eth2 Posted December 11, 2014 Share Posted December 11, 2014 I am confused about driver impedance. I understand the concept of impedance, but what are the practical implications for a system. Specifically, if I go with a 6 ohm driver, how does that effect the type and build of the crossover. In a K'horn, what other factors need to be considered if I go to a 6 ohm driver rather than the 16 ohm K-55? Thanks again Quote Link to comment Share on other sites More sharing options...
mboxler Posted December 11, 2014 Share Posted December 11, 2014 What crossover is installed? This will make it easier to describe the impact. Mike Quote Link to comment Share on other sites More sharing options...
eth2 Posted December 11, 2014 Author Share Posted December 11, 2014 I have just bought Eliptrac horns and tweeters. I now know I cannot use the standard Klipshorn crossovers. I was considering buying a set of AP-12 350's. A friend has offered to sell me a pair of Electro Voice EV DH1A's (6 ohm) for the Eliptrac's. I am using a 40 watt tube amp at present with the Khorns. 1 Quote Link to comment Share on other sites More sharing options...
mboxler Posted December 11, 2014 Share Posted December 11, 2014 I believe the AP-12 350's have a 10 ohm "swamping" resistor across taps 0 and 5 of the autoformer. A 16 ohm driver attached to the -6 db taps actually increases the impedance the amplifier "sees" by a factor of 4, in this case the driver's impedance is now 64 ohms. A 10 ohm resistor in parallel with a "64" ohm driver looks like 8.6 ohms of resistance. Replacing the 16 ohm driver with a 6 ohm driver, using the same taps, would be 6 X 4 or 24 ohms. A 10 ohm resistor in parallel with a "24" ohm driver looks like 7 ohms of resistance. That 1.6 ohm difference probably won't make much of a differance. If you replaced the swamping resistor with, say, a 14 ohm resistor, the difference would be even less. An e-mail to Al at alkeng.com might ease your mind Hope this helps. Mike 1 Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted December 11, 2014 Share Posted December 11, 2014 I am confused about driver impedance. I understand the concept of impedance, but what are the practical implications for a system. Specifically, if I go with a 6 ohm driver, how does that effect the type and build of the crossover. In a K'horn, what other factors need to be considered if I go to a 6 ohm driver rather than the 16 ohm K-55? Thanks again Are you talking about impedance or resistance? 1 Quote Link to comment Share on other sites More sharing options...
eth2 Posted December 11, 2014 Author Share Posted December 11, 2014 Thanks, Mike. I guess all I am sure of is that this is a 6 ohm driver, not the 16 ohm driver Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted December 11, 2014 Share Posted December 11, 2014 Are you talking about impedance or resistance? I used to drive my electrical engineering professors nuts with this. Quote Link to comment Share on other sites More sharing options...
djk Posted December 12, 2014 Share Posted December 12, 2014 "I guess all I am sure of is that this is a 6 ohm driver, not the 16 ohm driver" That means it's the 8Ω version, move it down one tap on the crossover and all should be well. 1 Quote Link to comment Share on other sites More sharing options...
pzannucci Posted December 12, 2014 Share Posted December 12, 2014 (edited) When using an auto-former / auto-transformer, I believe the impedance changes with the turns ratio within the transformer. As djk said, you can change the tap to change the impact on the crossover point to get a driver that is not the correct impedance back closer to the original drivers impedance. The impact on crossover points will be determined by the end result of both components put together impedance. You can look at the DIY audio's site for "crossover designer" to see various impacts of an impedance change on the component values. Impact on sound, you won't know until you try it. Does the driver have the same efficiency and usable frequency range? Since you already know what drivers you are trying to switch to, you can follow what has been everyone has said here. If you find out it is not adequate for your ears, the above information I put in will be helpful in you in your tweaking quest. Generic solutions are good but not optimal. Edited due to brain fade Edited December 12, 2014 by pzannucci Quote Link to comment Share on other sites More sharing options...
eth2 Posted December 12, 2014 Author Share Posted December 12, 2014 Thank you Quote Link to comment Share on other sites More sharing options...
mboxler Posted December 12, 2014 Share Posted December 12, 2014 When using an auto-former / auto-transformer, I believe the impedance changes with the turns ratio within the transformer. So if the is a 2 to 1 turn ratio, impedance should double. Actually, The impedance changes by the square of the turns ratio https://drive.google.com/viewerng/viewer?url=http://www.critesspeakers.com/3636atz.pdf Again, unless someone disagrees, the 10 ohm resistor in parallel with the varying impedance changes will eliminate the need for crossover mods. Without that resistor, every tap change would require modification of the squawker filter. If this were, say, a stock AA crossover, the 13uf cap to the K-55 would need to be replaced with a different value for each tap change. Otherwise, the crossover frequency would change. The 13uf cap's impedance is around 31 ohms at 400 Hz, matching the K-55 impedance doubling that the 0 - 4 output taps create. Cheers Mike Quote Link to comment Share on other sites More sharing options...
pzannucci Posted December 12, 2014 Share Posted December 12, 2014 When using an auto-former / auto-transformer, I believe the impedance changes with the turns ratio within the transformer. So if the is a 2 to 1 turn ratio, impedance should double. Actually, The impedance changes by the square of the turns ratio https://drive.google.com/viewerng/viewer?url=http://www.critesspeakers.com/3636atz.pdf Again, unless someone disagrees, the 10 ohm resistor in parallel with the varying impedance changes will eliminate the need for crossover mods. Without that resistor, every tap change would require modification of the squawker filter. If this were, say, a stock AA crossover, the 13uf cap to the K-55 would need to be replaced with a different value for each tap change. Otherwise, the crossover frequency would change. The 13uf cap's impedance is around 31 ohms at 400 Hz, matching the K-55 impedance doubling that the 0 - 4 output taps create. Cheers Mike Mike, Thanks for that correction. I was looking at current vs impedance. As for the other, your solution might work but if their are efficiency and response differences in the drivers, you may want to know a little more about the interaction of the components. I find the calculator very handy along with other items referenced off that web page on DIY. Quote Link to comment Share on other sites More sharing options...
mboxler Posted December 12, 2014 Share Posted December 12, 2014 When using an auto-former / auto-transformer, I believe the impedance changes with the turns ratio within the transformer. So if the is a 2 to 1 turn ratio, impedance should double. Actually, The impedance changes by the square of the turns ratio https://drive.google.com/viewerng/viewer?url=http://www.critesspeakers.com/3636atz.pdf Again, unless someone disagrees, the 10 ohm resistor in parallel with the varying impedance changes will eliminate the need for crossover mods. Without that resistor, every tap change would require modification of the squawker filter. If this were, say, a stock AA crossover, the 13uf cap to the K-55 would need to be replaced with a different value for each tap change. Otherwise, the crossover frequency would change. The 13uf cap's impedance is around 31 ohms at 400 Hz, matching the K-55 impedance doubling that the 0 - 4 output taps create. Cheers Mike Mike, Thanks for that correction. I was looking at current vs impedance. As for the other, your solution might work but if their are efficiency and response differences in the drivers, you may want to know a little more about the interaction of the components. I find the calculator very handy along with other items referenced off that web page on DIY. I'm just learning this stuff, and the terms still confuse me I agree that there are many factors to designing a passive crossover. The OP was referring to driver nominal impedance only. A drivers impedance curve varies so much by frequency, that crossover calculators are guidelines at best. I'm leaning more and more towards active crossovers. They seem to make more sense to me. Mike Quote Link to comment Share on other sites More sharing options...
djk Posted December 12, 2014 Share Posted December 12, 2014 "Again, unless someone disagrees, the 10 ohm resistor in parallel with the varying impedance changes will eliminate the need for crossover mods. " Prove it mathematically (you can't), it reduces variations, it does not eliminate them. The EV is 110dB/W on a horn with a Q=7, so is the K55V. If you move the 8Ω EV down a tap it should play the same level as the 16Ω K55V and have the same crossover point. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted December 13, 2014 Share Posted December 13, 2014 The DCR is fixed and the impedance isn't unless the frequency is fixed. Impedance is based on ACR, and worse it's a moving AC frequency. Quote Link to comment Share on other sites More sharing options...
mboxler Posted December 13, 2014 Share Posted December 13, 2014 Guess I have a lot to learn I'd appreciate it if someone would correct my math... The 8 ohm and 16 ohm drivers have equal sensitivities...110 db @ 1 watt. The 8 ohm driver would need a 2.83 volt signal to generate 110 db. The 16 ohm driver would need a 4 volt signal to generate 110 db. Putting the 16 ohm driver on the 0 - 4 taps would double its impedance to 32 ohms. 4 volts into 32 ohms equals 1/2 watt, which equals 107 db. Putting the 8 ohm driver on the 0 - 3 taps would quadruple its impedance to 32 ohms. 2.83 volts into 32 ohms equals 1/4 watt, which equals 104 db. Yes, the "crossover frequency" is unchanged, but the wouldn't the amplitude would be different? djk is correct. If I have this math wrong, I have everything wrong! Thanks, Mike Quote Link to comment Share on other sites More sharing options...
The Dude Posted December 13, 2014 Share Posted December 13, 2014 Not to go to far off topic, but if one is running a active crossover with amps that have different ohm taps should you go with the correct ohm tap for the driver. I guess my question would picking the same corresponding ohm tap to match the driver be the same as what eth2 is talking about with passive networks. Quote Link to comment Share on other sites More sharing options...
djk Posted December 13, 2014 Share Posted December 13, 2014 "but the wouldn't the amplitude would be different?" What are you on about? My head hurts, this is so simple. Feed 5.6V into tap 5, you get 4V on tap 4, and 2.8V on tap 3. 4V is 1W/16Ω, 2.8V is 1W/8Ω Both drivers are 110dB/W, so what is it you don't understand? Quote Link to comment Share on other sites More sharing options...
mboxler Posted December 13, 2014 Share Posted December 13, 2014 "but the wouldn't the amplitude would be different?" What are you on about? My head hurts, this is so simple. Feed 5.6V into tap 5, you get 4V on tap 4, and 2.8V on tap 3. 4V is 1W/16Ω, 2.8V is 1W/8Ω Both drivers are 110dB/W, so what is it you don't understand? Thanks for the clarification. And sorry about the headache. I knew I had something wrong...just couldn't see it. The turns ratio on tap 4 is 1.414. In your example, 5.6 volts / 1.414 = 4 volts. The turns ratio on tap 3 is 2.000 5.6 / 2 is 2.8. My apologies to the OP. Mike Quote Link to comment Share on other sites More sharing options...
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