Port close to the wall--effect on tuning? - 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 April 2008, 03:06 PM   #1
diyAudio Member
 
Join Date: Oct 2007
Question Port close to the wall--effect on tuning?

I understand the rule of thumb is to locate a port at least one port diameter from all cabinet walls (side and back). What are the correction factors when you have to get closer than that?

Came across this useful diagram, but couldn't quite follow how the coefficients apply to enclosure tuning calculations. If someone could explain it a little more clearly, I'd be much obliged:

http://www.diyaudio.com/forums/showt...24#post1148924

Also, how do I correct the calculations when I have to run a port closer than one diameter to the back wall of the cabinet?
  Reply With Quote
Old 26th April 2008, 03:28 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
It's not so much you have to apply a correction factor, it's that the port becomes strangled thus not acting fully as it should.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 26th April 2008, 03:51 PM   #3
diyAudio Member
 
Join Date: Oct 2007
I'm assuming (perhaps incorrectly) that I don't ever want to get any closer to the back wall than one-quarter the port diameter--that would definitely be strangled. Even then, I'd have to leave a zone well-clear of damping material, round all edges, etc.

But in between one diameter and one-quarter diameter, what are the effects on box tuning and performance (theoretical, empirical, or anecdotal)? Likewise for a port that runs really close to the side wall (or corner) of a box.
  Reply With Quote
Old 26th April 2008, 11:57 PM   #4
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by diesel_88

But in between one diameter and one-quarter diameter, what are the effects on box tuning and performance (theoretical, empirical, or anecdotal)? Likewise for a port that runs really close to the side wall (or corner) of a box.
The effect is that the tuning gets lower the more the opening of the tube is obstructed. The obstruction acts as a lengthening of the tube. The amount of lowering of the resonance frequency depends on the degree of obstruction in relation to the length of the tube. A long tube needs a tighter obstruction for the same effect on the tuning frequency.

Apart from this effect, there will be increased turbulence at the inner end if the opening is too close to the back wall. 1/4 of the diameter seems too close, intuitively, but I have no hard data to support this.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  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
Open baffle VERY close to back wall? Fast1one Multi-Way 6 4th April 2009 08:01 PM
Measuring a loudspeaker close to a wall wigginjs Multi-Way 2 3rd April 2009 03:02 AM
Good idea to close the port on a vented 8-inch 2-way ? brjoon1021 Multi-Way 6 10th December 2007 10:46 PM
Effect of enclosure volume deviation on vent tuning? rxwilson Multi-Way 2 7th January 2007 11:18 AM
Port Tuning bjackson Multi-Way 14 19th April 2005 12:22 AM


New To Site? Need Help?

All times are GMT. The time now is 08:36 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