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Loudspeaker Designs and Articles for the DIY Enthusiast
The
Stentorians
A high sensitivity / high SPL
design offered for PA, Music
and Home Theater
Applications
Links to:

Main / Design Goals

Driver Selection

Cabinet Construction

Crossover Design

Measurements

Listening Impressions
Measured Impedance
I'll admit I had some issues measuring this design. All
those woofers make it a bit more difficult than a
traditional MT or MTM. These response plots were
measured at 1 meter on the design axis, which was
about 15 degrees off the horizontal axis, and centered
at the woofer just below the tweeter. Gating was
selected to provide useful response down to 100 Hz.
Although there will be some room mode aberrations, I
don't believe they significantly effect the response.
-Note the total lack of a floor bounce in the woofer
measurement.   

I also found that I obtained greater response variations
with differing with differing tests stimuli. The plot to the
left was done using MLS, which I believe provides the
more accurate measurement in this case. The off axis
plots shown further below, were done earlier using
frequency sweeps.
Measured Frequency Response
The measured impedance plot indicated a very easy
load for just about any amplifier capable of a 4 ohm
load. The worst case is at 200 Hz at -45 degrees and
7.5 ohms. The impedance minima for the system is just
below 4 ohms, but is at the high end of the spectrum
where there is typically less energy present. It is above
5 ohms for a significant portion of the passband, so I
suspect that most decent amplifiers rated for 6 ohm
speakers will have no issues driving this design. 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. (green trace) Highly recommended for tube
amplification applications. 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.