2025 R1T Tri Max - Subwoofer Replacement - Upgrade to Premium Audio

[ksumnole]

This is my take on the subwoofer replacement in what was supposed to be "Premium" audio in the 25 R1T Tri Max.

Quite frankly, Rivian was very close to having premium audio, but dropped the ball on this by installing a 6x9 speaker in place of a good-quality sub. Maybe, by the time of this writing, this has changed.

The combination of the latest software, 2025.14.30, and the replacement sub makes this a truly premium audio system. It sounds amazing! No adjustments to the EQ! My wife, who never agrees with me on anything, let me tell you, even the color of the sky, was actually impressed by how good it sounds now.

The goal here was simple:
1. Make it easily reversible in case you want to sell the vehicle, service, or upgrade, etc.
2. Make it sound good, but not nuts (I don't know how either-wise to describe it).
3. Reduce any vibration coming from the sub onto the vehicle chassis (probably on overkill).
4. Maintain the under-the-seat storage space.

What did I use (BOM):
JL Audio 8W3v3-4 (8" 4-ohm subwoofer) - $349
JL Audio JD250/1 (JD Series mono subwoofer amplifier — 250 watts RMS x 1 at 2 ohms) - $229
JL Audio RBC-1 remote - $ 54.99
Crutchfield Amp Wiring Kit - $37.49
30-amp Fuses - $3.99
Cable, posi-connectors, rubber spaces, M6 bolts, etc. -<$50.
2x leftover pieces of 8020 Series 10 extruded aluminum.
1x leftover piece of 1/4'' cast acrylic (the kind used to make aquariums)
Some black spray paint
1x can of Sikaflex-252 - $21

The main bracket is designed from 10 Series 8020 aluminum and a piece of 1/4 cast acrylic slotted in the groove. I used Sikaflex-252 to hold the aluminum and acrylic together. It is used in the automotive industry to bond components together, and it has a slight flex to it. The entire bracket is suspended with 1-inch industrial rubber spacers. The bracket is drilled to accept longer M6 bolts that pass through the original subwoofer mounting points. The rubber spacers allow the sub to sit just about ~1.5 inches below the seat but high enough to allow the amp to sit below it.

High end paint booth:

Bracket template:

Layout planning:

Sub comparison to OEM:

I added a on/off switch in case I need it off, and the volume know to adjust the sub output. I just like switches.

The power was connected to this specific bolt on the 12v battery under the seat. It's long enough to accept additional customers. 30amp fuse within ~6 inches..

The power cable was routed along all the other 12v cable going to the back of the vehicle behind the side trim:

The final product:

FAQ:

Q. Why did you use 80/20 and acrylic?
A. It’s what I had around the shop.
Q. It’s an 8’’ sub. Is that big enough?
A. Yes, yes it is. I thought about using a 10-inch. It would fit, but after testing the audio with the 8”, I’m happy with the results.
Q. Any issues with the 12v battery?
A. No issues, no errors.
Q. Did you unplug the battery to plugin the power for the amp?
A. No, wire the switch first to the negative, wire everything else, and turn it on when ready.
Q. Where did you get the audio signal from?
A. The OEM sub wires connect direct to the 250w amp. The amp is configured to auto turn on when it senses a signal.

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[ksumnole]

I should add, I'm not an audio engineer or neither an electrician, so any feedback is welcome. Thanks

 

[23R1TFGFE]

What time should I drop off my truck for installation?

Truly well done, sir — enjoy your PREMIUM audio!

 

[Erik+]

I like it, nice work! I concur with your logic for going with the 8-inch and keeping everything hidden, easily convertible back to OEM, and ability to keep all standard storage options. Thanks for sharing.

 

[Seano]

What a great write up - happy for you: bet it does sound great!

 

[ja_kub_sz]

Damn, that's incredible. What was the total install time?

 

[ksumnole]

Damn, that's incredible. What was the total install time?

It took me three months. However, if you didn't have a one year old running laps around you, you can probably get it done in 4-5 hours. Including fabrication of the bracket, not including paint and sikaflex drying time.

 

[mkhuffman]

I assume the input to the JL amp is speaker level, not line level?

This is a great mod. IMO it is definitely the way to go. It is on my list as something I might tackle later this year.

 

[brancky3]

Nice! I have a JL 8w3v2 in a prefab JL box so I had to take out the storage tub, unfortunately. I did find that making it fire downwards increased the performance considerably, but every setup is different!

 

[2kwik4u]

What holds the amp in place? did you screw it down? Double sided tape?

 

[UnsungZero_OldTimeAdMan]

Interesting. I've always thought a sub needed to be in a fabricated enclosure, sealed or ported.

 

[ksumnole]

What holds the amp in place? did you screw it down? Double sided tape?

Excellent question. Forgot to mention that. Industrial strength velcro applied to bottom and side of the amp: https://www.amazon.com/dp/B09FY9MCQB?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

 

[ksumnole]

Interesting. I've always thought a sub needed to be in a fabricated enclosure, sealed or ported.

My thought exactly. But then I guess the space itself is small enough to act as a ported enclosure? This is my first iteration but I don't mind changing it around if an audio engineer comes by to provide feedback.

 

[shracks]

This is a super clean install. Absolutely killer job!

According to the sub specs, ideally it should be mounted in a sealed or ported enclosure with the following specs:

• sealed box volume: 0.3 cubic feet
• ported box volume: 0.35 cubic feet

I'm not sure how many cubic feet the under seat storage area is (with existing driver side tray in place). IIUC, it's "vented" since the opening of where the original 6x9 speaker is still present.

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