Question Help with car amplifier! Calibration?


Oct 6, 2016

I have the JBL S2-1224 12" 275 rms subwoofer paired with the JBL GX-A3001 amplifier. I had the subwoofer set at 4 ohms and the gain at 50%. Good base and it hit hard. Then I learned about clipping and that you should set the voltage from the amplifier to the subwoofer. I calculated the voltage. 200 watts(amp) times 4 and Square root of that. That's 28 volts. I Put a multimeter at the plugs of the amplifier, a 50 Hertz signal and volume att 75%. Low pass filter all the way up and no bass boost. That left me at 28 volts under 1/4 of the max gain/level. So now the bass is very low, not hitting at all. How do I fix this or have I calculated something wrong ? Thanks for reading. Tried at 2 ohms and same calculation but with 275 watts instead, but that left me at 1/4 gain and almost no bass again.

Sonic Illusions

Feb 16, 2019
Unless you have pink noise test signal and a spectrum analyzer, simply adjust the amp gain to suit your taste (with head unit FLAT- zero bass added) and set the crossover to 175Hz. Set the sub impedance to 4 ohms. I'd forget about the voltage because it constantly varies. Amps only clip when over-driven, which can be heard as audible distortion. Your sub handles 275 continuous, which is a good match for your amp at 4 ohms. According to the specs, you get clean 200W (RMS) into a 4 ohm load, which is decent power. I have a sub amp which delivers 1400W RMS @ 2 ohms, which I have it loaded at. I never approach that, because I prefer headroom over SPL and it would launch my woofers into orbit! Your personal preference rules.
As Sonic Illusions says above you set the woofer level to match the level of the other speakers in the system and to your taste not by the wattage of the amp and speakers. The woofer enclosure affects the efficiency of the speaker so that adds another factor you can't calculate from wattage alone.
Since this is a subwoofer it won't be damaged by the amp clipping which generates high frequency distortion that the driver can't reproduce anyway. A woofer would be damaged by over driving it with more power than it can handle for too long a time.
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