Folded Dipole Subwoofer - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

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 13th March 2012, 05:42 PM   #1
OllBoll is offline OllBoll  Sweden
diyAudio Member
 
Join Date: Nov 2010
Default Folded Dipole Subwoofer

Hello there all!

I've been wondering some about this: Open baffled subwoofers are more efficient the larger the baffle is, so why are most baffles on the subwoofer drawings on the net so small?

Shouldn't it be possible to approximate a much larger baffle and getting more bass by folding it like in my drawing?

If you already use DSP to handle delaying the other speakers and EQing the response is there some big disadvantage of doing this?

My other idea was stacking with 4 drivers to make my subwoofer, but the shouldn't the folded one in theory have the same output but with two instead of four drivers, thus at halved cost.

Click the image to open in full size.

Click the image to open in full size.

And now... feedback!

// Olle
Attached Images
File Type: jpg DSC_0065.JPG (123.0 KB, 492 views)
  Reply With Quote
Old 23rd March 2012, 09:03 PM   #2
Retsel is offline Retsel  United States
diyAudio Member
 
Join Date: Jan 2005
Location: Ann Arbor, Michigan
If you have the W-style cabinet as shown in the diagram, you can extend the frequency response by bolting a box on the backside of the cabinet such that the rearwave must travel that much further before it can cancel the sound coming out of the front of the cabinet. I made a two foot deep box which adds four additional feet to the pathway of the backwave. It really helped extending the frequency response of the open baffle subwoofer.
  Reply With Quote
Old 26th March 2012, 05:02 PM   #3
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by OllBoll View Post
Hello there all!

I've been wondering some about this: Open baffled subwoofers are more efficient the larger the baffle is, so why are most baffles on the subwoofer drawings on the net so small?

Shouldn't it be possible to approximate a much larger baffle and getting more bass by folding it like in my drawing?
The box you drew is effectively a bass reflex box with an very high tuning, with a big air leak on the right side .
  Reply With Quote
Old 26th March 2012, 08:21 PM   #4
OllBoll is offline OllBoll  Sweden
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by weltersys View Post
The box you drew is effectively a bass reflex box with an very high tuning, with a big air leak on the right side .
Either my drawing is unclear or then all open baffle dipole woofers are also bass reflex boxes.

To clarify my drawing:

The idea is to have a normal W-frame dipole wofer a la Linkwitz but to extend the path difference and by that reduce dipole roll off.

Having a several m long subwoofer isn't practical in my case though which is why I thought I might as well fold it like in the drawing. It should still have the same response as if it was the one above shouldn't it?

What made me wonder the most was that this easy mod should according to the datasheet provided by Linkwitz more than double low frequency response. So why aren't lots of people already doing it but instead spending lots of money on more drivers?

Which made me think of my second idea:

I want a subwoofer with maximal low frequency externsion but with smallest volume possible. Building on height after folding is too impractical but what if I simply added another pair of drivers like in my second drawing?

Impulse response impact should be minimal shouldn't it since the wavelength at 80 hz is still very very much longer than the distance between the drivers.

And if I can do that I can get twice the SPL again with the same box volume
Attached Images
File Type: jpg DSC_0070.JPG (89.6 KB, 310 views)
File Type: jpeg DSC_00732.jpeg (57.6 KB, 303 views)

Last edited by OllBoll; 26th March 2012 at 08:49 PM.
  Reply With Quote
Old 26th March 2012, 09:09 PM   #5
diyAudio Member
 
Join Date: May 2009
Location: New Zealand
Extending the path length too far will bring the lowest 1/4 wave resonance of the path down into the desired passband, which is not good. Linkwitz discusses that on his site:
Electro-acoustic models
  Reply With Quote
Old 26th March 2012, 09:20 PM   #6
OllBoll is offline OllBoll  Sweden
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by Don Hills View Post
Extending the path length too far will bring the lowest 1/4 wave resonance of the path down into the desired passband, which is not good. Linkwitz discusses that on his site:
Electro-acoustic models
Yes, but shouldn't it be quite easy to EQ away them with DSP?

The nulls shouldn't be that big in real life if I've understood his measurements correctly and when I tested in Edge with a 2.8 m diameter baffle the null was still at over 200 hz.

In the end I find the possible gain to be big enough to want me to test it. If the issues are too large to EQ away and it doesn't work then I will just make the standard non-folded dipole subwoofer but if it works...

Last edited by OllBoll; 26th March 2012 at 09:22 PM.
  Reply With Quote
Old 26th March 2012, 09:26 PM   #7
OllBoll is offline OllBoll  Sweden
diyAudio Member
 
Join Date: Nov 2010
Addition: If Edge simulates correctly then for each time I double path difference D then the frequency of the nulls are halved.

But the satelite Phoenix dipole has a D of ~ 250 mm, and it can be crossed at 1400 hz. So shouldn't it be possible to have a subwoofer with 250 * 2^4 = 4000 mm when the crossover is reduced to 1400 / 2^4 which is roughly 80 hz?

If the nulls are so horrible then why is such a large baffle at such a high frequency possible?
  Reply With Quote
Old 27th March 2012, 03:43 AM   #8
diyAudio Member
 
Join Date: May 2009
Location: New Zealand
Quote:
Originally Posted by OllBoll View Post
Yes, but shouldn't it be quite easy to EQ away them with DSP?
You can't EQ out a null.

Quote:
Originally Posted by OllBoll View Post
In the end I find the possible gain to be big enough to want me to test it. If the issues are too large to EQ away and it doesn't work then I will just make the standard non-folded dipole subwoofer but if it works...
By all means try it. It's what we're here in DIYAudio for. I just have this nagging feeling that if it were as simple as you say, everyone would be doing it...
  Reply With Quote
Old 27th March 2012, 09:09 AM   #9
Rudolf is offline Rudolf  Germany
diyAudio Member
 
Rudolf's Avatar
 
Join Date: Mar 2003
Location: Germany
OllBoll,
Your long pipes will triple or even quadruple the air mass trapped in them. This is equivalent to adding mass to the cone, which in return raises Qts. Raising Qts may be a good thing up to a point, but it can result in a large resonance hump at Fs if overdone.
Apart from that the air mass at the opening of the pipe could react with SOME delay compared to the cone. This would add to the group delay, possibly making the sound really "lagging behind".

Of course you can try to extend those quarter wavelength pipes, but this lunch is not as free as you may have considered.

Rudolf
__________________
www.dipolplus.de
  Reply With Quote
Old 27th March 2012, 10:48 AM   #10
OllBoll is offline OllBoll  Sweden
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by Rudolf View Post
OllBoll,
Your long pipes will triple or even quadruple the air mass trapped in them. This is equivalent to adding mass to the cone, which in return raises Qts. Raising Qts may be a good thing up to a point, but it can result in a large resonance hump at Fs if overdone.
Apart from that the air mass at the opening of the pipe could react with SOME delay compared to the cone. This would add to the group delay, possibly making the sound really "lagging behind".

Of course you can try to extend those quarter wavelength pipes, but this lunch is not as free as you may have considered.

Rudolf
Of couse I'd have to delay the other speakers to compensate the longer path, but that and the resonance bump should also be easy to fix with some DSP.

Quote:
Originally Posted by Don Hills View Post
You can't EQ out a null.

By all means try it. It's what we're here in DIYAudio for. I just have this nagging feeling that if it were as simple as you say, everyone would be doing it...

If I reduce the surrounding frequencies I can remove nulls. Even if I EQ away say 24 or even 36 db it isn't really an issue since the noise generated from the resolution loss will be lowpassed away. And in Linkwitz own dipole woofer the null isn't that big: http://www.linkwitzlab.com/images/graphics/w2a.gif

EDIT: When I say 24 or 36, I mean inclusive to a 24 to 36 db headroom for volume management. So in the end it's - 48 to -72 db or somewhere there but the same argument stands, the noise generated will be lowpassed away.

And if someone wonders: Currently I plan to be using a MiniDSP to take care of all the DSP needed for this project, it just seems too convenient not to use I'm of course expecting the response of this subwoofer to be a complete mess without lots of DSP, but if it can be fixed which I believe it can then the advantages would be enormous as far as I can see.

Last edited by OllBoll; 27th March 2012 at 11:17 AM.
  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
folded horn subwoofer for single 10" driver djdaveysprocket Subwoofers 22 5th April 2010 06:12 PM
Folded Dipole Dimensions Victoria Multi-Way 4 2nd February 2006 08:18 PM
Dipole subwoofer diy Subwoofers 1 5th June 2004 02:30 PM
Folded Baffle Dipole Sub questions johninCR Subwoofers 8 4th May 2004 07:32 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 10:24 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