Dipole Sub question

[theAnonymous1]

With these drivers there is a small amount of pole piece "chuff" at high excursions. I eliminated this problem by cutting off the dustcaps. If removing the dustcaps is too extreme for you, I suggest at least removing the pole piece screen.

[chops]

Originally posted by zobsky
Chops, off topic, ..doyou still use your U-baffle subs and did you ever try your drivers in a W-profile or ripole enclosure?
Secondly,(Dipole noob alert ) can't a W-profile sub work with the driver cones facing each other? Why are the drivers always mounted looking in the same direction ?

Thanks

H-baffles actually, and the answer is no unfortunately. They were great, excellent even while they lasted. They were just simply way too large for my room. I wasn't able to postion my main channels where they needed to be for proper imaging and soundstaging.

And no, I never tried them in a W-baffle or ripole. However, once I get the chance (since I still have the drivers), I do plan on building these ripoles. Getting a lower Fs from this design sounds very interesting, and it will be needed since the baffles will be much much smaller than the H-baffles I had.

And it looks like theAnonymous1 answered your last question.

Originally posted by theAnonymous1
If you can swing a bit more , these would be a better choice....

http://www.partsexpress.com/pe/pshow...TOKEN=59432710

I have 4 of them waiting to be put in ripoles. I have no way to cut the wood though, so it won't happen anytime soon (it's been over a year so far).

I agree 100% on this. Eventhough the Goldwood's have a higher Qts, they also have a slightly higher Fs. The higher Qts will allow the bass to possibly be a little floppy, and the higher Fs may not allow them to reach as deep.

The Pyle PPA15 on the other hand has a perfect Qts for dipole/ripole use (0.6 min) which means it's bass will be tighter and cleaner which I can definately vouch for, and the lower Fs of 27Hz will get you lower. Not to mention that in a ripole, that Fs will get even lower (not sure how much lower however) giving you even lower bass reproduction.

[zobsky]

Originally posted by johninCR
HINT, the thicker the driver mounting panels the narrower your cab can be....It's kinda counter intuitive, but true as long as you mount the drivers normally in relation to the holes.

John, could you elaborate? I lost you on that. BTW, ..thanks for all the useful info on my last open baffle array build.

Originally posted by chops


And no, I never tried them in a W-baffle or ripole. However, once I get the chance (since I still have the drivers), I do plan on building these ripoles. Getting a lower Fs from this design sounds very interesting, and it will be needed since the baffles will be much much smaller than the H-baffles I had.

Chops, ... I read through your thread. Do these drivers need EQ'ing up on the low end (possibly by the bass boost on a sub amp) ?


Thanks

[Daveis]

What's the math for sizing the dual driver ripole?

Do you have to compensate for OB type cancellation with EQ?

[johninCR]

Originally posted by zobsky
John, could you elaborate? I lost you on that. BTW, ..thanks for all the useful info on my last open baffle array build.

For a 4 driver Ripole in a W alignment the single pathway will be twice the width of the 2 pathways to the rear. You'll still want the cone to magnet mounting like the Linkwitz W to be able to get the pathways small enough for ripole behavior, in fact as small as possible taking into account cone travel (so it can't hit the other driver's magnet).

This give you 2 driver mounting plates with 2 drivers on each, facing opposite directions. With a very thin piece of wood, the magnets would each stick out almost the full depth of the driver. If the wood was as thick as the driver is deep, then the frame of the driver would be even with the back of the magnet of the other driver. Viewed from the side the structure would be almost twice as thick using the thinner mounting plate.

Essentially, thick mounting plates enable a narrower pathway, which is important for Ripole behavior. Since you're already getting the left and right sides as close together as the drivers permit, narrowing the pathway results in a narrower cab.

This is something I didn't appreciate until I started assembly. I used relatively thin wood and each cab with four 12" drivers was 12" wide by 24" tall. I could have easily knocked 2" off of the width by making those mounting plates each 1" thicker. That would have reduced my central pathway to 3" instead of 4" and the 2 rear pathways 1.5" each instead of 2".

Note that I added 8" with cross bracing to the rear of mine, which adds 16" of rear wave travel distance and some U baffle behavior. This increases extension by more than a full octave or over +6db at the bottom with only a small increase in overall size. Also note that my W/U/Ripole/push-pull/mechanical cancellation subs do require damping in the rear pathway for proper operation. Too bad I went to the trouble using cheapie woofers I already had. At some point I plan to build something similar using eight 6x9's per side, resulting in stable high bass output OB speaker stands in a very compact form.

[zobsky]

Originally posted by johninCR


For a 4 driver Ripole in a W alignment the single pathway will be twice the width of the 2 pathways to the rear. You'll still want the cone to magnet mounting like the Linkwitz W to be able to get the pathways small enough for ripole behavior, in fact as small as possible taking into account cone travel (so it can't hit the other driver's magnet).

This give you 2 driver mounting plates with 2 drivers on each, facing opposite directions. With a very thin piece of wood, the magnets would each stick out almost the full depth of the driver. If the wood was as thick as the driver is deep, then the frame of the driver would be even with the back of the magnet of the other driver. Viewed from the side the structure would be almost twice as thick using the thinner mounting plate.

Essentially, thick mounting plates enable a narrower pathway, which is important for Ripole behavior. Since you're already getting the left and right sides as close together as the drivers permit, narrowing the pathway results in a narrower cab.

This is something I didn't appreciate until I started assembly. I used relatively thin wood and each cab with four 12" drivers was 12" wide by 24" tall. I could have easily knocked 2" off of the width by making those mounting plates each 1" thicker. That would have reduced my central pathway to 3" instead of 4" and the 2 rear pathways 1.5" each instead of 2".

Note that I added 8" with cross bracing to the rear of mine, which adds 16" of rear wave travel distance and some U baffle behavior. This increases extension by more than a full octave or over +6db at the bottom with only a small increase in overall size. Also note that my W/U/Ripole/push-pull/mechanical cancellation subs do require damping in the rear pathway for proper operation. Too bad I went to the trouble using cheapie woofers I already had. At some point I plan to build something similar using eight 6x9's per side, resulting in stable high bass output OB speaker stands in a very compact form.

Do you mean like this (see rough figure) aiming to satisfy the following criteria:
1. minimize the center "common" chambers
2. ensure that the sum of the heights top and bottom chambers are equal to the height of the common chamber
3. ensure that the height of the top chamber = the height of the bottom chamber


Why do you prefer magnet to cone orientation vs. cone to cone or magnet to magnet orientation. Is it just for space efficiency?

In your experience, How does ripole bass compare to OB bass, subjectively?

[Saturnus]

Originally posted by zobsky
Why do you prefer magnet to cone orientation vs. cone to cone or magnet to magnet orientation. Is it just for space efficiency?

In theory cone-to-magnet orientation cancels out the compression distorion of each driver as the cone moves back and forth. And particularily in OB designs there might be more to gain from this orientation than in closed box where it creates it's own compression distortion.

[chops]

Originally posted by zobsky


Chops, ... I read through your thread. Do these drivers need EQ'ing up on the low end (possibly by the bass boost on a sub amp) ?


Thanks

Nope. They were pretty flat to about 16-18Hz on their own. The only bit of EQ I used was to take out a few dB between 90-125Hz where the xover freq was.

[johninCR]

Originally posted by zobsky
Do you mean like this (see rough figure) aiming to satisfy the following criteria:
1. minimize the center "common" chambers
2. ensure that the sum of the heights top and bottom chambers are equal to the height of the common chamber
3. ensure that the height of the top chamber = the height of the bottom chamber

All three, though I'm not sure you want to minimize the "common" pathway, since you could make it too small. With my thin mounting plates the thinnest possible was a little big, even with holes in the side panels for the 2 outward magnets to poke through (an added complication and detraction from beauty.

In your drawing the 2 mounting plates are different thicknesses and you definitely don't want that, because everything won't be symmetrical.

Why do you prefer magnet to cone orientation vs. cone to cone or magnet to magnet orientation. Is it just for space efficiency?

With all 4 in 1 cab, just space efficiency, since 2 cone to cone and 2 magnet to magnet would still be push-pull. With only 4 drivers I'd suggest 2 cabs for maximum flexibility in placement, in which case cone to magnet is required for push-pull. Also, I find stereo into the bottom octave more important with open alignments even if the signal is mono.

In your experience, How does ripole bass compare to OB bass, subjectively?

Same as a W, but flatter bottom end, just as discussed in the original ripole thread. ie EQ may not be needed.

Note that I believe the folded W's, N's, ripoles sound subjectively different than having the front wave directly radiated from the driver, with the folded types sounding slightly "mushy". Think about it, the sound wave has to be "mushed" out of that pathway. This may be an aural illusion caused by the limited upper end extension of the folded alignments. IMHO folded alignments are only for stealth (hide the drivers), space savings (U's can be smaller for same extension), mechanical vibration cancellation (for W's), prettier push-pull, flattening response (ripoles), and lowering Fs due to the air mass loading of ripoles (and lesser extent W's and N's that aren't ripole). In other words, fold only if EQ isn't an option or the bass cab will also function as the base of the main speaker.

Though a U may have a greater minimum width, given the same depth, in terms of bottom end potential, 1 driver in a U is equal to 2 drivers in a folded dipole. It doubles the rear wave pathway, adding +6db at the bottom (same as adding another driver). The radiation pattern is different, but I don't find a great sonic difference. This is probably because a dipole close to a wall isn't really a dipole anymore. It's a dipole + wall, which can't produce a figure 8.

[chops]

I don't know about you guys, but I am totally confused now.

Thicker baffles, smaller air spaces, ripoles that are part ripole, part W-baffle, part U-baffle... I don't know if I'm coming or going!

Isn't a ripole pretty much the same thing as an N-baffle (half of a W-baffle), but with the front and rear walls closer to the woofer to build up a little bit of a load on the driver, effectively lowering the Fs some? IOW, isn't a ripole a smaller, narrower, more compact N-baffle dipole?