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Old 05-13-2019, 08:27 AM   #1
TheDragon
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Join Date: Feb 2011
My Country: UK - 230 v
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 55
Default Frequency measurement

I have a old JBL car amplifier that has electronic HP/LP crossover with pots.
Now, the pots don't have any increment markings, just 32-320Hz variable.
I would like to set these at around 100Hz in HP, as close as possible, so the front component speakers don't play that frequency.

I don't have a Oscilloscope but apparently my Uni-T multimeter can read frequencies. So, I sent 100Hz test tones via phone app, measured the output on the amp and it reads 100Hz. I sent 1Khz and 10Khz and it measured correctly, all in Flat position. Great I thought.

I then switched on HP, sent 100Hz, measured and it still reads 100Hz!
I tried a few different below 320Hz and all measured correctly.
Turning the Pot had no effect on the measured output.
If I listened to a bass heavy track, and adjusted the Pot, bass was indeed removed. So audibly it works, but not as measured.
Is the amp only attenuating and not really blocking.

So whats going on? Is my my meter faulty or not suitable for this type of testing?

Incidentally, If I sent various tones from 500Hz -15Khz in the LP setting, the meter cannot read them. Flicking the switch to flat and then it reads them.
Odd.

Any help or advice would be appreciated.
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