Please help me figure these crossovers out

[DangerBoy]

I have a set of speakers made in the early to mid 1970s buy a mad scientist speaker maker who owned an audio shop in a nearby small town back in the 60s - 80s. Unfortunately, he passed away in the 80s so I'm unable to ask him any questions about his crossovers.

This guy made what were some pretty "out there"/innovative speakers for the time and may have been a little ahead of his time with his designs. The system I have still sounds great but I want to overhaul it to make it even better.

The system is a trio system comprising a bass unit and two treble unit/satellites. In the bass unit there are two 12" Phillips AD 12100/W8 8 ohm woofers in stereo, meaning there are identical crossovers for the left and right channels. The treble units each have a number of Philips' best tweeters and mid-ranges from that era. I will ask a question about the crossovers in those units later on. Both of the output lines (right and left) from the amp go into the bass unit and then output lines for each of the channels go out from the bass unit to the treble units.

The wiring in the bass unit is quite chaotic but here's the circuit diagram for the crossovers in that unit. Remember, there are two of these crossovers in the bass unit; one for each woofer/channel. I don't know the inductance of the inductor coils he used. They're just big unmarked spools of coated copper wire held together with tape.

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Here are my questions:

The caps are in parallel right? So the total capacitance is 175 uF? If that's the case, then it shouldn't matter if I re-cap it with a 100 uF and a 75 uF cap? Correct?

Is it possible to know what the crossover frequency is without knowing the inductance of the inductor coil? (I presently have no way of measuring it.) If yes, what's the crossover frequency?

Is the signal going to the output terminals and onto the treble units full range or is the bass filtered out of it?

Treble Units

I haven't drawn out the schematic for the treble unit crossovers but I'm wondering if we can figure out what's going on in there generally from what's in those units. Basically what's in there is a single 8.2 uF cap and two inductor coils. Again, there are mid-ranges and tweeters in those units and no woofers.

I don't know much about crossover design but I'm guessing what's happening there is that the crossover is separating the mid band from the treble and sending the two bands off to the appropriate drivers. Correct? This is assuming the signal coming out of the bass unit already has the bass frequencies filtered out. If this is not the case, please explain to me what's going on if you're able to based on the information I've been able to provide.

The bass unit was completely sealed so I had to cut into it to gain access to everything inside. The treble units are easily accessed so I got into them years ago and replaced the old 8.2 uF caps with audio grade Sonicaps and they made a HUGE difference to the sound quality. I'm hoping that replacing the caps in the bass unit crossover will have an equally huge effect.

Thanks!

 

[swechsler]

1. Yes, correct, caps in parallel give you the sum total of the capacitance.
2. You can determine the high-pass frequency if you know the impedance of the satellites, but determining the low pass without knowing the inductance isn't possible (assuming it's not marked ).
3. The bass is filtered out, that's what the capacitors in series with the satellites are for.
4. Yes, this is how crossovers normally work. For a sub/sat system such as yours, it's not unusually to have two different crossovers, for ease of wiring.

 

[DangerBoy]

Thanks for your help Swechsier. I'm ordering new 100 uF and 75 uF caps now. I'm really looking forward to hearing these speakers after I've overhauled the bass unit. Just replacing the caps in the treble units made such a huge difference. Re-capping the bass unit should make both the bass unit and treble units sound a lot better as well. I'm excited about that!

I'm also going to line the insides of the cabinets with butyl sound deadening, improve the cabinet sealing and rewire all three units with heavier wire. With all that and re-capping the bass unit, I'm expecting significant improvements to the sound quality of that system.

 

[DangerBoy]

I've just tore into the Treble Units and deciphered the mess of wiring in them. I created a wiring diagram for the Bass and Treble Units in Visio (see below). I'm no EE so forgive me if there's any deviations from proper wiring diagram protocol in my diagram. It may not be technically perfect but i think it gets the information it needs to across.

I understand everything he's doing in the treble units running the Tweeters and Mid-ranges in parallel and series, etc. I can see that Inductor I1 is acting as a low pass ahead of the mids and the capacitor is a high pass ahead of the tweets. What I don't understand is what Inductor I2 is doing. What is it's function in this circuit?

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[toddalin]

I've just tore into the Treble Units and deciphered the mess of wiring in them. I created a wiring diagram for the Bass and Treble Units in Visio (see below). I'm no EE so forgive me if there's any deviations from proper wiring diagram protocol in my diagram. It may not be technically perfect but i think it gets the information it needs to across.

I understand everything he's doing in the treble units running the Tweeters and Mid-ranges in parallel and series, etc. I can see that Inductor I1 is acting as a low pass ahead of the mids and the capacitor is a high pass ahead of the tweets. What I don't understand is what Inductor I2 is doing. What is it's function in this circuit?

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The tweets are on a 2nd order circuit. The cap lets the highs pass, and the choke steepens the slope by further routing lower frequencies to ground.

Interesting that the mids are not rolled off on top for the tweets but are just left to their natural rolloff. Nothing really wrong with that if it works with the speakers.

 

[DangerBoy]

The weird thing is that I2 is non-existent in the the other treble unit. I could put one in there but none of the inductor coils are marked so I have no idea what their inductance is. The guy who made the speakers has been dead 30 years so not too likely I'm gonna get much help there. I do have a function generator so I could figure out what the inductance of that coil is by wiring it in series with a precision resistor but I'm not sure I want to go to that much trouble.