Passive Radiator design

[mitch808]

I have a Dayton MKII 10" sub that I think I may want to try a PR on it. On the parts express website, they have an EBS box design that calls for 1.41 cu ft with a 3x19.3" port tuned to 25Hz. With such a small footprint, port length becomes an issue.


Can someone help me choose the right PR with the correct weighting to match the EBS design?

Parts Express did mention their own 12" PR with no weighting, but did not know how to calculate how much weight to add to make the recommended EBS design.

I tried using Unibox, but I kept getting all kinds of "#DIV/0" errors.

[Svante]

If you don't find a program that can handle PRs, you can use any program that can design a bass-reflex box. Make the port have the same area as your PR. You will end up with a rediculously long port. Calculate the mass of the air in that port as <area>*<length>*<density of air>. That is the total moving mass your PR should have.

HTH

[mitch808]

Originally posted by Svante
If you don't find a program that can handle PRs, you can use any program that can design a bass-reflex box. Make the port have the same area as your PR. You will end up with a rediculously long port. Calculate the mass of the air in that port as <area>*<length>*<density of air>. That is the total moving mass your PR should have.

HTH

Okay based on what you posted....

<area>*<length>*<density of air>
7.065 * 19.3 * <?>

What is the density of air? I got 1.29kg/m3 from a search on google, but can't figure converting that to US standard to work in this formula.

[GM]

Assuming you're referring to the 295-110, a 25Hz EBS needs to be ~2x this, at 2.79ft^3 based on published specs. In a ML-TL OTOH, the pipe length loads the vent more efficiently, reducing its length/vent mach considerably (all dims inside):

L = 42.93"

w x d = 111.87"^2

driver down 16.75" from top

vent = 3" dia. x 6" long down near/at the bottom

stuffing density = 0.2lbs/ft^3

If you still prefer to use a PR, I can help with the calcs, but unless you plan to make the cab really heavy or add weight to the top of it to damp down the PR's vibration, two PRs in a bipolar layout will be required. This will make a big difference in the required weight so I'll need to know which way you'll build it.

GM

[mitch808]

Whoops it's the 295-412 not the one you posted.
http://www.partsexpress.com/pe/showd...number=295-412


I was told that a single 12" Dayton PR was sufficient.
http://www.partsexpress.com/pe/showd...number=295-192
But the tech on the phone was unsure of the weight and how to achieve the EBS design. He did say I could go up to 150g and just keep adding washers until I get the desired effect. needless to say I didn't like that answer.


If I could accomplish it with a single 12" PR that would be great. Or if I need to get the Peerless PR I will try that as well.
http://www.partsexpress.com/pe/showd...number=297-610

[Svante]

Originally posted by mitch808




Okay based on what you posted....

<area>*<length>*<density of air>
7.065 * 19.3 * <?>

What is the density of air? I got 1.29kg/m3 from a search on google, but can't figure converting that to US standard to work in this formula.

Being grown up with the metric system I have a hard time working outside of it... I can't figure out what units you have on 7.065 and 19.3 so I'll give an example instead. Let's say that you have a PR with an equivalent piston area of 333 cm2. This is equivalent to 0.0333 m2. Let's also say that the software gives you a length of 2.54 m (100 inches). The density of air is 1.21 kg/m3 at room temperature, so you will need

0.0333*2.54*1.21=0.102 kg [m^2 * m * kg /m^3]=[kg]

1 in= 2.54 cm = 0.0254 m
1 sq in=2.54*2.54 cm2 = 6.4526 cm2 =0.00064526 m2

(Hope I got it right)

[mitch808]

Sorry I'm using inches. And let me tell you my head is starting to hurt


<area>*<length>*<density of air>


So re-reading the above formula where I went wrong is where I assumed it meant port area and length. But it's actually the PR's area and length.

Let me ponder that for a while, and see what I come up with.

However if I have to get two PR's to make it work, I may just do a slotted port and have multiple angles to get it right. Not ideal, but you gotta do what you gotta do to get it done.

[GM]

>Whoops it's the 295-412.......

====

It figures! This is the one I originally started to comment on, but decided to see if PE had a plain jane S2.......

Anyway, Tuning a T/S max flat Vb a few Hz lower isn't an EBS, 1.98ft^3/20Hz would be, so which do you prefer?

====

>I was told that a single 12" Dayton PR was sufficient.

====

Think about it, as long as you barely energize it, they're right, but what if the signal is strong enough to get ~10" dia. of mass swinging at 1" p-p (or more)? Then again, a wife and/or GF would probably like sitting on it during movie special effects, which has the side benefit of good damping through lossy mass loading.

====

>(Hope I got it right)

====

FWIW, here's what I use when the vent/PR dims are in inches:

Vvb = (dia/2)^2*Pi*length*0.0005787

grams = Vvb*34.26255

This is based on air mass = 1.20997kg/m^3

GM

[mitch808]

Originally posted by GM
>Whoops it's the 295-412.......

====

It figures! This is the one I originally started to comment on, but decided to see if PE had a plain jane S2.......

Anyway, Tuning a T/S max flat Vb a few Hz lower isn't an EBS, 1.98ft^3/20Hz would be, so which do you prefer?

Well if I can tune the box that low with a lowly 10" woofer, I'm all for it. I figured I would just go with what PE recommends and that was a 1.41cu ft with a 3x19.3" tuned@25.1Hz.

For a 80/20 mix of HT/music, what would you recommend? Size is an issue (even if the women says it's not ;0) So I was hoping to keep it under 16x16x16.

[GM]

>PE recommends and that was a 1.41cu ft with a 3x19.3" tuned@25.1Hz.

====

It's an OK alignment, but the vent mach is ~2x what it should ideally be, so you may hear it 'chuff'.

====

>For a 80/20 mix of HT/music, what would you recommend? Size is an issue (even if the women says it's not ;0) So I was hoping to keep it under 16x16x16.

====

Gees dude, sure would have been nice if you'd stated this from the get-go! Anyway, my subs are tuned to 16Hz and some movies really work them, so I would go with the 20Hz Fb. Assuming this is o.d. dims, PR(s) are the only viable tuning option.

GM