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Earthquake SLAPS-12″ Symmetrically Loaded Audio Passive System (SLAPS) SLAPS-M12

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Earthquake SLAPS are Tunable Passive Radiators that provide additional bass, without additional amplifier power or enclosure volume. Designed to perfectly complement all good quality long-throw woofers on the market. SLAPS add up to +6dB of bass compared to regular sealed and ported enclosures. The benefit of them being user tunable is they can be integrated into virtually any sub/ cabinet combination.

SLAPS is a patented type of passive device that significantly increases subwoofer efficiency and ability for ultra low frequency reproduction. SLAPS is short for  Symmetrically Loaded Audio Passive System. As the name indicates,  SLAPS is built symmetrically which distinguishes it from traditional passive devices. SLAPS integrates identical components in its suspension design, this results in identical stoke regardless of forwards or backwards motion. The high efficiency and performance is a result of the pneumatic coupling between SLAPS and an active driver.














SLAPS overcomes the limitations known from the conventional sealed and ported enclosures that tends to limit excursion. The unique design allows the active driver compression free excursion resulting in deep, dynamic and powerful bass response.














SLAPS design differs from other passive devices by having double edge suspension and no center spider. SLAPS is designed from the ground up to be operated and controlled pneumatically. Traditional passive devices are often just a normal active driver where the primary motor system (voice coil and magnet) has been been removed. Conventional devices are designed to be powered electrically, in which the force emanates from the drivers conical  center. A passive device is operated pneumatically by air pressure from the active driver. For pneumatic operation  a traditional unit does not perform identically in positive and negative pressure environments. (imploding edge suspension and positive over ring).















SLAPS have a dual structure of identical opposites, ie. that there is an introvert and an extrovert edge suspension and no spider. This gives identical properties in both the negative and positive pressure domain. SLAPS thus behaves  pistonically and accurately, they do not have the “hesitation” traditional passive devices seems  to have when you observe them in operation.

















SLAPS opens up for new subwoofer designs, where even very small enclosures can be tuned to low frequencies . The low weight allows great flexibility in terms of weight attachment. SLAPS can be custom tuned for optimum performance in a wide range of enclosure sizes and active device configurations.
















Damping is very important in a passive device because it does not have a magnet motor system to control it. It is essential that the passive device constantly is “leaning” up against the pneumatic environment in the cabinet. If the device’s compliance is too weak the result ss over-shoot and over-ring. This means, for example a transient in the music causes a rapid pressure ratio change in the cabinet and control  over the device can be lost – making it move more than it should. The same thing can happen to a normal woofer. unit if the suspension + motor system is not built correctly. The design of the edge suspension itself is important. If not correctly designed it  may  implode ie. be sucked backwards if the pressure in the enclosure is too strong. A full implosion is rare, but in most  typical slave/passive/drone  designs some “dimples” in edge suspension can be visible already at medium load. A normal passive device only has a one way edge suspension so the dimples will only occur when negative pressure is present – = asymmetrical artifacts = distortion.














SLAPS dual structure based on the principle of  – identical opposites – eliminate the circumstances that would allow asymmetric nonlinearities  because the device is subjected to identical loads. You could argue that it does not fundamentally resolve  dimples at high loads, as they will still occur, but they are offset as they now occur similar under both positive and negative pressure.












SLAPS enables the transfer of high amplifier power into low frequency output. Since the device does not have to fight against increasing pneumatic pressure in a closed cabinet or over-excurt  close to a port tuning frequency. SLAP has no annoying port noise and enables deep bass from a compact volume. SLAPS promotes the dynamics of a small system in which a closed enclosure design has difficulties. In a closed cabinet design the pneumatic loading of the woofer increases  as a function of its travel, this causes compression. SLAPS technology possesses none of these limitations.
SLAPS allows tuning below 10hz  making any worries about tuning frequency superfluous.

Sold and priced per piece. 


  • Coupled with almost all woofers, SLAPS increases output without added amplifier power or enclosure volume
  • Suitable for high output needs where space is limited
  • User-tunable adjustments can be set to match a range of vehicle requirements and musical preferences.


  • Model nr.: SLAPS-12M
  • Installs just like a subwoofer
  • Slim-mount design is only 3-inches deep
  • No increase over existing sealed subwoofer enclosure sizes
  • Easy tuning for quick adjustments


  • Overall Diameter: 314.2 mm
  • Cutout Diameter: 289 mm
  • Mounting Depth: 53.3 mm
  • Hex Nut Size: US 5/16 (M8)
  • Mass ID: 8 mm
  • Max Mass OD: 74 mm

TS Parameters*:

  • Fs: 25.5Hz (Free Air Resonance)
  • Vas: 4.52 cu.ft.
  • Qms: 7.00
  • Cms: 0.38661 mm / Newton (Mechanical Compliance)
  • Mms: 289g (Total moving mass it includes the air load)
  • Sd: 483 sq.cm.
  • Xmax: 4 in. / 10.2cm

*measured with only the bolts installed and without the mass


Subwoofer Design with SLAPS Passive Radiator Manual (ENG)


Question : How can a subwoofer driver play below its Fs (resonance frequency) point ?

A: The Fs of a driver is taken in Free Air. As soon as you put it in a box you add resistance same as if you made the moving mass heavier, this lowers the resonance point. This is referred to as system resonance.

With SLAPS you can tune this resonance point to be outside of the audible range. How low you can tune it really depends on the maximum excursion potential of the woofer you are using. You want the Slaps to start resisting the movement of the woofer before the woofer runs out of excursion as to prevent it from bottoming out. This is why only long stroke woofers should be used with SLAPS.The reason why subwoofers you might have heard in the past sound bad below their tuning point is simply because their design did not allow for a tuning point low enough for it to be outside of the audible range. Slaps can not fix the sound if the primary woofer is distorting, instead it prevents the woofer from distorting in the first place by allowing a tuning frequency below audible range.

With a Slaps energy below the tuning point typically below 20hz is translated by the slaps to powerful infrasonic energy (vibrations) that the human auditory system will detect as very low frequency sound, even though the  ears are not capable of hearing it, your body will sense it. Same as how tactile transducers can stitch back the missing fundamental to an audio range through the body, so will this low frequency airborne energy.