# CSS Passive Radiator Help



## theater_lover (Jun 4, 2009)

I am looking into the APR15 as a PR to use with my two ACI SV10s, but I want to make sure I am modeling it correctly in WinISD.

My understanding is that as the added mass goes up, it changes the Fs, so how do you calculate that?

Second, does the PR start with an initial mass, as in "added mass to cone" should never be zero?

Also, if someone here could double check that my concept is even workable (one APR15 with two SV10s in a 3-4 cubic foot enclosure), that would be most appreciated.

Thanks.


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## Mike P. (Apr 6, 2007)

Entering the parameters of the PR in WinISD starts with no mass added and the PR's default effect on the tuning frequency of the cabinet. Adding mass lowers the tuning frequency of the cabinet. Adding 9 - 45 gram washers to the APR 15 would tune a 4 cu.ft. box to 21.5 hz. The model is with 500 watts input power and a Hi-pass filter at 18 hz.


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## theater_lover (Jun 4, 2009)

Hi Mike, thanks for the info.

I was running this idea past a knowledgeable "expert" do-it-yourselfer on another website, and this was his response...

"The problem is you still can't do this with one passive radiator. Next just calculate the inertia of adding over half a KG of weight to the radiator, if the suspension could take it. Calculate the forces involved to move that much weight to and fro at 30 Hz. That is where the models break down, so the radiator will not move the way it is modeled, and distortion is going to go through the roof.

By the way Bullock and white wrote warnings into their program to alert the designer that the data can not be trusted. With your passive radiator, every item has a red dot against it, which is thumbs down, what ever you do with it. No green ones at all, which is the thumbs up.

I can't impress on you enough to stay away from passive radiators. Unless you have an alignment that works without that huge mass, they are a dead looser."

What do you think?


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## Mike P. (Apr 6, 2007)

It sounds like a 1980's conversation. Current PR's have advanced in the last 20 years and are designed to handle the weight and excursion. The above conversation only would make sense when PR's had 8 mm Xmax and were easily overloaded.(15-20 years ago) That is not the case today with PR's that have excursion in excess of 35mm. There are PR builds in the Database, I've yet to hear any complaints. I personally have tested the CSS 10 inch PR's. I tortured them with test tones with lots of mass added, they never missed a beat.


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## theater_lover (Jun 4, 2009)

Mike P. said:


> It sounds like a 1980's conversation. Current PR's have advanced in the last 20 years and are designed to handle the weight and excursion. The above conversation only would make sense when PR's had 8 mm Xmax and were easily overloaded.(15-20 years ago) That is not the case today with PR's that have excursion in excess of 35mm. There are PR builds in the Database, I've yet to hear any complaints. I personally have tested the CSS 10 inch PR's. I tortured them with test tones with lots of mass added, they never missed a beat.


I think what he was getting at wasn't that the design would exceed xmax, but that the force needed to move a heavy PR was so great that it would result in distorted sound. This is why he suggested two PRs were needed. Know anyone that would be able to answer this for sure based on math?
_Posted via Mobile Device_


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## Mike P. (Apr 6, 2007)

One CSS 15" PR is more the enough for a pair of 10" ACI's.

As you can see it's well under its limits.


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## theater_lover (Jun 4, 2009)

That looks almost identical to what I had figured, but XMax excursion doesn't necessarily address the other guy's point. Are you familiar with anyone who has done a design like this (dual smaller driver with a much larger PR)? Most designs I have seen call for either one driver and two similarly sized passives (like CSS' kits), or one driver with a next size up passive (15" passive for a 12" driver).


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## Mike P. (Apr 6, 2007)

Adire had a recommended alignment for the 12" Shiva with a 15" PR. As for dual smaller drivers with a much larger PR, it's all about the combined Vd of the subs and the PR being able to handle it. It doesn't matter if it's 2 - 10 inch subs or 4 - 8 inch subs, if modeling shows the PR is within it's limits, then it's fine.

As for "distorted sound" from "heavy PR's, There are alot of A.E. 2100 gram PR's out there capable of swinging 3 inches peak to peak, I've yet to hear anyone complain of distorted sound.


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## theater_lover (Jun 4, 2009)

Mike, do you know what the displacement is of the APR15?


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## Mike P. (Apr 6, 2007)

It's around 1.5 liters, if my memory serves me correctly.


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## theater_lover (Jun 4, 2009)

Thanks Mike. Sounds about right to me, but any chance you can confirm that for me?


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## Mike P. (Apr 6, 2007)

Not a problem, we'll find out for sure as soon as Bob gets back from the "Vancouver Island DIY Fest" that was held this weekend.


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## Mike P. (Apr 6, 2007)

The displacement for the 10", 12" AND 15" PR's is 1 liter, 1.5 liters and 2 liters respectively.


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