ELLAM-25

ScanSpeak 15W/8530-K00 + Vifa XT25TG-30-04

I've had very good response on the Ellam and Ellam XT constructions and how can we make a good thing better? An Ellam XT 2½-way is an attractive option and it pays off well. The lower bass driver will compensate for baffle step loss and provide enhanced sensitivity. Still 22 liters net volume is what it takes to make deep bass from a very modest footprint, a true high-WAF speaker.

With two bass drivers we're making 190 cm^2 membrane area, close to an 8" driver (220 cm^2). The impedance doesn't go below 3.5 ohms; still a manageable load for the majority of solid state amplifiers.
The magnificent midrange presentation of the 15W/8530-K00 is all there, only now augmented by a more solid bass, a thing that always will enhance upper mid and treble performance.

We might also call this speaker the "Ekta Mini" and should I point out one single important feature, then the lack of a high-pass filter for the midrange would be it. This is the great thing about 2½-ways: Simplified filters due to no baffle step loss compensation needed for upper bass driver, no midrange notch-filter needed and this construction is no exception. We can get away with a simple 2nd order filter for both lower and upper midbass and a 3rd order filter to the tweeter for proper SPL summation and phase integration.

The crossover
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Use standard MKP caps for lower bass section - and the best you can afford for the rest.

The Crossover Kit
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Complete kit as above excl. drivers available from: contact@jantzen-audio.com

In replacement of Vifa XT25TG-30-04, use e.g. ScanSpeak R2604/832000

The cabinets
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Cabinet volume from 19 mm MDF and 4 mm bitumen pads on all internal panels:
1.44 x 8.12 x 1.94 = 22.7 liter minus bracing, ports and drivers, approx 22 litres.
Driver panel is made from 22 mm MDF.
Place bracing between drivers and two below lower bass driver = 4 braces in all.

Port tuning 40 Hz.
Length of two ports:
45 mm (ID) x 140 mm (L), or
42 mm (ID) x 120 mm (L), or
40 mm (ID) x 100 mm (L)
50 mm (ID) x 160 mm (L), (use 2 x 145 mm as supplied with crossover kit, this will make Fb = 43 Hz)

Measurements
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Left: SPL/2.8 volts/1 meter distance. Right: Tweeter attenuation, R1011 = 1R5, 2R7 and 3R3 ohms.

Left: The well-known nulling effect from inverted tweeter polarity. Point of crossover is 2800 Hz.
Right: Final system impedance.

Left: Horizontal dispersion, 0, 10, 20 and 30 deg.
Right: Vertical dispersion measured at 1 meter distance from right above tweeter height (red) to the middle of lower bass (yellow)

Torben's crossover pics:

Torben's construction pics in random order