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Down4Sound
Sundown Audio
Welcome to JS Ultimate Sounds
Your Bass. Our Obsession.
JS Ultimate Sound is your destination for high-performance car audio products, bass packages, wiring kits, and installation accessories. Whether you are upgrading your daily driver or building a loud show-ready setup, we bring together the products you need to make your system hit harder, sound cleaner, and perform reliably.
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DS18
JS Alternators
Built for enthusiasts who demand dependable charging performance. JS Alternators provide the power needed for upgraded audio systems, accessories, and high-performance vehicles.
Learn moreCustom Colors
Available in a range of striking finishes, JS Alternators deliver premium performance while giving your engine bay a custom look that gets noticed.
Shop brandsJS Alternators
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Many in-stock orders ship quickly. Custom, built-to-order, oversized, special-order and supplier-direct items may need extra processing time.
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The biggest names in car audio, all in one place.
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Products In Stock
Subs, amps, speakers, enclosures and wiring.
Questions? We're here to help.
The most common questions our customers ask. Still stuck? Reach out and our team will get you dialed in.
How do I choose the right subwoofer size?
Bigger subs (15-21") move more air for deeper, louder bass but need more space and power. Smaller subs (8-12") are tighter and easier to box and power. Match your sub to your space, amplifier and bass goals — or contact us and we'll help.
Ported or sealed enclosure?
Sealed boxes give tight, accurate bass in a smaller footprint. Ported boxes are louder and dig deeper but are larger. We carry both, plus prefab and DIY flat-pack options.
What size amplifier do I need?
Match your amplifier's RMS power to your subwoofer's RMS rating at the correct impedance. Not sure? Send us your sub model and we'll recommend an amp.
What gauge wire should I run?
Rule of thumb: under 500W use 8-gauge, 500-1000W use 4-gauge, and 1000W+ use 1/0-gauge power and ground wire. Upgrade your Big 3 for high-power systems.
How long will my order take?
Many in-stock orders ship within 1-2 business days, but timing varies by item. Custom, built-to-order, oversized, special-order and supplier-direct products may need extra processing time.
What is your return policy?
Unused items in original packaging may be returned within 30 days after approval. Returns may be subject to a restocking fee. See our Returns & Warranty page or contact us for details.