JBL 250Ti Speaker System Review

The flagship model of JBL’s home speaker line is the 250Ti, a large four-way system that is described as a “no compromise” design, a characterization with which we would agree. The “Ti” in the name refers to the ribbed titanium diaphragm of the 1-inch dome tweeter, which is designed for an extended, smooth high-frequency response (up to 27,000 Hz on axis). The 250Ti supersedes the JBL L250, differing from it principally in the tweeter and upper-midrange drivers. The new drivers are also used in several other, smaller JBL systems in the Ti series.

The 250Ti has a unique and instantly identifiable shape: an asymmetrical, truncated, rectangular pyramid with a slightly backward-sloping front panel. The shape is said to offer the optimum baffle width for each driver and thus to minimize diffraction effects and improve imaging. The speakers are sold in mirror-image pairs, to be used with the vertical sides toward each other and the sloping ones on the outside. The speakers should be free-standing, away from walls.

The 250Ti’s four drivers are vertically aligned, from the 14-inch low-frequency driver in its own subenclosure at the bottom of the cabinet to the Ti tweeter at the top. The low-frequency driver crosses over to an 8-inch lower-midrange driver at 400 Hz. The next crossover, at 1,400 Hz, is to a 5-inch midrange cone. The final crossover, to the tweeter, takes place at 5,200 Hz. Each driver is acoustically isolated from the others (only the woofer system is ported, with the opening on the rear of the cabinet).

The woofer and lower-midrange drivers appear to be conventional cone radiators, though with very heavy magnetic systems (about 18-1/2 and 6 pounds, respectively) and large-diameter voice coils edge-wound with flat, copper wire. Their cone material is described by JBL as “Aquaplas,” apparently a laminate of paper and plastic materials that feels unusually stiff and solid to the touch. The upper-midrange cone is polypropylene with a gray filler.

Clearly, the titanium tweeter dome is the most striking feature of the speaker’s design. Titanium is extremely strong and light, but it is not easily fabricated by conventional techniques. JBL makes the domes, complete with stiffening ribs and a specially formed integral titanium surround, by swirling compressed nitrogen gas against a 25-micron (0.001-inch) film of titanium. The result is a remarkably light yet strong high-frequency dome radiator, which is driven by an aluminum voice coil in the field of a 2-pound magnetic structure.

The outputs of the two midrange drivers can be individually reduced in two 1-dB steps, and the tweeter level can be reduced by 1, 2.5, or 4 dB. However, the adjustment process involves loosening screws and moving shorting links, a cumbersome procedure at best. We suspect that most people will settle for the factory settings (the tweeter at — 1 dB, the other two at 0 dB). The input terminals are heavy-duty binding posts that are compatible with special “audiophile” cables and connectors.

The visual appearance of the JBL 250Ti is as striking as its special design features—probably even more striking to most people. It is finished in Burmese teak, with rounded edges, that is hand rubbed and oiled on all visible surfaces (the rear panel is in flat black). A dark-brown cloth grille covers all the drivers except the tweeter. Six sturdy plastic snaps hold the grille about 3/4 inch away from the front panel to minimize diffraction effects. If the cones are not subject to damage from children or pets, the speakers may be operated with their grilles removed, exposing the fully finished front of the cabinet.

The JBL 250Ti is 52 inches high, 22-1/2 inches wide, and 14-1/4 inches deep. Its weight is specified as 150 pounds. Although we did not weigh these speakers we can testify that one of them is beyond the capability of a single normal human being to lift (the shipping box resembles a refrigerator carton!). Price: $3,000 per pair.

Lab Tests

All measurements and listening tests were done using the factory settings of the level-balance adjustments. Unlike most speakers we have tested, the JBL 250Ti’s produced very similar frequency-response curves with the two rather different measurement techniques we employ. Our on-axis quasi-anechoic measurements using the IQS FFT signal-analysis system showed a mere ±2-dB response variation from 1,000 to 20,000 Hz. The lower-frequency response remained strong (in fact, it was as much as 2 or 3 dB greater than the output in the range of 1,000 to 1,500 Hz) as far down as the approximate 250-Hz lower limit of this measurement. Further-more, the output remained quite uniform above the audible range, up to at least 27,000 Hz, which is the effective upper limit of our FFT measurement system.

Our other response measurement, made in a live room at distances of 12 to 15 feet from the speakers, uses a swept (warble-tone) sine-wave signal. Normally this measurement is of little value below a few hundred hertz, where room resonances produce large irregularities in the curve. Therefore, we measure the low frequencies separately with the microphone placed close to the woofer cone or port and “splice” it to the room response to form a single composite curve that is more or less representative of what the speaker is doing in our room—but is not necessarily reproducible in another environment.

To our surprise, even the bass portion of the room curve was very much like the close-miked measurement, and the composite curve was strikingly similar to the FFT plot. Even including a couple of midrange “jogs,” which could have been room effects, the composite response was within ± 5 dB from 20 to 20,000 Hz, and it obviously extended to much higher frequencies, although our test equipment is limited to that frequency range. In all, the JBL 250Ti certainly had one of the widest overall speaker responses we have ever measured—approximately 11-1/2 octaves.

The 250Ti’s polar dispersion (horizontally) was good but not as noteworthy as its overall frequency range. Measurements made 45 degrees off the speaker’s axis revealed high-frequency “beaming” beginning at about 9,000 Hz as well as in the 2,000- to 5,000-Hz range (that covered by the 5-inch cone driver). The speakers’ phase linearity was good. Over most of the audio range, the impedance was between 6 and 12 ohms, indicating that the 250Ti should present a comfortable load to any amplifier.

We measured bass distortion with a 3.1-volt input (equivalent to a 90-dB midrange sound-pressure level). After combining the port and cone contributions, the results were excellent: the distortion was well under 1 percent from 100 Hz down to nearly 40 Hz, and there was a strong and usable fundamental output as low as 10 Hz! In short-term power-handling tests with tone-burst signals, the amplifier output clipped before the speakers reached their limit.

Comments

Our measurements of the JBL 250Ti clearly describe an exceptional loudspeaker, and that is pretty much the way it sounded to us. The sound stage was open, both in width and depth, giving little impression of coming from a pair of huge speakers that dominated our moderate-sized (15- by 20-foot) listening room. The spectral balance on some program material seemed to favor the mid-bass, with a tendency toward warmth that occasionally overshadowed the speakers’ extremely smooth and extended high-frequency response. Apparently our microphone heard much the same things as our ears, since the slightly elevated output below 200 Hz could be seen in all our measurements. The effect was not enough, however, to make the speaker sound unbalanced or unnaturally heavy. Rather, our overall impression was of a very smooth response.

JBL stresses the dynamic capability of the 250Ti (its lack of compression at high peak levels), and we put this to the test with some particularly potent LP’s as well as CD’s. The utter ease of the speakers’ output led us to increase the playback level beyond what would have been prudent (or even safe) with most speakers, but the 250Ti’s took everything our amplifier could give them. This amounted to average levels in the 30- to 50-watt range, frequent peaks to 350 watts, and occasional peaks of more than 600 watts. (Not wishing to imperil the speakers, or our ears, we refrained from lighting all the amplifier’s level indicators for extended periods.)

The impact of the acoustic output of the speakers, especially with percussion and organ recordings, was tremendous. We don’t normally listen at house-shaking levels, but the sound from the 250Ti speakers was so clean even at such levels that we felt no discomfort from it. There can be no doubt of the great dynamic capabilities of these speakers, or of their ability to handle the full output of the most powerful amplifiers likely to be used in a home environment.

What about more usual listening conditions? The 250Ti is relatively efficient and can operate happily with the output from any good 30-to 50-watt amplifier—or even less, although we doubt that many people who buy these speakers will use a low-powered amp. They sound as good at background levels as when attempting to re-create the sound of an orchestral concert. On the appearance side, perhaps not everyone will find the unusual shape (or massiveness) of the 250Ti to his liking, but no one will deny that the quality of the workmanship and finishing of the wooden enclosure is unsurpassed. And, all things considered, for this level of performance and craftsmanship, the 250Ti is not even a particularly expensive system.

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