[tubamark]

did I miss something?  What is a ripole?

Thanks,

Dan

I'm with you, Dan.  If something wasn't clear via a recent thread here, I'm often lost. I can't keep up with the zillion other forums out there.

I know John mentioned ripole recently, but the term was new to me.  I'm gathering that a ripole is simply a (loaded via restricted airflow) W-frame?  It is functionally still a dipole, right?

So . . . Where do we draw the line between W-frame Dipole vs Ripole?  Is it those "opening guidelines" Max brought up (where'd you find this stuff)?  -- Are those limits for regular W-frame, or a ripole?

Thanks to all, This is a great community,
Mark

[Maxdd_nj]

Hi Mark,

I have some of the same questions you have about the Ripole vs w-frame dipole. Others should chime in and fill in the blanks. I don't know who did what first but it seems Axel Ridthaler patented something he called the Ripole which seems like a variation on the linkwitz PHOENIX dipole woofer.

If interested, read about and see diagrams of the linkwitz PHOENIX dipole here: http://linkwitzlab.com/woofer2.htm and here: http://linkwitzlab.com/woofer3.htm

In that second link, scroll down to the very bottom. That last diagram is similar to the Ripole.

I haven't been able to find Ridthalers papers so I have no idea how or if his Ripole differs from w-frame dipole. On diyaudio, Rudolf who is able to read German, has read some of Ridthalers writings on the German boards and says this:
"The back opening should be as narrow as the driver dimensions allow. Possibly you could even fix the polepiece to the cabinet somehow and thereby reduce basket vibrations. If you use drivers with 25Hz<Fs(free air)<45Hz Ridthaler claims a reduction of Fs by 10-15Hz. He recommends 15"-18" PA drivers with a semi-hard suspension and Xmax >4-5mm (two 10" drivers per side is what I used). Qts should be at least 0.35. 0.7 would be preferable, and even Qts=1 is within limits. Suspension should not be too soft and might even be a bit progressive. The mass of the cone should be on the light side (no 10" with a 120 gr cone please)"

That's all I got, hope it helps.

Max

[Maxdd_nj]

JohninCR,

In the u-baffle where does the stuffing go if there's no back? Does it get squished between the "+" brace and the inside-front baffle? Do you have a diagram or photo of this? Thanks!

Max

[JohninCR]

The stuffing goes inside what is essentially an open backed box.  I just stuffed mine in the 4 cavities formed by the brace (no pics...too ugly right now).  See www.MusicAndDesign.com , especially the tech studies, for info about U-baffles.

Ripoles are discussed at the DIYaudio forum, in the subwoofer section, and in a few threads.  If I remember correctly the primary one is titled something like "honey I shrank the dipoles".  Those discussed are essentially 1/2 a W (an N baffle) with very narrow openings.  I built a doubled up pair in a W alignment with 4 cheapie 12's per side, which worked well.  I doubled it up for push/pull and vibration cancellation.  A hint for anyone building them...The thicker the driver mounting panels, the narrower your cab.  I used 12mm ply and fit 4 12's in a front profile of 12" wide by 25" tall, but I should have used 1" ply for a stronger and only 11" wide cab.

[wikin]

Guys, slightly off topic here, but I really have a burning question.

Currently I'm in the process of building a w-frame ripole sub using 2x15" and will be using DCX to eq it flat to 40hz; but personally I would like to have 20hz sub capability at my disposal just to cater for that final rumble.
My personal preference would be to build another set of w-frame ripole and add onto the current ones so that I can eq flat to 20hz. This has 3 advantages : simple add onto the current system and saves me from having another amplifier and also no need to add another eq point.
What's your opinion? Will OB bass to 20hz sound nice compared to an IB sub at 20hz? For sure there's a lot of wasted energy going the OB route.

cheers.

[JohninCR]

Guys, slightly off topic here, but I really have a burning question.

Currently I'm in the process of building a w-frame ripole sub using 2x15" and will be using DCX to eq it flat to 40hz; but personally I would like to have 20hz sub capability at my disposal just to cater for that final rumble.
My personal preference would be to build another set of w-frame ripole and add onto the current ones so that I can eq flat to 20hz. This has 3 advantages : simple add onto the current system and saves me from having another amplifier and also no need to add another eq point.
What's your opinion? Will OB bass to 20hz sound nice compared to an IB sub at 20hz? For sure there's a lot of wasted energy going the OB route.

cheers.

Wikin,

If you get your ripole right you may not need EQ.  Regarding your question, any OB bass project should start with Linkwitz's DipoleSPLmax spreadsheet.  Then you know your limits.  Yes, OB bass is a lot like IB, but without some of the negative room effects.  There are room limits though with regard to dipole bass.  Once you get down to your room's fundamental mode, dipole bass drops sharply.  Note that this is dependant upon your room dimensions and wall construction.

An alternative to the second cab is to add 50% more depth to the rear of your planned cab and stuff it.  This accomplishes 2 things.  First, it doubles "D", giving you an octave more (same as doubling up identical cab and drivers), but only 1/2 the additional space in the room and 0 additional drivers and power.  Second, it gets you away from pure dipole and it becomes a hybrid, so according to JohnK you pick up room gain too.  Depending upon your room and placement there is very little sacrifice. 

That's what I did with my ripole type W's.  With the drivers mounted all the way to the front, I added 8" to the rear plus some shelf bracing and stuffing.  They make a surprising amount of  very deep bass, and the only reason I don't use them is that they are extremely inefficient and the 3mm Xmax can't deliver what I need.

[wikin]

Thanks John. Extending the rear of the w-frame did cross my mind, just that the final cabinets now becomes a mini transmission line and well, doesn't look cute ain't it 
Sigh, so much to do, so little time...

[JohninCR]

Thanks John. Extending the rear of the w-frame did cross my mind, just that the final cabinets now becomes a mini transmission line and well, doesn't look cute ain't it 
Sigh, so much to do, so little time...

All of the folded versions of OB's are short TL's, but we operate them below the fundamental resonance.  The U-baffle extension I mentioned just makes it a little longer, but the stuffing helps damp the resonance and enable it to function properly.  Mine are 21" deep, and I have no resonant sonic signature if I cross at 100hz or lower.

[tubamark]

I would like to have 20hz sub capability at my disposal just to cater for that final rumble.
 . . .  Will OB bass to 20hz sound nice compared to an IB sub at 20hz? For sure there's a lot of wasted energy going the OB route.

cheers.

As John mentioned (see both John K and Linkwitz's site for in-depth explanation), your longest room dimension determines the lower limit possible with a dipole.
565/room length in feet = dipole bass limit (Hz).
To get 20 Hz, the longest dimension has to be at least 28'.
14' will still get you 40 Hz - not bad for most music.
It's best to avoid feeding dipole woofers below that room limit, because a dipole will still (quietly) pump away like crazy to its limits.

[Bob in St. Louis]

To get 20 Hz, the longest dimension has to be at least 28'. 14' will still get you 40 Hz

I've heard this before but my question is this; Does "the longest dimension" mean the length of one wall, or can it be a diagonal (corner to opposing corner)?
I assume this means a tape measure straight down the longest wall right??

a dipole will still (quietly) pump away like crazy to its limits.

Interesting sight.... I've seen this happen. 

Bob

[JohninCR]

Bob,

I actually believe the dipole threshold is based on the "on axis" room dimension, but I never have been able to get confirmation of that.  That's one of the things on my measuring list, and my 12'x21' room has solid enough walls, is a fairly good rectangle, and a big enough difference in width and length, that I should be able to obtain a valid black/white result regarding this issue.

[tubamark]

>>>I've heard this before but my question is this; Does "the longest dimension" mean the length of one wall, or can it be a diagonal (corner to opposing corner)?
I assume this means a tape measure straight down the longest wall right??

Bob,
Yep, for a typical enclosed rectangular room, just the longest sidewall of the room.
True, other tangental (diagonal) modes exist, but under typical real-world conditions they're weak and don't contribute much to the modal behavior of the room.
Think of the classic "wave-tank" illustration - 'Hard to get diagonal waves going.

--Mark

[Bob in St. Louis]

Think of the classic "wave-tank" illustration - 'Hard to get diagonal waves going.

AAhhh YES, a "visual". I love having a mental picture. I'll buy that theory. It would be interesting to see some measurements.

Thanks John, and Mark.

Bob