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Passive radiator??

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Shortrope View Drop Down
Young Croc
Young Croc


Joined: 08 July 2013
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    Posted: 16 February 2015 at 10:39am
I'm in the process of making a Boomcase from an Old pair of Tannoy speakers.
One of the Bass driver has a bust coil but is otherwise good.
Could this be used as a Passive radiator in conjunction with the working Bass driver, what are the considerations??

My Tinnitus is coming along nicely!!
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davey t View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davey t Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2015 at 11:02am
You can use any old driver as a passive radiator with a few considerations:

It needs to have a larger surface area than the active driver. about 1.5X bigger
It needs to have a large mechanical xmax as PRs move a lot. 
You will probably need to add mass to the cone to tune it low enough. Generally speaking you want to tune the PR to half the lowest frequency of your box. So if you would normally use a port tuned to 60Hz, use a PR tuned to 30Hz. 
You'll want to try to remove the magnet to save weight. 
You need to consider the VAS of the PR.... use a sim program to test it all
Minirig portable soundsystem movement
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shortrope Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2015 at 2:20pm
Thanks Davey, interesting stuff.
Not surprisingly it's not as simple as I thought.
I don't think it's a goer for this project then.

My Tinnitus is coming along nicely!!
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Old Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2015 at 6:03pm
Originally posted by davey t davey t wrote:

You can use any old driver as a passive radiator with a few considerations:

It needs to have a larger surface area than the active driver. about 1.5X bigger
It needs to have a large mechanical xmax as PRs move a lot. 
You will probably need to add mass to the cone to tune it low enough. Generally speaking you want to tune the PR to half the lowest frequency of your box. So if you would normally use a port tuned to 60Hz, use a PR tuned to 30Hz. 
You'll want to try to remove the magnet to save weight. 
You need to consider the VAS of the PR.... use a sim program to test it all
Cheers for the insight on that. Now it's got me thinking how to incorporate passive radiators into some of my designs.

Just picked up an ADX Fusion from Amazon with dual radiators for £30 - Poor man's Soundlink Mini basically, very impressive for the price, not the loudest and some tracks do distort but the radiators give implausibly powerful bass and build quality is like twice the price.
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