Talk:Nominal impedance

Temporary home for stuff to be moved
Loudspeakers Matching of loudspeaker impedance to the output of an amplifier is far more critical than matching of signal level impedance.

In the days of valves, most loudspeakers had a nominal impedance of 16 Ω. Valve outputs require an output transformer to match the very high output impedance and voltage of the output valves to this lower impedance. These transformers were commonly tapped to allow matching of the output to a multiple loudspeaker setup. For example, two 16 Ω loudspeakers in parallel will give an impedance of 8 Ω. It is possible to use several taps at once but the calculations can get quite involved, so as to balance the power between the loudspeakers, match the impedance of the output, and avoid overloading any part of the output transformer secondary winding.

Since the advent of solid-state transformerless outputs, these multiple-impedance outputs have become rare, and lower impedance loudspeakers more common. The most common impedance for a single loudspeaker is now 8 Ω. Most solid-state amplifiers are designed to work with loudspeaker combinations of anything from 4 Ω to 8 Ω, and many will go down to 2 Ω or up to 16 Ω.

Now moved back to article page to see if it fits--Light current 21:41, 7 November 2005 (UTC)

Source Impedances
Any electronic source device (electric guitar, microphone, amplifier output, battery, generator, turbine, etc.) can be simplified to two imaginary electronics components. This simplified model is only valid under certain conditions, but it is valid nonetheless. These two components are a source (Vsource) and a source impedance (Zsource). These are usually connected to a load (loudspeaker, amplifier input, motor, space heater, etc.) which can be simplified to only one component, the load impedance (Zload). This diagram shows the three components:



These three components form a voltage divider, one of the basic electric circuit configurations. The voltage across the load will be proportional to the ratio of the two impedances.

For instance, an electric guitar can be modeled as a voltage source (Vsource) in series with a general impedance (Zsource). The impedance will probably be mostly resistive and inductive, because the pickups of the guitar are a coil, which is an inductor. All of these properties are lumped together into one value. The value of this impedance and of the voltage source depend on the properties of the coil, tone circuitry, the position of the knobs, etc.
 * Do we talk about nominal impedances in guitars and guitar amplification? Im not sure. I dont! It just high or low isnt it? and you get what you get out of the amp. You cant change impedances without using a preamp between guitar and main amp.(unless yuo use a transformer which will lower the o/p)--Light current 21:56, 7 November 2005 (UTC)

Low level impedances in audio systems
Three common nominal impedances for low-level signals are:


 * High impedance.
 * Low impedance.
 * Line impedance.

High impedance
Guitar amplifiers normally have a nominal input impedance of about 50 kΩ, both to suit the original guitar pickups and because this was a convenient impedance for circuits based on valves such as the 12AX7. The actual impedance of the output of a guitar with magnetic pickups and no inbuilt preamplifier is typically about 250 kΩ. The first solid-state amplifiers had relatively low actual input impedance, which was one possible cause of the disappointment some guitarists expressed with their tone. Since the invention of the FET, solid state amplifiers have had actual input impedances up to about 500 kΩ.

Higher impedance means a relatively small current flows but a relatively large voltage is present. It creates greater noise problems, and this factor and the eventual loss of high frequencies limit the length of the cables that can be used.

Low impedance
Low impedance is used for longer lines than are practical for high impedance, particularly in conjunction with balanced lines and for microphone inputs. Typical impedances are from 50 to 600 Ω. The most common low impedance input connector is a 3-pin XLR connector, with pin 1 earth, pin 2 normal input, pin 3 inverting input. Stereo 6.5 mm jack plugs are also sometimes used for low impedance balanced lines, with the right channel (the ring or collar) used for the inverting input. See tip ring sleeve.

High impedance unbalanced signals can be converted to and from low impedance balanced signals by use of an audio balun.

'Line' impedance
Line impedance is 600 Ω, and line level is 100 mV for full output. Both of these, and the name "line", come from the standards of the earliest telephone networks.

This is a common standard for connections between pieces of electronic equipment, but 100 mV at 600 Ω is considerably more level than is common for a low impedance input, and represents a greater signal strength than is common for high impedance connections as well, so connecting a high or low impedance signal into a line input normally requires a preamplifier, and going the other way may require a dummy load.

The most common line input or output connector is the RCA connector, but 6.5 mm jack plugs for unbalanced lines and XLR connectors for balanced lines are also common.

General
The article is introduced as a layman's introduction. However even with quite a good basis in physics, I did no understand any of it. This is the first article of all the many great wikipedia articles that I have read, where I felt that it needs major improvement.

Ferdinand

Indeed, the basics are not clear: Why is high impedance useful? Why does '50K ohms ... suit the original guitar pickups'? And why is it a convenient impedance for circuits based on valves? Etc.

What we need is some insight in the causality at work here.

Rob


 * You should also explain what particular parts you are having trouble with, so we can clarify. - Omegatron


 * we should explain what impedance is. it took me years from when i first heard the word to really even having any idea of what it meant, because nobody explains it well at all.  i think an understanding of "source impedance" requires you to know the basics of thevenin/norton, right?  yeah it does.  we need to explain source impedance and load impedance (with the diagram):




 * we should explain the difference between impedance matching and impedance bridging and maximum power versus maximum voltage for a fixed source impedance (fixed because of the resistance and inductance of wires in a guitar pickup, for instance).


 * all of these things are necessary to know how this stuff works, but we can present very simple versions of all of these concepts. (leaving out the phase aspects of impedance and just saying it is a resistance that changes for different frequencies, for instance.) - Omegatron 20:42, Jul 29, 2004 (UTC)

i think this is wrong
"Most equipment is designed to operate with the internal impedance of a signal source roughly equal to the impedance of the input to which it is connected. This provides the most efficient coupling, and is best in most but not all situations"


 * Um. most audio equipment uses impedance bridging, where maximum voltage transfer is the ideal, not power transfer, not impedance matching.  some old equipment needs to be impedance matched, because it was designed for transformers and tubes.

"Matching of loudspeaker impedance to the output of an amplifier is far more critical than matching of signal level impedance."


 * Um. loudspeakers should also be bridged, not matched.  see damping factor.  maybe this paragraph doesn't mean they should be matched, but it sounds like it does.  this article is confusing. - Omegatron

Generally speaking, interfaces for low frequency analog circuits should have a low source impedance and a relatively high load impedance. As stated above, maximum voltage transfer is the ideal. Source, load, and transmission-line impedance matching becomes important in RF interfaces that are subject to reflections when unmatched impedances come into play. 76.211.225.16 01:54, 14 August 2007 (UTC)radioman

start with resistance!
note to self: give an example of plain resistances first, and then do an example of impedances. - Omegatron 23:42, Sep 13, 2004 (UTC)

Please Fix!
Hi!

I hope I don't come off as being harsh, because it's certainly great that someone went to all the effort to write this article, it's just that a large part of this information is incorrect. If the author doesn't mind, I'd be glad to help fix the technical mistakes in the text.

I'll save the longer-winded suggestions in the off chance I'm not just told where to stick it ;), but here's a what I mean:

-The resistive component of the input impedance of a guitar amp is almost universally just under 1M (1000k) ohms, not 50k ohms. FETs can be used in circuits for an input impedance many, many times greater than 500k, too. For instance, in a typical preamp for a piezo-electric pickup, a FET based input stage might have an input impedance of around 20M to 30M!

-Line level is not typically 100mV at full scale, it's 1Vrms (2.83Vpk-pk). 100mV is actually a pretty common test level to simulate the peak output voltage of a passive electromagnetic pickup, for what it's worth.

-Speakers were not usually 16 ohms in the "days of valves". Without a source, I don't think it's a reasonable guess that 8 ohms is the most popular value of speaker today either.

-Taps or multiple secondary arrangements on a tube output transformer are only to "allow matching of the output to a multiple loudspeaker setup" in the very vaguest sense. The taps are there to provide the ability to match to different load impedances. While adding certain combinations of speakers would require this flexibility, there isn't really any other correlation between adding speakers and having a multiple tapped secondary.


 * Please fix it! There isn't an "author".  The article was created by many people collaboratively and you sound like you should be one of them.  See the impedance article first and then try to make this article a simplified version that laymen (or musicians with no electrical experience) can understand. - Omegatron 19:06, Jan 4, 2005 (UTC)

"nominal"
which definition of the word nominal does this article mean? - Omegatron 21:21, May 23, 2005 (UTC)

nom·i·nal (n&#335;m'&#601;-n&#601;l) pronunciation adj.


 * 1.
 * 1. Of, resembling, relating to, or consisting of a name or names.
 * 2. Assigned to or bearing a person's name: nominal shares.
 * 2. Existing in name only.
 * 3. Philosophy. Of or relating to nominalism.
 * 4. Insignificantly small; trifling: a nominal sum.
 * 5. Business.
 * 1. Of, relating to, or being the amount or face value of a sum of money or a stock certificate, for example, and not the purchasing power or market value.
 * 2. Of, relating to, or being the rate of interest or return without adjustment for compounding or inflation.
 * 6. Grammar. Of or relating to a noun or word group that functions as a noun.
 * 7. Aerospace & Engineering. According to plan or design: a nominal flight check.


 * Yes, we definitely need to know what nominal means before we attempt to fix this article. I personally have only heard the term used with Loud Speakers (15ohms nominal etc) or maybe some device where the exact impedance does not matter. So what do we maen by 'nominal'??--Light current 22:05, 26 September 2005 (UTC)


 * I suggest cleanig this article by making it a disambiguation page. Each link would then point to the relevant page and thersfore indicate the usage of the term nominal in that specific application.--Light current 15:35, 7 November 2005 (UTC)


 * No, Ive changed my mind. Ive cleaned up much of it and tried to keep as much in as I can whilst still making the content have some meaning with regard to the term Nominal impedance. See what others think!--Light current 22:01, 7 November 2005 (UTC)

Rewrite
I have more or less completely rewritten this article (I kept a couple of existing paragraphs concerning speakers and valve amps). It is now cleared of all the myths and misconceptions (I hope) and is extensively referenced. On that basis I am removing the maintenance templates as I think they no longer apply. Please speak up if you think there is something dubious still in the article.  Sp in ni ng  Spark  19:04, 10 October 2009 (UTC)

Maslin source
Maslin's book was recently removed as a source on the grounds it had nothing ot say on nominal impedance. I dispute that and have restored it. The 1987 edition isn't previewable on gbooks but the 2017 edition on page 78 is previewable and includes "This is normally specified in terms of a nominal impedance (assumed to be resistive)..." SpinningSpark 01:15, 5 August 2020 (UTC)