VCL EX-15, 3-way speaker with 2 x Purifi woofer, 4 x Purifi passive radiator, Accuton midrange and Bliesma Be tweeter

This speaker with a Purifi - Accuton - Bliesma transducer combination is a more powerful version of our VCL EX-14 2-way monitor. It is a 3-way speaker also using a passive radiator woofer system. Two active and four passive transducers are used and mounted on both side walls to realize a good force cancelling.
The Accuton C90-6-724 is chosen as midrange and the Bliesma T25B-6 beryllium as tweeter.

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July 16, 2020
Specification Headlines

  • System: 3-way, passive radiator system, analog X-over
  • Woofer: 2 x Purifi PTT6.5W08
  • Passive Radiator: 4 x Purifi PTT6.5PR-01A
  • Midrange: Accuton C90-6-724
  • Tweeter: Bliesma T25-B6
  • Low frequency response: F3 = 38 Hz
  • Sensitivity: 86 dB at 1m, 2.83 Vrms, full space
  • SPL at maximum excursion, 38 - 20000 Hz: 102 dB, 1m, full space
  • Crossover: LR4 at 300 Hz and 2200 Hz
  • Impedance: mean value between 4 and 8 Ohm
  • Cabinet dimensions: width x heigth x depth = 26 cm x 110 cm x 38 cm

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July 31, 2020
Speaker System


Purifi PTT6.5W08, Purifi PTT6.5PR, Accuton C90-6-724, Bliesma T25B-6

As there are two woofers in this speaker, we choose the Purifi 6.5 inch 8 Ohm version, which is currently available. Placing such two in parallel, results in a total speaker sensitivity of 86 dB, 2.83 Vrms at 1 m.
For the midrange transducer, we had in mind the new Purifi PTT4.0W04, but its 84.3 dB sensitivity is just not enough for this concept. We have chosen the Accuton C90, it has an excellent sound, good reviews and is used in many commercial high-end speakers.
As tweeter, the new Bliesma T25B-6 beryllium will be used, a transducer with very good off axis radiation and a very low harmonic distortion.

Passive Radiator Woofer System - Small Signal Analysis

This speaker is equipped with two passive radiator woofer systems that are placed in parallel on both side walls. Doing it that way, a force cancelling of both woofers active on the cabinet is realized with much less cabinet vibrations at low frequencies.
The passive radiator system of each woofer is the same as the one used in our VCL EX14 2-way monitor.
For the VCL EX15 a system with two Purifi PTT6.5W08 active woofers, each provided with two Purifi PTT6.5PR passive radiators in a cabinet volume of 30 LTR, is used. All the passive radiator system details can be find in the VCL EX14 blog.

Midrange - Small Signal Analysis

The 5 inch Accuton C90-6-724 is placed in a cabinet of 17 LTR filled with sheep wool. The transducer Vas is only 5 LTR, in a way the TSP will not change much placing it in the midrange cabinet.

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August 02, 2020

Cabinet dimensions

3-D look in Leap

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August 05, 2020
Crossover Filter

Targets Crossover Filter LR4 at 300 Hz and 2200 Hz

Some arguments to choose the crossover frequnecies at 300 Hz and 2200 Hz
- the woofers on the side walls have a good uniform omnidirectional behavour up to 300 Hz.
- looking to excursion and harmonic distortion, the Accuton C90 midrange can be used between 300 and 2200 Hz.
- Power response and Directivity Index curves versus frequency are optimally flat.

Crossover filter schematic configuration

The component values are not stated in the schematic. Please contact us for more details if wanted.

Impedance with crossover flter

SPL of the filtered drivers and the sum at 1m, 2.83 Vrms

SPL off axis of the filtered drivers and the sum at 1m, 2.83 Vrms

SPL on axis in red, SPL at 30 degrees in green and SPL at 60 degrees in blue.

Power response of the filtered drivers and the sum in full space at 1m, 2.83 Vrms

Directivity Index in full sphere of the filtered drivers and the sum

DI of the woofers in blue, DI of the midrange in green, DI of the tweeter in red and DI of the sum in black.
The DI of the woofers becomes negative for high frequencies. Because the SPL on axis is lower than the radiated power for high frequencies, as the woofers are mounted on the side walls.

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