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How to flatten the phase for easier main+sub alignment

By Nathan Lively

Which is easier to read?

This?

30-400Hz

Or this?

30-400Hz

Proper phase alignment in the field is hard. It’s one thing to measure in the near field when you can get a nice clean trace, but once you get into the far field and add reflections it gets a lot harder.

One thing you can do to make the whole alignment process easier on yourself is to flatten the phase trace around the area of interest. To do this, add more delay to the delay finder.

A standard main+sub phase alignment goes like this:

  1. Measure Main solo. Auto set delay. Save trace.
  2. Measure Sub solo.
  3. Make the pictures match.

The easier it is to read the graph, the easier it will be to match the pictures. Let’s find out how.

Normally, using the procedure above, you’ll start out with a flat phase measurement in the high end (on time arrival relative to the reference) and it will slope up and wrap around as you move to the left in the low end (late arrival relative to the reference).

20Hz-20kHz

We want to move that flat portion to the left and we’ll do that by adding delay to the delay finder in Smaart.

But how much delay?

Start by adding delay with the arrow keys so you can see the gradual change. How much delay do you need to move the flat portion of the phase graph to 100Hz?

If I click down incrementally, I find that it takes 10.5ms to move the flat portion of the graph to 100Hz. Let’s see if we can do it faster with a quick calculation.

number of wraparounds * 10ms = additional delay

current delay + additional delay = total delay for an on-time arrival at 100Hz

Let’s try it.

Here’s a measurement of a Meyer Sound UPJ-1P. I can see that the phase is flat starting at 2kHz, but we want it to be flat around 100Hz. It looks like there are about 1 wraparound starting at 100Hz and moving left.

1 * 10ms = 10ms

90.52ms + 10ms = 100.52ms

Looks good. Much easier to read.

30-400Hz

Let’s try a real measurement from the field. This one is more difficult to read, but it looks about 1 wraparound.

20Hz-20kHz

Let’s add 10ms just like in the last example.

74ms + 10ms = 84ms

What have you found that helps you read the phase graph? Comment below and let me know.

Credit to Timo Beckman for introducing me to this idea.

Loved this post? Try these:
  1. 3 Phase Alignment Hacks to Make Your Sound System Tuning Easier
  2. Smaart® Beta: Will the new filter control in the delay finder help with your main+sub alignment?
  3. How to phase align main to sub in Smaart, REW, Open Sound Meter, SATlive, and Crosslite

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Comments

  1. Josh kim says

    February 8, 2019 at 16:52

    Can i translate this for our Korean friends??

    Reply
    • Nathan Lively says

      February 12, 2019 at 14:27

      Sure. Of course. Do you want to publish it on your own site or on Sound Design Live https://sounddesignlive.com?

      Reply
  2. Thomas Neumann says

    February 9, 2019 at 00:34

    Well, you’ve found the reason for the Low Delay Finder 🙂

    Reply
    • Nathan Lively says

      February 12, 2019 at 14:25

      Reply
  3. Markus says

    March 28, 2021 at 03:04

    A linear phase has a constant group delay. A flat phase has no constant group delay, except it is zero. Is that right? Why we want a flat phase?

    Reply
    • Nathan Lively says

      April 5, 2021 at 13:41

      Hi Markus!

      > Is that right?
      Hmmm, I don’t think I can comment. I’m not an expert with group delay, but I think you are correct.

      > Why we want a flat phase?
      This article is about making the phase slope less steep so that it is easier to read, not for any reasons of quality.

      Reply
  4. Craig Ross says

    February 12, 2022 at 12:56

    This is a great idea, I’m not sure why I hadn’t tried it before! Thanks

    Reply
    • Nathan Lively says

      February 13, 2022 at 11:28

      Me, either! 😉

      Reply
  5. Alexandre says

    May 30, 2022 at 18:20

    Est ce que il un application un peu plus simple à utiliser pour aligner les hauts parleurs ?

    Reply
    • Nathan Lively says

      August 16, 2022 at 11:07

      Yes, yes there is: https://www.subaligner.com/

      Reply

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