homemalow pass filter ??'s

[binsky3333]

Hey guys, im building my own subwoofer amp. Most subwoofers do frequencies from like 80-200hz. I know in order to achieve this, i must create a low pass filter. Would this work? Is this really all that a low pass filter is? http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/experiment/lowpass/lpf.html

Just a simple resistor and capacitor? Also where does the low pass filter go? Before the amp, or after it?

 

[richie00boy]

Subs typically do 20-100Hz.

That is a low pass filter, but it's not suitable for you because the rate of roll off is too shallow - it is a 1st-order filter. You need at least 2nd-order. It should go before the power amp as an active filter.

 

[binsky3333]

Subs typically do 20-100Hz.

That is a low pass filter, but it's not suitable for you because the rate of roll off is too shallow - it is a 1st-order filter. You need at least 2nd-order. It should go before the power amp as an active filter.

Crap, dont know what happened to the title, but what do you mean by 1st-order and 2nd-order? Could you elaborate a bit more?

Do you mean, those are the wrong cap and resistor values for my filter?

Thanks in advance!

 

[richie00boy]

It couldn't be more wrong. Well actually that is a bit harsh I suppose.

Read up about active filters, ESP site is a good one. I also have a sub-woofer controller project on my website.

 

[binsky3333]

It couldn't be more wrong. Well actually that is a bit harsh I suppose.

Read up about active filters, ESP site is a good one. I also have a sub-woofer controller project on my website.

Wow, thats exaactly what im looking for, thanks! Ill look at that, and come back here if i have any questions.

Also where does the low filter go, before or after the amp? Is this the kind of filter i need?

An externally hosted image should be here but it was not working when we last tested it.

OR

An externally hosted image should be here but it was not working when we last tested it.

Thanks!

 

[binsky3333]

Bump, i need this answer ASAP and cant find anything i can understand on the internet.

 

[richie00boy]

I couldn't open those pictures.

 

[binsky3333]

They're on this site.

Active Low Pass Filter

Also would this work? http://www.mouser.com/ProductDetail/Maxim-IC/MAX7480ESA+/?qs=9Cj2FLRihcNXK9knB80IXw%3d%3d

Also is this a second order? http://freecircuitdiagram.com/wp-content/uploads/2008/09/low_pass_filter_lm833.gif

 

[binsky3333]

Sorry for the double post, it wouldnt let me edit mine, but what kind of caps do i use?

Ceramic, electrolyte? Polarized or non-polarized?

 

[richie00boy]

It covers the basics quite well, but it's still not quite what you need as it's only 1st-order. Did you look at the ESP site?

 

[DaveSail]

Low Pass Filter :

Go to : www.parts-express.com Then , get on the " Tech Talk " page .

Those guys can answer all your questions . Also , PE sells every kind /value of Capacitor and Coil ! I've built three pair of awsome speakers using there materials .


David V. Webber

 

[DaveSail]

Low Pass Filters :

Here is a " Link " to a list of ready - made filters . High , Med. and Low .
Perhaps one which will work for you .

LOW/HIGH/BAND PASS CROSSOVERS from Parts Express ship same day and come with 45 day money back guarantee. Free Shipping Available. Order free 10,000 product catalog.

 

[DaveSail]

P.E. " Tech Talk " Page :

Techtalk at Parts-Express.com - Powered by vBulletin

You can read everyone's posts without " registering " , but to post , you need to Register .



Techtalk at Parts-Express.com - Powered by vBulletin

 

[star882]

You're probably looking for a Sallen-Key filter if you're trying to do it with just one opamp. You'll probably want a Butterworth response for a smooth transition.
Sallen?Key topology - Wikipedia, the free encyclopedia

If you need it, there are chips that offer as many as 8 orders of filtering tunable just by changing the clock frequency!
MAX7480 8th-Order, Lowpass, Butterworth, Switched-Capacitor Filter - Overview

Do not confuse the crossover filter with the output filter. The crossover filter is what you're designing to filter the signal at line level. The output filter is used to block the high frequency carrier in hybrid and pure digital amplifiers and operates at the full output voltage. You'll probably want a 50kHz or so carrier in a subwoofer amplifier to reduce switching losses. (Interestingly, the common LC filter used for an output filter is a second order filter.)

 

[binsky3333]

I did look at the ESP site. Didn't find much. And why wont those filters i posted work? Also will that IC filter work? If i use the IC, will i need anything else?

 

[richie00boy]

Here is a " Link " to a list of ready - made filters . High , Med. and Low .
Perhaps one which will work for you

Ready made passive crossovers are pretty poor because they fail to take account of driver acoustic response and impedance changes. He is on about making active filters anyway.

 

[richie00boy]

I did look at the ESP site. Didn't find much. And why wont those filters i posted work? Also will that IC filter work? If i use the IC, will i need anything else?

You didn't look very hard

From the articles section -

Active Filters

And there's many more informative articles and projects.

 

[AndrewT]

Richie,
I don't know why you continue to pass information to this Member.
He obviously has no intention of listening to good advice.
I suspect he won't listen to any advice, his mind is already full of crap.
Well that was the first word that came out of his reply to your help.

 

[AndrewGM]

I agree - he's worse than me

 

[binsky3333]

Thanks guys for your nice comments! Anyway I read that article(Thanks for that) and i found out a lot of useful infomation. Basically what i need to build is a 2nd order sallen-key active low pass filter. I believe that should get the job done, and i have found plenty of schematics and calculators to calculate resistor and capacitor values.