PR designs for the BPD 1803 (1 Viewer)

[Craig Woodhall]

Hey guys, I built my 10.5ft3 (tuned to 18hz) box for my 1803.. It has tons of output but I think it is underported..It sounds like there is port compression or chuffing on loud bass passages (U-571).. Also, the type of pressures in the box, i think is revealing my shortcommings as a woodworker .. Not to add to this but the box is about 200lbs..
Im thinking I might go to a passive radiator box/design to make it smaller and eliminate the port.. Can i achieve the same amount/type of bass as my big ported box in a smaller pr'd box? Is stryke the only company that makes a fairly cheap PR that will work with the 1803? Would I need 3 or would 2 be fine?
Any favorable alignments you could toss out would be much appreciated as well..
Thanks,
Craig
here is a link to the driver
http://www.missiondigital.net/product.asp?productid=21

 

[Jack Gilvey]

Is stryke the only company that makes a fairly cheap PR that will work with the 1803? Would I need 3 or would 2 be fine?

The Stryke 18's are the only ones I've found, cheap or not, besides the Contrabass models...I think the Strykes are better, though, a little more Vd. I'd say at least three PR's, fewer and you're reaching the PR limits long before the driver's...not the best use of the BPD's displacement.

 

[Craig Woodhall]

Jack,


thanks for responding! I am using a 8.25" port, 33 inches long. I did some dado cuts on my box that weren't perfect, I think the pressures in the box are causing the joints to move and the box to flex..

you say that a smaller pr'd box will roll off steeper at the tuning frequency? Couldn't I just tune it low (like 17hz) and use the rumble filter built into my Mackie amp to weed out the real low stuff?

I was thinking about a 22" cube (a box within a box) with a Stryke 18" PR on 3 sides and the 1803 on another.. Using my Mackie in bridged mode and feed it 1400 watts..

Craig

 

[Jack Gilvey]

I was thinking about a 22" cube (a box within a box) with a Stryke 18" PR on 3 sides and the 1803 on another.. Using my Mackie in bridged mode and feed it 1400 watts..

That's a pretty small box for an 1803 in reflex loading. In ~180 liters tuned to 18Hz, the response is closer to sealed than it is to an ideal reflex alignment ( which to me is about ~400 liters/18Hz). Have you modeled this to get an idea of what the response looks like? The advantage such a PR box would have is less driver excursion near Fb, so you could apply some eq/boost down there to flatten the response if desired.
It's still the driver which dictates box size requirements whether using ports or PR's.

 

[Craig Woodhall]

Have you modeled this to get an idea of what the response looks like?

ya, im just trying to get used to all the graphs in Unibox and I don't know a hell of a lot about PR design, im used to WinIsd..

Craig

 

[Brian Bunge]

Craig,

Sorry I didn't respond to your email as I was out of town most of the weekend. Jack has pretty much summed up everything nicely though!

Brian

 

[Craig Woodhall]

Thanks Brian!

 

[Jack Gilvey]

ya, im just trying to get used to all the graphs in Unibox and I don't know a hell of a lot about PR design, im used to WinIsd..

Yeah, there are alot of parameters to play with. Play with it and you'll get it.

 

[Jack Gilvey]

Here's a quick comparison among 300L vented to 18Hz, 180L PR tuned to 18Hz, and 180L sealed.

You can see the smaller reflex sub is somewhere between vented and sealed as far as rolloff is concerned.

 

[Craig Woodhall]

So basically, I wouldn't get as good as output as my vented box.. It would cost me about $700 CDN (3x18PR's)and all I would gain is a bit smaller box? I might just rebuild the box better at a cost of only $100.. It looks like the box I have now is the best for that driver. I might just go to a 10" port and have it come out the enclosure a couple inches..

Craig

 

[Jack Gilvey]

So basically, I wouldn't get as good as output as my vented box..

Depends. If you are currently actually limited by port compression, then the PR box could have more potential *output*, but you would have to eq the bottom to get it to what you want, as I mentioned.
When I was researching this topic waiting for delivery of my own 1803, I came to the conclusion that a vented box made the most sense. Since it had to be large anyway for the response I wanted, it could accomodate adequate porting.
PR are most beneficial with drivers like the new Adire being discussed, which dictates a fairly small box but which has almost as much Vd as the 1803...a port just can't be big enough in a 150-200L box.