Would this make for a Sunfire True sub competitor? (1 Viewer)

[Dustin B]

A mass 2010 S24 (Vd 1.4L, Vas 40L, Fs 25hz) in a 13" cube (outer dimension, say 3/4" mdf construction with some 1/2" bracing, net volume right around 1ft^3), 100% stuffed, tuned somewhere between 20 and 25hz with a pair of 12" PRs.

If I've managed to start to understanding specs right this should come pretty close to the performance of an EBS PR Shiva not? Just cost more and require a chunk more amp power. But it would be tiny.

Edit: Just occured to me, I really don't know how PR specs relate to tuning abilities. Could a pair of 12 PRs tune an enclosure that small to under 25hz?

 

[Anthony_Gomez]

The problem I have been having is to find a PR that will handle that type of mass.

 

[Jack Gilvey]

I tried it, tough to get a pair of Stryke 12" PR's to look good at all in 1 ft^3. A 15" 1400g one looks pretty cool with the 10" Mass, though, with an f3 of about 25Hz. You don't really give up much Vd at all, although it'll shake the cabinet something fierce.

 

[Wes Nance]

John at Stryke has a design with the SAE1204 12" driver, with 2 12" PR's in a 15" cube, pretty close to what you want, with EQ on the amp, I think fb and f3 were both around 25hz. That seems pretty good for the size. . .

Wes

 

[Jack Gilvey]

This 1 ft^3 goal intrigues me, so here's a little sub that looks like fun. Take an 8" Tang Band W8-740 and stick it in 0.85ft^3 with a Stryke SA-PR12-670 and 250 watts. Looks like a potent little sub down to about 25Hz or so. I don't know about "Sunfire killer", but fun.
(I have no idea where to get that woofer, but the stuff on that site looks pretty cool.)

 

[Dustin B]

This was just kind of a silly idea I thought I'd throw out to see what others had to say. I personally have no intention of building something like that any time soon. But it would seem that a high output 1ft^3 sub would be interesting to a lot of people.

Have you ever taken a look at the specs Sunfire gives on the True Subwoofers. They aren't very detailed but they are claiming a Vd of 5.9L for the Signature and 3.9L for the MarkII.

Which when you do the math means they are claiming Sd values of an almost perfect 10" or 8" circle that has a 60mm one way Xmax.

 

[Jack Gilvey]

Those claims seem a little optimistic, eh? Anyway, I don't think it's a silly idea, it's fun to see what can be had in a very small size.
I'm actually pretty interested in this, since I have a nice, finished ~1ft^3 box that I used for my sealed Dayton 12" DVC just sitting here, it'd be cool do do something fun with it. John is selling the Stryke 12" PR's for $35 now, so it would be a fun, cheap experiment.
I'd prefer opposing PR's, but two of them would require an enormous amount of mass each (twice a single for the same Vb/Fb), and I have no idea how much they can handle.

 

[Dustin B]

Could you throw out some numbers for me Jack so I can start to understand Passive radiators better.

Like the mass numbers for a couple different tunings (say 21hz and 25hz for 1 and 2 12" PRs (pick one of the stryke ones lets say) in a 1 ft^3 enclosure.

I'm too lazy to punch numbers into Unibox right now, and I really should be studing for my exam that I have in less than an hour :p)

 

[Jack Gilvey]

If you haven't already, do read the Lambda PR FAQ,lots of info.
Think of a PR as a port whose area is equal to the surface area of the PR. The mass of air contained in this theoretical port (in this particular box, this port could only be theoretical) would be represented by the Mms of the PR. Basically, when you double the number of given PR's for a given box/Fb, you must double the Mms in each PR.
So, while one Stryke SA-PR12-670 would tune a 30l cab to ~23Hz, using two would require 1340 grams on each PR to maintain the same Fb, likely well beyond what they could physically handle. In much the same way, increasing port area requires an increase in length.
When you start playing with the numbers in Unibox, the relationships become apparent very quickly.
For the 30 liter single 12" PR/8" Tangband system, 860g of Mms (probably ok) would yield a 20Hz Fb , and looks pretty flat down there (shelved down a bit like an EBS) with 100dB available from 20Hz on up with 150 watts while staying within excursion limits.

 

[Bob Christensen]

Being completely uninformed on the use of PR’s, what is the advantage of using two over a single one?

 

[Jack Gilvey]

Being completely uninformed on the use of PR’s, what is the advantage of using two over a single one?

There are a few advantages mentioned in that Lambda FAQ. As I see it, though, the advantages of doubling the PR surface area are: More resonator displacement for more potential uncompressed output, more Mms on each one pushing their intrinsic Fs (and resulting "notch" in FR)further out of the passband, and the cancellation of reactive forces on the cabinet by mounting them opposed to each other on opposite sides.

Unlike adding more and more port area, where length becomes the limiting factor, there are no drawbacks I see to adding PR Sd as long as they can handle the needed additional mass.

 

[Dustin B]

So in other words to make a 1ft^3 enclosure with a Mass 2010 tuned to 22hz work I'd need a 12" PR with a Vd of 2.8-3L loaded with 680 grams.
The SA-PR12-670 would have no problem with 680 grams, but it's Vd is a 1/2L short.
So where do you find a 12" PR with an extra 1/2L of Vd :p)
Or you up it to the smallest cube that will fit a 15" PR and then you shouldn't have any problems except for a dancing box

 

[Jack Gilvey]

Or you up it to the smallest cube that will fit a 15" PR and then you shouldn't have any problems except for a dancing box

Well, there's no reason it has to be a cube (unless it has to be a cube ). You might do something narrow, but taller and deeper, with a side just big enough to accomodate a 15". Maybe even a 16" sonotube in its side.

 

[Dustin B]

Ok, I actually did the calculations from that Lambda FAQ using a 30L enclosure. Does 2L difference in that small an enclosure equate to a 100g difference for the same tuning?

 

[Jack Gilvey]

According to Unibox and the specs from the Stryke site for the SA-PR12-670 (670g Mms), 30L(walls covered) leads to a 22.85Hz Fb, and 28L results in 23.57Hz. In 28L, 780g Mms tunes to 22.02Hz.