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Jensen Mystery Speakers

ronrico said:
John, I hope they sold lots of these to re-coup the cost of the back panel.
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I learned a lot about marketing back then. In a brochure you could explain things like the rear tweeter but in a dealer's showroom it was a complete waste. No one could see it. I read a story about how JBL designed the waffle grille simply so that it would stand out in a long line of competitive speakers at a dealer. The bright colors probably helped too against the mostly dark brown and black of everyone else.
 
I found an old original crossover print. Here is a copy. I just noticed from the drawing that the protective tweeter relay did not kill the signal but just attenuated it.
 

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Thanks John. Any and all info/history on these is appreciated as I was unable to find even the first mention in my google search.
 
Wow,this is a great thread! Congratulations on an interesting pair of Jensens. For the record, I have a pair of two-way Frazier Monte Carlo A speakers. The piezo tweeters naturally roll off the low frequencies and the bass drivers roll naturally roll off the high frequencies. The drivers are designed and matched to naturally cross over with no passive components whatsoever.
 
Here is the four page brochure. I have now emptied my brain of everything I remembered from 31 years ago. Remember when you read this that the Thiele-Small filter simulation modeling had just "hit the streets" and all the manufacturers were really using it for speaker design (EV with the Sentry series comes to mind). I actually spent most of my time, besides being an engineering manager, writing computer modeling software.

Note in the brochure the reference to Jim Novak. He was my boss and Fellow in the Audio Engineering Society. He wrote many papers on LF horn design in the 50s and 60s and was really a giant in his profession.

Unfortunately for me, high end car stereo really exploded in the late 70's (because of Jensen) and home audio became a stepchild.

John
 

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Good caps

ronrico said:
Here's a shot of the x-over, massive 8"X10". I imagine the caps will need replacing.
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Those are actually really good caps. The only other place I saw them was in Altec gear. I have a pair from an Altec that have held spec for 40 years...

If you do change them send me the old ones! And maybe only change them one at a time to be sure you're not changing the sound too much.
 
4343 said:
Those are actually really good caps. The only other place I saw them was in Altec gear. I have a pair from an Altec that have held spec for 40 years...

If you do change them send me the old ones! And maybe only change them one at a time to be sure you're not changing the sound too much.
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I was thinking the same thing. If it ain't broke don't fix it.
 
John, thanks for the catalog pages. I did a google search for Jensen System B and there was a fair amount of info, "Jensen Studio Monitor Model B" produced nothing. What was your role in the design of the System B John?
 
I have an MSEE from Illinois/Urbana with my thesis dealing with acoustical measurements. For most of the three years there (77-80) I was Manager of Acoustical Development dealing with both car and home speakers. There were three engineers and two technicians under me but I spent more than half my time writing computer software for Thiele-Small analysis and synthesis as well as test equipment software to run automated response curves. The T-S software was written for a Tektronix 4051 Motorola 6800 based computer having a storage tube display (no video memory required). This was about four years before the IBM PC. Instrumentation was done using the IEEE488 bus. The last year I was there, the company divided engineering into separate car and home departments and brought in a new home audio VP. He was an as*hole plus home audio was shrinking fast. The company was going up like a rocket because of their new car receivers. Luckily, I had just completed my MBA and left to go into technical product management. Ironically, they fired the new VP three months after I left. I would have loved to go into product management at Jensen but those jobs seemed to go to former audio store managers or audio manufacturers reps with sales experience. That was the last I ever dealt with audio on a professional basis. :tears:
 
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I got a tremendous pay increase when I left Jensen; 25K > 33K in 1980 but to be honest, I loved audio then and I love audio now. EV was in the middle of nowhere in SW Michigan as was Peavey in MS and I didn't want to bother looking at companies such as JBL in the LA metro area. I actually remember more about audio and acoustics than all the other projects I've been involved with. Unfortunately, my ears are shot due to heredity. All of the equipment you see listed under my name was probably sublimely bought because of my unobtainable equipment list back in the late 70's. I retired last year at 63 because of the job market.

You have to give me year very background (including yourage) so I can see who I am talking to.

John
 
Jensen B speaker system

I don't know if you already found this, but here it goes:

5 way
12" woofer
6" lower midrange
1 1/4" upper mid
1" tweeter
2" rear firing tweeter
Freq Resp. 37-21,000 Hz +2 dB/-4 dB
Crossovers at: 49/300/2000/8000 Hz
Recomended Input 9-150 watts
Sensitivity 90 dB 1 watt/meter
8 ohm nominal
Dark walnut on tilting wood grain base
33 3/4" H x 16 1/2 W x 11 3/4 D
$550 list (1980)
 
John L,

Excellent information. I recently acquired a pair of the "little sister" Jensen Monitor C (looks like a System C but is labeled "Monitor C"):

Jensen Monitor C

I presume that similar design was applied to this lowly sibling, since they appear to be very well constructed and reveal a lot of design thought. The model I have includes a very similar crossover with plenty of inductor for each driver, the typical R/C networks, and L pads for upper tuning.

I refoamed the surrounds just yesterday and after a few more hours of glue cure I intend to test the drivers down to 10Hz for excursion and compliance. The previous owner mistakenly thought that someone had pushed the dust caps inward, since very few drivers used the "inverted dome" dust cap design. That worked in my favor to lower the price even more. I have a total of $70 in them with new foam surrounds and the assortment pack of plastic shims I got to keep the coil centered for re-gluing.

I am impressed with the quality of something that many people disregard, as they seem to be as well made as my older Model 4 Jensens and likely have the results of experience acquired since the 4s were made.
 
hardrock94 said:
Heres a thread I found from 09 about these; Jensen System B

http://www.audiokarma.org/forums/showthread.php?t=213023
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They are complete and total JUNK... As a favor to you, I will let you send them to me, along with any other System B or C's you find :D


Refoam them carefully (order the correct foam, dont use a generic)

Unless you see one that looks bad, dont bother with the caps, unless you REALLY want to go into it. They are a rare type of film cap and mostly overkill in quality.

All I had to do was repair a couple popped solder points, refoam, and enjoy.


The advice about the screws is dead on, be careful, and patient. the molded foam/plastic is fragile.


I have toyed with relaminating them and swapping out the connectors which in my opinion seem like the one area that didnt jive with the rest. Simple small wire connectors on a pair of speakers attempting to compete at the very top of the consumer market.

Regardless, refoam them, check the board for popped solder points as that was the only problem my xovers had, and enjoy.

And if you hate 'em.. By all means, I'll pay the shipping :yes:
 
Hi all,
I am new member and very great to read this topic.
I am using this speaker with Revox A78 MKII amp. and Studer D732 CD.
Could you please suggest me the solution for better.
Thanks and best regards,
 
I picked up a pair of these Jensen's yesterday at a resale shop for 10.00 each. They are all intact and need nothing repair-wise. Hooked them up and "damn" they sound pretty good. They weigh about 56 pounds each and are very well made. Any one know the current value of these vintage speakers?
 
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