# Measuring transient response in the time domain?



## 3ll3d00d (Jun 6, 2006)

The avforums review of the KK DXD 12012 has the following statement



> Ultimately, if you want a subwoofer (or any speaker for that matter) to have a real kick, snap, hit, insert adjective of choice, you need to ensure that all frequencies it emits, are emitted at the same time and stop at the same time. A complex sound like an explosion, or a drum strike, is composed of lots of frequencies which all start instantaneously. If anomolies in the phase response of the subwoofer cause certain frequencies to start/stop at different points, then the impact of the effect or sound is softened. *The measure of how much a transducer slurs it's delivery is it's transient response and it is a distortion of the original signal as serious as any other, but in the time, rather than frequency domain. I'd also note that even the 'harmonizing' CEA 2010 subwoofer measurement standard, fails to take into account this sort of non-linear distortion.*


The suggestion is this is just group delay. Am I missing something? 

Thanks
Matt


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## jtalden (Mar 12, 2009)

You are correct that Group Delay is a measure of time shift. Be advised that the REW chart can be very difficult to interpret correctly however as the room modes can cloud the result.

Their assertion is that only 2 order (sealed box) SW designs can provide the optimum sound. There are many advocates of this idea, but also many that would disagree.

They are correct that the total 2nd order phase rotation (180°) is correspondingly less than 4th order or 6th order designs and that the lower the phase rotation the lower the time shift.

Note that there are numerous 4th order SW designs (ported box) and even 6th order designs that are very highly rated. 

I personally do not think that 2nd order SW design is the most important parameter in achieving the sound characteristics they describe. There are tradeoffs to any design choice and so we could list all the advantages to the 4th and 6th order designs if we wanted.

More important is:
> SPL smoothness over the entire frequency range.
> The timing of the handoff from the SW to the Mains. (this impacts SPL smoothness in the XO range)
> Room acoustics.

REW provides all the necessary measurements to optimize your system given the your equipment/room/setup constraints.


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## 3ll3d00d (Jun 6, 2006)

OK thanks for the info. What are the issues involved in interpreting group delay in rew? Is there some particular method required to capture good data for example?

Thanks
Matt


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## jtalden (Mar 12, 2009)

The phase rotation and GD are fixed for a given SW design. We will not be able to make any adjustments or changes to it. We can measure both with REW, but they are for info only.

For a clean measurement we need anechoic space. Outside pointed up or outside with a ground plain mic position will probably be best. 

Inside becomes a problem because the room modes will distort the otherwise clean SW signal. We can move the SW as far away from walls use a 1m ground plain mic position. That may provide a slightly better signal to work with, but there is not really much that can be done. 

For inside measurements we need to manually filter out the impact of room from the measurement. With experimentation we can learn to do this fairly well.

Using our standard SW and mic locations the signal may be very difficult to interpret depending on the room, but it can probably still be done. Adjusting the window settings can help greatly, but also distorts the chart at the low frequencies if the window is set too short.

This is all difficult to explain and best learned with many examples. If you really want to measure your SW GD and post an .mdat file I will see if I can interpret it for you if you. You may then be able to reverse engineer what is needed. I guess the key is knowing the expected result an then adjusting the window settings to best expose that result. Basically we expect 90° phase rotation for each order.
SW design:
Open baffle - 1st order.
Sealed box - 2nd order
Ported box (bass reflex) - 4th order
High pass filters added to protect the SW from over excursion at low frequency also add the appropriate additional orders.
Knowing the SW design and any additional HP filters and also knowing the cutoff frequency we can pretty much draw the expected Phase and GD curves. Knowing this expected result then we can try to find it in the measurement.

Just to emphasize the main message: Given a SW design the result is fixed. Measuring it is for info only. The other settings I bulleted above do provide capability actually impact the sound characteristics they mentioned. I probably should have listed another one: "> House Curve"


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## jtalden (Mar 12, 2009)

FYI - Perhaps you have seen this.

Here is a interesting experiment that suggests that a linear phase SW is an audible improvement.
http://www.bodziosoftware.com.au/LP_MP_Subwoofer_Tests.pdf

Raczynski tested using a 4th order SW, but also then used DSP software to linearize the phase by first applying inverse EQ to the signal before it's sent to the SW. This becoming more common for those using HTPC setups. Most of the "evidence" is in showing the expected IR and step response differences, but he was also able to hear differences with test signals and "concluded" or maybe just implied that it may be significant for program material as well.

The audibility of phase rotation on program material is well debated with no strong consensus that I have able to determine. My comments above are intended to point out that there are more basic setup issues that have more apparent impact to the sound that need to be given higher priority.

Any unless we have an HTPC setup or other equipment for linear phase, FIR filtering then we have no control over SW phase anyway.


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## AudiocRaver (Jun 6, 2012)

jtalden said:


> The audibility of phase rotation on program material is well debated with no strong consensus that I have able to determine.


FWIW, it can really mess with imaging if different between L & R speakers. SW frequencies don't affect imaging, though, of course.


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## jtalden (Mar 12, 2009)

Yes that's correct.
I usually think of differences between channels in; timing, delay or distance terms and differences within a given channel as; phase shift, phase rotation, or GD terms.


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## Barleywater (Dec 11, 2011)

In domestic listening rooms, the room and SW are essentially inseparable; at 1m the reflected sound is typically louder than the direct sound at <100Hz. 

With appropriate EQ, type of SW doesn't matter.


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## jtalden (Mar 12, 2009)

Barleywater said:


> In domestic listening rooms, the room and SW are essentially inseparable; at 1m the reflected sound is typically louder than the direct sound at <100Hz.
> 
> With appropriate EQ, type of SW doesn't matter.


Care to elaborate on this?

Is "appropriate EQ" only linear phase EQ? That is, where do you fall on the question of whether one can hear a difference due to high phase rotation?

You've put significant effort achieving linear phase for you system. Do you only find that beneficial for the MF and HF?


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> Given a SW design the result is fixed. Measuring it is for info only.


Thanks for the comprehensive reply. One thing confuses me immediately and that is the comparing the quote above against this earlier quote when commenting on "things that are important to SQ"



> The timing of the handoff from the SW to the Mains


from a measurements perspective, if aligning manually, aren't these 2 points addressing the same concern?


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## jtalden (Mar 12, 2009)

The innate phase rotation of a SW is fixed depending on its design. In pointing this out I was thinking of the article you referenced. They suggested their SW design was advantageous because it had low phase rotation. If so, then all such 2nd order SW designs then have the same characteristic. This point is probably not your question or interest, but it was my main takeaway from the article. You did quote from it, but I was not sure why.

Now, in thinking of system setup given a SW (no matter the design), the issue of the handoff between the SW and mains is the main concern. We can use REW to adjust the timing by using it to set speaker distance settings in an AVR. That impacts the smoothness of the SPL through the XO area. REW provides the capability to set this timing in several different ways. Using GD is one, but I find that one to be the most problematic due to the impact of the room response on the chart. 

For those interested in getting good results with a minimum of time and effort the RTA method is best choice.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> This point is probably not your question or interest, but it was my main takeaway from the article. You did quote from it, but I was not sure why.


just for context basically, the quote I placed in bold was the one I was seeking clarification on exactly what that means from an objective measurement perspective. 

The proximate cause of my question is "what is the most effective way to setup my system such that I can enjoy an optimal response (given room constraints)?". The ultimate cause is that I am curious & that going into the detail of loudspeaker response feels somewhat like peeling an onion blindfolded  but once an itch is scratched then it can stay scratched for a while. 

By this I mean there is a v large gap between the basic summary information (which at best relies on practical methods useful to the layman & at worst is a mass of old wives tales and half truthes) & the underlying detail (which is clouded by psychoacoustics and/or manufacturer claims and/or the difficulty of the subject itself and/or the relatively unfamiliar and unexplained terminology). It feels like this gap is started to close as I become somewhat more familiar with the terminology and read more though.

The relevance of sealed/ported is really just because I am imminently moving from a large ported SVS sub to a larger (in driver/power terms) sealed sub.

Thanks for your replies (to this and other threads) btw, I was considering trying the method you described in the thread from a while ago about using a narrow band sweep (XO +/- 3Hz IIRC) on sub & mains for checking alignment using impulse response as a next step. I just need to get time to actual do some measurements as opposed to reading about what measurements to take.


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## jtalden (Mar 12, 2009)

If you go beyond the basic RTA setup to learn more what the actual phase impact is, I can advise or assist if you like.

If you use the narrow IR method suggested by Bill (laser188139), I will be very interested to see how well it works. I have only tried that method once and had good results.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> If you go beyond the basic RTA setup to learn more what the actual phase impact is, I can advise or assist if you like.
> 
> If you use the narrow IR method suggested by Bill (laser188139), I will be very interested to see how well it works. I have only tried that method once and had good results.


that is a most generous offer and I will be happy to take you up on it. Would you recommend starting with the narrow IR method or an alternative method?


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## jtalden (Mar 12, 2009)

> What is your AV equipment?
> Do you have the capability to do loopback measurements?
> Are you intending to confirm or fine tune the SW timing of an automated setup program like Audyssey or is this a manual setup?
> Will you be doing manual SW PEQ?
> Anything else I should know?

[I need to have a better idea of scope of the job before answering.]


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> > What is your AV equipment?
> > Do you have the capability to do loopback measurements?
> > Are you intending to confirm or fine tune the SW timing of an automated setup program like Audyssey or is this a manual setup?
> > Will you be doing manual SW PEQ?
> ...


The relevant AV equipment includes


Marantz AV 7005 processor (has audyssey multeq xt)
BFD 1124 for PEQ
SVS PB 12 Ultra sub 
M&K S85 LCR 
M&K Surround 55 Mk2 tripole surrounds

In the next few weeks, the sub/speakers will be replaced by a 15" sealed sub powered by an inuke, MK MP150Mk2 speakers across the front & MK S150T tripoles for surrounds.

For measurement, I have 


 art usb dual pre mic preamp
 Dayton EMM6 from CSL
 PC connected to the processor via HDMI (with ASIO working) or laptop connected via front analogue inputs

I am familiar with operating REW having used it for years for EQing frequency response, venturing into time domain measurements is relatively new to me. 

I am mildly suspicious of audyssey. I find it fails to eq the sub anywhere near adequately hence the BFD so current method is to EQ the 2 main modes and then run audyssey. Previous measurements suggest audyssey is aligning LCR accurately but that the surrounds are way off. I find it fails to do much for the crossover region though room simulation suggests this is a function of the MLP. The MLP will be moving forward slightly away from the rear wall in the next few months and simulation suggests this should help. I intend to take some measurements to confirm or refute this (though the MLP is going to move forward anyway due to new sofa).

Therefore the intention is first to confirm/tweak audyssey and then to enable me to accurately setup this up manually so I can do a proper comparison of audyssey vs my manual setup.

As to anything else you should know... room size/construction perhaps? The room size is not unusual for this sort of Victorian house in the UK (4.1m x 3.6m x 3.05m) with suspended wooden floors and brick walls. Flooring is currently wood but soon to be replaced by a carpet. Room treatment is largely impractical due to size of room and mixed use. LCR are horizontally aligned underneath the projector screen, sub is positioned to the right of the R speaker in the corner. There is a pic in this post

Anything else?


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## jtalden (Mar 12, 2009)

Okay thanks!
The only thing there that concerns me a little is providing a manual EQ for the SW and then running Audyssey on top of it. This may work okay, but any personal house curve will be removed and replaced with Audyssey's house curve. Would we then manually EQ again on top the initial BFD settings?

I would tend let Audyssey do its EQ first and then confirm/adjust the SW to Main timing and then follow that with any additional BFD EQ that is needed. We should also keep in mind that the experts suggest that it is not a good idea use narrow filters to try to remove narrow dips from room modes.

Okay back to the subject.
It sounds like you intend to make several setups and compare the results. We can pick just one that we work together and then you can do the others. 

Options:
1. Setup using RTA. We can then still run sweeps to just see/confirm the Phase and GD results.

2. Setup using the narrow IR method. We can then still run sweeps to just see/confirm the Phase and GD results.

3. Setup using Phase to first select the which SW to Main timing we prefer to target.

The first is the most straight forward and normally used by those that want a well setup system but not wanting to delving into all the gory details. The second is likely to find the same result, but I am not sure of that as I have little experience with it. For either of these the optional confirmation full range sweep measurements will still show us the actual phase alignment we found. The third option is more complicated as we spend time looking at optional phase/GD alignment tradeoffs before we chose one to target. The first two try to target a conventional alignment. The third provides more insight into the Phase GD tradeoffs and provide the opportunity to setup and evaluate other options.

You can chose which you want to do. Just be advised that the third option can get pretty confusing as can be seen in this thread. My involvement started at Post 129.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> The only thing there that concerns me a little is providing a manual EQ for the SW and then running Audyssey on top of it. This may work okay, but any personal house curve will be removed and replaced with Audyssey's house curve. Would we then manually EQ again on top the initial BFD settings?


I used to do that but don't at the moment, I just eq to flat so that audyssey has little to do. 



jtalden said:


> Just be advised that the third option can get pretty confusing as can be seen in this thread. My involvement started at Post 129.


I will read that thread then decide if that's ok.

Cheers
Matt


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## AudiocRaver (Jun 6, 2012)

Backtracking just a wee bit on the thread, which I have followed with fascination...

I try to be objective about what we hear and what we think we hear. Phase response and the use of linear phase filtering and/or design approaches is something that SEEMS like should be more important because it SEEMS like we should be able to hear it. That is probably mostly wishful and idealistic thinking on my part. As I stated in post #6, I know that relative phase/timing between speakers at mid & high frequencies affects imaging. And I have heard speakers that had a punchiness where percussive instruments really pop out at you - and have imagined that tight phase coherence made that possible - but alas have no proof for it.

In the review referred to in post #1, the writer says "if you want a subwoofer (or any speaker for that matter) to have a real kick, snap, hit, insert adjective of choice, you need to ensure that all frequencies it emits, are emitted at the same time and stop at the same time." Speaking with no authority at all here, but from an intuitive/aesthetic standpoint, it seems like any frequencies contributing to "snap" or "kick" in a sound are going to be well above subwoofer frequencies. A snappy kick drum or plucked bass string can have frequencies well into the Khz range, most likely where the "snap" is being experienced.

In the article referred to in post #5, the author says he heard an "audible buzz" (MP design) in one case, and what was more like a "pop" or "click" (MP design) than a thump (LP design) in another. Almost sounds more like something going nonlinear and producing higher frequency distortion components than a sound that can be attributed solely to phase shift.

Bottom line, as far as I can gather from all this: I am having a hard time being convinced that LP design in a subwoofer IN ITSELF is a super important factor. No harm in it whatsoever, and as a somewhat obsessive perfectionist and "I think I can hear it" phase-response wishful thinker, I would probably go for it all other factors being equal - those were some mighty impressive measurement waveforms in that article, that HAS to sound better, right? But in reality, paying due attention to actual psychoacoustic research, other factors like integration with main speakers at crossover and overall frequency response - as already pointed out - seem like far more important factors in the real world.

My 2 cents worth.

jtalden: Thanks, as always, for your in-depth and valuable contributions.


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## 3ll3d00d (Jun 6, 2006)

I speak here with no authority as I understand v little of how the auditory system actually works. Furthermore one can read reams about hifi/av and essentially come away none the wiser because the authors are, most likely, similarly uneducated even if they are experts in the mechanics of how a speaker functions. This produces the subjectivity common to most reviews & discussion forum and explains why so many threads are derailed into what are essentially "he said, she said" arguments. 

I think this is anathema to the more objectively minded individuals hence the desire to investigate through objective measurements. Whether this directly contributes to a more enjoyable audio experience is hard to say, if not impossible, given that there is no fixed target to aim for but it surely *indirectly* contributes because it leads one to more critically appraise/compare different setups and hence one becomes more aware of what is better/worse.

To give one example, I am currently pursuing the understanding to be able to successfully time align my setup by hand yet one source I read says that humans enjoy the "fullness of sound" presented by a multi sub setup that is naturally (unless you place them miles apart) slightly out of time alignment. Is this true? I have no idea. Is it true but is a side effect of some other thing that appears to derive from multi sub setup? Again, no idea. 

If anyone has any recommendations of a good laymans "this is how we think the auditory system works" (popular science basically a la stephen pinker) then that would be interesting to read.

A somewhat OT ramble there, back to the 21 page thread on phase alignment!


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## AudiocRaver (Jun 6, 2012)

3ll3d00d said:


> To give one example, I am currently pursuing the understanding to be able to successfully time align my setup by hand yet one source I read says that humans enjoy the "fullness of sound" presented by a multi sub setup that is naturally (unless you place them miles apart) slightly out of time alignment. Is this true? I have no idea. Is it true but is a side effect of some other thing that appears to derive from multi sub setup?


The suggestion that speakers or subs that are not well time-aligned gives a "fullness of sound" that "humans enjoy" sounds like suggesting making use of the Haas effect, a slightly-delayed (under 30 ms or so) signal or sound that combines with the first electronically or acoustically and the ear cannot tell that the second signal or sound from the first but the combined result sounds "bigger." In recording and mixing, it is often used as an effect, as in guitar or vocal doubling. As an effect, it can sound great, but it also sounds _different,_ and might sound OK sometimes and not so OK other times. To suggest that "humans enjoy" it ALL THE TIME seems a bit of a stretch. It does not seem to be in the spirit of keeping the sound as accurate as possible to the original recording.

On the other hand, there are a lot of spacial processing technologies that play with delays and change the sound from the original and some people like it. So it depends on one's preferences. A purist would probably avoid the approach, I would think, or at least implement it in a way it could easily be turned on or off for comparisons.


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## 3ll3d00d (Jun 6, 2006)

FWIW The source of that comment is this page - http://www.soundoctor.com/whitepapers/subs.htm

Fundamentally the q remains what is "good" audio to the brain? 

Cheers
Matt


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## AudiocRaver (Jun 6, 2012)

3ll3d00d said:


> Fundamentally the q remains what is "good" audio to the brain?


And the a to that q is.... I know what *I* like, and if you don't feel the same there is something wrong with you.

Totally joking, of course. Funny, at some point we all turn into philosophers in these discussions. And at some point we end up referring unconsciously to powerful formative experiences - sometimes we remember them consciously and sometimes we do not - those moments when we choke up a little over some thing as silly as a certain pair of speakers set up just right, or a nexus moment in a home theater where all the forces of source and acoustics and electronics and transducers and maybe a glass of wine and the right company all conspire to bring chills or tears or delighted laughter - and even better when we begin to understand what goes into making _that sound_ and how to repeat it - but *why* we like that particular sound may remain a mystery - and it is those experiences that seem to define what you like vs. what I like vs. what she or he likes, and sometimes we agree on what we like and sometimes we do not. We try to be objective - everyone prefers flat frequency response over a bumpy response curve, right? - and objectivity can help us get clarity and even shift our preferences a bit sometimes - but in the end, "the heart wants what it wants," and I might scratch my head over your preference but waste your time and mine arguing about it. _I know I can convert her/him if I explain it JUST the right way._ It usually never happens, individual preference prevails. And the world is more interesting because of it (spoken like a true audio liberal, eh?).

Imaging - with tight, clear, laser-sharp localization at all frequencies - is the main audio experience that stops my beating heart, gives chills, etc. My listening brain does a double-take: is it real or is it from the speakers? Delights me every time. Why? Don't know or even care. For someone else it is... I can not know what else it might be or why. But it never hurts to try to understand that about another and take it into account as we discuss these video & audio matters. Of course it is objectivity that allows us to have these discussions, and nothing beats good old science and research and the common ground it gives us to work with.

Referring to the linked article (quite a good one), the rebel in me always reacts a little when someone lumps me into the category of "all humans" (maybe I am an alien - that might actually explain a few things) and tells me what I/we always like. Pride aside, back to imaging, my personal holy grail in audio -- and if that sounds like it borders on being mystical or auditorially spiritual, that is about what it feels like - _to me_ - when it happens -- a strong component in achieving it is a _minimum_ (zero) of what Barry points out twice in the article as being something magic that all humans like. To Barry's credit, he also bottom lines the importance of personal preference: "Indeed the only thing that does matter is an individual's happiness with their system, whether I or anyone else thinks it's right or wrong."

BTW, I know you weren't looking for another discourse, I am just in that kind of mood tonight.lddude:

Peace and love.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> The third option is more complicated as we spend time looking at optional phase/GD alignment tradeoffs before we chose one to target. The first two try to target a conventional alignment. The third provides more insight into the Phase GD tradeoffs and provide the opportunity to setup and evaluate other options.
> 
> You can chose which you want to do. Just be advised that the third option can get pretty confusing as can be seen in this thread. My involvement started at Post 129.


I'd like to try this approach. I have read that thread once fairly thoroughly & it seems reasonably straightforward from a method point of view & the systematic approach appeals. I have read a couple of different overviews of the approach (http://www.hometheatershack.com/forums/rew-forum/59784-first-measurement-20.html#post537709 or http://www.hometheatershack.com/for...ew-set-distance-main-speakers.html#post534896) but if there is some specific steps I need to take then pls let me know.

Thanks
Matt


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## 3ll3d00d (Jun 6, 2006)

AudiocRaver said:


> And the a to that q is.... I know what *I* like, and if you don't feel the same there is something wrong with you.
> 
> Totally joking, of course. Funny, at some point we all turn into philosophers in these discussions.


(rest of quote elided for brevity)

Interesting thoughts & I don't know whether I've ever really experienced imaging like that ("with tight, clear, laser-sharp localization at all frequencies"). My room is a compromise hence one has to make do as much best one can. I can certainly share the feeling though, of the moment watching (I am more av than hifi) something where the whole soundstage comes alive :clap:


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> I'd like to try this approach. I have read that thread once fairly thoroughly & it seems reasonably straightforward from a method point of view & the systematic approach appeals. I have read a couple of different overviews of the approach (http://www.hometheatershack.com/forums/rew-forum/59784-first-measurement-20.html#post537709 or http://www.hometheatershack.com/for...ew-set-distance-main-speakers.html#post534896) but if there is some specific steps I need to take then pls let me know.
> 
> Thanks
> Matt


Yes, either of those will get us started. Just follow the one that is more clear to you. Mark the mic location and note the height as there will be several measuring sessions. We should be careful to locate mic as close as possible to the same location each time. For a SW setup like this it is not overly sensitive, but we should try to keep it as close a possible without undue effort. I would think we can get relocated within 2 inches pretty easily.

After we find a setting for SPL fill through the XO, we can then look at the resulting phase alignment and see how well it tracks. To look ahead and get some idea of the process for doing that you can read this thread if you like.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> Yes, either of those will get us started. Just follow the one that is more clear to you. Mark the mic location and note the height as there will be several measuring sessions. We should be careful to locate mic as close as possible to the same location each time. For a SW setup like this it is not overly sensitive, but we should try to keep it as close a possible without undue effort. I would think we can get relocated within 2 inches pretty easily.
> 
> After we find a setting for SPL fill through the XO, we can then look at the resulting phase alignment and see how well it tracks. To look ahead and get some idea of the process for doing that you can read this thread if you like.


Mild confusion at the first hurdle. After the usual yak shaving whenever I pull out REW (turns out my laptop emits a serious mains hum when it is connected to mains power and driving REW), I followed the method in this post.

My questions are many 

* I assume I align peak to peak or trough to trough, correct?
* the initial peak or trough for the SW is v small (~-10%) and they get successfully larger, which one should I aim for? the first irrespective of size of a later one?
* based on physical distance, my SW is ~5ms behind (and BFD bypass pushes this out by 1ms so I presume it is accurate), ~5ms is ~1.7m which is about 1/2 100Hz wavelength which is what my XO is. If aligning large FR trough to small SW trough is accurate, this seems rather coincidental but I'm not sure what it means nor what to do with it.

My setup notes follow


```
Setup
=====

Physical Distance
-----------------
FR -> MLP = 2.95 + 0.28 = 3.23
SW -> MLP = 2.75 + 0.28 = 3.03

Initial Processor Setup
-----------------------
FR Delay = 5
SW Delay = 4.8
Audyssey = Off
Electrical XO = 100
Mode = Stereo

BFD Setup
---------
EQ'ed for a flat response

REW Config
----------
Mic at 0 degrees pointing at FR
Levels checked using Mains to 75dB
In levelled to -18dB FS
Ref In levelled to -14dB FS (seems quite twitchy so just got close)
44.1kHz throughout the chain
1/6 smoothing

Connectivity
------------
Win7 -- Art Dual Pre USB -- AV 7005 AUX R
AV7005 - BFD - SVS PB 12 Ultra

Sweep Config
------------
Range = 15-20k
Level = -12dB FS
Length = 256k
Sweeps = 1
```


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## h5tuu (Nov 26, 2011)

No sub in that .mdat file? Are you crossing over at 80hz? The full range sweep would point to this.


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## 3ll3d00d (Jun 6, 2006)

h5tuu said:


> No sub in that .mdat file? Are you crossing over at 80hz? The full range sweep would point to this.


strange, must be user error as I was sure I'd saved the file including the SW.

XO is 100Hz.

I would attach another mdat but the board is repeatedly saying "Your submission could not be processed because a security token was missing." so I will share it via my gdrive 

and to compound the user error, I see I misread this as "adjust the SW" 



> We will adjust the one that is set to 5 m. In this example that is the FR.


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## 3ll3d00d (Jun 6, 2006)

After some confusion with which direction is direction when it comes to shifting impulses via the calc method vs delays in the receiver (it seems backward to my mind), I think the calc method shows that shifting the FR by +5ms to meet the SW should give better SPL support through the XO range. My mdat is here (too big for upload) and I calculated in 0.5ms increments from +4.5 to +6.5ms (where the + refers to pushing the FR further out in time to meet the SW). The increase is between +3dB and +6dB in a roughly XO +/- 35Hz range (which is a range somewhat inside the -20dB points of the FR and SW individually).

I think that's my fill of measuring/calculating for the evening. A scriptable interface (e.g. a groovy console or similar) into REW would be a massive time saver & would lower the bar to entry to this sort of activity (e.g. publish script(s) on github that let you drive REW in a particular way).


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> * I assume I align peak to peak or trough to trough, correct?


No. It's not critical as it is just a starting point, but the best guess is to place the initial rise of the SW and FR IRs at about the same timing. I might say the SW initial rise appears to be about about 2 ms delayed from the FR. We just want to be in the ball park however and it is difficult to say much more that the SW is someplace between 2 and 4 ms delayed.



> * the initial peak or trough for the SW is v small (~-10%) and they get successfully larger, which one should I aim for? the first irrespective of size of a later one?


Yes, the first it is smaller than expected. Do you have the "phase" setting on the SW set to 0°? Increasing the SW "phase" control can create a small initial peak like this. We want "phase" set at 0°.

Yes, the SW IR peaks are still increasing even after the 2nd or 3rd peak where it is expected to be falling. I am not sure why this is. The .mdat you attached did not include the SW measurement even though it appeared on the chart you posted. Maybe I could get a hint of the issue if you post its .mdat. This may or may not be an issue, but I won't know until I review the data.



> * based on physical distance, my SW is ~5ms behind (and BFD bypass pushes this out by 1ms so I presume it is accurate), ~5ms is ~1.7m which is about 1/2 100Hz wavelength which is what my XO is. If aligning large FR trough to small SW trough is accurate, this seems rather coincidental but I'm not sure what it means nor what to do with it.


Yes, as you noted, the SW delay appears to be greater than expected based on the distance measurements. It's good that you indicate the BFD applies its delay even when in bypass mode. We want its extra delay to be included in this setup exercise. Since the SW IR delay appear to be greater than we wanted, a better starting point may be to increase the SW distance by 1 m In the AVR (which will reduce SW delay by almost 3 ms).


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> After some confusion with which direction is direction when it comes to shifting impulses via the calc method vs delays in the receiver (it seems backward to my mind), I think the calc method shows that shifting the FR by +5ms to meet the SW should give better SPL support through the XO range. My mdat is here (too big for upload) and I calculated in 0.5ms increments from +4.5 to +6.5ms (where the + refers to pushing the FR further out in time to meet the SW). The increase is between +3dB and +6dB in a roughly XO +/- 35Hz range (which is a range somewhat inside the -20dB points of the FR and SW individually).
> 
> I think that's my fill of measuring/calculating for the evening. A scriptable interface (e.g. a groovy console or similar) into REW would be a massive time saver & would lower the bar to entry to this sort of activity (e.g. publish script(s) on github that let you drive REW in a particular way).


Okay, you are moving ahead.
I just looked quickly at the data (If you zip the file you may be able to post it here, but your option is fine with me also).

My first observation is that you adjusted the wrong direction. The SPL support is indeed better, but the SW delay is now much greater. Excess SW delay will cause excessive GD of the system. Why don't you try again and in the meantime I will also find the conventional alignment and we can then compare notes. 
I like that you are able to do this adjustment via shifting the IR and recalculating the new response. It is much easier to do than resetting distances and remeasuring. Well done!


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## jtalden (Mar 12, 2009)

In looking at the SW IR it appears there may be a problem. The 1-2 leading smaller peaks suggest something may be wrong. I am not sure what it is. You are measuring only a single SW by itself - correct? 

Do you get a cleaner IR from a different mic position? Try just placing the mic 2-5 cm from the SW cone. Lower the level so you don't overload the signal. Is the measurement there cleaner? I have seen SW IRs with extra peaks in front before, and just assumed there was a problem. Maybe this is "normal" for some SWs and more common than I thought. Maybe this is a room effect but it doesn't look like it to me. I'm still thinking something isn't right.

Below is the IR for my SWs measured at my LP for your comparison.


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## 3ll3d00d (Jun 6, 2006)

To answer a few of the points;

* there is 1 sub which is placed quite near the FR speaker
* phase is at 0 on the sub, all controls on the sub are defeated except the subsonic filter (16Hz)



> a better starting point may be to increase the SW distance by 1 m In the AVR (which will reduce SW delay by almost 3 ms).


I definitely initially adjusted in the wrong direction but I didn't think I was in the last mdat that I posted. My naming convention is (CHANNEL)[+-](offset) so FR+4 means I have delayed the FR by +4ms and SW-4 would mean I have reduced the delay of the SW by 4ms. In these terms + means increase in processor distance and - means reduce (i.e. +x means I want the sound to arrive x ms later so it needs to be y m further away). 

Looking at the GD plots shows excess GD at 100Hz of

* SW = ~26ms
* FR = ~20ms
* FR+5 = ~25

If the above is incorrect then I am definitely missing something onder:

I will try and take some more measurements tonight, might be tomorrow before I get a chance though.

Thanks
Matt


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> * phase is at 0 on the sub, all controls on the sub are defeated except the subsonic filter (16Hz)


The SS filter should not have caused the additional IR peaks. The IR I posted also has a SS filter. It still may be a good idea to turn it off once and run a sweep just to confirm that it isn't the problem.




> I definitely initially adjusted in the wrong direction but I didn't think I was in the last mdat that I posted. My naming convention is (CHANNEL)[+-](offset) so FR+4 means I have delayed the FR by +4ms and SW-4 would mean I have reduced the delay of the SW by 4ms. In these terms + means increase in processor distance and - means reduce (i.e. +x means I want the sound to arrive x ms later so it needs to be y m further away).
> 
> Looking at the GD plots shows excess GD at 100Hz of
> 
> ...


??
Below is the IR plot of SW and SW-5 in your data. This appears to be an adjustment you made in the AVR distance setting of about -2 m (reducing the distance in the AVR by 2 m increases the delay about 5.9 ms). Above, you alluded to shifting the delays by calculation and this SW-5 is shifted by AVR distance setting so possibly you just linked the wrong .mdat? Regardless, it is clear that the SW-5 trace is a new measurement rather than a shifted version of the original SW measurement and that it is delayed about 5.9 ms more than the original SW measurement so something still needs to sorted out.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> The SS filter should not have caused the additional IR peaks. The IR I posted also has a SS filter. It still may be a good idea to turn it off once and run a sweep just to confirm that it isn't the problem.


I have gone back and checked some older mdats & can see that a previous nearfield measurement looks "clean" while most other LP measurements show the same sort of uneven impulse response. I'm not 100% sure which equipment I used to take those measurements now so later on I will take measurements (combinations of near & far field; direct connection to sub & through processor; SS on/off) to see whether I can track down the source of the "noise".



jtalden said:


> ??
> Below is the IR plot of SW and SW-5 in your data. This appears to be an adjustment you made in the AVR distance setting of about -2 m (reducing the distance in the AVR by 2 m increases the delay about 5.9 ms). Above, you alluded to shifting the delays by calculation and this SW-5 is shifted by AVR distance setting so possibly you just linked the wrong .mdat? Regardless, it is clear that the SW-5 trace is a new measurement rather than a shifted version of the original SW measurement and that it is delayed about 5.9 ms more than the original SW measurement so something still needs to sorted out.


I believe I have confused matters by posting multiple MDATs and not being specific about which one I'm referring to in my posts. Apologies. I posted 3 files across 3 posts, I will repost links here.

* initial.mdat - this one was the 1st one & was posted erroneously as it was missing the SW measurement
* initial_mk2.mdat - this one contains the SW-5 measurement when I was adjusting in the wrong direction
* initial_mk3.mdat - this is initial_mk2 + the shifted by calculation FR curves (aka FR+[4|4.5|5|5.5|6|6.5])

I did indeed take the SW-5 measurement & it was after this that I realised my error and started delaying the FR to meet the SW by calculation alone. 

Thanks
Matt


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## 3ll3d00d (Jun 6, 2006)

My sub does not have a setting to defeat the SS filter so here are some measurements taken from with REW connected directly to the SW moving the mic from the MLP to the SW in approximately 0.75m increments and ending with a nearfield reading. NF in my case means mic stand lying on the floor as it is a DF sub with a floor plate (see pic). 

The NF case looks similar to yours, everything else does not.

FWIW the sub is ported, in the corner and has 1 of the 3 ports blocked. I cannot hear any obvious distortion. The shape of the impulsee is the with 2 ports blocked and/or the sub pulled out into the middle of the room.

Could this be an artifact of the room construction, i.e. wooden floorboards on suspended wooden joists?

Cheers
Matt


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> I believe I have confused matters by posting multiple MDATs and not being specific about which one I'm referring to in my posts. Apologies. I posted 3 files across 3 posts, I will repost links here.


That's my mistake. I overlooked your 3 set of data. I will look it over later tonight and comment. My first glance is that it is aligned similar to what I found as a reasonable alignment.


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> My sub does not have a setting to defeat the SS filter so here are some measurements taken from with REW connected directly to the SW moving the mic from the MLP to the SW in approximately 0.75m increments and ending with a nearfield reading. NF in my case means mic stand lying on the floor as it is a DF sub with a floor plate (see pic).
> 
> The NF case looks similar to yours, everything else does not.
> 
> ...


Yes, this suggest the reason for the IR appearance is probably due to the room response with that SW placement. Since the IR didn't clean up until you did the NF measurement I don't think anything can be done to clean it up other than moving the SW. You may not have that option and I don't expect the sound will be significantly different even if you do. I think you have already found a good alignment located where it is. If the SPL response was very erratic I would suggest a change, but the SPL looks pretty good for EQ purposes so I will probably sound fine. Use your own judgment.


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## jtalden (Mar 12, 2009)

Matt,
I reviewed the 3rd data set. You identified FR+5 as a good alignment and I agree. This is as close as you can get to a "conventional" alignment where the phase tracks closely throughout the entire XO range.

I shifted your FR+5 and SW 20.111 ms to place the IRs near 0ms and then looked at the resulting phase tracking. As shown below the phase tracking is good with the only significant deviation appearing at the lower XO frequencies (<60 Hz).









In an attempt to improve on this I inverted the SW polarity and reduced its delay (4 ms). Below are the results. This helped the phase tracking in the 40-60 Hz range but the tracking around 80 Hz XO is not quite as good. The SPL chart shows the very minor SPL impact of these 2 alternate setups. This appears to be pretty much a tradeoff so either one could be considered the best "conventional" setup, but I lean toward the one you found.


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## 3ll3d00d (Jun 6, 2006)

Evening

Thanks for the info. I have a few questions for you if i may.

* is phase tracking significantly below the XO important? if so, why? aka what is the audible signature of poor phase tracking?
* why do we need to shift the responses to 0 to compare phase?

If the FR+5_SW is a good alignment, are the next steps

* adjust FR distance to actual tape measure distance
* adjust SW distance to maintain the offset from the FR+5_SW reading
* confirm via measurement
* align FL/CC/SL/SR with FR
* evaluate via (critical) listening sessions

Thanks
Matt


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> * is phase tracking significantly below the XO important? if so, why? aka what is the audible signature of poor phase tracking?


We can see that the SPL around 60 Hz was impacted a little as a result of the phase starting to diverge. The other alignment was better around 60 Hz but was not as good around 80 Hz. They were both very minor impacts however so from and EQ perspective there is not much difference. 

The phase of an ideal LR-4 acoustic XO would track throughout the whole range. We would hardly ever see an ideal acoustic XO as the drivers rarely follow and ideal phase shift. So even if we apply the ideal electrical XO accounting for expected driver characteristics there will still normally be some deviation in the acoustic phase response as we saw here. That is one reason why I like to look at the phase response and see which alignment tracks better.

As to audibility that is something that you may want to decide yourself. I have evaluated a couple hundred XO types using my DCX2496's. I would say that the SPL smoothness and the house curve is much more critical that the phase tracking. I do feel that I can tell a difference in both my XO areas with different XO setting even though I can keep the SPL response almost identical. It's normally pretty subtle however.

In my system I tend to like the sound when the SW IR precedes the mains IRs by 1/2 or even 1 full wavelength relative to the conventional alignment particularly when I am using steeper XOs. The conventional setup usually sounds a little too heavy particularly on some male voices. I have never seen anyone else indicate that they also do this and prefer it. So if you are only going to try one then stick with the conventional alignment. Its pretty easy to evaluate both as the only change is normally the SW distance and polarity change. The EQ is normally not impacted significantly.



> * why do we need to shift the responses to 0 to compare phase?


With the IR several ms from zero (the reference time) the phase slope is very steep this makes it very difficult to read the vertical offset indicating the phase differential. It's easier to read and get the correct mental perspective when the IR peak is someplace near zero. It's even more critical when looking at total phase rotation over the entire freq range. Then it is important the place the IR peak at, or very near zero.



> If the FR+5_SW is a good alignment, are the next steps
> 
> * adjust FR distance to actual tape measure distance
> * adjust SW distance to maintain the offset from the FR+5_SW reading
> ...


Yes that basically correct. You have the idea and it can be approached in several ways. 

I may have said:
> Align the IRs of the FL/CC/SL/SR with FR
> You will want to then check the FL (and possibly the CC) for SPL reinforcement through the XO range. If your room is symmetrical then I would expect both to be similar for both SPL an Phase. If the room setup is asymmetric there can be a significant difference. [My FR and CC are similar and the FL phase is maybe 70° different through the XO and its SPL is impacted accordingly.]
> You can then pull out the excess distances if you like. With most AVRs the actually internal delay is set by assigning 0 ms delay to the furthest speaker and then adding the needed delay to the others based on the difference in distance to that speaker. Adding or subtracting a fixed distance from all speakers will therefore have no actual impact on the actual AVR delays. 
> Set a house curve and EQ as needed.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> Yes that basically correct. You have the idea and it can be approached in several ways.
> 
> I may have said:
> > Align the IRs of the FL/CC/SL/SR with FR
> ...


OK thanks. I think more measurements will follow by the end of the week.

My room is asymmetrical due to the presence of an open fireplace & chimney on the R side. Am I right in thinking this just becomes a case of looking for the alignment that is most consistent across the range & channels?


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## jtalden (Mar 12, 2009)

Yes, I don't think there is one right way to do this. I have tried several approaches and have no idea if one is better than another. I usually do sort of a weighted average. That is I set the alignment mostly to the CC and FR that agree, but shade the timing a little toward the FL to ease the EQ burden there a little. [I am manually EQ'ing all 6 channels.]

Even though your room is asymmetrical the differences in the front channels may not be significant. Only testing will tell.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> Yes, I don't think there is one right way to do this. I have tried several approaches and have no idea if one is better than another. I usually do sort of a weighted average. That is I set the alignment mostly to the CC and FR that agree, but shade the timing a little toward the FL to ease the EQ burden there a little. [I am manually EQ'ing all 6 channels.]
> 
> Even though your room is asymmetrical the differences in the front channels may not be significant. Only testing will tell.


Some additional measurements 

1) processor set to physical distances, FR and SW measured -
View attachment physical_distance_fr_sw.mdat

2) final calculations for best alignment (as per previous posts) based on FR and SW alignment -
View attachment calculated_alignment_fr_sw.zip

3) processor set to calculated distances, FR and SW measured -
View attachment calculated_distance_fr_sw.zip

4) processor set to calculated distances, FL measured -
View attachment calculated_distance_fl.mdat


As far as I can see, this shows that the calculations were accurate and that manual alignment has improved the response through the XO. It also shows that the FL seems accurately time/phase aligned with the FR.

Do you agree? 

Next step repeat for CC/SL/SR & then compare against audyssey.

Cheers
Matt


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## jtalden (Mar 12, 2009)

1-3 look good. Nice work.
4 was a bit if a puzzle to me. I don't see enough info in data set 4 to make any comment. There is no measurement of the SW alone. I always need to see SW, Main and SW+Main to evaluate the alignment. 

I decided to import the 3rd data set in with the 4th set expecting that SW would be correct for IR timing and level. The SW level of FL-1.82m_SW was about 1.9 dB higher than it was for the measurements in the 3rd set (FR). I assume you changed SW level a little?

After manually adjusting the SW level I was still able to confirm that your settings are good.

The mic position was only off center enough to create a 2" difference in IR timing so your mic position is very nearly centered. The SPL support through the XO range was also good and the Phase alignment was similar to the FR as you noted.

All looks good.

A check of the CC distance and alignment is a good idea, but we would not expect to find a problem. 

The surrounds phase may look a little strange as they are a very different design. That is not really an issue though. We can just make sure the distance is set such the IR's align as well as possible with the front speakers.

You sure caught on to this procedure quickly. :sn:


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> 1-3 look good. Nice work.
> 4 was a bit if a puzzle to me. I don't see enough info in data set 4 to make any comment. There is no measurement of the SW alone. I always need to see SW, Main and SW+Main to evaluate the alignment.
> 
> I decided to import the 3rd data set in with the 4th set expecting that SW would be correct for IR timing and level. The SW level of FL-1.82m_SW was about 1.9 dB higher than it was for the measurements in the 3rd set (FR). I assume you changed SW level a little?
> ...


The mic was placed in alignment with the CC, for the FR readings I rotated it to point straight at the FR in the 0 degree alignment so for the FL reading I just rotated it to point straight at the FL. I thought that since the movement of the mic capsure was miniscule then it would be fine to reuse the previous SW reading (but I might also have been being lazy as it was getting late!). I think I had to restart REW for arcane reasons so that might explain the difference in level as I had to redo the SPL calibration.



jtalden said:


> You sure caught on to this procedure quickly. :sn:


your instructions have been v clear and methodical so it's been easy to follow. Your help much appreciated.


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> The mic was placed in alignment with the CC, for the FR readings I rotated it to point straight at the FR in the 0 degree alignment so for the FL reading I just rotated it to point straight at the FL. I thought that since the movement of the mic capsure was miniscule then it would be fine to reuse the previous SW reading (but I might also have been being lazy as it was getting late!).


Okay. That will work fine for a SW setup. 

> We can also point the mic forward in the direction of the CC and use that for all 3 front mains. The polar response of the mic is broad enough that I find no difference when being off angle to FL and FR by 30°

> Better yet, I do find it easier to orient the mic vertically at the LP for distance/phase/timing/levels. That way the mic has pretty much the same sensitivity all speakers. This works even if you don't have a 90° calibration file. The actual SPL level at HF is not the issue here. We are mainly interested in the distance/phase. We can also adjust the relative SPL levels of all the channels accurately with this vertical mic orientation. This way there is no need to move the mic for any of the channel measurements.

Once the distance/phase/timing/levels are established then we are ready for EQ. For EQ I normally point the forward in the direction of the CC and leave it there for the 3 front mains and then the point it in the direction of each surrounds. Others prefer to continue to use the vertical orientation for EQ as well. In that case they use a 90° mic calibration file to assure the HF response is accurate. I recently investigated the impact of this in my room and the difference was very minor. I think very good results can be achieved either way.



> I think I had to restart REW for arcane reasons so that might explain the difference in level as I had to redo the SPL calibration.


If you are careful not to change the input level on the Art Dual Pre there is no need to redo the SPL calibration. REW saves and reloads the calibrations for each session.


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## 3ll3d00d (Jun 6, 2006)

I had a new sub and speakers installed last week and so have started attempting to set them up. My process this time was;

* run audyssey to get initial distances
* take main, sw, main+sw measurements with and without audyssey
* examine IR, note that switching audyssey on incurs ~8ms delay
* switch audyssey off, examine IR, make adjustments to timing to try and achieve better alignment

At this point I note that audyssey has aligned the mains to the v start of the rise of the SW IR whereas, previously, I think we were aligning to the 1st peak. 2 things stand out

* attempting to shift the main to meet the peak of the 1st SW rise produces reduced SPL through the XO
* phase alignment in either case (shifted main or as is) doesn't look great

I'm not sure what to make of this. Any comments would be appreciated.

Thanks
Matt


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## jtalden (Mar 12, 2009)

The Audyssey timing is okay. The SPL reinforcement through the XO is reasonably good. The initial IR rises are at reasonably close timing as we should expect (as noted in Post 31).

I did find an alignment I liked better by reducing the SW delay by 13 ms (about 1 wavelength). This helped to align the phase a little closer through the lower XO range (about 45-100 Hz). I was not able to find good timing that helped the upper XO range (about 100-150 Hz). 

The small initial SW IR peak now leads the L IR. I guess this is an example of a case where a close look at phase was beneficial. See the charts below:















I think either the Audyssey timing or this one would work out okay.

I found this data to be very difficult to interpret. The very small initial IR peak is problematic. I think this is due to the room modes in the XO area, but also think the that the large single SW SPL peak is distorting the IR and the resulting phase making it difficult to interpret. EQ of the SW before setting the timing may help this situation, but I am not sure.

When you are not using Audyssey, just apply some EQ to the SW before adjusting the timing. The phase may be easier to read. There may be a some impact to the timing results as well. The final EQ can always be redone after the timing is finalized. 

When you are intending to use Audyssey and just optimize it, I would suggest that you work on the timing adjustments with Audyssey engaged. Again, the EQ smoothing may help to clarify the timing better and there may be some timing shift as well. You can then put some BFD EQ on top of that as a final step if needed.

Had we done this its possible I would have a found timing more in line with Audyssey?


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## 3ll3d00d (Jun 6, 2006)

My usual (eq only) workflow is to eq the sub to broadly flat and then run audyssey as I find audyssey generally does a good job at cleaning up the mains but has never adequately coped with the sub in my room. Perhaps this would be different if I had an XT32 or ARC powered processor but, atm, I do not.

I did attempt to tune with audyssey on but the shape of the impulse was v similar so I didn't present those results here. Therefore I think you're right that I should try to clean up the response first via eq and then retry fine tuning the alignment. I am also thinking that the narrow sweep method might be useful here in order to try and ameliorate the effect of the room.

Thanks
Matt


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## jtalden (Mar 12, 2009)

The narrow sweep method should work well to find an alignment at one very narrow set of frequencies. Unfortunately it does not give visibility to what is happening further away. [It does hint at it though.] I would expect that if we chose 75 Hz and use that method we would be able to identify these same two potential alignments.

Considering that we have already found them and also have full visibility to the alignment throughout the XO range we could just choose one and move forward with the process.

If you want to pause and experiment with narrow IR method or just spend more time experimenting with the phase interpretation that's great. Experimentation is how I develop a reasonable working understanding of the tradeoffs involved in various XO alignments.

Just a note regarding my previous post:
The acoustic XO is now at 75 Hz and the range only extends up to 100 Hz at the present time. There is very good SPL support in that range for both alignments. My comment on the upper range extending to 150 Hz is a recognition that the electrical XO is apparently at 100 Hz and the upper end would be nearer 150 Hz. With the current SW levels there is low relative SPL output in that range and thus there is no opportunity for support there. I probably shouldn't have mentioned this as it is a fine point. It is best to just focus on the actual acoustical XO range. We just need to understand that if the relative levels are changed significantly the acoustical XO and the resulting range will also change.


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## 3ll3d00d (Jun 6, 2006)

I much appreciate your continued attention to this thread. I think this thread (and the linked ones) has taught me more about what is going on & how to measure/examine/experiment than any other discussion I've participated in.



jtalden said:


> Considering that we have already found them and also have full visibility to the alignment throughout the XO range we could just choose one and move forward with the process.


OK well moving forward is good, leaving an itch unscratched is not ideal but may be an unsolvable problem in the near term. 

The thing that is playing on my mind is whether my "messy" IR is indicative of an actual problem that has a deleterious effect on SQ or whether it is just an irrelevant red herring. I find it interesting that audyssey aligns to the v first rise whereas REW targets the first large range (when you ask it to shift the IR). I am completely in the dark as to whether this is meaningful or not. 



jtalden said:


> If you want to pause and experiment with narrow IR method or just spend more time experimenting with the phase interpretation that's great. Experimentation is how I develop a reasonable working understanding of the tradeoffs involved in various XO alignments.


I would like to complete a solid 1st pass at the setup and then experiment at leisure. I don't have a dedicated room, my wife is most accommodating to refactoring the room to focus on the cinema but she has her limits when it comes to running sweeps etc.



jtalden said:


> The acoustic XO is now at 75 Hz and the range only extends up to 100 Hz at the present time. There is very good SPL support in that range for both alignments. My comment on the upper range extending to 150 Hz is a recognition that the electrical XO is apparently at 100 Hz and the upper end would be nearer 150 Hz. With the current SW levels there is low relative SPL output in that range and thus there is no opportunity for support there. I probably shouldn't have mentioned this as it is a fine point. It is best to just focus on the actual acoustical XO range. We just need to understand that if the relative levels are changed significantly the acoustical XO and the resulting range will also change.


FWIW the electrical XO is 80Hz in these measurements. 

It feels like there is a point here that I am not grasping. To my understanding/thinking, we have a XO that obviously rolls off each participant to a certain slope. We are below the transition frequency so modal interaction is to be expected which will impact the response accordingly. This means the theoretical XO is quite likely to not equal the acoustic XO and hence when looking for SPL support and/or EQ, we need to work off reality (the acoustic XO) while being mindful of theory (the electrical XO) in the event we decide to shift the XO frequency as we may find that moving the XO does not provide the additional output from any of the participating speakers. Is that what you mean when you talk about changing the relative levels or am I talking about something else entirely?

Cheers
Matt


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## jtalden (Mar 12, 2009)

3ll3d00d said:


> OK well moving forward is good, leaving an itch unscratched is not ideal but may be an unsolvable problem in the near term.


It will probably some time and experimentation on your own if you want to really have a good understanding. It took me quite a while but I enjoyed the process. 



> The thing that is playing on my mind is whether my "messy" IR is indicative of an actual problem that has a deleterious effect on SQ or whether it is just an irrelevant red herring. I find it interesting that audyssey aligns to the v first rise whereas REW targets the first large range (when you ask it to shift the IR). I am completely in the dark as to whether this is meaningful or not.


I understand. Unfortunately, I cannot help with the "messy" IR as my experiences are limited to my situation. With my lack of close knowledge of your entire situation and my lack of experience in other rooms it is only wild guesses that I can offer - not much help. My imagination pictures a room with limited soft features (a relatively reverberant room) and dimensions resulting in strong standing wave at 42 Hz and a mic position that is somehow near the peak of that standing wave. This is probably very far from reality, but it's the only thought that I have to explain the "slowly building" IR. Possibly others with more experience in various rooms would have more useful thoughts. If there is a standing wave or resonant surface (as suspended floor, wall or ??) maybe the response can build? We both could use some help here.

Regarding the impact on the SQ: I am again limited. I would guess that if the SPL is EQ'ed to a reasonable response in the LP area then the sound quality would still be very satisfactory. SPL is still the most important aspect in my book and if the sound is not right then a change to the house curve is the first thought rather than any attribution to phase, speaker quality, or other factors. In the end those can be factors but I would sure try to rule out house curve first.

Regarding the timing choice Audyssey made: It's the same as I would have made if I was developing an automated system. We expect the initial rise to quickly lead the largest peak and room response to follow at lower levels. We want to align the initial rise as that is the onset of the direct signal and the idealized LR-24 target XO would align well that way. We would not anticipate an IR like yours so the Audyssey timing choice was reasonable and will probably work just as well as the one I would have chosen. 



> I would like to complete a solid 1st pass at the setup and then experiment at leisure. I don't have a dedicated room, my wife is most accommodating to refactoring the room to focus on the cinema but she has her limits when it comes to running sweeps etc.


She need a hobby;... an out-of-the-house hobby!... Maybe a boyfriend?... I digress. :bigsmile:



> FWIW the electrical XO is 80Hz in these measurements.


I guessing as much. That much deviation is not unusual so nothing to worry about.



> It feels like there is a point here that I am not grasping. To my understanding/thinking, we have a XO that obviously rolls off each participant to a certain slope. We are below the transition frequency so modal interaction is to be expected which will impact the response accordingly. This means the theoretical XO is quite likely to not equal the acoustic XO and hence when looking for SPL support and/or EQ, we need to work off reality (the acoustic XO) while being mindful of theory (the electrical XO) in the event we decide to shift the XO frequency as we may find that moving the XO does not provide the additional output from any of the participating speakers. Is that what you mean when you talk about changing the relative levels or am I talking about something else entirely?


Everything you said is correct, but when I referred to "levels" above, I was referring to the basic relative SPL level of the SW Vs the FL. In the AVR you can adjust the level of each speaker to balance the SPL level of the 2 speakers. My point was that if the relative levels we are working with now are changed significantly as a result of future EQ settings the acoustic XO frequency will also change. [Imagine boosting SW level by 10 dB (leaving the FL unchanged) now the acoustic XO would be above 80 Hz.] So, if we are not close initially. We may need to revisit the timing. Said another way; EQ, Levels and Timing have an interaction. This only means that if we are far from the final settings on one of them we need to revisit the impact on the others. I mentioned this because your SPL is very peaked now and if significant EQ is needed to meet your target house curve that may result in a significant level change. 

In summary:
> Pick an initial timing.
> Confirm it is okay for the other front channels.
> Apply EQ and finalize relative levels.
> Confirm the timing and adjust any/all as needed.


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## 3ll3d00d (Jun 6, 2006)

jtalden said:


> Unfortunately, I cannot help with the "messy" IR as my experiences are limited to my situation. With my lack of close knowledge of your entire situation and my lack of experience in other rooms it is only wild guesses that I can offer - not much help. My imagination pictures a room with limited soft features (a relatively reverberant room) and dimensions resulting in strong standing wave at 42 Hz and a mic position that is somehow near the peak of that standing wave. This is probably very far from reality, but it's the only thought that I have to explain the "slowly building" IR. Possibly others with more experience in various rooms would have more useful thoughts. If there is a standing wave or resonant surface (as suspended floor, wall or ??) maybe the response can build? We both could use some help here.


I was thinking along the same lines, something like the IR being corrupted by excessive decay times & why the later peaks are larger. The room has no treatment & is a typical Victorian construction (suspended wooden floor over a ~1' deep void). I have wondered what impact that construction has at these wavelengths. It's not clear to me how an unsealed wooden floor will react. I intend to get carpet & decent acoustic underlay down soon so perhaps that will reduce the impact somewhat.



jtalden said:


> Regarding the timing choice Audyssey made: It's the same as I would have made if I was developing an automated system. We expect the initial rise to quickly lead the largest peak and room response to follow at lower levels. We want to align the initial rise as that is the onset of the direct signal and the idealized LR-24 target XO would align well that way. We would not anticipate an IR like yours so the Audyssey timing choice was reasonable and will probably work just as well as the one I would have chosen.


fair enough, I wonder why REW chooses the later one though. 



jtalden said:


> She need a hobby;... an out-of-the-house hobby!... Maybe a boyfriend?... I digress. :bigsmile:


I think she'll have the same problem if she wants to continue with the sound and picture quality she has become accustomed to :whistling:



jtalden said:


> Everything you said is correct, but when I referred to "levels" above, I was referring to the basic relative SPL level of the SW Vs the FL. In the AVR you can adjust the level of each speaker to balance the SPL level of the 2 speakers. My point was that if the relative levels we are working with now are changed significantly as a result of future EQ settings the acoustic XO frequency will also change. [Imagine boosting SW level by 10 dB (leaving the FL unchanged) now the acoustic XO would be above 80 Hz.] So, if we are not close initially. We may need to revisit the timing. Said another way; EQ, Levels and Timing have an interaction. This only means that if we are far from the final settings on one of them we need to revisit the impact on the others. I mentioned this because your SPL is very peaked now and if significant EQ is needed to meet your target house curve that may result in a significant level change.
> 
> In summary:
> > Pick an initial timing.
> ...


OK I see. 

Thanks
Matt


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