How many ohms?
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Unregistered guest | Basically what i have is 3 12" jlw0 subs in a box. The subs are 4 voice coil and are only using 2 of the voice coils on each sub and then all 3 positive and negatives from the subs come to one and thats where the amp hooks up. Im guessing from this info is how you can tell how many ohms its gonna run at? The amp im using is a 800 watt fosgate 2 channel that will be bridged. Can anyone explain to me how to tell how many ohms it will be running, how many watts it would use and also if this is a good way to wire them for the amp im using. Im thinking the subs are about 125 rms so the amp will have no problem, but i might be wrong. Sorry for the long post, any info appreciated |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1343 Registered: Sep-04 | Ok, first of all the w0's don't come in dual voice coil configurations. http://www.jlaudio.com/subwoofers/pdfs/10_12_15W0_MAN.pdf They have two sets of positive and negative terminals, but they both go to the same voice coil. I assume you have the 12w0-4's(4 ohm svc). Three 4 ohm subs in parallel(negatives's and positives to one neg/pos) would give you a 1.33 ohm load. There's not very many 2 channel amps that are stable bridged into 2 ohm(except RF T8002) much less 1.33 so you're going to have to change the wiring to series which JL doesn't recommend: http://www.jlaudio.com/tutorials/wiring/index.html You can still do it but you will lose some sound quality as there may be a slight phase shift between drivers. Really need to know exactly which amp you have but the P8002 would only provide about 270 watts bridged into a 12 ohm load(90 watts to each sub). Aside from the phase problems thats probably enough power for those 12's but they really don't match well with your amp(T8002 would provide even less power). You need to verify exactly which amp and which w0's you have, but you'd probably be better off looking for a different set of subs. Series wiring with what you have, although not recommended, would require you to hook the pos of one sub to the neg of another and then the pos of that sub to the neg of the last one. You'd then need to hook the free neg of of one of the "end" subs to the neg on your amp(bridged) and the free pos of the other "end" sub to the pos bridged amp terminal. Jl, RF, etc. don't have any pictures since they don't recommend the configuartion, but I found a pic for 2 subs in series: http://www.caraudiohelp.com/images/series_wiring.gif Just add one more sub in there and thats what it should look like. Disregard the amplifier connections as those will be different for your amp. I know this is confusing. Get us the the exact models of subs and amp and we can probably simplify things a bit. If by chance you have the 12 ohm version of those subs(12w0-12) then things will become much simpler(keep em wired in parallel like you have them) although you will be overpowering those guys by a significant amount with a P8002(267 watts each). -Fishy |
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B;AkcesoI/ Unregistered guest | so i looked at the subs and am kinda pissed. 2 of them are 12w08 and one is 12w012. The amp im using is an older model fosgate 800 watt. My buddy before me had these 3 subs running off 3 outta 4 channels from a kicker 4channel 800 watt amp and they hit nice. He had the 3 channels bridged into one, just like ill be bridging my 2 chanels to all 3 subs. Ill try to find out more info about the sub, but thanks fishy for all the help so far |
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B;AkcesoI/ Unregistered guest | At lower ohms i wont have to give the subs as much power? So if i had a 12 ohm sub wired normally to an amp, what would be the benefit at running it at 12ohm? Would it be easier on the amp or something? |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1350 Registered: Sep-04 | Yes, but remember wiring voice coils in series is ok whereas wiring actual subs in series ain't so hot as you can get a 15 degree phase shift(I think, Jonathan?) between drivers. Running subs in series is bad enough, but I'd have to say running subs of different impedances together is even a worse idea. Yikes! :P Ummmm.... in addition its quite impossible to bridge three channels into one. Are you sure your friend just didn't have each of three channels running to one sub? That would make more sense. Find the exact model number of your RF amp and I'll see if I can find the specs to determine the best way to do this thing. Oh btw, 2 8 0hm subs and a 12 ohm sub in parallel would give you a 3 ohm load. If you're good with math here's the formula for figuring out equivalent parallel resistance(or impedance) of 3 subs: 1/Req = 1/R1 + 1/R2 + .... 1/Rn = 1/R1 + 1/R2 + 1/R3 => Req = 1/(1/R1 + 1/R2 + 1/R3) = 1/(1/8 + 1/8 + 1/12) = 1/(3/24 + 3/24 + 2/24) = 1/(8/24) = 1/(1/3) = 3 ohms Figuring out the equivalent series resistance is real easy. You just add them up. -Fishy |
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B;AkcesoI/ Unregistered guest | So im not screwed that one sub doesnt match? thats good news.. So ive been trying to find out more about my amp, but not sure how. i Went through ebay and found a model almost exactly identical exept its a 750 and mines an 800. Looks identical though. Heres the link http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&category=39737%26item%3D5777883194% 26 |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1357 Registered: Sep-04 | Well maybe not totally screwed. It depends on the amp. So its a Power 800s? I really need the exact model/specs. -Fishy |
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B;AkcesoI/ Unregistered guest | How would i get the specs? |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1358 Registered: Sep-04 | Ok, I think you may be in luck. If you own a Power 800a2 then you'll be able to run the thing in mixed mono(3 channel mode) and avoid any series wiring. Normally passive filters would need to be employed but since your subs are of such high impedance they shouldn't be necessary. Maybe Jonathan, Isaac, or Glass could verify. Check this pdf: http://www.rockfordfosgate.com/scripts/rightnow.cfg/php.exe/enduser/fattach_get. php?p_sid=xP1UPvGh&p_tbl=9&p_id=311&p_created=1083353145 Scroll down until you see the three channel mode operation diagram for the 360, 500 and 800 2 channel amps. Wire the two 8 ohm w0's in stereo as is shown with w0-12 bridged. With this setup each w0-8 will be getting 100 watts rms and the w0-12 will be getting 267 watts. It'd be a good idea to make sure the 12 ohm sub is playing in the center of the enclosure. You could also get the same amount of power to these subs by runing the 8 ohm drivers in series, running this combo in parallel with the 12 ohm sub, and then bridging the amp into what would amount to a 6.86 ohm load. Unfortuantely you'd be experiencing phase problems between all 3 drivers that way. Running mixed mono should avoid this shortcoming. There still are a few problems. 1) Since the 12 ohm sub will be experiencing far greater excursion, maximum cone velocity will be much higher than that of the 8 ohm subs. I'm not exactly sure of the the results, but its not good for sound quality. Lets just hope the enclosure you're using is sealed and not ported. 2) Since the 12w-0 will be receiving nearly 3 times the power as each of the other two subs its going to be really easy to blow that sucker if you set the gains improperly and/or go crazy with the h/u volume or bass boost. You're going to have to be very careful. Your best, safest, although most expensive option, if you want to keep that enclosure, would be to get hold of three 12w3-d6's either the original or v2 models. You'd run the voice coils in series creating three 12 ohm drivers and then run the subs in parallel for a 4 ohm mono load. These guys would be able to handle 267 watts much better than those poor old w0's. Sorry thats about the best we can make out of a bad situation. Even if you had three 12w0-12's 267 watts is a helluva lot of power for those tykes and unless you went very conservative with the gains and refrained from applying any bass boost you'd run a good chance of blowing them. I'll see if I can get some of the smarties from CAC to come over and take a look at your situation and see if they can offer any better advice. -Fishy |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1359 Registered: Sep-04 | Oh yeah. Disregard what it says about running the amp's crossovers at "Full Range". That would only apply if you were running a typical mixed mono setup with passive filters where the stereo channels would be powering your mids and highs and the bridged channel would be powering your sub. Since all 3 drivers are subwoofers simply use the lowpass filter as you would normally. If your h/u has a built in lowpass you could run the amp full range and use the deck's xover instead, but that shouldn't be necessary. Sorry about all this. I know it must be confusing, but to be honest you have a pretty dorked setup here. :P Oh one other thing your going to need to run rca's to all four inputs on the amp. If you've got subwoofer preouts on your h/u it'd be best to run a single set of rca's back to the amp and then a pair of y-adapters to cover all four of the amp's inputs. You'd need two 1 female/2 male adapters like these: http://www.knukonceptz.com/productDetail.cfm?prodID=KAR-1F2M This can't be making too much sense, so don't be afraid to ask questions.  -Fishy |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1360 Registered: Sep-04 | Ok I though of another scenario which might be much simpler but would produce even less power, lol. Run one stereo channel to the 12 ohm sub for 67 watts(I know, weak) and run the two 8 ohm drivers in parallel for a 4 ohm load to the other channel for 100 watts to each of these subs. You'd get a very anemic output of merely 267 watts, but you avoid series wiring and wouldn't have to worry so much about overdriving that 12w0-12. It probably ain't goona hit like it did off your buddy's 4 channel Kicker, but it'd be much safer. Whew. This thread is making my brain hurt. -Fishy |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1368 Registered: Sep-04 | Ok, nix that last idea. I've just been informed by Jonathan that running an unbalanced load like that(67 watts one channel and 200 on the other) will eventually kill the amp. You could balance it out a bit more by running one side with the 12 ohm sub in parallel with one of the 8 ohms, but it still wouldn't be good. Run it mixed mono, or if that scares you and you're low on cash pick up a couple more 12w0-12's and be very conservative with the gains. I still think waiting awhile and saving up your money for a pair of really good dual 4 ohm subs(12w6v2's for example) would be a wiser choice. They would probably crank pretty good(and sound great) off that amp and match up powerwise just about perfect. -Fishy |
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Gold Member Username: FishyTamarac Ft.Laud, FL USA Post Number: 1369 Registered: Sep-04 | One other mistake I made that Jonathan pointed out: That amp doesn't have 4 sets of inputs, lol. You don't need any y-adapters, oops. -Fishy |
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