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21 December 2012 17:17. "It's been busy here working on three products with the Stentor on the front burner. Thus far all my personal expectations for the performance of this slim yet tall speaker have been well exceeded already. The xover design includes many novelties including constant group delay
in the audio band. The
downside is that unlike the Gladius which can sing with
low-power tube or transistor amps like your favorite SIT, the Stentor is
power hungry. However I think you will be surprised by its bass
extension. Below is a photo of its solid aluminum plinth with top-adjustable
carpet-piercing spikes and a teaser of the midbass section of the bigger speaker under development. These midbass horns have about 4-5 times the mouth area compared to
other rear-loaded horns and are 220cm tall. The mid/high section will have
its own stand and consist of a 330Hz solid
wooden horn encased in a bullet enclosure like our larger
Contento speaker and a large custom Raal ribbon tweeter in a
proprietary 360° flare horn again like our top
Contento."
"The Gladius woofer sits next to the raw Stentor cab above for size comparison. The Stentor really has a very small footprint but as a proper time-aligned speaker it makes
the best of large free space around it.
Its listening axis is a bit higher above the ground so the user must tilt
the speaker forward a bit depending on seat height. This is easily accomplished by adjusting the single rear spike."
31 December 2012, 17:03: "Below are the Stentor drivers. The Raal ribbon has their true Flatfoil aluminum foil
weighing a mere 0.007gr. Response via its constant group delay variable-order filter
is 3.2-100kHz.
The midrange has a very light cone made from plant fibers and
mica particles. We further treat this cone for much improved pistonic
behavior and pushed-out breakup zones. The frame is very sturdy
cast aluminum covered in felt for further vibration
control.
The 10'' woofer sits in a cast aluminum frame with a carbon fiber cone. Many such cones have nasty breakups with very high
Q due to the woven structure of their carbon fabric. This woofer
has no such woven structure and exhibits much better behavior throughout
the passband and well beyond."
"Although it has a low Fs and TS parameters suitable for closed-box
loading, its cone weighs a mere 50gr. That's a fraction of other
woofers of this size and especially for such extension.
I am currently working on the crossover tuning and waiting for the
last transformer coils from Mundorf.
Here are two short 5MB videos showing how the head unit is routed: 1 & 2."
"The above renderings of the main body without tweeter section show an inside look at the stacked Ply construction. Counting its layers I arrived at 70 individual Ply pieces or 140 layers for each Stentor. The crossover points, variable attenuation slopes and offset driver positioning create very high accuracy for both time coherence and linear directivity. The crossover parts count topped out at 30 per side. This includes top-quality air-core copper foil inductors, near zero-Ω inductors for the bass filters, paper-in-oil foil caps and supreme polystyrene capacitors. The mid/high filter sits at 3kHz with a variable/accelerated slope. The bass/mid filter sits at 450Hz and combines a classical 2nd-order function with variable slope addition. Impedance is an amplifier-friendly 5Ω minimum. Max phase variation between 70Hz and 50kHz is all of ±28°. Max phase deviation is -43 degrees at 11Ω. All of this presents a very easy load to any tube or transistor amplifier design. Dimensions are 131 x 45 x 36cm HxWxD. Weight is 50kg each, sensitivity is 88dB."
Impedance vs. phase plot
Impulse response of synchronized tweeter/midrange
"As it turned out, the veneering of Stentor's complex surfaces proved too costly at the quality I wanted. We thus have taken the road of 10-layer undercoat + automotive color of the client's choosing + semi-matte lacquer.
I'm sending along a laser alignment tool for proper toe-in and
tilt adjustments.
The alignment tool is a curved frame. It sits firmly atop the
ribbon dome to align itself with the speaker. Thus the laser pointer will aim at the right angle directly
at the listening spot. Adjust the rake angle with the rear spike until the laser sits exactly at ear height."
Polar response or directivity pattern at 15dB scale
