Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

TL cabinet rear port
TL cabinet rear port
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 29th March 2018, 04:02 PM   #21
Bill poster is offline Bill poster  Thailand
diyAudio Member
 
Bill poster's Avatar
 
Join Date: Jun 2008
Location: Bangkok/London
I notice PMC now extend the line well beyond the terminus in their latest floorstander. I'm not sure if it's acting as a chamber or they've just calculated it works better that way.
  Reply With Quote
Old 29th March 2018, 04:09 PM   #22
Scottmoose is offline Scottmoose  United Kingdom
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
They've been doing that for a while. Basically it's vent offset, as is often done in an MLTL.
__________________
"'That'll do", comes the cry of the perfectionist down the ages.' James May -The Reassembler
www.wodendesign.com Community sites www.frugal-horn.com http://frugal-phile.com/
  Reply With Quote
Old 29th March 2018, 04:13 PM   #23
Bill poster is offline Bill poster  Thailand
diyAudio Member
 
Bill poster's Avatar
 
Join Date: Jun 2008
Location: Bangkok/London
Quote:
Originally Posted by Scottmoose View Post
They've been doing that for a while. Basically it's vent offset, as is often done in an MLTL.
ah ok. I've not see this in an MLTL, only the driver offset
  Reply With Quote
Old 29th March 2018, 04:15 PM   #24
Scottmoose is offline Scottmoose  United Kingdom
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
Quote:
Originally Posted by Williams Audio View Post
I found the 1/6 wave calculation in a kind of article, with tapered line as I wrote.
But I really like to see a real made project with basic calcs, that can enlighten me.
I think that always is a pre chamber and then the TL, can be linear or tapered, no? My woofer is Scan-speak 21W/8555-00 8'' .
I was reading the
Perry S. Marshall
A Derivation and Analysis of the Transmission Line Speaker Enclosure
A Report for Electrical Engineering 498M Topics in Acoustics and Audio
University of Nebraskaת Fall, 199
0
He is talking about 1/4 wave TL, so the 1/6 wave TL is some wrong choice.
Very difficult finding an easy formula, for a given woofer.
Williams
Oh blimey, not that Marshall rubbish. Don't go there. Go here instead:

http://www.quarter-wave.com/TLs/Alignment_Tables.pdf

Excel spreadsheet derived from above:
http://www.quarter-wave.com/TLs/Alig...tor_3_3_09.xls

A summary of the physics:
http://www.quarter-wave.com/TLs/TL_Anatomy.pdf

Note that Martin's alignment tables assume you are tuning to the driver Fs, which isn't all that obvious / clear on first glance. Personally I prefer to tune a classic style TL with only a small amount of taper a bit higher than that.

And for variety, here is an alternative approach with slightly different goals & methodology but equally accurate in terms of the physics:
http://diyaudioprojects.com/Technica...mped-Pipes.pdf
__________________
"'That'll do", comes the cry of the perfectionist down the ages.' James May -The Reassembler
www.wodendesign.com Community sites www.frugal-horn.com http://frugal-phile.com/
  Reply With Quote
Old 29th March 2018, 04:20 PM   #25
Scottmoose is offline Scottmoose  United Kingdom
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
Quote:
Originally Posted by Bill poster View Post
ah ok. I've not see this in an MLTL, only the driver offset
It's ultimately just a matter of degree. It's a resonant QW pipe with a driver & a terminus offset from the respective ends; it doesn't matter in that sense whether it's mass-loaded or not.
__________________
"'That'll do", comes the cry of the perfectionist down the ages.' James May -The Reassembler
www.wodendesign.com Community sites www.frugal-horn.com http://frugal-phile.com/
  Reply With Quote
Old 29th March 2018, 05:09 PM   #26
pkitt is offline pkitt  United States
diyAudio Member
 
Join Date: Feb 2009
I've used an offset driver and port a number of times in ML-TLs and find it to be very advantages in some cases depending on several factors. What doing this does is to smooth out the response to a better degree as compared to having only the driver offset, but with an increase of f3 by 1-2 Hz.
Paul

Quote:
Originally Posted by Bill poster View Post
ah ok. I've not see this in an MLTL, only the driver offset
  Reply With Quote
Old 30th March 2018, 11:27 AM   #27
Williams Audio is offline Williams Audio  Jamaica
diyAudio Member
 
Join Date: Apr 2004
Location: far away
Hi all,
Thanks for the answers and the support
Now I have to read a lot, very interesting stuff
But, from first understanding, a linear tube at 1/4 wave is the easy way to start with, then the tapered one with narrow opening end will be second study
Learning the MATH CAD correction tables is very helpful.
What is ML and offset driver?
Best regards
Williams
__________________
williams audio
  Reply With Quote
Old 30th March 2018, 01:56 PM   #28
pkitt is offline pkitt  United States
diyAudio Member
 
Join Date: Feb 2009
ML means the end (the open end) of the line is Mass Loaded by a port. In an ML-TL the line usually has a constant area and the line's length is not long enough to allow its 1/4-wavelength resonant frequency to be the sole tuning mechanism. The port is added near (usually) the end of the line to complete the tuning process. An offset driver means the driver being loaded by the TL is not located at the very beginning of the line (the closed end), rather it's located away from the closed end of the line, typically around either 20% of the line's length or 33% of the line's length.
Paul

Quote:
Originally Posted by Williams Audio View Post
Hi all,
Thanks for the answers and the support
Now I have to read a lot, very interesting stuff
But, from first understanding, a linear tube at 1/4 wave is the easy way to start with, then the tapered one with narrow opening end will be second study
Learning the MATH CAD correction tables is very helpful.
What is ML and offset driver?
Best regards
Williams
  Reply With Quote
Old 31st March 2018, 07:07 AM   #29
Williams Audio is offline Williams Audio  Jamaica
diyAudio Member
 
Join Date: Apr 2004
Location: far away
Hi all,
Learning slowly the material,
If the line is not 1/4 wave and the load is as BL, there is a freq. shift from driver fs?
If the driver given Vas is134 liters, is it equivalent to Vd?
Then in this volume have to build the folded tube?
Suppose I have this volume in cabinet, the linear tube is a square structure; it will be same structure all the way to the open end port?
As a square structure tube say, long 2.5m and SO/SL=1, driver Sd=220cm² then the port should be same size, 220cm²?
By basic theory this will give 34 Hz resonate tube, is should be higher or lower then driver fs?
Can design a rectangular linear tube with same surface area? It is easier.
Thanks for your time
Williams
__________________
williams audio
  Reply With Quote
Old 31st March 2018, 01:34 PM   #30
pkitt is offline pkitt  United States
diyAudio Member
 
Join Date: Feb 2009
I'm going to respond to some of your questions. If you have a line with a constant area and a length that provides the 1/4-wavelength resonant frequency you want, the open end of the line (the terminus) will need to have the same area as the line, essentially independent of the driver's Sd. This would likely be called a classic TL, but you won't like the response shape you'll get as it will be full of significant dips. The line will have to be stuffed rather heavily in order to smooth out the response, but that will likely completely eliminate all of the terminus' contribution to the bass response. The optimum 1/4-wave resonant frequency depends on both the fS and Qts of the driver. If Qts is close or equal to 0.4, then the 1/4-wave resonance should be close to fS. As Qts becomes lower and lower than 0.4, the 1/4-wave resonance needs to be higher and higher than fS, and as Qts becomes higher and higher than 0.4, the 1/4-wave resonances needs to be lower and lower than fS. A 2.5-meter line with a constant area will have a 1/4-wave resonant frequency of ~34 Hz, but a tapered line will likely perform much better because the tapering will smooth out the response and require less stuffing and the line can be shorter. For instance if the line is tapered at 10:1 (area decreases from closed end to open end, the terminus), a line with a 34-Hz resonance would need to be only about 1.5 meters long.
Paul

Quote:
Originally Posted by Williams Audio View Post
Hi all,
Learning slowly the material,
If the line is not 1/4 wave and the load is as BL, there is a freq. shift from driver fs?
If the driver given Vas is134 liters, is it equivalent to Vd?
Then in this volume have to build the folded tube?
Suppose I have this volume in cabinet, the linear tube is a square structure; it will be same structure all the way to the open end port?
As a square structure tube say, long 2.5m and SO/SL=1, driver Sd=220cm² then the port should be same size, 220cm²?
By basic theory this will give 34 Hz resonate tube, is should be higher or lower then driver fs?
Can design a rectangular linear tube with same surface area? It is easier.
Thanks for your time
Williams
  Reply With Quote

Reply


TL cabinet rear portHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Is It Sensible To Use The Cabinet As Part Of The Port? (Slot Port) ReDress Subwoofers 4 19th October 2015 05:56 AM
Pair Monacor SP-60/4 in a stuffed port aperiodic cabinet? What size cabinet? danielwritesbac Multi-Way 28 3rd April 2013 05:15 AM
Rear port and front port barry.childs Multi-Way 10 27th February 2009 09:46 AM
Rear or front port? Speek Multi-Way 1 7th September 2005 08:58 AM
rear port vs front port Jimmy154 Multi-Way 22 6th March 2004 08:38 AM


New To Site? Need Help?

All times are GMT. The time now is 10:54 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki