Janszen Z-600, Z-900, & Z-960 loudspeakers

The Z-600 is the latest of the "console" (as opposed to "bookshelf") systems made by Neshaminy Corp., and using Janszen electrostatic tweeters (footnote 1) and a Neshaminy-designed 11" woofer. The nominal crossover frequency is 1500Hz, with a broad overlap between the woofer's top and the low end of the paralleled tweeters. Tweeter level is not adjustable (footnote 2).

Like all electrostatics, the Z-600 requires an external source of power (consumption: 2 watts), and the built-in power supply requires a 115V AC supply. The polarizing supply is designed for continuous duty, and the manufacturer recommends that it simply be plugged into any nearby outlet and left on.

The Z-600's predecessor, the Z-300, was our standard loudspeaker ever since 1959, not because it was necessarily the "Best" loudspeaker we had found, but because it had more of the attributes that we like than did any other available system.

A single Z-300 was hard to find fault with; it was very transparent (a quality that gives the impression of listening through the system instead of to it), and in most listening rooms, its balance, frequency range, detail and naturalness were almost beyond criticism. Its perspective was almost totally neutral, being neither distant nor close-sounding, but rather giving the impression that the instruments were about the same distance behind the grille as they were from the recording microphones.

The Z-300 did have one flaw, though. Its flat tweeter elements, arranged in a cross-eyed configuration, radiated the extreme highs in two fairly narrow crossed beams, and if you happened to sit in the way of one of the beams, you heard a perceptibly rising treble response. A single Z-300 could be "aimed" so that the beams wouldn't reach any of the listening areas, but when a pair of them were combined, for stereo, the beaming often caused some problems.

Pairing them increased their bass output so that, in most listening rooms, it was necessary to turn up the tweeters to maintain correct balance. But since the upper range of the woofers remained essentially unchanged, the resulting response was rather like that of a loudness control; bass and treble were about equal, but the range in between was depressed, making the speakers sound rather tipped up at the top and deficient in middle range. In addition, the treble beaming made it difficult to get good stereo distribution between the speakers, particularly when the listener had to sit closer than about 15 feet from the speakers.

We were aware of these shortcomings in the Z-300s, but stuck with them because, once we had lived with the transparency and detail of good electrostatics for a while, they spoiled us for systems with less of it. Now the Z-300 has finally been displaced.

The Z-600
Sweeping an oscillator through its range, we found the new Z-600 system to be totally devoid of any audible buzzes, rattles or response peaks throughout its entire span of about 35Hz to beyond 14kHz (which is where our ears fail us). A condenser microphone verified that the high-end response was still going strong at 20kHz, where the microphone takes a nosedive, so we have no way of knowing just how far out the upper range does extend. Below about 1kHz, a single Z-600 showed a very gradual rolloff of output until around 500Hz (amounting to, maybe, 2dB total), and then the response remained almost perfectly flat to around 40Hz. It was putting out an audible but weak signal at 35Hz, and was pretty much dead by 30Hz. There was no trace of distortion or fluttering at very low frequencies.

As might be expected, pairing two Z-600s brought up the entire low-end range, producing an overall response that was subjectively almost perfectly flat. A stereo pair of Z-600s has much the same overall sound quality as a single Z-300, minus the conspicuous treble beams. The middles are up and the low end and extreme high end are down a bit, and the result is almost perfect balance and naturalness in most listening rooms, with a very slight tendency toward "forwardness."

The only respect in which we would judge a pair of Z-600s to be inferior to the Z-300 is in their bass performance which, although as deep and as full as that of the paired Z-300s, is not quite as tightly controlled or as well defined.

Singly, the old Z-300 sounded better to us than a single Z-600, despite the former's high-end beams. The same middle-range response that made a pair of Z-600s sound very nearly flat made one used alone sound quite forward.

The Z-600's overall efficiency is quite low, in comparison with the larger horn-loaded systems, but is comparable to that of most good bookshelf systems (like the AR-2). Estimated efficiency is a bit less than 2%. It's important to note, though, that whereas the high efficiency of most horn systems exists only through the middle and upper-frequency ranges, that of most low-efficiency systems is fairly constant down to around 40 or 50Hz. A 25Wpc amplifier with good power response will drive a pair of Z-600s to fairly high volume without overloading, but for very high levels, 60 or more honest watts per channel will be needed. The system is rated at 100 watts maximum music power. Continuous power (for test purposes) should not exceed 10 watts at frequencies above 800Hz. Prolonged high-level continuous-power input may damage the crossover network.

An additional note about amplifiers: We have not tested every amplifier on the market (obviously), but it has been our experience that the only units which are really well suited for use with electrostatics are ones that were designed specifically to meet the stability and distorttion requirements of these speakers. Dynakits and Marantz units are among these, but we do not know of any others that meet the necessary standards. (We've been very happy with a Stereo 70.) The current crop of transistor amplifiers (except for the top-priced ones) are not eminently suitable; their distortion is excessive at low output power levels.

Summing up the Z-600
We have lived with a pair of Z-600s for several months now, and our initial enthusiasm for them has not dwindled in the slightest. They provide the clearest, most musically natural "window" to the sound of any generally-available under-$1000 system we have ever heard, and in our opinion, the resulting gain in sheer enjoyment of music more than compensates for their less-than-perfect stereo imaging. If your listening room has rather bright acoustics, or if you are particularly critical of instrumental location (rather than of stereo breadth and depth), then Z-600's are probably not for you. But if in doubt, we would strongly suggest trying a pair of them anyway, and giving them a decent chance (by suspecting the amplifier or pickup if they sound really bad), because they are inherently capable of a level of quality that is going to be very hard to beat.

Footnote 1: The electrostatic drive-unit used in the Neshaminy loudspeakers was developed by Arthur A. Janszen. Janszen presented a paper, "An Electrostatic Loudspeaker Development," at the Sixth Annual Convention of the Audio Engineering Society October 1954, which was subsequently published in the April 1955 issue of the JAES. In 1959, Arthur Janszen accepted an offer from Frank Wetherill of the Neshaminy Electronic Corp. to license the rights to manufacture and use the tweeter in their own loudspeaker designs.—Ed.

Footnote 2: A level control can be added in the form of a 5000-ohm 2-watt linear potentiometer in series with the AC supply to the tweeter. The control is "hot," so insulate all connections carefully.

Neshaminy Electronic Corp. (1969)
JansZen Audio( 2022)
480 Trade Road
Columbus, OH 43204
(614) 448-1811

RichT's picture

I can’t judge the sound quality of course, but the build quality is incredibly primitive. How far we’ve come in only 55 years!

Anton's picture

Adjusted for inflation, the Z-600, which was 200 bucks in 1966, would be about 1600 bucks a pair now. You're dead right, that build quality nowadays would only be tolerated if the speakers cost much more than that. ;-D

You made me think of the recent review of the Mayfly Audio speaker at 5800 per pair, with stands. They seem kinda home brewed in their physiognomy, as well.

Then, you made me think of the look of the original Advents and the early AR speakers, especially the AR3. Speaker makers in those days really seemed to have a thing for hot glue!

We certainly have come a long way!

scottsol's picture

I believe the quoted price is for a single speaker. The pair price adjusted for inflation would be ~$3700.

MattJ's picture

I love reading the vintage reviews.