Open Full Range with boxed, passive, helper woofer - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

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 21st March 2013, 03:56 AM   #1
TiMBoZ is offline TiMBoZ  Australia
diyAudio Member
 
Join Date: Aug 2012
Location: Sydney
Default Open Full Range with boxed, passive, helper woofer

a Low Pass filter question:

At moment I have semi open/U-frame, full range direct to amp, no filtering. With a low pass on a boxed 'helper' woofer - both parallel to a burly S.S amp.

I wanna do a 2nd or 3rd order filter at 150 Hz on the helper woofer

At 150Hz the amp is seeing a combined parallel load of 4 Ohms: the full range at @10.5 Ohms & Woof at 6.5 Ohms.

My Question?:

Do the coil/cap values for the low pass 'helper' woofer need to be at the combined value of 4 Ohms or the woofer input value of 6.5 Ohms?

I'm confused for some reason.

Last edited by TiMBoZ; 21st March 2013 at 04:12 AM.
  Reply With Quote
Old 21st March 2013, 04:17 AM   #2
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
As they are not pure resistance and we are talking about audio, what do
those numbers come from ?
I guess that you have just measured the DC resistance of the coils, which is
a factor of the lenght of the wire and its diameter.
The amplifier works by trying to mantain stable voltage ( potential) at its output . The load represented by a speaker presents something called complex load, so there is an argument (phase) and a module ( impedance).
The amplifier should be specified at (max power) and which load to be sufficiently stable ( phase deviation margin).
  Reply With Quote
Old 21st March 2013, 04:53 AM   #3
TiMBoZ is offline TiMBoZ  Australia
diyAudio Member
 
Join Date: Aug 2012
Location: Sydney
Quote:
what do those numbers come from ?
The numbers come from the graph that comes with the drivers. It's a fairly straight forward question isn't it. I'm hoping for a fairly straight forward answer. Thanks Pico.
  Reply With Quote
Old 21st March 2013, 05:13 AM   #4
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Uh, sorry: so you just pointed your finger at 150 Hz at each graph and you derived which impedance.
My skills made me writing what I wrote, my mathematic mind told me that it was just right so I submitted the post to the Forum.
To understand what I wrote ...well that's a mistery !

At 150 Hz probably you are very near to FR's Fs, on the descending side of the bell shaped graph of the impedance, which peak is located at Fs.
For the woofer side, it should be already a (nearly) straight line.
A boxed woofer presents an inductive type of load (the argument of the impedance, i.e. the phase angle) before Fs and a capacitative load above Fs.
  Reply With Quote
Old 21st March 2013, 05:37 AM   #5
TiMBoZ is offline TiMBoZ  Australia
diyAudio Member
 
Join Date: Aug 2012
Location: Sydney
Thanks Pico. Anyone else?

Do I set the filter values at the combined parallel load of both drivers or the just the load of the woofer at 150Hz?
  Reply With Quote
Old 21st March 2013, 06:22 AM   #6
TiMBoZ is offline TiMBoZ  Australia
diyAudio Member
 
Join Date: Aug 2012
Location: Sydney
Just to clarify, the impedance of woofer is pretty flat at zmin at 6.4 Ohm @ 150Hz. the woofer Fs = 27Hz. The impedance of Full range is just starting to rise toward Fs (42Hz) at 150Hz from zmin approx 9 Ohms up to 10.5 Ohms.

The low pass filter is being applied to the woofer only.

Yes, these numbers are approximate, not precisley engineered, but will do for me, for a 'DIY helper' woofer to fill in under the open full range.

Is the impedance created by the box interering with impedance curve of the woofer to such an extent we can't guestimate a basic value?
  Reply With Quote
Old 21st March 2013, 06:37 AM   #7
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Hi, yes, I hate to read A&Q made by only two guys
And I don't measure anything, just slap a big coil and some cap to model
the knee ...very basic
BTW haven't you read anything about F.A.S.T. ( fullrange and subwoofer tecnique) ?
Also a series crossover might work, just a coil and a cap ...
but it depends on which drivers you use.
BTW(2) Which drivers are those ? For a minimum guessestimate, like diameter, sensitivity....
  Reply With Quote
Old 21st March 2013, 07:17 AM   #8
Johno is offline Johno  Australia
diyAudio Member
 
Johno's Avatar
 
Join Date: Oct 2010
Location: Up in the alps - motorcycle heaven
As the low pass filter is in parallel with the full range you can ignore the the FR and the filter calculations need only consider the woofer impedance.
  Reply With Quote
Old 21st March 2013, 07:31 AM   #9
TiMBoZ is offline TiMBoZ  Australia
diyAudio Member
 
Join Date: Aug 2012
Location: Sydney
Phew! Thanks Johno. Was hard to get my head around for some reason? So the values need to be relative to the input of woofer.

Ride safe.
  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
Alpair 10 vs Alpair 7 - Open baffle with boxed woofer. Passive Xover. TiMBoZ Markaudio 56 3rd March 2014 07:21 PM
full range + woofer OR full range + tweeter ? Bigun Full Range 35 20th March 2013 06:47 PM
Which helper woofer in open baffle would you pick? Racket Scientist Full Range 15 21st December 2010 02:13 PM
full range+ passive radiator sintacto Full Range 9 15th May 2008 08:09 PM
full range (open baffle) then_dude Full Range 15 9th March 2004 02:58 PM


New To Site? Need Help?

All times are GMT. The time now is 12:45 AM.


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