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Just acquired a nice pair of these Trusonic 3-ways, model JR 2ooM and I'm wondering about efficiency / sensitivity ratings.
The old labels on the back of the cabs says 5ow program, 1oow peak, but that's not too helpful. I'd take that to mean something along the lines of a rating that means Rms +/- 25w.
But max allowable watt rating isn't really what I want to know. These seem pretty efficient for all their 3-way complexity, but I want to know how little I can get away with in an amp. Anyone have an idea ?
Were early (60s-7os) three-ways simpler to drive ?
Thanks!
Follow Ups:
Utah purchased the Stephens Trusonic namesake and dropped the Stephens part.
I've seen/heard them (thought they were JBL L100's @ first glance), but don't recall what gear/amps they were used with.
I'm guessing that going by the Altec and JBL designs that Stephens speakers were VERY akin to, the sensitivity would be in the 95-100 db for 1 watt area.
Wow, that would be cool if so; I was hoping they would be maybe 92 dBw. (And thus thinking maybe pushpull El34, ala dynaco, or similar...)
But upwards of 95 would let me use 3ooB or similar, SE.
Shrugging my shoulders here, I guess the orthodoxy about three-way-xover (being inefficient) doesn't always hold true if the 95-and-up-dBw figure is right ....
Fact is right now I'm listening on the 2.5 rms watts out of a B&O Beosystem boombox thing, and there is plenty of loud going on....
If you're matching them with a tube amp, efficiency is less an issue than the impedance curve. Ideally you're looking something that stays above 4 ohms and is fairly stable. I'm guessing they'd be somewhat friendly, but as I've said, that's only a guess.
I forgot to add that Tom may have some insight in regard to impedance of this design if it's a knock off of JBL,etc.
Yep, the other part of efficiency. 8 ohm is specified, but as you point out it's the full response curve not the nominal rating.
As mentioned, I'm temp-powering this with a B+O boombox that supplies a known 2.5 wrms to a four ohm tap, and no shortage of spl., so...
(I have a hard time believing the B+O has got all that much grunt, so it would seem that the Stephens/Tru are pretty efficient.)
This wknd I'll try my (kt88) tube amp from another system and that one gives a switchable 5w 'triode' or 8w ultralinear, so I can probably make better guesses then.
The triode-wired-pentode version of that one definitely wilts under a tough load, and really needs maybe 98 dBw to do its work, so that will be a good test. Fairly certain about the UL configuration working well, though, since that seems to drive anything north of 90 dBw.
I think you'll be fine. Most solid state receivers back in that era weren't keen on sub 4 ohm loads either, yet people drove speakers similar to yours for hours at high volumes with the average Pioneer or Sansui.
Above is the Stephens brochure for the model E3 (also a 3 way). You can see they did not offer any efficiency information. They will not need more than 10 watts or so.
Enjoy.
Idler
That speaker is *loaded* with cool design touches and forward thinking engineering. If you don't mind my asking, how much didja pay for 'em? No matter what, you have some very cool speakers, good on ya!
-CD-
Thanks
Only wish these were mine. I'm happy with my Vals.
Another Cool Stephens in-wall installation attached.
Idler
Thanks, that's more than I found.
Is it generally the case that the older 3-way speaker (anybody's) had to be more efficient than the recent/ current versions ?
I'm only guessing this insofar as a Sixties amp wasn't going to be hundreds of watts and able to drive an 84 db/w sort of speaker.
(Looking for a rule of thumb that says the further you get --in speaker timeline-- back toward low-power amps, the higher the efficiency the speakers are likely to be... )
And I'd much rather drive these spkrs with something like an El34 tube amp than start looking for a solidstate alternative.
If it were a 2-way, I'd guess mid-90s due to the tweeter, but since we don't know the drivers for the other two, it's hard to say.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
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