The Accuton Head

After some 15 years I decided to add an upper bass lower mid section
with a lower crossover points at 100Hz and an upper crosover at 500Hz,
to relax both the stress on the MSW and to improve the radiation of the Backes and Muller low section.
For the system uses a pair of Accuton C220-6-222 to cover that frequency band.

Actually, at the time of development of the head the real T/S parameters of the drivers
where quite different from the manufacturer datasheets.
Luckily the difference between my matched pair was negligible.
This free air impedance plot of the Accuton C220-6-222 was taken with a 47 ohm series resistor at 1 Volt
the measurments where taken after a 120 hour run in with 16Hz 6Volt.
Rdc was respectively 6.01 and 5.88 Ohm in stead of 6.7 Ohm in the datasheet.
We had a free air resonance of around 29Hz and 30Hz in stead of 24 Hz in the datasheet.
and Qts of 0.219 and 0.225 in stead of 0.19 Ohm in the datasheet.
As I am using the driver as upper bass from 100Hz up this is irrelevant for my purpose
After contacting the Accuton there representative confirmed me that the T/S parameters where slightly changed.
Meanwhile the manufacturer changed the T/S parameters on the website and they now are indeed close to the ones I measured.

Free air impedance plot of Accuton C220-6-222  

The boxed impedance in the actual 18.7 netto liter cabinet with lining.
The boxed speaker resonance was arround 57 Hz with a Qms = 5.830 Qes = 0.535 Qts = 0.490.
You can see the cone breakupr resonance at arround 4350Hz in the impedance (both phase and amplitude).

Boxed impedance plot of Accuton C220-6-222  

The inner Accuton cabinet made from 13 mm thick HPL (High Density Laminate).
It is not glued yet and without the top cover so you can see the internal structure.
Note the seperate compartment at the back for part of the filter.

The HPL cabinet before glueing  

The inner Accuton cabinet finished.

The HPL cabinet after glueing  

The inner Accuton cabinet is fully covered with 4mm Noene a visco-elastic material
If you want to see how it works you can see a Youtube movie of the effect.
The firm sells the product to the public as shock absorbent soles.

The HPL cabinet lined with NOENE  

Then comes the 22mm MDF outer cabinet.

The MDF cabinet  

the HPL inner cabinet is mounted in the MDF outer cabinet.
The inner cabinet floats on the Noene in the outer cabinet.

The HPL cabinet floating in the MDF cabinet  

Finaly the outer cabinet is glued arround the inner one.
Now it is ready for the paint job.

The finished cabinet ready for painting  

I choice to paint it in Signal-Violet (RAL 4008).
That way the complete speaker which is 1.5m in height is not such a monolith block.

The painted cabinet in RAL 4008 Signal Violet  

These are two pictures of the Accuton filter.
It is mounted in its own cabinet external to the loudspeaker cabinet
The straight-up M-cfc27-12 MCoil Foil coil 2.7mH AWG12 coil serves two functions.
Together with the 155uF
(100uF 47uF ClarityCap ESA and 8.2uF Jantzen Audio Superior Z-cap
it is part of the 500Hz 12 dB low pass filter.
The parallel 0.56uF Jantzen Audio Superior Z-cap (at the bottum of the first picture)
in series with the 8.2Ohm MOX resistor double as a
parallel resonant circuit to suppress the 4.3 KHz cone breakup resonance.
The three 22uF Mundorf mCap Supreme (which were recovered from the previous Manger MSW filter)
with the little 0.82uF Jantzen Audio Superior Z-cap mounted on the side
and the large 100uF ClarityCap ESA cap form a 166uF capacitor
which together with the parallel 5.6mH Mundorf coil form a 100Hz 12dB/oct high pass filter.

The Accuton filter  

Here is the other view.
The three parallel 3.9Ohm plus 6.8OhmMResist SUPREME Resistorsfrom Mundorf
in the signal path together with the parallel switch selectable (not yet on this picture) 33Ohm MOX resistors
form a divider to match the sensitivity of the Accuton to the (lower) sensitivity of the MSW Manger.

Another view of the Accuton filter  

The Accuton filter is mounted in its own cabinet external to the loudspeaker cabinet

The boxed Accuton filter  

And this is the impedance correction and
the RLC Parallel Resonant Circuit to suppress the cone breakup resonance around 8 Khz
This one is mounted in an acoustical separated compartment of the Accuton cabinet itself.

The 8Khz Accuton notch filter and impedance correction circuit  

Here you have the near field response and distorion from the Accuton in its cabinet.
It was measured in the living room

Accuton unfiltered near field frequence response in its cabinet  

Here you have the filtered near field response and distorion from the Accuton in its cabinet.
It was measured in the living room with my Earthworks MC30 Mic and the ARTA measuring software
Note the slow fall off from arround 150Hz towards the crossover frequency of 500Hz
This is to compensate the box front panel diffraction.
Remember this is a near field measurement and the response will flat at the listening position.

The Accuton filtered near field frequence response