Hi. I put a voltmeter across my tweeter and it read a fraction of a volt.
Why is it that people use 250v and 600v capacitors in the high pass filter when the actual voltage reading is so low. Why not just use a cap rated at a few volts and save money rather than paying extra for a 600volt cap when there is no need for it..
Why is it that people use 250v and 600v capacitors in the high pass filter when the actual voltage reading is so low. Why not just use a cap rated at a few volts and save money rather than paying extra for a 600volt cap when there is no need for it..
If you want to assess what voltage developing over capacitor , you should measure across capacitor, not across tweeter.
At HF cap is short and there is no voltage across them, but on bass frequency all LF signal voltage will be across capacitor. Could be 20-30-40-50 V at loud listening.
At HF cap is short and there is no voltage across them, but on bass frequency all LF signal voltage will be across capacitor. Could be 20-30-40-50 V at loud listening.
So many seem not to have a grasp of the basics.
Your meter will not be measuring the ac voltage accurately.
Go forth and research this to understand.
Your meter will not be measuring the ac voltage accurately.
Go forth and research this to understand.
Radule expressed the physics well.
Let's consider a simple crossover consisting of a single capacitor in series with the tweeter thus forming a frequency selective voltage divider.
The low frequency voltages appear across the capacitor while the high frequency voltages appear across the tweeter.
As Radule says, large low frequency voltages can develop across the capacitor.
However, you are correct in thinking that a 600V capacitor, or even a 250V one, may be regarded as overkill in a domestic loudspeaker system.
50V versions are available if you want to save a penny or two, but 250V seems to be pretty much the standard these days, and allows for a good margin of error.
Let's consider a simple crossover consisting of a single capacitor in series with the tweeter thus forming a frequency selective voltage divider.
The low frequency voltages appear across the capacitor while the high frequency voltages appear across the tweeter.
As Radule says, large low frequency voltages can develop across the capacitor.
However, you are correct in thinking that a 600V capacitor, or even a 250V one, may be regarded as overkill in a domestic loudspeaker system.
50V versions are available if you want to save a penny or two, but 250V seems to be pretty much the standard these days, and allows for a good margin of error.
You would need good oscilloscope, ideally digital with memory, to measure ac across the capacitor.
When it comes to ac signal levels, its true, they are very small at home during normal listening.
But if you run PA with 10000 watts amp, there will be significant voltages.
You can replace big voltage caps with lower voltage caps, no problem. I often use bipolar caps specified at 100 volts, but i would not go lower than 50. Safety and long term reliability.
The same MP caps used is crossover are used in tube amps, and voltages there are real.
Your car can do 6000 rpm before it runs into red zone, still its better to keep it around 3000 rpm most of the time. Elevator specified 5 person max can hold 10 people easily, but i would not recommend it.
When it comes to ac signal levels, its true, they are very small at home during normal listening.
But if you run PA with 10000 watts amp, there will be significant voltages.
You can replace big voltage caps with lower voltage caps, no problem. I often use bipolar caps specified at 100 volts, but i would not go lower than 50. Safety and long term reliability.
The same MP caps used is crossover are used in tube amps, and voltages there are real.
Your car can do 6000 rpm before it runs into red zone, still its better to keep it around 3000 rpm most of the time. Elevator specified 5 person max can hold 10 people easily, but i would not recommend it.
Do a little real world "market research".
Statistically over 95% (if not more) out of ALL speaker systems out there (include the millions of home mini-components, car speakers, etc.) use cheap bipolar electrolytics, commonly rated 50V.
Even many "good" speakers do.
A few try to improve sound and specs, which is good, and use "plastic film" capacitors.
Plastics (polystyrene, polypropilene, mylar, etc.) have such phenomenal insulation capabilities that even the thinnest ones achievable (because of "mechanical" reasons) will still stand a lot of voltage, so when you go shopping you´ll usually find them in high voltage versions.
Even considering humble paper in oil , you can only make paper so thin before it tears itself when trying to use it.
Hey, think about copper wires!!!!
You will find, say, 0.25mm wires in ribbon cables even if they pass micro to pico amperes of current , if at all, when feedin g, say, a Tube grid or Fet gate.
Same thing.
It's also because of the uF values that are needed. For typical hifi systems (mostly less than 150w) a 50V cap is mostly enough. But you don't find those in the uF values you need. But i do agree it's not needed to have higher voltages.
And i prefer film caps over elco's for stability. An elco changes over time, film caps when made right don't. And it goes faster than most think. A few weeks ago i had to rebuild a pair of 1999's B&W MD 604 crossovers as the 4 elco's in it were gone. I did replace them with simple and cheap generic Wima MKP's (wich needed more space, so i had to redo the whole crossover and adjust for the different esr also, and put it on an other place in the box) and the sound was much better than those worn out elco's. In sound the difference (when the elco's are new) is so subtile that in most cases it won't matter.
And i prefer film caps over elco's for stability. An elco changes over time, film caps when made right don't. And it goes faster than most think. A few weeks ago i had to rebuild a pair of 1999's B&W MD 604 crossovers as the 4 elco's in it were gone. I did replace them with simple and cheap generic Wima MKP's (wich needed more space, so i had to redo the whole crossover and adjust for the different esr also, and put it on an other place in the box) and the sound was much better than those worn out elco's. In sound the difference (when the elco's are new) is so subtile that in most cases it won't matter.
Thanks. Measured the voltage across the bass unit with crossover removed, loud volume, and it was 5 volts. The voltage for home listening at normal volumes appears to be quite low.
Would the voltage for a valve amp be any higher as they tend to operate on higher voltages. Don't have valve amp on hand to do a check.
Would the voltage for a valve amp be any higher as they tend to operate on higher voltages. Don't have valve amp on hand to do a check.
Then there is the difference between rms and peak voltage. Peak voltages are what the capacitor must be rated for, while rms or mean is what most voltage meters (try to) measure.
High voltage signals are found within the valve amp circuitry, but the output transformer reduces them to normal levels for delivery to the loudspeaker.