Ohms, Watts, speakers & AMPs - confused

**kingtut** · 07-10-2005, 03:15 AM

I am getting lost real fast, I am trying to put together an audio system in the car that could be intergated with the carpc but I am stuck on the audio part, I don't want to just put together a system that I don't understand. I spent few hours searching but could not find the answer to life's simple question:
an AMP could provid X watt @ 1 ohm but Y watt @ 2 ohm and then, there is the 4 ohm AMP - I think. So, the question is, how to make sense of all the Watts and Ohms as far as AMPs & Speakers are concerned. and then, there is the "bridged" AMP? I am lost.

Any simple explanation will be appreciated.

Bonus question, which "device" should be chosen first if I don't have system, the speaker and then the AMP or the AMP then the speaker that goes with it.

I could not find any car audio tutorial that ties it all together, each article I read covered only one subject but did not put it all together.

Any link will be appreciated. Thanks.

**SickVette** · 07-10-2005, 09:15 AM

http://www.12volt.com/

http://www.bcae1.com/defhome.htm

http://www.the12volt.com/

http://www.rockfordfosgate.com/rftech/

There are a few web sites for you. You should be able to find all the answers you need on one or all of those sites.

When choosing products I like to choose the sub first. Reason being is the sub is going to occupy the most space in your car so you have to be certain it will fit. There is no point in buying a 1000 watt amp when you only have room for a single 8". So determine how much airspace you are able to sacrifice then you can decide which sub(s) can fit in that area. Once you know the speaker specifics you can pick an amp that will work well with the drivers.

**Mad Ad** · 07-10-2005, 07:01 PM

An ohm is a measure of resistance, the less resistance there is across the outputs, the more power the amp can deliver (and more heat is made).

Car audio tends to use 4 ohm speakers on the whole, there are some (not all) amps that are called '2 ohm stable' and even less that are called '1 ohm stable'. Since you cant exactly turn up the inout power in a car (its stuck at 12 volts), you can double your output by running at 2 ohms instead of 4.

Most speakers are rated at 4 ohms to match a standard 4 ohm output from an amp. However to take advantage of the amps that can run at 2 ohm you can do tricks with the way you connect speakers to make two 4 ohm speakers show 2 ohms to the amp... also you can buy a 'dual voice coil' speaker that has 2 pairs of connections so you can do the same trick but using just one speaker.

Once you have your 2 ohm load you can then get twice the power out of the same amp as you would with a 4 ohm load. If you can afford an amp stable at 1 ohm its the same principle.

Bridged amps are a bit different, its a way of joining the power of two channels into one. EG take a normal 2 channel stereo amp, itll have a + and a - for each channel (so two + and two - ) so you can connect 2 speakers and get X power per speaker. But this amp is also bridgable so you can connect one channels + to one side of the speaker and the - from the other channel, that one speaker gets BOTH channels of power.

make sense?

**MrPerfectionest** · 07-10-2005, 08:07 PM

This is what happens when people that know a little bit and think they no a lot start giving advice. Yes, I am being an ***, but you will learn when to not try and sound smart on a message board.

Car audio tends to use 4 ohm speakers on the whole, there are some (not all) amps that are called '2 ohm stable' and even less that are called '1 ohm stable'. Since you cant exactly turn up the inout power in a car (its stuck at 12 volts), you can double your output by running at 2 ohms instead of 4.

The input voltage to the input is relatively pointless (within a given range). The internal DC/AC/DC converter is going to bump the voltage up to 35-60V regardless of the input. Less regulated amps will get to higher voltages (the classic X watts at 12.5V X+more @ 14.4V) than more tightly regulated amps.

Putting a 2 ohm speaker on the amp versus a 4 ohm will get you more power out of it, you can also just buy a bigger amp.

Bridging will take one output side and drive half of the wave and use the other side to drive the other half, essentially doubling the voltage the speaker sees (within limits).

As far as components, decide what kind of listener you are. If you are a bass head and have the room then get a 12 minimum and one that is ballsy (a 12w3 at least or an Infinity Perfect in addition to a lot of others). If you don't need tons of bass then a good 10" sub will work fine and help save you some space in your vehicle. If you are't a bass freak then for sure don't let a salesman try and sell you an amp that is too big. If you are on a budget then you can get a simple 4 channel amp and run your front speakers off 2 channels and bridge the back two to run the sub.

You can skin this cat a lot of different ways but if you are a noob at this then any simple 10" good quality sub and solid amp will probably be 500% better than your current factory set up.

**Mad Ad** · 07-11-2005, 11:12 AM

Originally Posted by MrPerfectionest

The input voltage to the input is relatively pointless (within a given range). The internal DC/AC/DC converter is going to bump the voltage up to 35-60V regardless of the input. Less regulated amps will get to higher voltages (the classic X watts at 12.5V X+more @ 14.4V) than more tightly regulated amps.

ffs stick your snide little insults where the sun dont shine matey, im only trying to help - anyway you can bump it to what you want internally but at the same time you cant get any more ampage out of the system than its got, unlike a house rig where 8 ohms is the standard and the greater power needed to drive them is much less in short supply (like having a mains supply, duhh!!) thats all I meant. Prick.

my only mistake was trying to explain a technical subject in as easier terms as possible for the thread starter, someone who probably couldnt give a shít about speaker waveforms and just wants to know how to interpret the confusing figures thrown around amplifier advertising... if you want to show off how much you think you know about internal amplifier design, this is not a thread to do it on- its just a bit of general information written in as plain terms as I could think of for an amp noob, something that I was one day and your criticism is unwarranted.

**evandude** · 07-11-2005, 11:39 AM

Originally Posted by Mad Ad

you can bump it to what you want internally but you cant get any more ampage out of it

I hate to be rude, but I'm going to have to back MrPerfectionest here; I don't think you know what you're talking about either.

an amplifier is an active load, not a big resistor, it is not limited to some fixed current from the 12v car electrical system... yes, using lower-impedance speakers will give you more power, but the more you bump up the voltage internally, the more power it can deliver to a given set of speakers (P=(V^2)/R), period. and the only thing stopping you from boosting the voltage to some huge level is of course heating in the amplifier, and the current handling capacity of the car electrical system.

if you could design a 100% efficient amplifier then you could supply infinite power to the speakers, it has nothing to do with the input voltage. the things stopping you are A) you can't build a 100% efficient amplifier, so you are limited by heat dissipation... and B) your car electrical system can't provide infinite output current (which isn't generally a problem in real life for smaller systems, such as just some speakers and a single small sub) so a higher-wattage amplifier is either more efficient, or has bigger heat sinks, or both, and CAN drive more power into a given speaker than a lower-wattage amplifier, with the same 12v input voltage.

yes, much of this is unnecessary for the noob explanation, however you did say:

Originally Posted by Mad Ad

Since you cant exactly turn up the inout power in a car (its stuck at 12 volts)

which is just blatantly wrong. P=VI, fix the voltage at 12v, and then power depends on current. more current = more power, plain and simple, and as discussed above, the higher the amplifier power rating, the more current it will draw, and the more power it will deliver.

the danger in telling that to a noob is of course that the more you push the impedance limits of the amp, the more strain you put on it... if you desire more power from your system with a 4-ohm sub, it would be wiser (although perhaps not cheaper) to replace the amp with one that pushes more power at that impedance, than to replace the sub with a 2-ohm one.

**Mad Ad** · 07-11-2005, 11:49 AM

ok ok ive edited it a bit - before I saw your post btw evandude btw... Im not making sense because im a bit ****ed at MrPrickfectionist... I did mention the heat issue and yes I know about the current issue, I just worded it like a buffoon to try and make it simple for the thread starter, thats all.... no problem with you evandude, at least you worded it without trying to be superior- we all have different levels of knowledge and like to pass on what we know, just a shame some cant do it without being condescending (MrP)

btw the original post was 4am in the morning and i was tired as hell, indeed p does equal v x a and not just V you are right about the mistake calling it power, lol.... criticism accepted... I was referring to power as in the overall draw, v and a together as an input- thats all. Sorry for being confusing but I didnt think id get jumped on by the chief of the goon squad for replying in general terms to a non technicnical persons question.

**evandude** · 07-11-2005, 11:57 AM

and as far as the original post is concerned, I would say first pick out the speakers/subwoofer that you want, based on reviews, advice from friends, whatever. then pick out a(n) amplifier(s) based on quality (again: reviews, etc), that is(are) rated to provide enough power, (but not more than the speakers can handle) for the speakers you have chosen.

other than that, you'll have to look to some audiophiles for more specific advice. Despite my technical arguments here, I am an electrical engineer, not a master of car audio equipment

**Mad Ad** · 07-11-2005, 12:23 PM

Originally Posted by evandude

the danger in telling that to a noob is of course that the more you push the impedance limits of the amp, the more strain you put on it... if you desire more power from your system with a 4-ohm sub, it would be wiser (although perhaps not cheaper) to replace the amp with one that pushes more power at that impedance, than to replace the sub with a 2-ohm one.

Thats why I specified the terms about amps that quote '2 ohm stable' etc... not all are and many that are not will simply not work at 2 ohm, the overload protection will trip it out.

**MrPerfectionest** · 07-11-2005, 12:31 PM

Look "mate", I don't sugar coat things. You learned an important lesson here and thats don't spout off about things you aren't an expert about and then get your pride hurt when others call you out on it. Call me a prick, dick, *******, whatever, I think it's cute.

my only mistake was trying to explain a technical subject in as easier terms as possible for the thread starter, someone who probably couldnt give a shít about speaker waveforms and just wants to know how to interpret the confusing figures thrown around amplifier advertising...

The only thing you have the concept of is 2 and 4 ohm resistance and how it has an affect on the power you can get out of amp (and it isn't necessarily double like you state) and you mention bridging.

if you want to show off how much you think you know about internal amplifier design, this is not a thread to do it on- its just a bit of general information written in as plain terms as I could think of for an amp noob, something that I was one day and your criticism is unwarranted.

Really, similar to how you tried to go into detail and failed?

You want it in as plain a terms for a noob as possible:
How about, the lower impedance (ohm) speaker you use the more power you can get out of an amplifier, provided the amplifier can drive the load. You can bridge (+ of the left channel, - of the right channel) to get more power out of an amplifier also (see specs for a given amplifier to know how much). Thats all that needed to be said about the amp.

Stay mad if you want to, or you can be the bigger man and not reply, its up to you. I think I made it clear though between the two of us who needs to be answering these types of questions.