When refurbishing crossovers, upgrading the caps & resistors has been straight forward.
I just replace with fresh resistors, and poly caps with the same values.
Inductors, on the other hand haven't been straight forward for me.
Apart from using the manuf specs, which aren't always available with vintage speakers, how would I go about determining the value of existing inductors?
cheers
Cliff
I just replace with fresh resistors, and poly caps with the same values.
Inductors, on the other hand haven't been straight forward for me.
Apart from using the manuf specs, which aren't always available with vintage speakers, how would I go about determining the value of existing inductors?
cheers
Cliff
Air core types you can measure well enough on a decent inductance meter. Use a frequency
near the crossover region. Or if necessary, you could measure the -3dB point of an LR network.
Iron core inductor behavior is more complex, though.
near the crossover region. Or if necessary, you could measure the -3dB point of an LR network.
Iron core inductor behavior is more complex, though.
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For basic measurements, buy a multimeter with an inductance scale. Search for 'multimeter LCR meter'. Mine gives readings which match the values stamped on the air core and ferrite core inductors in my spares box.
Like this: LCR Meter Digital Capacitance Inductance Resistance Tester with Battery Crocodile Clip Bag LCR Tester Measuring Meter: Amazon.co.uk: Car & Motorbike
For more advanced measurements, refer to rayma!
Like this: LCR Meter Digital Capacitance Inductance Resistance Tester with Battery Crocodile Clip Bag LCR Tester Measuring Meter: Amazon.co.uk: Car & Motorbike
For more advanced measurements, refer to rayma!
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Better impedance meters have settings for Ls/Rs and Lp/Gp for example,
and one will give better results than the other, for a given inductor.
https://assets.testequity.com/te1/Documents/pdf/series-parallel-impedance-parameters-an.pdf
http://www.sanwa-seiden.com/DiynicE...07-10adb7940f-2ef3-4f9b-8137-f75aef27cb35.pdf
If you have a "precision" film capacitor, you could determine its resonant frequency with the air core inductor.
Adjust the value of C so you get a reasonable frequency of resonance, roughly 1kHz for audio purposes.
and one will give better results than the other, for a given inductor.
https://assets.testequity.com/te1/Documents/pdf/series-parallel-impedance-parameters-an.pdf
http://www.sanwa-seiden.com/DiynicE...07-10adb7940f-2ef3-4f9b-8137-f75aef27cb35.pdf
If you have a "precision" film capacitor, you could determine its resonant frequency with the air core inductor.
Adjust the value of C so you get a reasonable frequency of resonance, roughly 1kHz for audio purposes.
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thanks guys. 🙂
I'll have to invest in a suitable tester.
My multi meter doesn't have these values.
I'll have to invest in a suitable tester.
My multi meter doesn't have these values.
Old air core inductors should still be in tolerance, unless they were somehow burned up.
If you have to replace an inductor, I'd use the same wire gauge as the original,
and also a similar form factor, to keep the parasitics about the same.
If you have to replace an inductor, I'd use the same wire gauge as the original,
and also a similar form factor, to keep the parasitics about the same.
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Thanks R
One set of speaker I have has inductors with very fine gauge copper winding.
My thoughts were that the manuf was economizing.
Are you saying that the inductor selection was deliberate and that I should replicate rather than select something more robust in gauge?
Also, aren't iron core inductors often used to economize, as air core inductors with equivalent inductance far more expensive?
Also, what is meant by "form factor"?
One set of speaker I have has inductors with very fine gauge copper winding.
My thoughts were that the manuf was economizing.
Are you saying that the inductor selection was deliberate and that I should replicate rather than select something more robust in gauge?
Also, aren't iron core inductors often used to economize, as air core inductors with equivalent inductance far more expensive?
Also, what is meant by "form factor"?
If the wire is a small gauge (must be for the tweeter), definitely replicate it. The DCR is part of the design,
or it could be. Air core isn't practical for larger value, higher current inductors. Form factor is the ratio of
length to diameter. There's a theoretically optimum value in some cases, I think typically around 1 to 2.
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A simple way is to connect a signal generator through a series 1k resistor to an LC network
(either series or parallel) to ground. Use a scope or DVM to adjust the frequency to maximum voltage
(for a parallel LC) or minimum voltage (for a series LC). That's the resonance.
Adjust the capacitor value so the resonance is roughly 1kHz to reduce various complications.
Needless to say, use only a stable, quality film capacitor of known value, if possible.
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You only need a multimeter with 2v AC range and 1W resistor of 3,9 ohm
connect the computer to an amplifier and put the coil and 3,9R in series on one channel output,
feed a 50Hz sine wave
Now adjust the volume that there is exactly 1.000V across the resistor.
Note down the amp out voltage Vamp
Augment the frequency until the meter reads 707mV
Check again if the amp out is still the same adjust the volume eventually.
Now read the frequency fg at exatly 707mV
DC-resistance Rdc = (Vamp -1)*3.9
L= (3.9+Rdc)/(2*pi*fg)
connect the computer to an amplifier and put the coil and 3,9R in series on one channel output,
feed a 50Hz sine wave
Now adjust the volume that there is exactly 1.000V across the resistor.
Note down the amp out voltage Vamp
Augment the frequency until the meter reads 707mV
Check again if the amp out is still the same adjust the volume eventually.
Now read the frequency fg at exatly 707mV
DC-resistance Rdc = (Vamp -1)*3.9
L= (3.9+Rdc)/(2*pi*fg)
The resistance of the new coil network should be about the same as the old,
you don't want a difference of 1 ohm because the filtering will be changed.
But if the new coil has a lower resistance you can add a resistor in series to match the old coil.
Think of a coil always in terms of inductance and resistance.
you don't want a difference of 1 ohm because the filtering will be changed.
But if the new coil has a lower resistance you can add a resistor in series to match the old coil.
Think of a coil always in terms of inductance and resistance.
I'm currently without my inductance meter cos my son 'borrowed' it! 🙁
The post from bansuri reminded me of how I instructed my son on how to measure the inductance of his home made guitar pickups in the days before we owned an inductance meter. I post the method here for interest and possible comment.
Finding the inductance (L), in henrys (H), of an unknown inductor
Comparison Method
The unknown reactance (X), in ohms, of the inductor under test is compared with a known reactance - in this case the resistance (R), in ohms, of a carbon film resistor.
Test Circuit
Since L = X/2πf , then L = R/2πf
Where,
X = reactance in Ω
R = resistance in Ω
f = frequency in Hz
L = inductance in H
π (pi) = 3.142
The post from bansuri reminded me of how I instructed my son on how to measure the inductance of his home made guitar pickups in the days before we owned an inductance meter. I post the method here for interest and possible comment.
Comparison Method
The unknown reactance (X), in ohms, of the inductor under test is compared with a known reactance - in this case the resistance (R), in ohms, of a carbon film resistor.
Test Circuit
- The inductor under test is connected in series with the carbon film resistor.
- An audio sine wave generator is connected across the series combination.
- A multimeter is connected across the inductor and a second multimeter is connected across the resistor. Each multimeter is set to read ac voltage.
- The frequency of the audio generator is varied until the voltage across the inductor is the same magnitude as the voltage across the resistor.
- The frequency at which the voltages are equal in size is then noted down.
- At this frequency the reactance of the inductor must be equal to the resistance of the resistor.
Since L = X/2πf , then L = R/2πf
Where,
X = reactance in Ω
R = resistance in Ω
f = frequency in Hz
L = inductance in H
π (pi) = 3.142
Well explained G.
Earlier explanations weren't in layman terms, some of which I wasn't comprehending.
Replacing Caps is straight forward as the redundant examples are marked.
Do specs appear on Inductors?
If not I'd have two issues.
Firstly, if an existing Inductor is faulty testing it may not give me the designers intended value.
Secondly, gearing up for hobby appears expensive.
I'll need two multi meters and an audio sine wave generator.
PS: What resistance value would you select for the Resistor to make the experiment work?
Earlier explanations weren't in layman terms, some of which I wasn't comprehending.
Replacing Caps is straight forward as the redundant examples are marked.
Do specs appear on Inductors?
If not I'd have two issues.
Firstly, if an existing Inductor is faulty testing it may not give me the designers intended value.
Secondly, gearing up for hobby appears expensive.
I'll need two multi meters and an audio sine wave generator.
PS: What resistance value would you select for the Resistor to make the experiment work?
Hi David.
Unless I ask, I don't know if sound improvements can be achieved or not.
That's why I've been posting.
I'm keen to learn how to go about economically refurbishing vintage speakers.
So far I've learned that electrolytic caps have a limited life span, that:
I was hoping to go a little deeper with Inductors.
Are there poor quality Inductors in circulation which, if identified could be replaced?
I was hoping for a simple way of assessing the performance of Inductors.
Maybe, my only way forward is to study electronics, in particular crossover design, and measurement of Loudspeaker performance so I can properly assess deficiencies and improvements.
A crossover designer I came across indicated that the design of crossovers has a critical role in the performance of Loudspeakers involving multiple drivers.
Ultimately I'd like to build the skill of measuring Loudspeakers and assessing their crossovers with the view to economically and measurably improving their sound
Measurements can include:
In think it was said, parts involving ferrous, such as Iron core Inductors, can lead to energy build up which can smear or distort the audio signal.
Unless I ask, I don't know if sound improvements can be achieved or not.
That's why I've been posting.
I'm keen to learn how to go about economically refurbishing vintage speakers.
So far I've learned that electrolytic caps have a limited life span, that:
- resistors seem to be pretty stable, that
- many manufacturers fit cheap parts to build to a price point,and
- it appears that Inductors should be OK if they visually look undamaged.
I was hoping to go a little deeper with Inductors.
Are there poor quality Inductors in circulation which, if identified could be replaced?
I was hoping for a simple way of assessing the performance of Inductors.
Maybe, my only way forward is to study electronics, in particular crossover design, and measurement of Loudspeaker performance so I can properly assess deficiencies and improvements.
A crossover designer I came across indicated that the design of crossovers has a critical role in the performance of Loudspeakers involving multiple drivers.
Ultimately I'd like to build the skill of measuring Loudspeakers and assessing their crossovers with the view to economically and measurably improving their sound
Measurements can include:
- flat response across a wide frequency range, including off access, left and right, as well as up and down,
- a suitable crossover point which matches the drivers,
- spectral decay (stored energy),
- smooth impedance,
- and any other worthwhile measurements.
In think it was said, parts involving ferrous, such as Iron core Inductors, can lead to energy build up which can smear or distort the audio signal.
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-quote-
In think it was said, parts involving ferrous, such as Iron core Inductors, can lead to energy build up which can smear or distort the audio signal.
-unquote-
All your coils and caps in a crossover work by storing energy so that is not the issue by itself. The issue is rather the non linear storage and release of energy in some passives. An iron core may lead to distortions in this respect, for example because of hysteresis or eddy losses.
In think it was said, parts involving ferrous, such as Iron core Inductors, can lead to energy build up which can smear or distort the audio signal.
-unquote-
All your coils and caps in a crossover work by storing energy so that is not the issue by itself. The issue is rather the non linear storage and release of energy in some passives. An iron core may lead to distortions in this respect, for example because of hysteresis or eddy losses.