BLH compression chamber. - 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 3rd July 2012, 01:00 PM   #1
diyAudio Member
 
Join Date: Aug 2011
Default BLH compression chamber.

What, broadly speaking is the effect of altering compression chamber volume in a back loaded horn and can this question be answered in a general sense without going into driver and horn specifics?
  Reply With Quote
Old 4th July 2012, 02:06 AM   #2
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
It's an acoustic low pass filter same as a vented cab, not a compression chamber like a sealed cab that's used to seal up a BLH to make it a compression loaded one, so the smaller it is, the higher it's HF corner frequency, Fc and vice versa.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 4th July 2012, 12:13 PM   #3
diyAudio Member
 
Join Date: Aug 2011
Forgive my stupidity, I don't understand "corner frequency" or "Fc and vice versa." Any clarification would be gratefully accepted as would an allowance for my ignorance.
  Reply With Quote
Old 4th July 2012, 01:32 PM   #4
diyAudio Member
 
Join Date: Jan 2012
Quote:
Originally Posted by doubtingthomas View Post
Forgive my stupidity, I don't understand "corner frequency" or "Fc and vice versa." Any clarification would be gratefully accepted as would an allowance for my ignorance.
Cutoff frequency - Wikipedia, the free encyclopedia

i think(?) that will help.

also subscribed for knowledge. these bloody things have me completely bamboozled.
  Reply With Quote
Old 4th July 2012, 02:16 PM   #5
zman01 is offline zman01  Bangladesh
diyAudio Member
 
Join Date: Feb 2011
Location: Dhaka
Quote:
Originally Posted by gafhenderson View Post

also subscribed for knowledge. these bloody things have me completely bamboozled.
+1 and add me to the list.
  Reply With Quote
Old 4th July 2012, 03:39 PM   #6
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
There is a difference between the volume of a chamber between the driver and the horn's throat and a "constriction" (of sorts) that takes the open face of a driver that faces into the throat of a horn and reduces that opening so the volume of air now has to run through a smaller orifice. The second causes an increase in compression ratio.

What the former does is to form a Low Pass Filter (LPF) which means that if you were using a speaker that had output up into the midrange or above, with a volume between the speaker and the throat, the higher frequencies would be made to roll off, acoustically. Not electrically.

Of course too much volume there and you lose the benefit of having a horn at all...

There are formulas for this stuff... and Hornresp (if you can figure it out) will simulate this stuff pretty well - I am told!

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 5th July 2012, 07:14 AM   #7
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by bear View Post
There are formulas for this stuff... and Hornresp (if you can figure it out) will simulate this stuff pretty well - I am told!
The attached Hornresp screenprints illustrate how a horn throat chamber can be dimensioned to act as an acoustic low pass filter. Screenprint 3 compares the power response of a horn having a throat chamber volume Vtc = 1000cc (gray trace) against the same horn with throat chamber volume Vtc = 2000cc (black trace).

Kind regards,

David
Attached Images
File Type: png Data.png (52.3 KB, 277 views)
File Type: png Schematic.png (45.3 KB, 279 views)
File Type: png Compare.png (63.5 KB, 283 views)
__________________
www.hornresp.net
  Reply With Quote
Old 5th July 2012, 02:34 PM   #8
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
sweet!

there it is...
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 5th July 2012, 06:49 PM   #9
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
Oh, somebody reading the thread mentioned to me about this:


http://www.quarter-wave.com/Horns/BL...gn_Article.pdf


Also, my presumption - perhaps wrong - is that the OP was discussing a speaker that is/was more or less like the standard "PA/SR" type folded bass horn, with the front of the driver directly radiating. One sees this with folded horns and the "J scoop" type.

The "horns" that people have been building with the rather small mouth (things less than several feet on a side for the mouth) in my mind are tapered, unstuffed, transmission lines, not true horns - no matter what anyone calls them.

If they were true horns, then the mouth size would be so small as to cause monster comb filter effects... which for all I know, they have (I have not seen them measured, maybe because I am not looking?).

Fwiw, Fyi, and all that good stuff...
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 5th July 2012, 07:36 PM   #10
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
It depends if you define a horn by laying down the stricture that it must be impedance matched down to Fc. If we are to apply our definitions so narrowly, then for example a 'tapered, un-stuffed transmission lines' is an oxymoron, since a transmission line, bysimilarly narrow defining standards, would be an untapered, stuffed (or otherwise damped) plane wave tube with the flattest possible impedance as the only objective.

It's really not worth getting hung up over definitions IMO. Life is far too short. As far as I'm concerned, I just call anything that expands toward the terminus a horn, since it will possess some degree of 1/2 wave behaviour.

Last edited by Scottmoose; 5th July 2012 at 07:43 PM.
  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
Question About The Effects of Damping Materials In the Compression Chamber of a BLH mister pig Full Range 13 25th January 2010 04:28 AM
So, what exactly does a compression chamber do?? NV&H Full Range 2 5th February 2006 12:40 AM
front loaded bass horn without rear compression chamber? paulspencer Subwoofers 9 28th October 2005 04:53 PM
Compression Chamber Size mrlots2do Full Range 29 17th August 2005 06:02 PM
Why, horn, compression chamber? tade Subwoofers 8 28th April 2005 06:04 AM


New To Site? Need Help?

All times are GMT. The time now is 05:32 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