Need info on operating below Fc - 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 15th February 2010, 06:14 AM   #1
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Default Need info on operating below Fc

I have seen a trick mentioned in sub design where the sealed box is deliberately made smaller than normal (Qc >> 0.7) and resulting sub driven entirely in the band below Fc with a 2nd order compensating filter. Unfortunately I can't find the information. Does anyone have a pointer to a discussion of this approach?
__________________
If We The People refuse to hear the truth we will be ruled by liars.
  Reply With Quote
Old 15th February 2010, 06:22 AM   #2
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
May be a search on "linkwitz transform"?
  Reply With Quote
Old 15th February 2010, 06:47 AM   #3
diyAudio Member
 
chris661's Avatar
 
Join Date: Feb 2008
Location: Sheffield
Blog Entries: 8
Quote from the web

An interesting variation on the sealed box is the Extended Low Frequency (ELF) design. (Note that "ELF" is a trademark of Bag End Loudspeakers, one of several companies supplying commercial subwoofers based on this design principle.) An ELF system is simply a sealed box which is operated only below the low frequency -3 dB point (F3). This has several advantages as well as several obvious disadvantages. The advantage include:

* Very small boxes are not only possible, but actually desirable since F3 becomes the upper limit rather than the lower limit of the passband.

* The impedance is quite constant and stable below F3. thus presenting an easier load for an amplifier.

Nothing's free, however, and ELF designs suffer corresponding disadvantages:

* Since the amplifier must equalized to put out an extra 12 dB/octave below F3, efficiency is extremely low and the required amplifier power is exceptionally high. For example, Bob Carver's Sunfire "True Subwoofer" is an ELF design which includes a built-in, dedicated 2,700 watt amplifier!

* The driver must be capable of handling all this additional power.

* Generally speaking, the more power a driver must dissipate, the more distortion it can generate due to the effects of voice coil heating.

* The driver must be designed with a high enough excursion to be able to achieve its equalized low frequency potential.

For more information on ELF designs, see the Bag End (for theory) and Elliot Sound Products (for information on the required electronic crossovers) web sites.


Question - why are you considering such a thing?
__________________
"Throwing parts at a failure is like throwing sponges at a rainstorm." - Enzo
My setup: http://www.diyaudio.com/forums/multi...tang-band.html
  Reply With Quote
Old 15th February 2010, 08:21 PM   #4
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
Sub-Woofer Controller

P48 Sub-Woofer Controller (Rev-A)

Use multiple drivers to allow use of cheaper subwoofers, instead of 30mm X-Max use 4 * 8mm
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 17th February 2010, 01:05 AM   #5
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Thanks. I have an application (portable "mini-console") where I am looking at options for getting the best low bass output in a small package. This seemed like one reasonable approach.

mike
__________________
If We The People refuse to hear the truth we will be ruled by liars.
  Reply With Quote
Old 18th February 2010, 11:12 PM   #6
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
I think this is worth playing with. I think the LT is unnecessarily complex for my situation.

I have an 8" driver from a 1 ft^3 vented sub to play with and I assume that I can determine the resonance in box by simply finding the Zmax frequency so tweaking a box for the desired top end should not be too tough. I have a 200W amp that I can use to power it and would just need to knock up an appropriate LP filter. Should be interesting.

My thinking is that the final driver that I purchase should probably be high Xmax, lowish Qts, lowish Vas, and high electrical power handling. Sound about right?
__________________
If We The People refuse to hear the truth we will be ruled by liars.
  Reply With Quote
Old 19th February 2010, 09:06 PM   #7
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
Re-reading the page on ESP I don't think you need any filters before Rods board.

He says you need the full bass signal < which makes sense, the ELF works below where your current bass drops off
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 19th February 2010, 11:49 PM   #8
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Quote:
Originally Posted by mashaffer View Post
My thinking is that the final driver that I purchase should probably be high Xmax, lowish Qts, lowish Vas, and high electrical power handling. Sound about right?
Works for me! FYI, Qts = 0.312 gives the maximum bass extension for the minimum box size.


GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 20th February 2010, 01:10 AM   #9
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
Quote:
Originally Posted by GM View Post
Works for me! FYI, Qts = 0.312 gives the maximum bass extension for the minimum box size.


GM
Interesting observation GM, never thought along those lines before, although looking quickly at my favourite woofers( Vifa M-22 and Cerwin-Vega Vega154) they have Qts of 0.33; very similar??

My woofers have much higher Vas and Qts so I was thinking of putting them in an undersized but Aperiodic box.
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 20th February 2010, 01:35 AM   #10
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Yeah, unfortunately I wasn't sharp enough to notice it though, it was pointed out to me way back when by an acoustical engineer employed by the local Altec distributor that helped me to get through all the math in Altec's T/S tech bulletins. Seems to me that djk? has posted it too.

Sounds like a plan as long as they aren't too undersized since less is always less in acoustics.........

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  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
FC or FM impsick Parts 3 2nd October 2007 02:46 AM
Panasonic FC or Elna Cerafines Borc Chip Amps 1 4th April 2005 08:34 PM
Panasonic FC in Aleph P bbakota2000 Pass Labs 8 8th January 2005 07:38 PM
RFI fc zahlm Parts 2 27th May 2004 12:45 AM
Biamp: Wich fc ? Higo Multi-Way 18 5th August 2003 12:24 PM


New To Site? Need Help?

All times are GMT. The time now is 08:12 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