Hi I am restoring a 1958 jukebox and would like help in improving the sound quality.
First a bit about the jukebox, this was the first ever stereo jukebox and used a tube amp which has been recapped and 2 off 12 inch 16 ohm extended range speakers.
There is an existing black box "crossover" which is just a 12db/octave low pass filter that gets switched in if external speakers are used and the machine is then just a bass cabinet. With no external speakers this is bypassed.
I have been advised to add two 8 ohm horn tweeters to improve the high frequencies by adding a 8 ohm non inductive 10 watt resistor and a 10uf capacitor which I'm told will give me a 6db crossover.
I have tried this and the sound is improved but would like it to be better if possible.
Should I be using a 2 way crossover or maybe different speakers???
I am a sparky by trade but my knowledge on audio speakers is limited.
Any advice is much appreciated.
Cheers
John
First a bit about the jukebox, this was the first ever stereo jukebox and used a tube amp which has been recapped and 2 off 12 inch 16 ohm extended range speakers.
There is an existing black box "crossover" which is just a 12db/octave low pass filter that gets switched in if external speakers are used and the machine is then just a bass cabinet. With no external speakers this is bypassed.
I have been advised to add two 8 ohm horn tweeters to improve the high frequencies by adding a 8 ohm non inductive 10 watt resistor and a 10uf capacitor which I'm told will give me a 6db crossover.
I have tried this and the sound is improved but would like it to be better if possible.
Should I be using a 2 way crossover or maybe different speakers???
I am a sparky by trade but my knowledge on audio speakers is limited.
Any advice is much appreciated.
Cheers
John
John,
I'm surprised you got no responses.
1) add pictures, please. We all like to see the shiny toys.
2) get a mic.
IMO, the best thing to happen to DIY audio in recent years is the availability of good, cheap mics and free software. It is much easier to work on a project when you can easily measure it.
For about $10 you can get a mic that plugs into a phone (look up DAYTON)
For about $100 you can get a mic that plugs into a USB port (look up mini DSP)
Cheers,
Craig
I'm surprised you got no responses.
1) add pictures, please. We all like to see the shiny toys.
2) get a mic.
IMO, the best thing to happen to DIY audio in recent years is the availability of good, cheap mics and free software. It is much easier to work on a project when you can easily measure it.
For about $10 you can get a mic that plugs into a phone (look up DAYTON)
For about $100 you can get a mic that plugs into a USB port (look up mini DSP)
Cheers,
Craig
I'm thinking about whether the tweeter is a good match to the woofer, is its response smooth, is it set to the right level, are they both cut at the right frequency.
Getting these things right will get you most of the way there. Measuring will get you further.
The non-inductive resistor is a relative non-issue. One last thought, is this a piezo tweeter or one that has a conventional voice coil? How did you connect the components?
Getting these things right will get you most of the way there. Measuring will get you further.
The non-inductive resistor is a relative non-issue. One last thought, is this a piezo tweeter or one that has a conventional voice coil? How did you connect the components?
Ok A link to a few photos and a schematic of the tube amp for those that are interested
As I stated earlier I'm a real noob when it comes to speakers and crossovers so don't be afraid of dumbing it down for me
Specs of the tweeter I am trying is there as well as how I have connected the tweeter to the extended range woofers.
Note that the photos in Dropbox are not in order.
https://www.dropbox.com/s/tgjxq7bspcvaujg/photo 30-06-2016 4 41 05 pm.jpg?dl=0
Cheers
John
As I stated earlier I'm a real noob when it comes to speakers and crossovers so don't be afraid of dumbing it down for me
Specs of the tweeter I am trying is there as well as how I have connected the tweeter to the extended range woofers.
Note that the photos in Dropbox are not in order.
https://www.dropbox.com/s/tgjxq7bspcvaujg/photo 30-06-2016 4 41 05 pm.jpg?dl=0
Cheers
John
If the Altec's are too old, consider the Eminence Beta's like this one. You'll need a crossover and tweeter but it's a good start. There are several compression drivers that would fit, not sure which would be the best in terms of matching efficiency though.
Sorry guys me and Dropbox hate each other.
Try this link should show a lot more photos
https://db.tt/IUTr130L
Try this link should show a lot more photos
https://db.tt/IUTr130L
There are a few things you should consider, one is that the tweeter is probably more sensitive than the woofer and a loud tweeter won't sound all that great. Your idea of using the resistor is on the right track.
The tweeter will likely have a peak in its electrical impedance around its resonance, which the capacitor will fail to negotiate properly and will inadvertently convert into a peak in the response. Resistors can be used to swamp the impedance and make it more consistent, but if you use a resistor in series like this the effect will be relatively minimal. Putting a resistor in parallel with the driver is more effective at this but won't on its own bring down the tweeter level. Using two resistors will give a better result. A second order filter might also reduce this problem somewhat.
The woofer should probably be crossed below 2kHz as 12" drivers struggle here for various reasons. Sometimes they can behave well enough to use above this frequency but your intention to cross to a tweeter complicates this.
The tweeter is small from the point of view that it will radiate a wide pattern around the crossover, and this suggests the crossover is best kept well below 2kHz. I think you will have to weigh up the compromises.
If you need a tool to assist the process of tuning by ear you might consider a variable L-pad.
The tweeter will likely have a peak in its electrical impedance around its resonance, which the capacitor will fail to negotiate properly and will inadvertently convert into a peak in the response. Resistors can be used to swamp the impedance and make it more consistent, but if you use a resistor in series like this the effect will be relatively minimal. Putting a resistor in parallel with the driver is more effective at this but won't on its own bring down the tweeter level. Using two resistors will give a better result. A second order filter might also reduce this problem somewhat.
The woofer should probably be crossed below 2kHz as 12" drivers struggle here for various reasons. Sometimes they can behave well enough to use above this frequency but your intention to cross to a tweeter complicates this.
The tweeter is small from the point of view that it will radiate a wide pattern around the crossover, and this suggests the crossover is best kept well below 2kHz. I think you will have to weigh up the compromises.
If you need a tool to assist the process of tuning by ear you might consider a variable L-pad.
What a GREAT project!! Interesting that it is "Stereophonic" when all the records it would play at that time (45s) were all cut in mono.
I believe that the first stereo records came out in the late 50s the same time as the jukebox I am restoring.
Having said that I agree the majority of 45s being played on the machine would have been mono.
Having said that I agree the majority of 45s being played on the machine would have been mono.
Yes, indeed! From History's Dumpster: The History of The 45 RPM Record :
"The very first Stereo 45 RPM record was introduced by Bel Canto Records in June of 1958: "almost square" by Larry Fotine."
"The very first Stereo 45 RPM record was introduced by Bel Canto Records in June of 1958: "almost square" by Larry Fotine."
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