Now I know a bit about subs, amps, HU's, etc... but one thing I was thinking about today was about the OHMs of the subs and what an amplifier can handle.
If an amplifier that see's 4 OHM at the subs puts out 200 Watts, and it puts out 400 watts at 2 OHM. Wouldn't it be better to use the full 400 watts at 2 OHM? So why do they even rate the 4 OHM? I however have read somewhere that the higher the OHM value, the higher the quality of the signal to the subs. Other than that isn't it stupid to hook up an amp that is capable of 2 OHM to see 4 OHM? I mean, you're only getting half the wattage.
because some subs are only capable of 4ohm loads (either with dual 8ohm coils or a single 4ohm coil). The higher the ohms, the more the resistance, meaning at times, lesser quality signal.
So the my original understanding of running the amp at it's lowest OHM is best? 2 OHM it is then. Thanx
What you're saying is basically true. The OHMs run in a given configuration depend on the connected speakers and how they're wired, and it's usually desirable to provide an amplifier with the lowest OHM load it can run stably. They provide different OHM rating for the amp for a couple of reasons:
1) Not everybody has speakers that can be configured to the optimum OHM load for their amp. This would be their fault, really -- since they could probably have chosen better.
2) Low OHM loads might result in the highest output from an amplifier, but sometimes driving it harder can cause overheating or sound quality issues. This would be more the manufacturer's fault, if they suggested that configuration should work. Some people even intentionally ignore manufacturer OHM limitations, which usually ends badly.
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Some people even intentionally ignore manufacturer OHM limitations, which usually ends badly.
Even unintentionally, it can end badly (ie - blowed up amp)
the higher the ohm load the higher quality of sound thats why home stereos run 8-16 ohms. As far as subs good clarity is not real important i run my subs at 1 ohm my old comp car was .5 ohms
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because some subs are only capable of 4ohm loads (either with dual 8ohm coils or a single 4ohm coil). The higher the ohms, the more the resistance, meaning at times, lesser quality signal.
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the higher the ohm load the higher quality of sound thats why home stereos run 8-16 ohms. As far as subs good clarity is not real important i run my subs at 1 ohm my old comp car was .5 ohms
You're both wrong. Impedance has nothing to do with sound quality. Impedance is decided by how much current and voltage is available in the amplifier supply rails. 4 and even 2 ohm speakers are popular because it's easy for cheap units to get decent power through these speakers without using a DC-DC converter. The reason home audio stuff is higher impedance is because higher voltages are available. Since all home audio receivers have transformers, the designers of this gear have the luxury of choosing the rail voltages where for transformerless car stuff, it's always +/-12v. Aftermarket car speakers are 4ohm because they're designed to work well with stock head units. Aftermarket amps are designed to push 4ohm (or less) speakers because they expect to power speakers which are compatible with cheap head units. Quality amps which use PWM power supplies can have any kind of rail voltage and can be designed around speakers with nearly any impedance, but it's not smart to design an amp around speakers nobody makes, so the 4 ohm standard isn't going anywhere soon.
High impedance speakers:
+Losses through wires are lower
+Better electrical damping factor for given amp (tighter bass)
-Can extract less power from the amp for a given rail voltage
Low impedance speakers:
+Can extract more power from the amp for a given rail voltage
-Heavier cables needed
-Poorer electrical damping factor for a given amp
Using lower impedances eventually causes diminishing returns. If your amp provides 2x the power at 2ohms than it does at 4, it most likely has a low voltage high current supply and is limited by voltage. If this is your amp, by all means go with a 2 ohm load. Some amps however might only produce 20% more power at 2 ohms than at 4. This is a sign of limited current drive and there's a good chance the amp will be working a lot harder and hotter to provide this extra bit of power at degraded sound quality. If this is your amp, you're better off going with 4 ohms, lower distortion and saving your amp a lot of grief.
2002 Cavalier 2200 5spd
Speaker impedance does have an effect on sound quality. An amplifier has it's own internal impedance and the ratio or it's impedance to the impedance of the speakers determines the damping factor (how well an amplifier applies the brakes to speaker motion). The motion of the speakers also generates a voltage just like a generator. The current generated by that voltage has to be absorbed by the amplifier. A lower damping factor means it is less able to handle the "regenerative" portion of the power.
Solid Snake wrote:Impedance is decided by how much current and voltage is available in the amplifier supply rails.
you are wrong. horribly wrong.
impedance is not decided, but determined. big difference. and, it's determined by the winding in the coils of the former in the speaker and the output transformer in the amplifier. it has nothing to do with the voltage rails in the amplifier.
for optimal signal transfer, the impedance on the output transformer has to match the impedance of the speaker. if this is off, you get what's called VSWR, or Voltage Standing Wave Ratio. the energy released by the amp will be reflected back to it due to the mismatch, causing the P/N junctions in the transistors/FETS... whatever is used... to saturate. then all sorts of things can happen, like thermal runaway, overheating, shutoff... nasty stuff.
now, if you want to know how the 4 ohms/2 ohms thing works, let's look at Ohm's law: E/I*R, where E is voltage, I is current, R is resistance. for ease of explanation, we'll use easy values.
we'll consider a normal 12 volt system, running at 4 ohms, and we're looking for current, in amps.
12/I*4. solving for I, we get 3 amps.
now, for a 2 ohm setup:
12/I*2. solving for I, we get 6 amps.
now, let's look for power, using P(watts)=I * E
for 3 amps:
P = 3 * 12
P = 36 watts
for 6 amps:
P = 6 * 12
P = 72
so you can see, by cutting your output load (from 4 to 2), you increase the power output.
Desert Tuners
“When you come across a big kettle of crazy, it’s best not to stir it.”
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you are wrong. horribly wrong.
impedance is not decided, but determined. big difference. and, it's determined by the winding in the coils of the former in the speaker and the output transformer in the amplifier. it has nothing to do with the voltage rails in the amplifier.
You misunderstood me. I agree that speaker impedance is determined by the coil. What I was trying to say is that the OPTIMAL speaker impedance is determined by the amplifier's power supply and the type of load it would prefer to drive in order to deliver maximum power. There's nothing magical about 4 ohms, it's more a de facto standard. If speaker impedance is too high, what happens is that the amplifier runs out of head room without being able to deliver its full power. If the impedance is too low, the amplifier's output devices and power supply are going to be highly stressed and unable to deliver maximum power.
That being said, if we wanted the highest damping factor, we'd use the highest possible speaker impedance with an amplifier with low output impedance and high current drive, this wouldn't give the best power though. It is possible to have a high voltage amp powering a 16ohm speaker and a high current amp powering a 2ohm speaker, both having equal electrical damping. It's a matter of what kind of load the amp's power supply would like to see attached to it. Each amp has an optimal speaker impedance that allows it to dump the maximum amount of power into its load. It's never higher/lower = better.
2002 Cavalier 2200 5spd
.... Follow Mfg suggested values.
End of story.
(Thats the condensed version of this)
Solid Snake wrote:Quote:
because some subs are only capable of 4ohm loads (either with dual 8ohm coils or a single 4ohm coil). The higher the ohms, the more the resistance, meaning at times, lesser quality signal.
You're both wrong.
Sorry... first half is right. thanks for playing
as for the reason I used the phrase "at times"...
one sub/amp combo at 4 ohms may have a better SQL than the same sub @ 2 ohms on a different amp
FReQ Z wrote:
you are wrong. horribly wrong.
<snippy>
I'd listen to teh FReQ. He knows his shizz when it comes to electronics
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one sub/amp combo at 4 ohms may have a better SQL than the same sub @ 2 ohms on a different amp
And it may be worse, because that "different amp" is a total wildcard. A good way to quantify this is speaker impedance / amp impedance. eg: 4/0.01 = 2/0.005 = 400.
2002 Cavalier 2200 5spd
Kardain wrote:I'd listen to teh FReQ. He knows his shizz when it comes to electronics
thanks Rob.
still... for optimum efficiency and for both the amp, the amp's power supply, signal transfer between the amp and the sub, the sub itself and true signal reproduction, you need to match impedances. there's no other way around it. if the amp manufacturer says it's 1 ohm stable, run that piece at 1 ohm. if it's 2 ohm stable, don't run it at 1 ohm. mismatching impedances can and will interfere with the electrical signals going from the amp to the speaker.
yes, I'm fully aware that amp and speaker manufacturers de-rate their products. it's normal to do this. every electronics manufacturer does this. I won't even go into what I work with. but... amp and speaker manufacturers don't warranty their true tolerances.
btw, a little more of Ohm's law...
say you have a 2 channel amp, and each channel is 4 ohm stable. you want to run one sub, so you decide to bridge those channels. effectively, you're putting those channels in parallel. what's your new impedance? here's the formula:
1/Rx = 1/R1 + 1/R2
given:
Rx is the result we're looking for
R1 is channel one impedance
R2 is channel two impedance
so, we have 1/Rx = 1/4 + 1/4
1/Rx = 1/2
Rx = 2 ohms.
next week, we'll get into capacitive and inductive reactance and how it's affected by high frequency.
not...
Desert Tuners
“When you come across a big kettle of crazy, it’s best not to stir it.”
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say you have a 2 channel amp, and each channel is 4 ohm stable. you want to run one sub, so you decide to bridge those channels. effectively, you're putting those channels in parallel. what's your new impedance? here's the formula:
1/Rx = 1/R1 + 1/R2
I don't know of any amp that bridges in parallel. It's more of a series connection because voltage doubles and current drive stays the same. It's why a lot of amps can do 2 ohms unbridged and 4 ohms bridged. In unbridged mode, one speaker terminal gets the output stage and the other gets ground. In bridged mode, the speaker is not connected to ground at all. One side is connected to the L output stage and the other to the R output stage (which provides an equal and opposite voltage to the L channel).
When impedances stay the same, going from unbridged to bridged mode results in a 4x POTENTIAL increase in power, because we're doubling the rail voltage a ( W=V^2/R). This is why many amps prefer to drive double the impedance in bridged mode than in unbridged, so power doubles without overloading the amp.
When you bridge an amp, each channel "sees" half the actual impedance of the speaker because the other terminal isn't at ground, it's fighting the output stage!
Unbridged 4ohm sub:
4
OUTPUT--------VWVWV-------GND
Actual bridged connection:
4
OUTPUT--------VWVWVW-------~OUTPUT
What each output stage "sees"
2 2
OUTPUT---------VWVW-----GND-----VWVW--------~OUTPUT
If you were to take a center tap off the voice coil of the sub in bridged mode, it would effectively be ground. From that point to each of the speaker terminals is only half of the nominal impedance of the sub. That's why amplifiers can only do about half the impedance in bridged mode than unbridged.
2002 Cavalier 2200 5spd
I see what you're saying.... kinda.
I'd have to see schematics. got any for a car stereo amp? I can wrap my head around that a lot better. I'm still unsure of why you're so focused on the rail voltage. a amp stage is only going to see Vsource... not Vsource * 2. current draw is something different, depending on the input amplitude and output loading effect.
Desert Tuners
“When you come across a big kettle of crazy, it’s best not to stir it.”
No, I don't have any schematics right now.
It's true that bridging an amp doesn't increase the source voltage, what it does is half the load impedance that the output stage sees. In unbridged mode, the output stage sees a 4ohm sub as a 4ohm load. That's because the other terminal is attached to ground. In bridged mode, that other terminal, is on another output stage, an inverted one. Because of that, it's basically driving half the voice coil.
If you've got a 4 ohm DVC sub and a stereo bridgeable amp, you've got:
1. Unbridged, one 4ohm coil per channel. Let's call this the reference 1x load.
2. Bridged, voice coils in series for an 8 ohm load. Provides 1x load.
3. Bridged, voice coils in parallel for a 2 ohm load. Provides 4x load.
4. Bridged, only one voice coil connected. Provides 2x load.
So when you bridge an amp, you're not putting the output stages in parallel, you're putting them in series. Output voltage doubles, output current stays the same ideally, but often decreases in the real world. In a perfect world, an amp could produce 4x the power on a sub in bridged mode than if it were connected on a single channel. Because they're in series, amps want to see twice the impedance in bridged mode that they can normally drive per channel.
What you can be sure of is that if a bridgeable amp can do 800W@4ohms bridged, it can do 400W@2ohms per channel. The sound quality in either of these arrangements would be exactly equal.
2002 Cavalier 2200 5spd
Two example amps:
Amp A:
200W RMS -> 4Ohms
400W RMS-> 2Ohms
Amp B:
350WRMS ->4Ohms
400WRMS ->2Ohms
Amp A is most likely voltage limited with a very good current drive. Running this amp at 4 ohms is like never shifting your car beyond 2nd gear. It won't really be working to it's full potential and you'll never see the speeds the car is capable of. Output into 2 ohms is double of that into 4 ohms. This is as close to perfect-world performance as you can get. You should definitely run this amp with a 2ohm load.
Amp B's specs are probably marketing driven. They do this so they can write 400W on the box. Output at 2ohms is barely better than that of 4. This amp is more current limited than voltage limited and you can expect THD (distortion) to be a lot higher pushing a 2 ohm load than a 4 ohm load. This means you will get a little more power at 2 ohms and the sound quality and damping factor will likely suffer, also the amp will run a lot hotter. Diminishing returns happen soon after the 4 ohm mark so this is load you should give the amp.
The claim "X ohm stable" means the designers of the amp feel this is the impedance the amp can drive without exploding, not necessarily the best sounding load to drive though. Amp A above is rated conservatively, it can probably do more than 400W into 1Ohm and put "600W" on the box, but either the company felt the risk of failure was too high or the quality at those levels was too poor, so they rated it at 2ohms.
Amp B is possibly overrated. At 2Ohms it doesn't have significantly more power and it's control over the sub is probably poor.
If we have the same model Infinity sub, one 8 ohm version and one 4 ohm version and we run them on Amp A, the 8 ohm model will be more easily controlled, but potential for power (not power handling) before the amp runs out of headroom will be lower. The 4 ohm sub will play louder on that amp, but it may ring a bit more. This is way more dependent on the type of box the sub is mounted in than the amp. If it's in a ported box, you'll probably never notice.
However, sound quality is determined by the amp and sub combination, so there's nothing inherently better sounding about subs with higher impedances, just like there's nothing inherently good sounding about amps with high voltage rails or high current drive. If the subs are properly matched to amplifiers, they can sound equally loud and good.
Speaker impedance is like the final drive ratio on a car. By itself, it does not determine the top speed or acceleration of a car. It's there to match the load (car) to the power source (engine). Two cars with different final drive ratios could have the same top speed and acceleration because of variables like engine redline, transmission ratios, tire size, etc. The only certainty is that the final drive ratio must be right for that car and that engine.
2002 Cavalier 2200 5spd
(((