Question new audio system (dual amp) but sub is quiet

Sep 10, 2022
hello there,

I just installed a two-amp audio system in my toyota sienna 2005. Amp #1 is a 4-channel amp (Skar Audio RP-75.4AB 500 Watt Full-Range Class A/B 4 Channel Car Amplifier, Connected 4 full range speakers and 4 tweeters, wired parallel. Amp #2 is a mono block amp (Skar Audio RP-350.1D Monoblock Class D MOSFET Amplifier with Remote Subwoofer Level Control, 350W,) for the subwoofer (Skar Audio VD-8 D2 8" 600W Max Power Dual 2 Ohm Shallow Mount Car Subwoofer, ).

Tested out the system today and the speakers connected to the 4-channel amp are awesome. Very loud and no distortion at all. On the other hand, the subwoofer is very quiet although it sounds good at low volumes.

I've tried several troubleshooting options:
  1. tried adjusting gain using several youtube videos; no success. there was obviously more bass but i'd have to turn up the gain very high for noticeable changes (>75%). lot of movement, but not a lot of sound. i felt like it was only gonna damage the sub so i turned it down.
  2. originally had it wired parallel (1 ohm load), but added two more speaker wires to connect directly to amp (2 ohm load); no change at all (14 guage).
  3. tried switching the rca cables from the 4-channel amp with the monoblock amp (also switched on head unit -> pioneer mvh s310bt); no change.
  4. took all speaker wires out of sub, and used a dmm to measure resistance of sub terminals; both voice coils read 2 ohms +/- 0.5
not sure where to go with this. i'm using distribution blocks for both the power and ground wires (4 guage). grounded ring terminal between two washers using passenger side seat rail bolt. sanded everything down.

for the 4-channel amp, i'm using two y-splitters in the head unit, and using the other two rca inputs for the sub.

both amps are on and has never gone into protect mode. speaker wire length is around 15 feet each. Is there something I'm missing? first time setting up an audio system, so any advice is appreciated. thank you!
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