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

'Dual folded line' Transmission Line?
'Dual folded line' Transmission Line?
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 23rd January 2018, 11:42 AM   #1
ChrisHill is offline ChrisHill  United Kingdom
diyAudio Member
 
Join Date: Jan 2012
Default 'Dual folded line' Transmission Line?

Apologies in advance for the long post.

TL : DR:
Can I build two separate folded tapered transmission lines into one cabinet, and can I drive an 8" and a 5" driver from a single amplifier channel without a crossover?

Longer version:
I’m looking for opinions on the possibility of building a transmission line speaker with two separate folded lines inside the cabinet.

I recently completed a long-running project to build a complete system myself, using a miniDSP 2x4 balanced system as the heart of my pre-amp, a Hypex 4-channel power amplifier and a pair of M3tlm speakers built from plans and components bought from IPL Acoustics. To my ears this is the best setup I’ve ever owned, and I love the sound of the M3tlms. The Hivi/Swans M5N 5” drivers give good strong bass from 40Hz up (thanks to the TL), and the Hivi/Swans RT1.3 ribbon tweeters give real sparkle up to beyond my hearing range.

Having finished the system I’m at a loose end, so I’m considering designing and building my own TL speakers, and I’m aiming for even better bass. I have a spare set of M5A 5” drivers (like the M5Ns only with a cast chassis), and a spare pair of the RT1.3 ribbon tweeters, so my thought was to add a pair of matching M8A 8” drivers (I do like the copper driver colour!), and build a cabinet to take all three drivers.

Having looked into the principles of TL cabinet design, I realise that a parallel-sided cabinet does not lend itself to a smoothly tapering folded line - at best I think you will end up with several discontinuities in the taper, or maybe some triangular/wedge filler panels. So I considered tapering the sides of the cabinet, but then I realised that the space that might be wasted by those triangular filler panels in a parallel cabinet could be used to accommodate a second folded line.

So whereas my original idea was to build a line to suit the 8” driver, and include a sealed or ported enclosure within the cabinet for the M5A and the tweeter, I’m now wondering if I could incorporate tapered lines for both the 5” and 8” drivers in the one cabinet. I sketched it out and it seems feasible - I’ll post the sketch later.

I do realise that the addition of the 8” driver means I don’t really need the bass extension properties of the transmission line for the 5” driver, but the opportunity is there, and I think the peak of the extended bass from the 5” driver could slot nicely into the gap left by extending the 8” bass. If I taper both lines I should be able to optimise them separately for each driver, and it should minimise complications from higher harmonics. Some miniDSP magic should be able to balance the contributions from both drivers.

So that’s the first question - are there any obvious pitfalls or problems with trying to build two tapered lines into one cabinet - will they tend to interact perhaps?

The second question concerns crossovers and amplification. I do have another 6-channel AV amp, but I’d need to find a way to split my stereo source up for the six drivers. A miniDSP device seems like an option - perhaps a miniSHARC+miniDAC8. But I’m wondering if it would be a sin to feed one 8” and one 5” driver from the same amplifier channel, which would allow me to get away with using my existing 2x4 miniDSP board and 4-channel amp. I’d then let the miniDSP EQ deal with any unevenness where the two drivers overlap. Is there any problem feeding the bigger driver with more mid range frequencies than it can reproduce, and the smaller driver with more bass than it can reproduce?

Last edited by ChrisHill; 23rd January 2018 at 11:49 AM.
  Reply With Quote
Old 23rd January 2018, 01:39 PM   #2
pkitt is offline pkitt  United States
diyAudio Member
 
Join Date: Feb 2009
Default Yes you can

You certainly can use a pair of TLs. I used a pair of mass-loaded lines for two 7-inch woofers in my 3-way TuLines design quite a few years ago. These obviously aren't tapered which makes them easier to implement and build, and the midrange driver I used was a dome, not requiring a separate enclosure (or another TL for that matter). I've attached a scanned side view drawing of this design in case it might help.
Paul
Attached Images
File Type: jpg TuLine Cab Sideview.jpg (602.3 KB, 272 views)
  Reply With Quote
Old 23rd January 2018, 02:00 PM   #3
midrange is offline midrange  United Kingdom
diyAudio Member
 
Join Date: May 2012
Location: London
This has been done commercially. From memory Castle Acoustics (British company) made a model called the Howard. It had 2 separate lines with one forward firing unit and one upward firing unit (plus a forward firing tweeter). The lines were tuned to different frequencies. Received very good reviews. 1970s/80s I think.
  Reply With Quote
Old 23rd January 2018, 06:11 PM   #4
ChrisHill is offline ChrisHill  United Kingdom
diyAudio Member
 
Join Date: Jan 2012
Thanks both, that's encouraging.

I did a quick and dirty mock-up based on line lengths that suit the M5A and the M8A. Even though the line tapers are a long way from being right in this drawing it seems doable, and won't make for too big a cabinet.

Click the image to open in full size.

I mocked up the top of the front panel to show which driver goes where.

Click the image to open in full size.

Putting the tweeter above the M5A allows me to locate the M5A at a small offset from the end of its line, which all helps with the higher harmonics.

Looking at the responses of the three drivers I think I can answer my own question about the 5" and 8" drivers sharing an amplifier channel without a crossover. It's not going to work. The tweeter needs a crossover above 2.5kHz, and the 8" driver seems to have a bit of peak at 2kHz, starting at 1kHz, which I'm guessing I should probably avoid. So I'm going to need to use the 5" driver to bridge the gap between these two, so I'll need two crossovers per cabinet, hence 6 channels of amplification.

Tweeter response:
Click the image to open in full size.

M5A response:
Click the image to open in full size.

M8A response:
Click the image to open in full size.
  Reply With Quote
Old 23rd January 2018, 08:36 PM   #5
IG81 is offline IG81  Canada
diyAudio Member
 
IG81's Avatar
 
Join Date: Feb 2008
I advise ditching the "small spoon" here.

In more concise terms, I'm not certain I understand the need for an overly complicated acoustical scheme when the setup will be active. A folded line for the 8" is fine, but of no use for the 5". It will not achieve anything the DSP can't do better and might only hurt midrange performance. Were this a passive setup, I could advise a short damped line to flatten the impedance of the 5", but this is of no consequence as the driver will be directly connected to it's own amp channel.

If you want to get away using only your 2x4 miniDSP, perhaps bi-amping the 8" + 5" as two channel, while going passive on the tweeter on a third channel (easier to pad down electrically and likely fewer/cheaper passive parts) could work. This would allow the DSP to take care of a fairly low frequency Xo as well as BSC and woofer/midrange level adjustments and time alignment.

Last edited by IG81; 23rd January 2018 at 08:45 PM.
  Reply With Quote
Old 23rd January 2018, 08:38 PM   #6
scottjoplin is offline scottjoplin  Wales
diyAudio Member
 
scottjoplin's Avatar
 
Join Date: Dec 2015
Location: Penrhyndeudraeth
Quote:
Originally Posted by IG81 View Post
I advise ditching the 8" driver's spooning partner.
I thought I was the only one!
__________________
Woofer Assisted Wideband is the New Testament renounce the anachronistic acronym FAST
  Reply With Quote
Old 23rd January 2018, 08:46 PM   #7
IG81 is offline IG81  Canada
diyAudio Member
 
IG81's Avatar
 
Join Date: Feb 2008
Quote:
Originally Posted by scottjoplin View Post
I thought I was the only one!
And you managed to nail-quote my pre-edit quip.
  Reply With Quote
Old 23rd January 2018, 08:49 PM   #8
scottjoplin is offline scottjoplin  Wales
diyAudio Member
 
scottjoplin's Avatar
 
Join Date: Dec 2015
Location: Penrhyndeudraeth
Quote:
Originally Posted by IG81 View Post
And you managed to nail-quote my pre-edit quip.
I'm experienced in nailing things before they disappear......
__________________
Woofer Assisted Wideband is the New Testament renounce the anachronistic acronym FAST
  Reply With Quote
Old 23rd January 2018, 08:57 PM   #9
soendervig is offline soendervig  Switzerland
diyAudio Member
 
Join Date: Oct 2008
Location: countryside
Quote:
Originally Posted by scottjoplin View Post
I'm experienced in nailing things before they disappear......
Is this a quantum-physics expert speaking....?
  Reply With Quote
Old 23rd January 2018, 09:23 PM   #10
ChrisHill is offline ChrisHill  United Kingdom
diyAudio Member
 
Join Date: Jan 2012
Haha, yes, my sketch does look a bit 'suggestive', I agree, but I figured there are worse TL designs out there.

But I think you're right - I'm over-complicating things. But I'm a complete novice at designing speaker enclosures, and only one build up from that as a builder. So if I'm going to use the 5" to just bridge the gap between the 8" and the tweeter, what's the best way to go about that? Should I just include a sealed enclosure for the 5" and the tweeter, or is a ported design better?

@IG81 - Can you explain the use of the miniDSP 2x4 again? I don't get what you're suggesting. Are you suggesting I treat them as a single driver - if so how do I handle that nasty looking peak in the 8" response curve between 1kHz and 2kHz? If that's not what you're suggesting, then wouldn't splitting them up use up all four of my miniDSP channels? Where would I get a signal for the tweeters?

Last edited by ChrisHill; 23rd January 2018 at 09:29 PM.
  Reply With Quote

Reply


'Dual folded line' Transmission Line?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Dual Fold On-Axis Transmission Line Enclosure Calculator nicasiox2 Subwoofers 9 27th January 2016 05:39 PM
Thread on dual B139s in a transmission line? surv1v0r Multi-Way 6 26th July 2015 11:02 AM
Dual transmission line Borus Full Range 3 26th June 2014 04:53 PM
Help with converting sealed box line array loudspeaker to transmission line enclosure jb0194 Multi-Way 3 7th January 2012 05:08 AM
the isobarik 6th order bandpass transmission line folded horn subwoofer idea Yoda Subwoofers 3 24th October 2001 03:00 PM


New To Site? Need Help?

All times are GMT. The time now is 02:02 PM.


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