Dual scan-speak passive radiators with alpine SWX-1043D subwoofers

[exoplasm]

So I am designing a subwoofer based on two alpine swx-1043d subwoofers and two 30w/0-00-00 12'' passive radiators. I am modeling them in winisd pro and appear to mate quite well. I have a couple question/concerns. These design looks to give quite a large group delay around 25 hz. Also do you think the 12'' passive will have enough volume displacement. I will be running it off a behringer inuke 3000 with dsp and I can put a high pass around 25hz to control excursion(Image 6/7). If you think this set-up will result in a sloppy muddy mess please suggest another box configuration for two swx-1043d. The EBP is a 52.6 which does lean toward a sealed alignment but like the idea of more output down low with less power and equalization. I have attached some screen shots to show the group delay frequency response and cone excursion. The box size is 2.6 cubic foot. This thread will probable turn into a build log if I can decide what to do with these woofers.

 

[exoplasm]

Just realized if I take off 100 grams it lowers the group delay and lines up better with the ported version of this enclosure that I wanted to build. Problem with the ported one is that the ports get extremely long with any decent port diameters to reduce chuffing and would also take up a lot of volume inside the box. Hence the passive radiators. The red curve I added to show the box alpine recommends. Seems kinda peaky no??? It has a 4.7db peak at 43/44 hz. does seem to have a bit lower group delay but at a higher frequency.

 

[bjorno]

..Seems kinda peaky no??? It has a 4.7db peak at 43/44 hz. does seem to have a bit lower group delay but at a higher frequency...

Hi exoplasm,

IMO: I would never build a BR using passive radiators if the Driver Qts is above 0.5 or if the PR Q cannot be controlled, i.e. the PR Stiffnes.

Any BR with Driver Qts above ~0.5 using PR's or not must be tuned low and damped in the Port(or Controlled PR Stiffness) too to achieve a flat response.

Here is an example that IMO,IME is second to none in terms of possible sonic performance if compared to a BR(Qts>0.5) using PR's:

b🙂

PS: If the Gldy follows a 1/f curve, i.e. blameless when compared to a typical Room- ETC. The only thing to consider is proper Phase/Time alignment at the XO frequency that would result in a System Gldy =~ < 25 mS at 20 Hz (50 mS allowed), like my Posted Picture shows.

 

[xrk971]

If you have some cheap woofers ($15 buyouts etc) you can turn them into tunable PR's by adding mass to the cone and adjust the stiffness by shorting the voicecoil with a power resistor. It is an interesting experiment to tie two woofers electrically in parallel and push the cone on one you will see the cone on the other move in equivalent response.

 

[exoplasm]

The alpine recommended box was the one that seemed rather peaky(red curve, second post, second picture) the one with the passive radiator setup is the yellow curve and the grey is the ported box equivalent. Seems to be flat frequency response wise but with any of the ported alignments there seems to be excessive group delay albeit quite low in frequency. I'm starting to think it would be inaudible because its so low in frequency. I really appreciate the effort you went through bjorno to model this but building two 2.8m horns with a a volume of 6 cubic feet each is not really what I had in mind. That is if im picking up what your putting down that is. Also I have no experience with building horns so it may be a learning curve.

 

[exoplasm]

Ok well has anyone built a passive system with a decently flat frequency response but a fair bit of group delay albeit very low in frequency and want to talk about there listening impressions compared to maybe a ported or sealed alignment. I'm really contemplating going ahead with this as I have the two type x subs already. I'm thinking dual apposed woofers and passives to mitigate vibration and the enclosure walking around the room...

 

[exoplasm]

Figured I post the last subwoofers...

Figured I post the last subwoofers I built (Assembled I should say) for my 2 channel set up, that were sealed with the scan-speak( 32W/4878T00 ) drivers, Dayton audio cabinets (2 Cubic foot) with added vertical brace, dynamatt, felt, mdf enclosure for the amp (SPA1000). Im thinking of using the 3 cubic foot enclosure for this alpine project with added hardwood or metal skeleton bracing on the top and bottom as all the sides will have either a driver or passive radiator. Maybe some cross braces tying the sides with the drivers together...

 

[Inductor]

...The red curve I added to show the box alpine recommends. Seems kinda peaky no??? It has a 4.7db peak at 43/44 hz. does seem to have a bit lower group delay but at a higher frequency.

In fact it seems more than... inadequate.
An alignment of the SWX-1043D Type-X with volume and tuning VB = 28 L, FB = 28Hz/29Hz is the best you cannot wish. High tuning in a small box, maybe for car audio and that's exactly the environment they are made for.
(1ft³ = 28.317L)

For the same reflex box (of the datasheet) a understandable alignment would be VB = 28 L, FB = 24 or 25 Hz. (longer port)

For an extended sub for the SWX-1043D Type-X, what would be a good volume/alignment of VB = 45 L and FB = 22 Hz tuning. (F3 20 Hz) 😀

 

[exoplasm]

Sealed???

Here is what the sealed response would look like. Doesn't seem to change much with the box volume unless its really small. The group delay is very low but cone excursion obviously limits the max low end output. The F3 is around 41 Hz. Do you guys think this is low enough with the room gain to sum to a flat response at least till around 20 Hz?