specifically?
you would think toole would love a shot at performing listening tests in something like blackbird C. it's a reflection-rich response on steroids.
does anyone know if they performed any tests on broadband diffusers?
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Old 06-13-2013, 07:51 PM
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True, but low frequencies wrap around the speaker, so the front wall is a good possible location for bass traps since they won't suck out mids and highs from that direction. Even more so if there is a false wall to hide the treatments, like Joe (jkasanic) has.

Where bass trapping should be placed is independent of whether they will suck mids/highs. Absorbent needs to be placed where it needs to be, period. But, if it happens to be a place where mid/highs are present, you may have to do the additional step of adding a reflective boundary in front of the trap to preserve those frequencies.

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Old 06-13-2013, 08:58 PM
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My first measurment;



Not too pretty. Looks like I've some learning and tweaking to do. wink.gif

Interesting...if I had to guess just based on how I think my system sounds, I wouldn't have expected FR like that.

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the poor salesman

after all he is in the professional audio business.

his company's showroom.
He is in retail business.
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Old 06-13-2013, 09:24 PM
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My first measurment;



Not too pretty. Looks like I've some learning and tweaking to do. wink.gif

Interesting...if I had to guess just based on how I think my system sounds, I wouldn't have expected FR like that.

Thanks for posting. The frequency response is just part of the story. It would be interesting to see a waterfall graph so we can see what is happening in the bass region. Measure L+R+sub(s). Also, some information on your room, including dimensions and pictures, and your equipment would be useful.

My first thought, looking at your graph, is that the low frequency response could benefit from some attention. Above 100Hz, the frequency response is pretty typical.
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Old 06-14-2013, 12:20 AM
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"That area" = studio design? I was asking because all those designs, as different as they are, can't all be equally 'accurate'. That would render the term meaningless.

Quite right but the problem is not necessarily the lack of knowledge but the lack of meaningful standards.

I'd like to be able to calibrate my room's acoustics just like I can calibrate my video equipment. Today there are no menaningful standards that would allow me to do so. The speaker/room interface is a vital part of the reproduction chain but it changes rather dramatically from room to room and studio to studio. The spatial presentation of a recording will differ dramatically when listened to in a LEDE room vs. a NE room vs. my living room. The same is true for loudness and timbre.

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Old 06-14-2013, 12:45 AM
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Quote:
Originally Posted by Nyal Mellor View Post

Yes XT32 does take care of the frequency domain issues though interestingly in my experience it does not take care of the room mode ringing as well as parametric EQ - see this case study: Audyssey vs parametric EQ.

A PEQ rings too and it rings similar to room modes. This is a rather fortunate coincidence than good engineering.

I still don't agree that minimum phase behavior can be assumed for low frequencies. REW offers an easy way of checking for MP:
- SPL & Phase > Controls > Generate Minimum Phase
- GD > Excess Group Delay
Detailed discussion: http://www.hometheatershack.com/roomeq/wizardhelpv5/help_en-GB/html/minimumphase.html

Markus

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Old 06-14-2013, 12:58 AM
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Quote:
Originally Posted by localhost127 View Post

are there any toole/olive studies out there regarding LEDE/RFZ/NE rooms? what rooms specifically?
you would think toole would love a shot at performing listening tests in something like blackbird C. it's a reflection-rich response on steroids.
does anyone know if they performed any tests on broadband diffusers?

They did look at reflection thresholds in different rooms. One was an IEC compliant room. But to my knowledge they didn't look at LEDE/RFZ/NE rooms specifically.

Markus

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Old 06-14-2013, 01:55 AM
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Originally Posted by jkasanic View Post

I did some extensive experimentation on my single sub placement.

Thanks for the .mdat. The frequency response looks good after applying XT32 but there's considerable ringing below 100Hz.
Could you try one more configuration? Put the sub very close to your ears (<2') behind your listening seat (put it on a chair with the driver pointing at your head). Then run MultEQ again. I'd like to hear how this sounds to you and see a measurement at the listening position (e.g. sub + L would be enough).

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Old 06-14-2013, 06:02 AM
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Originally Posted by markus767 View Post

The speaker/room interface is a vital part of the reproduction chain but it changes rather dramatically from room to room and studio to studio. The spatial presentation of a recording will differ dramatically when listened to in a LEDE room vs. a NE room ...

it will? how "dramatically" will it differ?
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Old 06-14-2013, 06:02 AM
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Originally Posted by Nyal Mellor View Post

"Yes XT32 does take care of the frequency domain issues though interestingly in my experience it does not take care of the room mode ringing as well as parametric EQ - see this case study: Audyssey vs parametric EQ."

If you carefully examine the FR graphs presented the conclusions that the parametric EQ is performing "better" than the XT32 EQ is in my opinion not valid. The FR graphs are neither at the same level or have similar responses. It is well recognized and documented within this thread and my own measurements that these changes will significantly impact the accompanying spectrogram results and decay times. So sorry to conclude that the article does not prove anything other then the author didn't take extreme care in his measurements and conclusions.

I have used both techniques and XT32 clearly performs better in all respects than my SVS-1 even though the FR responses may "look" very similar and be at the same level.

See my link for information on my room construction and design.

I quickly included an REW LF plot of my room just for comments, 1/48th smoothing. The noise floor for the mic EMM6 (Cross Spectrum calibrated) and ART USB amp is 57dB at 32Hz which is coincidently also the TOH at that frequency so that is where I have set my lower limit.

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