| moray james |
| A friend asked me what drivers would be best suited for a smalll 6.5 or 8 inch double ripole system. Thought I would fast track and ask here for recomended drivers. Thanks Moray James. |
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| Kensai |
I've not tried them yet, but the 8" Dayton shielded DVD drivers look excellent for the job, at least at the price (like $23usd).
The dual voice coils give you alot of options for running them. Minimally, you could just drive 1 coil and leave the other open. This should effectively double the driver's Qts, though you'll lose efficiency, so on top of the efficiency loss of the ripole itself, you'll be need a ton of amp power to get it up to level. The other option is to run them both in parallel to get a 4 ohm load, but drop a resistor in line with the + terminal to raise the Qts. You could also run the thing passively as the woofer in a multiway, and use inductors with the highest possible DRC to low pass. My calculations for a sealed enclosure show that 2-4 ohms total makes it almost perfect for running both coils in parallel. I'm thinking that you might want to shoot for at least 8 ohms and maybe even closer to 12-14 for ripole or other dipole variants. Just make sure you've got enough power and/or multiple drivers to make up for the efficiency loss.
Personally, I'm getting ready to use some cheap 6"x9" car speaks with the coax parts removed (cost me like $10 each at walmart, and they're very heavy duty with 30oz magnets). I'm planing to build a pair of ripole stacks using 4 on each side to be the woofers for some short line arrays. Should be a fun experiment, but the reason I'm mentioning it is that the 6"x9" form factor should give you about an 8"er's worth of cone in a 6.5"er's space since you can and should lay them horizontally in your ripole. Also, it can often be easy to find very likely candidates at retail, sometimes at closeout prices as car audio driver makers feel the pressure to refresh their lines annually.
Just a couple options. For anything else, you're looking for high Qts (at least .5, preferably higher), a decent Xmax (4-5mm is likely the bare minimum here; you'd probably need to double up on cheapie drivers sporting 3mm or less, just to keep them from bottoming out right off the bat).
Most folk are going to jump you (maybe rightly so) for looking for such small drivers for this purpose. Personally, it just makes me curious. What sort of plans do you have for putting these sizes of drivers in ripole. I've thought of a few interesting configurations myself, but I'm always interested what others might be dreaming up.
Kensai |
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| moray james |
Kensia: Thanks for all the greqt information. The system that my friend wants to build is for a small unused bedroom which he plans to use as a listening room. He intends to use a pair of smallish 6.5 to 8 in dual Ripole's each with a narrow 4-6 inch wide by 4 foot tall electrostst panel . The size of a 6.5 to 8 inch dual Ripole work well with the visual of the ESL panel size he wants to use. His thoughts are that if he needs more bass then he can add additional ripole subs of the same size to try to achieve more uniform control of the room. I am not personally keen on the idea of having to use a load resistor to make the speaker work and would rather see the power disapated within the driver. I had a look at the Peerless SLS 830667 and thought that driver seemed like a good candidate as the Qt is greater than the 12 inch version which workd well in a ripole. I don't know of many divers that fit the requirements for Ripole loading in this size.
The Walmart car drive idea is great but how do you know what the Qt of a car driver is? Is this kind of data normally posted in the specs of drivers like these? I can see a lot of advantaged to a 6X9 driver. Have you measured this specific driver? Which model is this driver? If the price is right one could use four per cabinet and still have a very small cabinet. I look forward to seeing where this project goes. Regards Moray James. |
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| Kensai |
Car drivers tend to have medium to high Qts by their nature. They're technically running in IB, so ideally, their Qts should be around .7. I'm sure there's lots of variation with that, but in general, you're pretty safe with the standard drivers (car sub drivers could be anything as some are intended for ported cabinets, other sealed; its easier to get real data on those, though).
The resistor isn't to make the speaker work. Its just an idea I'd gotten from Nelson Pass' work on current source amps paired with efficient, full range drivers. The fact is, though, that resitance in line with the + terminal of your driver will raise their Qts, and this includes the DRC of any inductors you might use to low pass the drivers. Its not really something to worry about, but is something you can work with if you feel like experimenting/tweaking.
Oh, another thing with car drivers is that they generally have very shallow mounting depths (like 3-4 inches). This can help you jam a ton of bass drivers into a slim ripole. The one I'm working on is basically two ripole stacks of 2 drivers each facing each other, the front wave of all 4 drivers sharing a chamber in the center which I have venting toward the listener (which leaves 2 back wave chambers to the edges). The panels on the backs of the drivers have cutouts for the magnets so the chamber is made only as deep as the basket minus the thickness of the panel the driver is mounted on. So they're really just depth of 2 drivers + 2" wide (about 10" total since these things have huge 30oz. magnets). These are just roughed in, so part of the magnets are hanging out, but that can either be boxed in (adding another inch or two width) or just concealed with another layer of panel (whatever material you are using) with cutouts for the magnet. That second option is likely what I'm going to do as width is an asthetic thing on my end, too. Should leave an interesting appearance ;-p
So, what sort of panel is he using? Something commercial he salvaged? Or something he built?
I'm actually planning to use these as the bases for a pair of short lines made of Monsoon planar drivers, so I've got similar plans, just not likely as refined ;-p
I've also thought of building an actual line array of ripole elements. They could be built extremely slender with the right drivers (6.5"ers with shallow mounting depth would be the best, actually, possibly bringing the thing to a 7"-8" square column). The best way to do that would be to use an even number of drivers, and stagger them, half facing left, the other half facing right, but all mounted on the same baffle. That sort of thing could be used as the bass line for a multiway line array, or used by itself as a powered sub. Seems like that would make very natural and authoritative sounding bass.
Smaller in scale, you could use pairs of 6.5"-8" drivers in ripole with a nice full range driver. Would take a little more xover work since you wouldn't be working in a line anymore (your friends panels will be a nice line, and since the wave length down in the area the ripole will work is so long, you shouldn't have any issue just letting it run without an xover, so if you use one at all, it could just be something you tweak after constructing it and starting to listen to it). You'd probably want to highpass your full range a bit (in the 100-200 Hz region) and then determine the need for lowpassing the ripoles by ear.
Anyway, its late and I'm rambling on a favorite subject.
Later,
Kensai |
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| Kensai |
Had another thought last night . . . the Dayton 7" aluminum cone driver (can't recall the exact model number) actually has a moderate Qts and a decently low Fs for such a small driver. Its also quite cheap and has a bit more than average Xmax for a driver its size. In ripole, it should have an effective Fs in the 20s and with 2-4 of them per side, you should get really decent low end (well, IMO, since I'm good with a system that's solid to 40Hz and rolling of smoothly from there, for music AND HT; also note that I can't stand traditional subwoofers, or at least any that I've heard, which would seem to run the gamut of what's available in a box, with or without a port).
Please get back to us if/when anything is constructed from this. We'll definitely want to see it :)
Kensai |
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