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One Simple Tool to Find the Right Size Speaker for Any Space

By Nathan Lively

one-simple-tool-find-right-size-speaker-space-screenThis is an article I wrote for SoundGirls. Here’s the original.

Do you usually choose speakers by guessing? I want to show you one simple tool to find the exact right speaker for any space.

It is called Forward Aspect Ratio (FAR) and it is simply the shape a speaker makes, defined by depth and width. Here’s how you can reverse engineer it to master the universe.

  1. Measure the depth of your space at mid-width.
  2. Measure the width of your space at mid-depth.
  3. FAR = depth ÷ width.
  4. Cov. Angle = 2 × arcsin(1 ÷ FAR).

Let’s walk through it together.

1. Measure the depth of your space at mid-width.

one-simple-tool-find-right-size-speaker-any-space-1

2. Measure the width of your space at mid-depth.

one-simple-tool-find-right-size-speaker-any-space-2

3. FAR = depth ÷ width

50 ÷ 40 = 1.25

FAR = 1.25

4. Cov. Angle = 2 × arcsin(1 / FAR)

2 × arcsin(1 ÷ 1.25) = 106º

We need a 106º speaker.

one-simple-tool-find-right-size-speaker-any-space-3

Yikes! How do I type this into the google calculator?

Easy. Search google.com for calculator. Make sure you are in degrees. Click inside the calculator input window and type 2 [shift + 8] [shift + s] 1 / 1.25 [enter]. On a mobile device, turn to landscape mode and use the Inv button to show sin-1.

one-simple-tool-find-right-size-speaker-any-space-4

What if I don’t have the right speaker?

Don’t worry. As long as you have no more than a 3 dB error on each side, you’ll be fine.

Drop this into Google: ABS((20 × log(FAR A))-(20 × log(FAR B))) where FAR A is the speaker you need and FAR B is the speaker you have. As long as the result is less than 3, you’re good.

What if the result is more than 3?

If your speaker is too wide, just know you’re going to get some extra wall reflections.

If your speaker is too narrow, consider subdividing the space. Take your FAR, cut it in half, and redo your calculations.

Further questions?

Click here to download 105 Questions about Sound System Tuning. It’s everything you wanted to know about live sound system setup but were afraid to ask.

Calculate it for me

Loved this post? Try these:
  1. How To Find Speaker Coverage In One Step
  2. Can you estimate line array splay in the field without software while the riggers are waiting?
  3. Make Space for Bass in Your Ableton Live Mixes

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Comments

  1. cq Robinson says

    April 6, 2021 at 16:49

    Shouldn’t it be 2 * arctan(1/FAR) ?

    Reply
    • Nathan Lively says

      April 8, 2021 at 14:05

      Hey cq, thanks for checking out the article. I could be wrong, but I think ArcTan would give you the effective coverage angle of the Lateral Aspect Ratio. Check it out.

      Reply
      • cq Robinson says

        September 7, 2021 at 19:10

        Ah, I see. Thanks. I was not clear on the concept of FAR vs coverage angle.

        FAR = (length of coverage area) / (width at half length),
        but coverage angle is the angle such that
        (level on axis at distance L) = (level on edge of coverage at distance L/2)

        Reply
        • cq Robinson says

          September 7, 2021 at 19:30

          To put it another way, I was confusing coverage angle and effective angle.

          Reply
        • sen says

          March 22, 2023 at 23:13

          “(level on axis at distance L) = (level on edge of coverage at distance L/2)”Where does the formula come from?

          Reply
  2. sen says

    March 15, 2023 at 22:24

    How to calculate FARA and FARB in the same space? Aren’t the FARA and FARB results the same in the same room? How to calculate the FAR difference between the have speaker and the need speaker?

    Reply
    • Nathan Lively says

      March 16, 2023 at 13:39

      hmmm, I guess I don’t know what you mean by FARA and FARB. Maybe you could provide an example?

      Reply
      • sen says

        March 21, 2023 at 04:34

        How to calculate FAR A and FAR B in the same space? Aren’t the FAR A and FAR B results the same in the same room? How to calculate the FAR difference between the have speaker and the need speaker?

        Reply
        • sen says

          March 21, 2023 at 20:39

          my mean is: In the text“…….. ABS((20 × log(FAR A))-(20 × log(FAR B))) where FAR A is the speaker you need and FAR B is the speaker you have. ……”How to calculate this FAR B?

          Reply
          • sen says

            March 21, 2023 at 22:38

            Is the angle a vertical coverage angle or a horizontal coverage angle?

  3. sen says

    March 21, 2023 at 22:26

    In the text“Don’t worry. As long as you have no more than a 3 dB error on each side, you’ll be fine.” How to define “each side”?
    “ABS((20 × log(FAR A))-(20 × log(FAR B))) ”Is the calculated result an error on each side? How to calculate the error on each side? Divide this calculation by 2, 4, or 6,or other?

    Reply

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