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Old 13th September 2006, 08:58 PM   #1
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Default Drivers / parameters for ripole subs

Am trying to get enough information to understand the necessary parameters for a ripole sub driver. Optimum characteristics for different size drivers. Seems that Qt increase as driver size decrease and decrease as driver size increases. What about cone stiffness and driver mass? What about acceptable linear excerssion? Larger cones would not have to move as far but what are the practical excursion ranges.? Would like to be able to search for suitable drivers but from looking at published designs it seems that there are no set parameters with many different drivers being used.
It would seem to me that dual ripole systems are the best compromise and that larger drivers in the 15 to 18 inch range would be the most practicle way to overcome the largest and most common complaint of this design which is output. Ripoles are not the most efficient design but they would seem to be the most compact. For home theate systems where outputs above 105 db at low frequencies are desired it would appear that either multiple dual 12 inch ripoles are required (and this makes good sense in terms of driving the room) or a smaller number of 15 - 18 inch dual ripoles. I am wondering where the turning point is. Larger drivers 15 - 18 inch usually end up costing more and long throw versions are not as common as the mechanics become more involved with the higher mass structures which is part of the increase in cost. The 12 inch driver would seem to be the best all round compromise in terms of moving a lot of air and keeping the cost from getting out of hand. For a given size of motor the 12 inch represents the best balance that I can see in the market place from a cost/performance point of view.
I understand that people want/need to generate large outputs of bass in HT systems and want to get as much as they can from as few boxes as is possible but really high output at low frequencies usually gets very large or very inefficient when made smaller. Interfacing large single cabinet subs into a room does not seem to be the answer.
I am also interested to know from those with hands on experience how much of an issue ported pole noise is in ripole sub designs. Hope that we can have a polite and useful intercourse here as this topic has had some heated differences of opinion in the past. I would like to get past that to discussing the reasons behind those differing opinions. Regards Moray James.
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Old 14th September 2006, 03:31 PM   #2
Kensai is offline Kensai  United States
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I'll second the need for more detail information on this subject.

James - if you'll allow 12" drivers, I've been wanting to try this one - Cheap Pyle Woofer . Cheap enough to experiment with, really good reported specs for dipole use, and in ripole, you can hide just how ugly the thing is.

Another tidbit I want to throw out there is that I was told by one of the more active OB "authorities" here that the depth of the ripole chamber (the dimension of the space parallel to the driver face) has something to do with the unit's roll off point. He seemed to be able to predict what that point was, so there must be some mathematical work out there we can start from.

Kensai
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Old 18th September 2006, 12:28 AM   #4
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Default possible driver choices

The Eminence series Alpha and Beta 15 inch units look promissing for inexpensive 15 inch units. Though these units do not have very high Xman they do have Qts values that would be better than average and this will help to bump the response at low frequencies. The fact that these are 15 inch units should also help matters. I guess the question is how much excurssion do you need to have good output with larger drivers like 15-18 inch? Regards Moray James.
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Old 18th September 2006, 06:18 AM   #5
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Default Eminence Delta 15LFA...

This driver is not to expensive and I have found it discounted to about $115.00 Cnd. Fs-41 Hz., Qts-0.58, xmax-4.8 mm, xlim-16.5 mm cone mass 64 grams, efficiency is said to be 96 db. This a tad high (Fs) but ripole mounting should bring response down into the low 30's and a pair of these should move considerable air. Any comments. The big question is will the suspension handle being pushed on a ripole cabinet?
Does any one know when Peerless will release the 15 inch SLS, I have heard talk of Dec. this year?
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Old 18th September 2006, 11:04 AM   #6
maudio is offline maudio  Netherlands
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Default peerless?

I use the Peerless XLS 12 (830500) in my dipole (not ripole) subs, the same driver proposed by Linkwitz.

They don't come cheap, but they do have very large Xmax (25 mm lin, 40 mm max) which gives it a pretty good air displacement vs $$ ratio

Using only one per channel I can still reach very realistic SPL's. However it must be said that I am not using them for home cinema and I am not aiming for 105 dB @ 20hz...

Because of the open voicecoil construction there is no pressure building up under the dust cap, so no strange noises at large excursions. This is very important in D/Ripole application.
All in all I am very pleased with their performance.

I believe that for high-quality applications drivers > 12 " are not advisable...

just my 0.02
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Old 18th September 2006, 05:47 PM   #7
Klimon is offline Klimon  Belgium
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Quote:
Another tidbit I want to throw out there is that I was told by one of the more active OB "authorities" here that the depth of the ripole chamber (the dimension of the space parallel to the driver face) has something to do with the unit's roll off point. He seemed to be able to predict what that point was, so there must be some mathematical work out there we can start from.
That's the only cabinet variable so it would be great to know how it affects cut-off. I'm also planning a pair of ripoles using cheap 12" car subs. Easiest solution would be to take the chamber dimensions given on the lautsprecher.de website and measure the result, then try a bigger chamber and test that one, benefitting from the little work needed to build a ripole cab.

Simon
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Old 18th September 2006, 08:46 PM   #8
Kensai is offline Kensai  United States
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Klimon,

I'm not meaning the width of the airspace from the driver face to the panel in front of it. That is the only variable, and from the same person I got the impression that that should be as shallow as possible, but more in a second.

What I was meaning was the "depth" or the across the driver face measurement. Like if you were using 8" drivers, it would be 8.5"-9", if you were using 15"ers, it would be 16"-18". That sort of thing.

Anyway, as for the width of the airspace chambers, I've gathered that narrower is better. What should be done is that the rear panel should have a hole cut in it to clear the driver's magnet. You'll want this panel to basically rest up against the joint of the basket and the magnet. Its also been recommended that the baffle, the middle panel that the driver is mounted to, be made thicker, to also compress this volume though you still have provide airflow clearance (rounding over or chamfering the back edge of the cutout). Then you simply make the front air chamber the same width (or possibly a bit less if you feel the magnet volume should be accounted for).

I'm sure there's a fairly early point of diminishing returns, but I think the cost is in driver efficiency, not distortion as these compressed air chambers actually act as partial acoustic suspensions, proping up the cone on both sides which will limit excursion to some degree.

As for drivers, I don't think the Peerless XLS are ideal. I know Linkwitz uses them in OB, but have you seen the amount of EQ he uses and amount of power he needs to feed them properly? Sure, they're pretty high quality drivers (not to mention pricey). They're rugged and can handle the high amp, heavily EQed abuse of drivers in OB that are intended for BR application. As long as you've got more power, you can get more dB out of them. There's another line of Peerless (can't remember the designation off hand) that is much cheaper (less than half), has less Xmax (about half), but has much higher Qts. If memory serves, the specs were very similar to the driver the ripole originator was using. Anyway, it looks like the quickest way to get in and try this out is really cheaper drivers, like the low end (and highest Qts with lowest Fs) Pyle Pro drivers, or various cheap car subs (again, some Pyle models come to mind first), providing you can find specs on them. As far as I can tell, you're looking for the highest Qts/lowest Fs combo you can get while making sure the driver is rugged enough to handle some mild abuse (though just from driving, as the ripole alignment is ideal for physically protecting a driver).

So, who's going to start building

Kensai
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Old 18th September 2006, 09:04 PM   #9
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Default Thanks for your input

I have found out that Eminence state thier Xmax figures as Peak values so doubel the distance if you are used to dealing in terms of peak to peak (as Peerless does). I am awaiting confirmation that they also state Xlim (mechanical limit (read damage)) in peak values as well and I will post that info as soon as I have a reply from Eminence tech support.

Maudio I am interested to hear your reasons for why you feel that larger than 12 inches for a dipole/ripole is not a good idea. Putting aside the size/cost issues I would think that with a suitable motor structure and with suitable parameters larger would in fact be better.

Klimon: yes this is the kind of information needed to be able to manipulate cabinets to work with available drivers. Kind of a working explaination or how to. Chamber size is the other variable and we need to understand the relationship between driver parameters and the cavity volumes. I have been told that the rear volume does not have the same degree of importance as the front cavity. This makes sense from a strictly dipole point of view in that the cabinet is simply a folded baffle. However the Ripole/BMC concept is so compact that chamber pressure must surely impact cone motion and symetry of load should be considered if minimum distortion figures are to be expected.
From what I can see a wide range of driver parameters can be used in a Ripole design but Qts values 0.6 to 0.7 would seem to be the ideal range and suspension stiffness which is progressive would also be a great benefit. The largest single concern I see is one of air turbulence and the resulting noise it causes. For this reason vents below the spider and smooth open basket designs will go a long way to reducing such noise which will be high in such long throw designs. Dust cap removal may also be worth considering for drivers that do not have vents below the spider assembly. Pole piece vent noise must also be a concern and wire screen covers which are often placed on the back and or front side of ported pole pieces would also probably be best removed.
Chamber volume experiments would be best done with single drive Ripole cabinets to hasten construction time and to reduce cost. Perhaps those with experience can provide readers with a good general rule of thumb to find a reasonable starting point for cavity volumes.
Lastly I would point those who may be looking for a larger more powerful output Ripole to have a look at the Eminence Kilomax Pro 18. This driver is a Beast built like a tank and can be found for as little as $300.00 US funds each. I should think that for home applications These drivers in dual Ripole cabinets would be spectacular without breaking the bank. One of the badest drivers that I have come across for Riple use would be the McCauley 6174. While more than double the cost of the Kilomax I am sure these would be awsome in a Ripole or Dipole design. Something to drool over. Regards Moray James.
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Old 18th September 2006, 11:49 PM   #10
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Default Driver deal at PE...

Here is a buy out listing for an Eminence custom OEM driver that would work in a Ripole/Dipole for very little money. Have a look regards Moray James.

http://www.partsexpress.com/pe/showd...number=299-392
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