Slot reflex port for bass reflex enclosure? - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

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 22nd April 2015, 10:12 PM   #1
diyAudio Member
 
monty78pig's Avatar
 
Join Date: Aug 2011
Location: London
Send a message via Skype™ to monty78pig
Default Slot reflex port for bass reflex enclosure?

How would I go about calculating a bottom slot bass reflex port for a speaker design?

Also does anyone else have any experience regarding these. I quite like the aesthetic qualities of them.
__________________
78RPM Restorations https://soundcloud.com/monty78pig With perfect linearity, it is impossible to go off on a tangent.
  Reply With Quote
Old 22nd April 2015, 10:22 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

You just need a simulator that applies the correct end corrections,
which yield a different port area / length to a free mounted port.

rgds, sreten.
__________________
There is nothing more practical than a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 22nd April 2015, 11:29 PM   #3
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
WinISD has option of round or rectangular ports. But basically the cross sectional area needs to be kept the same along with length. In the case of very narrow aspect profile slots there is more skin or surface drag that will be more than just the regular slot pressure losses. This is how an Onken reflex is different.
  Reply With Quote
Old 22nd April 2015, 11:34 PM   #4
IG81 is offline IG81  Canada
diyAudio Member
 
IG81's Avatar
 
Join Date: Feb 2008
WinISD apparently does not let users enter arbitrary end correction factors, outside of the 4 presets they have, the highest of which is nowhere near enough for a bottom slot port's value of 2.222, if I'm correct.

Funny you should post this today. Just yesterday, I did a tuning adjustment on large enclosures I have for TD15M, with such a vent scheme.

Click the image to open in full size.

Click the image to open in full size.

WinISD was little help getting me to where I wanted, but I did it empirically. If you implement a scheme like I did, with a drop-on panel setting vent length, it's easy enough to start too long, measure and adjust until you get it right. Which is basically the boneheaded way to do it lacking proper software or the will to look for it.
Attached Images
File Type: jpg td15m.jpg (174.5 KB, 303 views)
File Type: jpg td15m_2.jpg (205.8 KB, 302 views)
  Reply With Quote
Old 23rd April 2015, 12:39 AM   #5
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
This may help: http://www.diyaudio.com/forums/attac...ort-length.jpg

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 23rd April 2015, 01:30 AM   #6
diyAudio Member
 
Join Date: Nov 2006
Location: Adelaide, South Australia
Blog Entries: 30
The beauty of slot loaded ports is that they are damn easy to tune. My experience with them is that the errors in, for example, winisd, are not "catastrophic" more in the few Hz range.

This is something you can fiddle
  Reply With Quote
Old 23rd April 2015, 02:00 AM   #7
chrisb is offline chrisb  Canada
diyAudio Member
 
Join Date: Aug 2002
Location: victoria BC
excellent link, Greg

My personal experience with slots is that they work very well - particularly if you get a math geek to calculate, there are several methods to fine tune them, and depending on configuration, can add to enclosure bracing.
__________________
"Perception is a highly non-linear function" - Earl Geddes

Last edited by chrisb; 23rd April 2015 at 02:03 AM.
  Reply With Quote
Old 23rd April 2015, 02:01 AM   #8
diyAudio Member
 
monty78pig's Avatar
 
Join Date: Aug 2011
Location: London
Send a message via Skype™ to monty78pig
Those TD-15 cabinets look amazing. I like your use of cleats!

If the port is only 20cm wide it's not going to need any extra support?
__________________
78RPM Restorations https://soundcloud.com/monty78pig With perfect linearity, it is impossible to go off on a tangent.
  Reply With Quote
Old 23rd April 2015, 12:21 PM   #9
IG81 is offline IG81  Canada
diyAudio Member
 
IG81's Avatar
 
Join Date: Feb 2008
Quote:
Originally Posted by monty78pig View Post
Those TD-15 cabinets look amazing. I like your use of cleats!

If the port is only 20cm wide it's not going to need any extra support?
Assuming it's built from 18mm BB-ply, it's probably stiff enough not require support at 20cm width. OTOH, it can't hurt to have some and if you don't want the slot itself to be separated, like mine picture above for example, you can use a triangular brace on top that ties it to the front panel. The advantage with my drop-on-cleats-panel scheme (not that I pretend having invented it ) is the ease of adjustment. I'm glad to have implemented it this way as, since I've moved, the new room these are in does not agree with the previous tuning frequency.

Last edited by IG81; 23rd April 2015 at 12:25 PM.
  Reply With Quote
Old 23rd April 2015, 04:17 PM   #10
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Quote:
Originally Posted by chrisb View Post
excellent link, Greg

My personal experience with slots is that they work very well - particularly if you get a math geek to calculate, there are several methods to fine tune them, and depending on configuration, can add to enclosure bracing.
Thanks to bjorno and whoever did the basic one he started with for sharing it with us!

Agreed, the first and earliest date, shelf port I saw was a subdivided slot in a custom undersized Altec 604B cab circa 1948. Unfortunately, the driver was blown, so didn't get to audition it and was too expensive for my meager part time lawn maintenance allowance.

The second was in a 1952 Altec 820A horn where it did double duty as a short horn cum pedestal base, so short of contrary eyes-on proof, I'm assuming Altec pioneered slot/shelf/BVR ports.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  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
Bass reflex port question Javachip Multi-Way 12 11th April 2006 12:11 PM
Tuning bass reflex port beamnet Multi-Way 0 28th September 2005 01:03 PM
Q-factor of bass reflex port SSassen Multi-Way 6 26th March 2005 08:26 PM
Bass Reflex Enclosure & Port Tuning D_GR8_1 Multi-Way 2 2nd December 2004 09:11 PM


New To Site? Need Help?

All times are GMT. The time now is 03:24 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2