Ground Shaker GS-GMP28B Dual 8″ Ported Sub Box — Fits 14–18 GMC Sierra Crew Cab
Enclosure only — subwoofers not included.
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Ground Shaker GS-GMP28B Dual 8″ Ported Sub Box — Fits 14–18 GMC Sierra Crew Cab
Product Overview
Description
Here is Ground Shaker's dual 8" ported enclosure for the 14–18 GMC Sierra Crew Cab; it sits under the rear seat and fires down. Being ported and tuned to 35 Hz, it plays louder and deeper than a sealed box would in the same spot with 1.38 cubic feet of air volume, for anyone who wants the bass felt and not just heard.
Key Features
- Vehicle-specific enclosure for the 14–18 GMC Sierra Crew Cab
- Dual 8″ ported design — 1.38 ft³ air volume, tuned to 35 Hz
- 1 slot port (H-2″ W-4″ L-10″)
- Mounting depth 6 1/2″
- 5/8″ high quality MDF wood
- Carpeted with durable trunk liner finish
- Sealed with high quality Titebond silicone
- Glued with high quality Titebond wood glue
- 2 binding post terminals
- Fits under rear seat
- Down firing
Specifications
| SKU | GS-GMP28B |
| Application | 14–18 GMC Sierra Crew Cab |
| Enclosure Type | Ported |
| Woofer Size | Dual 8″ |
| Cutout Diameter | 7 1/8″ |
| Air Volume | 1.38 ft³ |
| Tuning Frequency | 35 Hz |
| Ports | 1 slot port (H-2″ W-4″ L-10″) |
| Weight | 44 lbs |
| Mounting Depth | 6 1/2″ |
| Height | 8″ |
| Length | 49 1/2″ |
| Depth | 16″ |
Subwoofer option
Add two DS18 SRW8.4 shallow-mount 8" subwoofers — 150W RMS / 300W MAX, SVC 4-ohm, 2.95" mounting depth, 7.12" front-mount cutout per DS18's dimension drawing — and they ship with the box, one per woofer opening. This box is cut 7 1/8″ with 6 1/2″ of mounting depth, so the SRW8.4 fits as shipped. Choose "Box only" to buy the enclosure alone.
Box-only option: subwoofers not included. Price is each.
Free shipping on orders $150+
If you have any questions, you are always welcome to contact us. We'll get back to you as soon as possible, within 24 hours on weekdays.
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FAQs
Please read our FAQs page to find out more.
RMS vs. MAX power — which number do I actually care about?
RMS is what your gear handles continuously; MAX is the short burst it can survive without complaint. Match your amplifier's RMS output to your speakers' RMS rating — sizing off the MAX number is how magic smoke gets released.
What does the IP65 rating on DS18 marine gear actually mean?
It's dust-tight and rated against low-pressure water jets from any direction — built for spray, rain, and the occasional wave over the bow, not for full submersion. If something's going somewhere it could sit underwater, that's a different conversation entirely.
How do I match an amplifier to my speakers without guessing?
Add up the RMS rating of everything the amp will power, and pick an amp whose RMS output (at your speakers' impedance — usually 4-ohm) lands close to that total. Undersized is thin sound; wildly oversized is a fast way to blow a voice coil.
Can I mix marine-grade gear into a standard car audio setup, or the reverse?
You can run marine-grade gear in a car — it's just over-built for that environment, no downside besides cost. Running non-weatherproof car audio gear in an open UTV or boat is the direction that causes problems.
What gauge wiring kit do I need?
It scales with your amp's power draw and the length of the run — DS18's OFC kits come in 4-gauge and 8-gauge for a reason. Undersized wiring on a high-draw system is a voltage-drop and heat problem waiting to happen; when in doubt, size up.