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post #1 of 9 Old 03-14-15, 10:36 PM Thread Starter
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REW basic questions

Hi guys,
so second post, first questions

I've read many threads/website/tutorials before, and the documentation is pretty good and complete on REW.
But I still have some questions, basic for most, or based on my false assessments maybe.

The short story:
I recently changed again my setup in the car, going back to 3 way.
Found some nice gears, installed them etc but I really wanted to make things a bit better this time.
I quickly tried an RTA app but was not convinced by the consistency.
So decided to get the UMIK-1 and a real software (REW).
Received it quickly and started diverse measurements to get the hang of it.
These measurements were made on same amp level, 1 measure of 8 sweeps per driver at a time, myself outside of the car, mic in different position pointing front, horizontal in the headrest.

The goal:
To get a better understandings about what's happening in the car and the effect of the Jbl ms-8 (popular car DSP that auto-time align and auto-EQ with a binaural headset).
I might fine-tune my crossover settings and maybe applying a little EQ manually at the end (but the ms8 only has a graphic 31 bands).
Hope someone can chime in and help!

So here they are:

- calibration
I use an mbp (11.3) with REW EQ v5.1
Do I need to calibrate anything else than the mic? I don't find any info on the soundcard
I used the two mic calibration files (0 & 90 degrees), I saw a little gap in highs (starting around 4K) between each files, few db
Is there a way to apply the cal file to all .mdat files at once after the measurements? (The preferences/mic/cal didn't do it)
No big deal but I had to re-cal 80 files since I forgot I have changed the mic position.

- driver protection
Since I bypass the DSP to test all speakers independently I used the amps XO to protect the tweeters, and the mids.
But can I run a sweep on the mids at full range without damages? Or at a lower level?
The 200Hz/12db high pass I used so far seems to be increased by the natural behavior of the driver (is this the "roll off"?).
Just to get an idea of the "untouched" FR curve.

- Average
Cool feature, but is it normal to lose all informations except the "All SPL" tab? Did I miss a setting?
I mean only the FR informations is saved after an "average", what about delay, phase etc
But it probably does not make sense now that I think about it… they don't use the same timing reference so they probably can't be combined.

- Waterfall / Decay
I think I got it, at least how to read them.
But how can we fix anything here, without filling the car with bass trap etc?
A good choice of crossovers could help or there is nothing magic? (it's just a 12" ib sub, firing at few inches to the rear glass)

- Phase
Still not clear for me, especially how to get info of the graph.
I got to the minimum phase reading, that is a bit more easy.
Does this mean we have to match the xo to this curve flat portions as possible, avoiding the peaks area?
I know this is not a simple question, and I will re-read the tutorial again and again.
Do you guys have any link on documentation?

- Impedance
Can REW calculate this? Or do I need a special hardware plugged on the speaker?

- Smoothing
Ok highs get easier to read, but it seems misleading too.
1/48 on tweeters shows crazy stuff going on, like 30db dips!
Are these real?
Or not important because not manageable?
Since these measurements are consistent, is it comb filtering?
Maybe I should try near field measures to compare.
Also, Variable smoothing seems pretty useful, but I don't see it a lot used in posted measurements.

- XO simulation

Since I used my amps directly I tried a bunch of settings on them to see the real impact.
And it was pretty informative, on the way the natural dips & peaks could influence the selected slope for example.
I would say eyes-opener, but don't want to jump on conclusion.
I saw a simulation method in the tutorial, but I didn't manage to make it work.
My dsp is not listed and it's natural, it has 31 bands EQ, graphical I guess.

- binaural headset
Is there a way to use the jbl ms8 headset? It would save time on the measurements process, to average left and right ear in one time.
Would need a new calibration file I guess, but this can be done outside with a reference no?

- distortion
Are these readible as this? I mean they're not near field or anything optimized like I can sometime see on technical reviews (ErinH's for ex).
But the fact that they're made speaker "in place" seems valuable to me.
I hope so because so far they're pretty good!

I had to clean all my .mdat files so I'm ready to share if you need.
Newbie error I didn't always name them right at the moment… good nomenclature is a must! :surprised:
I'll update later with few screenshots of the most interestings.
And with MORE questions but it might be too much at once

Oh and maybe you saw a BIG flaw in the process, something I missed that could make everything irrelevant… ??
And since I come from the car audio world, I may have missed some explanations or details, the big picture might not make sense to you (I still believe it does for me ).
I'm not a total newbie to generic audio questions, but still have much much more to learn.

Thanks a lot for any answers in advance guys, I know it could be too time consuming!

Last edited by Elgrosso; 03-14-15 at 10:55 PM.
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post #2 of 9 Old 03-15-15, 01:42 PM
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Re: REW basic questions

I’ll take a shot at some of this, perhaps JohnM will weigh in.

Quote:
Elgrosso wrote: View Post
- calibration
I use an mbp (11.3) with REW EQ v5.1
Do I need to calibrate anything else than the mic? I don't find any info on the soundcard
I used the two mic calibration files (0 & 90 degrees), I saw a little gap in highs (starting around 4K) between each files, few db
Theoretically both should get the same results if you use the appropriate physical orientation that each calibration requires (e.g. mic pointing at the ceiling with the 90° file). I could see where 90° could be tricky in a car since the head is typically higher than the tweeters, so the mic would have to be tilted to be an actual 90° to the tweeters. Even at that, 90° can get questionable results in highly reflective environments, and you do have all that glass in close proximity to the listening position. My rule of thumb is, if you get conflicting measurements with 90° vs. 0° measurements, trust the latter.


Quote:
- driver protection
Since I bypass the DSP to test all speakers independently I used the amps XO to protect the tweeters, and the mids.
But can I run a sweep on the mids at full range without damages? Or at a lower level?
Low-level would be fine. Your questions in this section would get better-informed answers at our DIY speaker building section.


Quote:
- Waterfall / Decay
I think I got it, at least how to read them.
But how can we fix anything here, without filling the car with bass trap etc?
A good choice of crossovers could help or there is nothing magic? (it's just a 12" ib sub, firing at few inches to the rear glass)
I’m not sure if waterfalls are even relevant in such a tiny environment. Hopefully JohnM will weigh in.


Quote:
- Smoothing
Ok highs get easier to read, but it seems misleading too.
1/48 on tweeters shows crazy stuff going on, like 30db dips!
Are these real?
Or not important because not manageable?
Since these measurements are consistent, is it comb filtering?
It is indeed comb filtering. The dips are real, but not especially audible. And it’s only “manageable” with extensive acoustical treatment, which can’t happen in a car unless you can figure out a way to legally drive with all the windows covered up. Full-range graphs smoothed to 1/3- or 1/6-octave give you a graph that looks more like what you’re actually hearing, so I find them more relevant than “misleading.” To me it's the unsmoothed graphs that are misleading. However, the opposite is true with low frequency graphs; they are better left unsmoothed or with minimal smoothing.

Regards,
Wayne



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post #3 of 9 Old 03-15-15, 03:31 PM Thread Starter
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Hi Wayne,
Thanks a lot for your time! This is very helpful.
I'm on my cellphone right now but will come back later!
Cheers

Last edited by Elgrosso; 03-15-15 at 10:04 PM.
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post #4 of 9 Old 03-16-15, 05:41 PM
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Re: REW basic questions

Quote:
Elgrosso wrote: View Post
Do I need to calibrate anything else than the mic? I don't find any info on the soundcard
No, with a USB mic only the output path of the soundcard is used so there's no way to calibrate its influence alone, though it is pretty much universally insignificant.

Quote:
- Average
Cool feature, but is it normal to lose all informations except the "All SPL" tab? Did I miss a setting?
I mean only the FR informations is saved after an "average", what about delay, phase etc
But it probably does not make sense now that I think about it… they don't use the same timing reference so they probably can't be combined.
Correct, but if you open the controls of the All SPL graph you will find an option to average pairs of traces in Trace Arithmetic, that is a vector average, but it requires traces to be correctly time aligned to be meaningful which isn't possible for USB mic measurements as there is no timing reference.

Quote:
- Impedance
Can REW calculate this? Or do I need a special hardware plugged on the speaker?
Drive unit impedance measurement needs a special hardware setup, it is described in the help.

Quote:
Variable smoothing seems pretty useful, but I don't see it a lot used in posted measurements.
It only appeared in REW fairly recently.

Quote:
- binaural headset
Is there a way to use the jbl ms8 headset? It would save time on the measurements process, to average left and right ear in one time.
Would need a new calibration file I guess, but this can be done outside with a reference no?
Perhaps, if you have a known reference you could calibrate against, though getting a reliable setup for calibration can be tricky.

Quote:
- distortion
Are these readible as this?
Yes
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post #5 of 9 Old 03-16-15, 08:45 PM Thread Starter
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Re: REW basic questions

Quote:
Wayne A. Pflughaupt wrote: View Post
I’ll take a shot at some of this, perhaps JohnM will weigh in.
Theoretically both should get the same results if you use the appropriate physical orientation that each calibration requires (e.g. mic pointing at the ceiling with the 90° file). I could see where 90° could be tricky in a car since the head is typically higher than the tweeters, so the mic would have to be tilted to be an actual 90° to the tweeters. Even at that, 90° can get questionable results in highly reflective environments, and you do have all that glass in close proximity to the listening position. My rule of thumb is, if you get conflicting measurements with 90° vs. 0° measurements, trust the latter.
Hi Wayne,
very good I now have a better understanding of the mic behavior.
So I'll use the 90 degree cal file when pointing up near my ears.
And 0 degree when pointing to each speaker, probably me outside.
I'll also play with angles aound my head just to see the difference.



Quote:
Wayne A. Pflughaupt wrote: View Post
Low-level would be fine. Your questions in this section would get better-informed answers at our DIY speaker building section.
It was confirmed too by a friend, low level is ok. Or I can try the sweeps settings too, based on the Fs on my mid drivers.



Quote:
Wayne A. Pflughaupt wrote: View Post
I’m not sure if waterfalls are even relevant in such a tiny environment. Hopefully JohnM will weigh in.
Apparently they use it here too (I posted my question on a car audio forum).
But they moslty use either position of the sub and EQ.
But it will be helpful for the choice of XO between sub and midbass.



Quote:
Wayne A. Pflughaupt wrote: View Post
It is indeed comb filtering. The dips are real, but not especially audible. And it’s only “manageable” with extensive acoustical treatment, which can’t happen in a car unless you can figure out a way to legally drive with all the windows covered up. Full-range graphs smoothed to 1/3- or 1/6-octave give you a graph that looks more like what you’re actually hearing, so I find them more relevant than “misleading.” To me it's the unsmoothed graphs that are misleading. However, the opposite is true with low frequency graphs; they are better left unsmoothed or with minimal smoothing.

Regards,
Wayne
Very helpful too, that's the most surprising thing, these 30 dips with the tweeter for example , that could become a 10db peak if you move few cm!
So I'll do my best with multiple measurements to get the most "relevant" curve once smoothed.
And variable smoothing is very simple to use indeed.


Thank you again Wayne!
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post #6 of 9 Old 03-16-15, 09:01 PM Thread Starter
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Re: REW basic questions

Quote:
JohnM wrote: View Post
No, with a USB mic only the output path of the soundcard is used so there's no way to calibrate its influence alone, though it is pretty much universally insignificant.
Hi JohnM,
Perfect! So I can restart arleady all my measurements.



Quote:
JohnM wrote: View Post
Correct, but if you open the controls of the All SPL graph you will find an option to average pairs of traces in Trace Arithmetic, that is a vector average, but it requires traces to be correctly time aligned to be meaningful which isn't possible for USB mic measurements as there is no timing reference.
Ok, I didn't expect the Arithmetic average to keep other informations.
But what do you mean about "correct time alignment"? I just tried to generate average of two mids measurements.
The only I could not generate was the Distortion plot. Waterfall and decay for example are not relevant here?



Quote:
JohnM wrote: View Post
Drive unit impedance measurement needs a special hardware setup, it is described in the help.
Good, I'll keep this for later.



Quote:
JohnM wrote: View Post
It only appeared in REW fairly recently.
Ok makes sense.



Quote:
JohnM wrote: View Post
Perhaps, if you have a known reference you could calibrate against, though getting a reliable setup for calibration can be tricky.
Sane here, I'll think about it only once I feel confortable with all REW options.



Quote:
JohnM wrote: View Post
(about THD) Yes
Ok then, I will try them again with higher volume once everything is fixed.


Thank you very much John, I still have more readings to do but it's much more clear.
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post #7 of 9 Old 03-17-15, 01:02 AM
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Re: REW basic questions

Someone asked me a question that I could not answer. So I thought I will ask JohnM and others in this forum. If using REW and a simple umik DSP, we can fix most speaker generated (as opposed to room generated) frequency response non uniformities, then why pay thousands of dollars to get a speaker that has the flatest frequency response? I had read a research paper that showed that in a large sample test, the speaker that has the flatest response was best liked. And the author concluded that most expensive speakers costing 10,000 or more try to get the flatest response. That was before REW and cheap DSP.
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post #8 of 9 Old 03-17-15, 07:09 AM
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Re: REW basic questions

There's a lot you can't fix, like the speaker's polar/off-axis response, its distortion and its power handling, for example. Deficiencies in the crossover can also be hard to fix. It is a good theme though, explored in this article.
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post #9 of 9 Old 03-24-15, 12:37 PM Thread Starter
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Re: REW basic questions

Hi everybody,
So I have some news about this, let me share and explain one of the process I tried, so far with the best result, on ears.
Since I have the jbl ms8 (no PEQ) the few things I can optimize are a good level match, a good choice of XO, and understand a bit more how the ms8 applies its magic.
Everything to make the autoEQ smooth in a way.
I may fine-tune later with the Graphical 31 bands EQ, but only at the really end.

So first I've made measurements of each speakers, with severals XO, for ex:








After I combined many together to get an idea of interactions (glad I had a big screen for that):



And pick the ones that showed good compromise, based on their flatness/minimum phase/distortion for ex:




Then I leveled them carefully while using mutliple averages to get the closest possible of the jbl curve:



I know I couldn't get the fall from 80 to 160Hz, but it's flat 20-50Hz (once with the ms8 subsonic filter), flat from 100Hz-2KHz and gradual slope after.
And since it's Left & Right separated here, maybe once combined they'll boost a bit the midbass?
The sub I kept it at reasonnable level, ms8 has a smart sub boost remote remote if I want more, and I really wanted cleaner mid bass first.

The final average gives this (I kept the same graph range for the thread only):



I then applied the level offset to the 3 amps output, was a bit surprised here by the numbers but I gave it a shot.
In db: Right woofer -5, Left woofer -1, Left mid -2.5, Left tweeter -8, Sub -10, everything else at 0)
And well… this is simply the best tune I ever had, it is great, very great!
I'm sure it could be better, well I know, it's still a bit bright, midbass could be even better probably (with a door enclosure?) but overall it is really cool!
Also it is just with a first choice of basic and safe XO, I still have many more to try.
+ finish the mids install, that could change something.

It's the first process I used last week. During the weekend I tried something else, a bit more empiric:
Started to level match the speakers with my old amp settings (that I liked for months)
Than used sweeps on L&R, with dsp on & off to see the effect of the ms8, to see what it's trying to do.
And then adjusted the level in the right direction, to help it, a bit dichotomy style.
Recalibrated and back to the beginning.

I realized that a 10/15db gap was no brainer to compensate for ms-8.
Sometimes I got exaclty the same result even if I moved 10db.
Sometimes it was stuck on some point, and move drastically on others.
But maybe it partially came from my measures (hard to be exactly on the same spot for 50 sweeps…)
Since I only use amp levels, sort of 4 bands EQ, didn't bother with 8 sweeps averaging here.
But you get the idea, I calibrated (auto TA&EQ) many times over the weekend.
And I just didn't get it right yet, on ears I mean.
The amp output settings were clearly not the same than on the first process.
It's strange because this basic technique seems more valid.

So tonight I retried the first one.
And since I forgot to take note of the offset I had to restart everything
Anyway, same great result!

I didn't measure it yet, didn't measure the effect pf dap on/off.
I'm sure it will look quite different than my graph version, I'll have to understand why.
The more I learn here, the more I realize how much I need to "unlearn", and learn more and more.
And this is just the super basic setup! no hand made TA, no EQ, no phase thing etc etc crazy stuff!

I know there are some flaws:
- L & R separated graph are probably not a perfect representation of the final sound.
- tweeter measurements are far harder to do, that's why I didn't try too many XO there
- The right tweeter seems still too high, I'll remeasure it
- something else you want to add?

Thanks for the help!
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