PTT4.0PR-NF2-01 Long Stroke Passive Radiator with Ultra Low Distortion

The PTT4.0PR-NF2-01 is a 4” high-performance passive radiator featuring Purifi’s research based technologies, including the Natural Surround and a cone made from a proprietary fibre mix.
99,95 €
Tax included
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The PTT4.0PR is a 4” high-performance passive radiator featuring PURIFI ’s research based technologies, including the Natural Surround and a cone made from a proprietary fibre mix.



  • A whole new take on passive radiator design
  • PURIFI ’s Natural Surround
  • Bimax spider
  • High linear excursion limit
  • Tunable mass
  • Engineered and manufactured in Denmark


Product Details

PURIFI PTT4.0PR Passive Radiator 


PURIFI is a fresh company that designs and manufactures extreme 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 performance degrading aspects for both amplifiers and transducers. Thanks to this understanding the passive radiators from PURIFI are the most high-end passive radiators available at SoundImports.


The challenge 

Loudspeaker drivers are known to add a large, if not the largest, amount of distortion on an audio signal chain. Reducing this distortion is a challenge with the complication of fine-tuning to improve one part (e.g. harmonic distortion) often results in a degradation of  another part (e.g. intermodulation distortion). These distortions consist out of several separate distortion mechanisms. By carefully mapping and completely understanding these mechanisms, PURIFI succeeded in improving the overall performance by a large degree.


A whole new take on passive radiator design

PURIFI developed mathematical models for the suspension, cone and surround. These models allowed for the optimization of different distortion mechanism separately. The result makes that the PTT6.5PR is a perfect passive radiator to accompany the PTT4.0W04 in a size efficient enclosure. Looking for a passive radiator the accompany the larger PTT6.5W04 or PTT6.5W08? Take a look at the PTT6.5PR


The mechanism


Low surround radiation distortion

Reduces harmonic and intermodulation distortion caused by surround



Q: Why is this surround odd shaped?

A: This is the PURIFI Natural Surround. Conventional surrounds create distortion as they deform. The shape of the Natural Surround reduces cone edge resonances and distortion. It might be odd looking, but form follows function here. A more detailed look shows that the surround actually represents complex sound wave. We are told that the Natural Surround is also called ‘wormy’ by insiders.


Data sheet

Driver type
Passive radiator
Frequency range
Resonance frequency (fs)
24 Hz
DC resistance (Re)
Mechanical Q (Qms)
Electrical Q at Fs (Qes)
Speaker diameter
Power handling
Voice coil inductance (L)
Effective mechanical mass incl air load (mms)
Effective piston radiating area (Sd)
57 cm²
Force factor (BL)
Equivalent volume of compliance (Vas)
6.4 liter
Overall diameter
125 mm
Mounting diameter
100 mm