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.



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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