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juggernaut
09-14-2013, 08:06 PM
I've been searching the inter-webs for an explanation on why speakers have different impedance. My search has lead me to a lot of people over-explaining ohms law and giving anecdotal examples of different stereo configurations, (this will work with that, wire this in parallel/series, bridged channels, this how my sister's husbands brother-in-law does it, etc..) But, I haven't heard why do speakers have different impedance in the first place. Would someone be kind enough to explain?

Thanks, Landon

PT Sportwagon
09-15-2013, 03:51 PM
Well is almost a standard. 99% of aftermarket speakers are 4 ohms. while some OEM speakers are 10 ohms, most home speakers are 8 Ohms. Don't really know why it may have been a manufacturers assoc decision Never heard. Maybe like the model car manufacturers decieding on porducing 1/25 and 1/24 scale model car kits.
Not sure if it helps.

Tim

scott_fx
09-16-2013, 09:12 AM
it's based on a few different things. it has to do with the speaker motor characteristics, what kind of amp that will be driving them among other factors. i haven't heard of any oem speakers being 10 ohms... maybe that is something that happened back in the day. but the 4-ohm/8-ohm comment is how things are now adays (oem's like bose use a different impedance all together though...).
generally speaking. 4 ohm speakers will allow the amp to push more power to them (less resistance) at the cost of sound quality. For home speakers and a quiet environment 8 ohm speakers will lend themselves to a better sounding speaker
you shouldn't shy away from 8 ohm drivers though. they do have their benefits (i actually have a pair of 7" seas mid bass drivers waiting to go into my next car... they are 8 ohms)

juggernaut
09-16-2013, 11:20 AM
Thanks SW and scott.

If you have time to answer another question, what happens if I would have an 100 amp running a 8 ohm 100w speaker and swap the speaker to a 4 ohm 100w

Seems to me switching the ohms won't make the speakers produce louder sound because no more energy is being added to the equation. Unless there is efficiency to be gained with lower ohms?

scott_fx
09-16-2013, 12:34 PM
if you have a 100 watt amp it's most likely 100 watts at 4 ohms (if we're talkign about car amplifiers) so if you had an 8 ohm speaker you're probably looking at the amp only producing 50 watts (8 ohms is twice the resistance as 4 ohms) there is a lot to take into account though. the efficiency of the speaker has more to do with the spl (sound pressure level aka volume) then the impedance. if you have a speaker that has a sensitivity of 89 db vs a speaker with 92 db. the 92 db speaker will be twice as loud (typically measured at 1m away) as long as everything else is the same. this is because for every 3 db increase, you double the spl.

scott_fx
09-16-2013, 12:37 PM
and to further emphasize my point with personal real world experience.

the first time i was really shown the value of sensitivity of speakers was when i heard the klipsch horns (http://www.crutchfield.com/p_714KHORNCH/Klipsch-Klipschorn-Heritage-Cherry.html?tp=185&awkw=55327875865&awat=pla&awnw=g&awcr=26260921945&awdv=c#details-tab) they have a sensitivity of 105db. (a lot of car speakers are rated at 89.) I heard it powered off of a 1 watt amp. That 1 watt amp would fill the entire room with sound... and it wasn't even maxed out. i think the volume knob was at 50% or so.

when compared to a car speaker driver with 89 db. the klipsch horn would be 5 1/3 times louder for every watt of power... and that is an 8 ohm speaker



here is a good write up about 8 ohm drivers in a car:
http://www.diymobileaudio.com/forum/how-articles-provided-our-members/31-real-deal-8-ohm-drivers.html

(http://www.diymobileaudio.com/forum/how-articles-provided-our-members/31-real-deal-8-ohm-drivers.html)

the take home:
"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."

mitch_04
09-16-2013, 03:23 PM
Curious why the resistance of the speaker would affect sound quality. I've never heard of this before, not challenging but would like the reasoning behind it.

Something to add about resistance is that it is, in a way, basic electrical math. Less resistance increases amperage if voltage is constant. Amplifiers, in cars, convert DC voltage into an AC voltage. The amount of current switching (normal home ac voltage, IIRC, is around 55) is what determines the frequency of the sound. So if you took a 4 ohm subwoofer and hooked it up to a 110 home outlet you would get a constant 55 HZ bass note of 3000 watts. If you had a 2 ohm sub, it would be 6000 watts. The 4 ohm sub would be drawing just over 25 amps, the 2 ohm would be drawing 55 amps. This demonstrates a point I'm about to make(and yes, I have seen this done at a car audio shop with a Kicker Solo X, it's awesome).

When building an amplifier, you generally build it for a specific ohm range. Cheap amplifiers generally are limited to 4 ohms, and sometimes struggle with that. Great amplifiers can go as low as 1/2 ohm. However, as the resistance of the speaker goes down, the amperage flow goes up as shown in the home demonstration. This also generates heat, more or less depending on the efficiency rating of an amplifier (Higher efficiency amplifiers tend to be lower sound quality, however that was 10 years ago when I was really into stereos. It could have changed). Now you have to figure in whether the subwoofers are going to be linked together. 2 4 ohm subs wired in parallel (positive to positive) will create a 2 ohm load. So now you have to find a 2 ohm stable amplifiers, or you can purchase 2 8 ohm subs and be back to 4 ohms.

I don't know if there is a specific reasoning behind the voice coils resistance other than to make it easier to purchase subwoofers that match amplifiers. This way you are able to purchase 1, 2, 4, 8, etc etc subwoofers and with a little creative wiring still be able to keep your amplifiers from frying while still maintaining a decent power output. Everytime resistance goes down, power goes up, but so does amperage draw.

Like it was said before, speakers with higher sensitivity will be louder with the same power than another sub with lower sensitivity. However, not all speaker manufactures are honest about their ratings either, so take it with a grain of salt (or just buy quality). Also remember that loudness and sound quality are unrelated, that comes down to how the speaker is made. Cone materials, magnet size, frame strength, etc etc.

Obviously I haven't told you what the reasoning is, but hopefully you learned something that may help you understand.

scott_fx
09-16-2013, 04:20 PM
Curious why the resistance of the speaker would affect sound quality. I've never heard of this before, not challenging but would like the reasoning behind it.

Something to add about resistance is that it is, in a way, basic electrical math. Less resistance increases amperage if voltage is constant. Amplifiers, in cars, convert DC voltage into an AC voltage. The amount of current switching (normal home ac voltage, IIRC, is around 55) is what determines the frequency of the sound. So if you took a 4 ohm subwoofer and hooked it up to a 110 home outlet you would get a constant 55 HZ bass note of 3000 watts. If you had a 2 ohm sub, it would be 6000 watts. The 4 ohm sub would be drawing just over 25 amps, the 2 ohm would be drawing 55 amps. This demonstrates a point I'm about to make(and yes, I have seen this done at a car audio shop with a Kicker Solo X, it's awesome).

When building an amplifier, you generally build it for a specific ohm range. Cheap amplifiers generally are limited to 4 ohms, and sometimes struggle with that. Great amplifiers can go as low as 1/2 ohm. However, as the resistance of the speaker goes down, the amperage flow goes up as shown in the home demonstration. This also generates heat, more or less depending on the efficiency rating of an amplifier (Higher efficiency amplifiers tend to be lower sound quality, however that was 10 years ago when I was really into stereos. It could have changed). Now you have to figure in whether the subwoofers are going to be linked together. 2 4 ohm subs wired in parallel (positive to positive) will create a 2 ohm load. So now you have to find a 2 ohm stable amplifiers, or you can purchase 2 8 ohm subs and be back to 4 ohms.

I don't know if there is a specific reasoning behind the voice coils resistance other than to make it easier to purchase subwoofers that match amplifiers. This way you are able to purchase 1, 2, 4, 8, etc etc subwoofers and with a little creative wiring still be able to keep your amplifiers from frying while still maintaining a decent power output. Everytime resistance goes down, power goes up, but so does amperage draw.

Like it was said before, speakers with higher sensitivity will be louder with the same power than another sub with lower sensitivity. However, not all speaker manufactures are honest about their ratings either, so take it with a grain of salt (or just buy quality). Also remember that loudness and sound quality are unrelated, that comes down to how the speaker is made. Cone materials, magnet size, frame strength, etc etc.

Obviously I haven't told you what the reasoning is, but hopefully you learned something that may help you understand.

totally understand and not taking it as a challenge. as you said about your amp working harder with lower impedance drivers. if you don't have a quality amplifier then it'll have to work harder at 4 ohms, increasing heat and also the signal to noise ratio... giving you a hit in the sq dept. that being said. if you have a quality amp then you don't have to worry about that. there are other factors that are far above my scope of knowledge and get into the function of the amp. it's more then likely the benefit of higher impedance speakers would be lost in an automotive environment.

Cobra 498
09-16-2013, 04:31 PM
Curious why the resistance of the speaker would affect sound quality. I've never heard of this before, not challenging but would like the reasoning behind it.

Something to add about resistance is that it is, in a way, basic electrical math. Less resistance increases amperage if voltage is constant. Amplifiers, in cars, convert DC voltage into an AC voltage. The amount of current switching (normal home ac voltage, IIRC, is around 55) is what determines the frequency of the sound. So if you took a 4 ohm subwoofer and hooked it up to a 110 home outlet you would get a constant 55 HZ bass note of 3000 watts. If you had a 2 ohm sub, it would be 6000 watts. The 4 ohm sub would be drawing just over 25 amps, the 2 ohm would be drawing 55 amps. This demonstrates a point I'm about to make(and yes, I have seen this done at a car audio shop with a Kicker Solo X, it's awesome).

When building an amplifier, you generally build it for a specific ohm range. Cheap amplifiers generally are limited to 4 ohms, and sometimes struggle with that. Great amplifiers can go as low as 1/2 ohm. However, as the resistance of the speaker goes down, the amperage flow goes up as shown in the home demonstration. This also generates heat, more or less depending on the efficiency rating of an amplifier (Higher efficiency amplifiers tend to be lower sound quality, however that was 10 years ago when I was really into stereos. It could have changed). Now you have to figure in whether the subwoofers are going to be linked together. 2 4 ohm subs wired in parallel (positive to positive) will create a 2 ohm load. So now you have to find a 2 ohm stable amplifiers, or you can purchase 2 8 ohm subs and be back to 4 ohms.
I don't know if there is a specific reasoning behind the voice coils resistance other than to make it easier to purchase subwoofers that match amplifiers. This way you are able to purchase 1, 2, 4, 8, etc etc subwoofers and with a little creative wiring still be able to keep your amplifiers from frying while still maintaining a decent power output. Everytime resistance goes down, power goes up, but so does amperage draw.

Like it was said before, speakers with higher sensitivity will be louder with the same power than another sub with lower sensitivity. However, not all speaker manufactures are honest about their ratings either, so take it with a grain of salt (or just buy quality). Also remember that loudness and sound quality are unrelated, that comes down to how the speaker is made. Cone materials, magnet size, frame strength, etc etc.

Obviously I haven't told you what the reasoning is, but hopefully you learned something that may help you understand.

The measurement is impedance and is different from resistance since it changes with frequency and a resistance does not.

cmac06
09-16-2013, 06:24 PM
Low Imp speakers are designed to handle more current without overheating the voice coil. Usually designed for high listening levels where large current draws will be seen over an extended period. The reason you want this is bass frequencies require more power to produce. This helps with controlling damping of the diaphragm to prevent over excursion in the driver.

scott_fx
09-16-2013, 06:30 PM
Low Imp speakers are designed to handle more current without overheating the voice coil. Usually designed for high listening levels where large current draws will be seen over an extended period. The reason you want this is bass frequencies require more power to produce. This helps with controlling damping of the diaphragm to prevent over excursion in the driver.

you learn something new every day:twothumbs

mitch_04
09-17-2013, 04:37 AM
Impendance and resistance are both resisting current flow, but yes impendance does change with frequency.

Quickboat
09-17-2013, 05:35 AM
The simplest way to explain what makes impedance of speaker different is in the voice coils wire thickness, length and to a lesser extent its coils shape or size. A voice coil of larger thickness wire and shorter wire length is going to be of lower impedance. Not unlike how a battery cable of greater thickness or "lower gauge" will handle more amperage and be of lower resistance/ impedance.
The amplifier has to be rated for the speaker impedance because it must be capable of handling higher current levels with a lower impedance speaker.

nekkidhillbilly
09-23-2013, 10:13 AM
most modern car stuff is 2 or 4 ohm

MonzaRacer
10-17-2013, 08:11 PM
OK so lets get this straight, first of all stock speakers can run as high as 18+ ohms resistance. Now get this one straight, you put in a 4 ohm speaker on these systems and you WILL overheat and possibly damage the stereo/amplifier.
NOW as you install stereo, and other equipment matching ohm ratings is critical.
NOW with drivers such as subs, the matching amps need to be rated for low impedance operation otherwise it will overheat and die.
Subs can be wired in series or parallel, and you can get amps rated down to sub 1 ohm ratings, and these produce huge dB numbers and sound pressure levels.
Most of these are class D amps.
If you dont understand the ohm ratings, stick with 4 ohm rated speakers or HIGHER and reasonably name brand audio equipment.
You will see either dual voice coil (hooked together can make 2 ohm, wired other way make different ohm ratings)
Dont understand it, dont try to hook it up. I have watched many great name brand amps burnt to a crisp. Got a Kenwood hooked up by an idiot, now it needs fixed.
Most cars can handle 4 ohm systems, sound great and not break the bank.
I ran 2 ,10" subs and 2 6x9s all rated at 100 watts, pushed by 90 watt amp.
I like to recommend keeping input power to 80% of the driver(speaker rating) ie 80 watts power into a 100 watt.
Stereo wattage all stack up just like wattage on CB's. mess it up and the driver chip burns out.
Idiots like to brag about over driving speakers and all sorts of god awful horsesh_t about building systems, STILL they dont have a DA_M clue about common sense, just throw crap together, use all the STUPID, IDIOTIC theories and practices.
THEY ARE STILL IDIOTS.
100 watt speakers, no more than 90watts power through first order freq control, IE caps or coils.
My last set of decent speakers are Scosche 6x9s from Walmart.
Getting ready to slap those in my 98 Buick Regal, also gonna put my Rockwood 6 1/4s in door and some tweeters I got.
Radio is only thing working as cd and cassette deck is toast.

scott_fx
10-17-2013, 08:32 PM
I like to recommend keeping input power to 80% of the driver(speaker rating) ie 80 watts power into a 100 watt.


i don't agree with you on this. you are more likely to damage a speaker with an amp rated under the rms handling rather then powering it with a amp that has more power.... there is a caveat to this. your system needs to be properly tuned (read: setting your gains and crossover points correctly)

what damages a speaker is when your amp clips. This clipped waveform is bad for the driver. If you have an amplifier that is rated at say 75 watts, you are going to have to have that amp do more work to get to the same output as an amp that is rated at 150 watts. When you have you amps pushing closer to their limit then you introduce noise. Also, your speakers can handle more power in the range that they are designed to play; for instance, If you have a tweeter playing the full spectrum you'll burn it out in no time. That is where the tuning comes into play and is very important. You need to set your gains correctly (i can find a link with a good write up describing how to do this if anyone is interested) and also limit the frequency to what the driver's sweet spot is.

The best system i have ever owned had two butler tube amps @ 2x150 watts and then a zapco reference 500.1 amp for the sub. I didn't have to push the amps hard at all and it was the cleanest sound i've ever achieved. Yes the components were top quality but the subtle nuances are largely lost in a car environment. Where the real benefits were had was from having the more powerful amps. That being said. my next system will be running a soundstream class d amp running 4x150. That amp is 1/4 of the price of just one of the butler amps and twice as many channels. My reasoning behind this is that the nth degree of clarity will be lost in the imperfect environment of a car. We are not sitting in a plush leather chair in the ideal spot in a quiet office. We are driving a car with big cams, road noise and loud exhausts.

cmac06
10-17-2013, 08:56 PM
^^^yep, for musical listening, the speakers are not held at peak power long enough to cause issues with heat. Clipping and distortion above 1% mean that the voice coil is not being controlled. Also speakers are a lot like springs, so as long as the excursions from peak to peak can be controlled, you are safer with the overrated amp. That being said if I were building a system with no damping such as free air, I would go with the conservative ratings and limit output. I will say that I wouldn't severely overdrive a speaker, but 10% or so allows the amp to stay in its most efficient range without taxing itself or the speaker.

The reality is most people wouldn't feel comfortable sitting in a car at full volume with adequate power handling capabilities.

scott_fx
10-17-2013, 10:49 PM
I just want to make one thing clear. I'm not saying that powering a speaker with 75 watts is bad. That was just a figure I used for my example.

mitch_04
10-18-2013, 04:48 AM
I agree with using the full rated power. However, this thread was originally started with the purpose of asking why speakers have different impedance, not how to hook them up or anything related. It has gotten off track and a lot of good information has came out, but I would say there is some bad information in here as well.

Many speakers and amplifiers are under driven. Kicker equipment, in my experience, can take much more of a beating than they say it can. A friend used to have a couple Comp 15's, rated at roughly 300 RMS. He has well over 1000 split between the 2 of them and they held up for years, he sold the system before they ever popped. And this was a true 1000 watts rms, not some $50 Wal-Mart amp that has 1000 watt stickers all over it. I purchased my system, all RF Power series, going by the specs, AKA 1000 RMS sub for a 1000 RMS amp. Well, when my birth sheet came with the RF amp, its true power was 1600 RMS which is not uncommon with RF equipment. I ran that sub for 2 years before I sold the car and took it out. It now sits in my attic waiting for my project pickup to get done, with absolutely no signs of wear.

I'm not saying buy a low rated sub and high rated amp, but I am saying that quality products are generally underrated and can handle much more than they say.

Also, something I found interesting is that distorted music causes more hearing problems than clear music. The reason being is that when the music distorts the frequency flatlines for a period vs peaking and dropping. This "flatline" causes too long of a constant frequency and your ear has trouble protecting itself. I'm sure there is a better explanation, but its just a thought.