Loudspeakers

I discuss the perils of measuring a long line driver in our boxout [see Holding the line]. The mid/presence droop seen in Graph 1, below, reduces to –6dB at 2m [dashed trace, Graph 1] and integrates out still further at greater (listening) distance. Response errors amount to ±4.8dB and ±9.1dB, respectively, with pair matching a poor 4.6dB because non-linearities in the planar driver were more exaggerated in one of our pair [red trace] than the other [black]. In practice, even with T+A’s famed production tolerances, the surface resonances that occur on all film-style (Kapton) drivers are tough to ‘match’ between one driver assembly and the next.

The mid/treble crossover is specified at 1.8kHz, but the ±mid/treble controls pivot at 2.8kHz, with the +ve treble mode lifting the response by +1.8dB and the –ve reducing it by –1.5dB. Again, the mid control acts below 2.8kHz, boosting output by +1.5dB in the +ve position and suppressing it by –1.8dB in –ve position [green/orange traces]. Sensitivity is also influenced, the default 86.6dB/1kHz figure increasing to 87.8dB (+ve setting) or falling to 84.8dB (–ve setting). The ±bass option provides a ±1.1dB cut and boost over a narrower bandwidth, the opposed 220mm woofers peaking at 94Hz, but even with the output of the port at 26Hz, bass extension is still a modest 47Hz (–6dB re. 200Hz).

Swings in impedance/phase angle are minimised by T+A’s driver and crossover design but the minimum 2.8ohm/113Hz is still low, as is the average impedance of 5.1ohm (20Hz-20kHz). The minimum EPDR arrives at higher frequencies (1.1ohm/20kHz) where signal and current demands are likely reduced, but 2.0ohm/25Hz and 1.9ohm/140Hz will still test your amplifier. PM