This is only partly true.Originally posted by n9xv@Feb 16 2006, 02:43 PM
Impedance matching is (and should be) used anywhere your interfacing/transfering a signal from one point to another. A quick example;
Mic to audio amp
Antenna to transmitter
preamp to driver, driver to amp, amp to power amp etc.
You ideally want the output impedance of one device to "match" the input impedance of another device so as to have maximum power transfer. Maximum power transfer means minimum power lost due to a mismatched load and thus ultimately to heat.
An audio microphone with an impedance of 600-ohms wont drive a 50-Kohm amp or have the predictable response as a mic with 50-kohm impedance.
Impedance matching is very important!
[post=14084]Quoted post[/post]
Apparently you know more about this than a company that's been making microphones for many years.Originally posted by n9xv@Feb 17 2006, 05:30 PM
Its true that the audio devices will seem to "work", but the best response will always be acheived when the impedances are matched. More drive may actually be required with matched impedance Vs mismatched impedance. At any rate thats speaking of the mic sensitivities at the input. The output if its of any significant power level, must be matched or it will "smoke"!
[post=14136]Quoted post[/post]
I did'nt say it would'nt "work". I said the best response will be acheived with matched impedance. There's a difference between simply hearing it and getting the expected response from the amp in question.Originally posted by Ron H@Feb 17 2006, 07:10 PM
Apparently you know more about this than a company that's been making microphones for many years.
Do you also believe that audio amplifier output impedance should match the speaker impedance?
[post=14138]Quoted post[/post]
I thought the amp would burn not because impedance mismatch, but because the output stage is overloaded. Assuming the voltage stay fairly constant, the amp had to provide twice the current at 4 ohm and dissipate close to twice the normal heat. Running an amp designed for 4 ohm with 8 ohm speakers, I think is not dangerous. You do get less power out, but nothing close to catastrophy.Originally posted by n9xv@Feb 19 2006, 04:12 PM
Try runing 50,000 watts into a 4-ohm speaker system, from an amp designed for an 8-ohm system or vice/versa. you'll have very short tube/transistor life lest it burn before your eyes. At high power levels impedance matching is crucial!
[post=14174]Quoted post[/post]
I think you've just proved that it is not matching the output impedance of the amp to the impedance of the speaker that's important, but observing the drive capability of the amp by selecting an appropriate speaker impedance so the amp is not overloaded during operation. Using an 8 ohm speaker with an amp designed for 4 ohm, although also constituted as an impedance mismatch per your example, would not be dangerous because the amp is not overloaded and per your example above would only deliver half the output current (although heat dissipation on the output power stage of the amp wouldn't necessarily be halved).Originally posted by n9xv@Feb 20 2006, 02:47 PM
When you change the impedance of the load, you radically change the limitations of the amp or device in question. Any audio device (especially high power devices) specifies the proper output impedance which must be seen by the output. For high end audio, there's a reason for that. The amp itself is designed starting with the load impedance and working back towards the power supply. When an amp designer sits at the drawing board, he starts with the load. Decides on a power level, at that point he knows what the power supply will be required to deliver. He then chooses the output devices that are best suited for this power level, tubes/transistors etc. Before an amp can be designed to deliver X amount of power reliably for X amount of time, you must know the impedance of the load it will be delivering all this power to! Impedance is very important to those who understand it.
Example of the 50,000-watt amp;
50,000 watts into an 8-ohm load is 79-amps. 50,000 into a 4-ohm load is 112-amps. When this magnificent amp is "maxed" out at its "designed" output of 50,000-watts into 8-ohms (79-amps of current), you are going to ask it to deliver an extra 33-amps into a 4-ohm load when maxed! Thats asking quite alot from an amp thats maxed at its design limits already! The power supply alone would cook.
You would have distortion due to clipping (MPP exceeded) etc.
As I said earlier, it would work for a while at lower power levels and up to a point. But if your running any real power, its a good way to destroy an amp.
[post=14208]Quoted post[/post]
It seems to me you are not talking about output impedance of the amp, becase if it should match the load, you would have to add 8 ohm 25,000Watt resistor in series with the amp, because audio amplifiers have out put imp. very close to zero.Originally posted by n9xv@Feb 20 2006, 03:47 PM
When you change the impedance of the load, you radically change the limitations of the amp or device in question. Any audio device (especially high power devices) specifies the proper output impedance which must be seen by the output. For high end audio, there's a reason for that. The amp itself is designed starting with the load impedance and working back towards the power supply. When an amp designer sits at the drawing board, he starts with the load. Decides on a power level, at that point he knows what the power supply will be required to deliver. He then chooses the output devices that are best suited for this power level, tubes/transistors etc. Before an amp can be designed to deliver X amount of power reliably for X amount of time, you must know the impedance of the load it will be delivering all this power to! Impedance is very important to those who understand it.
Example of the 50,000-watt amp;
50,000 watts into an 8-ohm load is 79-amps. 50,000 into a 4-ohm load is 112-amps. When this magnificent amp is "maxed" out at its "designed" output of 50,000-watts into 8-ohms (79-amps of current), you are going to ask it to deliver an extra 33-amps into a 4-ohm load when maxed! Thats asking quite alot from an amp thats maxed at its design limits already! The power supply alone would cook.
You would have distortion due to clipping (MPP exceeded) etc.
As I said earlier, it would work for a while at lower power levels and up to a point. But if your running any real power, its a good way to destroy an amp.
[post=14208]Quoted post[/post]
I don't think there are any here who would dispute that. My understanding of the OP's question was, do you have to match (meaning equal) source and load resistances. There are definitely places where you need to do that: Transmission line terminations (not always necessary, but sometimes), antennas, etc. There are many other source/load combinations where it is definitely not the best thing to do - including audio power amplifiers.Originally posted by n9xv@Feb 20 2006, 02:42 PM
The following is an exerpt from Shavano music online that re-enforces my point about the importance of proper impedance at significant power levels.
"Your goal is usually to load your power amplifier somewhere between 4 and 16 ohms (refer to your power amplifiers documentation to be absolutely certain of its limitations and never provide a load lower than the system was designed for). "
As I stated earlier, you should never run power into a load that is lower than the amp was designed for.
Going the other way, if you connect the power amp into a load that is higher than what the amp was designed for, your preventing the amp from delivering the amount of power the amp "could" deliver if it were connected to a matched load.
An amplifier's power rating is based on a specified load impedance. Without a specified load impedance, the rating means absolutely nothing.
Shavano Music Online
[post=14220]Quoted post[/post]
As Ron H stated above, this is not an impedance mismatch problem, but more of using the correct load impedance to achieve the designated performances. Your excerpt from above seems to support this argument.Originally posted by n9xv@Feb 20 2006, 09:42 PM
The following is an exerpt from Shavano music online that re-enforces my point about the importance of proper impedance at significant power levels.
"Your goal is usually to load your power amplifier somewhere between 4 and 16 ohms (refer to your power amplifiers documentation to be absolutely certain of its limitations and never provide a load lower than the system was designed for). "
As I stated earlier, you should never run power into a load that is lower than the amp was designed for.
Going the other way, if you connect the power amp into a load that is higher than what the amp was designed for, your preventing the amp from delivering the amount of power the amp "could" deliver if it were connected to a matched load.
An amplifier's power rating is based on a specified load impedance. Without a specified load impedance, the rating means absolutely nothing.
Shavano Music Online
[post=14220]Quoted post[/post]
That's what we've been saying all along, for RF amp it is absolutely necessary as you've so clearly explained above. However, for audio amplifier and speaker this is not the case. You argued that high power audio amplifier requires matching output stage impedance and speaker impedance, but this is not the case. Your previous excerpt shows that it is only necessary to select suitable load impedance, not matching it to the amp output stage impedance. Several other members had pointed out that the output stage impedance of audio amp is very low, much lower than the common 8, 4 or 2 ohm speaker impedances.Originally posted by n9xv@Feb 21 2006, 02:15 PM
With the possible exception of "front end" entertainment audio, the impedance of a load must match its source for maximum effeciency and proper operation. This is critical in RF work as well. A random wire antenna that yeilds 500-ohm impedance connected to a solid state tranceiver with 50-ohm impedance is going to be very ineficient and destroy the output power transistors without a means of tuning/matching the antenna to the transmitter. 500:50 is an SWR of 10:1. An SWR of 10:1 translates to a reflected power of 66.9-%. At an SWR of 3:1 (150:50) the reflected power is 25-%. In RF work, an SWR of 1.5:1 (.04-% reflected) is considered acceptable. The average guy running a "thumper" car stereo is probably running it into a somewhat mismatched load. Unless he's running it full bore 24/7, he'll probably never realize the error of his demize. If however, he were to do a case study and document the "life" of his power amp with a mismatched load Vs a properly matched load, He would realize a bit more "milage" from the properly matched scenario.
[post=14240]Quoted post[/post]
by Duane Benson
by Duane Benson
by Don Wilcher
by Duane Benson