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Old 17th January 2013, 06:05 PM   #1
pranab is offline pranab  India
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Unhappy RC Low Pass Filter problem

Dear guys , plz help me sorting out a problem with RC Low Pass Filter. I have made a LPF with a 1KOHM Resistor and 1 MicroFarad Capacitor as shown in many videos on youtube and many other forums , but it dosnt seem to work. Hopefully I have made it correctly but it is just not working. it should decay sound over 150Hrtz but all it does is that it lowers the volume upto 90% and very less sound can be heard . Kindly hlp me solv this problem , actually I am trying to make a HT Sub using a low pass filter and use some speaker with high pass filter to make a Hometheater system a DIY project, but the low pass filter dosnt seem to work . I have altered the caps with different values and resistor with different values but none of the combination worked .......kindly suggest something .......i will post the pics as well
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Old 17th January 2013, 06:09 PM   #2
Mooly is offline Mooly  United Kingdom
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It sounds as though whatever is driving the filter is struggling. If the source feeding the filter has a high output impedance then the 1K and 1uf will effectively "short" the audio.
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Old 17th January 2013, 06:32 PM   #3
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Quote:
Originally Posted by pranab View Post
...LPF with a 1KOHM Resistor and 1 MicroFarad Capacitor as shown in many videos on youtube and many other forums , but it dosnt seem to work.
Are you sure you were in the correct website?
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Old 18th January 2013, 01:19 AM   #4
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This low-pass filter should be getting an input signal from a preamplifier and the output terminals of the filter connected to the input jack of the power amp driving the sub-woofer. Is that what you are doing?

Regards,
Pete
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Old 18th January 2013, 05:15 AM   #5
WSJ is offline WSJ  United States
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Calculated the Transfer Function for the RC Low-pass filter, displayed on graphs, showing Bode diagram, Nyquist diagram, Impulse response and Step response.


(Sample)RC Low-pass Filter Design Tool - Result -
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Old 18th January 2013, 02:06 PM   #6
pranab is offline pranab  India
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Quote:
Originally Posted by Mooly View Post
It sounds as though whatever is driving the filter is struggling. If the source feeding the filter has a high output impedance then the 1K and 1uf will effectively "short" the audio.
I am using a player which has a Double IC built in amplifier, it has enough power to drive atleast 1 X 12" sub , and the player runs at 8 Ohms....... I am posting the link of the tutorial video kindly go though it. I need a very basic low pass filter to minimize the mid . I am not an electronic student and so i have very limited knowledge. Figured Out Simple Low Pass Filter AND single Capacitor LP filter - YouTube
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Old 18th January 2013, 03:07 PM   #7
pranab is offline pranab  India
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Quote:
Originally Posted by cT equals piD View Post
This low-pass filter should be getting an input signal from a preamplifier and the output terminals of the filter connected to the input jack of the power amp driving the sub-woofer. Is that what you are doing?

Regards,
Pete
The videos and forums that i have gone through didnt showed that the LP filter should be attached before the amplifier , it is a passive LPF which can be hooked directly to before a sub ................kindly go through the video Figured Out Simple Low Pass Filter AND single Capacitor LP filter - YouTube

Regards
Pranab
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Old 18th January 2013, 03:09 PM   #8
gootee is offline gootee  United States
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It will be difficult to get high power's current through a 1k resistor.

If you can only access the high power output then you need to consider your filter as speaker crossover. The implementation details will be different because of the high currents involved, and the low downstream impedance of the speaker.
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Old 18th January 2013, 03:35 PM   #9
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Quote:
Originally Posted by pranab View Post
The videos and forums that i have gone through didnt showed that the LP filter should be attached before the amplifier , it is a passive LPF which can be hooked directly to before a sub ...............
Either the videos and forums are incorrect or you have misunderstood the information. A sub-woofer (passive speaker system) generally has impedance of 10 Ohm or less. With a 1 k Ohm resistor in series with the sub-woofer, the woofer at any frequency does not receive more than 1/10th of the voltage applied across the resistor-woofer in-series.

That is, exactly what the previous post says.

Regards,
Pete
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Old 18th January 2013, 04:29 PM   #10
pranab is offline pranab  India
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Quote:
Originally Posted by WSJ View Post
Calculated the Transfer Function for the RC Low-pass filter, displayed on graphs, showing Bode diagram, Nyquist diagram, Impulse response and Step response.


(Sample)RC Low-pass Filter Design Tool - Result -
Friend I dont have that much knowledge regarding bode diagram etc. Here is a link of a Resistor & Cap calculator which I used to calculate the cut off frequency at 160 Hrtz .Low Pass Filter Calculator

Here is the link from where i have seen the tutorial Figured Out Simple Low Pass Filter AND single Capacitor LP filter - YouTube
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