LEAK prepares tasty Sandwich
63 years after its debut, a landmark British loudspeaker design returns – LEAK’s new Sandwich
speakers evolve their forebears’ revolutionary driver cones with the latest techniques and materials
One of the biggest names of the mid-twentieth century hi-fi scene, LEAK returned in 2020 with its first new products since the 1970s. The arrival of the LEAK Stereo 130 integrated amplifier and LEAK CDT CD transport rapidly became one of the most talked-about hi-fi events of the year, followed at the end of 2022 by a second integrated amp, the Stereo 230 – all fusing the vintage appeal of classic LEAK design with state-of-the-art audio circuitry.
This February, LEAK’s line-up expands further with the addition of two loudspeaker models, once again inspired by LEAK’s illustrious past. The Sandwich 150 and Sandwich 250 take the blueprint established by the original, highly innovative LEAK Sandwich speaker, which debuted in 1961, and apply state-of the-art technologies and materials to deliver the ultimate incarnations of a bona fide British classic.2
The original LEAK Sandwich – a landmark loudspeaker design
In the 1950s, loudspeaker cones suffered from a common problem – a lack of stiffness. To elaborate: in order to obtain low distortion, the movement of a speaker cone should follow the waveform of the signals applied to its voice coil as accurately as possible, and its ability to do so depends upon the lightness and stiffness of the cone assembly.
Many conventional cone materials – paper, impregnated fabric, plastics, aluminium and so on – exhibit less than ideal stiffness. This results in significantly larger areas of the cone vibrating in motion, uncontrolled by the voice coil. These uncontrolled motions produce transient ‘hangover’, amplitude distortion (peaks and troughs in the frequency response) and intermodulation distortion. All of these are detrimental to sound quality.
Introduced in 1961, the original LEAK Sandwich speaker tackled this issue in an innovative way. Its mid/bass drive unit was the first to be constructed from a ‘sandwich’ of different materials: expanded polystyrene foam between two sheets of aluminium foil. This made it both very light and extremely stiff, enabling true pistonic motion and therefore more accurate sound.
A publicity photograph produced at the time showed LEAK’s founder, Harold Leak, standing on a Sandwich cone to demonstrate its exceptional rigidity. But the cone was not the Sandwich speaker’s only innovation – for example, the cabinet introduced bracing techniques subsequently adopted by many other manufacturers – and LEAK went on to produce other two-way and three-way iterations. through the 1960s and early/mid 1970s to great commercial and critical success.
Innovation evolved – LEAK’s new Sandwich cones
63 years on from the introduction of LEAK’s innovative Sandwich cone, loudspeaker designers continue to face the same challenge: how to make driver cones both very light and extremely stiff. Whilst many cone in a contemporaneous new materials and construction techniques have been applied to speaker cones since, the sonic shortcomings caused by less-than-optimal stiffness remain inherent in most direct radiator speaker systems that use conventional cones, irrespective of cost.
LEAK’s sandwich cone construction, then, is as relevant now as it was in the 1960s. The new Sandwich 150 and Sandwich 250 speakers update the concept using modern materials, design technologies and manufacturing techniques, incorporating a stiff aluminium skin for the outer surfaces (where the stresses are greatest) bonded to a core of aircraft-grade polymethacrylimide (PMI) structural foam.
This precision-engineered use of ideal materials in optimal proportion and position delivers immense rigidity, ensuring the cone reproduces the signal applied to the voice coil with great accuracy, free from mechanical breakup and its associated distortions. The result is a remarkably smooth frequency response, avoiding sharp peaks or troughs over a very broad frequency range.
Classic ingenuity re-engineered for the modern age
The original LEAK Sandwich speakers were designed when vinyl and valve amps ruled the high-fidelity sound waves. The requirements of modern-day speakers are different: today’s solid-state amps deliver far greater power, and modern speakers need power handling to match. The demands placed on frequency response by contemporary digital recordings and sources, especially at the extremes of bass and treble, are also quite different to the midrange-focused vinyl records and turntables of the 1960s.
The new LEAK Sandwich 150 and Sandwich 250 are ideally adapted to these requirements. Both are standmount speakers, the former a two-way design with a height of 41.5cm and the latter a much larger three-way model standing 65.5cm tall. They are perfectly suited to a wide range of amplifiers and deliver excellent frequency and transient response – exceptional for speakers of their class.
The Sandwich 150 incorporates a 30mm textile-dome tweeter and a mid/bass driver with a 170mm Aluminium-Foamcore Sandwich cone, while the Sandwich 250 combines the same tweeter with 280mm bass and 108mm midrange drivers, both of which feature Aluminium-Foamcore Sandwich cones. The treble unit includes a damped rear chamber to absorb the output from the back of the 30mm dome, isolating it from the rest of the loudspeaker and reducing its resonant frequency to below the crossover region. This allows bass, mid and high frequencies to be sewn seamlessly together with an added
LEAK has modernised the original Sandwich cone concept with a layer of aircraft-grade structural foam between aluminium ‘skins’4 dimension of detail and harmonics, via a crossover network developed using sophisticated computer analysis and hundreds of hours of listening tests.
The LEAK Sandwich 150 and Sandwich 250 are supplied in matched, mirror-imaged pairs, with the treble unit (and midrange unit, in the case of the 250) offset from centre. With one speaker optimised for the left channel and the other for the right, a precise stereo image within a deep, broad soundstage is assured when sited appropriately.
The cabinet walls are sandwiches too
The enclosure is a critical part of any loudspeaker system, just as vital as the quality of the drive units. LEAK’s new Sandwich speakers utilise advances in cabinet design and construction during the 60-plus years since the original design to further elevate the speakers’ performance to an entirely new level.
In these new speakers, the driver cones are not the only things that benefit from a sandwich construction. The cabinet walls are formed from an outer layer of MDF and an inner layer of high-density particle board – the different densities of these materials help to scatter panel resonances –enhanced by a filling of special glue that bonds the layers and provides resonance-damping properties.
This is combined with precisely positioned spot-bracing, together with a specific front-rear brace that echoes the design of the original.
The cabinets are dual ported at the rear, augmenting the speakers’ bass response. The ports’ precisely flared design combines with the cabinet to ensure efficient air pressure equalisation, delivering deep, well-defined bass without a hint of ‘chuffing’. Specially sourced damping material within the cabinet eliminates cavity resonance and further extends bass response by converting internal air pressure changes from adiabatic to isothermal.
Externally, the new speakers take distinctive design cues from their forebears. When viewed side by side, they are recognisably LEAK Sandwich speakers, but with enhanced build quality and finish in line with modern expectations. Their cabinets are finished in sumptuous walnut wood veneer, painstakingly applied by hand, complemented by aluminium driver trims and an aluminium insert around the edge
The new Sandwich 250 speaker is considerably taller and wider than the Sandwich 150, incorporating a larger bass driver and dedicated midrange of the front baffle. The protective grille further enhances the speakers’ classic appearance whilst maintaining the highest acoustic standards.
The Sandwich 150 speaker is of a size that will suit many speaker stands, but the dimensions of the Sandwich 250 make it trickier to find a stand to match. For this reason, LEAK has created a dedicated stand for the larger model, constructed from high-carbon steel with an acoustically damped, walnut-veneered base and stainless-steel spikes, plus spike seats for hard floors. The stand ensures the Sandwich 250 is elevated to the ideal height for seated listening and manages the unwanted effects of vibrations and sound reflections.
The LEAK Sandwich 150 and Sandwich 250 speakers are available from mid-February at RRPs of £999
and £1,999 per pair respectively. If a customer wishes to purchase the dedicated floor stands with the
Sandwich 250, the combined RRP is £2,299.
SPECIFICATIONS LEAK SANDWICH 150 LEAK SANDWICH 250
Configuration Two-way standmount Three-way standmount
Enclosure type Bass reflex (2x rear-firing ports) Bass reflex (2x rear-firing ports)
Treble driver 30mm coated textile dome 30mm coated textile dome
Midrange driver N/A 108mm Aluminium-Foamcore Sandwich cone
Bass driver 170mm Aluminium-Foamcore Sandwich cone 280mm Aluminium-Foamcore Sandwich cone
Sensitivity (2.83V @ 1m) 86.5dB 88.5dB
Recommended amp power 25-150W 25-250W
Nominal impedance 6Ω (8Ω compatible) 6Ω (8Ω compatible)
Bass extension (-6dB) 38Hz 32Hz
Crossover frequency 2.4kHz 470Hz; 3.1kHz
Cabinet volume 19.6L 2.7L; 45.5L
Dimensions (HxWxD) 415x250x290mm 655x370x300mm (stand 375x430x362mm)
The new Sandwich speakers are a perfect match for the aluminium front panels and walnut-veneered enclosures of LEAK’s Stereo 130 and 230 integrated amps6
Founded in 1934 by Harold Joseph Leak, pioneering British hi-fi manufacturer LEAK was a mid-twentieth century trailblazer in the field of high-performance audio equipment.
LEAK has been responsible for many technological firsts. For example, the Point One series of valve amplifiers (1945) were the first to reduce total harmonic distortion to 0.1 per cent, and the groundbreaking Trough-Line FM radio tuner (1955) is still considered one of the finest FM tuners ever made. LEAK’s Sandwich speakers (1961) heralded true-piston cone action by sandwiching polystyrene foam between outer skins of stiff aluminium foil. And the Stereo 30 all-transistor amplifier (1963)
spearheaded the use of transformerless transistor output stages over then-standard transformer-coupled designs, thus paving the way for future solid-state amps.
In 2020, following a 40-year hiatus, LEAK – now part of the International Audio Group alongside Audiolab, Castle Acoustics,
Luxman, Mission, Quad and Wharfedale – launched two new audio components: the Stereo 130 integrated amplifier and CDT CD transport, fusing retro design, classic analogue engineering, and the latest digital technologies. In 2022, these components were joined by the Stereo 230 integrated amplifier, followed in 2024 by the remarkable rebirth of LEAK Sandwich loudspeakers.