Closed box roll off, a question - 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 March 2005, 05:52 PM   #1
SSassen is offline SSassen  Netherlands
diyAudio Member
 
SSassen's Avatar
 
Join Date: Mar 2005
Location: Edam, The Netherlands
Question Closed box roll off, a question

DIY-ers,

I'm modelling a few enclosures for a sub, and it has been several years since I've been doing anything with loudspeakers so things are a bit rusty, could you help out a little?

XLS10 in a 30-liter closed box
F3 = 78Hz
Qtc = 0.30

If my mind is not playing tricks on me below F3 the slope should be 12db/oct, hence with a reduction in frequency by 1/2 the output should be -12db lower right? Now look at the below graphs.

Click the image to open in full size.

Click the image to open in full size.

BassBox 6 Pro tells me I'll only see a -6db reduction, I'm sure I'm missing something here, but I just don't see it. Anybody care to enlighten me?

Thanks,

Sander Sassen
http://www.hardwareanalysis.com
  Reply With Quote
Old 15th March 2005, 07:02 PM   #2
diyAudio Member
 
Bill Fitzpatrick's Avatar
 
Join Date: Jun 2001
Location: Eugene, OR
Above about F20 the rate of roll-off will vary with Q.
  Reply With Quote
Old 16th March 2005, 04:32 AM   #3
diyAudio Member
 
Join Date: Jul 2003
Location: Silicon Valley
Quote:
Originally posted by Bill Fitzpatrick
Above about F20 the rate of roll-off will vary with Q.

What he said. Look between 5 and 10Hz.

Why would you model an XLS10 in a closed box? :-)
__________________
Davy Jones
  Reply With Quote
Old 16th March 2005, 08:05 AM   #4
SSassen is offline SSassen  Netherlands
diyAudio Member
 
SSassen's Avatar
 
Join Date: Mar 2005
Location: Edam, The Netherlands
Never mind, I overlooked the influence of Q, which is set far too low, as per the below explanation:

Qtc (closed boxes only) The system total Q. Usually Qtc should not be less than the total Q (Qts) of the driver. Many designers consider the optimum value for Qtc to be 0.707. Some commonly used Qtc values are listed below along with a description:

Qtc = 0.5 produces a “Critically Damped” closed-box response.
Qtc = 0.577 produces a “Bessel” or D2 closed-box response.
Qtc = 0.707 produces a “Butterworth” or B2 closed-box response.

The Qtc value is inversely proportional to the system damping. In other words, as the Qtc value is reduced, the system damping increases. Closed boxes with a lower Qtc value produce a “tighter” sound because they are damped more. You might conclude from this that a low Qtc (such as the critically damped 0.5 value) would often be preferred. However, this is not the case. To some listeners a low Qtc sounds a bit “thin” and they prefer a higher value—even as high as 1.0 or higher. Although Qtc values above 0.707 will produce a response bump at the system resonance frequency, the increased level produces a “warmer” sound which some prefer.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
  Reply With Quote
Old 16th March 2005, 08:13 AM   #5
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
I'd certainly disagree that a Q of 0.707 (or even higher) is to be prefered. I agree with Martin Colloms that Qtc of 0.5 to 0.6 gives a much more realistic LF end, and is likely to be a much better interface with the bass enhancement in the listening room due to the 'room modes'.

High Q speakers aways remind me of a teenager showing off his car sound system; impressive but hardly qualifying to be called 'faithful to the original recording'!
  Reply With Quote
Old 17th March 2005, 04:02 AM   #6
mike.e is offline mike.e  New Zealand
diyAudio Member
 
mike.e's Avatar
 
Join Date: Sep 2004
Location: NZ
Send a message via ICQ to mike.e Send a message via MSN to mike.e
http://www.geocities.com/kreskovs/Box-Q.html

  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
Attaching closed cell foam...quick question Glowbug Multi-Way 1 4th April 2008 07:13 PM
tangband closed box question matjans Multi-Way 5 19th January 2004 06:50 PM
Input cap (2.2uF) / 50k pot (bass roll-off) question: GrahamnDodder Chip Amps 6 23rd September 2003 10:32 PM
Opamp low-pass roll-off question ppereira Solid State 46 6th December 2002 04:44 PM


New To Site? Need Help?

All times are GMT. The time now is 02:18 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