Diving Into Gen2 Standard Audio to Add a Subwoofer

[Supratachophobia]

Done!

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[Supratachophobia]

Time for another update. In an attempt to make the bass more uniform across volume level and music genre, I'm going to install a NVX XLCA2X which is similar in function to a LC2i (original bass roll-off line output converter). An added benefit of the XLCA2X is that it will do remote amp turn on based on voltage detection from the speaker outputs. Not strictly necessary, but it will save that extra few milliamps when camping/forgetting the doors are open.

But while I was preparing for that, I went over the existing setup and realized I had wired the dual voice coil subwoofer in series rather than parallel, thus presenting the speaker load to the amp as 8 ohms instead of 2. Credit to the NVX amplifier that it didn't let out the magic smoke on me. But all that to say after it was wired properly, even with no gain adjustment and 2 volt input for the sensitivity, way too much bass if that's even possible. Definitely going to leverage the remote bass knob and output levels on the XLCA2X to address this.

The lessons learned here are that 200 Watts is plenty for a 10-in subwoofer in a properly sized sealed enclosure. Curious what the factory subwoofer wattage is.

 

[mkhuffman]

...
Credit to the NVX amplifier that it didn't let out the magic smoke on me.
...

I think smoking the amp is more likely at lower resistance than at higher resistance, since the lower resistance parallel connection pulls more current at the same voltage. I bet it got louder when connected in parallel also. It should have, anyway...

Thanks for the update! You are doing great work on this!

 

[Supratachophobia]

I think smoking the amp is more likely at lower resistance than at higher resistance, since the lower resistance parallel connection pulls more current at the same voltage. I bet it got louder when connected in parallel also. It should have, anyway...

Thanks for the update! You are doing great work on this!

Very much louder. In fact, I decided to finally use the remote bass knob that I orignally didnt think was necesary. It was another tight fit to get the wire snugged up under the trim, but yet another testament to a good build quality from Rivian that everything was designed to fit togther well.

Per a support request to NVX, they menioned that only one remote bass knob is necesary when using the XLA2CX and the VADM1 (they each have one).

 

[Supratachophobia]

More updates. I started looking into the issue of bass roll-off. I took this problem for granted back in 2014 because I used an LC2i as an LOC. I don't think I fully realized it also happened to deal with bass roll-off on the non-premium Model S sound system. Which is why it always sounded so good at all volume levels.

For the Rivian, I mixed the balance/fader to a single door speaker and did test tones at 40/50/60/70/80hz. Using an app that just reads the raw db from the phone microphone, I found that at about 19/20 volume level, those tones did not get any louder than exactly 90db. So one would conclude that the Rivian sound system does suffer from bass roll-off around volume level 20.

Armed with this knowledge, I'm going to go ahead and tune the XLA2CX with that in mind and hopefully have a very even bass signal across most listening levels. Again, premium audio that are tapping the subwoofer speaker wires would presumably not have this issue.

 

[Sundar]

Remind me again - where did you tap the speaker signal? Do you have a photo of the tap location and details on how you wired it e.g. t tap, spade into a connector, etc)?

 

[Supratachophobia]

Remind me again - where did you tap the speaker signal? Do you have a photo of the tap location and details on how you wired it e.g. t tap, spade into a connector, etc)?

I tapped it inside the B-pillar on the driver's side using a military splice. I popped the grommet away from the body where the door harness enters the car. There was just enough slack to let me pull the connector out enough to work with it. I then used my scope to fish a speaker wire up to the tap location through a pre-drilled hole in the b-pillar. From there, ran the cable under the door sill trim, up behind the interior carpet trim under the 3rd row armrest and down into the storage well.

 

[Supratachophobia]

I tapped it inside the B-pillar on the driver's side using a military splice. I popped the grommet away from the body where the door harness enters the car. There was just enough slack to let me pull the connector out enough to work with it. I then used my scope to fish a speaker wire up to the tap location through a pre-drilled hole in the b-pillar. From there, ran the cable under the door sill trim, up behind the interior carpet trim under the 3rd row armrest and down into the storage well.

I should add that by tapping inside the ingress point, you ensure you don't compromise any of the designs Rivian has of keeping water out, you don't need to disassemble the door, and you don't need to mess with the amp harness (color coding is a hot mess, it's much farther away, there's an airbag around it).

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