I've got a Goodmans XO 950/5000-2 crossover, a midax, a trebax and two 12" 8 ohm RCA woofers from a 1960's console that I'm going to try building a speaker with.
I never could afford an appropriate Goodmans driver back when I bought the midax (got three) Trebax (got two) and crossover (got two) so they sat for several years until I got the RCA woofers a few years back and casually experimented with them.
I put the woofers in series for a 16 ohm load as the other drivers I believe are 16 ohms.
I do not have the attenuators that could be used with these.
The midax and trebax are louder than the woofers and the trebax is a little louder than the midax.
Three questions.
1. Do the capacitors in the crossovers need to be replaced?
2. Are there 16 ohm variable l-pads or is there a schematic of the original attenuators so I can duplicate them?
3. Would it be better to pass these on to someone who can use them with a proper Goodmans woofer?
I never could afford an appropriate Goodmans driver back when I bought the midax (got three) Trebax (got two) and crossover (got two) so they sat for several years until I got the RCA woofers a few years back and casually experimented with them.
I put the woofers in series for a 16 ohm load as the other drivers I believe are 16 ohms.
I do not have the attenuators that could be used with these.
The midax and trebax are louder than the woofers and the trebax is a little louder than the midax.
Three questions.
1. Do the capacitors in the crossovers need to be replaced?
2. Are there 16 ohm variable l-pads or is there a schematic of the original attenuators so I can duplicate them?
3. Would it be better to pass these on to someone who can use them with a proper Goodmans woofer?
They are certainly available in the UK: https://willys-hifi.com/collections/l-pad-attenuators/products/16-ohm-l-pad-attenuator-100-watts
Details of the Midax and Trebax units: http://ukhhsoc.torrens.org/makers/Goodmans/1960_High_Fidelity_Loudspeaker_Manual/Page12.jpeg
Details of attenuator and 950/5000-2 crossover: http://ukhhsoc.torrens.org/makers/Goodmans/1960_High_Fidelity_Loudspeaker_Manual/Page13.jpeg
A 16 ohm vatiable L-pad control can be substituted for the variable 8-step attenuator.
If they are of the NP electrolytic type, I would replace them with modern equivalents.
I presume you have tested the drivers recently and found them to be in good working order?
Details of attenuator and 950/5000-2 crossover: http://ukhhsoc.torrens.org/makers/Goodmans/1960_High_Fidelity_Loudspeaker_Manual/Page13.jpeg
A 16 ohm vatiable L-pad control can be substituted for the variable 8-step attenuator.
If they are of the NP electrolytic type, I would replace them with modern equivalents.
I presume you have tested the drivers recently and found them to be in good working order?
Yes, just used the crossover and drivers today with the woofers. All seem to be in working order.
Could the caps being bad contribute to why the trebax seems a little louder and slightly harsh sounding in its lower range?
I myself would prefer the 8 step attenuator as it wouldn't change the attenuation by me accidentally bumping the knobs and it would just be easier to set.
I've never really liked variable l-pads or attenuators with several fixed steps as I prefer the drivers be matched in output using fixed resistors, however I cannot measure the woofers to know their sensitivity due to not having the proper equipment, so the stepped attenuators is what I will have to use.
Only reason I never recapped the crossovers is because I wasn't sure how it would affect their value in case I had decided to sell them.
Could the caps being bad contribute to why the trebax seems a little louder and slightly harsh sounding in its lower range?
I myself would prefer the 8 step attenuator as it wouldn't change the attenuation by me accidentally bumping the knobs and it would just be easier to set.
I've never really liked variable l-pads or attenuators with several fixed steps as I prefer the drivers be matched in output using fixed resistors, however I cannot measure the woofers to know their sensitivity due to not having the proper equipment, so the stepped attenuators is what I will have to use.
Only reason I never recapped the crossovers is because I wasn't sure how it would affect their value in case I had decided to sell them.
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Quite possibly.
In the case of an electrolytic capacitor that doesn't dry out, if no voltage is applied for a long time the capacitance increases. That may let unwanted low frequencies through, contributing to a harsh sound.
It is my understanding that, at present, you simply want to build a single loudspeaker enclosure employing the two 8 ohm RCA woofers connected in series in order to match the 15 ohm crossover network.
You have the additional XO, Midax and Trebax to furnish a stereo pair, but this would involve modification of the bass section of the crossover network to suit a single 8 ohm woofer.
I would be interested in learning what you decide to do. It's great to keep vintage components such as these going!
You have the additional XO, Midax and Trebax to furnish a stereo pair, but this would involve modification of the bass section of the crossover network to suit a single 8 ohm woofer.
I would be interested in learning what you decide to do. It's great to keep vintage components such as these going!
I had always wanted to find another pair of the RCA woofers and have two real nice open back speakers, however I would not gut a console for them.
The label on the crossover does state
LOUDSPEAKER IMPEDANCE RANGE 8-15 OHMS.
That said I'd want all drivers the same impedance.
The caps are as follows.
Two 10uF 20V
Two 2.2uF 63V
Will be easily and relatively inexpensive to get those caps from Parts Express and the new caps should fit where the old ones were.
I disconnected one lead of each cap and used my DATS V3 to measure the capacitance.
It's no wonder the trebax sounded so harsh.
I do have some 2.2uF electrolytic caps I can temporarily tack in place at work tomorrow just to see how much of a difference it makes. Think I have a couple 10uF as well.
That's the other crossover. The one I have at work is probably just as bad if not worse.
The label on the crossover does state
LOUDSPEAKER IMPEDANCE RANGE 8-15 OHMS.
That said I'd want all drivers the same impedance.
The caps are as follows.
Two 10uF 20V
Two 2.2uF 63V
Will be easily and relatively inexpensive to get those caps from Parts Express and the new caps should fit where the old ones were.
I disconnected one lead of each cap and used my DATS V3 to measure the capacitance.
It's no wonder the trebax sounded so harsh.
I do have some 2.2uF electrolytic caps I can temporarily tack in place at work tomorrow just to see how much of a difference it makes. Think I have a couple 10uF as well.
That's the other crossover. The one I have at work is probably just as bad if not worse.
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Inexpensive 2.2 uF and 10 uF non-polarized electrolytic capacitors rated at 100V are available at Parts Express. They are likely to be smaller than the old ones, but their dimensions are given.
In his book More About Loudspeakers (1965), Gilbert Briggs of Wharfedale described his crossovers as being suitable for 10-15 ohm speakers.
He wasn't obsessed with absolute accuracy and, let's face it, the impedance of a driver varies with frequency and does not remain constant at its nominal figure.
As I indicated earlier, the 12 dB/octave, low-pass section of the crossover could be altered to suit an 8 ohm woofer rather than a 16 ohm one.
Even decent quality film capacitors will be smaller than the originals and will never need to be replaced.
I tried the 2.2uF and 10uF electrolytic caps I had on hand just to see what improvement there would be and the trebax is now balanced with the midax nearly perfectly and not harsh sounding at all.
I'll need to attenuate both drivers though.
I'll start with 4dB which gives me a 5.5 ohm series resistor and a 25.6 ohm parallel resistor.
Closest I can get with parts on hand is two parallel 51 ohm resistors for 25.5 ohms and a 5 ohm resistor in series with a parallel combination of two 1 ohm resistors for 5.5 ohms.
I tried the 2.2uF and 10uF electrolytic caps I had on hand just to see what improvement there would be and the trebax is now balanced with the midax nearly perfectly and not harsh sounding at all.
I'll need to attenuate both drivers though.
I'll start with 4dB which gives me a 5.5 ohm series resistor and a 25.6 ohm parallel resistor.
Closest I can get with parts on hand is two parallel 51 ohm resistors for 25.5 ohms and a 5 ohm resistor in series with a parallel combination of two 1 ohm resistors for 5.5 ohms.
4dB helped but isn't good enough.
Tried 9.3dB and that seems close enough to my ears.
Requires a series resistor of 9.85 ohms and a parallel resistor of 7.82 ohms.
I used 10 ohms and 7.8 ohms.
Will listen a bit and report back.
I'm not expecting 100% audiophile quality as this is a speaker I'm using for work. My main system sits on my desk, but this will sit in a screen room (faraday cage) maybe 50' away.
A maybe 1/4" thick cardboard box is what I used for the two RCA 12" woofers and the midax. The trebax sits on top. Crossover is inside.
Tried 9.3dB and that seems close enough to my ears.
Requires a series resistor of 9.85 ohms and a parallel resistor of 7.82 ohms.
I used 10 ohms and 7.8 ohms.
Will listen a bit and report back.
I'm not expecting 100% audiophile quality as this is a speaker I'm using for work. My main system sits on my desk, but this will sit in a screen room (faraday cage) maybe 50' away.
A maybe 1/4" thick cardboard box is what I used for the two RCA 12" woofers and the midax. The trebax sits on top. Crossover is inside.
In the late 1970s, I obtained high clarity sound by using Goodmans Hifax 750P horns along with my Wharfedale RS/12/DD 12" drivers mounted in 3 cu ft reflex enclosures. The Hifax had an integral filter "for use with systems rated at 8 or 16 ohm". I included small horn tweeters to assist at the higher frequencies.
Unfortunately, the Hifax horns had to be returned to my mobile disco system when it was being divided up for sale!
Unfortunately, the Hifax horns had to be returned to my mobile disco system when it was being divided up for sale!
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Awesome.
So far I am pleased with the sound.
Will take some getting used to the fact that the treble isn't quite as crisp as a dome tweeter. Of course that may change when I install the film caps.
I'm going with the red Audyn film caps unless there's a better choice (nothing exotic as they are ultra expensive) that works best with the midax and trebax.
So far I am pleased with the sound.
Will take some getting used to the fact that the treble isn't quite as crisp as a dome tweeter. Of course that may change when I install the film caps.
I'm going with the red Audyn film caps unless there's a better choice (nothing exotic as they are ultra expensive) that works best with the midax and trebax.
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