Realistic Optimus 1B

Was donated a pair of these today, Crossover attached
The woofer (2519Aa Japan) looked promising with a low Fs & Qt, parameters:
Fs 20.75; Re 7; Qe .38; Qm 5.53; Qt .35; Vas 142.38; Sd 314; Le .84; eff 87.6
did some sims, Woofer looks good in 60L (Optimus oix is 38L), tuned to 22Hz
all this fun & I haven't listened to them yet....

The Big Q: Do I restore them to original, or 'improve' them to my own taste....???????

Bugger, just realised I left the tweeter switch out of the xover diagram, give me a few minuets....


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I just love investigating old speakers like these.

A pair of Optimus 1Bs cost $90 in 1975.

That's equivalent to $430 today!

Note: They are mid/tweeters, not simply tweeters.


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FWIW, the original 'Contex' 15uF bipolars measured 17.3 & 16.4, not bad for ~50 years in the saddle.
Q&D RTA plot attached (taken in a small & cluttered room)
How do they sound? - Very well balanced, to my ear anyway, good on Jazz, and a surprising amount of solid lows on Rock, punchy kick drum. Don't know that they'd handle a lot of volume, but good medium-loud


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All I know is I wouldn't want to have my highs emanating from two drivers spaced this far apart - concepts like these disappeared for a reason after the 1970s. The peculiar ring around them presumably mitigates the effects of no flush mounting, but it also puts them pretty far apart. And why is the baffle so far recessed inside the cabinet?

EDIT: Highs +8/-10 dB? Oh my. Wouldn't be surprised if this changed a lot with vertical angle angle.

Honestly, this concept as designed is so far removed from modern standards of sound reproduction that I wouldn't want to simply restore these, assuming you actually want to listen to them on a regular basis.

Maybe find a suitable midrange and relegate one mid-tweeter to tweeter duties, assuming it's suitable for that? Do some impedance transformation with the crossover if needed.
Plan B, use mid-tweeters for midrange only and find a tweeter to go with them, it's not like there isn't any space left on the baffle.
Plan C, butcher the baffle and find good mids and highs to go with the existing woofer. (Maybe even a compression driver / horn affair? Seems wrong for an insensitive woofer like that though.)
Plan D, use the woofers for something else entirely (sub?) and come up with an all-new interior for the Realistics. (Pioneer sold relatively sensitive all-cone 3-way jobs for a long time, maybe find a set with 10" woofers but trashed cabinets?)

It would be pretty neat to turn these into a "sleeper" speaker - keep the neat veneered cabinet, keep the grille at least looking authentic, but bring the acoustic performance (mostly) up to modern standards, maybe even with a waveguide for the tweeter and all that good stuff. Seeing how you can't afford much in terms of XO losses with the woofer, possibly a candidate for activation as well?

That's some seriously low tuning and seriously low Q on those woofers. They look more like something for a sub assuming the Xlin is there. (Any estimates on power handling? I can't imagine they'll go super loud, maybe 100-105 dB assuming 20-60 W?) While this is not really a CB driver, I would consider whether potential speaker placement is actually suitable for a BR - would you put these on stands, far away from any solid surfaces, or alternatively, is the room sucking up bass like crazy?
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diyAudio Member
Joined 2007
If that is the little Fostex cone I rather liked it in past resurrections. I can think of several ways to "improve" them by adding in a supertweeter and some extra stuffing but for the time they were pretty good for most peoples listening. I have picked up several similar boxes over the years to play with. Usually pay about $30-
Willing to wager they sound better than the 3" plastic boxes most kids listen to these days
re:' I wouldn't want to have my highs emanating from two drivers spaced this far apart' - actually they don't sound as bad as you might think,
however, I second Dave's opinion, the woofer is the strength of these speakers. I think I'll restore the cabs & use them as a closed .5 way woofer & stands for a 2 way on top, they're just the right height.
Unfortunately need a box about twice as big to make porting worthwhile, & they sound OK as is.
Re:'little Fostex cone' - I don't think so, the numbering doesn't match other Foster drivers I've seen, but I haven't seen many... But I do have one really good pair which I've done exactly that, added a Piezo supertweeter & 6" woofer - and use them for mixing music....
Thanks for the offer Moondog, but I'm a bit over committed with projects at the moment, retired a few weeks ago & making up for lost time....:)
The Tweeter - Fs is 533 Hz, Re is 14 ohms, Le is .08mH. some pics attached, including a Foster to compare, typeface looks similar, bad shot of the impedance graph, which on the rough side (both the photo & the plot)


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diyAudio Member
Joined 2007
Magnet looks a lot smaller than in the 8R units I am familiar with; I guess there were many iterations of the unit over the decades. Supertweeters are there if you ever want them, stupid me could not resist the clearance bargain for a buy of 10 and I have a couple of pairs left
Refurbed these:
Replaced Foster mid/tweeters with a Dayton PS95
Replaced the nasty Fibreglass with Polyester from an old pillow
Too tightarsed to spend $60 on inductors, so running the woofer full range - xover ATM is a single cap
(annoyingly I have the right sized inductors, but AWG is too fine, would loose 3 precious dB if I used them)
Unsurprisingly, they have a somewhat forward sound, I'll need to put a small resistor in front of the PS95 at a minimum


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Optimus 1B mods

Read your comments, thanks!

Bought a pair and made some mods.
Most significant was replacing the cap with an Obbligato Gold.
I like these speakers for the human voice.

The images aren't pinpoint like mini-monitors can do but big, more like
electrostats. Is this due to the arrangement of the two tweeters? Line array?

Also, I put these speakers on stands where when seated my ears are at the same height as the area between the woofer and the lower of the two tweeters.

No crossover elements on the woofer is fairly unique?
I only know of the Dynaco speakers that do this but they aren't acoustic suspension.

Also, later, replaced inductor with Jantzen wax coil and put felt strips around tweeters and on cabinet protrusion but only small improvement in focus
due to these changes.
Diffraction Doesn't Have to be a Problem

Used the crossover calculator,

2-Way Crossover Calculator / Designer
with tweeter = woofer = 8 ohm , frequency = 1326 and type = 2nd order Chebychev Q=1, but I am not a speaker designer so are these correct?
Founder of XSA-Labs
Joined 2012
Paid Member
I had a pair of these as a kid (found them used for a song) and had them until they were stolen when my house was broken in and robbed in broad daylight (in Southern California, crime like this was rampant). The cabinet had a nice walnut veneer. They sounded ok but I recall the acoustic suspension made the bass rather limited. I recall they were heavily stuffed with fiberglass. The two mid tweets had their own plastic cylindrical rear chambers also stuffed with fiberglass. That was many years ago and I never knew they were model 1B’s - I remember the made in Japan designation.
Or maybe the Optimus 5B ?

Its good you were not in the house when the robbers came in

Maybe you would have preferred the Optimus 5B speakers since they use a 12 inch woofer rather than the 10 on the Optimus 1B speakers.

You raise the critical question though that, "the acoustic suspension made the bass rather limited" and I used to believe this was true of all acoustic suspension speakers.

Stock, I did not like the 1Bs but changing the cap is important.

But there is something to the 1Bs that I find interesting. I particularly like how it presents the human voice. On the bass, I have heard a lot of bad bass reflex speakers. Lots of bass but not accurate bass. The 1Bs have better bass if not enough.