Current draw between 1 and 4 ohms? SQ difference?

[kingsxman 10+ year member]

If I run a set of subs at 1 ohm or 4 ohms....which will be a harder drain on my battery/alternator? Noticable?

Also, is there a noticable difference in SQ between 4 ohm and 1 ohm. I've heard there is..but that seemed odd to me.

Click to read more...

 

[n2audio 5,000+ posts]

We would need to know what type of amps are being compared.

A class a/b doing - say - 1000w at 4 ohms will be quite a bit more electrically demanding than a class D doing 1000w at 1 ohm - especially at anything less than full output. Class D efficiency stays fairly constant (~75%) at all output levels whereas class a/b's peak at around 60% at full output and drop to ~30% at low-moderate volumes.

The THD debate is subjective. There are those that swear by their a/b amps for subs and others that say THD in the sub frequency range is a non issue and the price/efficiency of a class D far outweigh any SQ disadvantages vs. a/b.

 

[Raven 10+ year member]

Pretty much what ^ said.

The SQ thing at 4 / 1 ohm comes more from the subs themselves. Some lesser quality subs just work better wired in series.

 

[kingsxman 10+ year member]

Well, the quality of subs is JL Audio W6v2's. So hopefully the quality is there. The reason I'm asking the other question is that I have had a few recommendations on sub amps. One recommendation was for a Precision Power csx-2200 which would do 800w at 4 ohms and drive my subs. ITs a 2 channel amp which would be bridged...theory being that 4 ohms is less current than 1 ohm and better SQ. I'm debating on that or going with somehting like a Directed Audio 1100D, Orion 1200D, or something of that ilk. Thinking there is that class D mono amps should be more efficient. When the Lanzar optdrive I recently purchased (which is A/B I believe..) was working....at 1 ohm I definitely noticed my lights dimming, etc. I dont want to put strain on my electrical if possible...but would sacrifice if it was for better SQ.

For the record, the SQ on that optidrive sucked. N2, you and I have been discussing and it sounds like you think it is a bad amp. going back today.

 

[tRiGgEr 5,000+ posts]

As far as current draw goes, the Orion will be a good choice. They are efficient little buggers with plenty of power.

Regarding your SQ question. There will be no audible difference in either choice. The ohm load does not directly play a role in the accuracy of the driver. The signal, amp, sub, and box do that...

 

[Saint211 10+ year member]

So does the current draw change between the different loads? Im thinking that it doesn't but I'd like someone whos been doing audio longer to explain.

The reason I dont think it does is because, a 4 Ohm load has more resistance than a 1 Ohm load. We know that the 1 ohm load with less resistance is more efficient at using the power, which is why we see more power at the drivers. So in reality, they are both using the same amount of juice, but at 4 ohms more of it is lost supplying the power than at 1 ohm?

Am I right or wrong? The reason Im curious is Im thinking about an upgrade as far as my amp, and I want to make sure I'm prepared for ana extra stress on my electrical system. If they use the same current at different loads then it won't be nearly as bad as I was preparing for.

 

[n2audio 5,000+ posts]

So does the current draw change between the different loads? Im thinking that it doesn't but I'd like someone whos been doing audio longer to explain.
The reason I dont think it does is because, a 4 Ohm load has more resistance than a 1 Ohm load. We know that the 1 ohm load with less resistance is more efficient at using the power, which is why we see more power at the drivers. So in reality, they are both using the same amount of juice, but at 4 ohms more of it is lost supplying the power than at 1 ohm?

Am I right or wrong? The reason Im curious is Im thinking about an upgrade as far as my amp, and I want to make sure I'm prepared for ana extra stress on my electrical system. If they use the same current at different loads then it won't be nearly as bad as I was preparing for.

//content.invisioncic.com/y282845/emoticons/eyebrow.gif.fe2c18d8720fe8c7eaed347b21ea05a5.gif

Current draw is really not a function of impedance. It's a function of the amp's efficiency (class), and it's power output.

A class a/b amp that puts out 1000w at 8 ohms is going to draw more current than a class D that puts out 1000w at 1 ohm.

A class a/b amp that puts out 500w at 4 ohms will draw less current than a class D amp that puts out 1000w at 2 ohms.

 

[Saint211 10+ year member]

Yes, the class difference I realize. What I mean is will a 1000W class d amp at 1 ohm draw any more current than a 1000W class d amp at 4 ohms?

And I thought no because the amp was doing the same amount of work, but because of the loads, actually supplying different amounts of power.

Or does it do more, will it draw more current from your electrical system?

Thanks for the reply though.

 

[n2audio 5,000+ posts]

I don't know the answer to that - but I would expect them to be similar.

If there's a class D out there that does 1000w at 4 ohms it would probably cost you close to a grand b/c it most likely does at least 2000w at 2 ohms, or even ~4000w at 1.

 

[Saint211 10+ year member]

Assuming its the same amp... at the two different loads(it wouldnt be 1000rms at 4 obviously, just for reference...)?

 

[n2audio 5,000+ posts]

For ouput to stay constant at varying impedances there would have to be a voltage adjustment inside the amp -- IE JL slash and PG xenon. I don't think the slash's or xenons current draw changes much when the impedance changes. Maybe a few percent.

 

[HeatSeeker 10+ year member]

I don't know the answer to that - but I would expect them to be similar.
If there's a class D out there that does 1000w at 4 ohms it would probably cost you close to a grand b/c it most likely does at least 2000w at 2 ohms, or even ~4000w at 1.

Orion 2500D is rated 1000@ 4ohm I believe =P

 

[squeak9798 5,000+ posts]

Yes, the class difference I realize. What I mean is will a 1000W class d amp at 1 ohm draw any more current than a 1000W class d amp at 4 ohms?
And I thought no because the amp was doing the same amount of work, but because of the loads, actually supplying different amounts of power.

Or does it do more, will it draw more current from your electrical system?

Thanks for the reply though.

They would draw the same amount of power if their efficiency was the same. Though, generally you'll have less efficiency as impedance drops.

The impedance the amplifier is connected to isn't going to affect the current it consumes in any way....that is purely a function of input voltage, wattage output and efficiency.

 

[squeak9798 5,000+ posts]

For ouput to stay constant at varying impedances there would have to be a voltage adjustment inside the amp -- IE JL slash and PG xenon. I don't think the slash's or xenons current draw changes much when the impedance changes. Maybe a few percent.

According to the review from CS, the Xenon 100.4 had a 25% difference in current draw between 4ohm and 2ohm, and a 21% difference between 4ohm and 1ohm.

Efficiency varied greatly aswell (40% decrease from 4ohm to 1ohm), as did actual power output.

http://carsound.com/articles/publish/article_413.shtml

 

[Raven 10+ year member]

IIRC, it's just easier for voltage to travel through wire than current is. Since a lower impedance means a higher current and lower voltage, I guess we have one reason why this happens..