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-   -   Passive Radiator - Enclosure Volume (http://www.diyaudio.com/forums/subwoofers/217916-passive-radiator-enclosure-volume.html)

Astera 14th August 2012 02:46 PM

Passive Radiator - Enclosure Volume
 
I picked up a Dayton Audio SD270A-88 10" DVC Subwoofer and a couple of matching passive-radiators to play around with.

I built a small, unusual polyhedral enclosure but I calculated the volume of my enclosure is less than a cubic foot.

The Vas for the 10" DVC is 3.8 cu ft.

I'm new to subwoofer design - even more so to passive radiator systems: does this thing have even a chance to fly?

Is the Vas to be treated as the recommended enclosure size to "balance" the driver? If I'm so wildly small in volume, can this be made up for by adding additional mass to the passive radiators? What is the effect of having too small an enclosure?

bear 14th August 2012 05:17 PM

no, not good.

It is basically a ported design.
So you can run the "numbers" in any of the free or shareware box simulation programs and see the results for yourself...
...the effect of a PR is not exactly the same as a port, but close enough to see what is likely to result.

You can make it work two ways:
A) set the PR [i] up in frequency [i] to near where the 10" sub is going to naturally work in a small volume
or
B) set the PR down where you want it (say 35Hz.) and live with the dip between the 10" response in the box and where the PR works - the PR will also be lower in level.

there is a (C), equalize the dip, set the PR down to the intended F3 point (maybe 30Hz would be ok, and that is lower than you think) and live with the reduced SPL and power eating of that set up... you also need a HP filter below the PR freq...

Probably better to just EQ the 10" in the small box, and stuff it fully at that point... gotta run the numbers for max SPL and excursion vs. power and extension...

_-_-bear

theAnonymous1 14th August 2012 05:34 PM

This driver needs about 4cu.ft for a br alignment with a Fb=23Hz and F3=26Hz.

Doh... was going to post the Fb and F3 with a 1cu.ft enclosure and the program crashed... don't feel like typing all the params in again. :(

bear 16th August 2012 04:46 PM

aim for 32-35Hz. you will get a decent result, and maybe a not tooo large a box, reasonable max SPL and will sound very good.

_-_-bear

PS. you only need to type in the box volume, VAS, Qt, F3 and Port freq...

_-_-bear

tb46 16th August 2012 09:25 PM

Hi Astera,

Post #1: "...What is the effect of having too small an enclosure?"

In the extreme case you end up with a transmission line enclosure. The free volume of the enclosure becomes a coupling chamber, and the passive radiator becomes the transmission line (duct or pipe). This can be modelled in Martin J. King's MathCAD spreadsheets, or (without the stuffing) in Hornresp. bjorno is the expert on this subject, I think he calls his design's MLTL and OD-MLTL, etc. (for mass-loaded transmission line and Offset-driver mass-loaded transmission line). I would recommend you search for bjorno's posts on this subject, but be warned that it can become a little deep quickly. Just thought I point it out while you're asking.

Basically, bear has you on the right path with the vented passive radiator enclosure.

Regards,

Astera 20th August 2012 05:21 AM

Thanks.

tb46 21st August 2012 02:18 PM

Hi Astera,

A software you might find applicable for your design is Jeff Bagby's "Woofer Box and Circuit Designer", an Excel based spreadsheet application that is especially usefull for passive radiator systems:

jbagby

Regards,


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