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PTT6.5X08-NAA-08 Ultra Low Distortion Extended Woofer

Negligible force factor modulation and surround radiation distortion. Low magnetic hysteresis distortion. “Real” long-stroke performance: distortion remains low over full excursion. Uncompromised midrange performance. Designed and manufactured in Denmark.

€455.85 Save 3%
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The PTT6.5X08-NAA-08 is the standard stroke 6.5" bass-midwoofer from the PURIFI woofer family. It incorporates similar breakthrough technology, but due to a reduced excursion limit the efficiency is improved over the PTT6.5X04-NFA-01 long-stroke woofer.



  • A whole new take on driver design
  • PURIFI’s Natural Surround
  • Extreme low distortion over full excursion range 
  • Engineered and manufactured in Denmark
  • Excellent midrange performance
  • High power handling
  • Perfect balance between volume displacement and midrange efficiency


Product Details

PURIFI PTT6.5X08-NAA-08 Ultra Low Distortion Extended Woofer


PURIFI is a fresh company that designs and manufactures extremely high-performance transducers and amplifier modules. Don’t let the freshness fool you; Their leadership team consists out of some well-respected audio technology pioneers. PURIFI developed a deep understanding of many performances degrading aspects for both amplifiers and transducers. 


The PTT6.5X08-NAA-08 is an aluminum-cone member of the famous PTT6.5X extended-stroke product family. PURIFI’s research has identified the parameters that have so far prevented extended stroke drivers from breaking through in truly high-performance audio. The distortion of the acoustic output of a driver is a combination of several separate distortion mechanisms in the motor, cone, and suspension. When testing a complete driver with sine waves, a situation often arises where a small tweak seemingly improves harmonic distortion (HD) by letting two mechanisms counteract each other. This always leads to a clear worsening of intermodulation distortion (IMD) that becomes obvious when testing the unit with a more complex signal. This is why traditional HD tests fail to predict subjective sound quality.


PURIFI takes care to optimize the various distortion mechanisms separately, thus guaranteeing that any measured improvement truly reflects a real audible improvement no matter what the signal is. Accurate mathematical models are developed for the motor, suspension, and vibroacoustic of the dome and surround. These models clearly explain several distortion mechanisms in each domain, which provides fundamental insights into better ways of constructing the motor, cone, and suspension. Finally, the same models are used to numerically fine-tune the geometry. This way of working reliably reduces multiple distortions mechanisms which secure low IMD for complex signals.


Low Force Factor Modulation

Prevents voice coil current from modulating Force Factor (Bl). The PURIFI motor completely avoids this classical Achilles’ heel of long-stroke drivers. This translates into low intermodulation (IMD): clean, undistorted midrange even in the presence of heavy bass. Equates to low impedance modulation, meaning that drive current is not distorted by cone motion.


Very Constant Force Factor over Excursion

Prevents voice coil position from modulating the force factor. This is the classical cause of “burbling” i.e. amplitude modulation of the midrange by large low-frequency cone excursions.


Low Surround Radiation Distortion

The surround contributes to sound output. Conventional surroundings produce distortion as they deform. PURIFI’s Neutral Surround geometry avoids this mechanism without constraining motion. This reduces harmonic distortion as well as intermodulation distortion.


Low Magnetic Hysteresis Distortion

Hysteresis means that magnetic domains in iron retain traces of previous magnetization/demagnetization cycles which cause distortion when magnetized or demagnetized again. This distortion masquerades as benign harmonic distortion when tested with a sine wave but takes on a crackling or noisy character with more complex signals. Removing hysteresis distortion translates into a very “fluid” presentation with excellent front/back separation in the stereo image and a perfectly black background between instruments.


Cleaner than large-cone short-stroke drivers
The combination of the above characteristics results in a compact long-stroke driver that delivers complex sound with clarity and lack of effort that was previously the exclusive province of large-cone short-stroke drivers. Additionally, thanks to the small cone size, the driver has excellent midrange reproduction. It is highly suited for two-way systems.


Data sheet

4 Ohm
2.83Vrms/1m 85.0 dB
Resonance frequency (fs)
34 Hz
DC resistance (Re)
5.9 Ω
Mechanical Q (Qms)
Electrical Q at Fs (Qes)
Total Q factor (Qts)
Speaker diameter
Voice coil inductance (L)
0.50 mH
Effective mechanical mass incl air load (mms)
27.2 g
Effective piston radiating area (Sd)
132.7 cm2
Force factor (BL)
9.0 N/A
Equivalent volume of compliance (Vas)
20.4 L