The loudspeaker I am building is a little unusual, mainly due to the driver selection. I am using two drivers; a Jordan JXr6HD for the midrange and treble and a Tangband W6-1139SI for the bass. I will write about the downwards facing bass driver in another entry, so let’s turn our attention to the Jordan driver. The designer, Ted Jordan, is a stone cold legend in the loudspeaker business, having engineered some of the best drivers ever, including the superlative Goodmans Axiom 80. (For all those Lowther fans out there, this driver will redefine what you think a full range driver can achieve! Listening to a well set up original pair driven by a fine, handmade Single Ended Triode 50 in a dark shop basement in Akihabara, Tokyo is one of my enduring audio memories….) Ted then founded Jordan-Watts with his now ex-wife Doreen (who then created Bandor), and finally started Jordan/ E J Jordan Designs in 1975. He has continually refined his driver design ideas for nearly sixty years now, only recently giving up day-to-day running of his company!
His primary concept is elimination of crossovers within the critical 1-3kHz region. Nearly all speakers have a passive crossover in this area. (A crossover is a combination of capacitors, inductors and resistors that ‘joins’ the bass/midrange units to the tweeter – removing the high frequencies from the midrange driver, and rolling off the bass from the tweeter – protecting it from large excursion. A crossover essentially manipulates the phasing between the drivers to create these necessary roll offs. The size of speaker’s cone determines the width of high frequencies that emit from the driver – for example, a 12” bass speaker can produce treble, but it will only be a tiny beam directly in front of the driver, whereas the bass will be heard all around the room. In order to get a regular dispersion of sound at all frequencies, there are usually a range of driver sizes in each loudspeaker.
Humans are particularly sensitivity of the 1-3kHz band, apparent in the Fletcher –Munson curves plotting human hearing, it is also the frequency band for speech intelligibility, and famously the frequency of babies crying; the most emotive sound for human beings. A crossover is the most difficult part of loudspeaker design; matching two dissimilar drivers in this critical range is particularly troubling. Proponents of full range speakers (a speaker that covers the entire listening range – commonly considered 20Hz-20kHz) cite the ‘togetherness’ and ‘holistic’ nature of the sound while having to ignore the severe colourations that such loudspeakers generally give. Personally, I am a proponent of the ‘augmented fullrange driver – which means that you design a loudspeaker around the all important tone of the midrange driver, and add bass and treble as needed. This creates a loudspeaker that subjectively sounds complete, allowing listeners to relax into the recording, rather than blowing them away with etched (read: distortion) detail.
The average fullrange driver is based on an 8” paper cone and an exotic magnet, costing many hundreds of dollars. The Jordan driver while certainly not cheap is the antithesis of these drivers. It is a mere 50mm across, and made from aluminium. It does not pretend to produce bass (the reason for the usual 8” cones), but it has an amazingly flat frequency response over 7 octaves, allowing it to create an integration of higher frequencies that the standard ‘fullrange’ speakers can only dream about. Due to the small size and low cone weight, the Jordan driver can respond to the smallest change in micro-dynamics within a complete sounding package.
In this loudspeaker I drive the Jordan across a wide range, relieving it of bass duties by placing the crossover far lower than usual, provisionally at 160Hz, an area where it is far harder for the ear to differentiate phasing problems. By avoiding an additional tweeter, phase performance is constant across the higher frequencies – this also means that the directivity is constant in all directions. This usually correlates with good stereo imaging, and in this case gives the speaker a very coherent sound. The dome at the centre of the cone acts as the tweeter, and the cone, while metal, flexes when in use. At higher frequencies, just the centre dome moves. As the frequency lowers more of the cone is coupled to the voice coil – moving more air. It is this frequency dependant decoupling of the cone that is Ted Jordan’s strongest technical breakthrough. It is extremely difficult to achieve this decoupling without severe colouration, and nasty cone breakup.
I use an active crossover, directly driving each driver with a dedicated amplifier, avoiding the inefficient passive crossovers of regular loudspeakers. The Jordan JXr6HD is an ideal driver; indeed, if one is after the highest fidelity in this configuration, the only loudspeaker driver in serious contention. It sounds fantastic.
