Wow! Just got through re-working a pair of University Senior II speakers... circa about 1963 or so, if IIRC what the owner told me (he bought them new!). 12" 3-way, with accordion-surround 12" woofer, 4" paper-edge cone midrange, and 3/4" phenolic dome semi-horn-loaded tweeter. Cabinets are classic "large bookshelf" size... almost dimension-for-dimension match for the JBL L100, to give a point of reference...
Hooked them up at first... was somewhat non-plussed. Highs were dull, but hissy. Like a peak between 5KHz-10KHz, and a rolloff above that.
Well, first thought- tired cap. Went inside... sure enough, the date code on the caps was from 1947 (!). Replaced those post-haste.
A little better then... still kind of hissy and sibilant. Time for more thought...
After consideration, it looks like these were decent drivers... crippled by a ridiculously primitive crossover. The woofer is OK- a single coil (first order... the woofer behaves well, so this is just fine). HOWEVER- the midrange AND tweeter are on a SINGLE cap and L-pad... in parallel. This results in the tweeter getting MUCH too much low-end... apparently, near its resonance, which was what made for the hissy, shrill sound.
Separated them... left the midrange on the L-pad (with a smaller cap- 2uf as opposed to the 4uf originally equipped- since I was doubling the impedance, by NOT having the tweeter on the same circuit). Gave the tweeter its own cap... after experimentation, a .68uf, with NO padding needed (i.e, the tweeter and cap wired directly to the input terminals), was the best choice... good top-end, and all the nasties on the bottom of the tweeter, GONE.
Buttoned them up... since the owner has a newly-restored Scott LK-72B (which I restored, about a month ago), I hooked them up to the Scott 208 power amp, we have here at the shop (belongs to Pete, the store owner)... which I had also just restored...
WHOA NELLY. These things sound REALLY good. Sure, they're not ruler flat... a little rolled-off in the upper highs, even afterwards (but not "dead" sounding by any means!), a bit of a small dip in the mids (think BBC dip, only smaller)... but BOY, are these things EASY to listen to. Darn decent dynamics. They do need some power (the 40w/ch or so from the Scott is enough, though- they'll get quite loud)... and if you seriously crank on them, you can hear the woofer start to over-excurt on the deepest notes (they're aperiodic damped sealed- a port with rolled-up fiberglass inside, from the factory)... but only after you start to feel the FLOOR SHAKE a bit. That said, I LIKE these. Once you get the midrange L-pad set properly (around 2/3 the way up, IIRC), they just "come together"... really coherent.
Pleasant surprise, overall. If you find a pair cheap somewhere, I wouldn't hesitate to snag 'em... after the simple mod I described above, I think most people would be seriously impressed...
Regards,
Gordon.
Hooked them up at first... was somewhat non-plussed. Highs were dull, but hissy. Like a peak between 5KHz-10KHz, and a rolloff above that.
Well, first thought- tired cap. Went inside... sure enough, the date code on the caps was from 1947 (!). Replaced those post-haste.
A little better then... still kind of hissy and sibilant. Time for more thought...
After consideration, it looks like these were decent drivers... crippled by a ridiculously primitive crossover. The woofer is OK- a single coil (first order... the woofer behaves well, so this is just fine). HOWEVER- the midrange AND tweeter are on a SINGLE cap and L-pad... in parallel. This results in the tweeter getting MUCH too much low-end... apparently, near its resonance, which was what made for the hissy, shrill sound.
Separated them... left the midrange on the L-pad (with a smaller cap- 2uf as opposed to the 4uf originally equipped- since I was doubling the impedance, by NOT having the tweeter on the same circuit). Gave the tweeter its own cap... after experimentation, a .68uf, with NO padding needed (i.e, the tweeter and cap wired directly to the input terminals), was the best choice... good top-end, and all the nasties on the bottom of the tweeter, GONE.
Buttoned them up... since the owner has a newly-restored Scott LK-72B (which I restored, about a month ago), I hooked them up to the Scott 208 power amp, we have here at the shop (belongs to Pete, the store owner)... which I had also just restored...
WHOA NELLY. These things sound REALLY good. Sure, they're not ruler flat... a little rolled-off in the upper highs, even afterwards (but not "dead" sounding by any means!), a bit of a small dip in the mids (think BBC dip, only smaller)... but BOY, are these things EASY to listen to. Darn decent dynamics. They do need some power (the 40w/ch or so from the Scott is enough, though- they'll get quite loud)... and if you seriously crank on them, you can hear the woofer start to over-excurt on the deepest notes (they're aperiodic damped sealed- a port with rolled-up fiberglass inside, from the factory)... but only after you start to feel the FLOOR SHAKE a bit. That said, I LIKE these. Once you get the midrange L-pad set properly (around 2/3 the way up, IIRC), they just "come together"... really coherent.
Pleasant surprise, overall. If you find a pair cheap somewhere, I wouldn't hesitate to snag 'em... after the simple mod I described above, I think most people would be seriously impressed...
Regards,
Gordon.
