# For techies...How do I read those darned measurement graphs?

Discussion in 'Archived Threads 2001-2004' started by Ted Lee, Feb 26, 2002.

1. ### Ted Lee Lead Actor

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hi all -
i'm referring to the speaker review graphs in SGHT as an example here.
hopefully someone is up to this challenge...
one thing i've never really figured out is how to read those graphs. i can read a basic one that tells how flat a speaker is, but these new ones look so "different".
the left side says "db SPL", the right side says "Deg" and the bottom has the frequency response. i'm not sure how to read/cross-reference these different fields. the way i read those graphs...none of them appear even close to flat.
so, if anyone has info on how to interpret these graphs, i would be very appreciative.
i have the february 2002 sght issue at my desk...you can use that issue as an example if you think it would help.
thanks in advance...i'm hoping to get something out of this for sure!

2. ### Patrick Sun Moderator Moderator

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If I had to guess, the left hand side has the scaling for the SPL output of the speaker across the audible frequency range of 20Hz to 20KHz. So, you should see a graph that starts low in SPL for low Hz values, and it ramps up as the frequency increases until it gets to the tuning frequency of the enclosure (if it's vented), or smoothly reaches its nominal output level if it's a sealed enclosure. Then the curve should level off, and continues along a straight line, hopefully within +/- 3dB of the average of the line. So that's the frequency response of the speaker in terms of SPL.

The right side scale sounds like it's showing the phase of the speaker through 20Hz to 20KHz. Phase can be described as time delay at any given frequency, but it's tougher to get a grasp of it. Phase tends to fall in units of degrees as frequency increases.

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