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LS 5/9

LS 5/9 LS 5/9 LS 5/9

Graham Audio recognised the qualities of the BBC's legendary LS5/9, but were troubled by the lack of spare parts and support for any loudspeakers still in use. This studio monitor loudspeaker is much sought after by conniseurs of high fidelity audio so after consultation with the BBC it was agreed to relaunch the original design under license.

BBC Research and Development staff from that era had long-since retired but from surviving documentation it was possible to discover the essence of the original LS5/9 as intended by R&D. The challenge was to recreate it in a form that has all of the essential qualities of the original design while using modern design and manufacturing techniques to avoid the longevity issues inherent in the original design.

Key to this project was involving Derek Hughes, son of Spencer and Dorothy Hughes, who of course formed Spendor when Spencer left his job in BBC R&D to build the BC-1. Of all the designers in the UK today Derek was best placed to understand and reinvent the original design.

The first objective was to re-create the bass/midrange drive unit. This was never going to be an easy task; nothing remained from the original production at Rogers. So it was going to have to be recreated from what data existed, using surviving examples as a starting point, and very early on, it was clear that Volt, who make some of the most respected drive units in the industry, had the necessary expertise. Working closely with Derek Hughes, a design was produced using the same translucent polypropylene diaphragm material as the original.

Things were more straight forward for the high frequency unit as Audax still produce the 34mm soft-dome tweeter that was originally used. The BBC modified this by adding a metal grille to protect the vulnerable diaphragm and this grille has been faithfully reproduced today.

The two drive units must be married together using a sophisticated crossover network. This circuit provides the basic function of routing the low frequency signals to the bass drive unit and sending the high frequencies to the tweeter. But additionally it is used to equalise the response of the drive units when mounted in the enclosure and it is responsible for the overall tonal balance that you hear when you audition the loudspeaker.

If the two drive units were identical to the models produced 30 years ago then the crossover wouldn't need any modification. However, the bass driver is a new improved design and the tweeter had changed slightly as well. Derek Hughes was able to take the new drive units and knit them together using a highly sophisticated crossover design that results in an overall response that is true to the original BBC prototypes.

Once the revised design had gained full BBC approval, full production at last could begin.

System : 2 Way Reflex

Cabinet : Thin wall construction (critically-damped) Birch plywood

Finish : Teak Veneer

Dimensions : 28cm x 27.5cm x 46cm

Weight : 14kg

Responses : 50Hz~16kHz +/-3dB

Nominal Impedance : 8 ohms

Sensitivity : 87dB SPL (2.83V, 1m)

Maximum Output : Over 100dB for a pair @ 2m

Bass/Midrange : 200mm Diaphnatone Polypropolene

Tweeter : Son Audax HD 13D34H

Crossover : FL 6/36, 24 Precision Elements

Recommended Amplifier Power : 50 to 200 watts unclipped programme

Hifi Review recension her