Thiel CS1.2 loudspeaker Measurements
Fig.1 shows the plot of impedance with frequency for the Thiel CS1.2. It agrees with the appropriate specified impedance in the review heading, but it is noteworthy how little change there is for each speaker. Obvious features can be distinguished, such as the port tuning, but I would conjecture that Jim Thiel has used some form of conjugate load system in his crossover designs to give such a flat curve with frequency. (This is where elements are added to the crossover to compensate for phase and impedance changes to result in a simple resistive load.) I would suggest, therefore, that the CS1.2 should be easy to drive, even given its 4-ohm rating.
Fig.1 Thiel CS1.2, electrical impedance. (2 ohms/vertical div.)
Moving on to the in-room, spatially averaged response, fig.2 shows that obtained for the pair of CS1.2s with their grilles on. Disregarding the peak at 63Hz, whch is a room mode that was not minimized by the spatial averaging, the steep roll-off and relatively limited extension—the nearfield –6dB point lay at 50Hz, not counting the contribution from the port—are typical of the enclosure size, but from then on up the in-room response is one of the flattest I have measured. The broad depression in the lower midrange is common to all speakers measured in my room, though it is normally a little deeper, while the moderate rise in the presence region I would suggest is a function of the wide dispersion of the tweeter in its first two octaves. There is less extra energy than usual in the room here, however, suggesting that the grille sculpting used by Thiel does offer a degree of diffraction control.
Fig.2 Thiel CS1.2, spatially averaged, 1/3-octave response in JA's listening room.
Looking at the off-axis performance in detail reinforces this idea, as the high frequencies gently roll off to the sides without strong discontinuities. Vertically, with the wide frequency overlap between the drivers given by 6dB/octave crossover slopes, the situation is more complicated. Sit too high (45", say) and the low treble depresses; sit too low and the same region becomes too high in level. In my room, sitting with my ears around 33" off the ground gave the best balance.—John Atkinson