Pioneer Elite TZ-9 loudspeaker
The TZ-9 is the top of Pioneer's new line, and costs a cool $4000/pair, placing it firmly in the high-end category. But for that outlay, the TZ-9 owner acquires a largish and quite handsome speaker, finished in a rather orange-colored oak veneer and standing some 4' high. Both tweeter and midrange units feature domes fabricated from an amorphous form of carbon termed by Pioneer "Ceramic Graphite," which is said to have 10 times the bending stiffness and two times the internal loss or self-damping of an equivalent titanium dome. The practical result should be accurate pistonic motion in each unit's passband, with a better-damped HF resonance than a metal dome. In practice, these Ceramic Graphite diaphragms can be quite brittle. Despite the presence of protective wire grilles over the mid- and high-frequency units, the first pair of TZ-9s we received had had the midrange domes shattered, due to inadequate early packaging.
The TZ-9 features the tweeter placed between the mid and LF units on the front baffle, presumably to aim the main lobe in the vertical plane toward the listening position. The tweeter dome is recessed within a shallow straight horn flare, with a plastic phase plate around its rim, and both the mid- and HF units have a thin felt material applied to the baffle in their immediate vicinity to lower the level of diffraction problems.
In addition to the frontal woofer, there is a second woofer mounted at the same height from the floor on the rear panel. The woofers are reflex-loaded with two 3.5"-diameter by 7.5"-deep ports on the front baffle, and both appear to be relatively old-fashioned 9.5" paper-cone units, with pleated surrounds. They are connected with the same polarity, thus providing a fundamentally omnidirectional radiation pattern in the bass, with reduced distortion and increased power handling compared with a single drive-unit.
There is more to the use of two woofers than that, however, as the woofer magnets are braced with an internal bar. The reaction forces from cone motion on the drivers' basket/magnet structures will therefore be in opposite directions and will cancel, reducing the transference of the reaction forces to the enclosure walls, where they otherwise would have excited panel resonances. In a paper presented to the 85th Audio Engineering Society Convention last November (footnote 1), two Pioneer engineers showed how this significantly reduced the measured amplitude of panel vibrations, lowering the amount of secondary, "parasitic" sound radiation from the enclosure by between 10 and 15dB at some frequencies. I must point out, however, that variations on this idea have appeared before in commercial loudspeaker designs: both the KEF R107 and R104/2 use two (internally mounted) woofers with their chassis connected by a tie-rod for exactly the same reason.
The hardwired crossover is fastened to the inside surface of a removable rear panel, sealed with a thin rubber gasket, and is reasonably complex. A single series coil rolls off the highs from the front-woofer signal, giving a first-order 6dB/octave low-pass slope, while the rear woofer is fed by a second-order network consisting of a series coil and a shunt non-polarized electrolytic capacitor. This sharper roll-out of the rear woofer is, I assume, to minimize interference effects in the midrange that would otherwise occur with two drive-units carrying the same signal at different distances from the listener. It does mean, however, that the cancellation of woofer reaction forces will only be effective to an octave or so above the rear woofer's upper roll-off (which I measured as being 6dB at approximately 240Hz).
The signal to the midrange dome, connected with the same polarity as the woofers, is conditioned by what appears to be some kind of hybrid second-order band-pass network, with a non-polarized electrolytic cap, bypassed with two plastic-film caps, in series with an inductor, with then a capacitor and another inductor in parallel to ground. The nominal bandpass is 600Hz4kHz, and modeling the network appears to give initial 18dB/octave high- and low-pass electrical slopes, reducing to 12dB/octave about 20dB down. The tweeter is fed by a second-order high-pass network and is connected with opposite polarity to the other drivers. Both midrange unit and tweeter are padded down resistively to match their sensitivity to that of the woofers.
Electrical connection is via two sets of recessed five-way binding posts at the bottom of the cabinet's rear panel, and while as supplied these are connected in parallel by copper jumper bars, the bars can be removed to allow bi-wiring or bi-amping.
Internally, the cabinet sides are lined with a ¼" layer of felt, but apart from the tie-rod joining the two woofer chassis and some crossbars on the rear panel and base, there is no other bracing. Surprisingly, there is no reinforcement of the side-walls, the woofer reaction-canceling brace supposedly assumed to prevent any excitation of these large unsupported panels. The front baffle, however, is complex, with a second layer of 1"-thick particle board supporting the tweeter and midrange unit. The tweeter, in fact, is almost completely sealed within the baffle. The vertical edges of the baffle are radiused to avoid the radiation in the treble experiencing a sharp discontinuity, which would otherwise lead to diffraction problems.
The TZ-9s were positioned for the best sound, this being some 3' from the rear wall (which is faced with books and LPs) and 5.5' from the side walls, also faced with bookshelves. Small cones were used to couple the base of the speakers to the tile-on-concrete floor beneath the rug. Initially, the speakers were toed-in toward the listening seat. I was somewhat bothered by an excess of energy in the brightness region (58kHz), however, and ended up firing the TZ-9s straight ahead. All the critical auditioning was done with the speakers set up in this manner.
Footnote 1: "A new loudspeaker system with reduced radiation of sound pressure from parasitic enclosure vibration," Hideto Fukura and Takashi Fukura, AES Preprint 2739 (C-12). Available from www.aes.org.