Why More Resistance?

[sungwei 10+ year member]

I've heard that it's better to have more ohms pushed by more power for better SQ. How does this work? I've oftened wondered why speakers (mainly subs) have the option of being wired in 1, 2, 4, and 8 ohm loads. I always thought that the less resistance the better cause you get more power. So when does having more resistance play a roll?

Is it better to have more ohms pushed by more power or less ohms pushed by less power? Don't know if I'm making sense, but hopefully I can get some direction here.

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[paikiah 5,000+ posts]

yes, i have heard about this theory as well, but I think it was said that difference in ohm itself is indistinguishable to the human ear. Regardless, home audio stuff is still 6 ~8 ohms.

 

[sungwei 10+ year member]

So perhaps then this is more of a capacity/safety issue more than anything. I mean if you can't hear a difference between more and less resistance than why should you run a sub/speaker with more ohms only to need more watts to push it?

 

[urwhatueati8god 10+ year member]

As the amount of resistance decreases, the amp is forced to work less hard to produce the given amount of power. As a result, higher ohms means lower total harmonic distortion.

 

[maylar 10+ year member]

There is no difference in SQ just due to speaker impedance. 8 ohms has been the standard for home speakers for many years. I don't know the history of why that number was chosen, but it's somewhat arbitrary.

Ohms, volts and watts are all related mathematically. You need more voltage to get power with higher ohms impedance. In home systems you start with 120 volts AC, and tube amps use 300-400 volts DC to operate so it made sense to use high impedance speakers.

But in a car we start with only 12 volts (battery). To get more power without raising the voltage, lower ohms speakers are used (4 ohms is standard in car systems). Plus solid state amps work better at high currents and low voltage, so really high power stuff like subs sometimes go to 2 ohms or even lower.

The multiple voice coil options is just a way to make subs adaptable to the capabilities of different amps. It's a convenience thing.

 

[paikiah 5,000+ posts]

errr..... ok... that's too much info for me. lol~

 

[scottrc5391 10+ year member]

There are some advantages to different ohm loads however as I've observed. An amp is most efficient at higher impedences like 4 ohms as opposed to 1 ohm. Therefore to get the same power at 1 ohm as you did at 4 ohm, the current draw is a lot more. It has something to do with output transistors or something and rail voltage. One time I ran an amp in 1 ohm when I didn't need to and it bounced the voltage needle all over the place because of the huge current draw. I then wired it for 4 ohm and the needle is rock solid because of the huge increase in efficiency and the lower current draw for the same amount of wattage ouput. This is kinda weird since we think lower ohms means more efficiency in terms of Ohm's Law, but amps are different. Obviously you can get MORE power out of an amp running at 1 ohm than at 4 ohm but it won't be as efficient. As far as SQ, I've even heard that the number of voice coils can affect it, so who knows.

 

[helotaxi 5,000+ posts]

First, you weren't getting the same power at 1 and 4 ohms. You saw a huge increase in current draw because the amp was trying to flow much more current on the output side of things because of the 1 ohm load. The amp "wanted" to produce 4 times more power into the 1 ohm load. More power means more current because the input voltage (12V) is fixed.

That being said, there is a difference in efficiency between to amps of the same topology (Class A, A/B, etc...) making the same power at different loads. Take the HCCA series Orions. Set the gains on a 225HCCA to bridge to exactly 400W @ 1 ohm. Set a 2100HCCA to make exactly 400W @ 4 ohms. The 2100 should draw less current than the 225 and the 225 will run hotter (fan on the 2100 notwithstanding). At 1 ohm the output voltage is 20 and the amperage is 20 for 400W. At 4 ohm the voltage is 40 and the amperage is 10 for 400W. As you flow more current through a resistance, the amount of heat created increases exponentially. Since the output devices of the 225 are flowing twice as much current, they will give off 4 times as much heat as the 2100 assuming that the output devices of each amp have the same "on resistance". Since they are putting out the same amount of power, the amp that is running hotter is not as efficient and must be drawing more current.

 

[scottrc5391 10+ year member]

Thanks for clearing that up. I know the amp can't put out the same amount of power at 4 ohm as it can in 1 ohm, but I was saying I had the gains set so they put out about the same amount to the sub.

 

[paikiah 5,000+ posts]

Your ears cannot determine how many watts an amp is pushing. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I'm sure many people have already tried testing it left and right with it.

 

[n2audio 5,000+ posts]

Higher speaker resistance increases the DF of the system which some people believe is directly related to SQ. Those of us that have a clue know better //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[sungwei 10+ year member]

So when all is said and done it is ok and probably makes more sense for me to run 1 ohm on my sub so long as my amp can handle it right? I mean in that case I will have more power going to the sub so I can play louder. Correct?

 

[scottrc5391 10+ year member]

If you have to run at 1 ohm (and the amp's stable at 1 ohm) to get all the power you need for your sub(s) then you should run it at 1 ohm. I was just saying that if you get plenty of power at 4 ohm, then it's best to run it at 4 ohm because of increased efficiency, decreased current draw, and less heat as helotaxi said. If you absolutely want all the power possible then by all means run at 1 ohm, but run at 2 or 4 ohms if you get sufficient power that way.

 

[sungwei 10+ year member]

Well everything seems stable. Ever since I ran the inputs as balanced that amp has been just slightly hot. You can leave your hand on it no problem. So I guess that means this amp IS in fact 1 ohm stable. Sweet! I'm thoroughly impressed with the 403a.

 

[adam71 5,000+ posts]

If you have to run at 1 ohm (and the amp's stable at 1 ohm) to get all the power you need for your sub(s) then you should run it at 1 ohm. I was just saying that if you get plenty of power at 4 ohm, then it's best to run it at 4 ohm because of increased efficiency, decreased current draw, and less heat as helotaxi said. If you absolutely want all the power possible then by all means run at 1 ohm, but run at 2 or 4 ohms if you get sufficient power that way.

Don't forget to mention that as your ohm load (resistance) decreases your distortion increases.

Adam //content.invisioncic.com/y282845/emoticons/wave.gif.002382ce7d7c19757ab945cc69819de1.gif