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Altec 604-8h frequency response
G'day All! Has anyone measured the Altec 604-8h drivers frequency response before? Attached it a measurement taken 1/3 octave smoothed and 10db per division - taken 1 meter on axis, notice the 3khz dip. These are used with the original Altec 604-8h crossovers. I initially thought the compression driver may have been wired out of phase but this is not the case. I have tried all different crossover adjustment and this is the flattest I could get. I have also tried a different mic /measurement system with the same results! Any ideas guys? Both speakers measure the same. Thanks in advance.
Could be a reflection from the floor
With c = 344 m/sec at 3 kHz the wavelength is about 11 cm. If a part of the sound travels 5.5 cm more from speaker to microphone it would add out of phase to the direct sound, leading to cancellation.
Put a quilt, pillows, pullovers and jackets on the floor between speaker and mic and see what happens.
Ruediger