The Truth About Ohms...
#1
07-06-2010
The Truth About Ohms...
I figured some folks could use a little good info in between all of their misinfo....
The following was Taken from the manual of a Zed Audio Amplifier...
moral of the story, quit torturing your amps.
The "Real Deal" with 8 ohm drivers, by npdang - founder of diyma.com
I've seen many people say, "Well I want to use this speaker, but I'm put off by the fact that it's 8 ohms."
Let me explain why it's ok to use an 8 ohm speaker, and why it could actually be better than a 4 or 2 ohm speaker.
First of all, using a higher impedance than what your amp is nominally rated for is always ok. In fact, if your amp is rated for 4 and 2 ohm impedances, typically you will get less power into 8 ohms meaning that your amp will run cooler and more efficiently at higher impedances. It won't hurt your amp, and in fact it's actually much better for your amp's longevity.
Now, you're probably saying how is getting less power out of my amp a good thing? Think of your amp's power reserves as your bank account. Just because you have 100 dollars in your bank account doesn't mean you have to spend it all. Quite the opposite. Wouldn't you rather spend LESS and get MORE? That's exactly what you're doing when you use less power from your amp, and get the same amount of output from a high efficiency speaker.
Remember, most speakers are rated at 2.83V. A 4 ohm speaker rated for 90db spl at 2.83v is really being rated at 2 watts! Whereas an 8 ohm speaker rated for 90db spl at 2.83v is only being rated at 1 watt. You can do the math for yourself, Power = Voltage^2 / resistance. At 2 watts, we can assume that same 8 ohm speaker is actually rated at 93db spl (remember, every doubling of power gives you a theoretical 3db gain in spl). So using that 8 ohm speaker will give you the same amount of output, at half the power required as a 4 ohm speaker. Your amps run cooler and draw less power from your vehicle's charging system, your speakers run cooler, and everyone is happy!
Ok, now let's look at another example of an 8 ohm versus 4 ohm voice coil. Typically, the efficiency of a speaker is given by:
Efficiency = ( B^2 * L^2 ) / ( R * Sd^2 * Mms^2 )
B = magnetic field strength
L = length of wire
R = resistance
Sd = surface area
Mms = mass
So for your 8 ohm voice coil, using the same wire as a 4 ohm voice coil, you would need twice the L or length to get an 8 ohm impedance. That makes sense doesn't it? A longer wire will have more resistance. Now, looking at the formula above, doubling L actually causes your efficiency to rise, even though the impedance also rises. So in this very oversimplified example, raising the impedance actually causes efficiency to go up and lowering the impedance actually causes a loss of efficiency.
What's important to remember is that it's the overall output and efficiency of the speaker that's important, not the impedance. A high impedance, high efficiency driver can get just as loud off a small amount of power as a low impedance, low efficiency driver that sucks a ton of power! Just because you have a 100 watt amp doesn't mean you have to use all 100 watts.... it's all about being efficient.
I also found this excellent post by Dan Wiggins over at carstereos.org:
"I think one thing to consider is that going to a higher impedance voice coil will result in better packing of the voice coil, meaning a higher cross-sectional-area of copper in the flux, for a given mass.
If you take a given driver, and simply swap out voice coils, you end up with more efficiency as you increase the impedance. Take a voice coil, say 2" diameter, 1" winding length, 24AWG 4 layer, and swap it with a 2" diameter, 1" winding length, 27AWG 4 layer, and you double the impedance, but the efficiency also goes up - less mass and better packing density."
It's because the moving mass has dropped, and if desired - because of the thinner wire diameter which packs in tighter - you can put more layers in the voice coil and potentially raise the BL."
I've seen many people say, "Well I want to use this speaker, but I'm put off by the fact that it's 8 ohms."
Let me explain why it's ok to use an 8 ohm speaker, and why it could actually be better than a 4 or 2 ohm speaker.
First of all, using a higher impedance than what your amp is nominally rated for is always ok. In fact, if your amp is rated for 4 and 2 ohm impedances, typically you will get less power into 8 ohms meaning that your amp will run cooler and more efficiently at higher impedances. It won't hurt your amp, and in fact it's actually much better for your amp's longevity.
Now, you're probably saying how is getting less power out of my amp a good thing? Think of your amp's power reserves as your bank account. Just because you have 100 dollars in your bank account doesn't mean you have to spend it all. Quite the opposite. Wouldn't you rather spend LESS and get MORE? That's exactly what you're doing when you use less power from your amp, and get the same amount of output from a high efficiency speaker.
Remember, most speakers are rated at 2.83V. A 4 ohm speaker rated for 90db spl at 2.83v is really being rated at 2 watts! Whereas an 8 ohm speaker rated for 90db spl at 2.83v is only being rated at 1 watt. You can do the math for yourself, Power = Voltage^2 / resistance. At 2 watts, we can assume that same 8 ohm speaker is actually rated at 93db spl (remember, every doubling of power gives you a theoretical 3db gain in spl). So using that 8 ohm speaker will give you the same amount of output, at half the power required as a 4 ohm speaker. Your amps run cooler and draw less power from your vehicle's charging system, your speakers run cooler, and everyone is happy!
Ok, now let's look at another example of an 8 ohm versus 4 ohm voice coil. Typically, the efficiency of a speaker is given by:
Efficiency = ( B^2 * L^2 ) / ( R * Sd^2 * Mms^2 )
B = magnetic field strength
L = length of wire
R = resistance
Sd = surface area
Mms = mass
So for your 8 ohm voice coil, using the same wire as a 4 ohm voice coil, you would need twice the L or length to get an 8 ohm impedance. That makes sense doesn't it? A longer wire will have more resistance. Now, looking at the formula above, doubling L actually causes your efficiency to rise, even though the impedance also rises. So in this very oversimplified example, raising the impedance actually causes efficiency to go up and lowering the impedance actually causes a loss of efficiency.
What's important to remember is that it's the overall output and efficiency of the speaker that's important, not the impedance. A high impedance, high efficiency driver can get just as loud off a small amount of power as a low impedance, low efficiency driver that sucks a ton of power! Just because you have a 100 watt amp doesn't mean you have to use all 100 watts.... it's all about being efficient.
I also found this excellent post by Dan Wiggins over at carstereos.org:
"I think one thing to consider is that going to a higher impedance voice coil will result in better packing of the voice coil, meaning a higher cross-sectional-area of copper in the flux, for a given mass.
If you take a given driver, and simply swap out voice coils, you end up with more efficiency as you increase the impedance. Take a voice coil, say 2" diameter, 1" winding length, 24AWG 4 layer, and swap it with a 2" diameter, 1" winding length, 27AWG 4 layer, and you double the impedance, but the efficiency also goes up - less mass and better packing density."
It's because the moving mass has dropped, and if desired - because of the thinner wire diameter which packs in tighter - you can put more layers in the voice coil and potentially raise the BL."
I cannot resist getting into this subject. Scenario: Kid
buys gizzilion watt amplifier with manufacturer’s specifications of x watts into 4 ohm, y
watts into 2 ohm and z watts into 1 ohm. Well let’s take a wild guess and I bet you all that
the vast majority will drive the amplifier into 1 ohm. Why? Easy, he feels that he is getting
his “moneys worth” by doing this. OK let’s see what reality is. Said amplifier is maybe
rated at say 600w into 4 ohm, 1000w into 2 ohm and 1500w into 1 ohm. We will assume
that the speaker impedance is resistive. The difference between the 4 and 2 ohm power is
2.2dB, the difference between the 2 and 1 ohm power is 1.76dB and the difference
between 4 and 1 ohm power is 3.9dB. So what do these numbers tell us. First if the
speaker is 4 ohms vs 2 ohms, no way you can hear any difference. Same issue
comparing 2 as to 1 ohm. I grant you that between 4 and 1 ohm there is almost 4dB
difference BUT at what price. Two issues. Low impedance loads affect the amplifier’s
sound quality adversely and this is quite easy to prove. Load an amplifier with a 4 ohm
woofer and listen. Add parallel resistors to the speaker to make the amplifier “think” that it
is driving a low impedance speaker and listen to the difference in sound quality. You will
be surprised. This test is not 100% valid in fact as the resistive loads added, let the
amplifier off the hook as the reactive components of the load are confined to the 4 ohm
part. The idea of this test is to keep the loudness about constant but load down the
amplifier.
The average person can just perceive a 3dB (doubling of power) difference and to
actually double the sound pressure on your eardrum, you require TEN TIMES the
amplifier power. Yes TEN TIMES no kidding!
The other consequence of driving amplifiers into these ridiculously low impedances is that
the amplifier is stressed substantially more as compared to when driven into more sane
impedances. Efficiency drops as the losses in the output stages increase dramatically
even with “super efficient” class D amplifiers.
It serves ONLY to boost the ego of the owner of the car so he can quote numbers to his
buddies.
buys gizzilion watt amplifier with manufacturer’s specifications of x watts into 4 ohm, y
watts into 2 ohm and z watts into 1 ohm. Well let’s take a wild guess and I bet you all that
the vast majority will drive the amplifier into 1 ohm. Why? Easy, he feels that he is getting
his “moneys worth” by doing this. OK let’s see what reality is. Said amplifier is maybe
rated at say 600w into 4 ohm, 1000w into 2 ohm and 1500w into 1 ohm. We will assume
that the speaker impedance is resistive. The difference between the 4 and 2 ohm power is
2.2dB, the difference between the 2 and 1 ohm power is 1.76dB and the difference
between 4 and 1 ohm power is 3.9dB. So what do these numbers tell us. First if the
speaker is 4 ohms vs 2 ohms, no way you can hear any difference. Same issue
comparing 2 as to 1 ohm. I grant you that between 4 and 1 ohm there is almost 4dB
difference BUT at what price. Two issues. Low impedance loads affect the amplifier’s
sound quality adversely and this is quite easy to prove. Load an amplifier with a 4 ohm
woofer and listen. Add parallel resistors to the speaker to make the amplifier “think” that it
is driving a low impedance speaker and listen to the difference in sound quality. You will
be surprised. This test is not 100% valid in fact as the resistive loads added, let the
amplifier off the hook as the reactive components of the load are confined to the 4 ohm
part. The idea of this test is to keep the loudness about constant but load down the
amplifier.
The average person can just perceive a 3dB (doubling of power) difference and to
actually double the sound pressure on your eardrum, you require TEN TIMES the
amplifier power. Yes TEN TIMES no kidding!
The other consequence of driving amplifiers into these ridiculously low impedances is that
the amplifier is stressed substantially more as compared to when driven into more sane
impedances. Efficiency drops as the losses in the output stages increase dramatically
even with “super efficient” class D amplifiers.
It serves ONLY to boost the ego of the owner of the car so he can quote numbers to his
buddies.
#3
07-06-2010
so if u buy a sub that is rated at 2000rms, then u, by what ur saying, need to get a amp that puts out 2000 at 2 or 4 ohms. that is dumb especially since it will cost like double than what u would pay for a 1 ohm amp. any good amp will be fine running at 1 ohm or .5 ohms. is it better to run at a higher load, yes but u are going to pay alot more to get the power u need. and if heat is a issue then the amp is probably not tuned right, so it is clipping. clipping causes heat and heat will kill subs and amps. so if u know how to tune a amp then u wont need to worry about anything.
#4
07-06-2010
#5
07-06-2010
The Answer, seriously, F-ing read, try to understand... then get back to me.
mothman, your amp can run at one ohm. its built for that kind of abuse, atleast for a while. It is hell on the circuits though, your basically 1 ohm away from being a direct short between your speaker terminals. sure your amp is dissipating the heat well but the amp is still stressed even if its not burning hot.
when you have a higher resistance voice coil, your passing more electrons through the magnetic field at any moment making your sub more efficient. this also puts less stress on the amp. but your actually doubling the amount of current inside the actual sub. at less stress on the amp.
One thing that everyone should understand most all audio companys are only out for one thing thats $$$
BTW i didn't write this up. the second part is from steven mantz. the guy that designed some of the best moble audio equipment on the market till this day... ill take an electrical engineers advice over a marketing teams' any day.
mothman, your amp can run at one ohm. its built for that kind of abuse, atleast for a while. It is hell on the circuits though, your basically 1 ohm away from being a direct short between your speaker terminals. sure your amp is dissipating the heat well but the amp is still stressed even if its not burning hot.
when you have a higher resistance voice coil, your passing more electrons through the magnetic field at any moment making your sub more efficient. this also puts less stress on the amp. but your actually doubling the amount of current inside the actual sub. at less stress on the amp.
One thing that everyone should understand most all audio companys are only out for one thing thats $$$
BTW i didn't write this up. the second part is from steven mantz. the guy that designed some of the best moble audio equipment on the market till this day... ill take an electrical engineers advice over a marketing teams' any day.
Last edited by RangOH; 07-06-2010 at 04:45 PM.
#6
07-06-2010
I can appreciate the fact that you took the time to post this, its nice to see some more people get into the technical side of things, but its going to be a hard sell to most people in a general audio/video thread ya know mayne?? Theres always people who will disapprove either way.
Thanks either way for posting it.
Thanks either way for posting it.
#7
07-17-2010
Ill simplify it for the simple people...
Im running my dual 4 Ohm sub at 8 ohms. It f-ing slams.
when I hook it up at 2 ohms it was very weak and gutless and sounds distorted..
who wants to listen to the distortion or their amps? I like listening to music myself.
You can have your mad SPL's and sound quality too! spl people and marketing teams are mucking up the audio industry for the rest of us. nothing but 100000w amps and million watt subs so stupid... 300w is plenty for a car sub, 500w is plenty for those who love it loud! anything above that and your just buying overrated inefficient crap.
...another thing turn your bass boost **** down! they should never pass 3-6 db (they go as high as 18db). and its preferred to not use them at all! i can personally guarantee over half of this forum is clipping their subs and don't even know it. turn the boost down or off and turn the gain up a bit. if you don't have enough bass then something else is wrong. cabin gain aloan is providing you with HEAVY boost at 100hz and below so you don't need more. after about 3db, the bass boost clips the signal, which is why many people burn their subs up. that and most people don't know what it sounds like when your sub distorts.
ps.. this is coming from someone who LOVES BASS! im on your side.
Im running my dual 4 Ohm sub at 8 ohms. It f-ing slams.
when I hook it up at 2 ohms it was very weak and gutless and sounds distorted..
who wants to listen to the distortion or their amps? I like listening to music myself.
You can have your mad SPL's and sound quality too! spl people and marketing teams are mucking up the audio industry for the rest of us. nothing but 100000w amps and million watt subs so stupid... 300w is plenty for a car sub, 500w is plenty for those who love it loud! anything above that and your just buying overrated inefficient crap.
...another thing turn your bass boost **** down! they should never pass 3-6 db (they go as high as 18db). and its preferred to not use them at all! i can personally guarantee over half of this forum is clipping their subs and don't even know it. turn the boost down or off and turn the gain up a bit. if you don't have enough bass then something else is wrong. cabin gain aloan is providing you with HEAVY boost at 100hz and below so you don't need more. after about 3db, the bass boost clips the signal, which is why many people burn their subs up. that and most people don't know what it sounds like when your sub distorts.
ps.. this is coming from someone who LOVES BASS! im on your side.
#8
07-17-2010
I don't think my sub is clipping. I've been running my sub and amp combo for over 5 years and never had a problem. I talked to the original installers and said that the combo was tuned correctly. I don't remember the specs though
The remote for the amp is usually set at around 75%.
When it comes to setting up a system. I always rely on someone who knows their stuff
The remote for the amp is usually set at around 75%.
When it comes to setting up a system. I always rely on someone who knows their stuff
#9
07-17-2010
how do you know the installer know what they where doing? many shops are no better then just some guy off the streets. was the sound tuned to your liking or theirs? people can't hear up to 10% clipped signal. subs can handle clipping just as long as as the power of the clipped signal does not exceed the subs thermal characteristics. (the gains being set low compensates for this)
try setting the gains on your amp with the boost off first. your system should sound good without any eq'ing. any eq'ing that is done should only be very small adjustment. 1-3 db.
when you say usually, that means your adjusting it for something... if you need to adjust your boost that means you are not quite tuned right.
the proper way to eq something is to cut frequencies not boost. say your speakers don't put out the bass you want, try backing down frequencies in the upper range, then turning the volume up, it will route more power to the lower frequencies thus giving a proper boost and no clip.
try setting the gains on your amp with the boost off first. your system should sound good without any eq'ing. any eq'ing that is done should only be very small adjustment. 1-3 db.
The remote for the amp is usually set at around 75%
the proper way to eq something is to cut frequencies not boost. say your speakers don't put out the bass you want, try backing down frequencies in the upper range, then turning the volume up, it will route more power to the lower frequencies thus giving a proper boost and no clip.
#10
07-17-2010
#11
07-17-2010
#13
07-17-2010
after reading this you still want .5 ohms. seriously? i don't believe you read it then.
I swear im going to start my own audio company,
Ill build .0001 ohm 20,000w rms (1 million watt max) subs with 1 sq inch cone area and 1' excursion and 100lb magnet structures. the voice coil wouldn't even be a coil it will just be a single loop of 1/0awg. plaster SPL all over it and sell it for a ton of money... thing wouldn't even make a peep.
I swear im going to start my own audio company,
Ill build .0001 ohm 20,000w rms (1 million watt max) subs with 1 sq inch cone area and 1' excursion and 100lb magnet structures. the voice coil wouldn't even be a coil it will just be a single loop of 1/0awg. plaster SPL all over it and sell it for a ton of money... thing wouldn't even make a peep.
#16
07-17-2010
Well you obviously don't like loud systems since all you have for bass is a Basslink I see. Basically all I got from that first article was that he is saying is things efficiency goes up with more resistance. It may go up, but not enough to make it at all worth it. It seems like you have this idea in your head that if you wire something for example at 4 ohms versus 2 ohms that since it's more efficient that it's going to like sound the same, which it obviously won't. It's not going to be exactly half as loud but it's going to be pretty obvious that it isn't as loud.
#17
07-17-2010
thats my old system,
I have a Image Dynamics v3 d4 now. and yes i have it running at 8 ohms. i love my **** loud and clean.
I will post a video of it running off of my two channel us acoustics that does 150 per chan at 4 ohms.. you can visually see just how quiet it is...
i really dunno how you can speak when you've never even tryed a higher impedence speaker before.
I have a Image Dynamics v3 d4 now. and yes i have it running at 8 ohms. i love my **** loud and clean.
I will post a video of it running off of my two channel us acoustics that does 150 per chan at 4 ohms.. you can visually see just how quiet it is...
i really dunno how you can speak when you've never even tryed a higher impedence speaker before.
#18
07-17-2010
thats my old system,
I have a Image Dynamics v3 d4 now. and yes i have it running at 8 ohms. i love my **** loud and clean.
I will post a video of it running off of my two channel us acoustics that does 150 per chan at 4 ohms.. you can visually see just how quiet it is...
i really dunno how you can speak when you've never even tryed a higher impedence speaker before.
I have a Image Dynamics v3 d4 now. and yes i have it running at 8 ohms. i love my **** loud and clean.
I will post a video of it running off of my two channel us acoustics that does 150 per chan at 4 ohms.. you can visually see just how quiet it is...
i really dunno how you can speak when you've never even tryed a higher impedence speaker before.
#20
07-17-2010
LOL WUT? I've never tried a higher impedance speaker before? My old sub was a dual 4 ohm and I tried it at 8 ohms once since I was bored. It was stupid. I've done speakers at 1 ohm, 2 ohms, 4 ohms, and 8 ohms. My new system will be 1 ohm. Running higher than 2 ohms is stupid is pointless.
#21
07-17-2010
I'm not an idiot...
You're the one over here talking about distortion and stuff when I bet if you hooked up an o scope to your stereo it would probably look square since you're pushing you're amp trying to make up for your higher resistance so you've got the gain set higher. I'd be willing to bet it would look horrible, unless you've got it so that your stereo just isn't loud at all. I hate people like you. Literally have no idea what they're talking about but act like experts.
You're the one over here talking about distortion and stuff when I bet if you hooked up an o scope to your stereo it would probably look square since you're pushing you're amp trying to make up for your higher resistance so you've got the gain set higher. I'd be willing to bet it would look horrible, unless you've got it so that your stereo just isn't loud at all. I hate people like you. Literally have no idea what they're talking about but act like experts.
#22
07-17-2010
8ohm sub 300w on Flickr - Photo Sharing! 8 ohms 300w... 27 sec is when i turned it up. as you can see im hitting my x-max with no problems at all on a sealed box.
like wise..
Ive personally have an education in electronics how about you? and electricity. Ive built a damn amplifier from scratch... i know that you don't just gain wattage from an amplifier without giving up something.
I hate people like you. Literally have no idea what they're talking about but act like experts.
Ive personally have an education in electronics how about you? and electricity. Ive built a damn amplifier from scratch... i know that you don't just gain wattage from an amplifier without giving up something.
#23
07-17-2010
#24
07-17-2010
how do you know the installer know what they where doing? many shops are no better then just some guy off the streets. was the sound tuned to your liking or theirs? people can't hear up to 10% clipped signal. subs can handle clipping just as long as as the power of the clipped signal does not exceed the subs thermal characteristics. (the gains being set low compensates for this)
try setting the gains on your amp with the boost off first. your system should sound good without any eq'ing. any eq'ing that is done should only be very small adjustment. 1-3 db.
when you say usually, that means your adjusting it for something... if you need to adjust your boost that means you are not quite tuned right.
the proper way to eq something is to cut frequencies not boost. say your speakers don't put out the bass you want, try backing down frequencies in the upper range, then turning the volume up, it will route more power to the lower frequencies thus giving a proper boost and no clip.
try setting the gains on your amp with the boost off first. your system should sound good without any eq'ing. any eq'ing that is done should only be very small adjustment. 1-3 db.
when you say usually, that means your adjusting it for something... if you need to adjust your boost that means you are not quite tuned right.
the proper way to eq something is to cut frequencies not boost. say your speakers don't put out the bass you want, try backing down frequencies in the upper range, then turning the volume up, it will route more power to the lower frequencies thus giving a proper boost and no clip.
I can't say anything for installer himself, but the shop has a lot of experience. I've never heard a bad thing about them
The controller is just for bass boost. I leave it at 75% because I don't want to be shaking my stuff too much, but I can turn it up to show people I can bump pretty good.
The controller is a bass boost if that helps any
#25
07-17-2010
