Arecapacitors,capacitors? What's the difference between a 100uf cap rated at 12v, and a 100uf cap rated at 100v? Does the voltage rating matter if the cap is going to be used as a passive filter?
Also, while looking for a 4mH coil, I found 2. 1 looks like a little oval shaped can about 1 1/4" taLL, and the other is a coil that's about 3" in diameter. Will either one work in a passive filter?
Replies (5)
uochronos on 03/7/2005 01:48:31
you wanna mathch the cap to the amount of power going threw it... dont use a 12volt cap on something thats going to pull 100volts threw it.... that is if my memory on caps is accrate which i belive it is.
as for the coil... thats not enough info to tell you anything about either one... my friend who builds his own Xovers has tons of coils all over the place and he has a super small one that is like the best you can get. and he has a really large one comapred to the first that is a good one. he also has alot inbetween some good some not so good.
size isnt really the deciding factor. well it is hehe but more in length not dimensions of the coil
Chronos
swez on 03/7/2005 04:56:13
That value cap will filter out lows below 400 Hz at a gradual -6dB/oct., slope. That would be fine for midrange applications and blocking lows from small format speakers under 5". (assuming we are discussing a 4 ohm speaker)
Your F3 (-3dB down point) is 300 Hz and will net -6dB attenuation at 200 Hz. (Butterworth design) The cap to use will need to be "non-polorized" (bipolar) and rated at 30 volts or higher. It will be an electrolytic cap too.
FYI: Here's how a 100 uF, 6 dB/oct. slope filter will work
400 Hz = zero attenuation (say 20 volts source)
300 Hz = -3dB attenuation (15 volts passed)
200 Hz = -6 dB attenuation (10 volts passed)
100 Hz = -12 dB attenuation (5 volts passed)
50 Hz = -18 dB attenuation (2.5 volts passed)
If you wanted to add a coil to this for a 12 dB/octave slope, that value would need to be 1.6 mH. This coil would be in parallel with the voice coil and the cap will be in series with amp to speaker/inductor circuit. This is a 2nd order Butterworth alignment. The slope rolloff is much faster here as opposed to a single element passive filter.
Slope comes out like this:
400 Hz = zero attenuation (say 20 volts source)
300 Hz = -6 dB attenuation (10 volts passed)
200 Hz = -12 dB attenuation (5 volts passed)
100 Hz = -24 dB attenuation (1.25 volts passed)
50 Hz = -36 dB attenuation (0.3 volts passed)
The "take away" to ponder here is:
1. What is the desired frequency pass range you need?
2. What is the slope characteristic required? (6 or 12 dB/oct.)
Give more details and can guide you on component choices and how to buy/make a crossover and install.
Swez
gearhead on 03/7/2005 07:25:30
The schematic I have for connecting my amp for tri-mode shows a 100uf cap on the + of both fullrange speakers, and a 4mH coil on the + of the sub. I have access to a military electronics surplus store for a couple of days (I'm on vacation), so I figured I'd pick up what I need.
swez on 03/7/2005 11:16:27
That inductor will give you a shelf point of 160 Hz to a 4 ohm sub. Meaning, everything below 160 Hz will pass with zero attenuation. Is a bit high in frequency, but it will work. Going closer to 100 Hz., would be a better option. That would require a coil value of 6.4 mH.
As for the cap value, again... 100 uF will begin cutoff at 400 Hz., and below. For full range speakers, a better choice would be 400 uF as that would pass all signals above 100 Hz., and attenuate those below.
These values assume all speakers are 4 ohms.
Swez
PS The schematic mentioned above would give you a low pass signal of 20-160 Hz. The filter cap noted above will be usable above 400 Hz. That will leave a wide band gap between 160-400 Hz. Not a well designed crossover.
Victor on 03/10/2005 09:42:29
agreed...
Also, while looking for a 4mH coil, I found 2. 1 looks like a little oval shaped can about 1 1/4" taLL, and the other is a coil that's about 3" in diameter. Will either one work in a passive filter?
Replies (5)
uochronos on 03/7/2005 01:48:31
you wanna mathch the cap to the amount of power going threw it... dont use a 12volt cap on something thats going to pull 100volts threw it.... that is if my memory on caps is accrate which i belive it is.
as for the coil... thats not enough info to tell you anything about either one... my friend who builds his own Xovers has tons of coils all over the place and he has a super small one that is like the best you can get. and he has a really large one comapred to the first that is a good one. he also has alot inbetween some good some not so good.
size isnt really the deciding factor. well it is hehe but more in length not dimensions of the coil
Chronos
swez on 03/7/2005 04:56:13
That value cap will filter out lows below 400 Hz at a gradual -6dB/oct., slope. That would be fine for midrange applications and blocking lows from small format speakers under 5". (assuming we are discussing a 4 ohm speaker)
Your F3 (-3dB down point) is 300 Hz and will net -6dB attenuation at 200 Hz. (Butterworth design) The cap to use will need to be "non-polorized" (bipolar) and rated at 30 volts or higher. It will be an electrolytic cap too.
FYI: Here's how a 100 uF, 6 dB/oct. slope filter will work
400 Hz = zero attenuation (say 20 volts source)
300 Hz = -3dB attenuation (15 volts passed)
200 Hz = -6 dB attenuation (10 volts passed)
100 Hz = -12 dB attenuation (5 volts passed)
50 Hz = -18 dB attenuation (2.5 volts passed)
If you wanted to add a coil to this for a 12 dB/octave slope, that value would need to be 1.6 mH. This coil would be in parallel with the voice coil and the cap will be in series with amp to speaker/inductor circuit. This is a 2nd order Butterworth alignment. The slope rolloff is much faster here as opposed to a single element passive filter.
Slope comes out like this:
400 Hz = zero attenuation (say 20 volts source)
300 Hz = -6 dB attenuation (10 volts passed)
200 Hz = -12 dB attenuation (5 volts passed)
100 Hz = -24 dB attenuation (1.25 volts passed)
50 Hz = -36 dB attenuation (0.3 volts passed)
The "take away" to ponder here is:
1. What is the desired frequency pass range you need?
2. What is the slope characteristic required? (6 or 12 dB/oct.)
Give more details and can guide you on component choices and how to buy/make a crossover and install.
Swez
gearhead on 03/7/2005 07:25:30
The schematic I have for connecting my amp for tri-mode shows a 100uf cap on the + of both fullrange speakers, and a 4mH coil on the + of the sub. I have access to a military electronics surplus store for a couple of days (I'm on vacation), so I figured I'd pick up what I need.
swez on 03/7/2005 11:16:27
That inductor will give you a shelf point of 160 Hz to a 4 ohm sub. Meaning, everything below 160 Hz will pass with zero attenuation. Is a bit high in frequency, but it will work. Going closer to 100 Hz., would be a better option. That would require a coil value of 6.4 mH.
As for the cap value, again... 100 uF will begin cutoff at 400 Hz., and below. For full range speakers, a better choice would be 400 uF as that would pass all signals above 100 Hz., and attenuate those below.
These values assume all speakers are 4 ohms.
Swez
PS The schematic mentioned above would give you a low pass signal of 20-160 Hz. The filter cap noted above will be usable above 400 Hz. That will leave a wide band gap between 160-400 Hz. Not a well designed crossover.
Victor on 03/10/2005 09:42:29
agreed...
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