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Author Topic: which ohm is best ohm?  (Read 2811 times)

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tacklebox455

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which ohm is best ohm?
« on: January 04, 2011, 07:35:49 pm »

just curious to know if running 16 ohms is better for making more drive since it has the most windings or would 4 ohms be better since it has less windings?


i sure someone is going "thank god this was not a can i run a 4 ohm cab if my head is 16 ohm"  lol
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rot gut

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Re: which ohm is best ohm?
« Reply #1 on: January 05, 2011, 06:03:20 pm »

2ohms.

tacklebox455

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Re: which ohm is best ohm?
« Reply #2 on: January 05, 2011, 08:14:56 pm »

ok but why the lowest why would lower ohms sound better than higher ohms?
1975 Sunn model T
2007Crate Blue voodoo BV 120(mercury magnetics upgraded)
Randall RT 503
Jet City JCA 22H
Creepy fingers harakiri superfuzz
Creepy fingers doomidrive
Earthbound Audio supercollider
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fithers

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Re: which ohm is best ohm?
« Reply #3 on: March 07, 2011, 09:20:35 pm »

bump
you got it dude

mike_sims

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Re: which ohm is best ohm?
« Reply #4 on: March 14, 2011, 01:19:58 am »

2Ohms would be a fun roll of the ol' dice haha. Realistically, I'm not sure if the OHM settings sound any better. I hope someone can correct me on this if I'm wrong, but my interpretation of it would be the lower the ohm rating the more power TO the cab, yes? So if you're running one head, with 2 cabs, each cab rated at 8ohms, you would want double the power (less resistance) from the amp, running the amp at 4ohms would distribute enough power to power both of those cabs. I don't really know the exact science behind it but I'm hoping someone can help out with this. Ed?
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EdBass

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Re: which ohm is best ohm?
« Reply #5 on: March 14, 2011, 08:23:28 am »

2Ohms would be a fun roll of the ol' dice haha. Realistically, I'm not sure if the OHM settings sound any better. I hope someone can correct me on this if I'm wrong, but my interpretation of it would be the lower the ohm rating the more power TO the cab, yes? So if you're running one head, with 2 cabs, each cab rated at 8ohms, you would want double the power (less resistance) from the amp, running the amp at 4ohms would distribute enough power to power both of those cabs. I don't really know the exact science behind it but I'm hoping someone can help out with this. Ed?

Only with transistor amps without an impedance matching output transformer. With tube amps, the best performance is when the speaker load matches the impedance of the output stage, so they use transformers to match them up, which is why there are all those posts about impedance matching and output taps.

Transistor amps will generally deliver more power as the impedance lowers pretty much right up to the point they become unstable and melt down, which is why you find posts about whether an amp is "stable" @ 2 ohms, etc.
Tube amps deliver the same power regardless of load impedance because the tubes themselves are actually seeing the same impedance, because that big piece of iron is matching the output to the load.

In reality, there are transistor amps with output matching transformers, and tube amps without  output matching transformers, but neither of those really have any bearing on discussion as far as the context of this forum, and likewise this whole post is really an overall generalization. Also, there is the fact that speaker impedance is "nominal", and therefore it's not an exact impedance across its entire frequency spectrum, power range, etc.
But; I think it should cover the "lower ohms = more power" thing for the purposes of this discussion.

tacklebox455

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Re: which ohm is best ohm?
« Reply #6 on: March 14, 2011, 08:42:37 am »

Thanks edbass for replying
1975 Sunn model T
2007Crate Blue voodoo BV 120(mercury magnetics upgraded)
Randall RT 503
Jet City JCA 22H
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mike_sims

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Re: which ohm is best ohm?
« Reply #7 on: March 15, 2011, 04:05:35 pm »

Cool, thanks Ed. Now I know!
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Rex B

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Re: which ohm is best ohm?
« Reply #8 on: March 16, 2011, 12:49:44 pm »

Well put Ed. How low of an impedance a normal solid state amp will drive is pretty much a function of it's ability to get rid of the heat, PLUS what the designer did to make the amp stable at low impedances and/or short-protection. 2 ohms is VERY close to No Ohms...or a dead short. Speakers are motors, and produce a BACK EMF, or electromotive force, which comes flying back down the line at the output transistors. So while the transistors are trying to control voltage and current to the speakers, the speakers are also sending voltage and current back at the transistors. You can see this by hooking a voltmeter up to the speaker terminals, and thumping on the cone with your fingers ( careful...don't poke a hole in it !). Depending on the phase of this complex voltage/current/impedance mess, the back EMF can appear to be a short to the amp at low impedances. A well-designed amp will HOPEFULLY protect itself and shut down if it thinks it is shorted....but some will just fry the outputs, or lock up to one of the rails and fry itself and the speakers. OUCH.  It's best to not use an amp at an impedance lower than what it is rated for.

Cutting the impedance in half rarely doubles the power. If an amp can produce 100 watts at 8 ohms, it may only do 160 watts or so at 4 ohms.This is because the transformer can only deliver SO much current, it "sags".  Remember, twice the power is NOT twice the volume...it's only 3 db louder. Twice as loud is 10 DB....ie 10 X the power.  So, going from 100w at 8 ohms to 160 watts at 4 ohms is only 2 db louder...really not much of an increase. Going to 2 ohms would probably only add about another 1 db, and may risk frying everything. Not worth it.

The best and safest way to get louder with a given amp is to use a higher sensitivity speaker. Look at the sensitivity rating for the speaker... XXX DB at 1 watt, 1 meter. By using a speaker that is 3 db more sensitive, you get the same result as doubling the power, without any risk to the amp.  Hope this helps.
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mckinnon audio

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Re: which ohm is best ohm?
« Reply #9 on: March 16, 2011, 02:40:22 pm »

   Rex,correct me please if i'm wrong,but with higher output impeadances,don't you also get a higher dampening factor ? This is why I thought Sunn bass amps had a 16 ohm tap for the main speaker out,most other amps use 8 or 4 ohm taps,thanks,Mel.

EdBass

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Re: which ohm is best ohm?
« Reply #10 on: March 16, 2011, 04:22:50 pm »

Well put Ed. How low of an impedance a normal solid state amp will drive is pretty much a function of it's ability to get rid of the heat, PLUS what the designer did to make the amp stable at low impedances and/or short-protection. 2 ohms is VERY close to No Ohms...or a dead short.

All of which is pretty much reversed with a properly connected tube amp, further illustrating the difference between then in practical use. In fact almost the opposite; a tube amps foe is infinite impedance (unplugged from any speakers with a load) rather than a dead short. In fact, Fender tube amps used to default to a dead short (zero ohms) if there weren’t any plugs in the jacks.
If a transistor amp dead shorts at the output, it can become a very expensive, short lived (and foul smelling) space heater, and a tube amp, while generally very forgiving to abuse, can be exposed to expensive damage if run with an open output.

Cutting the impedance in half rarely doubles the power. If an amp can produce 100 watts at 8 ohms, it may only do 160 watts or so at 4 ohms.This is because the transformer can only deliver SO much current, it "sags".   

This is a similar principle to the “sag” often referred to when using a tube rectifier vs. a SS rectifier in a tube amp. The power transformer “sag” Rex describes isn’t generally as determining a factor with tube amps because the output is more stable; the lower impedance/more power scenario becomes essentially a mute point. A tube rectifier can “sag” under high current demand situations which some players feel is desirable, causing a usually subtle “brown” effect distortion from the power starved tubes.
A tube rectifier also “ramps up” to the operating voltage of the circuit, because a tube needs to heat up before it starts conducting, which may extend component life.
A SS rectifier slams the circuit with full voltage when you hit the switch.

Brianna1

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Re: which ohm is best ohm?
« Reply #11 on: May 20, 2011, 04:33:17 pm »

Well put Ed. How low of an impedance a normal solid state amp will drive is pretty much a function of it's ability to get rid of the heat, PLUS what the designer did to make the amp stable at low impedances and/or short-protection. 2 ohms is VERY close to No Ohms...or a dead short. Speakers are motors, and produce a BACK EMF, or electromotive force, which comes flying back down the line at the output transistors. So while the transistors are trying to control voltage and current to the speakers, the speakers are also sending voltage and current back at the transistors. You can see this by hooking a voltmeter up to the speaker terminals, and thumping on the cone with your fingers ( careful...don't poke a hole in it !). Depending on the phase of this complex voltage/current/impedance mess, the back EMF can appear to be a short to the amp at low impedances. A well-designed amp will HOPEFULLY protect itself and shut down if it thinks it is shorted....but some will just fry the outputs, or lock up to one of the rails and fry itself and the speakers. OUCH.  It's best to not use an amp at an impedance lower than what it is rated for.

Cutting the impedance in half rarely doubles the power. If an amp can produce 100 watts at 8 ohms, it may only do 160 watts or so at 4 ohms.This is because the transformer can only deliver SO much current, it "sags".  Remember, twice the power is NOT twice the volume...it's only 3 db louder. Twice as loud is 10 DB....ie 10 X the power.  So, going from 100w at 8 ohms to 160 watts at 4 ohms is only 2 db louder...really not much of an increase. Going to 2 ohms would probably only add about another 1 db, and may risk frying everything. Not worth it.

The best and safest way to get louder with a given amp is to use a higher sensitivity speaker. Look at the sensitivity rating for the speaker... XXX DB at 1 watt, 1 meter. By using a speaker that is 3 db more sensitive, you get the same result as doubling the power, without any risk to the amp.  Hope this helps.
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« Last Edit: July 15, 2011, 11:58:05 am by Brianna1 »