Crossover question

RxDx · Apr 14, 2015

I'm digging around in some old Stromberg-Carlson speakers, and this is what I find under some tape around a cap. Can I, say, gently heat the wax and slide the coil off so I can replace the cap? Is the cap part of the effective value of the coil in the circuit? I've never seen anything like this.

rmeade · Apr 14, 2015

I suspect that the coil (an inductor) and capacitor are wired in series (not unusual in crossover design) and are therefore integral components. I can't tell by the picture. So perhaps you could replace the existing pair with a new one (just not installed on top of one another like this).

I know that JBL packages an inductor and capacitor together in a tube like structure in the L100; I wonder if this is what is inside.

toxcrusadr · Apr 14, 2015

I've seen something similar in antique radios but with a wirewound resistor over a cap.

Check the coil for DC resistance. It should be very low. If it's not, it might be a resistor, but my money's on inductor.

In which case you could do exactly as you propose. In fact radio restorers often melt and slide out the contents of an old cap and stuff the new cap into the old sleeve to preserve the appearance.

One thing I don't know is whether the two together actually interact somehow. It does not seem like a good idea, sonically.

RxDx · Apr 14, 2015

Here's a better shot. The coil and cap are connected on the right end, but not on the left.

Retrovert · Apr 15, 2015

RxDx said:
I'm digging around in some old Stromberg-Carlson speakers, and this is what I find under some tape around a cap. Can I, say, gently heat the wax and slide the coil off so I can replace the cap? Is the cap part of the effective value of the coil in the circuit? I've never seen anything like this.

I think your entry wins the bizarre crossover design contest.

If the cap is metal than it alters the value of the inductor, just as a metal slug would. Remember, air core inductors need a lot more turns of wire than metal core ones. I'd suggest measuring the inductor before you remove the cap.

You might need to just leave that assembly alone and put the new cap in parallel.

woodj · Apr 15, 2015

Intriguing design. Question would be does the coil alter the capacitance?

Retrovert · Apr 15, 2015

woodj said:
Intriguing design. Question would be does the coil alter the capacitance?

Eh. Not significantly. This phenomenon is called "self-capacitance", "parasitic capacitance", "stray capacitance", or "miller capacitance", depending upon where it shows up. Further reading:
en.wikipedia.org/wiki/Parasitic_capacitance

The short answer is no, not to any extent that actually matters.

This tweak appears intended to up the inductance a shade for free, and I can't believe it does all that much as the amount of metal in that cap case is small. Having said that, before I used a suspect and corner-cutting design like this I'd just measure the speaker performance and put in a proper crossover with components not doing double duty.

toxcrusadr · Apr 15, 2015

I think it's a cost saving measure. Cuts production time to handle and mount one component instead of two, and all that.

Not surprising the two are connected at one end and not the other. Signal goes in the joined end, treble comes out of the cap and bass out of the inductor. It's a first order crossover all in one package.

Zonker92 · Apr 15, 2015

woodj said:
does the coil alter the capacitance?

Scroll down toward the bottom of this page for some empirical data on the related / inverse issue of inductance:

http://www.troelsgravesen.dk/coils.htm

I like to use a propane torch or stove burner to heat a think flexible steel putty knife, to melt wax or hot glue when removing crossover bits.

Retrovert · Apr 15, 2015

toxcrusadr said:
I think it's a cost saving measure. Cuts production time to handle and mount one component instead of two, and all that.

Not surprising the two are connected at one end and not the other. Signal goes in the joined end, treble comes out of the cap and bass out of the inductor. It's a first order crossover all in one package.

Ahhhh, yes, that makes significantly more sense than saving a few turns of wire. Except there's assembly time for that coil/cap combo, so how much savings is really present?

In any event, I would still replace it with a better laid out unit. Nothing sacrosanct about these parts...

RxDx · Apr 15, 2015

Retrovert said:
Ahhhh, yes, that makes significantly more sense than saving a few turns of wire. Except there's assembly time for that coil/cap combo, so how much savings is really present?

In any event, I would still replace it with a better laid out unit. Nothing sacrosanct about these parts...

These are a strange mixture. It's over-engineered- aluminum cups for both small drivers and all the pieces for the grilles, for instance. OTOH, someone on the assembly line poked two holes in the midrange cup, stapling the cabinet together.

The cabinets, aside from the plywood face, are a flimsy pressed wood 'product'. But the woofer looks substantial. If it doesn't perform (I'm testing one of them in a different cabinet), there's no reason to keep messing with this. They were only $5 each. If the woofer is worth keeping, I'll look at the crossover.

Retrovert · Apr 15, 2015

RxDx said:
These are a strange mixture. It's over-engineered- aluminum cups for both small drivers and all the pieces for the grilles, for instance. OTOH, someone on the assembly line poked two holes in the midrange cup, stapling the cabinet together.

Oh, that is too bad because it's a nice mid. The assembler just damaged the aluminum, right? Not the cone?

RxDx said:
The cabinets, aside from the plywood face, are a flimsy pressed wood 'product'. But the woofer looks substantial. If it doesn't perform (I'm testing one of them in a different cabinet), there's no reason to keep messing with this. They were only $5 each. If the woofer is worth keeping, I'll look at the crossover.

I have a single one of those cabinets that I bought. 12" woofer, 6" mid, and a tweeter. Tossed that compressed cardboard—"wood product" is being generous—as it was mildewed, slimy, and disintegrating. Bleh. The seller had thrown out the other speaker because the cabinet was falling apart. Annoying, because the drivers were probably fine.

Stromberg-Carlson drivers are very nice, though. I have an S-C bookshelf (acoustical labyrinth) that I also found at an estate sale. It sold cabinets separately from speakers, and the idea was to put a midrange in as a full-range driver. Which actually works. Nice for the size, and the bass is impressive for a 6", but it really needs tweeters as it sounds muddy without them. The cab has space for them, but covers the hole with a small piece of plywood.

The woofer I was going to try as an open baffle experiment if I ever found another one.

I still have the crossovers (only the one, though, as I only had one speaker) somewhere in a box, but I forgot what it looked like. If you need the inductor from it, let me know, and I'll try to find it. I was going to build my own since I didn't trust the rest of the circuitry, even recapped.

Let me know how yours sound so I know if I should continue on my quest for another one.

RxDx · Apr 15, 2015

Retrovert said:
Oh, that is too bad because it's a nice mid. The assembler just damaged the aluminum, right? Not the cone?

I have a single one of those cabinets that I bought. 12" woofer, 6" mid, and a tweeter. Tossed that compressed cardboard—"wood product" is being generous—as it was mildewed, slimy, and disintegrating. Bleh. The seller had thrown out the other speaker because the cabinet was falling apart. Annoying, because the drivers were probably fine.

Stromberg-Carlson drivers are very nice, though. I have an S-C bookshelf (acoustical labyrinth) that I also found at an estate sale. It sold cabinets separately from speakers, and the idea was to put a midrange in as a full-range driver. Which actually works. Nice for the size, and the bass is impressive for a 6", but it really needs tweeters as it sounds muddy without them. The cab has space for them, but covers the hole with a small piece of plywood.

The woofer I was going to try as an open baffle experiment if I ever found another one.

I still have the crossovers (only the one, though, as I only had one speaker) somewhere in a box, but I forgot what it looked like. If you need the inductor from it, let me know, and I'll try to find it. I was going to build my own since I didn't trust the rest of the circuitry, even recapped.

Let me know how yours sound so I know if I should continue on my quest for another one.

Yes, just the aluminum was punched, the mid was not touched.

There are some nicely-engineered aspects to this. These cabinets fit in consoles or separate finished boxes of various designs and finishes. Audiophool has the 411 on things S-C. It's like vintage JBL; there were two or three levels of drivers. The speakers I have are the RS-406, which had the middle price woofer (RW-489) and the expensive mid (RM-485) and tweeter (RT-477). The next year, the components were clearly lesser beasts, and a year or so after that, S-C disappeared as a consumer electronic company, best I can tell.

I will post results right here.

Retrovert · Apr 15, 2015

RxDx said:
There are some nicely-engineered aspects to this. These cabinets fit in consoles or separate finished boxes of various designs and finishes. Audiophool has the 411 on things S-C. It's like vintage JBL; there were two or three levels of drivers. The speakers I have are the RS-406, which had the middle price woofer (RW-489) and the expensive mid (RM-485) and tweeter (RT-477). The next year, the components were clearly lesser beasts, and a year or so after that, S-C disappeared as a consumer electronic company, best I can tell.

Yes, Tom's Website for Stromberg-Carlson info is great, and I've read much of the info there. Amazing that things like this used to be made in the USA, isn't it?

That's the same speaker I have, well, without the box, of course. S-C sold a LOT of these, but most did not survive, being used in consoles which were mostly junked when everyone moved to components.

General Dynamics bought S-C in 1966 and ran the audio division until 1961. All it wanted was the military side and the telephone switches. The speakers you have were all made in the 1950s. Nice big alnicos.

RxDx · Apr 16, 2015

Well, these don't have the compliance to work well in a sealed box. Your open baffle idea might work better. Bass is weak, but solid down to about 35 hz, then it drops off pretty quickly. Advertising material says something about going to 18, and the cone moves, but there's no real sound.

They'll take more power than the AR3as, though, without breaking up. The Onkyo amp said they were handling 200 watts of power at 33 hz. I stopped there

Sam Cogley · Apr 16, 2015

1) that big-magnet Slimline woofer is very nice.
2) Stromberg-Carlson built those as inner cabinets. They could either be dropped into a console or separate speaker cabinets. Made it easy to pivot their production lines to adapt to any changes in furniture styles, and provided better performance and isolation than most console designs.

RxDx · Apr 16, 2015

Sam Cogley said:
1) that big-magnet Slimline woofer is very nice.

Yes, it is. I'm attempting to determine how nice. It's winning the contest at the moment. I haven't found an enclosure it really likes yet. Perhaps ported, 'cause the factory box didn't do much, and sealed didn't either.

2) Stromberg-Carlson built those as inner cabinets. They could either be dropped into a console or separate speaker cabinets. Made it easy to pivot their production lines to adapt to any changes in furniture styles, and provided better performance and isolation than most console designs.

Yes, I actually have a third 12" speaker system, the RS-506, with one of the finished boxes. The '406s were from a console that was long gone by the time I got these at a yard sale. The '506 was the middle channel. It has a woofer with the small magnet and I think was part of their last consumer audio effort.

Retrovert · Apr 16, 2015

RxDx said:
Well, these don't have the compliance to work well in a sealed box. Your open baffle idea might work better. Bass is weak, but solid down to about 35 hz, then it drops off pretty quickly. Advertising material says something about going to 18, and the cone moves, but there's no real sound.

I suspect that if you want to use them in a cabinet you'll need either a standard bass reflex, acoustical labyrinth, or Karlson to make them really sing.

I wondered about that rolloff, which I hadn't yet tested on mine.

You know what the open baffle proponents say: If you aren't listening open baffle, you're missing half the music.

I figured these should be fine for omnis.

I was going to use mine in my Karlsons but I never picked up a second set of drivers and decided to go full-range on the Karlson.

RxDx said:
They'll take more power than the AR3as, though, without breaking up. The Onkyo amp said they were handling 200 watts of power at 33 hz. I stopped there

Ummm, I suspect that's way too much power, even for the exaggerations of the solid state era. That's probably (handwaving guess, using some an RMS 1.4 derating factor and some avg/peak adjustment) about 70 watts of tube-era power which probably exceeds the rating.

I'm amazed it didn't deafen you, as those have high SPL. I think you were saved by a response that's many db down at 33Hz.

RxDx · Apr 16, 2015

Retrovert said:
I suspect that if you want to use them in a cabinet you'll need either a standard bass reflex, acoustical labyrinth, or Karlson to make them really sing.

I wondered about that rolloff, which I hadn't yet tested on mine.

You know what the open baffle proponents say: If you aren't listening open baffle, you're missing half the music.

I figured these should be fine for omnis.

I was going to use mine in my Karlsons but I never picked up a second set of drivers and decided to go full-range on the Karlson.

Sealed is all I had. I snagged a pair of Crown 6a for $5 at the thrift, and dropped the S-C woofer right in. The next thing would be determining the size of port to cut. I'll get around to open baffle, probably, but I'm already reaching my level of engineer competence as it is.

Ummm, I suspect that's way too much power, even for the exaggerations of the solid state era. That's probably (handwaving guess, using some an RMS 1.4 derating factor and some avg/peak adjustment) about 70 watts of tube-era power which probably exceeds the rating.

I'm amazed it didn't deafen you, as those have high SPL. I think you were saved by a response that's many db down at 33Hz.

Yeah, the woofer is rated at 50 watts (continuous, I suspect). I was feeding it a 30 hz tone (actually 25, 26, 27, etc). So it wasn't even loud, at 12" away from the woofer. The AR3as, on the other hand, were close to ear-drum-collapsing loud, at 1/3 the volume. I guess loud isn't the exact word. It really is sound pressure.

RxDx · Apr 17, 2015

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