You may be looking at the picture and thinking “Ho hum, just another mid-sized two-and-a-half-way floorstander, with doped paper cones and a soft dome tweeter”. And you’d be wrong.
Yes, it is a mid sized, two-and-a-half-way floorstander and, yes, it has doped paper cones and a soft dome tweeter, but no, the Russell K Red 150 is anything but ‘just another floorstander.’
Like its standmount siblings, the Red 150’s cabinet is undamped. Its designer, Russell Kauffman, argues that damping materials store energy and then release it, out of time from the music, leading to blurring and smearing of the sound. You can’t realistically prevent a cabinet from resonating, so Russell K makes an undamped cabinet to resonate in sympathy with the signal and, crucially, still in time with the signal, and then control that resonance by internal bracing as necessary.
That bracing also serves to divide the cabinet internally into cavities optimised for the output of each driver. The bracing comprises panels mounted horizontally between each driver, and additional panels in the bass cavity, each with holes of a specific size and number, different for each panel. Their function is to alter the mechanical impedance within the cabinet, so that only sounds within a certain frequency range can pass freely through the panel. In effect, the driver ‘sees’ a sealed box at mid range frequencies, a mechanically damped box at mid bass, and a reflex box at the lower bass. This gives many of the benefits of a sealed box, while allowing the bass extension and efficiency of a ported design.
Two ports vent from the bottom of the cabinet but are of different lengths, and there is also an internal port between two of the cavities in the bass section, responsible for the main tuning of both 165mm drivers to a very low 20Hz, while the asymmetric lengths of the two external ports affect the phase of the speaker system. The result is a bass output that is deeper, but also tighter and more tuneful, than is the norm for speakers of this size and, coupled with the other design features, leads to a high degree of phase coherence across the audio band.
Regarding the drivers themselves, these were chosen after extensive tests just listening to the raw output of the driver when fed a music signal directly. The bass/mid units are treated paper cones, but the cone profile has been carefully selected to control breakup modes by making the radiating area progressively smaller with increasing frequency. The crossover is a modified second-order for the bass/mid to treble and has been designed to ensure minimum phase distortion through the crossover region, while the sub bass unit is first order from a very low 80Hz roll off and it, again, is designed to minimize phase distortion. Only one component is in the crossover circuit between the amplifier and each of the three drive units, all of which are working in positive phase.