Go Back   Home > Forums > >

Multi-Way Conventional loudspeakers with crossovers

port length
port length
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
Old 6th March 2008, 12:18 PM   #1
jwhit67 is offline jwhit67  United States
diyAudio Member
 
Join Date: Feb 2008
Default port length

Maybe a simple question. When you calculate a port length does this include the baffle thickness? Is this strictly speaking the actual "cut" length of a tube and then placed in the enclosure? What if the length of the port is shorter than the baffle thickness? Does this change the tuning frequency?
  Reply With Quote
Old 6th March 2008, 01:29 PM   #2
Corax is offline Corax  Germany
diyAudio Member
 
Join Date: Feb 2005
Location: south of lower saxon
The calculated port length (whatever software you're using) is just the resulting effective port length. In real designs the measured port length is usually shorter than the calculated length, depending on the length, diameter, and "style" (i.e. straight, single/double sided trumpet, exponential opening, ...) of the port duct. As a rule of thumb for straight ports, take the calculated (and reasonable) length and subtract approx. the diameter (round port) from the length as a starting point. For any fine tuning (if necessary) use variable ports with the same diameter. As soon as you know the correct length you can swap to fixed ports and cut to the length as desired.


A length shorter as the baffle thickness would be a bad design .
In this case increase the diameter of the port, (re)calculate your port length again, and you'll see that the length will increase too.

One design rule would therefore be the following:
A short port with a small diameter might have the same tuning frequency as a long port with a large diameter (see also the formula for the Helmholtz resonator - which I do not attach here).


If the port is to long the air will resonate within the bandwidth of interest of that bass (headword: comb filter). If the port is to short, the diameter is ofter very small though, the air speed inside the port is very high (larger or equal to i.e. 0.2mach) and will introduce unwanted vent/port noise at higher sound pressure levels. That's by the way the reason why ducts have very often a round-off shape at the/both port end(s) to lower that effect noticeably.
  Reply to this post

Reply


port lengthHide this!Advertise here!
Thread Tools

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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Question considering port length cumesoftware Multi-Way 3 21st May 2008 12:46 PM
Help with port length please Bobhof Multi-Way 3 2nd May 2006 07:32 PM
port length busterno1 Multi-Way 5 27th October 2003 09:05 PM
port length dave k Multi-Way 13 13th July 2003 03:32 PM


New To Site? Need Help?

All times are GMT. The time now is 01:56 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki