ADS L780 Series 2 Speaker System Review

The ADS L780 Series 2 is the company’s smallest and least expensive three-way speaker system. Its single 8.3-inch acoustic-suspension woofer is nearly identical to that of the larger ADS L1290 system, differing only in its voice-coil impedance (nominally 8 ohms). The first crossover, at 650 Hz, is to a 1.5-inch soft-dome midrange driver, and the second, at 5,000 Hz, is to a 0.75-inch soft-dome tweeter that is identical to the tweeter of the L1290.

Both dome drivers provide an exceptionally flat and smooth frequency response, and their voice coils are damped and cooled by a proprietary ADS magnetic fluid. The second-order (12-dB-per-octave) crossovers give the L780 system a smooth frequency response and good phase behavior. The system’s rated sensitivity is 88 dB sound-pressure level (SPL) measured at 1 meter with 2.83 volts (1 watt) of pink noise from 20 to 20.000 Hz. Its frequency response is specified as ranging from 42 to 27.000 Hz ± 3 dB.

The L780 Series 2 has several improvements in detail over the original version of the L780. The new midrange driver has a higher power-handling ability, allowing the earlier model’s protective fuse to be eliminated. The tweeter’s fuse has been replaced by a solid-state protector, essentially a bistable resistor whose temperature closely tracks that of the tweeter’s voice coil. When excessive power is applied, the protector’s resistance (in series with the voice coil) suddenly increases about a thousand times, protecting the delicate voice coil from burnout. A few seconds after the power drops back to a safe level, the resistance returns to its normal low value and normal system operation is restored. Other minor changes in the Series 2 speakers include new binding-post connectors able to accommodate larger-diameter wires and the elimination of a tweeter-level switch.

The ADS L780 Series 2 is housed in an attractive wooden cabinet with beveled side edges and a black perforated-metal grille. It is available finished in walnut veneer or a black laminate. The speaker’s dimensions are about 21 inches high, 12-1/4 inches wide, and 11-1/2 inches deep, and it weighs slightly less than 30 pounds. Optional floor stands are available, or the speakers can be installed on shelves either vertically or horizontally. Price: $680 per pair in walnut, $650 per pair in black; stands, $60 per pair.

Lab Tests

The minimum impedance of the ADS L780 Series 2 speakers was 4.1 ohms at 110 Hz, with maximum readings of 12 ohms at 53 Hz and 21 ohms at 780 Hz. Although the average impedance throughout the audio frequency range was close to 8 ohms, it might be advisable to consider this a 4-ohm system if more than one pair of speakers are to be driven from a single amplifier. The system’s sensitivity was slightly less than the rated 88 dB SPL, measuring 85 dB at 1 meter when it was driven by 2.83 volts at 1,000 Hz.

The L780 Series 2’s room-response curves were exceptionally flat and smooth. Our close-miked woofer response curves—which exactly matched the supplied curves ADS ran on our test samples— spliced easily to the room curve, resulting in one of the most nearly ideal speaker response curves we have yet seen. The 3-dB overall variation from 250 to 20,000 Hz was a close match for an ADS-run response measurement made over the same frequency range, but under very different conditions. When we spliced our close-miked woofer curve to the room curve, the composite revealed a slight bass emphasis, but bass response is very much dependent on the actual room-speaker relationship and a response curve serves as merely a rough guide to a speaker’s actual bass performance. The very flat composite frequency response of +6,-2 dB from 40 to 20,000 Hz speaks eloquently of the capabilities of this compact speaker system.

To measure bass distortion, we drove the L780 Series 2 with 5 volts (equivalent to a 90-dB midrange SPL). The distortion was just over 1 percent from 100 to 60 Hz, increasing smoothly to 5 percent at 41 Hz and 10 percent at 28 Hz. The manufacturer recommends driving the speaker with an amplifier rated between 15 and 125 watts per channel. The conservatism of the maximum-power rating was demonstrated by our pulse-power tests, in which we were able to drive the speaker into nonlinear operation only at 100 Hz, where the woofer cone reached the end of its suspension travel range with an input of 685 watts into the speaker’s 4.1-ohm impedance. At 1,000 and 10,000 Hz, our amplifier reached its clipping point before the speaker did, with power outputs of 212 watts into 18 ohms and 710 watts into 5.1 ohms, respectively.

Our quasi-anechoic FFT measurements amply confirmed the unusually flat response of the ADS L780 Series 2. The speaker’s axial response varied ±1.5 dB from 180 to 20,000 Hz. Its output had dropped only 3 dB at 27,000 Hz, meeting the manufacturer’s response specification. Horizontal dispersion was good. Response curves measured on-axis and 45 degrees off-axis diverged by no more than 6 dB up to about 12,000 Hz, although the difference increased rapidly at higher frequencies. The speaker’s phase response was as noteworthy as its response flatness, as shown by its overall group-delay variation of less than 0.2 millisecond between 1,500 and 21,000 Hz.

Comments

It would be surprising to find flaws in the sound of a speaker whose measurements were as outstanding as those of the ADS L780 Series 2, and we received no such unwelcome surprises. The speakers sounded as seamless and effortless as their nearly ideal measured performance would imply. In fact, our only surprise (and it was not entirely unexpected) was that this moderate-sized “bookshelf’ speaker sounded very much like some of the better floor-standing units we have tested.

In view of the ADS speaker’s extended high-frequency response (well beyond the upper limits of most speakers we have tested), it might have been expected to have a tendency toward brightness in its sound. On the contrary, its sound quality was exceptionally neutral, tending (if at all) toward the side of softness or warmth. Whatever music we played through these speakers, the highs never had a piercing or shrill character. This result is not surprising when you realize that shrillness is almost always caused by a peaked or irregular high-end response, the antithesis of what we measured from the L780 Series 2. The bass and lower midrange sounded rich and powerful, with the character of a much larger speaker.

We made all our measurements and did our listening to the ADS L780 Series 2 with the speakers placed on stands about 26 inches from the floor, 30 inches from the back wall, and 5 feet from the side walls. Most speakers of this size perform at their best in such a freestanding position, but we suspect that the L780 Series 2 would also acquit itself nicely placed against a wall. Although the speaker is fairly large for bookshelf mounting, its moderate weight should not require specially reinforced supports.

The only respect in which this speaker did not fully measure up to its specifications was in its sensitivity, for which our measurement conditions differed slightly from those used by ADS. Nevertheless, the speaker can easily be driven by the smallest amplifier worthy of use in a hi-fi system, as well as by the largest. We never succeeded in tripping its tweeter-protection circuit even while driving it at peak levels of hundreds of watts (nor was it damaged in any way by this treatment). The ADS L780 Series 2 impresses us as a big speaker in a small box, capable of delivering a quality—and quantity—of sound out of all proportion to its size and cost.

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