Critical Q design theory - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

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
Reply
 
Thread Tools Search this Thread
Old 26th January 2008, 04:33 AM   #1
diyAudio Member
 
Join Date: Sep 2005
Default Critical Q design theory

I failed to find a thread that deals mainly with this subject. As I am planning an all sealed project and some members seem to favor this design over sealed, what is this design, what separates it from sealed, where can I learn more, etc, etc.
  Reply With Quote
Old 26th January 2008, 04:58 AM   #2
ppfred is offline ppfred  Canada
diyAudio Member
 
Join Date: Jan 2002
Location: Montreal
Try this
http://www.customanalogue.com/sub_index.htm
__________________
Believe nothing you read and only half of what you see.
  Reply With Quote
Old 26th January 2008, 05:26 AM   #3
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN


Rasmussen critical Q sub
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  Reply With Quote
Old 27th January 2008, 03:35 AM   #4
diyAudio Member
 
Join Date: Sep 2005
Apparently, there are different opinions, even about this design, so I'll leave it for now.
  Reply With Quote
Old 27th January 2008, 03:55 PM   #5
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Well, the engineering terms on this are quite clear. Critical Q, more precisely called filter response with critical characteristic (opposed to any other characteristic with higher Q like Bessel, Butterworth, Chebycheff), is when you have a set of all real and identical poles in the overall acoustical transfer function's denominator. It is not dependent on the construction type and can be had with CB, BR, BP, OB, Horns and what have you.

The specific merits of a highpass of this type (with the highpass variant we deal with in subwoofer design) is that it shows the minimum overshoot in the time domain, when fed a square pulse, which is synonymous with the flattest achievable group delay change. That's what is critical about it, you can't get beyond these barriers. The compromise (if any) is the very gradual transition into the roll-off. Like Linkwitz put it: the merits of a butterworth highpass are no other than to look good.

The simplest way to model it electrically is a buffered(!) cascade of identical first order highpass networks (simple C-R combos). The electrical analogies are also a good starting point for studies, see for example http://focus.ti.com/lit/ml/sloa088/sloa088.pdf (unfortunately critical filters are not discussed directly by uising that naming -- they call it simple low-pass, but high-pass isn't covered -- , but you can still get the overall concept).

- Klaus
  Reply With Quote
Old 27th January 2008, 07:34 PM   #6
gfiandy is offline gfiandy  United Kingdom
diyAudio Member
 
gfiandy's Avatar
 
Join Date: Jul 2003
Location: Cambridge UK
I am fairly sure that what you have described as a critical Q filter is in fact a Bessel filter. A bessel filter is maximally falt in the time domain, i.e there is no peak in the group delay. It has a Q of 0.505 and this is consistant with the information on the sub design.

Personaly I don't think that the Q of 0.5 is the important factor in this type of Sub sounding good. I think it is because it matches the kind of rise you get from the room gain so you are less likely to get a big hump in the response at the bottom end.

Since the acoustic response is what is important in the waveform shape, it is unlikely that this has a Q of 0.505 in room so it is unlikely that the group delay advantage is mantained.

Having said this, when working on a sub design I had the benifit of an adjustable linkwitz transform box and I can definately say that the sub intergrated into the room best at a Q of arround 0.5 so this is what I designed the LT that when in the amp to do.

Regards,
Andrew
  Reply With Quote
Old 28th January 2008, 12:24 AM   #7
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
A 2nd order Bessel filter has a Q of 1/sqrt(3) = 0.577~
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  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
The Critical Ear fauxpas Tubes / Valves 36 18th December 2007 05:16 PM
Equations,Calculations & Theory of FERRITE TRANSFORMER design dhanukak Power Supplies 4 17th September 2007 02:41 AM
critical Q for car Chris8sirhC Subwoofers 9 28th October 2004 09:47 AM


New To Site? Need Help?

All times are GMT. The time now is 10:22 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