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  #1  
Old 02-19-2005
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rockford amp questions

ok let me start by saying i dont pretend to know much about car stereo stuff

my brother gave me the system out of his focus, so this is what im running in the F150 right now

pioneer deck DEH series
pioneer TS686 somethings on the doors, 3 ways
2 pioneer 12s, i dont know the model numbers, but they arent top notch
rockford P series 900 watt amp

ok so my friend wired the subs + to + - to - on each speaker, he said thats all you need since its already bridged, its printed over the terminals on the amp "bridged"

they sounded good, but did not as hard as when my brother had it, even at full gain and all the setting up.

my brother got home today and said he had them wired parallel since the subs were 4 ohm, so now the left - is hooked the - on each, and the right + to the + on each, which i assume is parallel

now it hits really hard and i like it BUT!! when i get it hitting nice and hard how i like it, it starts turning itself off for a few secs and then back on. it did this in my brothers car too. i assume its a safety setting or something,

someone explain this to me and give me some kind advice here
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  #2  
Old 02-19-2005
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i think the amp is a rockford P8002

http://www.rockfordfosgate.com/produ...h%20Amplifiers
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  #3  
Old 02-19-2005
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If you're bridging the amp, then you are probably overloading that amp. Notice how it says 800 W x 1 @ 4 Ohms Bridged RMS? (not 2 ohms)?

Two 4 ohm speakers in parallel should produce a 2 ohm load.

So try wiring it up so it's not bridged, but keep the wiring path to the speakers the same (just use all terminals on the amp). It'll be half the power, but only 3 dB quieter.
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Old 02-19-2005
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michael youll have to walk me through that wiring in baby steps. im a carbureted performance kinda guy
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  #5  
Old 02-19-2005
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This is an excellent site that will show you the difference in parallel and series:
http://www.bcae1.com/srsparll.htm

By Bridging the Amplifier, you are only using half the terminals for output, thereby forcing the output to go through two wires instead of 4. "Bridging" basically means "halfing" the output channels. You lose the number of channels, but gain wattage.

Typical 2 channel amplifier Has 4 terminals.
Speaker 1 + / Speaker 1 - / Speaker 2 + / Speaker 2 -

By bridging, you typically use the + from speaker 1 and the - from speaker 2, leaving the other two unused. Remember that this is only the wiring attached directly to the amplifier. It can daisy chain or split up however you want it to from there, but as far as the amp is concerned, it's bridged. And since your amplifier doesn't specify a 2 ohm rating when running in bridged mode, therefor it isn't stable running a 2 ohm load when bridged. It may work with the gain turned down real low, but realisticly, you should wire it up so that you use all terminals.

But that brings you back down to 2 channels @ 4 ohms. Which is about 1/4 the power, and probably was too weak as you reported it was earlier. Long term I would pick up some 2 ohm subs, or dual voice coil (@ 4 ohm) subs. That will allow you to run that amp at the power rating you want. (400 watts per sub for example). Either that or pick up a mono amp (1 channel only) that produces around 800 watts @ 2 ohms and you'll have 1 happy amp and 2 thumpin subs. The last option is to get 1 sub, rated @ 800watts RMS @ 4 ohms.
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Old 02-19-2005
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so, my best and cheapest option other than wiring what i have like i should, is to find some 2 ohm subs?
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Old 02-19-2005
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Well cheapest is to run them at 100 watts each, that just takes wire, but if that's too weak for you then yes, find 2 subs that run @ 2 ohms or dual voice coil subs where each voice coil is 4 ohms. But it might be cheaper to just buy a new amp (depends on brand etc). But I would recommend the subs before the amp, even if that amp wouldn't be my first pick for an 800 watt sub amp. Especially if you don't think they are "top notch"

Basically your target is 800 watts @ 4 ohms or 400 watts @ 2 ohms.

two 2 ohm subs wired in series = 4 ohms (800 watts)
two 4 ohm subs can be wired up as 2 channels @ 2 ohms or 1 channel @ 4 ohms. Either way both speakers would get 400 watts of power.

And in case you are wanting to know what Dual Voice Coil is, it's basically 2 sets of terminals on 1 speaker. That means that speaker is really two speakers in one, giving you much more flexibility (or headaches) in wiring. Just make sure you take note of the ohm rating of each coil, and remember DVC or Dual Voice means 2 speakers in one. So two DVC subs have 4 pairs of terminals to wire up.

You could go with 1 12" (or bigger even) but that would require a new box obviously. It would only be worth while if you got a killer sub, like 15 inches big with exact maching specs to your amp (~800 watts RMS @ 4 ohms) The watts don't have to be matching exactly, but the ohms do. For instance I push about 950 watts to a 12" sub rated for 700 or 800 watts (I forget off hand). It's a sealed enclosure so I have a little better power handling than ported enclosures.

Anyway, let me know if you need anything else...
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Old 02-20-2005
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thanks michael. im not sure what will be cheaper, the amp or the subs. im going to be building a full length center console / concealed sub box, so i could even go for just one sub.

if i get one sub, id want it to be a 4 ohm with close to my amps output at that resistance?

if i get 2, i should get 2 4ohm dual coil subs?

thanks
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  #9  
Old 02-20-2005
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ok heres what im looking at michael.

its a pioneer 12, i would get 2 of them, dual 4 ohms, 400w rms, 1000 peak

tell me if im on the right track
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  #10  
Old 02-20-2005
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Alpine

haha solves everything

the amp is just turning off due to an overload/heat protection thing....turn the bass down on u're head unit, maybe mess eith the gain on the amp....it'll stop doing it...
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  #11  
Old 02-20-2005
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wow this changes things, here the amp i actually have

http://www.rockfordfosgate.com/produ...h%20Amplifiers

so this says bridged its 4 ohm 300 watts. so then i suppose bridging it with 4s in parallel is giving me 2 ohms, so less of a load that its rated for. so it must be trying to put out 600 watts.

is there a way to wire my 4 ohm subs to this amp to get the max bridged power?

if i wire the subs in series and bridge it to get 8 ohms, shouldnt i get 150 out of the amp? i guess maybe thats still only 75 per sub in series.

ug

Last edited by SoundPer4mance; 02-20-2005 at 12:18 PM.
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  #12  
Old 02-20-2005
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Cool, Rockford Fosgate is adopting CEA certification. That's a good thing.

Quote:
is there a way to wire my 4 ohm subs to this amp to get the max bridged power?
Nope, sorry.

Quote:
if i wire the subs in series and bridge it to get 8 ohms, shouldnt i get 150 out of the amp? i guess maybe thats still only 75 per sub in series.
Yes, you're right.

If you wire up your current speakers to produce an 8 ohm resistance, then that amp would put out around 150 watts TOTAL, which is the exact same power you would get if you just hooked up each sub individually, using both channels. (The 75w x2 @4ohm rating)

Quote:
if i get one sub, id want it to be a 4 ohm with close to my amps output at that resistance?
Yep. If you found one killer sub, the ideal RMS power handling would be in the 200watt to 400 watt range, but I would find a quality sub rated ~ 300 watts because most quality products are underrated. So two underrated products @ 300 watts would probably be well balanced. Another good reason to stay in one brand, because these tolerances would likely be the same. This is not required in the least though, just look at my setup...

Quote:
if i get 2, i should get 2 4ohm dual coil subs?
Two subs would be optimal. But you are limiting yourself with the current amp. You should still be able to find something that'l work, just it won't be in the upper power ratings which usually come with the better performing components. That doesn't mean to say that you have to stick with cheap stuff at all, just that subs meant to handle 150 watts RMS won't be competition level (at least in SPL, but maybe in SQ)
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  #13  
Old 02-20-2005
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heres what i did michael

i took just ONE of the subs i have, and ran it bridged to the amp, so the sub and the amp are both at 4 ohms now. the amp should be putting out 300 watts. the sub is a pioneer, 400w nominal, 800 watt max. it sounds pretty good and should hold me off for a while now. i took the center seat out of the F150 up front and made some new brackets for the center console that flips up, so the box will go between the front seats and under the console. ill start building the box probably next week.

thanks for all your help!
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  #14  
Old 02-20-2005
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Sounds like you're all set. Lol, I sorry I didn't think of one sub, but since we know now that it could handle the power (and more) then you're good to go. If your box currently shares the airspace between both the subs, then you are hurting yourself because the other unpowered sub would act as an air dampener. But if it has it's own airspace then you should be fine.
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  #15  
Old 02-20-2005
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the temporary sub box im using now has a divider between the 2 spaces. so its ok for now. as soon as i get the time im going to be building that center console box i was talking about, all 3/4" mdf, filberglassed on the inside. any other tips on the box?

i do interior trim, so im good with wood, my buddy is doing the glassing. ill probably glue the edges with subfloor glue and nail the **** out of it
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  #16  
Old 02-20-2005
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Yeah, I just used a whole bunch of polyurethane glue, and sheet metal screws every 2 or 3 inches. Then ran another bead of the glue down the inside seams. I've never worked with fiberglass though, that would be neat to see. Gonna make it all circular and reflective on the inside?

The biggest thing to making a good box is thinking about the sound waves. There is a whole science about wavelengths and what not that is beyond me. What I do know is that you want the sound waves to reflect around the box as much as you can. A simple square where the subwoofer and the rear panel are parallel isn't optimal. That's more of a trial an error thing, and to some setups, it's just splitting hairs. But every little bit adds up, and is good for insurance or peace of mind.
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Old 02-21-2005
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yeah the fiberglass on the inside should give the box a lot more stability and rigidity, my friend swears by glassing the inside, so its worth a shot. the box will be a very strange shape, more elongated than square. so shall see what happens, ill get some pics
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