# Time Alignment



## jcmusic

How can I use REW to time align my tweeters to my mid horns? I know I have to align the drivers vertically then use REW to check it. What should I be looking for???


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## AudiocRaver

jcmusic said:


> How can I use REW to time align my tweeters to my mid horns? I know I have to align the drivers vertically then use REW to check it. What should I be looking for???


You will need to use a 2-channel audio interface so you can use the loopback timing reference feature of REW. That way you get actual delay times when you look at the impulse diagrams. You will also need a non-USB mic to do this.

Then you can compare delay times - using the impulse diagrams in %-full-scale mode - for each of your drivers. You want the peaks of the impulses to line up. It might look something like this (ignore the picture caption, it was just an easy one to grab from another "time alignment" project):



EDIT: Time alignment is indicated when the _beginnings_ of the impulses line up, not the peaks. See post 48 for details.


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## jcmusic

OK I have the mic and the m audio interface how do I set it up?


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## AudiocRaver

Follow this link to our online guide to hooking up the mic and sound card. You will use the fourth exampole shown, titled

REW connections using an ECM8000 microphone and an external USB audio interface with integral microphone preamp with phantom power (recommended combo, simplest connections)​
There is an additional paragraph that will apply to you, about 1/4 of the way down the guide. It starts out...

Alternatively, for more advanced users,​


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## jcmusic

OK thanks I already know how and have calibrated file. How do I use the file to help with time aligning my tweeters? Or do I need to make another one?


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## AudiocRaver

OK. The speed of sound is 1126 ft/sec at sea level.

1126 ft/sec = 1.126 ft/mS = 13.5 in/mS

1 / 13.5 = 0.074 mS/in = 74 uS/in

So, let's say you measured two drivers from 2 feet away, mid driver A and tweeter B, and that the peak of the impulse for A landed at 148 uS, and the peak for B landed at 166 uS.That would mean that B is farther from the microphone, and needs to move closer to it (or move A farther away). The amount of movement needed to match them is

( 166 uS - 148 uS ) / 74 = 18 / 74 = 1/4 inch

So you make the adjustment and remeasure. I would think a target of 4 or 5 uS matching -- or 1/16 inch -- would be pretty good.

Also remember that REW will measure the delay difference by doing a Ctrl-Rclick-Drag, starting at one peak and dragging the cursor to the second peak.You will get the answer in uS, feet, and meters, but maybe not at the resolution you desire.

EDIT: Time alignment is indicated when the _beginnings_ of the impulses line up, not the peaks. See post 48 for details.


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## subterFUSE

What is the suggested frequency range for a sweep to measure speakers for time alignment?


What if the impulse response peak for one driver is on top of the graph, but the other driver is on the bottom?


Lastly, in my situation I have a compression horn and midbass. The compression horn is located approx 12" further away from the listening position than the midbass, but when I measure them the midbass impulse peaks are later than the horns. This seems counter-intuitive to me. What am I missing?


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## AudiocRaver

subterFUSE said:


> What is the suggested frequency range for a sweep to measure speakers for time alignment?


You can use the range it will handle in normal use in your application. Be sure you go well beyond the crossover frequency so you have plenty of overlap, but not lower than half the crossover frequency with an unprotected tweeter.



> What if the impulse response peak for one driver is on top of the graph, but the other driver is on the bottom?


That can happen, depending on phase response and other factors. It could actually indicate an out-of-phase problem, but not necessarily. One thing to check is thee phase response of each driver at the crossover frequency. When properly aligned, they should have the same phase response art that frequency.

On the main REW screen in Impulse mode, there is a check box for inverting the impulse. Go ahead and check it for one driver if you need to, and complete the alignment process, verifying phase alignment at crossover. At that point, i believe you should get the two impulses in the same direction without the "invert" box checked, but I am not certain about that. Those impulses are strange little furry creatures, it can be hard to make much sense of them at a glance.



> Lastly, in my situation I have a compression horn and midbass. The compression horn is located approx 12" further away from the listening position than the midbass, but when I measure them the midbass impulse peaks are later than the horns. This seems counter-intuitive to me. What am I missing?


A compression horn is an air impedance transformer. The speed of sound is changing at different points along its length. So it is hard to say exactly what point along its length will line up with the cone of the other driver. You will just have to trust the impulses, along with other measurements when they are working together.

EDIT: Time alignment is indicated when the _beginnings_ of the impulses line up, not the peaks. See post 48 for details.


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## subterFUSE

AudiocRaver said:


> You can use the range it will handle in normal use in your application. Be sure you go well beyond the crossover frequency so you have plenty of overlap, but not lower than half the crossover frequency with an unprotected tweeter.


So if the crossover frequency between the midbass and horn is 800Hz, I should sweep from maybe 600Hz to some point well above, like 3000Hz?

I am using active crossover in my DSP. Should I have the crossovers disabled for these measurements, running the drivers in full range mode?


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## AudiocRaver

subterFUSE said:


> So if the crossover frequency between the midbass and horn is 800Hz, I should sweep from maybe 600Hz to some point well above, like 3000Hz?


I suggest seeping the full range of the driver when in use, plus beyond the crossover freq.

300 to 20k for the tweeter
50 to 1200 for the midbass



> I am using active crossover in my DSP. Should I have the crossovers disabled for these measurements, running the drivers in full range mode?


Disable the crossovers while measuring. But then re-check the phase alignment at crossover freq with crossover enabled.


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## subterFUSE

Thanks for the help. I'm going to re-measure soon.
I might post the measurements here for assistance if I get stumped again.


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## subterFUSE

Another question:


Is there a way to determine the distance from the microphone to the driver from the impulse response?

In other words, how can I determine the latency of the sound card? I assume that if the latency were subtracted from the time measurement of the impulse peak it would result in a time that could be converted to distance assuming the air temperature and pressure were known.

The reason I ask is because I have 5 drivers to time align. 2 Horns, 2 midbass, and a subwoofer.
Knowing the distance of each driver to the listening position is helpful because the delay times are relative to the furthest driver, which is not delayed at all.


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## AudiocRaver

By using the loopback timing reference feature of REW (the loopback cable left in the second channel of your sound card), REW subtracts all the sound card and computer latencies and gives you the actual driver to microphone delay, ASSUMING your signal path beyond the sound card introduces no additional delay. Be sure any AVR is in Pure Direct mode or some mode that bypasses all processing. Delays from cables and purely analog electronics will be low enough to ignore, speed of light type delays (or close to it).

That leaves the miniDSP acting as crossover and providing delay management. It is made to keep its outputs in sync (aside from the delays you add for driver alignment), but there will be some additional processing latency to account for - should be in their specs, but not sure if you can count on it to be a constant. Best do as you suggested, subtract it from a carefully measured (physically) driver-to-mic example, then subtract _that_ amount as miniDSP latency for future measurements.

Actually, if you got really crafty, you could run the loopback timing reference cable from the least-delayed output of the miniDSP and have its delay compensated for by REW also, but that is beyond the scope of what we should cover here - try at your own risk, don't come running to me if you break your leg, etc.:bigsmile: Sounds like you are not a beginning DIYer, If you are an electrics whiz, you can figure it out.

I would take a delay measurement with the shortest-path driver, calculate the air delay and subtract it out, and use the remainder as your "measured" miniDSP delay. Then simply subtract that from every subsequent measurement to get your driver-to-mic distances.

One more thing - REW's impulse delay measurement is not accurate for subwoofers - says that in the help file somewhere. You can manage the delay with the miniDSP, just can not trust the REW measurement as reliable.


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## g60

How about using the excess group delay graph? Is there anything wrong using this?

I've compensated Woofer to Mid delay (xover @ 400Hz) with this method and it seemed to work well.


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## subterFUSE

AudiocRaver said:


> By using the loopback timing reference feature of REW (the loopback cable left in the second channel of your sound card), REW subtracts all the sound card and computer latencies and gives you the actual driver to microphone delay, ASSUMING your signal path beyond the sound card introduces no additional delay. Be sure any AVR is in Pure Direct mode or some mode that bypasses all processing. Delays from cables and purely analog electronics will be low enough to ignore, speed of light type delays (or close to it).
> 
> That leaves the miniDSP acting as crossover and providing delay management. It is made to keep its outputs in sync (aside from the delays you add for driver alignment), but there will be some additional processing latency to account for - should be in their specs, but not sure if you can count on it to be a constant. Best do as you suggested, subtract it from a carefully measured (physically) driver-to-mic example, then subtract _that_ amount as miniDSP latency for future measurements.
> 
> Actually, if you got really crafty, you could run the loopback timing reference cable from the least-delayed output of the miniDSP and have its delay compensated for by REW also, but that is beyond the scope of what we should cover here - try at your own risk, don't come running to me if you break your leg, etc.:bigsmile: Sounds like you are not a beginning DIYer, If you are an electrics whiz, you can figure it out.
> 
> I would take a delay measurement with the shortest-path driver, calculate the air delay and subtract it out, and use the remainder as your "measured" miniDSP delay. Then simply subtract that from every subsequent measurement to get your driver-to-mic distances.
> 
> One more thing - REW's impulse delay measurement is not accurate for subwoofers - says that in the help file somewhere. You can manage the delay with the miniDSP, just can not trust the REW measurement as reliable.


Thanks for the help!

I realize that I misspoke when I asked if there was a way to remove the latency of the "sound card."
What I meant to ask, and what you have covered in your response, was whether the latency of the "processor" could be determined and removed from the measurements?


That's a good idea about routing the loopback through the processor and back out with an un-delayed output. I could certainly do this, and that theoretically should remove the latency of the DSP.


Oh, and just a minor detail - I'm not using a miniDSP. My current processor is an Audison BitOne, which is in my car. I'm going to be swapping that out soon, however, for an Arc Audio PS8. :bigsmile: That's why the horns are so far behind my midbass. Horns are under the dash, and the midbass are in the doors. There's about a 12" difference between horns and midbass, and the left midbass is much closer to the driver seat than the right midbass.


For the sub, I think I'm going to have to use some pink noise near the crossover point with the midbass. I will flip polarity on the sub, and then play the subs and midbass together while adjusting the subwoofer delay until I hear a low point in the sound. Then flip the polarity on the sub back and I should be in phase and aligned.


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## AudiocRaver

g60:

Good idea to look at the excess group delay. I have never done much with it and rarely think to even look at it. Not sure the resolution is there for a crossover at higher frequencies, but it might be a good resource at lower frequencies. I will check it out.

subterFUSE:

Glad to help. Sounds like you have a pretty firm handle on things. Beg pardon on my over-explaining a few points, we are not always sure the expertise level we are dealing with, and sometimes get carried away in our efforts to be thorough.

And I have miniDSP on the brain these days, so that substitution was kinda involuntary.

Best of luck, and have fun!


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## g60

AudiocRaver said:


> g60:
> 
> Not sure the resolution is there for a crossover at higher frequencies


You're right, in the kHz range it will become unprecise, and in addition to that there's generally lots of spikes caused by the room response.

But in the >500Hz range it's quite good.


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## jcmusic

????


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## jcmusic

AudiocRaver said:


> You will need to use a 2-channel audio interface so you can use the loopback timing reference feature of REW. That way you get actual delay times when you look at the impulse diagrams. You will also need a non-USB mic to do this.
> 
> Then you can compare delay times - using the impulse diagrams in %-full-scale mode - for each of your drivers. You want the peaks of the impulses to line up. It might look something like this (ignore the picture caption, it was just an easy one to grab from another "time alignment" project):


Do i need to have anything ticked in the preferance box are leave it as default???


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## AudiocRaver

jcmusic said:


> Do i need to have anything ticked in the preferance box are leave it as default???


That will depend on the setup specifics for your sound card Follow the links in post #4 to get to the online REW setup instructions.


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## jcmusic

Ok in rereading the loopback feature it seems I must have it ticked to enable the other channel, or am I mistaken???


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## AudiocRaver

Sorry, yes, under 

_Preferences - Analysis - Impulse Response Calculation_

you will check the box for

_Use Loopback as Timing Reference_

to activate the feature.


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## jcmusic

Ok great now once I am setup in the preferences then it's on to the measuement, do I measure all the drivers together? Or one at a time and if so what sweep do I use?


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## AudiocRaver

jcmusic said:


> Ok great now once I am setup in the preferences then it's on to the measuement, do I measure all the drivers together? Or one at a time and if so what sweep do I use?


It works best to measure them one at a time. Then they can all be viewed together on the Overlays panel to see how they line up.

As mentioned before, take care what frequency range you use for your tweeter sweeps. You can safely sweep starting at 1/2 the crossover frequency, or go down to 1/4 of that frequency if you drop the drive level down. Actually, if you are measuring close to the driver (< 1 meter) and using 75 db as your test level, that should be plenty safe down to 1/4 of the crossover freq.

Same basic rule for a midrange driver, if it is not meant to handle low frequencies. Let the HF part of the sweep go all the way to your chosen max.

Measure all drivers individually without moving the mic. This is usually done on the tweeter axis, mic pointing at the tweeter. Some might choose the midrange driver axis as a compromise - that would be my choice as I usually get the best imaging with the ear at midrange driver level, but others may argue against it. The main thing is not moving the mic between driver measurements.


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## jcmusic

I planned on measuring from the LP that is where I have taken all my measurements from. Can you give me some examples of the frequency ranges you mentioned? My speakers are xover at 400hz and 6000hz I am also using LPF and HPF's at 80hz for the mains and subs...


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## AudiocRaver

jcmusic said:


> I planned on measuring from the LP that is where I have taken all my measurements from. Can you give me some examples of the frequency ranges you mentioned? My speakers are xover at 400hz and 6000hz I am also using LPF and HPF's at 80hz for the mains and subs...


Of course, measuring at the LP works. For repeatability, a string taped to the ceiling with a knot at ear height makes a good reference point. Hang a key on it to pull it tight.

Sweep ranges:

5 Hz to 22 kHz - woofer
100 Hz to 22 kHz - midrange
1.5 kHz to 22 kHz - tweeter
For driver safety, keep eweep SPL at 75 dB or below.


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## jcmusic

Ok thanks I will be taking some measurements later today...


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## jcmusic

Some measurements from today I am not 100% sure I did this correctly so let me know if it doesn't look correct.


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## AudiocRaver

First, I assume you realize that all of those measurements can be part of the same project, so they can be overlaid and looked at together... File size can be an issue for uploading to the forum, though, probably why you left them split up. Three or four measurements can usually be left in a project and still be under the max size.

The two tweeters line up nicely, as do the two midrange drivers, and the two woofers, and that is good, but you also want the tweeter and midrange and woofer to line up on each side. In essence, you would like all six impulse peaks to line up. As you have them now, the tweeters are about 300 uS ahead of the mids in time, or about 0.3 ft. Remember you can measure on-screen by hovering on one peak, pressing Ctrl-Shift-RMouseClickAndHold, and drag the cursor to the next peak. You will get time and distance measurements on screen.

The woofers are 4.8 mS later, or 4.7 ft, which sounds like a lot, they must be in different enclosures.

Ideally they would all line up at the peaks. Which peaks? Some are inverted, and that happens, it is related to phase, etc. You can check the "invert phase" box in the controls for the impulse diagram on the main REW screen to get them all going in the same direction.

The 4.8 mS is big, that should be corrected. Hard to say how audible the mid to tweeter delay might be, but you should be able to get closer than 4 inches.

There are arguments both ways about how readily the ear can hear that kind of delay between driver pairs. That is, can the ear tell that the tweeter is 4 inches ahead of the mid at 6 kHz? Hard to say in absolute terms, and depends on how you test, no doubt. But when you get into imaging and soundstage, I am convinced it makes a BIG difference.

Can you describe your enclosures to us? How easy is it to adjust the tweeter/mid timing? mid/woofer?

EDIT: Time alignment is indicated when the _beginnings_ of the impulses line up, not the peaks. See post 48 for details.


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## jcmusic

First of all thank you so much for your help and time, moving the tweeters is simple. Moving the other two drivers is impossible, the woofers are part of a folded horn design so the path is long hence the delay. The passive xover is suppose to take care of the delay. which I am not sure of. Now that I understand how to use the impulse measurement a little more I can try a few things. You have been a huge help in helping me understand how to use this wonderful tool thanks. One last thing in trying to get the mid/tweeter to line up how close do I want them? Oh yea how do I get them overlaid?


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## subterFUSE

AudiocRaver said:


> Remember you can measure on-screen by hovering on one peak, pressing Ctrl-Shift-RMouseClickAndHold, and drag the cursor to the next peak. You will get time and distance measurements on screen.


What temperature does REW assume for the distance calculations? Speed of sound is dependent on air temp.


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## AudiocRaver

If you could get the midrange and tweeter lined up within 10 uS, or about 1/10 of an inch, that would be ideal. The wavelength at 6 kHz is ( 1126 ft/sec / 6000 cy/sec ) = 0.19 foot/cycle or 2.25 in/cycle. I know that timing differences of 100 us start to affect imaging and soundstage so 1/10 of that would be plenty safe. I would definitely want to get within 1/4 inch (25 us). 

Don't know what to say about that folded horn woofer. Can you compensate for some delay error in your active crossover (or was that someone else?) and reduce the woofer/mid error? That one could really affect imaging & soundstage.

Keep us posted.


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## AudiocRaver

subterFUSE said:


> What temperature does REW assume for the distance calculations? Speed of sound is dependent on air temp.


Looks like 1125 ft/sec, which is for 20 deg C (68 deg F), dry air, sea level.

I use 1126 for 22 deg C (72 deg F). It is a difference of 0.1%, not worth worrying about.


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## subterFUSE

I've been measuring in my car, and since it is summer the temps in the car during measurements have been 98F. :gulp:


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## jcmusic

OK I can work on the mid/tweeter more that is an easy fix. The woofer I can do nothing about unfortunately unless I go to an active setup which I have no desire to do at this time maybe down the road. I am hearing a huge difference in the soundstage already with where I am now vs where I was. Thanks again for your help. Now can you tell how to overlay the impulse response feature?


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## AudiocRaver

subterFUSE said:


> I've been measuring in my car, and since it is summer the temps in the car during measurements have been 98F. :gulp:


Here is a formula that is pretty accurate between -100 degC and +100 degC:

speed of sound at sea level = ((331.3 + (0.606 x t)), where t = temp degC

= 1143 ft/sec at 98 degF, about 1% faster


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## AudiocRaver

jcmusic said:


> Now can you tell how to overlay the impulse response feature?


"Open" all of your measurements into a single REW project (open, select one of your current projects, open; do again...).

With all six measurements showing, press the _Show Overlays Window_ button at top of screen.

Select _Impulse_ function.

View the range from 0.033 (33 ms) to 0.035, you will see the tweeter & mid impulses clearly. The woofer impulses are off screen to the right.


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## jcmusic

OK thanks will try it tonight.
Edit: Got the overlays to work thank you again. This weekend I will dial in the tweeter/mid to within 1/10th.


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## jcmusic

AudiocRaver,
You have helped to understand how to use and read the IR. Now will you help me to understand how phasing works and what to about it?


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## draki

AudiocRaver said:


> Follow this link to our online guide to hooking up the mic and sound card. You will use the fourth exampole shown, titled
> 
> REW connections using an ECM8000 microphone and an external USB audio interface with integral microphone preamp with phantom power (recommended combo, simplest connections)​
> There is an additional paragraph that will apply to you, about 1/4 of the way down the guide. It starts out...
> 
> Alternatively, for more advanced users,​


Would this Behringer Xenyx 302USB be suitable for that (with ECM8000)?

http://www.behringer.com/EN/Products/302USB.aspx

Thanks.


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## AudiocRaver

jcmusic said:


> AudiocRaver,
> You have helped to understand how to use and read the IR. Now will you help me to understand how phasing works and what to about it?


Phase is difficult to read or do much with directly, because at a given distance from the speaker, it varies directly with time. There is no simple view of phase that is easy to get useful data from. Group delay and excess group delay are useful because they are given in terms of system delay time, like that which we have been working with, and the ideal is represented by a straight-line graph. 

Phase response can be useful when looking at a particular frequency range. At crossover frequency, it is important that the crossed speakers be in phase so there is no dip in the frequency response. Time alignment helps accomplish this. The phase response diagram at crossover frequency should be smooth and continuous with the two drivers measured together.

Smooth phase response will also contribute to good imaging and soundstage. Phase matching between left and right speakers is very important for system imaging and soundstage performance, especially between about 250 Hz and 2.5 kHz.

Are there any specific questions you have about phase response?


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## AudiocRaver

draki said:


> Would this Behringer Xenyx 302USB be suitable for that (with ECM8000)?
> 
> http://www.behringer.com/EN/Products/302USB.aspx
> 
> Thanks.


According to an entry in our handy REW sound card database, found HERE, the Xenyx series mixers are not compatible with REW due to a signal path feedback loop when used in the way that REW requires. I don't think anyone ever tried it, but the poster, EarlK, is pretty thorough about such things and I trust his assessment from Behringer's online info.


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## AudiocRaver

Two drivers would be "in phase" if they had the same phase response angle at their crossover frequency. If looking at two separate sweeps for the drivers - say your midrange and tweeter - then at 6 kHz, the phase angle for each should be the same.

According to your original plots, your left mid and left tweeter are at about -70° and +70° at 6 kHz (view from 5800 to 6200 hz) - this is just an example, the plots referred to are from before you did any time correction. With proper time/'phase alignment, they should be within +/- 15° of each other. The absolute number does not matter in this case, just that they match.


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## jcmusic

Ok my friend you have an inspiration to push further thanks so much. Here are the measurements from today, I am so enjoying this new better sound wow!!!


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## AudiocRaver

jcmusic said:


> ...I am so enjoying this new better sound wow!!!


That is why we do what we do, the thrill of hearing someone else's thrill at achieving a new level of performance from their system. Glad you are enjoying the improvement!

I am downloading your new graphs...


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## subterFUSE

I was reading in another forum about using REW impulse response for time alignment, and one of the points made was that for tweeters the actual peak of the impulse response was at the top of the "hump"... but for aligning speakers that have a low pass filter the point to aim for was not at the top but at the base.

Is this correct?

Is this why IR is not effective for time aligning subwoofers?


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## jcmusic

AudiocRaver said:


> Two drivers would be "in phase" if they had the same phase response angle at their crossover frequency. If looking at two separate sweeps for the drivers - say your midrange and tweeter - then at 6 kHz, the phase angle for each should be the same.
> 
> According to your original plots, your left mid and left tweeter are at about -70° and +70° at 6 kHz (view from 5800 to 6200 hz) - this is just an example, the plots referred to are from before you did any time correction. With proper time/'phase alignment, they should be within +/- 15° of each other. The absolute number does not matter in this case, just that they match.


 AC I can not find the measuements in question can you post them or tell where exactly to look thanks.


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## AudiocRaver

subterFUSE said:


> I was reading in another forum about using REW impulse response for time alignment, and one of the points made was that for tweeters the actual peak of the impulse response was at the top of the "hump"... but for aligning speakers that have a low pass filter the point to aim for was not at the top but at the base.
> 
> Is this correct?
> 
> Is this why IR is not effective for time aligning subwoofers?



Good catch, you made me dig a bit deeper.

Here are some modeled crossover results showing what the impulses will look like, how they should line up, and how much error can be introduced if they are not lined up properly. This example is a 1 kHz crossover, purposely designed "non-ideal" so the errors would stand out (HP Filter f0=800Hz).

The basic crossover characteristics were modeled as follows:

HP Filter for tweeter: 800 Hz High-Pass, Butterworth, 3rd order, Q=0.5, D=0 (no added delay)
LP Filter for woofer/mid: 1 kHz Low-Pass, Butterworth, 4th order, Q=0.5, D=0 (no added delay)

Additional variables:

Delay is added to the tweeter to show the effect of positioning variations between drivers in an enclosure.
The woofer/mid band is also shown with a high-pass filter added, making it a bandpass filter, as though it was the mid band in a 3-way crossover.
The woofer/mid band's main low-pass filter is also shown as a low-order (6 dB/oct) filter, showing how much the impulse shaoe changes as a result.
Examples:
1. Here is the frequency response for the basic configuration of the 1 kHz example crossover, showing how the two bands combine "ideally" - in this imperfect design - to create about +/-1dB of error at 1 kHz. See also how the error gets worse as the tweeter is delayed in 30us increments. This equates to 11.25° (360° / 32) of error at 1 kHz, or about 1/3 inch of driver positioning error per increment. There is no standard for this, +/-11° as a goal seems achievable and would perform well.

 

2. Timing error is shown in 30 uS increments. As subterFUSE pointed out, it is the beginnings of the impulses that should line up, not the peaks. This is easy to spot on a tweeter impulse, not so easy on lower frequency bands, impossible on a subwoofer impulse.

 

3. Same as (2), but zoomed in, and the 2nd and 4th peaks are not shown so more fine detail is visible. Only at maximum zoom can one see that the impulse for the LF band (slowly rising) is starting at the same time as the impulse for the tweeter. In this picture, it almost looks like the green impulse is lined up correctly, but that one is 60 uS late. The first impulse, blue, is properly aligned.

 

4. The Simple Configuration frequency response

 

5. Three additional LF band configurations.Blue and violet are overlaid above 1 kHz.

 

6. Here are what the other LF band configuration impulses look like. Lots of HF content gives a sharper peak, as in two examples. But the main point to be observed here is that, whatever the shape of the impulse, the impulses should all begin together when they are properly aligned.


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## jcmusic

Ac how do these look to you? I think the left is good the right maybe needs a tad more work?


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## AudiocRaver

I would agree. Looking at the .mdat files you last uploaded, they were right on.

How does it sound?


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## jcmusic

It sounds awesome I mean everything is in focus huge soundstage and very very cleear!!! I will tidy up the right side just a tad more next time out. I want to thank you for all your help much appreciated, this stuff really interest me but I don't know anyone who can teach me except online.


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## AudiocRaver

Glad I could help.:T


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## subterFUSE

Forgive my bumping this thread, but I have another question.


So let's say that I recorded measurements with loopback as timing reference and I have my Impulse Responses ready to analyze. Should I click the Estimate IR Delay button in the controls before looking at the IR Overlays? Or is this not correct to use when trying to measure for time alignment?


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## jcmusic

Once you have everything setup for the measurement you just measure like you would normally...


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## subterFUSE

jcmusic said:


> Once you have everything setup for the measurement you just measure like you would normally...


Right. I'm asking about after the measurement is taken. Do we need to use the Estimate IR Delay button before comparing the IR measurements in the Overlays to determine the time alignment?


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## jcmusic

subterFUSE said:


> Right. I'm asking about after the measurement is taken. Do we need to use the Estimate IR Delay button before comparing the IR measurements in the Overlays to determine the time alignment?


I did not use it but, I don't know for sure try it both ways...


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## AudiocRaver

When using an external loopback timing reference, you would not us the Estimate IR Delay function.


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## jcmusic

Hey AudioCraver the tweeter alignment is sounding awesome. Now I noticed that my left woofer is a little more than a ms ahead of the right. Do you think I need to fix this?
EDIT: I was looking at it wrong sorry, I think this looks pretty good.


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## subterFUSE

OK, so I measured the impulse responses today and applied time alignment to my Horns and Midbass drivers.

Here is the graph after I aligned everything. Does this look correct?


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## AudiocRaver

Previous posts 2, 6, 8, and 29 have been edited to clarify that time alignment should be at the _beginnings_ of the impulses. Post #49 shows this in detail.


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## jcmusic

AudiocRaver said:


> Previous posts 2, 6, 8, and 29 have been edited to clarify that time alignment should be at the _beginnings_ of the impulses. Post #49 shows this in detail.


Hey AC are you talking to me?


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## AudiocRaver

jcmusic said:


> Hey AudioCraver the tweeter alignment is sounding awesome. Now I noticed that my left woofer is a little more than a ms ahead of the right. Do you think I need to fix this?
> EDIT: I was looking at it wrong sorry, I think this looks pretty good.


It would be easier to tell if zoomed in tighter on the tweeter and midrange impulses so we could see their beginnings plus a couple of cycles of the ringing. From what we can see, it looks like good alignment. Woofer alignment error of 1 mS with a crossover frequency of 300 Hz is fairly significant:

1 / 300 cycles per second = 3.33 mS per cycle

So 1 mS of error is about 1/3 of a cycle of timing error. True, 300 Hz is around the LF limit for affecting imaging and soundstage, but that is enough error that I would try to tighten it up, if possible. A 4x tighter target would be consistent with what you have worked to achieve with your other drivers, so a max error of 0.25 mS would be good.


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## AudiocRaver

subterFUSE said:


> OK, so I measured the impulse responses today and applied time alignment to my Horns and Midbass drivers.
> 
> Here is the graph after I aligned everything. Does this look correct?


In some of our earlier posts, I talked about aligning the peaks of the impulses. It was pointed out by one of our members that correct alignment occurs when the _beginnings_ of the impulses are aligned. See Post # 29 for details. Sorry about the confusion, I have edited those earlier posts to point readers toward post # 29.

In other words, you need to re-align your timing _slightly_ so that the beginnings of the impulses are aligned, not the peaks of the impulses. Again, I apologize for the confusion.


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## AudiocRaver

jcmusic said:


> Hey AC are you talking to me?


Post #62 is your response.


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## jcmusic

AudiocRaver said:


> It would be easier to tell if zoomed in tighter on the tweeter and midrange impulses so we could see their beginnings plus a couple of cycles of the ringing. From what we can see, it looks like good alignment. Woofer alignment error of 1 mS with a crossover frequency of 300 Hz is fairly significant:
> 
> 1 / 300 cycles per second = 3.33 mS per cycle
> 
> So 1 mS of error is about 1/3 of a cycle of timing error. True, 300 Hz is around the LF limit for affecting imaging and soundstage, but that is enough error that I would try to tighten it up, if possible. A 4x tighter target would be consistent with what you have worked to achieve with your other drivers, so a max error of 0.25 mS would be good.


Ok I don'tknow how much a difference this will make but, the xover is at 400hz not 300hz?


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## AudiocRaver

Thanks. The calculations would only change a little. I would still try to improve that matching, using the same target as before.


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## subterFUSE

AudiocRaver said:


> In some of our earlier posts, I talked about aligning the peaks of the impulses. It was pointed out by one of our members that correct alignment occurs when the _beginnings_ of the impulses are aligned. See Post # 29 for details. Sorry about the confusion, I have edited those earlier posts to point readers toward post # 29.
> 
> In other words, you need to re-align your timing _slightly_ so that the beginnings of the impulses are aligned, not the peaks of the impulses. Again, I apologize for the confusion.


Could you explain where the "beginning" of an impulse is so I can understand exactly where to aim?

Is it at the point where the line crosses the X axis before the largest peak? Or is it the first of the smaller peaks before the largest peak?


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## jtalden

subterFUSE said:


> OK, so I measured the impulse responses today and applied time alignment to my Horns and Midbass drivers.
> 
> Here is the graph after I aligned everything. Does this look correct?


Most of the IRs do not look normal in this screen shot. A normal IR should have larger initial peak and then drop off. I do not know the cause of all the initial smaller ripples in your measurement, but would think that it is the first thing to investigate. It may be impossible to do any more detailed time alignment than already done until that is corrected. If we can correct the IR issues then I would be able to help you work through an find a good time alignment. 

It will take some commitment of effort on your part to provide measurements and provide more detailed info regarding your setup. This would best be done in a new thread.


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## jtalden

jcmusic said:


> Hey AudioCraver the tweeter alignment is sounding awesome. Now I noticed that my left woofer is a little more than a ms ahead of the right. Do you think I need to fix this?
> EDIT: I was looking at it wrong sorry, I think this looks pretty good.


I understood your W and MR were fixed; same box and passive XO? If you can move the drivers independently or add delay to one of them then the time alignment can be changed otherwise it cannot.

It is impossible to comment further on time alignment than what AudiocRaver has already done without looking in detail at the direct sound phase tracking. You current timing may be a good one or it may not. There may be a better one that is possible if a delay can be implemented. 

If you just want to know where you are relative to a good alignment I can comment in that regard. If the measurements in Post 28 are current I could use them. I don't want to spend time work on old data if it may be out of date. Please advise if you want my help.


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## subterFUSE

jtalden said:


> Most of the IRs do not look normal in this screen shot. A normal IR should have larger initial peak and then drop off. I do not know the cause of all the initial smaller ripples in your measurement, but would think that it is the first thing to investigate. It may be impossible to do any more detailed time alignment than already done until that is corrected. If we can correct the IR issues then I would be able to help you work through an find a good time alignment.
> 
> It will take some commitment of effort on your part to provide measurements and provide more detailed info regarding your setup. This would best be done in a new thread.


The measurements are taken in a car, which might explain the unusual IR.

I'm running a pair of horn loaded compression drivers under the dash, and a pair of 8" midbass in the front doors. Also pair of 12" subwoofers in a trunk baffle, but those were not included in the IR measurements.


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## jtalden

Possibly that is reason. I would have expected an individual driver's IR to look more conventional than that. Are you testing one driver at a time? For timing purposes each driver must be measured individually unless there are 2 or more drivers working together to cover the same range of frequencies on the same channel.


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## subterFUSE

jtalden said:


> Possibly that is reason. I would have expected an individual driver's IR to look more conventional than that. Are you testing one driver at a time? For timing purposes each driver must be measured individually unless there are 2 or more drivers working together to cover the same range of frequencies on the same channel.


Yes, one driver at a time. All others muted.


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## jcmusic

jtalden said:


> I understood your W and MR were fixed; same box and passive XO? If you can move the drivers independently or add delay to one of them then the time alignment can be changed otherwise it cannot.
> 
> It is impossible to comment further on time alignment than what AudiocRaver has already done without looking in detail at the direct sound phase tracking. You current timing may be a good one or it may not. There may be a better one that is possible if a delay can be implemented.
> 
> If you just want to know where you are relative to a good alignment I can comment in that regard. If the measurements in Post 28 are current I could use them. I don't want to spend time work on old data if it may be out of date. Please advise if you want my help.


Hi jtalden,
the W and MR are in a box and can't be moved with passive xover correct, the tweeter can be moved as it sits on top of the box. Yes the measuements in post 28 are the current measurements, please have a look.
AudiocRaver has been a huge in helping me understand IR and how to read it, I just wanted to get the MR and tweeter time aligned because that was possible. Now I can use delay but not for a single driver it would be for all drivers together...


----------



## jtalden

subterFUSE said:


> Yes, one driver at a time. All others muted.


If you want to post a .mdat of one channels drivers in a new thread. I will look to see if anything can be learned from it. Without that I can only comment in general to generic questions.

If we can determine how to correct the IR then I will be able to comment on time alignment. If not, I probably cannot help. I also assume you have a way to adjust delays or there is no time alignment to be done anyway.

Be advised I have no experience in the automotive arena. That is a problem as I am completely unfamiliar with common practices. I would think that there are better resources available someplace. For instance, I have no idea what is common practice for mic positioning and timing of the channels. Is everything timed to the drivers location, or possibly to the center of the vehicle? Maybe timing is handled completely differently in an automotive setup.

I may not comment to you on any specific questions in this thread as I cannot keep both your and jcmusic questions/issues separated in my aged and one track mind. Generic questions are not a problem, but they are of limited value as the answer is often dependent on the context of the situation.


----------



## jtalden

jcmusic said:


> Hi jtalden,
> the W and MR are in a box and can't be moved with passive xover correct, the tweeter can be moved as it sits on top of the box. Yes the measuements in post 28 are the current measurements, please have a look.
> AudiocRaver has been a huge in helping me understand IR and how to read it, I just wanted to get the MR and tweeter time aligned because that was possible. Now I can use delay but not for a single driver it would be for all drivers together...


I will review that data and report back the current phase tracking situation.


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## jcmusic

Thank you very much....


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## jtalden

jcmusic,
My first look at Post 28 data shows the polarity of all 3 left channel drivers to be the reverse of all 3 right channel drivers. The first step is to set them both alike. It is not important which polarity we use so long as both channels are set the same. 

The 3 left channel IRs show the initial peak to be positive going (indicative of positive polarity). The 3 right channel IRs show the initial peak to be negative going (indicative of a negative polarity). 

We may want to invert the TWs, or MRs, or Ws in this process to improved phase tracking, but both channels must be alike. They cannot be reversed from each other. Do you know how this happened? Is there a simple wiring mistake? Please advise your findings as soon as possible. I can post charts if those are needed so see the problem.

Since the absolute polarity is not an issue in timing, I can still go forward with the timing analysis. I will use the left channel as that is the more conventional starting point. It may take me another day or two to do the analysis.


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## jtalden

jcmusic, 
I just noticed the chart in post 58. There, the 2 Ws appear to be the same polarity (positive). I am confused as to why the data in Post 28 does not agree with this? In Post 58 it is not possible to see the polarity of TWs and MRs, but possibly they are the same as well? Can you clarify?


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## jcmusic

jtalden,
I am trying to think back on this I recently double checked all the wiring and connections to be sure this didn't happen. Let me check again to be sure and get back to you. What I am thinking is the custom xovers my friend built for me, they may be opposite of each other. That is the only thing that I can think of I know the wires are connected properly!!! They may seem dumb but how can it sound so good and have this issue at the same time?

EDIT: I just thought of something when I was taken the measurements I think I ticked the invert box in the prefrences while doing one side, and never undid it!!!


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## jtalden

The .mdat file data should save whether inversion is applied or not and I checked for that. The box was not selected on any of the measurements Your chart looked okay so maybe that is were it was checked. It is not too important so long as both channels are actually the same. If you can confirm that, we are good to go. I will go ahead with the initial timing analysis by inverting the 3 right channel measurements so they agree with the left channel (and your chart).


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## jcmusic

I checked the wiring again and I far as I can tell everything is correct...


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## jtalden

When you get a chance just measure again to confirm all drivers are same polarity between channels.

Your 6 files IRs are shown below when the they are aligned at 0ms. In all cases the left channel is positive going and the right channel is negative going. None of the IRs are indicated in REW as "inverted" so the discrepancy is still unexplained. The legend identifies the driver ID and color of the trace.


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## jcmusic

I will measure again first chance I get probably Friday morning thanks.


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## jtalden

TW-MR timing:
I spent several hours working on this and finally satisfied myself that the following charts represent the optimal timing. This was more difficult than usual as there are a lot of reflections in the data that tended to obscure the direct sound phase trace.

I then started to compare the optimized timing to the current timing to determine the TW shift needed, but I stopped when I noticed that the data I was working on from Post 28 did not agree with the chart you posted in Post 49. I therefore question whether you have since moved the TW and thus may not know the exact TW position used for Post 28 data. specifying a needed TW shift would therefore be meaningless. It's not really concern however as you can just move the TW as needed until you achieve the same IR timing as shown in the chart below. It may be pretty close to where it was when you created the Post 49 Chart. It is difficult to tell as the resolution of that chart is not great enough. We would need to expand the ms scale all the way to read it accurately. It's also hard to see if the polarities are consistent in that chart.

Just set the IR timing and polarity as shown below and all will be optimized.

























MR-W Timing:
I also looked at the MR-W and found the optimized timing. It is shown below. The needed increase in delay of the MR to achieve this timing is 3.418ms. I also show the current phase of the MR-W. There is steep crossing of the phase and several 360° phase wraps of the direct sound due to the poor timing. This will result in several nulls in the direct sound. Those nulls are typically obscured in room measurements as the reflected sound tends to smooth the SPL response.

I would expect a slightly noticeable sound quality difference, but it might be difficult to identify which is better.

I understand that this cannot be addressed with the current setup and so this is just FYI.

























Below is the overall phase tracking of the optimized timing.









This same timing and polarity will work just fine for the right channel as well.


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## jtalden

Attached the optimized timing for the left channel drivers.
Accurate IR offsets can be measured in this file for comparison to current measurements and determining needed adjustments.

View attachment jaPost 28-4.mdat


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## jcmusic

Jtalden I was just thinking about the situation wondered if I could have unticked the invert box after measuring? Would that be a reason for it not showing when you looked?


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## jtalden

There is an Invert box in the REW soundcard preferences window. If that was changed for any of the measurements then those would be automatically inverted. When the file was saved they would not be indicated as inverted. That box is only used in the odd cases where the soundcard inverts the signal. Clicking that box will correct that issue. Once set properly for the soundcard in use during the calibration process it should not be changed for any future measurements. 

The Invert box in the Impulse control window can be used to invert a particular measurement as needed for analysis. It can be turned on or off as needed for the analysis. When the file is saved then the condition of that control is saved and reestablished when the file is again loaded. 

The only important issue now is that all the drivers are actually the same polarity between the two channels. If there was somehow a confusion in the original files that is not a concern at this point. 

I would suggest measuring each drive successively in the same REW session. If the right channel drivers match the polarity of the left channel then all is well. If not there is still a problem. To match my suggested timing alignment the polarities should also match the file I posted.

I forgot to mention in my previous post that I did quickly check to see which polarity will work best for the 400Hz XO given your current locked timing. The SPL support looks a little better when the polarity is as shown in the file I posted. The initial rise of the IR is positive for both MR and W.


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## jcmusic

OK that is what happen I am sure of it. When AudiocRaver mentioned inverting the curves I misunderstood him, I thought he meant the invert box in the preferences. I didn't know about the invert box in the impulse window. I am still going to measure all again on Friday just to be sure and save those.


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## subterFUSE

How would we determine if our sound card inverts the signal?


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## jcmusic

It might tell you in the instucions or you can tell by testing for it.


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## jtalden

subterFUSE said:


> How would we determine if our sound card inverts the signal?


If during the loopback calibration process you see that the phase is tracking near 180° through most all the freq range then the soundcard is inverting the signal. This happens sometimes with older PC internal soundcards, but not so much recently so far as I know. The better external audio interfaces would not be expected to do this. It is no real issue for us as the box can be checked and REW will then automatically invert all the future measurements for us. That way a loopback measurement will indicate the phase is at 0° and the impulse will be positive going. The mic measurement of the sound will also then be correct. There is no need to rewire anything to see the correct Impulse and phase traces.


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## jcmusic

jtalden,
Ok you were correct I think the right xover has two wires reversed, so I fliped the imput wires from the amp to correct the polarity issue I hope this helps. Here are all the measurements from today.


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## AudiocRaver

A HUGE thanks to jtalden for helping out on this thread this week. I have been unable to do much for a few days, and knew he would be the perfect HTS expert to keep you guys progressing.

Thanks again!


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## jcmusic

Hey AC,
I hope you are feeling better soon, thanks to you for getting me started in the right direction.


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## jtalden

jcmusic,
Well done finding the polarity issue cause and correcting it. :sn:

*TW / MR Timing Analysis of Post 92 Data*
The best phase tracking for the direct sound results in the following charts:









The above SPL shows there was a significant SPL level difference between the channels for some reason. This allowed me to show both channels on the same chart.









The above phase chart is not very clean due to heavy comb filtering of the TW as suggested in the comments below. The direct sound phase timing has been accurately found however with the IR timing shown in the charts below for the left then right channels.

















We want to know the distance to move the 2 TWs to create this condition. It is easiest to determine this by measuring the relative timing of the old (current) positioning TW / MR vs the new (desired) TW / MR positioning. We can then calculate the needed distance change.

To measure the TW / MR timing of the current TW / MR we could try to measure the initial rise of the TW vs the initial rise of the MR IRs. That is not a good option as it is very difficult to identify those points on the charts. We could chose to measure at the first peak of each IR and that would probably be much more accurate. That would probably be a perfectly good choice. I chose instead to measure at the first 0% crossing following the first peak. I find that easier to measure accurately. 

Below are my measurements:

Old Left Timing:









Old Right Timing:









New Left Timing:









New Right Timing:









The timing and resulting TW distance change in table form:









The old TW IRs are being pulled closer to the LP to reach the new positions that is the direction the TWs must be moved to achieve the new timing.

*General Comments:*
> The very congested phase response of the TWs that made the identification of the timing so difficult may be due to your physical setup. It occurs to me that, since you are using a large horn MR and moving the TW for timing, that the TW probably is positioned several inches back on the top of the MR / W cabinet. The heavy reflection off the cabinet top is then likely be the cause of all the TW phase congestion. I would expect this type of TW positioning to create heavy comb filtering and be considered a poor choice for best sound quality. A TW would normally be positioned flush with the baffle to avoid these reflections. I suspect the sound quality tradeoff of direct sound timing vs a flush baffle position would be expected to clearly favor the flush baffle position. With this info you can try both to find which way you prefer.

> Another aspect of a TW that is located well behind the mouth of the MR horn is that the horizontally off-angle timing is impacted. If the mouth of the horn and the TW are at the baffle the timing is retained as the listener moves off center horizontally. With a trailing TW position the distances are changed differently and thus the timing relationship is not maintained. The vertical off-angle timing is very sensitive with a large horn system and 6k XO even with both timed properly and aligned and positioned at the baffle. so it is hard to say either has an practical advantage.

> The only practical way I know to achieve both conditions is with a flush mount TW and the ability to add signal delay to the drivers. That would require a DSP speaker management unit of some sort. I normally only comment on direct sound timing when there is a speaker management unit involved. This serves to remind me why. I presume you want to retain an all analog system so It is just a decision to be made relative to which configuration options sounds best to you. I suppose it is possible to implement analog all pass filters into your XO to add the TW delay, but suspect that is not too practical?


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## jcmusic

jtalden,
jcmusic,
Well done finding the polarity issue cause and correcting it. 

Thanks my brother I am trying to understand and learn this stuff and with your help along with AC I am slowing getting there. Thanks for helping out much appreciated. I am still refining the adjustments after measurements so there may be more improvement in the sound quality. More later.....


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## AudiocRaver

jtalden,

You absolutely rock! Thanks again for helping and for showing us all how it is done by the Master!


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## jtalden

I just noticed that I indicated the direction wrong for the TW position. The TW IRs actually need to be moved back (further from the LP) to properly align with the MRs in the IR charts above. Sorry for the confusion.


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## jcmusic

jtalden said:


> I just noticed that I indicated the direction wrong for the TW position. The TW IRs actually need to be moved back (further from the LP) to properly align with the MRs in the IR charts above. Sorry for the confusion.


Yes I kinda figured that no worries thanks again...


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## jcmusic

Here are my final alignment IR for mid/tweeter...


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## jtalden

Here are your current TW/MR alignment.

Left IR timing Alignment:









Right IR timing Alignment:









I notice that the relative TW/MR alignments do not agree with the recommended alignments I suggested in Post 95. The "old" IR timing in Post 95 had the TWs IRs leading the MR IRs a little too much. This new timing shown here has the TW IRs trailing the MR IRs a little too much so the TW delays have been shifted too much. 

I did not do an exact measurement of the error as that should not be necessary. You can again adjust the TW delay until the relative alignment of the TW/MR IRs are as shown in the recommendation of Post 95. If the visual positioning is achieved then the alignment is optimized. A quick rough estimate of the needed shift is; 0.46ms (16mm) and 0.80ms (24mm) for the Left and Right TWs respectively. 

The current timing is really not all that bad. It is a very small shift amounting to about 100° (left) and 150° (right) from ideal. It is probably not a major concern with a 6kHz XO. Changing the LP height a little makes a pretty rapid shift at a high frequency like this; particularly with a large TW to MR spacing. A gross timing error may be audible at this frequency, but a small error like this is likely not significant. Anyplace between your timing in Post 95 and this one is pretty good.


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## jcmusic

I think the difference is that I used the peaks in the measurement instead of the back of the curve crossing 0 again as you did...


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## jcmusic

Maybe I missed something but, this is what I was looking at.


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## jtalden

I suggest you zoom in on the time scale to the maximum extent. The relative positions of the IRs will then be easier to see. The width of the IR on the chart will then be the same as it is in my charts. 

The objective is to move the TW position so that its IR is positioned relative to the MR IR just as I recommended in Post 95. This can just be done by trial and error. My distance calculation should be correct (if I did not make a calculation error), but you can just move the TW a little and observe the new overlap of the 2 IRs and then move again as needed. When they overlap the same way as the recommendation, the job is done. 

We are not aligning the peaks of the IRs or any other particular feature. My recommendation for timing alignment was based on the phase tracking of the direct sound. I just adjusted the relative IR positions by moving one of them until the phase tracking was optimized. Then the relative IR positions on the Impulse chart represents our target timing.

The absolute values on the MS scale are not relevant to this effort. That is dependent on mic distance. My chart shows the IRs near 0ms, but that is because I moved them both there so I could read the phase. This is not necessary once the correct relative positioning is identified. We are only looking at the relative IR positioning now.


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## jcmusic

OK how do I go about reading the phase as you did to help me understand what you stated earlier?


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## jtalden

Reading a phase chart? Maybe the following will help.

In the example below from Post 84, I had already adjusted the IR timing to provide good phase tracking and also set several REW charting controls so that:
> The phase of the TW and the MR track as closely as possible through the range of XO freqs (~3-9kHz determined from the SPL chart).
> The phase chart is "wrapped" at ±180° so when a trace falls off the chart top/bottom it is picked up on other side. 
> I added the heavy dashed lines to show a reasonable estimate of the direct sound phase for the 2 drivers. The tracking is reasonably close through the XO range. 
> The direct sound phase is smoothly changing. Any rapid irregularities are normally due to reflections of the sound and should be ignored. 
> I picked this example as it shows the effect of strong reflections at 10k and 12k. If reflections like this are present in the XO range, it can be very confusing to read the chart correctly.


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## jcmusic

So is it the idea of having both of the dotted lines as close to each other as possible throught the xover area?
By moving the tweeter this adjust the phasing?


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## jtalden

Yes, That is correct. We particularly want to be as close as possible nearest to the XO freq where both drivers are contributing nearly the same SPL to the acoustic output (near the acoustic crossover point on the SPL chart). According to this chart, I could have ideally made a small adjustment to have the 2 dashed lines cross right at the actual XO freq.

The process of moving the IRs near zero and setting the windows on the chart can get very complicated. If it is not properly handled the true phase traces can be distorted leading to erroneous timing. 

I hope I made it clear that this is a complicated process that is completely unnecessary to get perfectly good results. It is more for the hobbyist who wants want to assure the timing is as close as possible and enjoys learning and experimenting with the setup process. The other methods work well and are much less complicated.


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## jcmusic

That is why I am asking all the questions, I want learn about this body of work.


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## jtalden

Okay 

Sorry if I said that warning before. I can't keep track. I like to mention it regularly as some readers may not put this method into perspective.

I just scanned this thread quickly and did not any links to other similar threads, but I think I referenced some recently in other threads. I hope you have seen those. If you need some links repeated here just let me know. 

I did a general overview several years ago that is okay, but it is probably a little dated is some spots. I hope you saw that one. I will link it again *Here* just in case. In that thread I tried to cover the basics in a little more organized way.

Your working at a bit disadvantage in that your setup is not as conducive to providing clean phase traces and easy/accurate delay adjustment as some others setups. Using a 1m mic position would be make things a little easier for experimentation.


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## jcmusic

Ok that was a good read now I need to lear how to setup the screens for the process??? Thank jtalden


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## jtalden

Maybe *this* will help.


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## jcmusic

jtalden,
Thanks for the link that is a bit complicated but, I guess with some practice I could figure it out. Right now I am having trouble with the screen adjustments. I can't figure how to use the zoom???


----------



## jtalden

Options:
Per REW: "HELP/Graph Panel"
> "Graph Limits Button"
> "Horizontal Axis Zoom Buttons"
> "Vertical Axis Zoom Buttons"
> "Variable Zoom"
> "Zoom to Area"


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## jcmusic

jtalden,
That helps thanks now I see some of what you are talking about. I now understand more about when you were saying that ms is not the target but, the phase is but they are related correct?


----------



## jtalden

Maybe -

My point was that we are interested in the relative positions of the 2 IRs. That is what controls the phase alignment. When measured, your 2 IRs were delayed about 20ms ms on the chart. This is the result of delays in the measuring equipment, the speaker XO, speaker drivers and mostly due to the time of flight of the sound from the speaker to the mic position at the LP. Moving the mic closer or further does not change the relative timing difference between the 2 IRs. They will measure at different ms positions on the chart however. We don't care what the position on the chart is, we only care what the relative IR overlap is. 

In order to read the phase and determine the correct overlap, we need to move both IRs the same amount to place them near 0ms. This is just to make the REW phase chart readable. Once we adjust the delay of one of the drivers and find the relative overlap position that creates the best direct sound phase tracking then we have the answer. We can set that new delay and then remeasure to confirm that the 2 IRs overlap each other the same way on the chart. The IRs will be back near 20ms again, but if they overlay each other the same then we were successful.


----------



## jcmusic

Jtalden 
I remember a while back you or AC asked why the left channel was measuring a little higher than the right. Well I got that corrected seems the input knobs were off some.


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## jtalden

That's the benefit of measuring the setup! We find things that we would not otherwise suspect. That raises questions and experiments and that leads to corrections and better measurements.

My setup, and I suspect yours, is very much better now than it was originally. :sn:


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## jcmusic

Jtalden
Yes the difference is staggering!!! I want to learn more if you have time to help? Also there is one other issue that is baffled me.
I installed new tweeters and the curves were drastically different than the originals. Now the curves for some reason look like they did before I changed tweeters. Does that make any sense to you?

Jay


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## jtalden

Different TWs may have significantly different characteristics; SPL response, phase response, sensitivity, and dispersion. If so, then the setup process should be revisited. If the dispersion is significantly different then it will probably effect your preferred house curve target also.


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## jcmusic

Well that's what I don't understand I changed nothing except the tweeters, and for the next handful of measurements the new tweeters displayed as they should. A few measurements later the curve now looks like the old tweeters???


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## jcmusic

I should have said the new tweeters curve was significantly higher than the old tweeters. Now the new tweeters curve looks like the old curve, this just happened I can't explain it.


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## jtalden

Measurements should be repeatable, if no changes are made. If you a are seeing differences that aren't explained by differences, e.g., mic position, then there is a problem somewhere.


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## jcmusic

That's what I don't understand I changed nothing and the next thing you know the curves are different. I will find the two when I get home and post them.


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## jcmusic

jtalden,
Here are the two different tweeter curves, now for what ever reason the current curve looks like the red one and I didn't change anything. 
The darker curve is the new tweeters when I installed them the curves looked like that and then just changed???


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## jtalden

Yes, that is a big change. Is this happened on both channels? 

I don't really have anything particularly to helpful to suggest, but...

If it is clearly audible that suggests the measuring system is okay. If it isn't audible then something in the measuring system is at fault.


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## jcmusic

Exactly there is nothing audiable just on the graph.


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## jcmusic

Yes this is both channels from the LP with the old and new tweeters. Now the curve looks like the one from the old tweeters but there is no change in sound quality. Which makes me think my laptop or the software?


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## jtalden

It's not a good idea to measuring more than one speaker when you want to look at MF/HF response. There is interaction (comb filtering) that can make the response look very bad. That said, this chart does not look like a comb filtering problem. Comb filtering has a very different effect in the response.

Since you can't hear that big a difference then I agree it is probably in the measuring system. I don't know where. If it is a rare occurrence then it will be hard to troubleshoot. I would start with lots of loopback measurements just to confirm it is not in the soundcard or computer. If those are clear then the mic, amps and cabling is suspect. Maybe one of the TWs is dropping out occasionally.


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## jcmusic

I can clearly hear the new tweeters working all the time, so I think I need to measure one channel at a time to get a feel for what's going on.


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