Trying to diagnose a couple of notches
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:
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:
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?
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.
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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