# Help needed for phase reading



## Loak (Dec 19, 2010)

Hi everybody,

Still working on my control room (http://www.hometheatershack.com/forums/pro-audio/37520-another-small-home-studio-control-room.html), this one is now equipped with 2 S800 Tannoy and one sub TS10 (Tannoy too). The acoustic treatment isn't done yet, I've spend some times on the building of furnitures and stands for the speakers (and working a bit too ...).

After finding a good place for the speakers (thanks REW), I've received the sub and start moving it around. A good place seemed to be between the speakers. So I've start to play with the phase knob of the TS10. The phase may be linearly adjusted between 0° and 180° with this knob. You can see in the attachments the measurements done at 0°, 45°, 90°, 135° and 180°.

The three first (0, 45 an 90) are nearly the same, you start to see a change with the fourth (little, not 135°) and a phase inversion in the fifth (normal, 180°).

Are these graph correct ? Shouldn't I read values shifting accordingly with the phase knob position ?

Thanks in advance for advice.


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## EarlK (Jan 1, 2010)

> Are these graph correct ? Shouldn't I read values shifting accordingly with the phase knob position ?


My best guess is that you should turn off all smoothing ( or at least make it 1/24 octave ) and then see if the expected phase shift shows up in the graphs .


<> EarlK


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## JohnM (Apr 11, 2006)

If you want to see absolute phase values you need an absolute time reference, which REW can get from a loopback connection on the unused input channel. You also need to tick the box in the Analysis settings to tell REW to use the loopback. That will give phase results that include the time of flight delay from the sub to the mic, to remove that you can use the controls in the Impulse panel to ahidt the response by the time corresponding to the distance.

That is all somewhat academic though, as the aim of the sub's phase adjustment is to achieve a good blend with the mains, so it is best adjusted by referring to sub+main measurements at the various settings.


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## Loak (Dec 19, 2010)

Hi Earl and John,

Here are some new graphs of the phase response of my system.

The 2 first graphs are the five values of phase I use for the test (0° 45° 90° 135° 180°), on the 2 last the 180° draw isn't shown, to have a better view of the 4 first values that don't really change despite I'm moving the phase knob. All the graphs are no-smoothed, hicut of the sub around 90 Hz, one set is only the sub, an other set is sub+mains.

Does the size or the acoustic of the room may act on the measurments of phase ? It's a 4,4m x 3,5m room, 3,2m height (14ft5in x 11ft5in x 10ft5in height), rather small.

I'd like to be sure of my measurements before contacting Tannoy.

Again, thanks for your help.


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## EarlK (Jan 1, 2010)

Hi Loak,

- I think you better follow JohnMs advice ( posted above ) to setup your soundcard so that it can measure absolute phase .
- ( especially if you're trying to determine if your Tannoy sub is faulty and in need of returning ) . 

<> EarlK

PS: Measuring absolute phase isn't something I normally do ( relative is usually good enough ) / therefore you'll need to rely on JohnMs advice .


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## JohnM (Apr 11, 2006)

To clarify, you need to look at the sub+main *SPL* response, particularly through the crossover region, to determine the best phase setting.


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## Loak (Dec 19, 2010)

Hi again guys,

I've forgot to mention that the loopback is wired, and checked into the "Analysis" tab of the "Preferences panel". During the measurements, signal is present on the 3 meters of the "Measure" panel. Do I have any other setup to do before measuring ?

For information, when I look at the impulse responses of the sub only, they are all the same except the 180° phased which is out of phase. In the case of sub+main, the 5 measurements are the same as far as I can zoom in.


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## Loak (Dec 19, 2010)

Back again, (now my linux can save graphs), here is a graph showing the spl of sub+mains, at the 5 phase values. It seems to say the same as the phase plots, nothing moving until I reach 180°.


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## JohnM (Apr 11, 2006)

Could you attach the mdat file for the measurements, please.


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## Loak (Dec 19, 2010)

Sorry John, I can't post any .mdat file (I've divided the primary .mdat file into 5 to be under the size limit, they are around 3.6mo each). Each upload finish with a "upload failed" message.

I will try again later in the day.

Thanks for the time you're according to me.


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## JohnM (Apr 11, 2006)

Easiest is probably to email me the file at [email protected].


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## JohnM (Apr 11, 2006)

I got the mdat files, thanks. I'd agree that the intermediate settings of the phase control (45, 90, 135) have no measurable effect. An alternative way to tune the integration between sub and mains is to have a delay in the path to the sub or the mains and adjust that. In Home Theater setups the speaker distance settings can be used for that purpose, you may have some processing in your setup that can achieve the same effect. If you do that would also allow you to play with locating the sub much closer to your listening position and delaying the signal to it to allow for the relative difference to the mains.

A couple of more general points: when looking at the low frequency responses (below 200Hz, say) it is best not to use smoothing. Also when measuring the subwoofer alone, or when focussing on the low end response, the end frequency for the sweep can be set to 200Hz rather than 20kHz, which will improve the measurement quality because the test signal spends all its time within the frequency range of interest.


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## Loak (Dec 19, 2010)

Hi john, 

I've contact the support of Tannoy, they told me that "The adjustment phase is linear. It assumes an artifact of the system / listening area" that we do not find on the graph.

This sub is new (out of the box for several days) so, can I think that this phase knob (or something in the phase part) is out of order according to REW curves ?


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## JohnM (Apr 11, 2006)

Well, the phase knob does not appear to be doing anything until you get to 180 degrees. You could try making measurements with the mic very close to the sub, and the sub away from the walls, to see if that shows any measurable difference (the group delay overlay might show something if it is really having an effect). Overall though, phase controls (beyond the ability to invert) do not add much when it comes to tuning the sub integration so I would not personally bother too much about it.


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## ghozt (May 4, 2006)

Loak,
I tuned my sub to my mains and was able to align the sub in phase with the mains by using the phase knob. I used SMARRT. I unfortunately did not save any screen shots. I did much like John M was describing and looked at the crossover region of the sub and mains and aligned only at that crossover point, which now I can not remember what it was. If memory serves it was pretty high, like 95 or 100hz. The TS10 does not get very Sub frequency low, but is fairly acurate at what it does produce. But it is a small driver, so I can't expect more from it. If I have time I will try and measure again and take screen shots.


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## Loak (Dec 19, 2010)

Hello all,

At first, thanks to all the guys who helped me thinking around absolute and relative phase, knob phase ... and all of this phase stuff, and more specially JohnM for the time passed on my mdat files.

I made ​​new measurements, away from the walls, mic close to the sub or not, same behavior of the phase when I turned the knob. So I've decided to see deeper into the part where the phase reversed.

I've started with the knob at 180, and go down 3° by 3°. "3°" is an approximation from the scale written on the knob but, even if it's wrong (more or less than 3°), measures were made ​​by moving the knob rather regularly. The reference frequency is 55Hz, chosen out of peaks and deeps of the spl curve of the TS10. You can see the plot of measurements in the attached file.

Two things are obvious : first : REW is a very good tool for measurements and analysis, helping efficiently to "see" parts of the sound and there behavior in front of changes. Second : As Tannoy told me that "The adjustment phase is linear", there is something with the knob or with electronics around the knob unless I'm missing something.

I've managed to set a correct phase joining between the TS10 and the S800, at first with REW, confirmed by the spl behavior around the xo frequency (85Hz for me). 

Now, I'm going to contact Tannoy, to explain them the behavior of this damned phase knob, and see if there is reactions from them, I like to be sure that things are working as they should.

In a probably distant future, I plan to manage this system with something like that : http://www.xilica.com/?c=78&cat=2&id=2, but for now I hope that my old Ultracurve will do the eq job, rather than hanging out anywhere.

I will give soon some news on my "control room" in the old thread concerning it (http://www.hometheatershack.com/forums/pro-audio/37520-another-small-home-studio-control-room.html)

Thanks again to all


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