RickMo Posted June 1, 2003 Share Posted June 1, 2003 I'm familiar with speaker impedance and Ohm's law but I've a question about real world situations. My Yammie receiver (5550) wants rear surrounds at a minimum of 6-ohms. What's the potential for "real world" problems if I use 4-ohm speakers (kg 2)? I know the 4-ohm speakers will or might create a strain on the amp but in reality, will it? Quote Link to comment Share on other sites More sharing options...
bkrop Posted June 1, 2003 Share Posted June 1, 2003 What are your main speakers, my yammie can run 4 ohm mains and 8 ohm rears but not 4 ohm all around. Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 1, 2003 Author Share Posted June 1, 2003 Forte II's upfront with an SC-1 center channel. Each is 8 ohm impedance. Quote Link to comment Share on other sites More sharing options...
bkrop Posted June 1, 2003 Share Posted June 1, 2003 Unbalanced loads presented to the amp can shorten the life of an amp, so I looked long and hard to find one that can. I have been told this and rember from reading manuels that the recievers I have owned ( stereo) that you could use sp A or spB @4ohm but not A+B , 8 ohm you could do aA+B. Quote Link to comment Share on other sites More sharing options...
bkrop Posted June 1, 2003 Share Posted June 1, 2003 Just looked at the book for my Yamaha RXV-800, the lowest rating for surrounds it can be set for is 6ohm. I would not take a chance. Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 1, 2003 Author Share Posted June 1, 2003 Yeah, it would be a chancey situation. I can see why combining the A speakers with the B could be a problem. If all the speakers are 4 ohm, the A+B would probably put them in parallel, making the load the amp sees as 2 ohm. That would be taxing. What helps though is the Yammie's internal circuitry which, theoretically, would shut down the surrounds (or any speaker) if it's going to harm the amp. I'm unsure as to what I'm gonna do ... Thanks for your input. Quote Link to comment Share on other sites More sharing options...
lubbie Posted June 3, 2003 Share Posted June 3, 2003 Your worries are justified. Most amplifiers parallel the speakers in the A + B position. DC resistance and AC impedance are compleatly differant. Your 4 ohm rated speakers will more then likely show the amp less then 1/2 ohm under use(yes almost a short)and alot of bipolar output amps don't like this and will short if pushed too hard. Here is the other thing. When you run a amp that is designed for minimum of 6 ohms down below the 4 ohms range and lower under normal operating conditions you end up with large amount of distortion because the amp just runs out of gas. I've watched people do this and smoke the amp, then bring it to me to fix. I gladly handed them a big bill... Anouther solution would be to put another pair in series with the surrounds you have, bring the dc resistance to about 7.5 ohm and an impedence of about 8 ohms and under heavy use the amp may see as little as 4 ohms impedance. Running the amp with higher impedance will never hurt and in the end the amp will last longer with less distortion. Hope that helps. Ralph Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 3, 2003 Share Posted June 3, 2003 agreed that, depending on the protection circuits within the amp, running lower than recommended impedance speakers could result in damage to your amp. on the other hand higher impedance does nothing more than lower the output of the speaker. so the idea of another pair could be a solution. my electronics backgournd is weak but let me float this as se if any techies say yes or no...how about adding a wirewound 4 or 8ohm power resistor in series with the speaker? wouldn't that assure higher impendance? regards, tony Quote Link to comment Share on other sites More sharing options...
efzauner Posted June 3, 2003 Share Posted June 3, 2003 Adding a resistor in series would certainly increase the impedance of the speakers. But why not just add a 2 Ohm resistor instead? Say 2 4ohm power resistors in parallel or 4 8ohm resistors in parallel. That would bring up the impedance to 6 ohms. It would also reduce the wasted power compared to a 4 ohm resistor. Adding a resistor would also reduce the damping factor, but if you surrounds are small, and you set your receiver for small surrounds, less bass will go to the surrounds and reduced damping will not be a problem at all. Certainly alot cheaper than getting new speakers! Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 3, 2003 Author Share Posted June 3, 2003 Great ideas, gentlemen. I had toyed with the idea of adding resistors in series and I think that may be my solution. I do like the idea of adding another set of speakers, too, but my budget won't allow it. I'll hop on over to partsexpress.com and see what they've got. Thanks for all the input. It's been very helpful and much needed. Quote Link to comment Share on other sites More sharing options...
efzauner Posted June 3, 2003 Share Posted June 3, 2003 4 8 ohm 5 watt resistors in parallel should do the trick. That would be 20 watts total. I series with 4 ohm speaker will handle a total of 60 watts. In other words, the 2 ohm resistor needs to handle a third of the total power from the amp. Quote Link to comment Share on other sites More sharing options...
lubbie Posted June 3, 2003 Share Posted June 3, 2003 The only reason i suggested another speaker is because who wants to waist amplifier power on creating heat. I'd rather create music. Even in a Canadian winter I dont need heat in my entertainment room with the amps i run. Series resistors will promote noise. Yes resistors are noisy, unless you use a high quality metal film resistor. Common upgrade to old amps is to replace the old carbon resistors with quality films, when they are in the signal path. I have no experience in electronics. Okay, maybe just a little.15 long and grueling years making no money, and am still enjoying it. Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 3, 2003 Author Share Posted June 3, 2003 I posted this similar question over on Partsexpress.com regarding what TYPE of resistor to use since I was planning on doing the resistor-thingie. One responder said that on one hand that's doable, but, he said, adding a resistor would change the characteristics of the speaker, specifically the woofer. (He figured that the box would look too small for the woofer, though he didn't explain how). His ultimate solutions to the problem was to fuse each speaker. (If only the KG2 were 8 ohms I wouldn't have this problem.) Quote Link to comment Share on other sites More sharing options...
lubbie Posted June 3, 2003 Share Posted June 3, 2003 My god. did he know what he was talking about??? The resistors don't change the speakers at all, they just limit the current flow. And the fuses are used for what?? Noise generators? Fuses were used to prevent excessive current flow throught the output transistors if the speaker should short. Common in the early years of speakers, but nowadays almost never. The fuses were not there to protect the speakers, they were there to protect the amp. Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 4, 2003 Author Share Posted June 4, 2003 Lubbie, in a way, the "solution" on partexpress of using a fuse would be to protect the amp, not the speakers. And as you stated previously, a 4-ohm impedance load could, at times, go down to 1/2 ohm, almost a dead short. That would tax the amp. However, you do bring up a point about a fuse becoming a noise generator. Things start getting complicated electrically when dealing with fluctuating frequencies and I'm uncertain as to the adverse effect of a fuse. Quote Link to comment Share on other sites More sharing options...
lubbie Posted June 4, 2003 Share Posted June 4, 2003 Well with all the years fixing big amps on monitor speakers my ears don't hear the differance. Others say the fuses make a differance. Who knows. Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 4, 2003 Author Share Posted June 4, 2003 Lubbie, I don't think my 54-year-old ears can hear the difference either. Maybe when I was 17, but ... Quote Link to comment Share on other sites More sharing options...
WMcD Posted June 4, 2003 Share Posted June 4, 2003 I've posted this solution elsewere on the forum from time to time. I was faced with the problem of driving Quartets from the speaker leads of an old Trinitron. (This required taking the Trinitron apart. Anyway. . . . I used the primary windings of an RS 70 volt line transformer as an autotransformer. They cost about $10. You'll see that one side of the transformer has taps labeled C, 4, 8, and 16 ohms. That is the side you want to use. Not the one labeled in watts. Hook the amp output plus (red) to the 16 ohm tap. Hook the amp minus (ground or black) to the C. Hook the speaker input plus (red) to the 4 ohm tap. Hook the speaker minus (ground or black) to the C. Granted, this will take soldering skills. However, this is a way of altering the impedance the amp sees. You loose some voltage. If the sound is too much reduced, hook the plus to the speaker to the 8 ohm tap. Gil Quote Link to comment Share on other sites More sharing options...
RickMo Posted June 5, 2003 Author Share Posted June 5, 2003 Wow! I had completely forgotten about the ol' 70 volt line transformers. I used them back in the '70s for a P.A. system but haven't had much calling for them ... maybe until now. I like this idea. I'll see if partsexpress might have them. Thanks for the tip. Quote Link to comment Share on other sites More sharing options...
efzauner Posted June 5, 2003 Share Posted June 5, 2003 Guys GUys GUYS!!! A 2 ohm resistor will generate less noise than the 4 ohm Speaker coil! And I have never come across anyone complaining that speaker voice coils are noisy! Noise in resistors are of concern in preamps, preamp stages of power amps, but NOT IN SPEAKERS! Also, it is carbon type resistors that are the culprit, not wirewound power resistors. For a good link see http://www.aikenamps.com/ResistorNoise.htm As for power robbing, yes a 2 ohm resisor in series with a 4 ohm speaker will dissipate one third of the power as heat. That will result in a 1.8 db power loss. I suspect if you change speakers, the difference in efficiency may be in the same range, making any difference hardly noticeable! As for fuses, they are straight wire that melts when too much current goes thru. Yes they have a tiny bit of resistance (that is how they heat up and melt), but again negligible compared to the resistance in the speaker cable and voice coil! Come on gentlemen, do your homework first! This info is easy to find on the web1 If you don't, you will be talked into buying $5000 power cords that cost $20 to make! I will add "No Bull ****" to my signature! This board needs a bit of it now and then! and PWK will be proud! Quote Link to comment Share on other sites More sharing options...
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