Hi:
A couple things....
Elizibeth..how goes it? Your analogy to language is fine except it covers only part of the issue. If impedances are matched you get more power. (Power = current x voltage.)But a mismatch in impedances is not just for stability.
Power is not always the goal and sometimes you want to avoid it because you do not want to load down the prior circuit. For example, if you are in the front-end (pre) of a system with a small voltage that you want to pass to the amp you want a small to larger impedance in order to do it. One of the reasons a tube's grid is used to develope the signal is that it has an almost* infinite resistance. Perfect for developing a voltage signal. Anyway, what I wanted to emphasize is that in order to think about "matching impedance" you have to figure out what the goal is. transferring voltage or current.
Esteemed Dr. Greenman:
I am not a physicist but I know how amps work. You certainly are matching impedances from amp to speaker. This is at the heart of the OTL issue in fact. The primary purpose of a transfermer in a tube amp is to match the output tube plate circuit, which requires a large (some thousands of ohms) impedance as a load, to a speaker that is small impedance (2-8typically). The impedance is changed by the square of the turns ratio of the output transformer. This is the fist thing you must spec in a transformer. This is the primary reason conventional tube amps have transformers and why OTLs are, well, different. Now most folks don't need to know this except it makes it easier to understand that when they look at the 4 and 8 ohm taps on their amp they are looking at different taps to the transformer's secondary and using one tap or the other
changes the turns ration, which in turn, changes the nominal impedance match from amp to speaker.
A further note, most amps would do a lot better if the folks who built knew what speakers were going to be attached to them because they would know the load. Unfortunately we are all in love with separates.
Matching Z takes place through the entire system, is not limited to transmission lines as you seem to suggest, and IMHO, if folks understood it (and a little RLC) about 3/4 of the magic and synergy would disappear from the wires used in audio. It is fatal if overlooked with passive pres and such. There are many places you can go to get a little more on this simple point and, if anyone is interested, you might try online. Here is one short piece.
http://www.aikenamps.com/OutputTransformers.html
Sincerly
I remain
not a physicist, and
A couple things....
Elizibeth..how goes it? Your analogy to language is fine except it covers only part of the issue. If impedances are matched you get more power. (Power = current x voltage.)But a mismatch in impedances is not just for stability.
Power is not always the goal and sometimes you want to avoid it because you do not want to load down the prior circuit. For example, if you are in the front-end (pre) of a system with a small voltage that you want to pass to the amp you want a small to larger impedance in order to do it. One of the reasons a tube's grid is used to develope the signal is that it has an almost* infinite resistance. Perfect for developing a voltage signal. Anyway, what I wanted to emphasize is that in order to think about "matching impedance" you have to figure out what the goal is. transferring voltage or current.
Esteemed Dr. Greenman:
I am not a physicist but I know how amps work. You certainly are matching impedances from amp to speaker. This is at the heart of the OTL issue in fact. The primary purpose of a transfermer in a tube amp is to match the output tube plate circuit, which requires a large (some thousands of ohms) impedance as a load, to a speaker that is small impedance (2-8typically). The impedance is changed by the square of the turns ratio of the output transformer. This is the fist thing you must spec in a transformer. This is the primary reason conventional tube amps have transformers and why OTLs are, well, different. Now most folks don't need to know this except it makes it easier to understand that when they look at the 4 and 8 ohm taps on their amp they are looking at different taps to the transformer's secondary and using one tap or the other
changes the turns ration, which in turn, changes the nominal impedance match from amp to speaker.
A further note, most amps would do a lot better if the folks who built knew what speakers were going to be attached to them because they would know the load. Unfortunately we are all in love with separates.
Matching Z takes place through the entire system, is not limited to transmission lines as you seem to suggest, and IMHO, if folks understood it (and a little RLC) about 3/4 of the magic and synergy would disappear from the wires used in audio. It is fatal if overlooked with passive pres and such. There are many places you can go to get a little more on this simple point and, if anyone is interested, you might try online. Here is one short piece.
http://www.aikenamps.com/OutputTransformers.html
Sincerly
I remain
not a physicist, and