[LTD02]

most folks know that drivers have an impedance spec and a resistance spec. for the most part, we use the impedance spec when discussing subs.


it is almost universally true that pro-audio drivers target an ~8 ohm impedance.


what drives this decision?


what is so superior about 8 ohm? how is it better or worse to move toward 4 ohm or 16 ohm?


what would the tradeoffs be?


is it somehow related to our 110-120v power? would we choose differently if using 220-240v power?


.desufnoc

 

[NEO Dan]

On the amp side:

To date I think it's been motivated by cost of manufacturing primarily. As SMPS brings the ability for amps to deliver truly high power into higher impedance loads, things may change somewhat as this technology proliferates.


Everything is a trade when it comes to driver design.


I think it's obvious that the 120v standard has held us back in the power department quite a bit too. But safety first.

 

[2100]

For sound reinforcement products, they usually come with dual speakons....they are wired in parallel, so that you can "upgrade" by adding another unit. Lower distortion, higher SPL, wide coverage for those designed for arraying, can extract more power from the amp in 4-ohms etc.

So not an issue. Multiples are very common..... You can do 16-ohms and have 4 drivers/boxes, but that's would be too much for the smaller venues. 8-ohms is a good universal standard between performance, requirements and most importantly costs/profitability (you have to consider transportation, packing and setting up too).


For home, multiples are not so common and its only the crazy enthusiasts who run multiples and go anal about setting them up so that they don't cancel, EQ etc..., though you can argue that you can bridge with singles....but that's another story.

 

[Ivan Beaver]

Just a couple of thoughts-and there is nothing "special" aobut 8 ohm-except that is pretty much a "standard".


Why is the Space shuttle fuel tank a certain size? If you trace it back you will find that the width of a horses butt during Roman times is part of the answer-because of "standards". But that is a different story.


If a lower impedance is used-there is more loss across the cable and the damping factor of the system gets lower-resulting in a more sloppy bass.


If the impedance is higher-you have to have a higher voltage swing in order to produce the same amount of "watts". Most amps are designed to produce max output in the 2-4-8 ohm range. Of course you could use a much larger amp and drive higher impedance loudspeakers and still get the "watts" you need to produce the output level you want.


There are lots of advantages to higher impedance loudspeakers-but the current "state fo the art" does not support that and if anybody started making higher impedance loudspeakers, then there would not be amps to drive them and if they made amps specifically to drive them-then you would not be able to drive "normal" loudspeakers as easily.

 

[John_E_Janowitz]

It's the same as power transmission lines. Higher voltage is better than higher current. P = I^2 * R Higher resistance = less current transferred along long cables.


John

 

[michael hurd]

Good point Ivan. A couple of things i'd like to add though: In the pro world, there is generally a lot more cable in between the amplifiers and the boxes, compared to 'most' home setups.


Like mentioned, long runs of cable ( especially if it's smaller in diameter ) can add to the loop resistance and degrade damping to a degree. It's a lot worse on low impedance boxes.

 

[penngray]



Quote:
If a lower impedance is used-there is more loss across the cable and the damping factor of the system gets lower-resulting in a more sloppy bass.

maybe a dumb question but are you saying high impedance is better for bass? some difficult speakers have impedance curves that go below 2 ohms (Paradigm 100s), thats not good for bass?


I always thought wiring into 4 ohms instead of 8 ohms was perferred.

 

[michael hurd]

Amplifiers create voltage gains. If we have 60 v into a 4 ohm load, that's 900 watts ( 60x60 = 3600: 3600/4 =900)


The same 60 volts into an 8 ohm load is 450 watts. The difference is the amount of amperage that's flowing in the circuit.


You can put that same 60 volts on a 16 ohm load, that's only going to be 225 watts.


Why does any of this matter? Higher impedances need higher voltage sources.


If you look at the impedance spikes on most woofers, it can get up to 45 ohms or higher. At that frequency, power across the coil is low: this can contribute to lower power compression. ( dependant of the design )


Actual in box impedance should be considered as well as the linear excursion limits / mechanical limits. It's a balancing act.


If you have too high an impedance spike, you could be voltage limited, or too low an average impedance, you could be current limited.

 

[Mark Seaton]



Quote:
Originally Posted by penngray /forum/post/16886620


maybe a dumb question but are you saying high impedance is better for bass? some difficult speakers have impedance curves that go below 2 ohms (Paradigm 100s), thats not good for bass?


I always thought wiring into 4 ohms instead of 8 ohms was perferred.

Seems like there is a lot of confusion on something so simple.


There is no "preference" other than the practicalities of wiring and amplification. In home audio we generally have one speaker per amplifier, apart from some wilder DIY subs (I'm lumping a passive speaker as one speaker for now).


In pro audio applications it is very common to parallel multiple enclosures as they are used to drive the same signals to greater levels rather than moving and handling a single box 4x the size. There are also much larger amplifiers available to common pro audio use to facilitate using a single amplifier to power a block/stack of subwoofers or speakers. While many amplifiers are capable of 2 Ohm operation, as Ivan noted, you have to be more conscious of the wiring length and size, as the resistance can quickly becomes a notable percentage of the load which means your power amp is working to simply heat up the wire.


You will also find that many pro audio drivers are available in 4 or 8 Ohm versions, and some in 16 Ohm. It all depends on how you intend to use them and what sort of power you need to deliver to each driver or speaker.

 

[LTD02]



Quote:
Originally Posted by John_E_Janowitz /forum/post/16886539


It's the same as power transmission lines. Higher voltage is better than higher current. P = I^2 * R Higher resistance = less current transferred along long cables.


John

so that would be an argument for 16 ohm or 32 ohm speakers, no?


why don't we see them?

 

[LTD02]



Quote:
Originally Posted by penngray /forum/post/16886620


maybe a dumb question but are you saying high impedance is better for bass? some difficult speakers have impedance curves that go below 2 ohms (Paradigm 100s), thats not good for bass?


I always thought wiring into 4 ohms instead of 8 ohms was perferred.

no. here my question is honest. my views agnostic.


i am just curious why the pro audio world seems to have settled on the 8 ohm standard.

 

[LTD02]



Quote:
Originally Posted by michael hurd /forum/post/16886754


Amplifiers create voltage gains. If we have 60 v into a 4 ohm load, that's 900 watts ( 60x60 = 3600: 3600/4 =900)


The same 60 volts into an 8 ohm load is 450 watts. The difference is the amount of amperage that's flowing in the circuit.


You can put that same 60 volts on a 16 ohm load, that's only going to be 225 watts.


Why does any of this matter? Higher impedances need higher voltage sources.


If you look at the impedance spikes on most woofers, it can get up to 45 ohms or higher. At that frequency, power across the coil is low: this can contribute to lower power compression. ( dependant of the design )


Actual in box impedance should be considered as well as the linear excursion limits / mechanical limits. It's a balancing act.


If you have too high an impedance spike, you could be voltage limited, or too low an average impedance, you could be current limited.

based on this line of reasoning, we should be running voltage sources. extremely high voltage amps with extremely high impedance speakers.


but we are not. why not?

 

[LTD02]

so is the idea that there are two x two variables to consider:


1. voltage at the outlet and amperage at the outlet (typically 110/120v, 15-20 amps)


2. voltage at the amp, amperage at the amp


and that for most applications in pro audio a net 4 - 8 ohm system (nominal) achieves a good balance between being voltage limited and current limited in 1 and 2 above?



while for car audio, 12v systems, they are much more voltage limited, so ideally the drivers have a much lower resistance in order to strike a better balance between the current available in cars with the lower voltage and this is why we see 1-2 ohm net systems in use in car audio?

 

[Ivan Beaver]



Quote:
Originally Posted by penngray /forum/post/16886620


maybe a dumb question but are you saying high impedance is better for bass? some difficult speakers have impedance curves that go below 2 ohms (Paradigm 100s), thats not good for bass?


I always thought wiring into 4 ohms instead of 8 ohms was perferred.

You have to look at the SYSTEM. The system includes the amp- the loudspeaker-the cables and all the connectors. The biggest thing that you can vary would be the size of the loudspeaker cable. If it is large enough (in relation to the loudspeaker load and distance), then the impedance does not matter in terms of sonic quality.


4 ohms is not "better" than 8 ohms-it just allows you to "pull" more power out of the amp. Is that better? You tell me. But what if the sound quality is less-even if you have more "power"?

 

[Looneybomber]



Quote:
Originally Posted by Ivan Beaver /forum/post/16887286


But what if the sound quality is less-even if you have more "power"?

I would say there's a flaw somewhere and that faulty piece of equipment (amp) would need to be removed from the signal chain. Otherwise, why would there be a change?

 

[LTD02]

i don't think that is what he meant.


my guess is that he was saying what if more current degrades sound quality, ceteris paribus. i think i would agree with him.

 

[LTD02]



Quote:
Originally Posted by LTD02 /forum/post/16887254


so is the idea that there are two x two variables to consider:


1. voltage at the outlet and amperage at the outlet (typically 110/120v, 15-20 amps)


2. voltage at the amp, amperage at the amp


and that for most applications in pro audio a net 4 - 8 ohm system (nominal) achieves a good balance between being voltage limited and current limited in 1 and 2 above?



while for car audio, 12v systems, they are much more voltage limited, so ideally the drivers have a much lower resistance in order to strike a better balance between the current available in cars with the lower voltage and this is why we see 1-2 ohm net systems in use in car audio?

i think i am starting to understand, no?


yeah, i know, replying to my own post is lame, but here is something worth considering:


r = e/i


for homes in the usa, let's use:


e = 120 volts


i = 15 amps


solving for r, gives 120/15 = 8 ohms.


so an 8 ohm system at 120 volts will draw 15 amps.


yeah, yeah, i know this doesn't consider the frequency dependant nature of impedance, but as a first order approximation, this puts us right on the mark!

 

[Looneybomber]



Quote:
Originally Posted by LTD02 /forum/post/16887638


i don't think that is what he meant.


my guess is that he was saying what if more current degrades sound quality, ceteris paribus. i think i would agree with him.

Well sure, if switching from 8ohm to 4ohm causes a degradation of sound, then sure.


I'm just trying to figure out how more current will degrade sound quality. The speaker should still function the same, so the degradation of sound would be in the amp right?

 

[LTD02]



Quote:
Originally Posted by Looneybomber /forum/post/16887716


Well sure, if switching from 8ohm to 4ohm causes a degradation of sound, then sure.


I'm just trying to figure out how more current will degrade sound quality. The speaker should still function the same, so the degradation of sound would be in the amp right?

more current causes all kinds of additional problems in the driver.


i'm not a driver design guru, but eddy currents, thermal builup, etc. are among some of the problems.

 

[Mark Seaton]



Quote:
Originally Posted by Looneybomber /forum/post/16887716


Well sure, if switching from 8ohm to 4ohm causes a degradation of sound, then sure.


I'm just trying to figure out how more current will degrade sound quality. The speaker should still function the same, so the degradation of sound would be in the amp right?

That depends...


Remember speakers are nothing like a simple resistive load. They vary greatly in impedance vs. frequency. If the amplifier changes behavior while driving different loads, this can lead to frequency dependent changes based on peaks and dips in the impedance.


The other aspect related to the varying impedance of the speaker is that the losses you might incur from long speaker wire runs to a 2 Ohm load will then be frequency dependent, and can affect the response and power delivered from the amplifier. More power will be delivered at impedance peaks, and less at minimums. Of course if wire resistance is kept very small the difference becomes very small. "Small" is relative to the load, so a higher impedance load will vary less for a given wire resistance. To be clear, this isn't really an issue with 10' runs in a home, but make that 50-100' in pro audio use and bump the power up by a factor of 10, and those losses get significant and expensive in terms of wasted power.