Vintage Amps
sunrayman123 asked:

I bought a pair of nice nut I cashed 4 speakers momentum II Jennings search for meaning. You have never heard of it? They are good? 6 Ohm are estimated rather than 8 ohms, I have a familiar with. 35W to 150W rms continuous. What a difference nell'impedenza 6 ohms mean? My transports watt amps! I need to bind a different degree of the speaker or what?


1 Comment so far

  1. Grogster on December 23, 2008 6:07 pm

    The 2-ohm difference will not make that much difference, provided you don’t wind the volume up too much.

    If your amp is supposed to drive an 8-ohm load(speaker), and you put a 6-ohm one on it, this represents a 25% mis-matched load to the amp output.(because 8-ohms represents a 100% perfect load, and 6 is 75% of 8, or in other words, the difference between 6 and 8 is 2, representing 25%)

    The difference of 25% will be dissipated as heat in the output transistors of the power amplifier.

    At low volumes, this is no problem at all, however, if you tend to wind the wick up a fair way(say 20-watts or more) when you are playing your music, this extra heat in the output stage of the amplifier might prove a problem.

    It also depends on the class of amplifier.
    Most amps are Class-B push-pull complementary-pair type, and the output transistors only conduct when there is an audio signal present – this reduces heat generation.
    Class-A amps are the type used in studios and very expensive home-theater setups, and generally weigh a ton(and cost a fortune!), and run hot all the time, so a mismatched Class-A amp would get even hotter then it normally would at high volumes, with an incorrect impedance load(speaker).

    If the speakers were mine, and assuming a very loud volume, I would open the back of the speaker cases, and install a crossover network – these can be had from places like Radio Shack for only a few dollars. Choose one with an appropriate power rating(in watts) corresponding to the power of your amp.

    The crossover network will present the correct load to the amp, and also make the speakers sound better too.

    You can get 2-way and 3-way crossovers: 2-way are used in speaker cabinets with only two speakers – a woofer and a tweeter, and 3-way ones for cabinets with 3 speakers(a tweeter, a midrange & a woofer).

    Technically, so long as your speaker wire is at least 0.75mm thick(the copper part!), and the runs are at least 8-10 meters, then the resistance of the speaker wire itself will make up the difference, and the amp will actually see a total load of around 8-ohms(6 from your speakers + 2 or so wire resistance).

    …so it’s not really a problem, unless you really gun your amp.

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