Repairing realistic optimus 4s, a tweeter impedence question?

[Anonky]

Optimus 4s have a woofer two identical tweeters, each of the tweeters are 16 ohm. None of the tweets were working so I disconnected the tweets from crossover and none had continuity. Didn't appear to be a simple fix on any of them (broke tinsel lead, etc), so I've ordered replacement 8ohm 2 in paper cone tweeters as a drop in replacement but now that I'm thinking about it more, will the difference impedance of these tweeters (original 16ohm vs 8 ohm replacements) cause an issue? I'm relatively new at this and have not tackled modifying a crossover so hopefully I haven't accidentally signed myself up for that. Depending on what all I would need to modify, I think it's within my capability.

I'm also reading in other threads that if I only used one 8 ohm tweeter in each cabinet instead of two in each cabinet that might work. I'm not totally opposed to this idea if that is my only option without modifying the crossover. I like these speakers mostly for the novelty of them being able to double as stools in a sun room anyways, but I would like to preserve their "omnidirectional" aspect if possible. Any advice is appreciated.

 

[Binkman]

G'day..
If the two 16 ohms were wired in parallel that would be 8ohms. I don't know the X-over wiring but I guess one
8Ω tweet per cab would get you by. even so I don't think wiring the 8Ω tweets in series for 16Ω shouldn't be a load impedance issue, the woofer-mid will do most of the work. If the amp is rated for 4ohms then you can wire them in parallel. Assure correct speaker polarity.
((I can't find much online about alternative wiring though))

 

[Bill Ashton]

Trying to remember way back from the memory banks. Is the Optimus 4 a little small square cab with maybe the woofer firing down and cone tweeters on two sides? Sort of designed for corner placing with a cushion on top? Suspect the same cone tweeters used in many Radio Schaack Optimus speakers from that time, and most probably a "real" crossover network (RLC) and not just filter caps on the tweeters. I think you would need 16-ohm tweeters for this, if that is what came out.

Of course, I could be wrong, just cannot remember if I ever had one opened up...

 

[Anonky]

Trying to remember way back from the memory banks. Is the Optimus 4 a little small square cab with maybe the woofer firing down and cone tweeters on two sides? Sort of designed for corner placing with a cushion on top? Suspect the same cone tweeters used in many Radio Schaack Optimus speakers from that time, and most probably a "real" crossover network (RLC) and not just filter caps on the tweeters. I think you would need 16-ohm tweeters for this, if that is what came out.

Of course, I could be wrong, just cannot remember if I ever had one opened up...

I have it opened up at home and can send pics of the crossover later but yes that is the right speaker that you’re thinking of. I really want to replace both tweeters on each cabinet and have it fully functioning. I’m willing to dump money considering I got these for just $20. I don’t see any of these tweets on eBay at the moment so I may just replace one tweeter so it is still an 8ohm load and wait for someone who is selling them at a reasonable price.
Another question is about the speaker cabinet. It is labeled as 8 ohm. So what would that mean the woofer is? Also, is there a way for me to modify the crossover to accept 8 ohm replacement tweeters?

 

[Anonky]

G'day..
If the two 16 ohms were wired in parallel that would be 8ohms. I don't know the X-over wiring but I guess one
8Ω tweet per cab would get you by. even so I don't think wiring the 8Ω tweets in series for 16Ω shouldn't be a load impedance issue, the woofer-mid will do most of the work. If the amp is rated for 4ohms then you can wire them in parallel. Assure correct speaker polarity.
((I can't find much online about alternative wiring though))

These would be hooked up to a pioneer qx949 as rear two speakers in a quad setup, which would rarely get used anyways. From what I can tell this receiver accepts 4ohm yes? Another question, would this be a problem for the speaker crossovers?

 

[Binkman]

From what I can tell this receiver accepts 4ohm yes?

4, 8 and 16Ω
https://www.hifiengine.com/manual_library/pioneer/qx-949.shtml

 

[Anonky]

4, 8 and 16Ω
https://www.hifiengine.com/manual_library/pioneer/qx-949.shtml

So would the woofer impedance confound this plan of trying to wire both 8ohm tweeters in parallel? For example, if the woofer is 8 or 4 ohms would this still work in either scenario?

 

[Bill Ashton]

Personally, not sure I would muck with speaker impedance on an old receiver. Yes, it can "handle" a 4 ohm load, but a speaker's impedance is just an average of sorts, depending on the frequency. When you change the Op-4's tweeters to something other than original, what do you wind up with? Yeah math might give you an idea, but what do you really get? With such a complex receiver, not sure I would take the chance.

I do love the idea of the Op-4's as a rear channel pair. Probably better suited to that than the front or single pair as originally RS intended

 

[Binkman]

So would the woofer impedance confound this plan of trying to wire both 8ohm tweeters in parallel? For example, if the woofer is 8 or 4 ohms would this still work in either scenario?

With respect to @Bill Ashton 's post... he hits on variables that an amplifier "sees" a changing effect in higher volumes that would pressure an amp. in other words even a 4 ohm may present as low as a 2ohm load under amp stress but a lot of this is theory depending on continuous high volume output. (in a sun room? I would expect low vol. listening anyway if a lot of glass.)
Imo considering the amp of that era, mid 70's, I'd wire the tweets in series as the orig. spiders were 16Ω rated and that amp can handle 16Ω without stress. You might find that those two perform better than 4 cabs in the room being omni directional.
------------
Now... you haven't given any clue on the x-overs per service and I can't find any diagram on the net. pic might help... e.g. what blew the tweets in the first place?

 

[Anonky]

With respect to @Bill Ashton 's post... he hits on variables that an amplifier "sees" a changing effect in higher volumes that would pressure an amp. in other words even a 4 ohm may present as low as a 2ohm load under amp stress but a lot of this is theory depending on continuous high volume output. (in a sun room? I would expect low vol. listening anyway if a lot of glass.)
Imo considering the amp of that era, mid 70's, I'd wire the tweets in series as the orig. spiders were 16Ω rated and that amp can handle 16Ω without stress. You might find that those two perform better than 4 cabs in the room being omni directional.
------------
Now... you haven't given any clue on the x-overs per service and I can't find any diagram on the net. pic might help... e.g. what blew the tweets in the first place?

Here is a pic of the crossover. Not sure what to make of it. Perhaps y’all can educate me? As far as what happened to the tweeters—I’m not sure (as I’m not the original owner) but I would bet they were pushed too hard. I tested all four tweeters for continuity and they were all toast. Bought on fb marketplace for $20. I knew the woofers worked and this seemed like a cool little project since the cabinet were in otherwise great condition. Seems like it’s going to leave me frustrated for the time being as I would really like to preserve these being omnidirectional. However after looking at it more closely the woofer is also rated at 8 ohms which all in parallel would have the receiver seeing like 2.67 ohms by my calculations. I think I’m going to just throw in an 8 ohm tweeter in each cabinet on the side with the woofer, place a dead tweeter back in the other tweeter hole just to seal the cabinets and put this project on hold while they play as is in the sun room (yes, low volume listening). I’m going to keep my ear to the floor on eBay in search of some 16 ohm drop in replacements (ideally from realistic Optimus of a similar model). If anyone finds some realistic 16 ohm tweeters give me a ring!

 

[Anonky]

With respect to @Bill Ashton 's post... he hits on variables that an amplifier "sees" a changing effect in higher volumes that would pressure an amp. in other words even a 4 ohm may present as low as a 2ohm load under amp stress but a lot of this is theory depending on continuous high volume output. (in a sun room? I would expect low vol. listening anyway if a lot of glass.)
Imo considering the amp of that era, mid 70's, I'd wire the tweets in series as the orig. spiders were 16Ω rated and that amp can handle 16Ω without stress. You might find that those two perform better than 4 cabs in the room being omni directional.
------------
Now... you haven't given any clue on the x-overs per service and I can't find any diagram on the net. pic might help... e.g. what blew the tweets in the first place?

Would wiring the two 8ohm tweeters in series work with the 8 ohm woofer in this cabinet? What would that make the receiver “see?”

 

[Anonky]

With respect to @Bill Ashton 's post... he hits on variables that an amplifier "sees" a changing effect in higher volumes that would pressure an amp. in other words even a 4 ohm may present as low as a 2ohm load under amp stress but a lot of this is theory depending on continuous high volume output. (in a sun room? I would expect low vol. listening anyway if a lot of glass.)
Imo considering the amp of that era, mid 70's, I'd wire the tweets in series as the orig. spiders were 16Ω rated and that amp can handle 16Ω without stress. You might find that those two perform better than 4 cabs in the room being omni directional.
------------
Now... you haven't given any clue on the x-overs per service and I can't find any diagram on the net. pic might help... e.g. what blew the tweets in the first place?

So wiring the two 8ohm tweeters in series with the 8ohm woofer in parallel would put the amp “seeing” 5.33 ohms I think (see pic for calc). Correct me if this is wrong please. Considering I would be doing mostly low volume listening, this should be safe for a 4~16ohm amp? My only concern is now that I’m looking closer the specs for qx949 say 40wpc into 8 ohms for quad mode. So does it specifically need to be 8 ohms to use this function? Apologies for so many questions. Appreciate yall

 

[Binkman]

two 8ohm tweeters in series with the 8ohm woofer in parallel

(Add a Question mark...?)
I'm a bit confused.. How many woofs and tweets per cab? I grabbed a snippet off the net and shows two directional arrows? (with a single ea. + & - screw lead and one optional RCA connector.)
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In addition I'd like to see a diagram of the wire lead connects as the Yellow wire goes where? a tap off the woofer + terminal? and that goes thru the coil and out to the the cap... then blue + wires to which speaker leads? ....which it not shown.. as how the wiring to the orig tweets and woof are wired.
--------
snippet

 

[Anonky]

(Add a Question mark...?)
I'm a bit confused.. How many woofs and tweets per cab? I grabbed a snippet off the net and shows two directional arrows? (with a single ea. + & - screw lead and one optional RCA connector.)
------
In addition I'd like to see a diagram of the wire lead connects as the Yellow wire goes where? a tap off the woofer + terminal? and that goes thru the coil and out to the the cap... then blue + wires to which speaker leads? ....which it not shown.. as how the wiring to the orig tweets and woof are wired.
--------
snippet
View attachment 2403464

I’m away from my home for thanksgiving so I can’t send pictures at this time. Will do so late this upcoming weekend. But I’ll try to explain..
So they’re omnidirectional. The cabinets each have one side with one woofer + one tweeter. Then another side of the cabinet has another tweeter. So each cabinet has a total of one woofer and two identical tweeters (the tweeters are just on different faces of the cabinet). In the photo of the crossover, the blue wires are positive going to each tweeter respectively, and the black ones circled are the negative connection to the tweeters. The yellow wire goes to the woofer, but I can’t recall what the second woofer connection is. Again, if this isn’t helpful I will send more detailed pics this weekend.

 

[elnaldo]

The tweeter impedance shouldn't be an issue for the amplifier. It's not a resistor in parallel with the woofer. It has at least a capacitor in series, which has a very high impedance to low freqs (where the woofer has the lower impedance), and the woofer impedance at the tweeter freqs is very high. If in doubt, connect the 4 ohm tweeters (8 ohm in parallel), and do some impedance measurements. LIMP software can do that.

 

[Anonky]

The tweeter impedance shouldn't be an issue for the amplifier. It's not a resistor in parallel with the woofer. It has at least a capacitor in series, which has a very high impedance to low freqs (where the woofer has the lower impedance), and the woofer impedance at the tweeter freqs is very high. If in doubt, connect the 4 ohm tweeters (8 ohm in parallel), and do some impedance measurements. LIMP software can do that.

Sorry I just want to make sure I understand. Two 8 ohm replacement tweeters (in place of the original two 16 ohm tweeters) would probably work you think?

 

[Binkman]

The tweeter impedance shouldn't be an issue for the amplifier. It's not a resistor in parallel with the woofer. It has at least a capacitor in series, which has a very high impedance to low freqs (where the woofer has the lower impedance), and the woofer impedance at the tweeter freqs is very high. If in doubt, connect the 4 ohm tweeters (8 ohm in parallel), and do some impedance measurements. LIMP software can do that.

LOL I was going to page you.;.
above post #14 explains the wiring (less the woofer connect) the orig 16Ω tweets are wired at the xover in parallel. Q? is running this quad amp in quad mode (8Ω) with the tweets in parallel = 4Ω. Assuming the other 2 speakers, in quad, are 8ohm.
It has been suggested and OP might just wire up one tweet. perhaps find some 16ohm spiders? or another set of tweets.

 

[elnaldo]

Sorry I just want to make sure I understand. Two 8 ohm replacement tweeters (in place of the original two 16 ohm tweeters) would probably work you think?

They will work, but they6 will be probably too loud. I'd connect them in series as a 1st try, and with a smaller capacitor. 30uF is not giving too much protection or "crossover" . check the crossover freq with any online calculator. 30uF and 8 ohm load (2 x 16ohm in parallel) gives less than 800Hz crossover point. I doubt those tiny tweeters can go that low without getting damaged.

 

[Binkman]

They will work, but they6 will be probably too loud. I'd connect them in series as a 1st try, and with a smaller capacitor. 30uF

I didn't consider the loudness but I did state above to hook them in series (didn't consider the cap value either as I couldn't see the printing)

 

[Anonky]

I didn't consider the loudness but I did state above to hook them in series (didn't consider the cap value either as I couldn't see the printing)

Honestly the more I see I am feeling better about just replacing one tweeter in each cabinet with the 8 ohm replacement and looking for 4 original 16 ohm replacements as they come available. Anything else seems like a bear to make work