Why is off-axis horizontal MTM bad? - 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 12th March 2004, 04:23 PM   #1
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Default Why is off-axis horizontal MTM bad?

I'm starting my research on building a center channel. It seems like the most popular designs are MTM (2/2.5way) or WMTW (3-way) type of designs. I also read a lot that MTMs have pretty crummy off-axis behavior. It seems like people are refering to nodes and lulls created by the 2 element "line array" of the Ms for this conclusion. But if the CC is horizontal, wouldn't it mean that you are always listening on-axis? My listening angle would be something like +/- 30deg.
thx.
--
Danny
  Reply With Quote
Old 12th March 2004, 04:47 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
At c/o a vertical 2-way MTM can be treated as a 3 element line array.

Horizontal dispersion is not a problem, but vertically due to the
3 elements dispersion has more nulls than a MT 2-way.
(Typically 4 versus 2, and the angle of the 1st null is smaller)

When turned on its side, so the vertical dispersion becomes
the horizontal dispersion basically the extra nulls are not
a good idea in terms of horizontal seating position coverage.

For a horizontal box :

--T--
WMW

Is the way to do it, have vertical MT array with woofers either side.

sreten.
  Reply With Quote
Old 12th March 2004, 05:15 PM   #3
diyAudio Member
 
Join Date: Nov 2003
Location: NW Washington
Send a message via MSN to officeboy
As you can see.. It's not that pretty, unless youíre really off axis.
Attached Images
File Type: jpg sidemtm.jpg (87.1 KB, 314 views)
  Reply With Quote
Old 12th March 2004, 05:52 PM   #4
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Ok, I just missed something. I've also been reading up on line arrays and I thought the papers indicated increased sensitivity on-axis with line arrays while the lulls started appearing off-axis. The sound field becomes more like a cylinder so any point vertically on-axis should be the same as any ohter point. Is this wrong? That's the way it's indicated in the vpr excel program.
  Reply With Quote
Old 12th March 2004, 06:19 PM   #5
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Is only true for a perfect line array, e.g. a ribbon or similar.

Or lots of units at frequencies with wavelengths greater than the spacing.

sreten.
  Reply With Quote
Old 12th March 2004, 06:26 PM   #6
diyAudio Member
 
Bill Fitzpatrick's Avatar
 
Join Date: Jun 2001
Location: Eugene, OR
Quote:
Originally posted by officeboy
As you can see.. It's not that pretty, unless youíre really off axis.
Where is that ripple tank program located. I want to play.
  Reply With Quote
Old 12th March 2004, 06:29 PM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: NW Washington
Send a message via MSN to officeboy
http://www.falstad.com/mathphysics.html

I can spend hours playing with these things.
  Reply With Quote
Old 12th March 2004, 06:41 PM   #8
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Quote:
Originally posted by sreten
Is only true for a perfect line array, e.g. a ribbon or similar.

Or lots of units at frequencies with wavelengths greater than the spacing.

sreten.

But when the wavelength starts to equal or become shorter than the spacing, the dispersion pattern is on both axises?
  Reply With Quote
Old 12th March 2004, 06:50 PM   #9
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally posted by azira

But when the wavelength starts to equal or become shorter than the spacing, the dispersion pattern is on both axises?
Oh yes, sreten.
  Reply With Quote
Old 12th March 2004, 06:51 PM   #10
diyAudio Member
 
Timn8ter's Avatar
 
Join Date: Jul 2003
Location: Seattle, WA
It's interesting how much it cleans up when you add a 4th source at nearly the same point as the center source. This seems to simulate what would happen if you add a mid-ranger under/over the tweeter. This app is way
  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
Horizontal MTM Center channel: avoiding off-axis nulls DcibeL Multi-Way 27 10th October 2009 05:57 PM
Horizontal woofers steve_mak Multi-Way 5 5th April 2006 11:28 AM
OPT axis tenderland Tubes / Valves 2 8th March 2005 12:54 AM


New To Site? Need Help?

All times are GMT. The time now is 01:10 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