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Multi-Way Conventional loudspeakers with crossovers

Ribbon Crossovers: Need help...
Ribbon Crossovers: Need help...
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Old 13th September 2018, 09:37 PM   #1
SanJoseMichael is offline SanJoseMichael  United States
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Default Ribbon Crossovers: Need help...

Kenleigh Focused Field Monitors. I bought them thinking they'd have a great midrange and top end based on the ribbon tweeter in a small horn, but there is no real presence, no crisp top end. Even my wife says "muddy"

Dimensions 16 wide by 10 tall, about 8 deep on top tapering to 6 deep on the bottom. Low frequency is an 8 inch French Polydax HD20B25VHV marked 8 ohm and stamped 1184, presumed to be the production date. High frequency is an unmarked ribbon horn measuring 4 1/4 wide by 3 inches tall. Woofer shows 7.2 ohms resistance, tweeter shows .3 ohms resistance. No specs known or found about these drivers.

Woofer is direct connected. Path to the tweeter goes through 2 poly caps, the first cap in parallel with 4 resistors. First cap is marked 2.2uf and measures 2.17, second caps is marked 4uf and measures 4.2uf. Two caps in series measures 6.4uf.

The resistors have me stumped, and I have never seem them used this way before if a crossover. Why 4 in parallel and not one single? Are these referred to a shunt resistors to drop impedance?

Resistors are 2 watts. I know how to read resistors: Two resistors are Red Black Green Gold which means 2 meg ohm 5% but they measure 15 ohm. Other 2 resistors are Red Black Orange Gold which means 20K ohm 5% but they measure 18.3 ohms. Calculating resistors in parallel, and reading the color stripes, I should come up with 9.9K. Measuring the resistors in parallel, I get 4.2 ohms.

Question Number One: What am I not understanding about resistors here?

Question Number Two: What do I change to recover top end and get these out of the audio mud? Is there anything special about as ribbon tweeter versus a dome when it come to crossovers? Can I just replace what I have with a 2nd order 12db LR? What frequency do I crossover at?

Thanks!
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Last edited by SanJoseMichael; 13th September 2018 at 09:39 PM. Reason: add photo
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Old 13th September 2018, 10:17 PM   #2
Old'n'Cranky is offline Old'n'Cranky  Australia
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For the resistors, I think your reading them backwards.
With time the colours can change, so the gold may actually be brown.
This would line up with what your measuring.

So your Red Black Green Gold becomes, brown green black red. 1 5 0 (multi) red (tolerance) = 15 Ohms.

These days I find colour coding not very clear. Primarily due to thin bands with 'washy' colour saturation.
Not helped by the bands now being (mostly) evenly spaced rather than grouped with a clear obvious space to the tolerance band of olden days.

edit.
too me the resistors body being a blueish colour suggests metal film, which also lines up with 2% tolerance.

Last edited by Old'n'Cranky; 13th September 2018 at 10:23 PM.
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Old 13th September 2018, 11:59 PM   #3
SanJoseMichael is offline SanJoseMichael  United States
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Maybe I am an idiot? Maybe not, but what a doofus! I have read carbon resistors for ages and always saw gold as the last band for 5%. If I reverse them, you are right Brown Green Red Black = 15 ohms (measured 15) and the others must be Brown Grey Black Red = 18 ohms (measured 18.3). Thanks for pointing that out...

But why four in parallel instead of one?

Next question still stands: What do I change to recover top end and get these out of the audio mud? Is there anything special about as ribbon tweeter versus a dome when it come to crossovers? Can I just replace what I have with a 2nd order 12db LR? What frequency do I crossover at?
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Old 14th September 2018, 12:23 AM   #4
Old'n'Cranky is offline Old'n'Cranky  Australia
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No your not a doofus.
Just caught out by the lack of companies not sticking with the standards recommendations.

If it wasn't for DMM's these days I'd be up the proverbial re color coding on resistors.
Even with 'work bench' glasses and magnifying lamps and good lighting, it's still close to a guessing game these days.

Four instead of one will be to increase power handling.
And I do know of some that think multiple smaller metal films are better than a single 10w.
I won't go into that rabbit hole

You said your ribbon measures as 0.3 ohm.
So unless you want to kill any amplifier connected to it you will have to include a series resistor (4+ ohms) irrespective of whatever crossover you use.

Why has it lost it's output ?
I'm betting the actual ribbons (foil element) are gone.

All you've measured is the transformer on it.
That won't tell you what the actual ribbon element is like.

Last edited by Old'n'Cranky; 14th September 2018 at 12:28 AM.
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Old 14th September 2018, 01:05 AM   #5
Galu is offline Galu  Scotland
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If you can measure the resistance of the ribbon itself, it should be around 1 to 3 ohm. If it reads open circuit then, unfortunately, there is a break in the ribbon.

Sometimes, it is possible to bridge the break with conductive paint - search the interweb for how you might do this.
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Old 14th September 2018, 01:16 AM   #6
Galu is offline Galu  Scotland
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Here's a link to a conductive paint repair:

Infinity Qb EMIT Tweeter Repair | Steven Eudaly
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Old 14th September 2018, 01:56 AM   #7
SanJoseMichael is offline SanJoseMichael  United States
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Old'n'Cranky: With a handle like that, I'll guess you began working on hot chassis since the All American Five days!

Per your note on a series resistor, I posted approximately the same thing on Audiokarma, and a guy from the UK said What this circuit will do is to initially give a highpass filter of 3600Hz with the 4.3ohm resistance acting as an attenuator in series with the 4.2uF cap. The 2.2uF cap will effectively be open circuit at this point, until at about 6000Hz when the 2.2uF cap starts to conduct, gradually bypassing the resistors. Therefore, what you have is a dual slope highpass filter for the tweeter which has a low level (attenuated) output between 3600Hz and 6000Hz with increasing output above that point.

The ribbons do put out audio, I disconnected the ribbon entirely, and connected a small 2 watt amp (pulled from a small Bluetooth box running at 5V) to them, and I did get Joe Morello's cymbals on Take Five, albeit at a low volume.

Next, I will desolder the inductor in parallel with the ribbon and test the ribbon itself. (Is the inductor a "shunt coil" for impedance, not that I truly understand that...)

The search for a better top end continues.

Continued thanks for all the help!
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Old 14th September 2018, 09:49 AM   #8
system7 is offline system7  United Kingdom
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I'm not clear what is going on here:

Click the image to open in full size.

What is this? A small 5" bass speaker? Is that bass paper or plastic?

This is rudimentary to the max, bass running without crossover, guess just a glorified 4.2uF to the tweeter:

Click the image to open in full size.

This ribbon or magnetodynamic tweeter has an input transformer:

Click the image to open in full size.

It's probably very fragile to low frequencies. I wouldn't even test it without a series capacitor around 2.2uF.

What is that round plate? Some sort of small port? There's probably the makings of a goodish small speaker there. Maybe replace the ribbon, maybe build a decent crossover. All been done before. Right now you are just poking around aimlessly.
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Old 14th September 2018, 11:46 AM   #9
chris661 is online now chris661  United Kingdom
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Series capacitors don't sum that way - something's off with your measurements there.

Can you take acoustic measurements of the speakers themselves?
If not, play some music quietly through them and put your ear to each driver. Does it sound as you'd expect?

Chris
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Old 14th September 2018, 12:28 PM   #10
Galu is offline Galu  Scotland
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Quote:
Originally Posted by SanJoseMichael View Post
Next, I will desolder the inductor in parallel with the ribbon and test the ribbon itself. (Is the inductor a "shunt coil" for impedance, not that I truly understand that...)
As has been pointed out by Steve and Old'n'Cranky, that 'inductor' is a transformer. The crossover connects to one side of the transformer and the ribbon connects to the other side of the transformer.
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