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Old 28th September 2012, 04:06 PM   #1
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Default Trying to diagnose a couple of notches

Hi Guys,

I'm trying to diagnose the source of a couple of notches in the frequency response of a couple of beaten up speakers. I'm using these speakers as a learning tool for when I work on something more significant.

I made the following measurements on axis at 2m outdoors at aprox 86db average level using a radio shack 33-2050 meter and a set of meter corrections found on the net. Charting is courtesy of excel.

This is what the frequency response looks like:
Possible Cancellation or Diffraction.png
The red line is the raw response and the black is a corrected response I managed using a basic digital 10 band graphic equalizer.

I've circled a couple of notches that make graphic eq style correction difficult.

Thinking the problem through the notches are at ~1600Hz and ~4kHz. If I convert these frequencies into distances we're looking at just over 7 inches and about 3 inches.

Looking at the speakers I found this:
Possible cause of 1600 Hz notch.jpg
and this
Possible Cause of 4kHz notch.jpg

Can these notches be created by a cabinet edge protroding 1/4 inch from flush with the baffle? Am I barking up the wrong tree? Any suggestions on how I could verify this?

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Old 28th September 2012, 11:02 PM   #2
Ron E is offline Ron E  United States
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Location: USA, MN
Put absorptive foam over the edges and see if the anomalies go away.
You might be better off using holmimpulse and the RCA output of your SPL meter.

edit: given the look of that tweeter it may not be making any noise below about 4kHz.
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Last edited by Ron E; 28th September 2012 at 11:05 PM.
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Old 28th September 2012, 11:42 PM   #3
tvrgeek is offline tvrgeek  United States
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Location: Md
Don't worry about the notches as much as the humps. These may all be mostly baffle diffraction. Do near field measurements ( as close to the tweeter as you can get) and see what the response looks like.

Head over to True Audio and read the Olson papers .
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