Talk:Impedance bridging

Complex Impedance
For the general case of complex impedance, the load voltage is maximal at $$Z_L = \frac{2 Z_S \bar{Z_S}}{Z_S - \bar{Z_S}}$$. I believe this must be mentioned. Leokor (talk) 02:57, 12 February 2013 (UTC)

Article name
I moved this to impedance bridging since it gives this idea that it is the "opposite" of impedance matching, but the term "voltage bridging" i think is more common.

Also they are not opposites really. One maximizes power and one maximizes voltage. Not opposites.

Also to differentiate it from a bridged amplifier, in which two positive outputs are inverted from each other and used to drive a load in a floating type configuration. not the same thing.

Also I am going to keep editing these. - Omegatron 20:54, Jun 23, 2004 (UTC)

Voltage bridging
 Moved from Talk:Impedance matching — Omegatron 19:51, 13 April 2007 (UTC)

Is this an acccepted term in the industry?--Light current 03:29, 16 December 2006 (UTC)


 * No. We kind of made it up, from the common term "bridging".  Do you know of a better one? — Omegatron 04:08, 5 January 2007 (UTC)


 * No, but I didnt think neologisms or original research (terminology) were allowed 8-)--Light current 17:48, 5 January 2007 (UTC)


 * The only terms I can think of is 'parallel connection' or 'tapping' as in phone tapping--Light current 18:53, 5 January 2007 (UTC)

It's not actually made up, but it's not commonly referred to by name:


 * "Calculation the damping of impedance bridging or matching an interface connecting Zout and Zin""
 * "If the load impedance is 10 times or more the source impedance, it is called a "bridging" impedance. Bridging results in maximum VOLTAGE transfer from the source to the load."
 * This might be related?
 * "High-impedance bridging input does not load signal source"
 * "High impedance/bridging" inputs
 * "High-impedance bridging inputs allow connection from either high or low impedance sources."
 * "Actual output impedance is 100 ohms (47 ohms unbalanced) and the TB-6 "Mic-All" amplifiers will drive virtually any line load from 600 ohms to high impedance bridging!"

"High-impedance bridging" might actually be a better term? — Omegatron 19:14, 5 January 2007 (UTC)


 * Since the term 'high impedance bridging' is in the literature, I think we could use that. Voltage bridging merely redirects to impedance bridging, so its just a matter of deleting the voltage bridging page. —The preceding unsigned comment was added by Light current (talk • contribs) 20:11, 5 January 2007 (UTC).


 * What literature?
 * Why would you delete the redirect? — Omegatron 21:21, 5 January 2007 (UTC)

Here is a book that mentions "bridging" vs "matching".

http://books.google.com/books?id=wBlRtAlKPFsC&dq=%22impedance+bridging%22&q=bridging#search — Omegatron 19:50, 13 April 2007 (UTC)

"Second Device" vs. "Previous Device"
"It is a bridging connection if the second device does not appreciably load the previous device." Which is the "second" device? The load or the source? How is "previous" defined here? I'm pretty sure that this means that the source does not appreciably load the load device, but this language could be clearer. Steve carlson 23:27, 9 March 2007 (UTC)

Amp-versus-speaker not relevant at all!
The connection between an amplifier and speaker is not an instance of impedance bridging. Amplifiers are current sources.

The reason why a low output impedance is desired is for two reasons: damping, which is an electro-mechanical effect, and maximum power transfer to the speaker.

The purpose of this connection is not to pass along a signal to the speaker with minimal voltage drop, but to drop current into the speaker while dissipating as little heat as possible in the amplifier and controlling the speaker's motion. — Preceding unsigned comment added by 192.139.122.42 (talk) 23:46, 2 June 2011 (UTC)
 * I too saw this section and came here to comment that it's not relevant in an article about impedance bridging. The whole section should be deleted or moved somewhere else. — Brianonn (talk) 07:39, 12 September 2011 (UTC)
 * This section seems to be VERY important. There is too much lack of understanding.
 * Amplifiers are voltage sources. A voltage source allows maximum power transfer to the speaker. And .. it is often said the amplifiers has 8 Ohm, but the source impedance of the amplifier will be like 0.1 Ohm. Edited to show the peculiarities of this special bridging.
 * --AK45500 (talk) 12:56, 5 September 2018 (UTC)

Reference 404's
I'm just pointing out that the Rod Elliot reference now 404's. I found this article. http://sound.whsites.net/impedanc.htm but am not sure if it's equivalent. — Preceding unsigned comment added by Petergcook (talk • contribs) 00:52, 28 November 2016 (UTC)
 * seems to work --AK45500 (talk) 13:08, 5 September 2018 (UTC)

Move section "Maximizing power transfer given a fixed source impedance"
The section "Maximizing power transfer given a fixed source impedance" belongs better in Impedance_matching. Can I or can someone else just cut and paste it there, and just keep the first sentence or so here? Em3rgent0rdr (talk) 05:23, 25 May 2022 (UTC)


 * As a technical matter, you can copy and paste from one article to another. Just be sure that the edit summary where you paste it states where it came from. Constant314 (talk) 07:04, 25 May 2022 (UTC)
 * ok. Well what I ended up doing was trimming this article down to only be specifically about impedance bridging, and simply deleted stuff I deemed to not be about impedance bridging.  The other things like Damping factor and impedance matching are now in a "See also" heading at the end.  Those other articles were already pretty full, so I didn't even paste into those articles.
 * And then since this article became much smaller, I next tried to organize what was left into being two subheadings in an "Applications" heading, which are I've called "Receiving voltage signals from sources with unchangeable impedance" and "Maximizing power at a load with an unchangeable impedance" for now. Em3rgent0rdr (talk) 03:32, 26 May 2022 (UTC)

Couple of concerns
When a load is connected across a parallel transmission line, that load is bridged, regardless of its impedance. If one side of the transmission line is ground, or the environment, the load is still bridged regardless of the impedance. Bridging is a real thing. The power company, the gas company, and the water company all use it. Roman viaducts use it. Irrigation water distribution uses it. Trees use it to distribute nutrients. Impedance bridging seems to be a less general term. The only cited sources are from the audio engineering community. It has never been about efficiency. It is about convenience. We use it because it is available, and it works. If you only know the output impedance of a source, then you know nothing about its internal power dissipation. If the source is truly a voltage source, then maximum efficiency is approached with a near infinite load impedance. A synchronous generator probably well modeled this way. If the source is actually a current source, then maximum efficiency is approached with a near zero load. If the source internally is a voltage driving a voltage divider, then maximum efficiency is neither near infinite nor near zero. This model would apply to a battery with self-discharge leakage. Audio amplifiers are complicated and difficult to generalize. The whole efficiency discussion only applies in a mathematically hypothetical case. Again, it is not about efficiency. If you want the best efficiency to the electric system, then just shut the whole thing off.
 * Perhaps we should restrict the scope of this article to audio engineering.


 * I think that the entire efficiency discussion is unwarranted and is effectively OR. Constant314 (talk) 15:23, 14 June 2022 (UTC)


 * Regarding the term "impedance bridging", indeed when I google search, the only results are indeed from the audio community, so this term seems like a very audio-specific term. But the concept is more general and I'm wondering if there is a general term.  For instance, oscilloscope high impedance probes can be in the 1-10 megaohm range for a similar reason...but I'm wondering is there a general term for that practice?
 * Regarding conveninece, I'm not sure it *just* is about convenience. Audio world used to use 600 ohm as a standard for both output and input impedance, which was used for telephones, and that was "convenient" too.  But the audio world then switched to "impedance bridging" because it was better, both in reducing attenuation of the signal and reducing power consumption, so it is more efficient in terms of watts spent to produce useful output (to measure the signal) over total watts spent. Em3rgent0rdr (talk) 17:48, 14 June 2022 (UTC)
 * I believe that it is the convenience of being able to drive multiple loads that leads to the architecture of having a low impedance output with high impedance loads. In many other disciplines, we would call it a bus.  In the audio world attenuation is usually not important.  There is plenty of gain available to take care of attenuation except maybe in the case of unpowered microphones, but I think in those cases the microphones want a specific load impedance for the correct frequency response rather than minimizing attenuation.
 * The power levels are so low in audio, that efficiency is generally not a concern. The Electronics' operating power dwarfs the audio power.  Lost audio power just doesn't show up in the electric bill. Constant314 (talk) 19:53, 14 June 2022 (UTC)
 * The power capability of a pickup or mic is extremely low. So efficiency in getting the most use out of the power is very important. And that is why impedance bridging is used for receiving both mic and pickups. And also when powering speakers efficiently, impedance bridging is used instead of matching when want to efficiently get the most output sound power relative to input electric power (edit: even if concerned just with getting the most power output). That can be a significant amount of the power budget. Though I would say for the case of sending audio between devices at line level that what you say about the power efficiency isn't much of a concern because the power is small relative to the budget is true. Em3rgent0rdr (talk) 21:52, 14 June 2022 (UTC)
 * Perhaps some others will weigh in. It would be great to find some reliable sources saying that efficiency and attenuation were important considerations in choosing to use impedance bridging and not just a happy discovery after the fact.  I suspect people were paralleling speakers from the beginning of audio, even when the output impedances of the early tube amps were fairly high. Constant314 (talk) 01:46, 15 June 2022 (UTC)
 * I read your reference from Muzine. I have a few take-aways.
 * I see a fundamental misunderstanding of signal/noise ratio and attenuation. By default, you should always consider power and energy, because it is power and energy that do things.  It is OK to consider voltage, if the impedances are fixed.  But if are comparing circuits with different impedances, you have to compare power.
 * To make this concrete, let’s suppose you have a 600 ohm source producing 1mV and driving an amplifier with a 10K input impedance. You get 1mV at the input of the amplifier.  If you place a 600 ohm resister across the input of the amplifier, you do lose 6 dB.  That is because you did a dumb thing and threw half the signal away in the resister.  But that is not the way to do it when limited by s/n ratio.  Instead, you place a 1:4 transformer at the input of the amplifier.  You still see 6dB of voltage attenuation at the input to the transformer, but the transformer has a voltage gain of 12 dB.  You get 2mV at the input to the gain stage.  This means that you get twice the signal and signal to noise ratio with a proper match.  The advantage is not less attenuation nor better signal to noise ratio.  The advantage is that you have the convenience of not using an input transformer if you accept the disadvantage of 6db degradation. Constant314 (talk) 00:05, 16 June 2022 (UTC)
 * Ok, thanks. I tried to put your example into circuitjs:
 * Comparison_of_constant314_examples.png
 * Did I copy your example right? I see that the final voltage is much higher with this closely matched circuit.
 * I see the impedance bridge ratio results in .943 mV or -.51 dB. While the transformer results in 1.951 mV or +5.81 dB. Em3rgent0rdr (talk) 02:56, 16 June 2022 (UTC)
 * That is it. Constant314 (talk) 03:08, 16 June 2022 (UTC)
 * That is it. Constant314 (talk) 03:08, 16 June 2022 (UTC)

"Impedance Matching" article section on "Loudspeaker Amplifiers" seems more appropriate in "Impedance Bridging" article
The first sentence of reads:

"Audio amplifiers typically do not match impedances, but provide an output impedance that is lower than the load impedance (such as < 0.1 ohm in typical semiconductor amplifiers), for improved speaker damping."

So it seems that that entire section should just be cut from that article and pasted into this article. Maybe just leave a note saying that and linking to its new location in Impedance bridging.

Attempting to do impedance matching to achieve the goal of maximum power transfer to a speaker does have a significant downside of burning a lot of heat in the resistance of the output impedance.

Copyrighted material
There is a lot of material copied from copyrighted sources in the notes. Does this exceed fair use? Constant314 (talk) 04:00, 17 June 2022 (UTC)


 * Sorry, I probably did put too much quoted excerpt. I've removed the quote now. Em3rgent0rdr (talk) 04:46, 17 June 2022 (UTC)

Why mic preamp input impedance isn't nearly as large as input impedance of line or pickup.
There is a question that this page doesn't address, which is if large ratios are good, then why do mic preamps input impedance only go to about 10x of typical low impedance mics Why not use the same very high input impedance of line or pickup inputs. I found this explanation in https://www.soundonsound.com/techniques/understanding-impedance that there would be too much noise from resistors, which maybe could be paraphrased into this page:

"Typically, most microphones therefore have an output impedance of 150-200Ω, and most preamplifier inputs offer an input impedance of between 1.5kΩ and 3kΩ — on the limit of the 'ten times higher' rule of thumb I mentioned earlier. It is a good idea to keep the input impedance of mic amps relatively low (at least compared to typical line inputs) since resistors generate noise when current flows through them; the higher the resistance the greater the noise. Since the signal level from microphones is relatively weak, a lot of gain is generally required, amplifying the resistor noise along the way. This is the reason why mic preamp specs should quote the source impedance when providing the Equivalent Input Noise (EIN) measurement; the lower the source impedance, the lower the noise will be. A good EIN figure can be achieved for the spec sheet by measuring the input stage with a 50Ω source impedance. However, this noise figure will be totally unrealisable with a real-world 200Ω microphone!"

And regarding why it is crucial for guitar inputs to be very high:

"If the input has too low an impedance, the most noticeable effect will be a loss of high end — in fact, even using guitar cables with too high a capacitance can audibly reduce high frequencies"

And in a follow up article https://www.soundonsound.com/sound-advice/q-do-i-need-think-about-matching-mic-and-preamp-impedances says both "In fact, there can be benefits in using a higher input impedance to reduce the source loading even more" than 10x, though also talks about sometimes people like the coloration from using lower input impedances. Em3rgent0rdr (talk) 06:45, 17 June 2022 (UTC)


 * I think you are getting into out-of-scope system issues. The guitar pickup is, I believe, inductive.  Any significant loading whether resistive or cable capacitance would interact with that to produce a high frequency roll off.  This isn't a bridging vs reflectionless issue. It is about making it work with a specific source, load, and cable. Constant<b style="color: #4400bb;">314</b> (talk) 21:46, 17 June 2022 (UTC)