# Plse Help Interpret First REW Meas



## jstrouth (Aug 19, 2010)

First, this is a great forum and a great tool. 

I've just completed my first measurements as shown below and could really use some of the expert advice out there on interpreting these results - and as importantly - what to do next.
I've also attached a room drawing with enough detail to give you the picture. No existing - or potential for - wall treatments, bass traps, etc. as this is our living room and the WAF is very low as is.... Den (System room) floor is carpeted w/ 8' ceiling. The rest is wood floor w/ 12' vaulted ceiling.
FWIW, system is BDP83-se, VPI Classis w/Shelter 7000, BAT vk-55se amp, BAT vk52-se pre, Aqvox phono pre, Ref 3a Grand Veenas
I really appreciate your advice. thanks!!


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## jstrouth (Aug 19, 2010)

I forgot to note that I used calibrated ECM-8000 and E-MU 0404 interface, FWIW.
Thanks again!


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## Wayne A. Pflughaupt (Apr 13, 2006)

First, welcome to the Forum!

That’s a _really _severe roll-out of the high end you have. Hopefully it's a result of your measurement technique and not your speakers. What mic orientation (e.g. 0-degree, 90-degree, etc.) and calibration file (ditto) are you using ? Is that a measurement of one speaker, or both?

Not sure what to recommend next if the wife has ruled out treatments and bass traps.  But it looks like you could benefit from some full-range equalization.

Regards,
Wayne


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## jstrouth (Aug 19, 2010)

Yeah, not sure what to think about that rolloff myself...
I used 0 degreees mic orientation and the 0 deg calibration file.
pointed the mic straight ahead. both speakers on.
did it twice to make sure ...both the same.

experimentating a little now with vandersteen speaker placement method to see if it helps.....

any other thoughts about what the rolloff might be caused by?


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## Wayne A. Pflughaupt (Apr 13, 2006)

It would take some pretty severe absorptive treatment to account for that. Or perhaps EQ from the pre amp. Did you have all tone controls/auto EQ etc. bypassed?

Regards,
Wayne


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## jstrouth (Aug 19, 2010)

The BAT preamp has no tone controls....balance and phase only. The system is all fairly high end stuff, and it doesn't sound dull, so I'm thinking I must have done something technique wise...but don't know what it would have been...


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## EarlK (Jan 1, 2010)

jstrouth said:


> I've just completed my first measurements as shown below and could really use some of the expert advice out there on interpreting these results - and as importantly - what to do next.


Hi,

To get a better idea of the speakers' true response , I suggest that you take a few more measurements of the individual speakers ( ie ; singularly ) . 

(i) Take a measurement of each at a distance of 1 meter / on axis, with the mic located equal-distance between the tweeter & midrange . ( & then )

(ii) One of each at 1/2 meter / same mic location as above .

(iii) One of each at 2 meters / same as above .

(iv) Then one of each at the preferred listening position ( test mic located at ear level ) 

(v) Then ( at the listening position ) both speakers ( tested at ear level ) .

- Doing all this will give you a good idea of what the HF response of the speaker actually is ( the closer the mic is to the actual source / the less, you're measuring the effects of the room acoustics on the speaker ) . 

- FYI, there is a preferred listening curve ( for some listeners , the X-Curve "works" well ) that one should see at the listening position ( the "X-Curve" is somewhat less severe in it's HF roll-off than what you show ) .


















- Personally, I prefer more top & bottom than what the X-Curve gives .


<> cheers EarlK


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## jstrouth (Aug 19, 2010)

Thanks!, That was actually what I'd thought about doing next as well. These speakers are supposed to be 36 - 20K +-3db.... and they have a murata supertweeter as well, so I can't believe they're rolling off that much. I can also test the response straight out of the preamp easily enough. Not sure how to test from the amp out, though.


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## wackii (Jul 13, 2006)

jstrouth said:


> Thanks!, That was actually what I'd thought about doing next as well. These speakers are supposed to be 36 - 20K +-3db.... and they have a murata supertweeter as well, so I can't believe they're rolling off that much. I can also test the response straight out of the preamp easily enough. Not sure how to test from the amp out, though.


Agree with Earl. Do a close-mic measurement. It will give you a general idea of your speakers FR. My mains do roll off at listening position but not that much... Have you try to listen to your tweeters? I have a tweeter failed on me before... I didn't realized it until I feel something is missing...

Al,


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## jstrouth (Aug 19, 2010)

Thanks for the good advice. I don't know exactly what I was doing, but here are results that seem more like it. So back to my original question..... Can you help me interpret these graphs? And what advice for improvement? Thanks!!!

Right Speaker at 3'








left speaker at 3'








Both speakers at listening position








and the rest of the graphs - both speakers at listening position.











































I appreciate your help!!!


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Can you help me interpret these graphs? And what advice for improvement?


Hard to say; with a 150 dB scaling, even speakers with Grand Canyon peaks and valleys would look good “on paper.”


Getting Graphs Ready to Post


Regards,
Wayne


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## jstrouth (Aug 19, 2010)

Many apologies.... neglected to see the '-' part of 45....

In addition to your general advice, what explanation is there for the roll off at the listening position, relative to the much more flat response nearfield? if that's a room issue, i presume there's something i can do about it? although it pretty well matches the x curve provided above (or does it?), a little more high end energy would be ok by me. thanks for your patience with my newbie fumbling!

both speakers at listening position








left only at 3'








right only at 3'


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## jstrouth (Aug 19, 2010)

Also, I'm presuming that much of the difference in left and right speaker nearfield response is due to the non-symetric room?


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## Wayne A. Pflughaupt (Apr 13, 2006)

> In addition to your general advice, what explanation is there for the roll off at the listening position, relative to the much more flat response nearfield? if that's a room issue, i presume there's something i can do about it?


Hard to pinpoint an exact cause not knowing anything about your room, distance from the speakers, etc., but the fact that they’re measuring flat up close tells me it might be just the way they are. I would expect speakers with the highs measuring fairly flat at the listening position to show a rise in the high end up close. You might try Googling for some reviews to get some more insight.




> although it pretty well matches the x curve provided above (or does it?),


You don’t want an X curve for home theater. You can find a piece about that in my signature. Google “x curve” and you can find another good article from HomeTheaterHiFi.com.




> Also, I'm presuming that much of the difference in left and right speaker nearfield response is due to the non-symetric room?


 Most likely but notice that they track pretty close down to ~500 Hz. Below 500 Hz the room is more of an influence.

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

In response to your general question, what can you see in the graphs, here are a couple of other observations. 

1) Looking at your earlier graph that included the impulse response, you can see the elevated response about 3ms and 6ms after the initial impulse. This matches distances of about 3.5 and 7 feet, perhaps reflections off the front wall and the side walls. (You did not give the dimensions in your first picture to confirm this.)

2) In the RT60 and the spectrogram, you can see the longer decay times in the middle frequencies, 700Hz-4kHz. That's a little unusual, one would expect furnishings and walls to be more absorptive as the frequency rises. I'm not sure exactly what that indicates, whether that says something about the materials in your walls. 

3) In the waterfall, obviously the longest decay is ~16Hz. Not much you can do about that, but as your speakers' frequency response already falls off above that point, I don't expect this to be an audible issue. 

Have fun,
Bill


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## jstrouth (Aug 19, 2010)

Wayne, thanks. I'm at an equilateral triangle with speakers, which are ~91/2 feet apart.
This is a 2-channel setup. Does that mean that x curve IS what I should strive for? 
If I understand, you're saying it is a room response issue that causes the rolloff of the highs? What might cause that? Any way I can get a little more high end at the listening position?

Laser, Thanks. Although I didn't include distances, you're correct I believe, about the front and side wall reflections. Traps are out of the question in this room, however. I have no treatments at all. 
Could it be that perhaps the high vaulted ceiling in the main part of the room (not the L where the system is located) is causing the longer delays you mention? What is the audible result of the RT60? And decay in general....
Thanks so much. I'm learning .... hopefully!


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## Wayne A. Pflughaupt (Apr 13, 2006)

> This is a 2-channel setup. Does that mean that x curve IS what I should strive for?


No, I would not recommend an X curve for any home audio system.



> If I understand, you're saying it is a room response issue that causes the rolloff of the highs?


No - as noted above, I think this is just the way they are. That they measure flat up close means they will naturally show reduced high end several feet away at a normal listening position. You don’t have the treble control of your pre-amp dialed down do you?

In addition, you could see some inaccuracies in the top frequencies if you’re using our generic calibration file for your ECM8000 mic. Perhaps it’s not a good match for your particular example. Also if you're measuring with the mic positioned vertically that would show a roll-out of the high frequencies, as our calibration file was generated for a horizontal orientation.

Regards,
Wayne


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## jstrouth (Aug 19, 2010)

I'm at a bit of a loss. Where does the high end go if its going out of the speakers but not making it to the listening position? The preamp has no tone controls.
Mic is calibrated from cross-spectrum.

Is off axis possibly part of the problem? I can't go straight on axis with the speakers (per mfgr recommendations) or I'll loose their phase alignment. But some toe in is possible - I have about 5 degrees now. Would that help? Anything else?


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## laser188139 (Sep 19, 2009)

jstrouth said:


> ... Is off axis possibly part of the problem? ...


That's a likely hypothesis. As you are already doing near field measurements of the speakers, you could move the microphone off axis, still pointed at the speaker, and take measurements at various angles to see how the response curve changes. 

Or you could just try pointing the speakers at your listening position, and measure whether and how much the curve changes. 

Bill


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I'm at a bit of a loss. Where does the high end go if its going out of the speakers but not making it to the listening position? The preamp has no tone controls.


It’s a known acoustical fact that as sound travels through air, high frequencies are attenuated more than low frequencies. This is why speakers exhibit greater high frequency energy when measured up close. And you can easily hear that speakers will sound brighter if you sit closer to them.

You can easily observe this using REW’s RTA feature. You will see the highs increase or decrease as you move the mic closer or farther from the speaker.



> Is off axis possibly part of the problem?


Partially, but I’d be surprised if that’s a significant factor. That would mean your speakers have a really tight “laser beam” dispersion pattern from the tweeters. That’s generally not the way hi-fi speakers are designed.

Regards,
Wayne


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## jstrouth (Aug 19, 2010)

Can someone give me some advice on using REW and the phase readouts to adjust toe in to get max highs without harming phase alignment? This is supposed to be one of the Grand Veena speakers strengths (not that I really understand it). how do I interpret the phase graph to understand what's going on and adjust the speaker position to best effect?


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## laser188139 (Sep 19, 2009)

To compare the phase between two front speakers, you need to connect the left channel of the soundcard as a loopback to provide an absolute time reference, and change the preferences to indicate to use the left channel for timing. 

Because of the large distance to the speakers, the phase will change rapidly with frequency. After you take the measures, in the Impulse window controls, you can use the Estimate IR Delay, clicking Cancel and not Shift IR, to determine the time to each speaker. Then adjust the two measures by the same time, using the t=0 offset (ms) field. This will make it a little easier to compare the two phases. 

The problem you will have is that, at the higher frequencies, small distance changes have a large effect on phase. So the curves may not be very valuable to you. At these frequencies, you will inevitably see comb filtering effects where the identical signal from two speakers sometimes subtract. Fortunately, we have two ears and a brain which are much smarter than a single microphone. With real stereo content, the two left/right signals are not identical. This was one of the motivations for inventing the center channel, to avoid comb filtering on mono content to stereo speakers. 

Personally, I generally don't measure the two front speakers together, because the comb filtering especially at the high end make the results so hard to interpret. It may be that this is all you are seeing. You could try measuring your left and right separately at your listening position, to see what the high-end rolloff is. You will probably find that the two together appear much worse than each individually. I would trust the individual measures, not the combined one. If you still think the rolloff is excessive, you could try adjusting the toe-in of one of the speakers alone and see if its curve changes. 

Have fun,
Bill


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## Wayne A. Pflughaupt (Apr 13, 2006)

jstrouth said:


> Can someone give me some advice on using REW and the phase readouts to adjust toe in to get max highs without harming phase alignment?


The two have nothing to do with each other. REW only measures phase that occurs in the room due to delayed reflections. 

Phase alignment, on the other hand, refers to a vertical physical alignment of the drivers in a speaker system. The situation is that the voice coils of drivers of different sizes do not physically align when mounted in a baffle board, as the picture below shows. The result is that the sound from the smaller drivers reaches the ears slightly ahead of the larger drivers.


View attachment 25841​

Grand Veena uses an old trick to minimize this, tilting the front baffle back to give a better physical- (and therefore time-) alignment of the drivers. 

I frankly do not see how toe-in could make much of a difference. Indeed, there is some debate as the effectiveness or necessity of vertical driver alignment. For instance, if you sit off-centered between your stereo speakers, you’ll of course notice that the closer one sounds louder. This is actually more a function of _time delay_ than proximity – i.e., the sound from the closer speaker arriving to your ears sooner than the farther one. If you delay (time align) the sound from the closer speaker by an appropriate amount, you’ll find that the difference in volume largely disappears. By contrast, you typically don’t get this kind of audible contrast from vertical driver alignment, because the ear is less sensitive to vertical than horizontal alignment.

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

For an example of what Wayne just described, you can look at the third graph in my description of the Group Delay graphs. At around 4kHz you can see the difference in time/distance between my midrange and tweeter drivers. From Wayne's description of your Grand Veena speakers, you should see a better alignment of drivers than mine when you look at the full range group delay of your near field measures.

You can see in the Wikipedia article on group delay that it takes a significant difference to be audible at the high end (2ms at 8kHz) or low end (3.2ms at 500Hz). 

Bill


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## EarlK (Jan 1, 2010)

Here's a pic of the "Grand Veeneras" .

One can see that a lot of on-axis HF energy gets aimed above the listeners ears when the listening position is far enough back. This fact alone will reduce apparent measured HF energy / & then coupled with the fact of greater air absorbtion for the higher frequencies , it's fairly easy to understand the dramatic HF roll-off ( as measured ) .

There are a few other speakers that are designed like this / seemingly with the purpose of splashing some HF energy off the ceiling to create a sense of spaciousness . 

JBLs' L series from the 1990s ( L1, L3, L5, & L7 ) was a fine example of a speaker design that used this approach .

Hey, if it sounds good to you , I wouldn't mess with it very much ( no matter how it measures ) .




I guess it should be asked of jstrouth ; what were the circumstances that brought you to use this software and what is it that you hope to achieve ( or change ) with it ?

<. cheers EarlK


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## jstrouth (Aug 19, 2010)

Thanks for your feedback guys. 
Wayne, I get the phase alignment piece. not so sure I understand phase in the room, though.

Goals? well, i'm always trying to improve my system, and have done so incrementally over the past couple years or so.. equipment wise. i'm also a bit of a geek, so the actual measurement of what I could hear was of interest to me, as well as the possibility of improving sound even more. i see what you mean about directing some sound over my ears, and can experiment with the leveling spikes to direct downward a bit more.

Ultimately, however, this 'first' round is primarily an exercise. I'm in the design process of a mancave, dedicated listening/watching room. that room (i'll post a drawing) will be a golden trapagon with ideal average dimension ratios. i'm trying to design in the acoustics to the degree possible. i wanted to know how to measure and interpret the REW output relative to the current setup so i could use it to best advantage when I start actual construction in the spring.


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## jstrouth (Aug 19, 2010)

Drawing of the mancave design.
Super chunks are in the corners. Broadband base traps designed into the walls at the early reflection points on side walls, ceiling, and behind speakers. Diffusion might be a good option behind speakers? as well as rear wall?

That's the sort of utility I eventually want to get out of REW....and the ability to understand what I'm seeing and what I can do to correct it.

Somewhat toying with IB sub install, but haven't decided yet. If so, I'd want to put the sub in a place where its signal could be the one I delayed to keep arrival time in best control...don't want to muck with the signal path in the main components since its very good as is. 

And yes, the speakers (and overall system) already sounds very good! even is the current sub-optimal room.

Any thoughts for the mancave? and again, I appreciate your help. I'm learning things that will be very helpful.

View attachment 25862


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## Wayne A. Pflughaupt (Apr 13, 2006)

You’ll get better advice on room-building and acoustics at our Acoustics Forum.

Regards,
Wayne


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