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impedence setting for speakers

Discussion in 'Home Cinema Speakers' started by dazed&confused, Mar 19, 2005.

  1. dazed&confused

    dazed&confused
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    I have a Yamaha DSP-AX750SE amplifier and Castle Compact 5.1 speaker system.

    I am rather dissappointed with the stereo sound and thought it was down to the speakers (because my old Morduant Short speakers sound ok with the amp). However a bloke in an up-market hifi shop tody suggested that it is because my 'speakers are showing the amp up' (and the Morduant Shorts are a bit knider to it, and better balanced) and I should be looking at the something like the Arcam Diva for £1, 300.

    Anway, he did recommend that in the meantime I switch the impedance setting on my Yamaha amp. I had it set on 4 ohm minimum, even though all the Castle satellites are 8 ohm, because the Castle Centre is only 6 ohm. The bloke told me to switch the amp to 8 ohm anyway, saying I was unlikely to hurt the centre and in fact was more likely to hurt the sattellites with the amp switched on 4 ohm.

    I have tried this and, unless it is my imagination, it does seemed to have opened up the sound a bit.

    But do you think I am likely to hurt my 6 ohm centre speaker, or any of the others, by doing this? And is the apparent improvement more likley to be my imagination?

    Thanks.
     
  2. lynx

    lynx
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    The selector switch exists to protect the amp output devices, not the speakers.If you only have an option on the amp,of 8Ω or 4Ω, then select 4Ω. You could select 8Ω if you are mindful of the stresses of high sound pressure levels and don't get too carried away. This is at your own risk though.
     
  3. dazed&confused

    dazed&confused
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    Thanks.

    By "you could select 8Ω if you are mindful of the stresses of high sound pressure levels and don't get too carried away", dod you mean I'll probably be ok if I don't turn the amp up too loud.

    Also, am I right in presuming that it is ok to have it set on 8 ohm when I am listening to the amp in two channel stereo only (and flick it to 4 ohm when I watch movies, etc.).

    Thanks.
     
  4. lynx

    lynx
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    I don't know how resiliant your amp is to loads of low ohmic value. I don't think it will matter whether it's two channel or multi channel - 4Ω is 4Ω regardless of how many speakers are being driven. If in doubt set the amp up for driving a more difficult load, i.e 4Ω.
     
  5. dazed&confused

    dazed&confused
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    "4Ω is 4Ω regardless of how many speakers are being driven". I don't follow you. The sattellites are 8Ω and the centre is 6Ω, so surely if I am using two channel stereo then this does not involve the centre (unlike with 5.1) and thus does make a difference to how many speakers are being driven?

    Also, the sub woofer doesn't seem to mention impedence in its specification. Is this likely to be important when using the sub with just the two sattellites in stereo?

    Thanks.
     
  6. eviljohn2

    eviljohn2
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    The main issue here is not the nominal impedence rating of the speakers but how their impedence drops with frequency. That is to say, the impedence value isn't a constant but it varies with frequency so for low notes it will be lower.

    I would be inclined to leave it at 8ohms and see if you have any trouble. If the amp starts shutting itself off voluntarily then go back to the 4ohm setting. Your dealer is wrong about either impedence setting being "better", it's simply a matter of how your amplifier integrates with the speakers.

    I think the dealer may well be right when he says the speakers are "showing up" the amp, how is the sound not as good as with the old Mordaunt Short speakers? Is it a problem present with all recordings or just ones that are better or worse? Does using the source direct mode help? In general, I think there are a number of factors that could be the culprit for a problem like this - the settings within the amplifier and subwoofer will be key so double check that you've got these right too. :)
     
  7. dazed&confused

    dazed&confused
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    Thanks for the replies. I think I will keep it on 8 ohm setting, at least for stereo music which is all I'm using it for at the moment. Perhaps when I get a dvd player I will try it on 4 ohm just for movies.

    Thanks to John also for touching on the broader issues.

    With some music, for example relatively simple modern dance music, the amp sounds fine with the Castles. However they don't really come near the old Mordaunt Shorts when it comes to more complex music with a lot more subtle stuff going on through the mid-ranges, for example Pink Floyd. . They seem to miss out on a lot of what is going on. The worst performance so far is with a live recording, namely Nirvana Unplugged, (they sound quite flat and sluggish) and guitar-based music in general just doesn't sound as good. They tend to sound fine at first and become more dissappointing with extended listening, causing a bit of a headache and less and less pleasure.

    As for pure direct, in some ways it sounds a little better but overall too hollow, and the benefits are outweighed by the befit of having the sub on when pure direct is not used.

    Appologies of the lengthy reply. I don't really expect much of a solution. I was quite surprised by the delaers response though, because my own conclusion was that no matter how much speaker technology had moved on, a small speakers are just not going to be as good as bigger ones. So I was surprised when he suggested the problem was with the amp.
     
  8. Mason @ B&M

    Mason @ B&M
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    Speaker impedances normally rise around their resonant frequency so if your speaker says 6 ohm it's unlikely to ever present the amp with a load lower than 6 so you should be fine..

    If you set your amp to 8 ohm it will be running with a higher voltage on the amps internal power rails which in theory should give slightly better dynamics although it's one of those things thats hard to notice.

    So if you crank the amp to full whack the 6 ohm speaker has the potential to overload the power rails as they are only expecting to see a 8 ohm load. But you'd have to really push it to do this and your amp should simply shut down without any harm being done.

    Setting an amp at a certain ohm level is never going to hurt speakers.
     

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