Passive 40Hz HPF - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

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
Reply
 
Thread Tools Search this Thread
Old 20th June 2014, 12:30 PM   #1
moldo2 is offline moldo2  Denmark
diyAudio Member
 
Join Date: Jul 2013
Default Passive 40Hz HPF

To protect the woofer in a horn I'm building I'd like to filter out the frequencies below 40Hz so the excursion doesn't kill the driver(Hornresp sim says excursion will be 7mm max, but the driver has 5mm xmax). As far as I understand a single bipolar cap in series with the woofer will act as a passive HPF, but I assume it has to handle a significant amount of power? My question is, how would you guys go about cutting the low frequencies and protecting the driver?
  Reply With Quote
Old 20th June 2014, 12:34 PM   #2
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by moldo2 View Post
To protect the woofer in a horn I'm building I'd like to filter out the frequencies below 40Hz so the excursion doesn't kill the driver(Hornresp sim says excursion will be 7mm max, but the driver has 5mm xmax). As far as I understand a single bipolar cap in series with the woofer will act as a passive HPF, but I assume it has to handle a significant amount of power? My question is, how would you guys go about cutting the low frequencies and protecting the driver?
At 40 Hz? The only sensible option is active filtering.
__________________
www.diysubwoofers.org
  Reply With Quote
Old 20th June 2014, 12:39 PM   #3
diyAudio Member
 
Join Date: Mar 2013
+1, a single cap won't provide any protection with only a 6db slope you need an 18db-24db filter and that will cost you big dollars, so the better solution is to buy a PA processor(LMS) since you will likely also need delay and EQ for these things anyway.
  Reply With Quote
Old 20th June 2014, 12:50 PM   #4
diyAudio Member
 
Join Date: Sep 2009
I used to have a pair of 3-way Infinity speakers with a 12 inch woofer. They had excellent bass. At some time I measured the dc resistance and found they acted like an open circuit. I presume they had a bipolar series capacitor
  Reply With Quote
Old 20th June 2014, 01:09 PM   #5
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by jaclement View Post
I used to have a pair of 3-way Infinity speakers with a 12 inch woofer. They had excellent bass. At some time I measured the dc resistance and found they acted like an open circuit. I presume they had a bipolar series capacitor
Sealed or vented speakers?
__________________
www.diysubwoofers.org
  Reply With Quote
Old 20th June 2014, 01:15 PM   #6
Jonhny is online now Jonhny  Sweden
diyAudio Member
 
Join Date: Mar 2005
Location: Sweden
Is it a problem if you exceed xmax that Little with sine Waves?
  Reply With Quote
Old 20th June 2014, 01:35 PM   #7
diyAudio Member
 
Join Date: Sep 2009
The Infinity speakers were acoustic suspension (sealed) .
  Reply With Quote
Old 20th June 2014, 02:59 PM   #8
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by jaclement View Post
The Infinity speakers were acoustic suspension (sealed) .
Using a very large capacitor in series with the woofer is a well-known but hardly-used way of extending the bass response of a sealed alignment. You end up with a lower F3, but a sharper rolloff below that point.
__________________
www.diysubwoofers.org
  Reply With Quote
Old 21st June 2014, 12:42 PM   #9
moldo2 is offline moldo2  Denmark
diyAudio Member
 
Join Date: Jul 2013
Quote:
Originally Posted by Jonhny View Post
Is it a problem if you exceed xmax that Little with sine Waves?
I'd like to know that as well, but I assume it is?
  Reply With Quote
Old 21st June 2014, 05:35 PM   #10
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by Jonhny View Post
Is it a problem if you exceed xmax that Little with sine Waves?
The type of signal makes no difference as far as excursion, but sine waves have only a 3 dB crest factor, much more average power than typical music, and double the power of the AES test signal which has 6 dB crest factor. Sine wave testing needs to be done quickly if done at the AES rating, or the voice coil can be burnt up.

Hornresp does not consider that excursion is often limited by the suspension, and as Xmax is exceeded, the magnetic force becomes less, requiring more power to move the cone any further.

An example of measured vs. Hornresp simulated excursion below.
HP is certainly a good idea to keep from wasting power and tearing up drivers, but I probably would not worry about a predicted difference from 5 to 7mm.
At any rate, I'd measure the excursion to see what it actually is.

Art
Attached Images
File Type: png Excursion.png (61.3 KB, 62 views)
  Reply With Quote

Reply


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
lpf and hpf setting. olsound Analog Line Level 26 25th July 2012 04:13 PM
Simple passive HPF for 2 channel fronts qguy Multi-Way 5 19th September 2011 09:41 PM
OPA627 Active HPF D_GR8_1 Chip Amps 22 24th February 2010 12:37 PM
split hpf issues? jethdub Chip Amps 0 6th June 2008 01:22 AM
CAP for HPF ? foo Multi-Way 0 27th March 2005 04:25 PM


New To Site? Need Help?

All times are GMT. The time now is 07:52 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2