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Old 19th June 2012, 05:06 PM   #1
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Default Different drivers in same sealed cabinet

What are the effects of using two drivers with differing T/S parameters in the same sealed sub-woofer enclosure?
(Qts: .40, .56; Vas: 149 l, 157 l; Fs: 16, 21)
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Old 19th June 2012, 09:27 PM   #2
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by patrickkopson View Post
What are the effects of using two drivers with differing T/S parameters in the same sealed sub-woofer enclosure?
(Qts: .40, .56; Vas: 149 l, 157 l; Fs: 16, 21)
Hi,

Quick answer:

Coupled oscillators.

http://physics-animations.com/Physic...sh/bit_tmp.htm


Mechanics

Click on ?-mark at: Coupled oscillators.

Put your cursor over the picture with:Coupled spring oscillators. Beating effect.

Watch the effect.

Imagine the spring is the air-volume i a speaker-box, When both drivers are with different TS parameters fighting against the same air spring a beating effect occurs...The 'weaker' driver will suffer most.

b

Last edited by bjorno; 19th June 2012 at 09:37 PM.
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Old 19th June 2012, 11:46 PM   #3
sreten is online now sreten  United Kingdom
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Hi,

Its not a coupled oscillator due to the intrinsic damping if connected in parallel.

More details are really needed to ascertain if dividing the box evenly will help.

rgds, sreten.
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Old 20th June 2012, 04:38 AM   #4
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Default Can use single volume also!

Hi, Nestorovic and Modaferri did some interesting things with dissimilar drivers in the same volume.

Modaferri's 1983 patent in particular looks very interesting: by adding increasing phase shift to one of the drivers, starting with very little at ultra-low and gradually increasing to 180 degrees at higher, he was able to get up to +6dB more low bass when compared to a single driver or two in parallel in equivalent volume enclosures. He also was able to significantly reduce the impedance bump in the lows.

Have a look at the patent at
PAT2PDF - Free PDF copies of patents: Download and print!

It may come up with an error message, but when you conduct the search on 4403112 the info will come up. It's 21 pages of REALLY interesting work which directly addresses how to do it. And the patent has expired so we're all free to play with it.

I've previously done some 2.5 type enclosures with identical drivers but a lower freq roll-off on one driver. It worked better than predicted in the sims, with more extended bass than it was supposed to have. Now I know why! Turns out Modaferri covered a similar example in his patent and predicted much more bass extension with his models. I'll be trying something like his examples with larger phase shift real soon, looks like a great way to build subs.
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Last edited by Jack Caldwell; 20th June 2012 at 04:41 AM.
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Old 20th June 2012, 06:20 AM   #5
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There is already a name for a less elaborated variant : Double Driver Dynamic Loading for Low Q Drivers, or dddllqd.

some details are available in the Single Driver Website, but the link supposed revealing the theory is dead for me.
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Old 22nd June 2012, 11:53 AM   #6
djk is offline djk
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The Wilson Audio X-1 had a 12" glass-fiber-reinforced pulp-cone upper woofer, and a 15" pulp-cone lower woofer in a single vented enclosure.

Click the image to open in full size.
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Old 22nd June 2012, 01:12 PM   #7
Zero D is offline Zero D  United Kingdom
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Lightbulb DDDL

@ Radugazon

RE - Double Driver Dynamic Loading for Low Q Drivers

And the dead link http://www.fortunecity.com/rivendell...d/dddllqd.html

I was able to retrieve it from the Wayback Machine http://web.archive.org/web/200502121...d/dddllqd.html

Quote:
The first time I advanced the original idea any number of professional speaker designers jumped up and told me flat out: "This WILL NEVER WORK".

Only Servodrive Inc's Tom Danley and Jean-Michel Le Cleac'h encouraged me and offered some assistance, so most what is written here is attributable more to those gentlemen than to myself.
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Old 22nd June 2012, 01:55 PM   #8
sreten is online now sreten  United Kingdom
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Default DDDL

Hi,

The DDDL principle certainly works but uses drivers with wildly different
parameters. In this case without knowing driver sensitivities and Xmax
its not easy to say, but I imagine they won't be fine in the same box.

All depends on what they are and what your trying to do with them.

rgds, sreten.
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