bridging and ohms - Honda Prelude Forum

nuro · 07-30-2007, 12:38 AM

I'm confused about basic electronics. If I have 2x 4 ohm outputs and bridge them, it becomes one two ohm signal? How is this compatible with a 4 ohm sub with dual voice coils?

Rodmunch · 07-30-2007, 12:56 AM

Well if you have a 2 channel amp and a dual voice coil sub, you should be able to just connect one channel from the amp to one input on the sub, then connect the remaining channel to the other input on the sub. Probably the easiest thing to do.

ExodusFX · 07-30-2007, 12:57 AM

The resistor (subwoofer) determines the ohm load that the amplifier sees. A dual 4 ohm subwoofer can be wired up as 8 ohm (series), or 2 ohm (parallel) on the subwoofer.

For your 2ch amplifier, wire the sub up in series & then bridge at the amp, then you'll be fine. That's all I'll tell you, without getting into more specifics and confusing you.

nuro · 07-30-2007, 03:58 AM

ok thanks...

one day i should open my electronics textbook from college that i never studied. :/

nuro · 07-30-2007, 04:39 AM

ok so.... if i wanted to do a 2 speaker + sub system, can i bridge two of the outputs on a 4chan amp?

if the amp is running at 4 ohms, that means when i bridge two of the channels i get a 2 ohm output. so should i choose a sub with 2 ohm dual voice coils or 4 ohm dual voice coils and what would the difference be if i can use both?

this stuff hurts my head.

ExodusFX · 07-30-2007, 12:34 PM

Quote:

Originally Posted by nuro

ok so.... if i wanted to do a 2 speaker + sub system, can i bridge two of the outputs on a 4chan amp?

if the amp is running at 4 ohms, that means when i bridge two of the channels i get a 2 ohm output. so should i choose a sub with 2 ohm dual voice coils or 4 ohm dual voice coils and what would the difference be if i can use both?

this stuff hurts my head.

Yes, you can bridge 2 of the channels on a 4ch, to use for a subwoofer. Like I said before, the amplifier doesn't create the ohm load. You won't be making a 2 ohm output with the amp. The subwoofer determines the ohm load. Your amplifier has output specifications for 4ohm & 2ohm loads, on each channel. (check your spec sheet, or manufacturer's web site) Bridging on the amp will give you more power output, but you have to keep in mind that the two combined channels will still split the ohm load they are connected to. So a 2 ohm load, wired to 2 bridged channels on an amplifier... each channel will actually be seeing a 1 ohm load. Most amps aren't 1 ohm stable on their channels, and it'll overheat. A dual 2 ohm sub wired in series (at the subwoofer) will give a total 4 ohm load. As stated before, a dual 4 ohm subwoofer wired in series (at the subwoofer) will give a total 8 ohm load. After being split (by the bridged channels on the amplifier) each channel will recieve a 2 ohm load (for the dual 2 ohm subwoofer) or a 4 ohm load (for the dual 4 ohm subwoofer). Those are both acceptable, and the 2 ohm load will allow the amplifier to supply more power, than the 4 ohm load. Now that you know all of that, you have to check the power requirements of the subwoofers that you have/want, and match that to the power output specifications of the amplifier you have/want, for the given ohm load that you plan. Remember, the spec you're looking for is "xxx watts RMS x2 @ xx ohm" (for a 4 channel amplifier, that you're going to bridge two channels to a subwoofer)

nuro · 07-31-2007, 05:02 AM

ok... i think whats throwing me off is the terminology. An 4chan amp spec reads, for ex, 100x4 @4 ohm 200x2 @ 2 ohm

now if i go with a diagram like this (note the diagram is for a mono amp)

so the amp is seeing a 2 ohm load. But if i am bridging two channels to acheive this, then each channel is seeing a 1 ohm load... but do i care about what each channel is seeing or what the whole system is seeing? agh....

to put it specifically all i want is too see the power output declared on the little sticker that says "200x2 RMS @ 2 ohm". what resistance would i need to see on a SVC sub and what resistance would i need to see on each voice coil of a DVC sub

even more simply put, can i substitute the 2 ohm stable mono amp in the diagram with a 2 ohm stable stereo amp, bridged ?

marcucci · 07-31-2007, 11:06 AM

Don't worry about what individual channels are seeing when bridged; the amp will be rated for X ohms stereo operation and Y ohms mono operation based on what the mfr. deems the amp can handle.

Note I say what they "deem" as these things are never as easy as they seem. The actual resistance of the coil is not going to be 4 or 2 (it will likely be less) and the resistance will vary as a function of the frequency being reproduced, where the coil is in it's movement, and there are also series inductances and parallel capacitances that come into play. Basically, go off the stated spec and you should be OK.

So- if your amp is rated at xxx watts x 1 channel at 2 ohms, it's OK to parallel two 4 ohm voice coils. The mfr says it is OK, make it so.

Keep in mind that you should also look at the ratings when determining whether to run a stereo amp as stereo into two voice coils on one sub vs. bridging the amp and putting the coils in parallel. I say that because not all amps will provide 2x the power when bridged mono, some will give more and some will give less. Also, not all behave as well when bridged mono- some will generate more heat. It all depends on the design.

The best place to start may be to tell us the amp make/model or share the specs. IIRC you have an amp that is local/Swiss made?

nuro · 07-31-2007, 03:39 PM

its all US stuff you're familiar with

I'm looking at the alpine mrf-450
http://www.alpine-usa.com/US-en/prod...model=MRP-F450

which will run a pair of component speakers ( infinity reference 6020cs)
http://www.infinitysystems.com/car/p...=US&Region=USA

and i want to bridge the other two channels to run one 8" sub at the 200 W RMS rating (but it says @ 4 ohm?), most likely a JL Audio 8w3v3
http://mobile.jlaudio.com/products_s...p?series_id=27

of which I can't decide if i need the 8w3v3-4 or the 8w3v3-8

if neither "match", rockford fosgate has a similar sub running dual 2 ohm voice coils

ExodusFX · 07-31-2007, 08:50 PM

Maybe I got into the specifics a little too early for you. But the ohm load at the individual channels is the reason they don't list a power output for XXX x2 @ 2ohm. A 2 ohm load on two bridged channels will be split and each channel would see 1 ohm, and then fry. Most consumer level amplifiers aren't 1 ohm stable on their individual channels. (excluding mono amplifiers)

Anyways, I'll keep it simple from here on out for you guys. LOL.

The amp that you have is good. I sell/install it all the time. Bridge two channels at the amp and hook it up to the 8w3v3-4. It's a single voice coil (SVC) subwoofer with a 4 ohm rating. That will net you the 200W rms output that you're looking for.

As for what manufacturer's "deem." It used to be the case where manufacturer's ratings were sometimes misleading and just plain false, to sell more product. With the new industry standard CEA-2006 rating system (which is voluntary for manufacturers), you can pretty much take the rated specs as true. (only if they are CEA-2006 rated/labeled)

Info on the CEA-2006 rating, for the curious and bored.

nuro · 07-31-2007, 09:24 PM

from my experience with JL subwoofers, they can take a hell of a beating before anything happens to them, which is one of the reason i'm re-buying the brand.

ExodusFX · 07-31-2007, 09:41 PM

Yup, JL makes some great subs.