Xmax Question - 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 2nd February 2005, 02:21 PM   #1
jwatts is offline jwatts  United States
diyAudio Member
 
Join Date: Jan 2004
Location: Erwin, Tennessee
Default Xmax Question

Is the Xmax a measure of the linear displacement from the neutral position of the woofer to the maximum excursion (the woofer completely up) or a measure of the linear displacement from below the neutral position (the cone completely bottomed out) to maximum excursion (the woofer completely up).
  Reply With Quote
Old 2nd February 2005, 02:41 PM   #2
diyAudio Member
 
Join Date: Nov 2004
Location: Rakkestad
Send a message via MSN to Snickers-is
The term x-max is the linear displacement from neutral position. It is defined only as a linear workspace, but the linearity has to be defined. Normally that is height of VC minus heighy of gap /2, and in some cases + 15%. Since most drivers mostly multiplies the Le by 2 from X-max pos to X-max neg the definition of linearity is somehow less interesting. The suspension does also play an important role here. The X-max must therefore be understood as "effective workspace".

Some manufacturers (Seas is an example) gives x-max as Linear Coil Travel (p-p) wich means peak to peak. That is x-max * 2.

Aurum Cantus adds more than 15%. That may lead people to believe that they have longer excursion than they really have.

Manufacturers like TC sounds has a controlled roll off in the magnet gap that makes the x-max harder to define. They often give the x-max as the same as the x-mech-parameter.

For an underhung coil the x-max will be more difineable as you will get a collapse in BxL when exceeding the gap. The 15% add will not work well in that case.
__________________
Live sounds better than HiFi.
  Reply With Quote
Old 2nd February 2005, 03:46 PM   #3
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Jason:

It should be neutral position to the max, either way. There is a happily growing trend for manufacturers to do it that way, and now most do.

For a long time, and even still now, cheaper manufacturers try to cheat and list the travel all the way from the back to the front maximum. That way is called peak-to-peak excursion. Most good manufacturers, however, list it the right way.

Seas seems to be something of an exception, but at least they tell you it is peak-to-peak, so you can cut the figure in half for comparison purposes.

Just to restate the formula above

Xmax = (length of voice coil-length of voice coil gap)/2.

So a speaker with a 25mm voice coil and a 7 mm gap will have:

Xmax = (25-7)/2 = (18)/2 = 9mm.

As Snickers stated previously, some testing methods add another 15% on to this, but that is not a big difference- it adds less perhaps 1 dB to your total SPL.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous
  Reply With Quote
Old 2nd February 2005, 04:02 PM   #4
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Incidentally, the two charts listed here give you the bass SPL, at all bass frequencies, for a given volume of air moved.

The volume of air moved is your maximum excursion times your cone area. The Xmax used in this chart is the correct one-fromneutral position to the max travel in front. In other words, not peak-to-peak.

The chart is given in both normal and metric measurements.

This chart is taken from an article by Richard Small, of Thiele-Small fame, from the Journal Of The Audio Engineering Society.

Volume Displacement For SPL Chart

By the way, all the Thiele-Small papers, from which this chart is taken, are available for download here:
http://www.richie00boy.pwp.blueyonde...pers/index.htm

Richie00boy generously donated the webspace to make them available to the diyAudio community.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous
  Reply With Quote
Old 3rd February 2005, 01:58 PM   #5
diyAudio Member
 
Join Date: Nov 2004
Location: Rakkestad
Send a message via MSN to Snickers-is
Quote:
Originally posted by kelticwizard The chart is given in both normal and metric measurements.

You mean both normal measurement and inches?
__________________
Live sounds better than HiFi.
  Reply With Quote
Old 3rd February 2005, 02:59 PM   #6
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
You caught that, did you? I figured I could sneak that one by.

Well, it's normal measurements for the guy who posted it, who is me. If someone from Norway posted it, it becomes normal measurements and inches.

Actually, the chart from Small's article is in metric only . The only people in America who have any familiarity with the metric system are engineers, scientists or people who work in technical fields. I, like most people, do not fit any of those descriptions.

When I first came on to this website, I found I had great, great difficulty dealing with metric, which I never had to do in my entire life. I assumed others did as well, so I just computed the English equivalents and put them onto the chart using MSPaint.

There are still manufacturers who give their cone area, etc. in inches, so it works out well to have the chart in both systems.

The decision as to which is "normal" was pure editorializing on my part.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous
  Reply With Quote
Old 3rd February 2005, 03:27 PM   #7
jwatts is offline jwatts  United States
diyAudio Member
 
Join Date: Jan 2004
Location: Erwin, Tennessee
Default Papers

Thanks for the downloads. I was missing the last paper.
  Reply With Quote
Old 3rd February 2005, 06:13 PM   #8
diyAudio Member
 
Join Date: Nov 2004
Location: Rakkestad
Send a message via MSN to Snickers-is
I just had to

I generally have problems dealing with square and cubic inches/feet. Not that there is any problem to recalculate them, but for me it is clearly easier to deal with the metric system when I am dealing with known sizes.

But what suprises me is that you still use both decimal and "7 3/16 inches".

Does USA try to adopt to the metric system at all?
__________________
Live sounds better than HiFi.
  Reply With Quote
Old 3rd February 2005, 06:38 PM   #9
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Actually, I see Peerless and other manufacturers like Focal calling their speakers 10 inchers, or rating 7" speakers as 7Nxxxx, etc. So I presumed there was some familiarity with inches, etc. On the other hand, I gave box volume advice to a member from Scandinavia, and he went way off using feet and inches. So I guess that familiarity is limited.



Quote:
Originally posted by Snickers-is
Does USA try to adopt to the metric system at all?
Back in the seventies, there was much brouhaha made about how we are all going to go maetric. News magazine articles were dealing with the economic impact of redoing all the machine tools in metric, Celsius temps were put on those big time & temperature signs outside banks, etc. It really was a big story.

Thirty years later? A complete fizzle. People know what a liter is because that is how soft drinks are bottled these days. Outside of that, unless they are in a technical field, the average American has no idea of kilometers, centimeters, degrees Celsius, or anything like it.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous
  Reply With Quote
Old 3rd February 2005, 06:47 PM   #10
diyAudio Member
 
Join Date: Nov 2004
Location: Rakkestad
Send a message via MSN to Snickers-is
In Norway one liter is defined as 100centi liters, but one half liter (of beer) is defined as somewhere between 25 and 40 centiliters.
__________________
Live sounds better than HiFi.
  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
Linkwitz's Xmax calculator question cuibono Multi-Way 4 3rd February 2009 08:14 PM
Question about xmax mitchyz250f Subwoofers 12 2nd August 2008 08:02 PM
Xmax Question morfius Multi-Way 5 15th April 2008 09:26 PM
Xmax dallaire Multi-Way 2 25th December 2007 09:47 AM
Xmax mik Subwoofers 12 1st December 2004 04:39 AM


New To Site? Need Help?

All times are GMT. The time now is 09:58 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