passive notch filter, how much power do they take? - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 31st January 2006, 09:19 PM   #1
Puggie is offline Puggie  United Kingdom
diyAudio Member
Join Date: Oct 2004
Default passive notch filter, how much power do they take?

IF I wanted to build a passive notch filter to flattern out an impedance hump in a speaker (and the resulting hump in the passive Xover response) what percentage of the power sent to the speaker would the filter recieve. the speaker is an 8Ohm VC, and the (currently planned) notch consists of a 14Ohm resistor 6.5mH inductor (is laminate core ok) and a 6.8uF cap.

So if my speaker is recieving 1000W (its a big sub) how much power will the filter be required to take? what wattage values will I want for the components?

  Reply With Quote
Old 31st January 2006, 09:22 PM   #2
Stocker is offline Stocker  United States
diyAudio Member
Join Date: Dec 2003
Location: Austin
power at what frequency? I haven't done anything like the maths involved, but it seems to me that the only frequencies where the filter will take much power would be the ones where the filter has its main AC reactance. The rest of the time I am guessing most filters will take less than a watt (not even warm).
Jesus loves you.
  Reply With Quote
Old 31st January 2006, 09:26 PM   #3
Puggie is offline Puggie  United Kingdom
diyAudio Member
Join Date: Oct 2004
Well its for a PD 2150 sub (, and with a 16uH inductor in series as a low pass filter (starts to roll off about 100Hz) and the peak is centred around 90-100Hz so I presume that is pretty close to worse case scenario.

and before someone says I know active would be better but thats not what I want to know
  Reply With Quote
Old 1st February 2006, 12:12 AM   #4
owdi is offline owdi  United States
diyAudio Member
owdi's Avatar
Join Date: Sep 2003
Location: Bellevue, WA
Default Re: passive notch filter, how much power do they take?

Originally posted by Puggie
So if my speaker is recieving 1000W (its a big sub) how much power will the filter be required to take? what wattage values will I want for the components?

A lot. You can figure it out pretty quickly.

Assuming you have a 4 ohm nominal sub, it takes roughly 60 volts to get 1000 watts rms. When you wire a 6.8mH coil in series with the subwoofer you end up with

(assuming the sub is a 3.2 ohm resistive load, which I know it's not)

60v @ 20hz, 888 watts total, 700 watts to sub, 187 watts to inductor
60v @ 40hz, 733 watts total, 478 watts to sub, 255 watts to inductor
60v @ 80hz, 544 watts total, 263 watts to sub, 281 watts to inductor
60v @ 160hz, 359 watts total, 114 watts to sub, 244 watts to inductor
60v @ 320hz, 213 watts total, 40 watts to sub, 173 watts to inductor

So you need at least a 300 watt inductor. I'm pretty sure my math is right, but don't take my word for it. I've been figuring this stuff out from DIY websites and forums.

  Reply With Quote
Old 3rd February 2006, 01:19 AM   #5
hermanv is offline hermanv  United States
diyAudio Member
Join Date: Apr 2004
Location: Northern California
If I understand your post, you are talking about a network to smooth out the low frequency resonance bump (Fs) in a woofer.

The values you supplied 6.5mH, 14 Ohms and 6.8uF resonate at about 720Hz when connected in series accross the woofer. This is an unusual resonance frequency for a sub-woofer, there is probably a mistake.

Calculating the resistor dissipation is very tricky because it depends on how much of the time power at the resonance frequency is present. At other frequencies the resistor dissipates almost nothing.

If a film capacitor is used and a large wire gauge coil the reactive components will dissipate almost zero power.

Additionally even a 1000 Watt amplifier only delivers about 100 watts of average power because most music has a 10:1 peak to average ratio. So given that all notes are present and only 720Hz notes dissapate much network power, a 10-25 watt resistor will be fine (except if this speaker is being used as a guitar amplifier speaker then you will need at least a 100 watt resistor).

If you change the values, my results will not be valid.
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Passive Notch Filter for Eminence Alpha 15As Horizons Multi-Way 3 27th February 2009 04:22 AM
Passive Notch Filter For Thd Measurement fotios Solid State 8 7th July 2008 07:29 AM
need help wana change 60-Hz twin-T notch filter to 279 Hz filter prorms Solid State 0 9th February 2008 11:38 PM
Can Zaphs notch filter be used without the BSC filter? GuyPanico Full Range 0 21st July 2007 01:27 AM
software for designing passive notch filters Puggie Multi-Way 2 28th June 2005 03:32 PM

New To Site? Need Help?

All times are GMT. The time now is 09:48 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2