Serious Impedance help for JBL n24 + vr-507

Discussion in 'Archived Threads 2001-2004' started by Jeff Sch., Dec 30, 2001.

  1. Jeff Sch.

    Jeff Sch. Stunt Coordinator

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    I just recieved all my speakers and didnt really think about if the speakers would be compatible with my Kenwood VR-507 reciever. I just suspected they would. Maybe they are, and i just need some help.

    Basically, i bought these speakers

    JBL N26's fronts

    JBL N24's Rears

    JBL ncenter

    and was reading over there specs when i realized it said the nominal impedance for the N26's and Ncenter was 8ohms while the nominal impedance for the N24's was 6ohms.

    After checking things out, the Kenwood vr-507 says nothing about supporting 6 ohms and seems only to support 8ohms.

    Please help me out and tell me what to do. This is my 1st ht that i financed for my dorm rooms and I dont want to screw anything up.

    I also have 30ft ea. 16g monster xphp wire for rears and 10ft. ea 16g monster xphp wire for my fronts.
     
  2. Sean Conklin

    Sean Conklin Screenwriter

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    I use exactly what you do, only my receiver is the 407.

    My N-24 specifications (owners guide) says the nominal impedance is 8 ohms! Not 6.

    Besides I wouldn't concern myself with ohms, nominal ratings are not an accurate indication of a speakers true resistance. I've read tests where most speakers regardless of rating will fluctuate between 2 and 16 ohms, depending on volume and frequency.

    Just hook 'em up and enjoy, it seems this system is made for each other, I can testify I am very happy with my set up!
     
  3. Steve Berger

    Steve Berger Supporting Actor

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    As a service tech for 30 years I have found that running an 8 ohm amp into a 6 ohm load for an extended period usually kills the outputs. It might not happen right away but all it takes is the right combination of heat,volume level,source material,or turn-on surge and POP, you're in my shop and I'm trying to figure out why your previously perfect amp just died. Any company that won't tell you impedence amd RMS wattage of their speakers is usually hiding something.
     
  4. Sean Conklin

    Sean Conklin Screenwriter

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    Steve, the N-24's do give you RMS and impedance specs, the N-24's are 8 ohm rated. But even if you were to run a 6 ohm speaker as a surround it wouldn't be like it was being continuously driven.

    Your a tech, you probably know about speakers and ohms, can you confirm that speakers rated in nominal impedance(all speakers that I know of), the resistance will fluctuate considerably depending on volume and frequencies?
     
  5. Steve Berger

    Steve Berger Supporting Actor

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    Well, I'm not positive but I think that impedence remains constant while resistance varies.An Electrical enginer would probably know. This is why it is so hard to measure impedence with an ohmmeter (DC not AC) and it is so valuable for the manufacturer to list specs. Many of their specs are things like "8 ohm compatible" and "usable with amps from 20 to 200 watts" rather than real numbers.

    As far as surround output , it depends on internal wiring as to what will work. A DD/DTS amp might be forgiving as long as they didn't cut corners on components. A surround amp might be very forgiving if they wire the two speakers in series (12 ohm load)or very unforgiving if they wire in parallel (3 ohm load)

    As long as the mains and center are 8 ohm and not 8 ohm compatible he will probably be OK but I wouldn't boost the rear very much.
     
  6. Chu Gai

    Chu Gai Lead Actor

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    Jeff i don't believe you've anything to worry about whatsoever. your speakers and receiver are quite 'normal' and should have no problem meshing with each other. however to alleviate your concerns, consider contacting both kenwood and jbl about your system. that should put you at ease.
     
  7. Chuck Kent

    Chuck Kent Supporting Actor

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    I'm struggling with some of the viewpoints in this thread, so I'm posting my thoughts as an alternative opinion.

    Can you safely drive 6 ohm rated speakers with an 8 ohm rated receiver? IMO, most certainly!

    Should you have any concerns?? Again, most certainly. But not (IMO) for some of the reasons given above.

    Receiver failures indeed occur due to combinations of heat, high volume playback levels and surges. But none of these problems go away if one connects 8 ohm rated speakers to a receiver rated to drive 8 ohm loads (surges for one!) And likewise, these problems don't necessarily occur automatically if one connects speakers that have impedence ratings below 8 ohms.

    What (IMO) does matter are a number of factors.

    On the receiver side, the size and design of the heat sinks (also the inclusion of a fan or not), the number (and quality) of output devices per channel and the location of the receiver itself (whether or not it has access to plenty of ventilation) all lead to how well the receiver can deal with low load impedence and/or high playback volumes.

    On the speaker side, there are mostly 2 main concerns. Impedence and sensitivity.

    If a speaker has impedence measurements of less than 8 ohms, it will draw more current from the amp/receiver to return the same volume level back to you than one that is 8 ohms (if both have the same sensitivity maesurements.) The additional current drain WILL cause the amp/receiver to get noticeably hotter. (And if the receiver suffers from it's own problems, as I've noted above, then you will indeed have problems.)

    But, if a less than 8 ohm speaker has a higher sensitivity, it may not draw enough (or in some cases, any) additional current to cause any problems. (An example would be an 8 ohm speaker with a sensitivity of 86db/watt/meter. If you compare it to a 4 ohm speaker that measures 89db/watt/meter, you may find that the 4 ohm speaker may not make the amp/receiver any hotter than the 8 ohm one would.)

    Bottom line is that I believe most decent receivers can safely drive speaker loads of less than 8 ohms. Especially if you use some common sense on how loudly you play your setup. But like anything else in life, there are no free lunches...(and lots of things to consider if you're going to play things very loud and long.)

    (One other thing to point out is how several makers deal with lower impedence speakers. Many include a 4/8 ohm switch on the speaker outputs. This switch lowers the potential power output available to the speakers by (an average of) 10 to 20 percent. Less wattage output means less current is needed. This translates to less heat generated. The reason for this switch is to more cost effectively pass UL or CSA heat safety ratings when feeding lower impedence loads. The switch allows receiver makers to save money by avoiding the use of more/better heat sinks or fans. This approach does work but should never be considered as necessary for low impedence drive capability.)
     

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