Second Spin Audio

Buying used KEF LS50 speakers (the original passive model)

A compact passive standmount built around KEF's Uni-Q driver, with no grille to hide damage. How to check a used pair of original LS50s and avoid mixing them up with later models.

Updated

A pair of KEF LS50 Black Edition loudspeakers
Photo: david falkner from Birmingham, England, CC BY 2.0, via Wikimedia Commons

At a glance

Type
Passive two-way standmount, rear reflex port
Drive units
Uni-Q array, 25 mm vented aluminium dome tweeter in a 130 mm magnesium/aluminium alloy mid/bass cone
Crossover
2.2 kHz
Frequency response (±3 dB)
79 Hz – 28 kHz
Frequency range (−6 dB)
47 Hz – 45 kHz
Sensitivity
85 dB (2.83 V / 1 m)
Nominal impedance
8 Ω (minimum 3.2 Ω)
Amplifier requirements
25–100 W
Maximum output
106 dB
Dimensions (H x W x D, with terminal)
302 x 200 x 278 mm
Weight
7.2 kg each

What to check before you pay

  1. Make sure it's the original passive LS50. KEF has since sold the LS50 Meta (a passive successor) and the active LS50 Wireless models, so make sure you know which one you're looking at. The original passive LS50 has speaker terminals only, with no mains lead, digital inputs or network sockets. Check the rear label and ask for a photo of the back of both speakers before you agree a price.
  2. Look closely at both cones. The LS50 has no grille, so the Uni-Q driver is exposed. Shine a torch across the mid/bass cone at a low angle on both speakers and look for dents, creases or any change in shape. Damage like this is reported by owners (see Reported faults), and a replacement driver is a real cost, so it should come off the price or send you elsewhere.
  3. Listen at low and moderate volume. Play something with steady bass and clear vocals on each speaker in turn. Listen for buzzing, rattling or a speaker that sounds noticeably duller or thinner than its partner. A matched pair should sound the same from the same position.
  4. Check the port and the cabinet. The reflex port is on the back. Look inside for anything loose or torn, and check the cabinet and the curved front baffle for knocks, especially on the corners. Cosmetic marks matter less than a damaged driver, but they still affect what the pair is worth.
  5. Terminals. Check that the binding posts tighten and hold the cable firmly on both speakers. Loose or damaged terminals cause intermittent sound and are worth pointing out before you pay.
  6. Think about your amplifier. KEF quotes 85 dB sensitivity and a 3.2 Ω minimum impedance, and Stereophile's measurements led it to recommend a good 4-ohm-rated amplifier. If your amp struggles with lower-impedance loads, factor that in before you buy.

Reported faults

Problems reported in the sources listed with each item. Not every unit has them, but they are worth asking about.

Deformed or creased mid/bass cone
What you notice
A visible change in the shape of the cone, or a crease in it.
What the source says
One owner reported one clearly deformed and one slightly deformed driver, attributed to over-excursion from being driven hard, and replaced both before selling. Another owner found a crease in the cone of original LS50s with no cause identified.
What to check
Shine a torch across both cones at a low angle and compare them. Ask whether either driver has been replaced, and how loud the pair has been played.

Repair report: StereoNET forum, "KEF Uni-Q LS50 drivers with deformed cones" (February 2017); Repair report: What Hi-Fi? forum, "KEF LS50 driver issue!" (September 2023)

Dented driver needing replacement
What you notice
Dents in the driver.
What the source says
A second-hand pair arrived with dents in the driver; the owner replaced the driver himself, noting the local KEF dealer in Sydney sold replacements for $570 each.
What to check
Inspect both drivers closely in person, and price a replacement driver into any offer for a damaged pair.

Repair report: StereoNET forum, "Procedure to change driver on KEF LS50" (December 2016)

A small speaker with a big idea

The original KEF LS50 is a compact passive standmount, about 30 cm tall, built around a single Uni-Q driver: the 25 mm aluminium tweeter sits right in the centre of the 130 mm mid/bass cone, so both come from the same point. KEF launched it as a 50th Anniversary Model, and the SoundStage! review notes it was inspired by the BBC LS3/5A, the classic little monitor.

What you’re buying is a carefully engineered box. The cabinet uses constrained-layer damping, the curved front baffle is shaped to reduce diffraction, and the reflex port on the back is elliptical with a flexible inner tube, designed to cut down port noise. All of that is there to let the Uni-Q driver do its thing cleanly, which is exactly why the condition of that one driver matters so much on a used pair.

No grille, so look hard

Here’s the catch for second-hand buyers: the LS50 has no grille. The tweeter has its own small waveguide in front of it, but the mid/bass cone is out in the open, in every home and on every shelf it has lived on. Dents and creases are easy to spot in good light and easy to miss in a dim listing photo. Ask for clear, close-up photos of both drivers taken at an angle, and check them again in person.

Feeding them properly

At 85 dB sensitivity, the LS50 wants a decent amplifier. KEF’s figures say 25–100 W, with a nominal 8 Ω but a minimum of 3.2 Ω, and Stereophile’s measurements found it dips low enough to recommend a good 4-ohm-rated amp. Small speakers like this also tempt people to push the volume for more bass. Owners report cones deformed after being driven hard, so ask how the pair has been used, and take it easy with the volume when you test them.

Who it suits

If you want a small passive speaker for a desk, a bookshelf-sized room or a pair of stands, and you already have an amplifier you like, the original LS50 is the one to look at. If you’d rather have the amplifiers built in, the active LS50 Wireless models are a different product altogether, and if you want KEF’s later revision of the passive design, look at the LS50 Meta.

What to ask the seller

  • Is this the original passive LS50, not the Meta or a Wireless model?
  • Have either of the drivers ever been replaced or damaged?
  • How has the pair been used, and with which amplifier?
  • Is the original box included? It makes shipping a pair of speakers with exposed drivers much safer.

Which version is it?

ModelKey difference
LS50 (original)Passive Uni-Q standmount; the model this guide covers
LS50 MetaKEF's passive successor: 12th-generation Uni-Q with Metamaterial Absorption Technology (MAT), a revised port, Constrained Layer Damping in the cabinet and mounting inserts for KEF's S2 Floor Stand. KEF quotes the same 85 dB sensitivity and 79 Hz – 28 kHz response, with a 3.5 Ω minimum impedance and 40–100 W recommended amplifier power

Manuals

Links open external manual archives or the manufacturer's site. We don't host these files.

Sources