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Measured Impedance
This response plot was measured at 1 meter on the
design axis, which was about 15 degrees off the
horizontal axis, and centered on the tweeter.  
Measured Frequency Response
The impedance minima is 3.9 ohms at 160 Hz, but rises
to above 7 ohms above 350 Hz. The worst amplifier
load is 10 ohms and -30 degrees at 110 Hz. This
suggests an easy load for any amplifier capable of 4
ohm operation, and likely many 6 ohm rated amplifiers
may tolerate them as well.

Those with tube amplification will likely want to add an
impedance normalization network shown below. This
knocks the impedance peak at 900 Hz down to about 8
ohms.
Horizontal Off-Axis Response
Although measured earlier with sweeps and will less
filtering, it suggests the design has good power
response, with little change in timber when listened to
off axis. Note here that the 0 degree plot is reference to
orthogonal with the front baffle, rather than the design
axis, which would be closer to the 15 degree plot.
Harmonic Distortion Magnitude
Harmonic Distortion Percentage
The HD plots were measured at 2.8 volts, and look
surprisingly good for a design using $10 drivers. The
bump in third harmonic distortion around 2K is due to
the Aura woofer, which otherwise does quite well.

The HD% plot below is the same data expressed as a
percentage.
Impedance Normalization Circuit
This plot shows the effect of the Impedance normalizer
circuit.  Highly recommended for tube amplification
applications. Note the improvement in impedance
phase as well. It won't hurt to run it on a solid state
amplifier, -but don't expect any overwhelming sonic
improvements.

The circuit can be found on the Crossover page.
The
Sten II
Big sound for a very small
price. Suggested for
bookshelf or near-wall /
on-wall applications.
Links to:

Main / Design Goals

Driver Selection

Cabinet Construction

Crossover Design

Measurements

Listening Impressions