Newbie Dipole woofer help please...

[santiu]

hey guys... I've got some subwoofers lying around that I want to make dipole woofers from.

But, they were meant for car audio and consequently are 4ohm woofers, and I don't want to give my amp a 2ohm load. Can I wire the woofers in series (with opposite polarity)?

Also, where can I find out how big my baffle/frame needs to be. I plan on using a W-frame like the Phoenix woofer. But I don't know how big the frame needs to be and I can't seem to find that info on Linkwitz's site (although I'm probably just be retarded).

thanks a bunch

[johninCR]

http://linkwitzlab.com/woofer.htm

[santiu]

okay ...read it again... I guess the first time i wasn't paying much attention.

So, just to make sure I understand...
1) it's okay to connect the drivers in series, I'll just result in a lower maximum SPL.
2) The W-frame is pretty much sized to just fit the woofers inside. So using essentially that same phoenix box for all drivers is alright? What are the issues if I go smaller? I see that if I decrease the effective path difference, I'll loose SPL. What about the sides? Wider is better than deeper for me, so I'm trying to understand how I can futz with that.

Just wondering, he mentions in the models page that the phoenix woofer has a 19" separation between it's openings. But looking at the drawings, that seems to be more like 20.25"... I'm I looking at this wrong?

Finally, what do you guys think about using this 10" driver to build a pair of dipoles:
Fs 26.6 hz
Xmax 13 mm (I think this is +- 6.5mm)
Qts 0.23
Sd 346 cm2


alternatively what do you think about this buy-out woofer from PE:
12" buyout Woofer. X-max seems like it's too small to be used for a dipole. But for $11 I thought I'd check anyways.

Hopefully that 10" driver I mentioned will work, and I can build some dipoles to hear what all the hype is about

thanks so much for your help

[454Casull]

Connecting the drivers in series [assuming two of the same type] will double the impedance and leave sensitivity unchanged. Max loudness is doubled (due to twice the displacement).

Yes, you are looking at the drawings wrong. The side panels are 19" deep (looking from the front).

You'll need to equalize that driver. A Qts of 0.23 won't give you much bass.

The buyout driver doesn't have enough excursion, unless you bought a lot of them, in which case you'd have a very wide W-frame.

[santiu]

Ah... i see. For some reason I thought that 'D' was the distance between the two woofers. But in the H/W frame the openings essentially act as the point of radiation right? So the effective distance is the length of the sides. Does the relative positioning of the two woofers matter at all? How about the width and height of the W-Frame? Seems like that doesn't really matter.

I noticed the low Qts... but I also saw that Linkwitz used the Peerless 830500 which has a Qts of 0.2 so I figured that with some equalization these woofers wouldn't be a lost cause. I thought that the EQ specified for the Peerless driver would be a good starting point for tweaking (I think I'm gonna bite the bullet and buy a DCX2496 to deal with my x-over and EQ needs).

thanks again for all your help. Once I sort out my total lack of understanding of the W-frame sizing, I think this project is a GO!

[johninCR]

"D" is the extra distance the rear wave travels to get to your ears compared to the front wave. In that design the woofers are center depth wise, as they are in symmetrical H baffles, so "D" just happens to equal the side panel depth. If you take the linkwitz W and slide the interior pieces forward flush with the front edge of the top and sides you'll pick up and extra 4.5" of "D" with little or no change away from pure dipole radiation without introducing cavity resonance. In addition, just turning the woofer around to face the other direction will pick up a little "D" as well because the rear wave will have to travel from the center of the rear to the sides before traveling to the front.

Regarding the width: As you shrink the air pathways, you will start to add some resistance to the woofer operation. Check out the thread on ripoles which takes that to the extreme. If you go that route it becomes imporant that each of the 4 sides of the 2 cones see the same air volume.