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Chris A

Using REW to Determine Time Delays Between Drivers

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25 minutes ago, Chris A said:

Sorry, I misread the horizontal scale.  I usually take full-range sweeps, so I didn't notice.  In general, below 100 Hz, GD values will go as high as 120 ms.  Here is a more representative GD plot for bass frequencies:

 

1920310933_SPUDandJubBassBInGroupDelay.thumb.jpg.abd61adf88d18e0f7a1a48b3e4c30918.jpg

 

In the case of 4 subs in room corners, is there anything that can be done to improve the GD?  Is that even necessary? 

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Chris, you are definitely on to something.  Just finished working on my left main and it is a good example of what you recommend.  I had never tried to do any SPL leveling prior to Audysey and I think this will pay huge dividends.  As you can see by my setup picture, my Oris is very close in driver alignment to my bass bin woofers.  So, I have not used and did not expect much of a time change needed to align the drivers.  Here is the data for this system.

 

 

Left Main EQ before Xover.jpg

Individual drivers with EQ and no xover set.

 

Left main Drivers scaled.jpg

 

Original sweeps of drivers without any EQ, xover or delay

 

No delay GD.jpg

 

Full system sweep to 5000hz with EQ, but no time delay

 

No delay spectrogram.jpg

 

Even without delay, the system is very close due to the simple setup between the bass bin and the Oris.

Full RAnge delay diff..jpg

 

Above is the difference in SPL when adding the .2ms delay

 

Phase after Xover and Delay.jpg

 

This is how the phase relationship ended after EQ and Time delay of 0.2ms.

Final Main GD.jpg

 

Final GD.

 

Final Setup Spectrogram.jpg

 

Chris and Rich. Thank you for all your help.  This has been a lot of fun!  Now on to the center channel and I will be done for the night.

 

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@Rudy81 go back a couple of pages and look at Chris's settings for spectrogram. I think you need an adjustment or two.

 

Glad to see you are making progress. How does it sound?

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1 hour ago, rplace said:

@Rudy81 go back a couple of pages and look at Chris's settings for spectrogram. I think you need an adjustment or two.

 

Glad to see you are making progress. How does it sound?

 

Ha ha. How does it sound?  Who the heck knows.  All I have been doing all day is working with REW.  I really need to pay more attention to the graph settings.  I will go back and check it out.  I now have all 3 mains EQ'd and aligned.  Nothing surprising really.  Tomorrow I will EQ the entire speaker as a whole and then re-run Audyssey. 

 

I have always felt Audyssey did a good job since the sound was so much better with Audyssey as opposed to without.  But this process explains it.  I figure the less  Audyssey has to do the better. 

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@Chris A when you have time, can you tell me the settings you use for your spectrogram plot? I tried to mimic your time span and my entire graph is solid read with the default time window.  I reduced the time window until the 20hz portion just shows up, but it is all red. I have to expand out to 100ms or so to see blue and have it look more like your graph.  I;m sure I'm doing something wrong.

 

The good news is that this exercise verified the time delays I had set for my stuff a long time ago.  Back then I used the REW time measurement and then verified by inverting one driver's polarity.  Running a tone at the xover frequency and changing the delay slowly until minimum SPL was achieved, then go back and remove the inverted polarity.  I do know that is an alternate way of setting the timing.  BUT, this method has to be superior since the drivers are EQ'd before you select the xover.  I did note that I had to move my center channel xover to 350Hz.  The center Oris is an Oris 250 and has a higher rolloff at the low end. 

 

This has been a very interesting exercise.  At this rate, I won't need Audyssey.  This has also brought up a limitation of my Ashly xover.  It only allows 4 EQ actions to the output and 6 to the input.  Not a lot of flexibility if you want to do your own EQ work. How many EQ settings can you add in the Xilica product?

 

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8 hours ago, Rudy81 said:

How many EQ settings can you add in the Xilica product

 

8 in and 8 out

 

Try this for spectrogram. Scale Top and Scale Bottom will change. Set everything else as shown

1741145043_Screenshot_20191025-0638262.thumb.png.7129ad2b7a29f1537f336ae557f4b909.png

 

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@rplace, using your graph suggestions, here is what I got.  Not sure what it all means, but I'm sure you or Chris can explain.

 

 

Final Spectrogram L Main per Rich.jpg

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I can't explain what it actually means, but I know enough to know it looks pretty good. Ideally you want it vertical 20k to xo point then gently curving off to the right. No harsh cuts or zigzags....at least I think I know that😁

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2 hours ago, Rudy81 said:

@rplace, using your graph suggestions, here is what I got.  Not sure what it all means, but I'm sure you or Chris can explain.

 

 

Final Spectrogram L Main per Rich.jpg

It means that you have your Oris horns and bass bins time-aligned up to 3 kHz, as will be seen in your phase plot, too.  It looks like you're crossing at ~300-400 Hz.

 

Where did you take the measurement?  The reason why I ask is that I don't see any room reflections down to below 40dBSPL from the peak: it's completely black.

 

Chris

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I took the reading at 3' from the speaker.  There are very large poly diffusers and bass absorbers pretty close to the speaker.  Not sure if that makes the difference.  I just used the readings I took yesterday and modified the graph to match what Rich indicated. A few posts up I show a picture of the setup.

 

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25 minutes ago, Chris A said:

It means that you have your Oris horns and bass bins time-aligned up to 3 kHz

 

Is that because the graph does not extend up to 10/20K so you are not sure what happens or does the graph end there because no data. I guess I'm asking it this how @Rudy81 has REW configured or is it the actual measurement?

 

Rudy did you cut it off at 5K on purpose? Did you do a measurement 20-20K?

 

25 minutes ago, Chris A said:

as will be seen in your phase plot, too

 

What would you see/not see on the phase plot if they were not time aligned? Reason being from time to time I get an un-vertical line up in the 3K to 10K range which I don't see how the XO point or bass bin could impact.

 

25 minutes ago, Chris A said:

It looks like you're crossing at ~200-300 Hz

 

Curious how you know that because of slight hump at 200k or because it starts to tail off around 700 so you are guessing 200-300 is a reasonable mid point if you start to see changes? If he had a 600 XO point would you expect to see that movement to the right higher "up" the scale?

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Yesterday I did not take readings all the way to 2kHz since the area of interest was the crossover region at 300Hz. I am crossing the mains at 300Hz and the center at 350Hz. The Fostex driver goes from 300Hz on up in the mains.

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28 minutes ago, rplace said:

I guess I'm asking it this how @Rudy81 has REW configured or is it the actual measurement?

Yes, the measurement doesn't extend up to 20 kHz, as was mentioned above.  The measurement as shown looks good to me.

 

Rudy, one way to see the level of room reflections is to show the "RT60" plot from that measurement.  If it shows the RT30 or EDT curves down in the 0.1 s range, it might explain why it's so black outside the initial impulse regions.

 

28 minutes ago, rplace said:

What would you see/not see on the phase plot if they were not time aligned?

You would see a horizontal discontinuity in the peak energy time curve.

 

28 minutes ago, rplace said:

Reason being from time to time I get an un-vertical line up in the 3K to 10K range which I don't see how the XO point or bass bin could impact.

That's probably driver-related where the driver diaphragm suddenly "shifts gears" into a different mode of movement--like a wizzer cone suddenly separating its movement from the rest of the woofer cone area.  It could also be a reflection from the spider or the basket of the driver itself.

 

28 minutes ago, rplace said:

Curious how you know that because of slight hump at 200k or because it starts to tail off around 700 so you are guessing 200-300 is a reasonable mid point if you start to see changes? If he had a 600 XO point would you expect to see that movement to the right higher "up" the scale?

Look at the broadening of the spectrogram horizontally around 300 Hz, and the smoothness of the decay (width of the spectrogram) with increasing frequency above that frequency.  Below that frequency, there is something occurring in the 100 Hz and 60 Hz regions, but that's typical for woofers to show that kind of behavior (i.e., resonances internally, in the box, or simply the 1/4 wavelength depth of horn point has been reached.  If he had crossed over at a higher frequency, you would have seen it to the right of the main impulse area as a broadening where the characteristic internal damping of the HF driver hands over to the LF driver (woofer).

 

Chris

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1 hour ago, Chris A said:

Look at the broadening of the spectrogram horizontally around 300 Hz, and the smoothness of the decay (width of the spectrogram) with increasing frequency above that frequency.  Below that frequency, there is something occurring in the 100 Hz and 60 Hz regions, but that's typical for woofers to show that kind of behavior (i.e., resonances internally, in the box, or simply the 1/4 wavelength depth of horn point has been reached.  If he had crossed over at a higher frequency, you would have seen it to the right of the main impulse area as a broadening where the characteristic internal damping of the HF driver hands over to the LF driver (woofer).

 

 

Pointy part getting wider and shifting to blue?

If not too much trouble could you mark up that Spectrogram with paint or similar and post back? I'm guessing you are talking about the colors and curves. All I've really determined so far is I want a straight line vertically. I often see on my multiple sweeps with minor changes that the line will stay the same but the intensity or the colors or the shapes will change. I'm sure it means something but I don't know what. I'm a pretty visual learner. Show me once and I'll learn it....tell me 10 times and you might need an 11th.

 

As always thanks so much for being helpful and quick to respond.

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As to how it sounds.  Did some listening without Audyssey since the speaker SPL and response had changed.  Overall, it sounds really good, honestly about the same it did before with an improvement in the HF range.  Originally I went for a flat response to 15khz.  That was a mistake.  With those settings, it is just too overblown in the highs.  I do know Audyssey pro attenuates the HF as it approaches 20kHz so maybe that is what I am used to.  So, I reduced the EQ in the high range and figured filters to flat nearing 10kHz. That was much more comfortable.  Running Audyssey right now.

 

Generally speaking, I hope this fine tunes things. The only down side is that if I change drivers, I will have to start all over since the EQ settings are particular to these drivers.  Very cool process though.

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17 minutes ago, Rudy81 said:

Originally I went for a flat response to 15khz.  That was a mistake.  With those settings, it is just too overblown in the highs.

 

Can you post your phase plot, full range (10 Hz to 20 kHz--unwrapped, if you can)?  Same thing for spectrogram. 

 

Chris

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22 minutes ago, Chris A said:

 

Can you post your phase plot, full range (10 Hz to 20 kHz--unwrapped, if you can)?  Same thing for spectrogram. 

 

Chris

 

Yes please @Rudy81 and your Group Delay? PEQs for the highs if not too much trouble. I know we have different drivers, but same horns.....just curious.

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21 hours ago, Rudy81 said:

In the case of 4 subs in room corners, is there anything that can be done to improve the GD?  Is that even necessary? 

If you use GD plot for your combined bass bin/subwoofer measurement, you will see whether you have polarity issues (same thing with phase plot).  The GD plot is pretty sensitive/noisy, especially at low frequencies.  Phase plots seem to be a better way to see polarity and time delay issues at subwoofer frequencies.  Generally, I usually wind up just using my ears to hear whether there are issues at those frequencies, since it is fairly difficult to measure well. 

 

Chris

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Here you go. PEQ settings to follow for the Oris.

Edit: Updated graphs with proper Info.

 

 

 

 

 

 

 

 

 

 

 

 

CTR spectrogram final.jpg

CTR Phase Final.jpg

CTR GD.jpg

CTR final SPL.jpg

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Rich, here is the deal on the EQ settings.  My Ashly Protea only has 4 slots for EQ settings per output channel.  I has 6 slots for the input channel.  I originally tried adding the EQ to the input channels, but that added noise to the channel that I did not like.  So, I decided to re-visit the EQ added at the beginning of the process and reworked the plan to set the timing and xover before making EQ changes to the HF section. This way, I could use the  4 output slots just for the Oris.  REW came up withe the following recommendations:

 

5540 Hz     +6.9dB  Q of 1.6

8500Hz      -9.6dB    Q of 5.6

2620Hz      -6.2dB    Q of 5.6

 

Below is a full range sweep at 3 feet with no EQ on the Oris.  In comparing these plots and the Audyssey plots with the Tang Band drivers, the Fostex have better HF performance in the Oris horns.

 

 

LMain no EQ on Oris.jpg

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