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Old 10th November 2009, 02:24 AM   #1
tinitus is offline tinitus  Europe
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Default Passive radiator, build your own

Just an idea I thought I would share with you

Commercial passive radiators does actually cost quite a lot

Chassis could be simple plywood
Or if proven to work, constructed directly into the sub
Surround should be available as repair component
The passive cone itself could be anything you can imagine
From the most simple to advanced laminated materials

The third one is a crazy idea from another thread
Surround is a bicycle tube
Airpressure should keep it in place
Thats the cheapes one
But may take some experimenting
But thats the fun part, right

Have fun
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Old 10th November 2009, 05:52 PM   #2
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Interesting idea, Tinitus. I wonder if you would need a spider and dummy coil assembly to keep everything moving in one axis?

Jim
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Old 10th November 2009, 07:24 PM   #3
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Funny, i was just thinking of the same exact thing the other day. Two sets of surround with some offset between them should keep the 'cone' moving in one axis?

The bicycle tube idea looks real neat, but would be hilarious, as well as embarresing, if the sub literally blew up (both PRs cones bust out) during a loud explosion while watching a movie.
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Old 10th November 2009, 08:04 PM   #4
Collo is offline Collo  Australia
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If ever you blow a driver, you can cut the magnet off it for a diy PR.

Here's one I "prepared" earlier...

Some MDF with a bolt epoxied onto the coil former would accept the weights.

Click the image to open in full size.
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Old 10th November 2009, 10:17 PM   #5
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Quote:
Originally Posted by tinitus View Post
Just an idea I thought I would share with you
Tinitus, I made something like #1 many moons ago. Found it to be too much work when what Collo suggests is a good starting point. A plywood "basket", a piece of wood paneling, the sidewall of a small bicycle innertube, rubber cement and a whole lot of staples. Thanks for the memories.

Quote:
Originally Posted by J.R.Freeman View Post
I wonder if you would need a spider and dummy coil assembly to keep everything moving in one axis?
Probably a good idea but some manufacturers do make the "flapper plates"

Quote:
Originally Posted by Collo View Post
Some MDF with a bolt epoxied onto the coil former would accept the weights.
You can also add weight by filling the dust cap from the rear and painting the cone with multiple layers of PVA glue. To get really funky, you paint small coins onto the cone with it.

Good to see these suggestions coming out again. Just the sort of thing that piqued my interest when I was but a wee tyke.

All those years ago...
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Old 10th November 2009, 11:49 PM   #6
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I did this when I was ~17 years old. I had a 12" Radio Shack woofer in a very big box and built in a passive radiator in it. I started with a big hole in the box (around 20") added a flat ring of rubber (truck inner tube) about 3" wide to this. The diaphragm was cardboard, 2 pieces with the rubber sandwiched between. The outer edge of the rubber surround was held in place by a plywood ring screwed through it to the box. On first play, it was a bit sloppy so I added a thick rubber band from the centre of the diaphragm to the rear of the box (makeshift spider).

In the end, it didn't sound bad - way more bass than the 12 could do alone but lacking any of the knowledge I have today () I could probably do better.
Looked excessively cool though.
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Old 11th November 2009, 12:21 AM   #7
pjanda1 is offline pjanda1  United States
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I once used a passive radiator from CSS that didn't have a rear suspension of any sort, just a big, fairly stiff surround (what I assume Cal meant by "flapper plate", it was made in Germany, I can't remember the brand). The diaphragm was mdf (ish), and had a bolt to which one could attach washers as mass. I used it in a small, low tuned sub with the MCM 55-2421, and it sounded good! (I gave it to a friend). I don't know that it is super linear, nor how long it will last, but it was fun and price was right. I actually choose that design because most of the inexpensive PR's (at the time at least) didn't have nearly enough excursion and mass to work in the box. It sure beat trying to tune that little box to 30hz with a bunch of PVC elbows!

I think you can do as well. The biggest problem (I think) would be getting a suspension that will allow enough excursion, but is also reasonably linear in the range you will use it. Even that little 8" sub could really get the 10" plate flappin'. I honestly really like the inner tube idea. You might need to play with the gap a bit. Glue would allow it to be pretty wide.

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Old 11th November 2009, 01:15 AM   #8
tinitus is offline tinitus  Europe
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To be honest, I wouldnt expect it to be optimal at loud SPL
On the other hand, I wouldnt expect ANY design with passive radiator to be optimal at loud SPL, but what do I know about it, not much really
I heard the first good one just recently, which got me interested
When others asked about modifying a cheap broken woofer into a passive radiator, I thought why the hazzle
It may never be any good
But Im a bit late it seems, when MJL did it the age of 12
But he may be disappointed if he think he can do better today(grin, lost the smiley)

I dont think that the spider and ordinary basket does any good in linearity
Its only needed fore a conventional design
And the ordinary design with a standard cone mounted with additional weight at the voice coil, I really dont think thats very good at all
Seems to me like it would be much better to have the weight spread over the entire cone
And I expect it to be more linear when in no need fore a spider

Another thing, I suppose we have much better tools today, calculating the design
The one I heard at båndseis place was just a rather cheap dayton, but careully adjusted with weight

How is this ScSp 10" fore a passive radiator, at 150EUR
And maybe you need two of them, pr sub
Thats a lot of money
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Last edited by tinitus; 11th November 2009 at 01:21 AM.
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Old 11th November 2009, 01:57 AM   #9
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I always liked the idea of a large passive with a wirewound pot across it's terminals, the pot alows you to tune the passive.

Terry
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Old 11th November 2009, 03:49 AM   #10
gooki is offline gooki  New Zealand
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Originally Posted by rhapsodee View Post
Funny, i was just thinking of the same exact thing the other day. Two sets of surround with some offset between them should keep the 'cone' moving in one axis?
That's essentially what the Earthquake SLAPS passive radiators are.

And since we're talking PRs, here's my baby:

Click the image to open in full size.
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