Question about ohms

Discussion in 'AV Receivers' started by Dave.Zeb, Dec 19, 2003.

  1. Dave.Zeb

    Dave.Zeb Extra

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    Real quick, while most speakers and receivers all seem to be rated for 8 ohms, my new PSB's, silveris and mini's, are rated at 4 ohms. The C6 center is 8 ohms, which seems a bit strange, but hopefully someone a good bit better informed than I am will be able to explain that seeming disparity.

    My main questions are 2

    1) How does this lower impedance translate with effect towards power from receiver/amps? Do I get more power to the speakers due to less resistance, or is it the other way around?

    2) Does the fact that the center is 8 ohms mean that there will be a power difference in that one channel in relation to the others?

    Thanks for your help
     
  2. John S

    John S Producer

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    Less ohms = more power.

    Don't be to hung up on it. In the calibration you get to set your speaker levels. It should be ok...

    But, while I say that, I suggest and choose to use the exact same speaker all the way around myself. Always seems better to me.
     
  3. Dave.Zeb

    Dave.Zeb Extra

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    Thanks for the reply John.

    I guess I find it interesting, if not a bit odd, that they change the impedance setup on speakers that are meant to be matched together. They are all from the Stratus line, and there is no other option but to have the four around at 4 ohms and the center(2 choices, both the same) at 8ohms.

    Even more interesting, at least to me, is that if you look at the C6 center on the stratus line, it's basically 2 mini's (component wise) put together as a center. Can't wait to get it, as I've heard the mini's, and they are phenomenal, so a center with this kind of innards must really be the foundation I'll want for my home theatre watching. Still, the mini's rate 4 ohms, while the center is 8. Strange.

    Or maybe not, as I'm sure they must have had a reason to build them this way.

    Specs can be found here: http://www.psbspeakers.com/s/StratusSpecs.html

    Again, thanks for the help!
     
  4. CalvinCarr

    CalvinCarr Supporting Actor

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    Can you just put a 4 ohm resistor across the contacts?
     
  5. MikeTz

    MikeTz Stunt Coordinator

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    Nope. A four ohm resistor (let's assume you got one rated for the correct amount of power) in parallel with the speaker would lower the resistance by half. So if your speaker impedance was four ohms, and all resistive (and it isn't), then your impedance looking back into your amp would be two ohms. Since impedance varies with frequency (because it's not purely resistive) your amp would see values below two ohms. Unless your amp can supply lots of current and remain stable below two ohms it will overheat and shut itself off (or die). Receivers were not meant to handle loads like this.

    Long story short, no resistors across the speaker terminals and check to make sure your receiver is rated to drive a four ohm load (many aren't).

    MT
     
  6. Dave.Zeb

    Dave.Zeb Extra

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    That's another good point, Mike, and thanks for bringing it up. I often see the ratings of receivers at 8 and even 6 ohms, but very rarely do I see them rate for 4 ohms. When speaking to my PSB rep, he replied to this question that in order to drive the 4 ohm speakers, you can use just about any receiver, but you will need higher current and in general, higher power over-all, or it would be easy to hit the clip level for these speakers, risking damage.

    Currently I'm using a denon avr1700, older model, and I'm getting solid, if low powered results, and I know the speakers won't truly shine until I get a proper receiver powering them. I guess I worry about the possibility of damage I might be causing without even being aware of it. I don't push the speakers to any extent because of this, and have heard nothing anomylous in the sound, yet it's still in the back of my mind.

    The salesperson also said that the more I add to the system in way of speakers, the greater the load on the amp will be, and the higher likelihood of poor sound reproduction. Currently, I'm just driving the 2 silveri's up front, and two small Athena AS-B1's for surrounds, sub and center turned off. As I continue to build around these silveri's (the Athenas are only temporary until I get the mini's), the direction I go in next will likely be determined by how quickly I need to upgrade my current receiver.

    If anyone has a good grasp of this issue, and could perhaps give me some of the technical information I'm lacking at this point, and/or perhaps recommend or drop links to recommended receivers that will drive my set-up, I would be very grateful.

    While I'd love to grab the C6 next, as I hate having no center, two easy for the soundstage to be 'off' just moving a few inches left or right on the old center seat position... I worry that my current denon will begin to show serious weakness when driving 5 channels, and that I might be better off spending the cash on the receiver next, and suffering the lack of a center for another month or so until I'm ready for my next purchase.

    Again, thanks for all of your posts and information, and sorry about the length of this post. [​IMG]

    Oh, one other quick question: If running the silveris and mini's at 4 ohms, which actually increases the power rating due to the lower impedance, will the C6 at 8 ohms sound very underpowered in comparison? Thanks again!
     

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