Loudspeaker Designs and Articles for the DIY Enthusiast
While every attempt was made to keep the crossovers between the Sten II and the Sten I as similar as possible, some crossover changes were required due
to the differences in impedance and sensitivity. While I could get away with using raw measurements from the Stens to model the new crossover, the
crossover was designed from scratch.
The two woofers are connected in parallel for the sensitivity gain, and best resembles a low Q transfer function with a broad knee initially, but transitions into
a roll off between 3rd and 4th order. I found a topology with a simple two component 2nd order electrical filter was sufficient. The crossover frequency
models around 3kHz.
The tweeter also uses a simple 2nd order electrical filter to and a low Q broad knee, but ultimately becomes a 4th order acoustic response below 2kHz.
The low Q filter designs, result in initial transfer functions that resembles 1st order. But unlike a true 1st order design, are crossed in phase, rather than
phase quadrature, and exhibit a broad deep null around 3kHz when the tweeter polarity is reversed. To say that I chose these transfer functions after
considerable investigation, might make good copy, but would be far from accurate. In truth the drivers themselves suggested what they wanted during the
modeling process. -Insisted in fact, and who am I to argue? What I did insist on was the two designs were voiced as closely as possible, which the drivers
seemed to have allowed me to do...
Tips and Tricks:
As noted in the Cabinet construction section, I
made the crossover board out of 1/4" perf
board, cutting it slightly wider then the internal
dimension of the cabinet. I then placed it over
the internal side braces and tapped it into a
tight mechanical fit, for additional side panel
For Tube Amplification Affectionarios:
As in the Stentorians, an impedance
normalization LCR network can be added to
flatten the 900 Hz peak, keeping the
impedance between 3.5 and 7.5 ohms over
the entire bandwidth with the exception of the
60 Hz box resonance.
This circuit will significantly reduce the
impedance peak, which may make the
speakers a bit too forward with higher source
impedance amplifiers. See the measurements
page for an impedance plot showing the
effects of these optional circuits. Because of
the series resistance, the DCR of L0021 is of
no consequence. Use a 20 gauge here. A
NPE cap is fine for C0021. You might want to
parallel smaller value NPE's to keep the ECR
Click here or on the crossover layout or
network schematics for larger drawings.
|Big sound for a very small
price. Suggested for
bookshelf or near-wall /