My first Dipole Subwoofer!!!

[Rudolf]

From the data on paper I would stay with the Pyles. My reasons:

Qts~0,7 is perfect for good transients and you will have to equalise less. BTW. If you equalise both drivers to have the same frequency response, the resulting Qt (from driver plus EQ) will be the same too.

The single virtue you will need most is Xmax. There is a clear leader in that!

You shoudn´t try to push the driver below Fs. So 26,4 Hz seems to be better than 31,3 Hz.

Since any dipoles will reach their mechanical limits WAY before the electrical, 3 dB difference in efficiency is no issue at all.

[johninCR]

What Rudolph said plus the Pyle is a 15" driver so with the 50% more Xmax you're talking about moving more than twice the air which is the truly important factor for a dipole sub. Yes the Pyle, no contest.

[AJinFLA]

The only issue with the Pyle PLG15 as I pointed out in this thread The Current Maximum Bang For Your Buck Driver
is vent noise when used as a dipole (I have 2 PLG15s bought a while back for dipole use). The solution (or compromise, since VC temp will rise) is the either remove the dustcap Removing dustcap from a Polypropylene driver
or drill maybe a 1.5" hole in the center of the cap (the VC is 2.5" dia. - another reason I bought the driver) then glue an disc of the type of foam used in the back that allows "breathing". This will slow the air velocity within the gap and cut down on the noise. As I stated before, it comes at the price of increased VC temp. However (yet another reason I chose this driver) it also has vents around the spider. I don't think the VC temp will be an issue under "normal" listening, since, "normally" this driver would be in a box (higher temp) and booming bass that can be herad half a mile away(aka "car" stereo)
Here is a pic from the original thread of the cooling vents.

Cheers,

AJ

[Arctophile]

Thanks very much everyone

//Adam F

[Arctophile]

OK, I've ordered 2 (the only remaining stock apparently, phew!). Hope they survive being shipped a couple of thousand miles from Brisbane to Melbourne

Now I'm wondering, would another, slightly easier option be to drill several small holes in the dustcap?


TIA,

//Adam F

[AJinFLA]

That would be fine, you would retain greater stiffness in the cap that way. But you also increase your chances of a slip up - so be careful! Also make sure you do this with the driver facing downwards (kinda like working underneath your car). You must be careful not to get debris in the gap. A vacuum of some sort going at the same time would not hurt either. BEFORE you do any of this of course, you should mount the driver on a baffle and drive it hard so you see if you find the noise objectionable. If you are mounting in a W-frame, it may not even be an issue. Again, be careful, it won't take that much power to drive it to Xmax @ 20hz mounted free-air.

Cheers,

AJ

[johninCR]

Due to the drastically lower power handling in a dipole configuration, what's wrong with just plugging up the vented pole, or at least stuff something in the vent to slow the air movement and eliminate noise that way. Won't opening up the dust cap end just increase the air flow and give you another source of noise?

[AJinFLA]

Hi John,

what's wrong with just plugging up the vented pole, or at least stuff something in the vent to slow the air movement and eliminate noise that way.

- no, no, no - you definately don't want to do that! Plugging/stuffing the pole vent would increase pressure underneath the dustcap cavity are force the air out through the small vent holes drilled into the base of the cone near the spider (sorry, no pics of those). Not good!

Won't opening up the dust cap end just increase the air flow and give you another source of noise?

- the opposite! Lets put it this way. If you removed the cap entirely, there would be NO airflow in/out the vent. Thats what the dustcap is doing. When the cone moves back and forth, the dustcap is pushng and pulling air through the vent. By opening the cap and allowing it to breathe (see my post about puting a foam disc on), you get much reduced pressure inside the cavity above the pole and less air is going to be pushed/pulled along the vent.
Perhaps a little driver internals 101 is needed. Look at the pic below of a dustcap removed (not a PLG15 btw). Now you just have a hole running through the pole. There is nothing forcing air through the hole when the cone moves. With the cap on, you would have a (almost) sealed cavity of air under the the cap. The cones outward motion would pull air into the vent as the size of the cavity increases, then push air out as the cone/cap moves backwards and the size of the cavity decreases. thats one of the many functions of the cap. Another is stiffness added to the cone structure. Removing it will reduce stiffness - and affect the drivers performance. Multiple small holes, or one bigger one in the center won't be quite as bad. It's all about compromises, which is why I stressed in my post above to try the driver without any mods 1st, then decide. Luckily, if you wreck the Pyle, its $37! Still my reigning value champ

Cheers,

AJ

[Arctophile]

Hmm I've just taken delivery of my Pyle drivers (heh) and re-read page 39 of this thread.

Rudolf recommends a symmetrical arrangement for a W-frame like the one at the bottom of this page: http://www.linkwitzlab.com/woofer3.htm

I was planning to build the other one just above, but this comment has given me pause. Can someone please explain in lay terms why Linkwitz only recommends the symmetrical arrangement for stacked woofers and not a single W-frame?

SL says:
"the two drivers in each of the stacked cabinets can be mounted for a cleaner front-to-rear acoustic path. In that case even order distortion reduction is obtained by reversing one of the cabinets as shown below."

Does this imply that the a single symmetrical w-frame as recommended by Rudolf (I think) is going to have higher even-order distortion?

Finally I am going to have to connect these drivers in series or to separate channels due to the load on the amp - does that make a difference to which design I should choose?

As a better informed contributor once said, thanks for your patience

//Adam F

[johninCR]

Hi Adam,

The Linkwitz 2 driver Wbaffle isn't symetrical with regard to the left and right pathways not being equal, because he uses push/pull to reduce distortion. What he is saying about stacking is that with a stacked pair (4 drivers), you can build them symmetrically (cones facing each other and equal size pathways left and right). Then you just turn one around and swap the wiring to end up with push/push in one cab and pull/pull in the other cab, which nets to push/pull and you get the distortion reduction benefit and symmetrical pathways.