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Old 5th August 2015, 07:15 PM   #1
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Default Will a DIY passive radiator work if built?

Hey
To keep things small and snappy, I would love to integrate a PR in a stereo setup, 0.15 ft3 box, with two TC9FD-18-08. No internal separation(Is it necessary?)

Calculated the port for it to be 8.94inch length with 2inch dia, gives 75Hz tuning.
Appropriate PR mass to add = 250gms
PR size = 4*2.5inch = 65cm2 > 36cm2 Sd of Tymphany

- So if I am building such a PR, will it be straight forward like using a plain thick paper sheet, with some kind of rubber surround and adding 250 gms of weight on back of it?

- Will the setup actually now tune itself to 75Hz?

- Also, I read a lot that the Fs of PR should be 1-1.5 octave below speaker Fs. So while building a custom PR, how do you take care of that?

- And, lastly, how do you find the max allowable low end tuning for the speaker with PR when DIY.

Thanks.

Last edited by arjunm009; 8th August 2015 at 06:50 PM.
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Old 5th August 2015, 08:15 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

Your best bet is probably just using a cheap driver with a decent suspension.

When you add mass to it it automatically drops the the driver Fs.
A resistor across the coil can adjust the effective damping.

For DIY you want most of the mass to be the diaphragm. Adding a surround
will give a Vas and Fs which interacts with box volume for the tuning.

rgds, sreten.
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Old 6th August 2015, 03:27 AM   #3
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Sreten's suggestion seems pretty good to me, particularly if you were clever about how you added mass to the cheap speakers' cones.

If I were building a PR, I'd use a heavy duty surround (purchase from a speaker recone supplier). I can't see any easy way to DIY this part to be uniform and nice looking.

The PR membrane would be two discs of thin plywood or similar, laminated together with a generous amount of glue.

The inner edge of the surround would be sandwiched between these discs.

The outer edge of the surround could be glued directly onto a cutout in the cabinet, or mounted to a ring like a regular driver.

The benefit of using a thick, stiff membrane for the PR (rather than a paper cone plus weights) would be that midrange output from the rear of the active drivers would not pass through it as readily.

This is not something I'd try to get right (correct mass on the PR) without test equipment, though.
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Old 6th August 2015, 04:25 AM   #4
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Sreten's suggestion seems pretty good to me, particularly if you were clever about how you added mass to the cheap speakers' cones.

If I were building a PR, I'd use a heavy duty surround (purchase from a speaker recone supplier). I can't see any easy way to DIY this part to be uniform and nice looking.

The PR membrane would be two discs of thin plywood or similar, laminated together with a generous amount of glue.

The inner edge of the surround would be sandwiched between these discs.

The outer edge of the surround could be glued directly onto a cutout in the cabinet, or mounted to a ring like a regular driver.

The benefit of using a thick, stiff membrane for the PR (rather than a paper cone plus weights) would be that midrange output from the rear of the active drivers would not pass through it as readily.

This is not something I'd try to get right (correct mass on the PR) without test equipment, though.
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Old 6th August 2015, 06:04 AM   #5
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http://www.caninialtoparlanti.it/images/passivo.gif
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Old 7th August 2015, 07:07 PM   #6
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I wonder how to work around for the rubber surround part. Since that size is a bit non-standard, it would be real hard to get hands on one which would suit. And also, for this application, I have to employ a PR of approx that size.

Is therr any DIY way for rubber surround?
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Old 8th August 2015, 12:49 PM   #7
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by arjunm009 View Post
I wonder how to work around for the rubber surround part. Since that size is a bit non-standard, it would be real hard to get hands on one which would suit. And also, for this application, I have to employ a PR of approx that size.

Is therr any DIY way for rubber surround?
Bicycle inner tubes. Also, at garden supply stores they sell buytyl rubber sheets to line ponds and act as water barrier. It would be a flat (non curved) surround but that will still work to some extent.

If you want to make curved surrounds you need to make a positive and negative mold and use it to clamp a sheet of depron (egg carton) foam with heat. That can make a curved foam surround. Rubber sheets have to curved during initial formation either wise they want to stay flat.
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Old 8th August 2015, 03:20 PM   #8
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Quote:
Originally Posted by xrk971 View Post
Bicycle inner tubes.
That was ingenious Thanks. I will definitely give that a try.
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Old 8th August 2015, 04:06 PM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by arjunm009 View Post
Calculated the port for it to be 8.94inch length with 2inch dia, gives 75Hz tuning.
Appropriate PR mass to add = 250gms
PR size = 4*2.5inch = 65cm2 > 36cm2 Sd of Tymphany

- So if I am building such a PR, will it be straight forward like using a plain thick paper
sheet, with some kind of rubber surround and adding 250 gms of weight on back of it?

- Will the setup actually now tune itself to 75Hz?

Thanks.
Hi, 250 grams is way, way too high, rgds, sreten.

As long as Fs is low, i.e. Vas high, PR mass, cone
area and the box volume determine the tuning.
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Old 8th August 2015, 06:48 PM   #10
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I used these to arrive at the conclusion, for 0.15ft3 volume and 75Hz tuning.
LinearTeam
mh-audio.nl - Home

250gms did seem high, but thats what I am getting. Would have to actually try it.

At present, just from the sealed box, I am getting roughly 140Hz tuning. It does seem to go till 100Hz but not below that.

Last edited by arjunm009; 8th August 2015 at 07:08 PM.
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