Quote:
Originally Posted by VP Electricity
If you don't have a load on the passive crossover, the test results will have errors.
If you don't have the speaker load connected to the HU, your test will have errors (unclear whether or not you had such).
The rear speakers, as have been published elsewhere, have an active high pass filter in the HU.
I don't see any screenshot of a flat response. Did you take a screenshot of this "flat" response? I don't see anything you've posted that comes close to what a normalized signal looks like, in my experience.
All in all, you seem to be verifying that the HU response is nasty without recoding or without external normalization.
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The passive crossover measurements was done with the Alpine speaker as a load. The voltage at the speaker terminal was used to plot the response. The lowpass filter for the midbass is a second order (12dB/Oct) and the highpass for the tweeter is a first order (6dB/Oct). The crossover frequency is about 7KHz.
The response of the HU was done with a 47 Ohms load (Alpine amp input impedance). BTW, audio amplifiers have low output impedance in order to get high damping factor (
http://en.wikipedia.org/wiki/Damping_factor). This means that if you measure the frequency response of an audio amplifier with a load or without a load, there should not be large difference.
Recoding to disable the equalization in the HU is a better option. I am looking at doing that. In the interim, I am seeking at getting acceptable results, a flatter response. I know I will not be able to get a flat electrical response with the parameters that I can tune: Bass, Treble and the switch on the Alpine amplifier.
In post#20 second figure, I show the acoustical response of the drivers in the door after adjustment of the bass and treble. In the next figure, I show the response from the driver seat at ears level. As I said before, the peak and valley for acoustical measurements in a car are to be expected. You move the microphone by few inches and you get differents results. To get accurate measurements from speakers, the test has to done in a anechoic chamber (
http://en.wikipedia.org/wiki/Anechoic_chamber), not a car.
I do not have a figure with the settings that result in the best response because I take the results from many measurements, post-process and estimate the best setting after post-processing. I will try to take another acoustical measurement and post the results.