I am considering a mono speaker – not an exact clone of any 1950’s design, but true to the standards of that day.
My speaker collection (all Magnavox)
One - 15” woofer from a 1959 or 1960 Belvedere console. 5.6 ohms per the schematic
Four 4” tweeters from that same console, 3.2 ohms each per the schematic
Two horns from the late 60’s or early 70’s. 7.6 ohms DC resistance
One ten-inch woofer from the late 60’s or early 70’s 7.4 ohms DC resistance
What do I know about them?
The Belvedere had a three way system – 15” and 8” run in parallel both are 5.6 ohms in the schematic. Plus two 3.2 ohm 4” tweeters in parallel protected by a 16 mfd capacitor. This implies 5500 Hz crossover, right? It also implies a very low total impedance. 2.8 ohm total impedance for the two bigger drivers assuming the tweeters are totally isolated by the capacitor. Even lower impedance at frequencies that lit up the tweeter? Am I missing something? I have to assume that Magnavox engineers in 1959 knew something. When I got the console there was one woofer and four tweeters. The 8” midranges were broken (mechanically). I had the tube amp rebuilt and it happily drives 8-ohm speakers and sounds great. It is still stereo. So this grab bag of speakers is laying around, while I wonder why the amp drove such a low load back in 1960.
The two horn speakers, a later design, maybe into the 70’s, came with 2.2 microfarad capacitors attached, which I think means crossover at 9500 Hz??? I have no idea what they were paired with. I have seen pictures of consoles with a 15” woofer and a horn, but older than these horns. I have seen pictures of newer consoles with similar horns but smaller woofers in the 70’s. I searched old forums and people on the internet call these 8 or 12 ohm, and maybe there were different values over the years. People recommend 1, 2.2, 3 and even 6 mfd capacitors.
The 10” woofer seems 1970-ish, it has a plastic cover over the back of the magnet. I cannot find out anymore about it, the numbers on it yield nothing in internet searches.
I could buy exact duplicates of the 15” woofer and replace the broken 5.6 ohm midrange speakers but I have better more modern speakers. I do not want to throw a lot of money at these speakers, I basically got them free. I have decided o build a mono speaker. Large case, open back, just what a Hi-Fi enthusiast might have built just before stereo became “the thing.”
Ideas (all would be mono) - In every case I would put a capacitor in series with the tweeters:
A. 15” and two parallel tweeters - this is the original without the broken 8” 5.6 ohm speaker.
B. 15” in parallel with the younger 10” (8-ohm?) and the two tweeters in parallel – this is as close to original as I can get, but the low impedance bothers me. Still Magnavox did it.
C. 15” and two series tweeters (better impedance match, but the original designers did not do this)
D. 10” and two series tweeters (better impedance match, 8 ohms and 7.2 ohms)
E. 15” and 10” and two series tweeters – series still makes more sense to me – but, again, Magnavox did not do this.
F. 15” and 10” in parallel with all four tweeters in series/parallel to give 3.6 ohms for the four tweeters
G. 15” with a vintage Magnavox horn tweeter
H. 10” with a vintage Magnavox horn tweeter – this approximates what I think Magnavox evolved to in the 1970’s
I. 15” and 10” with a vintage Magnavox horn tweeter – because why not?
Modern audiophiles may scorn open back speakers or Magnavox as an entity, and I know as the 1950’s rolled on to the 1970’s all US companies struggled and cut costs as they slowly declined. But I have to think that in 1959 the engineers actually listened to their product and tried different crossover frequencies and asked each other “does that sound better?”
Whatever I build will be tested with the original tube amp (one channel, anyway!) It survived the crazy all parallel speakers with whatever low impedance they gave. The catalog implies that you could buy one console and run it mono then add a second channel, there is a switch that lets you turn the extension cabinet off or on. I would run it with no input into one channel and an 8 ohm resistor on the output of the “dormant” channel.
If you have read this far I thank you! I would love some idea.
My speaker collection (all Magnavox)
One - 15” woofer from a 1959 or 1960 Belvedere console. 5.6 ohms per the schematic
Four 4” tweeters from that same console, 3.2 ohms each per the schematic
Two horns from the late 60’s or early 70’s. 7.6 ohms DC resistance
One ten-inch woofer from the late 60’s or early 70’s 7.4 ohms DC resistance
What do I know about them?
The Belvedere had a three way system – 15” and 8” run in parallel both are 5.6 ohms in the schematic. Plus two 3.2 ohm 4” tweeters in parallel protected by a 16 mfd capacitor. This implies 5500 Hz crossover, right? It also implies a very low total impedance. 2.8 ohm total impedance for the two bigger drivers assuming the tweeters are totally isolated by the capacitor. Even lower impedance at frequencies that lit up the tweeter? Am I missing something? I have to assume that Magnavox engineers in 1959 knew something. When I got the console there was one woofer and four tweeters. The 8” midranges were broken (mechanically). I had the tube amp rebuilt and it happily drives 8-ohm speakers and sounds great. It is still stereo. So this grab bag of speakers is laying around, while I wonder why the amp drove such a low load back in 1960.
The two horn speakers, a later design, maybe into the 70’s, came with 2.2 microfarad capacitors attached, which I think means crossover at 9500 Hz??? I have no idea what they were paired with. I have seen pictures of consoles with a 15” woofer and a horn, but older than these horns. I have seen pictures of newer consoles with similar horns but smaller woofers in the 70’s. I searched old forums and people on the internet call these 8 or 12 ohm, and maybe there were different values over the years. People recommend 1, 2.2, 3 and even 6 mfd capacitors.
The 10” woofer seems 1970-ish, it has a plastic cover over the back of the magnet. I cannot find out anymore about it, the numbers on it yield nothing in internet searches.
I could buy exact duplicates of the 15” woofer and replace the broken 5.6 ohm midrange speakers but I have better more modern speakers. I do not want to throw a lot of money at these speakers, I basically got them free. I have decided o build a mono speaker. Large case, open back, just what a Hi-Fi enthusiast might have built just before stereo became “the thing.”
Ideas (all would be mono) - In every case I would put a capacitor in series with the tweeters:
A. 15” and two parallel tweeters - this is the original without the broken 8” 5.6 ohm speaker.
B. 15” in parallel with the younger 10” (8-ohm?) and the two tweeters in parallel – this is as close to original as I can get, but the low impedance bothers me. Still Magnavox did it.
C. 15” and two series tweeters (better impedance match, but the original designers did not do this)
D. 10” and two series tweeters (better impedance match, 8 ohms and 7.2 ohms)
E. 15” and 10” and two series tweeters – series still makes more sense to me – but, again, Magnavox did not do this.
F. 15” and 10” in parallel with all four tweeters in series/parallel to give 3.6 ohms for the four tweeters
G. 15” with a vintage Magnavox horn tweeter
H. 10” with a vintage Magnavox horn tweeter – this approximates what I think Magnavox evolved to in the 1970’s
I. 15” and 10” with a vintage Magnavox horn tweeter – because why not?
Modern audiophiles may scorn open back speakers or Magnavox as an entity, and I know as the 1950’s rolled on to the 1970’s all US companies struggled and cut costs as they slowly declined. But I have to think that in 1959 the engineers actually listened to their product and tried different crossover frequencies and asked each other “does that sound better?”
Whatever I build will be tested with the original tube amp (one channel, anyway!) It survived the crazy all parallel speakers with whatever low impedance they gave. The catalog implies that you could buy one console and run it mono then add a second channel, there is a switch that lets you turn the extension cabinet off or on. I would run it with no input into one channel and an 8 ohm resistor on the output of the “dormant” channel.
If you have read this far I thank you! I would love some idea.
