Buying Guides
L-Acoustics KS21 vs KS28: Which Sub to Buy Used in 2025
Choosing between the L-Acoustics KS21 and KS28 comes down to output needs, budget, and the systems you’re pairing them with. Both are cardioid-capable dual-driver subs built for touring and fixed install, but they serve different ends of the market.
This guide breaks down the real-world differences, typical used pricing, and what to inspect before you buy.
Output and Driver Configuration
The KS28 is the heavier hitter. Two 18-inch drivers in a front-loaded bass-reflex enclosure, rated at 146 dB max SPL. It’s designed for large-scale touring, festivals, and arenas where sub-bass extension and headroom matter.
The KS21 uses dual 21-inch drivers in a similar cardioid-capable configuration, but peaks at 137 dB max SPL. Still powerful, but optimised for mid-sized events, corporate AV, and fixed installs where you need punch without the full KS28 weight and power draw.
| Model | Drivers | Max SPL | Weight | Power (AES/Peak) |
|---|---|---|---|---|
| KS21 | 2 × 21″ | 137 dB | 95 kg | 2000 W / 8000 W |
| KS28 | 2 × 18″ | 146 dB | 117 kg | 2000 W / 8000 W |
Both subs run on LA12X or LA4X amplifiers and support cardioid deployment via Soundvision presets. The KS28 extends lower (29 Hz vs 32 Hz), which matters if you’re doing EDM festivals or stadium shows with heavy sub-bass content.
Typical Use Cases
KS21:
- Corporate events and conferences with K2 or Kara II tops
- Mid-sized touring productions (1,000–5,000 capacity)
- Fixed install in theatres, houses of worship, or mid-tier venues
- Rental inventory for clients who spec L-Acoustics but don’t need festival-scale output
KS28:
- Large-scale touring (arenas, stadiums, festivals)
- EDM and bass-heavy genres where extension below 30 Hz matters
- K1 or K2 systems requiring proportional low-end headroom
- Rental houses servicing major production clients and festival circuits
If your typical rider asks for K2 or Kara II, the KS21 is usually sufficient. If you’re regularly deploying K1 or supporting 10,000+ capacity events, the KS28 justifies the cost and logistics.
Used Pricing and Value Retention
As of early 2025, expect the following on the used market:
| Model | New RRP (approx.) | Used price range | Typical condition |
|---|---|---|---|
| KS21 | £6,500–£7,200 | £4,000–£5,500 | Good to excellent, light touring use |
| KS28 | £10,500–£11,500 | £6,800–£9,200 | Good to excellent, festival and arena use |
Stock fluctuates — these are indicative ranges. KS28 units from major rental houses often come with full service history and recent driver replacements, which justifies the higher end of the range.
Both models hold value well. L-Acoustics subs depreciate slower than most competitors due to brand loyalty, rider frequency, and robust build quality. Expect 30–40% depreciation over the first three years, then flattening out.
What to Inspect Before Buying Used
L-Acoustics subs are built to last, but touring and festival use takes a toll. Check these areas:
- Driver condition: Remove the grille if possible. Look for cone damage, surround deterioration, or signs of water ingress. Play a low-frequency sweep (30–60 Hz) and listen for distortion or rattling.
- Amplifier module: Both models use passive designs, so no onboard amp to fail — but verify the seller includes compatible LA12X or LA4X units or confirms compatibility with your existing rig.
- Rigging and casework: Inspect the integrated rigging points for cracks or stress. Check the plywood enclosure for delamination, especially around the handles and base. Road cases should be included — verify they’re original L-Acoustics flight cases, not generic aftermarket.
- Connectors: NL4 Speakon inputs should be tight and corrosion-free. Test continuity if you can.
- Service history: Ask for proof of driver recones, amplifier servicing, or Soundvision calibration files. Units from major rental houses often come with detailed logs.
If buying a batch of 8+ units, budget for at least one driver replacement or recone in the first year. It’s normal wear, not a dealbreaker.
Running Costs and Amplification
Both subs require LA-series amplification. If you’re buying used subs without amps, factor in:
- LA12X: 4-channel, drives up to 4 KS21 or KS28 units. Used price £3,500–£5,000.
- LA4X: 4-channel touring amp, smaller form factor. Used price £2,200–£3,200.
Power draw per sub is identical (2 kW AES), but the KS28’s higher output means you’ll typically run them harder, so factor in generator capacity for outdoor events.
Transport costs differ. The KS28 is 22 kg heavier per unit, which adds up when you’re moving 12+ subs. Standard Euro truck fits roughly 20 KS21 or 16 KS28 in flight cases.
System Compatibility
Both subs integrate with the full L-Acoustics range via Soundvision and LA Network Manager. Common pairings:
| Top system | Recommended sub | Why |
|---|---|---|
| K1 / K1-SB | KS28 | Output and extension match large-format line arrays |
| K2 | KS21 or KS28 | KS21 sufficient for most, KS28 for stadium/festival scale |
| Kara II | KS21 | Balanced output, easier logistics |
| A15 / Syva | KS21 | KS28 overkill for these applications |
If you’re running a mixed inventory with K2 and Kara II, the KS21 offers better flexibility across jobs. If you’re a K1 house or specialise in large outdoor events, the KS28 is the only logical choice.
Frequently Asked Questions
Can you mix KS21 and KS28 in the same system?
Technically yes via Soundvision delay and level matching, but it’s not recommended. The different driver sizes and SPL capabilities make seamless integration difficult. Stick to one model per deployment.
How many KS21 or KS28 subs do I need for a 2,000-capacity venue?
Depends on genre and venue shape, but as a rough guide: 6–8 KS21 in cardioid configuration for rock/pop, or 4–6 KS28 for the same application. Use Soundvision to model your specific space.
Do L-Acoustics subs require special maintenance?
No more than any passive sub. Keep drivers clean, check rigging hardware annually, and verify Speakon connections before each tour. Driver recones are typically needed every 5–7 years under heavy use.
What’s the resale value like after 5 years?
L-Acoustics holds value exceptionally well. A well-maintained KS21 or KS28 will retain 50–60% of original RRP after five years, assuming no major damage and regular servicing. Demand remains strong on the used market.
Can I use KS21 or KS28 with non-L-Acoustics tops?
Physically yes, but you lose the Soundvision integration and preset optimisation. Most buyers stick within the L-Acoustics ecosystem to maximise system performance and resale value.
Which sub is better for fixed install vs touring?
KS21 suits fixed install better — lighter, easier to rig permanently, and sufficient output for most venues. KS28 is touring-focused, built for the rigours of festival and arena circuits where maximum SPL and extension justify the weight and cost.
Ready to Buy?
Both the KS21 and KS28 are solid investments on the used market. If you’re expanding rental inventory for mid-tier events or fixed installs, the KS21 offers better value and logistics. If you’re servicing large-scale touring clients or festival circuits, the KS28 is the only choice that delivers the required output and extension.
Browse current stock in our used audio equipment section or get in touch if you’re looking for specific quantities or configurations.