It weighs 27kg and sits on a stand. The bass goes lower than most bookshelf speakers manage.

Overview

The Yamaha NS-690 II is hard on small amplifiers. It weighs 27 kilograms and stands 630mm tall, so it is a bookshelf speaker in name only. The cabinet is sealed. , it was Yamaha's answer to the demand for high-fidelity systems that could deliver deep, controlled bass without venting to the outside world. It is a 3-way, airtight (sealed) system. Call it bookshelf if you like, but it is really a stand-mount speaker in the Japanese style of the late 1970s - overbuilt, over-specified, and ambitious.

The NS-690 II refines the NS-690, and it sits between the NS-690 and NS-690 III in the product family. The low-end driver is the JA-3060, a 30 cm cone woofer borrowed heavily from the NS-1000M. It has the same size, the same basic construction and the same 156 φ ferrite magnet. Yamaha made one deliberate change: urethane foam replaced the cloth surround. That altered the damping and, reportedly, softened the transient edge a little, which suited a wider range of rooms. Whether that was a step toward warmth or a compromise in longevity is still debated. Either way, this was not just a cut-down NS-1000M.

The sealed enclosure matters a lot here. The lowest resonance frequency is 40 Hz and the frequency response extends down to 35 Hz, with no port. That avoids the time-smearing and chuffing that can plague reflex designs. The cabinet is heavy: front and back panels are 25 mm thick, sides and top 20 mm, in particleboard with 10% higher density than the previous model. The back panel is now glued rather than screwed, which helps the seal last. That matters in a system where the air inside is part of the suspension.

Sensitivity is 90 dB/W/m and nominal impedance is 8 Ω, so on paper it is not hard to drive. But the 35 Hz lower limit wants a controlled amplifier, and the 80W maximum input suggests Yamaha expected receivers or separates of some muscle. The crossover is passive 3-way, set at 800 Hz and 6 kHz with a 12 dB/octave slope. It uses MP capacitors and ferrite-cored coils mounted at right angles to minimize interference. It is not exotic by modern standards.

Owners report that the mid and high drivers are the best part. The 7.5 cm JA-0701B soft dome squawker has a double-coated diaphragm with a proprietary mixed coating agent, the same as the 3 cm JA-0509B tweeter. Both have integrally molded tangential edges and aluminum die-cast frames, which add rigidity and cut resonance. The tweeter has a 15,500 gauss flux density and an edgewise-wound aluminum ribbon voice coil, which keeps mass and inductance low. Both mid and high ranges get continuously variable level controls, so the tone can be adjusted to the room.

Some describe the sound as "transparent but pleasing." It doesn't scream "monitor" like the NS-1000M, but it doesn't retreat into euphonic flattery either.

Specifications

Key Features

30 cm Cone Woofer with Urethane Foam Edge (JA-3060)

The JA-3060 is a 30 cm cone woofer that shares its core structure and materials with the flagship NS-1000M. The biggest change is the urethane foam surround in place of cloth. That likely made production more consistent and cut cost, but it hurt long-term reliability. Urethane foam edges are notorious for drying out and crumbling over decades, a known failure point in many vintage speakers. At the time, though, the foam offered a more predictable damping profile and tighter manufacturing tolerances. The cone is Yamaha's proprietary paper formulation in a corrugated conical shape for stiffness. The voice coil is copper ribbon on a Nomex bobbin, which is light, heat resistant and resists deformation. A 156 φ ferrite magnet and copper center cap help control inductance and improve transient response.

Double-Coated Soft Dome Midrange (JA-0701B)

The 7.5 cm JA-0701B soft dome squawker is built for low distortion and high linearity. The diaphragm is a double-coated material with a new mixed coating agent, presumably a blend to balance stiffness and damping. The integrally molded tangential edge eliminates adhesives that could introduce non-linearities. The FRP (fiberglass-reinforced plastic) bobbin is rigid without excess mass. Air holes in the bobbin aid cooling, and glass wool inside the rear chamber damps the enclosure. With a Q of 0.5 and a free-air resonance of 280 Hz, the unit sits well above its resonance at the 800 Hz crossover point. The 120 φ ferrite magnet gives a 14,500 gauss flux density in the gap.

3 cm Soft Dome Tweeter with Edgewise-Wound Voice Coil (JA-0509B)

The JA-0509B tweeter is all about low moving mass. The 3 cm soft dome uses the same double-coated diaphragm as the midrange. The edge is integrally molded, which reduces breakup modes. The voice coil is wound edgewise from lightweight aluminum ribbon wire, which gives more surface area for cooling and less inductance. The magnetic circuit is a 80 φ ferrite magnet with a 15,500 gauss flux density, which contributes to the transient response. An air hole in the outer pole piece behind the edge equalizes pressure and reduces diaphragm rocking.

Hermetically Sealed Cabinet with Reinforced Particleboard

The sealed enclosure is the basis of the bass performance. Unlike ported designs, it has no port noise or group delay. The compliance of the air inside the cabinet acts as part of the suspension. The cabinet uses particleboard with 10% higher density than the NS-690, which adds rigidity and reduces panel resonance. The front and back panels are 25 mm thick, and the woofer cutout in the baffle is bonded to the back plate as structural reinforcement. The back panel is sealed with adhesive rather than screws, a change from the previous model that improves long-term airtightness. Any leak would hurt the bass response.

Continuously Variable Mid and High Frequency Level Controls

The NS-690 II has continuously variable level controls for both the midrange and high-frequency drivers. These let the user tailor the sound to room acoustics or personal preference. It is not a simple bass/treble cut. It is driver-level attenuation, which gives real control over balance. That helps most in rooms with reflective surfaces or unusual dimensions.

Historical Context

The NS-690 II was developed as a refinement of the NS-690, with improved materials and construction. It sits in the middle of the NS-690 series, between the original NS-690 and the later NS-690 III. This was incremental development, typical of Yamaha's speaker design in the late 1970s. The drivers derive from the NS-1000M, but with adjustments like the foam surround that suggest a balance between performance, cost, and manufacturability.

Collectibility & Value

The most commonly reported issue with vintage Yamaha speakers like the NS-690 II is degraded foam surrounds. Over time, the urethane edges on the woofer and potentially the midrange can dry out, crack, or disintegrate, and they need refoaming. One repair technician reportedly quoted around $120 for such work, though prices vary. Market values are inconsistent. One source suggests a pair in need of foam replacement might sell for $250 - $300, while another estimates average used prices between $350 and $500, with higher figures for mint examples. A Facebook listing once asked "70k" for a pair, though currency and condition were unspecified. Given the lack of comprehensive pricing data, value depends heavily on condition, restoration status, and regional market demand.

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