Estimation of Xmax w.o. any VC data? - 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 18th August 2010, 08:54 AM   #1
diyAudio Member
 
Join Date: Sep 2005
Default Estimation of Xmax w.o. any VC data?

I have an 8" sub, Response RW-8 that I'm planning to use in a ported enclosure. Apparently, I'm in need of the data for Xmax and there is nothing useful in the very sparse data sheet to help me out. I know I've read somewhere of a way to at least approximate the Xmax value, but I cannot recall where it was.

Anyone knows how to do it?
  Reply With Quote
Old 18th August 2010, 10:53 AM   #2
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
Shine a light through the spider, see how much overhang there is on the VC, add about 25% of the top plate.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 18th August 2010, 06:35 PM   #3
diyAudio Member
 
Top Shelf's Avatar
 
Join Date: Apr 2010
Location: Midland, Ontario
Like djk said, I use a green pen laser for better illumination thru
the spider. It also helps to have a good eye @ estimating inches or
millimeters.
__________________
JEREMY M_________________________________
I like it loud, BUT NOT TOO LOUD!.... Hey do you hear that high pitched ringing sound ?
  Reply With Quote
Old 19th August 2010, 12:47 AM   #4
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally Posted by buggsson View Post
I have an 8" sub, Response RW-8 that I'm planning to use in a ported enclosure. Apparently, I'm in need of the data for Xmax.
What do you want to know? Really, there is nothing wrong with putting in a value of say 5mm just to see what you get. If you can't see the coil, many inexpensive woofers have an xmax of about 1/2 to 1 times the top plate thickness....
__________________
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 19th August 2010, 12:59 AM   #5
diyAudio Member
 
Join Date: Nov 2005
You don't need Xmax data for design except for choosing minimum port diameter, of course. If you are sensitive to harmonic distortion it's pretty easy to tell when a woofer is reaching its excursion limit by driving it in free air with a good amp and a clean 20Hz sine tone until you start hearing something other than 20Hz. With a decent eye, measure the excursion when unacceptable harmonics (hardly any more than you start off with) are detected. That's woofer Xmax. Watch that parallax.

Last edited by Andrew Eckhardt; 19th August 2010 at 01:04 AM.
  Reply With Quote
Old 21st August 2010, 08:12 AM   #6
diyAudio Member
 
Join Date: Sep 2005
Quote:
Originally Posted by Andrew Eckhardt View Post
You don't need Xmax data for design except for choosing minimum port diameter, of course.
That's the very reason! That seemed to be a good parameter to know, if attainable. I'll give the visual inspection a try, and if it doesn't work, a guesstimate will have to do. It's not very important, the result of theese/or that wooferbox (dual), as I'm just gonna have this pair of drivers to train measurements on, so I don't wreck the "real" drivers when they arrive.
  Reply With Quote
Old 24th August 2010, 12:59 PM   #7
HK26147 is offline HK26147  United States
diyAudio Member
 
Join Date: Jan 2008
You could attempt to measure it yourself:

Click the image to open in full size.
  Reply With Quote
Old 26th August 2010, 09:43 AM   #8
diyAudio Member
 
Join Date: Sep 2005
For getting the dust cap to move, do you play some test tone, music or other means when doing the trick as per the attached image?

On another forum, there was a guy who measured Xmax electrically, I didn't really understand the method, but it takes some gear to be able to do it, and knowledge of course.

I've arbitrarly decided on 6mm as "my" value. I've pressed down gently with my fingers, and I believe 6mm will be a safe figure. However, I've to read more carefully in the future, I missed you are supposed to shine through the spider, will do later this evening. Maybe I get something different after that.
  Reply With Quote
Old 26th August 2010, 01:05 PM   #9
HK26147 is offline HK26147  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
On another forum, there was a guy who measured Xmax electrically,...
( I believe I've seen this and the embedded link about Xmax, requiring the ability to measure T/S with large signals )

Sigfried Linkwitz's article "Excursion-Limited Spl Nomographs ( SpeakerBuilder 4/84 ) was one of the first articles on the subject.
I linked that pic from his site.

Electrical and mechanical limits
Page index

Perhaps he would provide insight into it's use.
( My first inclination would be to use sinewaves not music,
I've had some ideas for bringing this micrometer into the 21st century, but they are untested )

Last edited by HK26147; 26th August 2010 at 01:11 PM. Reason: addition info
  Reply With Quote
Old 26th August 2010, 01:20 PM   #10
diyAudio Member
 
Join Date: Nov 2005
I didn't see anything about in at your links, but it should be fairly plain to see the coil leaving the gap on an FFT of the current running into it. Just wire your speaker through some resistance and hit it with a test tone. Send the signal across the sense resistor to your PC running a spectrum analyser and when the harmonics start to spike you're leaving linear excusrion. With a good eye you might even be able to see it on a scope, but you could probably hear it earlier. Any way you do this yoiu're still faced with actually measuring the excursion somehow, which is probably the greater error source. Accuracy is not incredibly important, since getting 3 dB higher output requires double the excursion anyway.

Last edited by Andrew Eckhardt; 26th August 2010 at 01:24 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
Inductor estimation? art West-VL. Parts 4 19th March 2008 07:31 PM
3" VC Verses 4" VC Safe_Cracker Car Audio 2 16th October 2007 04:03 PM
KT88 Lifetime estimation Salas Tubes / Valves 4 3rd March 2007 12:18 AM
Volt Amp Estimation bjackson Parts 8 5th August 2005 02:40 AM
heatsink estimation elizard Everything Else 4 11th June 2003 06:48 AM


New To Site? Need Help?

All times are GMT. The time now is 08:39 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