re xxx 12" with ae passive radiator

[dennis09x 10+ year member]

So, port length in my 2.6 ft^3 box is huge when i want 34 hz. So i stumbled upon the thought of passive radiators. i got my 08 re xxx 12" with a qts of .404, so its almost in the realm of acceptable PR use. But im at a total loss on what kind/size/weight of PR i should get ( i assume a larger PR than the sub, so a 15"), Now how do i configure the tuning of a PR with the size of the box. I also assume the heavier the PR the higher the tuning. Is there a formula or a calculator one can use to determine these things with variable box sizes?

This is the PR brand and size im looking into http://aespeakers.com/shop/catalog/product_info.php?products_id=42

(im also looking at the TC VMP)

any help would be great

Click to read more...

 

[helotaxi 5,000+ posts]

Basic rule is that you need 2x the swept volume of the sub for the PR. A heavier PR has a lower Fs and leads to a lower tuning for the system. WinISD will do PR calcs for you is you know the parameters of the PR(s) that you want to use.

 

[dennis09x 10+ year member]

Now, as i navigate winISD beta, I cant find any outright PR options...Do i have to make a new driver with the PR's t/s parameters and then see how the box will peak?

Man, im lost, this winISD is tough ****. Ill pay someone via paypal some smackeroo's if they can figure out my tuning with a PR.

 

[Immacomputer 10+ year member]

The nice thing about PRs, is that you can change the tuning on the fly by adding or taking away mass on the PR. The mass can be applied with bolts behind the cone. To find the tuning, you can play frequencies around where you think it is tuned and see where the PR moves the most and where the sub moves the least (same frequency).

You will need Winisd Alpha to calculate the PR mass.

 

[dennis09x 10+ year member]

So i found me a sweet calc. http://www.mhsoft.nl/PassiveRadiator.asp

And this is what im thinking.

With a total internal box volume of 2.65ft^3 after dispalcement, and a driver sd of 480 cm^2 and an xmax of 54mm. I will use a 18" Audiopulse VMP that has a sd of 1100 cm^2 and an xmax of 40mm, which will give me the capabilities of tuning the box from 33hz all the way down to ~16.75hz just by adjusting the weight(.5 to 2kg can be the range of weight of this PR).

How does this look gentlemen? am i lacking in an area that i can't comprehend?

 

[dennis09x 10+ year member]

So i also read that one cannot have a PR facing up(towards the roof) as this will cause a bias in the spider due to gravity and change its characteristics... I can see it being true, but how much does it affect the PR performance and how the Hel1 does one incorporate this PR if they dont have room on the side of the box?

 

[dennis09x 10+ year member]

as i suspected, i will not be able to fit the 18", so i will have to go with a 15"er. Maybe ae will make a light PR just for me

 

[lolwut 10+ year member]

What's a PR do/for?

 

[memphisman 10+ year member]

What exactly does the passive radiator do??

 

[Immacomputer 10+ year member]

It acts like a port for when you can't fit the length of a port in an enclosure.

Ports are radiating surfaces made up of an air mass (yes, air has mass and takes up space). The air moves back and forth and that gives you sound (yes, in a ported enclosure you are hearing sound from the air moving back and forth as one object around tuning). Passive radiators take the place of that air mass with an easier to see object that moves back and forth. Altering the mass alters the tuning frequency just like altering the port length does in a ported enclosure (which you're really just altering the mass of air in the port).

 

[x2o 10+ year member]

Passive radiators allow lower tuning in smaller enclosures than is possible with standard ports. You can get that extra low end output without all the problems with vent noise and compression associated with ports.

They work as ports.

 

[1ndatrunk 10+ year member]

will a pr system be as loud as a slot tuned enclosure of the same tuning, in a box that can support the length of a proper port?

 

[dennis09x 10+ year member]

I hear they have a steep roll off below/near the PR's Fs, so tuning the Fs low would keep that problem miniscule. I think that is one of the main diffs. Also a big plus is how low you can tune the box without having miles of port eating up your displacement.

 

[dennis09x 10+ year member]

Using the above link for calculations, i tried putting two 10" PR's in (with a sd of 320). SO i put the diameter of the PR x 2 in the port diameter box. I then plugged in my volume and my tuning frequency and it gave me a mass. Now would this mass be the mass per PR or the total mass (for both PR's combined) for that given tuning frequency?

 

[helotaxi 5,000+ posts]

You really need to download WinISD Pro Alpha. It will give you one more piece of info that I think you're overlooking and that is PR excursion. I think that you might find that you don't have enough vertical surface area on your box to mount enough passive radiators to keep from stroking them all out. The more power you run, the higher the tuning, the larger the driver the more swept volume you need from your PRs to keep from damaging them. This is one of the main reasons that you don't see PRs used in car audio systems that much. Building a port is just easier most of the time.

You must have the PR mounted on a vertical surface for it to work correctly. if you can't fit it on one, you can't use a PR.