Jazzman
3-Way ScanSpeak made by Sven
Felsby/Denmark
Copyright
© Troels Gravesen
Scan Speak
22W/8857T00 + 15W/8530-K00 + Vifa XT25TG30-04
Sven Felsby:
"This speaker was designed for maximal bass
extension on a minimal footprint. As a result we end up
with an expected sensitivity of 85dB/2.8V".
So far, so good.
By coincidence, this job arrived at the same at time as
the Ellam-25 construction. Same midbass and tweeter,
only here supplemented by an 8" dedicated bass
driver taking us all the way down to 30 Hz. The price to
pay is modest sensitivity, but impedance stays above 6.5
ohms and phase angles are modest, so no problem for a
good minimum 100 wpc solid state amp.
  
The cabinets were designed by Sven Felsby and
manufactured at www.snedkeri.dk.
The Cabinet
Box simulation. Click image to view large.
Please note that even LspCAD is wrong about vent length
calculation.
For Fb = 25 Hz, the vent has to be 70 mm (ID) x 290 mm.
Bitumen on most internal surfaces. Egg crate foam in
midrange chamber, upper bass chamber and
on top plate. MDM-3 synthetic wool in midrange chamber
and behind tweeter (acting as wave trap)
To tune the port
to 25Hz, the port has to be placed vertically. Use a
flanged port to minimize chuffing.
Minimum distance to floor is 40 mm.
Volumes:
Inner dimension
with 4 mm bitumen pads on all internal panels are:
198 mm (W) x 274 mm (D) x 898 mm (H) = 48.7 liters (42.4
liters netto)
Port, drivers, bracing and crossover is likely to occupy
some 1-2 liters, thus close to 40 liters netto.
Midcap outer
dimensions:
198 mm (W) x 170 mm (D) x 186 mm(H) = 6.3 liters.
Midcab net volume:
206 mm x 148 mm (D) x 154 mm (H) = 4.7 liters.
 
The Crossover
Due to low efficiency of the bass driver, some
attenuation is required for the midrange, hence
paralleled 10 watt MOX
resistors in midrange section. These will stay cool even
at high playback levels.
The
crossover made from the very best components is
not particularly cheap. The 68 uF in the bass
section can be standard MKP. No need to use super
caps here. The 32 uF is important and if I had to
choose between super-caps for the mid and treble,
this 32 uF would be my first investment. Yes,
treble can be slightly grainy from standard caps,
but I find enhanced midrange transparency more
important here.
List
includes additional 3R9 and 4R7 resistors to
fine-tune treble level to personal taste and room
conditions.
3.3 mH has
to be as low-ohmic as possible. Use a good cored
inductor. The 5.6 mH can be from 1 mm wire, cored
or air cored and DCR = 0.5-1.5 ohm, no big deal.
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Measurements
 
Left: Response from drivers in cap without crossover.
XT25 smooth as always.
15W.... remarkable driver. Really goes up to 10 kHz
without any trouble.
22W: Doesn't start breaking up until 3-5 kHz. Excellent
from an 8" alu cone.
 
Left: SPL @ 1 meter, 2.8 volts. System sensitivity = 85
dB. Reading merged with bass nearfield response at 250
Hz.
Right: Impedance doesn't go below 6.5 ohms. Maybe even a
50+ watt PP valve amp may do well here.
 
Left: Point of crossover between mid and tweeter is 3200
Hz. Right: Blue = reverse mid polarity at tweeter height,
1 meter distance.
Point of crossover between bass and mid is around 500 Hz
with shallow slopes on both drivers.
 
Left: Horizontal dispersion at 0, 10, 20 and 30 deg.
(red/blue/green/purple)
Right: Vertical dispersion at 1 meter from 10 cm above
tweeter height (red) to bass height (purple).
Overall this speaker provides an even power response. No
hot-spot here.
 
CSD at 20 and 40 dB scaling.
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page.
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