ADS L620 loudspeakers

The Drivers

ADS manufactures all of the drivers used in its speakers. This fact alone distinguishes ADS from a large majority of speaker system manufacturers, who must purchase most or all of their drivers from bulk suppliers. ADS thus maintains total control over system matching quality and engineering improvements. Proper design and manufacture of the drivers obviate the need for unnecessarily complex, efficiency-robbing crossover networks typical of many "sophisticated" speaker systems which represent nothing more than valiant attemps to match inherently incompatible drivers. Each ADS driver, furthermore, embodies the most advanced design, materials and manufacturing techniques in the industry.

The Tweter

The L620 (L520 and L420) have in common ADS 1-inch acoustic suspension soft-dome tweeter, which accounts for their ultra-clean, "airy" high-frequency response. This unit's unusually small diameter and precise shape results in high-frequency extension and wide, uniform dispersion unmatched by other designs. The dome is constructed of a super-light fabric-like material coated with a proprietary "sticky" damping compound. It has none of the "ringing" and other resonance-related distortions common to other materials. Soft to the touch, the tweter nonetheless functions as a perfectly stiff piston through its operating range, thus ensuring low distortion and coloration.

The tweeter's voice coil features a sophisticated and unusual single-layer winding. (Most similar tweeters must use two layers of windings in their voice coils to achieve the required number of turns.) Although difficult to execute, this technique yields an incredibly high force-to-mass ratio through lowered moving mass and increased magnetic field intensity. Further aided by a powerful Barium Ferrite magnet, the ADS 1-inch tweeter delivers superb high-frequency extension, excellent transient response, extremely low distortion and high efficiency.

The tweeter also features an all-metal voice coil structure which is unsurpassed in dissipating heat. Its narrow-gap magnet design, more-over, promotes efficient thermal transfer for effective cooling of the voice coil during high-current drive. This "air-cooled" voice coil structure  can only be achieved through high-precision assembly, and it is more efficient than "liquid-cooled", ferrofluid-filled systems. It should not be surprising, therefore, that very few tweeters, including those with voice coils of larger diameter, can handle as much power as the ADS 1-inch soft-dome tweeter.

All ADS soft-dome tweeters, furthermore, feature airtight cavities behind the diaphragm. In effect an independent miniature air suspension system, the tweeter enjoys total acoustic isolation; and, equally important the trapped air acts as a highly linear diaphragm "spring" which does not deteriorate with age as in other designs.

The Woofer

While a woofer obviously need not be as light as a tweeter, low mass (relative to a given driving force) is an absolute necessity for well-damped, hangover-free bass. A woofer cone must simultaneously be as "dead" as possible - it must have a high degree of internal damping -  in order to avoid imparting its own chaaracter to the sound. (Tapping a woofer cone with the eraser-end of a pencil should produce a dull "thump" rather than a sharp, "live" sound.) and yet, the cone must be as stiff as possible in order to avoid "breaak-up" and other non-piston;like behavior. These three seemingly contradictory requirements take on added importance in two-way designs because the woofer is called on to accurately reproduce midrange frequencies in addition to bass information. While many driver manufacturers have used various exotic materials in attempts to meet these requirements, ADS firmly believes it has the closets thing yet to the ideal woofer cone: Stifflite

The L620 (L520 and L420) have 7-inch (8-inch and 10-inch) diameter woofers, respectively. All three woofers feature ADS tapered Stifflite cones. Stifflite is a relatively thick material formed of air-filled, randomly-oriented pulp liber in a unique "sandwich" construction. The internally trapped air damps resonances and keeps the structure very light, while the thickness of the construction lends high structural rigidity. And yet, the Stifflite cone is thick only where it needs to be - toward the outer edge - and tapers off where the extra mass is not required for rigidity.

Coupled to each cone are a low-mass high-temperaature metal voice coil at one end, and a highly flexible and uniform rubber surround at the other. The voice coils feature two layers of windings (where most other woofers use four), and they are precision-aligned into deep, narrow magnetic gaps. The results speak for themselves. The woofers have exceptionally light moving systems (lighter than voice coils alone in typical competitive designs). They excel at midrange frequencies, a sore point with most larger two-way systems. They do not "color" the sound, and their ability to excurse freely and linearly makes possible surprising aamounts of deep, undistorted bass. Correctly dimensioned Barium Ferrite magnets coupled with low moving mass ensure high efficiency and damping. The woofers boast exceptional power handling capability thanks to their high-temperature voice coil assemblies. Their efficiency and power-handling combine to give the L620 (L520 and L420) unusually wide dynamic range.

The Crossover Network

Many speakers have crossover networks with numerous power-robbing, distortion-inducing components, which are needed to correct driver performance anomalies and match grossly different driver efficiencies. Other have ridiculously simple, inexpensive crossovers too embarrassing to show or discuss in literature. ADS networks are necessarily sophisticated because musical accuracy is highly dependent on proper transition from woofer to tweeter. But, thanks to ADS advanced driver technology, ADS crossover networks are free of excessive complexity and have the lowest power loss and distortion figures in the industry.

The crossover characteristics and frequencies for the L620 (L520 and L420) systems have been selected through computer analysis and extensive acoustic measurements and extensive auditioning. The network components, furthermore, are of the finest quality. All critical capacitors, for example, are computer-grade metalized polyester-film rather than the more common and less expensive electrolytic variety. Bass section inductors are "over-designed" with extra-heavy-gauge copper wire and special low saturation, low dynamic distortion ferrite cores. All high-frequency inductors are air-core designs. The coils, as a result, are extremely linear over the system's operating range and have the lowest measured DC resistance among modern production loudspeakers. The corossover networks of the L620 (L520 and L420) thus provide seamless transition from low to high with maximum daamping and minimum distortion throughout the speakers entire frequency and dynamic range.

Advanced Acoustic Suspension Design

All enclosed ADS speakers employ the acoustic (air) suspension principle for two basic reasons. First, it is ADS belief that a properly designed acoustic suspension system offers the best, most consistent bass performance for a given size and cost, for the widest range of applications. Second, since acoustic suspension provides a highly linear diaphragm restoring force (trapped air) which is not dependent on the mechanical suspension of the driver, it delivers the most stable performance over years of use.

ADS acoustic suspension designs, however, go far beyond these basic considerations. ADS superior drivers and networks ensure the highest system efficiency. The L620 (L520 and L420) are demonstrably more efficient than other acoustic suspension systems of comparable bass performance. Surprisingly, they are also more efficient than most bass reflex systems of comparable internal volume and bass rsponse, even though theeory dictates the revers. (Most bass reflex systems lose their theoretical efficiency advantage to poor drivers and/or networks) This enables the L620 (L520 and L420) to be driven to startling sound levels with amplifiers as small as 15 watts per channel, an important economic consideration since amplifier power is not a cheap commodity. ADS acoustic suspension design, furthermore, ensures maximum bas accuracy and extension. All parameters are carefully chosen to maximize system damping and provide a smooth, gradual bass rolloff. Unlike "one-note" boom boxes which may initially impress the unseasoned listener, the  L620 (L520 and L420) produce bass of substance and subtlety, apprecaiation and enjouymebt of which can only grow over years of ownership.

The Enclosure

The  L620 (L520 and L420) cabinetry is a supreme example of ADS attentionto detail. The enclosures are precision-constructed from 3/4-inch extra-high-density particle board, which provides the mass, rigidy and acoustical properties necessary to keep sonic coloration to an absolute minium. They are beautifully finished in select natural walnut. The drivers are carefully flush-mounted onto the piano-finish front baffle to minimize  surface diffraction effects. The curved metal grille is acoustically transparent, and it eliminates the need for frames and supports, which cause further diffractive interference in conventional grille designs. ADS thus achieves remarkably diffraction-free performance in the  L620 (L520 and L420) without resorting to unusual, and frequently unsightly cabinet shapes. The lack of diffractive interference gives these speakers an open, "unboxed" sound quality and pinpoint-accurate stereo imaging, characteristics unusual in bookshelf speaker systems.

Tweeter protection

Since the tweeter is the most likely driver to be damaged by amplifier misbehavior (including clipping and oscillating) or abouse, the  L620 (L520 and L420) have tweeter protection fuses located in special compartments on their rear panels. Spare fuses are included in these compartments for convenience.

Accuracy Above All

Sonic accuracy is often defined as a lack of recognizable character. Since ADS believes that speakers should be transducers rather than sound generators, it should not be surprising that the  L620 (L520 and L420) sound remarkably similar to one another. They sound, in fact exceedingly like all other ADS speakers. And you will find this sound exciting and spectacular only if you find live music exciting and spectacular. If upper-bass boom, larger-than-life "presence", and sizzling highs are your cup of tea, you will find the  L620 (L520 and L420) unimpressive and perhaps even disappointing. If these speakers have a sonic "signature" at all , it is their transparent, effortless and neutral sound character, a feature common to all ADS speakers.

L 620

Specifications

Frequency Response:  30 - 20,000 Hz ±3 dB (20 - 22,000 Hz ±5 dB)

Impedance:  6 Ω (nominal), 4 Ω (minimum)

Efficiency:  92 dB SPL with 2,8 V RMS ( 1 watt) pink noise input measured at 1 m in typical listening room (2000 ft²)

Driver Complement:

HF :  1" soft dome tweeter

LF :  10" Stifflite woofer

Crossover:  1,500 Hz  12 dB/octave

Power Rating:  75 watts (nominal),  150 watts (max peak program)

Recommended Amplifier Power:  15 watts (minimum), 150 watts (maximum)

Cabinet:  Selected natural walnut over extra-high-density particle board

Baffle:  piano black finish with diffraction corrected flush driver mounting

Grille:  Acoustically transparent removable frameless grill in bronze finish.

Dimensions (Hx W x D):  25-1/2" x 14-1/8" x 11-3/4"

Weight:  18 kg (40 lbs)