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Hi Guys,

I'm posting this here because we are building our own speakers and subs often because we want to eek the best from our systems. Once they are built, they need to be integrated. Many rely on audyssey to take care of this. I've run it several times and found the subs and mains aren't usually very close in phase alignment.

How important is this? If it's not important skip to the end and tell me to stop wasting my time and why!

Rythmic has a great little write up on how to phase align your subs to your mains in order to get constructive summation through the crossover point.

http://www.rythmikaudio.com/phase3.html

@mtg90 has a great thread on how to integrate subs and it touches on this subject but does not go into detail.

https://www.avsforum.com/forum/155-diy-speakers-subs/1713458-mtg90a-s-multiple-subwoofers-mains-integration-how-thread.html#/topics/1713458

I've looked around and can't seem to find a tutorial on how to do this with REW. Has anyone come across one?

So far I've measured my speaker at the mlp with the sub off and then measured again with the sub on but the speaker disconnected. I use the phase section in the overlay tab in rew with each measurement selected. At 200hz, (the crossover point I'm playing with) I see the speaker at -24deg and the sub at 166deg. This is where I'm stuck. Do I just add or remove delay in the avr until the two phase lines meet? Can I calculate what to add/remove in the avr? The rythmic link isn't clear enough for my pea brain. I'd like to get this figured out and write it up so it's available to others as an Rew focused tutorial.

Pete
 

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The phase alignment of two sources with similar outputs will have a direct impact on the frequency response. While I don't say much about phase or have graphs showing it in that thread the process I follow for integrating the subs with the mains is in fact aligning the phase response of the subs with the mains.

Just because the phase at a specific frequency matches between two sources does not mean you have good phase alignment. You must take a broad look at the phase response to see how well they track against each over. Ideally you want the phase response of the subwoofers and mains to track very close to one another for as much of their bandwidth as you can. Usually an octave above/below the crossover would be plenty if using your mains with a standard crossover.

You can see an example of this in my thread looking at the where I experiment with 12', 19' and 26' of delay on the subwoofer. At 80hz every 7' of delay will give you roughly 180 degrees of phase rotation at which point you can reverse the polarity on the subwoofer and end up with an aligned phase response at 80hz. Add too much or too little delay and you begin to reduce the bandwidth over which the phase tracks well. If you look close you can see that the 19' of delay I chose had the best phase tracking because as a result of that phase tracking it has the widest bandwidth of constructive gain from the two sources.
 

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The impulse chart in REW.

Once you'd set the delay for the distance difference, there shouldn't be much tweaking left. Maybe a few ms here or there.

With a HPF on the mains and a LPF on the subs, the phase becomes less important.
Also, as frequency drops phase becomes less important, at 10hz no part of the wave fits in the room, so even a 5% deviation isn't gonna make a big difference in SPL from phase de-coherence. For tweeters on the other hand, it is a big deal if you want centered imaging.
 

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The phase alignment of two sources with similar outputs will have a direct impact on the frequency response. While I don't say much about phase or have graphs showing it in that thread the process I follow for integrating the subs with the mains is in fact aligning the phase response of the subs with the mains.



Just because the phase at a specific frequency matches between two sources does not mean you have good phase alignment. You must take a broad look at the phase response to see how well they track against each over. Ideally you want the phase response of the subwoofers and mains to track very close to one another for as much of their bandwidth as you can. Usually an octave above/below the crossover would be plenty if using your mains with a standard crossover.



You can see an example of this in my thread looking at the where I experiment with 12', 19' and 26' of delay on the subwoofer. At 80hz every 7' of delay will give you roughly 180 degrees of phase rotation at which point you can reverse the polarity on the subwoofer and end up with an aligned phase response at 80hz. Add too much or too little delay and you begin to reduce the bandwidth over which the phase tracks well. If you look close you can see that the 19' of delay I chose had the best phase tracking because as a result of that phase tracking it has the widest bandwidth of constructive gain from the two sources.


Going to have to go back and study the thread some more. So in Rew in the phase section I'm looking for the phase of the speaker and the sub to overlay and rotate at the same rate through the crossover? That's optimal? Will the best summation also have the best phase tracking?
 

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The impulse chart in REW.



Once you'd set the delay for the distance difference, there shouldn't be much tweaking left. Maybe a few ms here or there.



With a HPF on the mains and a LPF on the subs, the phase becomes less important.

Also, as frequency drops phase becomes less important, at 10hz no part of the wave fits in the room, so even a 5% deviation isn't gonna make a big difference in SPL from phase de-coherence. For tweeters on the other hand, it is a big deal if you want centered imaging.

Isn't phase important when your crossing at 200hz?
 

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Do I just add or remove delay in the avr until the two phase lines meet? Can I calculate what to add/remove in the avr? The rythmic link isn't clear enough for my pea brain. I'd like to get this figured out and write it up so it's available to others as an Rew focused tutorial.

Pete
I know it's an old thread, but in case this comes up in a search, here's what you can do. Do this after your subwoofer(s) have been set up and EQ'd:



1. Disconnect the subwoofer(s) and leave the center channel on (but leave the crossover engaged) and run a short sweep (+/- 15Hz on both sides of the crossover point). So, from 185Hz to 215Hz if it's a 200Hz crossover point.

2. Connect the subwoofers and disconnect the center channel, and run the same sweep.

3. Compare the phase measurement in the "Overlays" tab. Here's an example of my measurements. The number after Subwoofer is the distance measurement in the receiver (so "Subs 54.0" means the distance was set to 54 feet.) The pink line is the center channel, and the blue line is the Subs at 54.0 feet.






4. Adjust the subwoofer distance in the receiver and note how the phase moves. Find the distance setting that matches the phase. Here's what it looks like as I adjust the sub distance to different settings. The center channel is bright green. You can see that the phase at the crossover point (80Hz) is closest with the subs set between 42.8 and 43.0 feet.





5. Now that you know where they're in phase at the crossover point, you need to make sure they're in sync. Calculate the length of the wavelength at the crossover point. For 80Hz, it's 14 feet. That means the speakers and sub will be in phase not just at 43.0 feet, but also 29 feet, and 15 feet, and 57 feet. So then you can look at the impulse response to see if the waveforms are in sync, or you can play some music with good bass content around the crossover point and see if the sound is blended, or out of sync. The subs should just disappear into the mains.
 
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