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Scuba
Dodge Dakota
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12/06/2003
21:40:20
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 Subject: I just installed a sub box under my seat
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I just installed a box w/2 10" subs under my backseat. Sadly the kicker CVR 10" subs wouldnt fit in so I had to put some old school hifonics in. Bad thing is it doesnt really sound too good. The box fits all the way under my backseat and is about 6" high. What subs would fit in there and sound good with the little air space? Also can these subs I currently have in there run at 8ohms. Can I run them at 2ohms even though I have only one voice coil? If not how can I run it at 4? And is there really a differece in 8g and 16g wire?
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CJ
Dodge Dakota
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12/06/2003
23:06:18
| RE: I just installed a sub box under my seat
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single voice coil 8 ohms each can be run in parallel to get 4 ohms but not 2....to connect them in parallel connect + on one sub to + on the other sub and also + on the amp...do the same with the - and that will be in parallel....as far as the wire size...the bigger the wire the more power you can push through it...for normal use I would use either 14 or 12...I use 12 for everything just because I have a 500 foot roll of it...but that's just me
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scuba
Dodge Dakota
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12/07/2003
00:01:48
| RE: I just installed a sub box under my seat
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how do i hook the 2 positives on the subs together and hook that to the amp? wouldnt that be like a 3 way wire how would i do that? just like hook the 2 together then hook the + of the amp to just 1 sub ?
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DSW
Dodge Dakota
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12/07/2003
03:57:31
| RE: I just installed a sub box under my seat
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Just did the same thing you did, put 2-10's under the back seat (I used seperate boxes). I used some RF 8 ohm 10's that were spec'ed for a .65 to 1 cu ft box (.75 optimal) and they sound great at .65 cu ft. Don't know which model they are, but they are about 4 years old.
As far as hooking up the 8 ohm subs in parallel to a "bridged" amp you have 2 choices, run both + wires from the subs to the amp+, your going to connect the 2 + sub wires to the amp. Same thing for the subs - wires, both sub - wires go to the amp -. Or, if both subs are in one box you can go + to +, and - to - on the subs and then run the common + and common - to the amp, this way you will only have one pair of wires going to the amp. Both configurations put the subs in parallel and they look to the amp like a 4 ohm load. Agree with CJ, go with 12ga wire for the subs. I lucked out since the pair of 12 ga wires barely fit into the terminal block of my RF amp.
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some guy
Dodge Dakota
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12/08/2003
23:29:37
| RE: I just installed a sub box under my seat
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Running two 8 ohm subs in parallel runs your amp in a 2 ohm state (mono). Yes, I know two 8 ohm resistors in parallel make a 4 ohm load, but your amp will see a 2 ohm load. The amp will work just as hard as two 4 ohm speakers in stereo.
DSW, sounds like you had XLC's.
Scuba, don't run 16 AWG wire to your subs.
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92Dakota
Dodge Dakota
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12/09/2003
00:37:30
| RE: I just installed a sub box under my seat
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"Running two 8 ohm subs in parallel runs your amp in a 2 ohm state (mono). Yes, I know two 8 ohm resistors in parallel make a 4 ohm load, but your amp will see a 2 ohm load. The amp will work just as hard as two 4 ohm speakers in stereo."
Heh. The BS continues.
A voice coil is a resistor, right? Its a coil of wire that is a certain length, gauge, and material that is wound to be a certain ohm load. Why would the amp see anything else than 4 ohms??
Two 8 ohms in parallel are 4 ohms. For resistors, subs, etc. Its not that difficult. I'm pretty slow and I get it :)
A 2 ohm mono load is a LOT harder on the amp than 4 ohm stereo. A 2 ohm mono load is equivalent to a 1 ohm stereo load.
12-14 gauge is fine. 16 is okay for a short run of wire off a 200-400 watt amp.
I'd get JL Audio W0's. They have a shallow mounting depth and sound good. Not sure how small of a box they go in.
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some guy
Dodge Dakota
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12/09/2003
12:26:18
| RE: I just installed a sub box under my seat
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"Two 8 ohms in parallel are 4 ohms. For resistors, subs, etc. Its not that difficult. I'm pretty slow and I get it :)"
Ah, kids. Let's try to make it simplier for your 3 yr old mind. Let's forget about having more than one speaker, because somehow you actually understand the two 8 ohms in parallel is 4 ohms:
*If you run a 4 ohm load to a MONO amp, the amp will run @ 4 ohms.
*If you run a 4 ohm load to a 2 CHANNEL AMP BRIDGED, the amp will run at 2 ohms.
Why do people always forget that bridging an amp doubles it's power?
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FMF
Dodge Dakota
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12/09/2003
12:35:23
| RE: I just installed a sub box under my seat
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"someguy" is right. when you run a single 4 ohm load to a 2 ch amp it drives tha amp at 2 ohm mono BUT if the amp is a mono amp then it will just run at 4 ohm.
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Barry Potter
Dodge Dakota
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12/09/2003
12:59:50
| RE: I just installed a sub box under my seat
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"Some guy" is dead on, except for one thing:
A 4 ohm load to a bridgeable 2 channel amp WILL run the amp at 2 ohms. THIS is the same as running that same amp in 1 ohm stereo not 4 ohm stereo.
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abnscout82
Dodge Dakota
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12/09/2003
18:58:29
| RE: I just installed a sub box under my seat
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They make a couple of vehicle specific sub boxes for the dakotas. I have a 03 club cab and order one from Q-logic, fits right under the bac seat and nobody knows it is there. The Q-logic houses a single 8", works nice. MTX also makes one with 2 10" subs, but I didnt like the idea, didnt seem like enough volume in the box for 2 10"ers.
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Scuba
Dodge Dakota
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12/09/2003
19:53:48
| RE: I just installed a sub box under my seat
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Where are the q-logics found?
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abnscout82
Dodge Dakota
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12/10/2003
10:05:04
| RE: I just installed a sub box under my seat
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Was pretty hard to find the Q-logic site for some reason, but I found it, bad thing was they did not have a picture. I went through my local audio shop for my box. Here is a site that gives a picture of the box in the truck: http://www.sounddomain.com/sku/QLCQLCDDX108B01. If you need to find a loca dealer, then here is Qlogics site that you can find one through: http://www.qlogic.ws/2003/products/qcustoms_detail.jsp?classID=58&productID=6510. Notice that the description says for up to 2002 models, but it works with the 03 as well, they didnt change anything.
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Adminvtt
Dodge Dakota
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12/10/2003
10:20:57
| RE: I just installed a sub box under my seat
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Simply go to Best buy they always keep a fat stock of them. Dude buy a speaker box building book and build your own its very simple and you get alot more pride out of making something for 20 dollars vice spending 38.95$ on prefab.
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92Dakota
Dodge Dakota
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12/10/2003
23:37:46
| RE: I just installed a sub box under my seat
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A 4 ohm load is a 4 ohm load!!!
If the sub hooked up is 4 ohms, the amp is driving a 4 ohm load.
It doesn't matter if it is bridged or not.
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Jim Z
GenI
12/10/2003
23:55:42
| RE: I just installed a sub box under my seat
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"A voice coil is a resistor, right?"
No, on its own it's an inductor. Moving through a magnetic field, it has an inductive component, a capacative component, and a resistive component. Electrically speaking, a speaker has a complex impedance.
"Why do people always forget that bridging an amp doubles it's power?"
It doesn't "double the amp's power." It doubles the voltage across the speaker's voice coil, since in bridge mode you're running the output differentially instead of single-ended. And keep in mind that not all amps can sustain that in bridge mode if the power supply is incapable of delivering sufficient power- and this is quite common.
"A 4 ohm load to a bridgeable 2 channel amp WILL run the amp at 2 ohms."
No, the nominal impedance is still 4 ohms. What happens in bridge-mode is two-fold. 1) the output voltage is referenced to its negative value instead of ground, and 2) the demand from the amp's power supply is similar to that of running two 2-ohm speakers in stereo.
THIS is the same as running that same amp in 1 ohm stereo not 4 ohm stereo."
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92Dakota
Dodge Dakota
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12/11/2003
02:28:58
| RE: I just installed a sub box under my seat
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Thanks JimZ
I stand corrected on the resistor part.
I don't know why I wrote that when I know that the coil's impedence varies...hence the impedence plots for drivers.
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DSW
Dodge Dakota
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12/11/2003
03:12:15
| RE: I just installed a sub box under my seat
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Dead on Jim Z, thanks for setting it straight.
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adminvtt
Dodge Dakota
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12/11/2003
07:39:30
|  RE: I just installed a sub box under my seat
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Nice JimZ, you can always tell who has electronics experience on these forums. One thing not to correct you, Bridged amps don't double power they reduce load resistance and thus increase current. But then again maybe its just a termanology thing and we are saying the same thing I'm just going by what Navy electronics school teaches, and MECP.
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Jim Z
GenI
12/11/2003
08:25:34
| RE: I just installed a sub box under my seat
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"Bridged amps don't double power they reduce load resistance and thus increase current."
we all a bit fuzzy here. Again, what bridging does is theoretically double the voltage across the voice coils. Ohm's law tells us that P=E^2/R, so doubling the voltage can theoretically *quadruple* the power into the speaker. Look at it like this: using that formula with a single 4-ohm woofer, and a bridgeable amplifier that's capable of a +/- 20 volt swing on the outputs. If you connect that woofer to one of the outputs, the peak voltage across the voice coil will be either +20 volts or -20 volts. So, Ohm's law says that P=(20^2)/4=100 watts. Now, let's bridge the amp. The speaker's now being driven differentially (the signal on one side is the inverse of the other side) so now the peak voltage across the voice coil is +40 volts or -40 volts. So, P=(40^2)/4=400 watts. This is all theoretical, as the efficiency of the amp's power supply goes down as the demand rises. If my example were a real-world amp, then you could expect about 330 watts bridged, not 400.
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GraphiteDak
GenIII
12/11/2003
23:12:00
| RE: I just installed a sub box under my seat
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Dude, it is still considered a 4 ohm load no matter how you hook it up.
Here's the difference.
When you run your amp bridged, it doubles the signal (the voltage in AC to the speaker) therefore at the same 4 ohm load you get double the power.
Now. Amps are rated as such like 4 ohm stable, 2 ohm stable etc as to their design and size of the output transistors and power supply. BTW the power supply steps up the voltage to usually somewhere around +/- 55 volts DC or so on monster amps (using a Pulse Width Mudulator to switch a transformer with MosFet transistors). Think of your power supply of having two 55 volt batteries connected in series. Therefore running in stereo mode the peak to peak sine wave voltage would be close to 110 Volts AC to each speaker. It would be less when calculated to RMS voltage. Ran into a 4 ohm load that is a sh*t load of power.
Now in stereo (2 channel mode) most amps have one of the speaker wires simply connected to a common terminal to the power supply. To be simple think of the power supply having two 12 Volt car batteries connected in series. The terminal in between connecting the one batteries + terminal to the other batteries - terminal will be the COMMON. If you read from the common terminal to the neg (-) term of one batt you would read -12 VDC. If you then went to the pos (+) terminal of the other batt you would read + 12 VDC. Now. If you connected one of the speakers terminals to the common terminal and switched the other from the neg of one batt to the pos of the other batt you would then get a 24 Volt swing. When you bridge the amp (you are using two channels of the amp) the terminal is not connected in between the two power supplies like that. You have one lead on one amp (say the left channel) and the other speaker lead on the other amp (say the right channel). While one amp is switching to the neg voltage the other amp (with the input signal out of phase) would do the opposite and be connecting that output to the positive voltage. So at one point in time with one amp connecting one lead to say the neg of one batt and the other amp does the opposite connecting the other lead to the poss of the other batt you get a 24 volt DC current to the speaker pulling it one direction, Then the amps switch polarities as the sine wave goes to the other direction. now the amp that was at neg goes to the pos of the batteries while the other amp was at pos it goes to the neg of the batteries causing the current to go the OTHER WAY in your speaker moving it the other direction. You then basically have a 48 volt signal going to that speaker peak to peak when looked at with an O-Scope. The output signal is twice as much when an amp is bridged. Twice the voltage to the same load will get twice the watts (power). Newer decks in your dash have bridged amps. There is actually two channel amps for each speaker output. That way there is close to a 24 Volt signal coming out of a deck that has only a 12 VDC input. That is how they are now getting 40 Watts from a deck vs. the old 20 watts we used to get.
I hope this makes some sense to people. The amp does not SWITCH modes by changing the load. But when it is bridged, you get twice the voltage to your load. That is why it can KILL an amp to bridge two 4 ohm loads to it in parallel. That would make a 2 ohm load and most amps will not be able to power that. The amps that put out more power just have a larger power supply, one that steps the 12 VDC input to a higher voltage and has a large enough or enough mosfets paralleled together to sustain the power and a large enough transistor output drivers to handle the load.
Also, at a higher voltage, your amps are lower. That is why you need something like a 6 gauge wire to power your amp from the 12 volt battery and only a 16 gauge wire (for example) to get that same power to the speaker from the amp. The amperage on the output to your speakers would be like 10 times less than the amperage it used on the 12 VDC input to the amp. To get 400 watts from a 12 VDC source you would get something over 30 amps or better. But the higher voltage coming out of the amp to the speaker has a lot less amperage (the same power) so the wire does not need to be that heavy. You can get away with some pretty light gauge wire on the output and not see much of a voltage drop to even hear the difference.
Sorry for the book here, but I was trying to make it easy to understand. I rebuild and repair my own amps from time to time plus know a tad about electronics.
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GraphiteDak
GenIII
12/11/2003
23:14:11
| RE: I just installed a sub box under my seat
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Hey JimZ. That response wasn't aimed at you. I just spent over 30 minutes writing it while being bugged by my kids and when I posted you beat me. So don't take offense ok.
This is funny sometimes tho.
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