1st-Order high value capacitor in parallel is possible?

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msh1999

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Joined 2017
#1
Hello guys, I`m experimenting on some project using 4ohm Tweeter.

I got some very interesting results for my needs using just a cap in parallel (without anything else in the crossover) with a value of 10K-MFD, but of course the amplifier didn't like that move😀

I read that using a resistor in series will make it possible using just the capacitor without adding a coil, is that true? if so what resistor value i should add for the task?

Another thing, the capacitor is not bipolar, it must be bipolar type for crossover applications?
 
#2
msh1999 said:
using just a cap in parallel I read that using a resistor in series will make it
possible using just the capacitor without adding a coil, the capacitor is not bipolar
Click to expand...


The capacitor must be in series with the tweeter to form a high pass filter. A shunt capacitor would put the amplifier in distress, without doing any filtering at all. A series resistor is often used for padding, but a series resistor with a shunt capacitor would form a low pass filter, just the opposite of what you need. Often a series resistor (a few ohms) and a
series capacitor (several uF) are used for a simple high pass filter with padding. A bipolar capacitor must be used for a passive crossover.
 
#3
rayma said:
The capacitor must be in series with the tweeter to form a high pass filter. A shunt capacitor would put the amplifier in distress, without doing any filtering at all. A series resistor is often used for padding, but a series resistor with a shunt capacitor would form a low pass filter, just the opposite of what you need. Often a series resistor (a few ohms) and a
series capacitor (several uF) are used for a simple high pass filter with padding. A bipolar capacitor must be used for a passive crossover.
Click to expand...
I`m trying to create a gentle lowpass, not a highpass, the normal 1st order coil lowpass didnt do the trick, the capacitor did.

so you're saying that if i add a resistor in series along with the capacitor the amplifier will no longer be in distress since its now basically a 2nd order crossover?
 
#4
msh1999 said:
I`m trying to create a gentle lowpass, not a highpass, the normal 1st order coil lowpass didnt do the trick, the capacitor did. so you're saying that if i add a resistor in series along with the capacitor the amplifier will no longer be in distress since its now basically a 2nd order crossover?
Click to expand...

Can you post the crossover schematic? A tweeter needs a high pass filter, since it cannot produce low frequencies.
Generally, for n-th order filters you need n reactive elements (not including similar parts in parallel or series together). Resistors don't count toward the filter order number, since they cannot filter by themselves, only attenuate.
http://www.physics.unlv.edu/~bill/PHYS483/filters.pdf
 
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#5
rayma said:
Can you post the crossover schematic? A tweeter needs a high pass filter, since it cannot produce low frequencies.
Generally, for n-th order filters you need n reactive elements (not including similar parts in parallel or series together). Resistors don't count toward the filter order number, since they cannot filter by themselves, only attenuate.
Click to expand...
I`m building headphones out of an AMT tweeter, this is why i need lowpass filter instead of highpass, the crossover is as simple as it sounds, and ofc there are no other drivers that are working along with it.

so i understand there is no real way to make it happen unless i start making things much more complex, i guess i will give up on the idea, thanks for the help!
 
#6
msh1999 said:
I`m building headphones out of an AMT tweeter, this is why i need lowpass filter instead of highpass, the crossover is as simple as it sounds, and ofc there are no other drivers that are working along with it.

so i understand there is no real way to make it happen unless i start making things much more complex, i guess i will give up on the idea, thanks for the help!
Click to expand...

Converting AMT tweeters into headphones. Why would you need a low pass filter, since they drop off below 1kHz?
 

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#9
To boost the highs, you have to cut the lows instead.

The factor for cutting the lows is: Rheil / (Rheil + Rseries).

In dB that is: cut (dB) = 20 x log (Rheil / (Rheil + Rseries))

Choose the capacitor for the frequency where the cut starts.
 
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#10
msh1999 said:
I read that using a resistor in series will make it possible using just the capacitor without adding a coil, is that true?
Click to expand...
Yes. It is more popular with tweeters when you use a series resistor and a shunt inductor as the only crossover components.

It can also be done with woofers but it is not popular. The thing with the series resistor is it should be high enough so the amp is not uncomfortable. With a tweeter you are already using a resistor to reduce the level. This is how you decide the value.

With a woofer you should use a few ohms at least, this resistor may get hot. It will change the bass at resonance a little, this is easier with the tweeter because the inductor reduces the impedance peak.

Is it worth it?
 
#13
AllenB said:
Yes. It is more popular with tweeters when you use a series resistor and a shunt inductor as the only crossover components.

It can also be done with woofers but it is not popular. The thing with the series resistor is it should be high enough so the amp is not uncomfortable. With a tweeter you are already using a resistor to reduce the level. This is how you decide the value.

With a woofer you should use a few ohms at least, this resistor may get hot. It will change the bass at resonance a little, this is easier with the tweeter because the inductor reduces the impedance peak.

Is it worth it?
Click to expand...
thanks🙂
what do you mean by "is it worth it"?
 
#14
I think what msh1999 is trying to achieve is to use the tweeter way below it's usable frequency range.

ie drop it maybe 30 or 40 db at the higher frequencies somehow trying to make a flat response from possibly the low 100's of hz.

Possibly I'm wrong, but I think that is the intent......

edit: ok looks like I'm wrong 😉

Tony.
 
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