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Thread: 30 ohm bass drivers

  1. #1
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 944
    I'm Chris.

    Default 30 ohm bass drivers

    As part of a 3 way speaker system I currently run the 8 ohm 15 inch Eminence Alpha drivers from a dedicated Rotel transistor amp.

    I want to try a vintage pair of 15 inch drivers, but they are only available at 30 ohm impedance. Are there any issues I should be aware of if I plug them in, apart from changing component values in the low pass filter.
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  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 5,592
    I'm Alan.


    Yes, you will only achieve 1/4 of the power into 30 ohm speakers compared to 8 ohm.

    If the drivers have a greater sensitivity you should be OK.

  3. #3
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,737
    I'm Chris.


    Quote Originally Posted by Firebottle View Post
    Yes, you will only achieve 1/4 of the power into 30 ohm speakers compared to 8 ohm.

    If the drivers have a greater sensitivity you should be OK.
    Certainly that is the case with solid state amplifiers, but not valve amplifiers http://education.lenardaudio.com/en/...ve_amps_7.html

    "because Valve and solid-state amps operate in opposite ways to how power is delivered into a changing Impedance, the resultant audible difference is very noticeable.
    Voltage Current drive comparison

    Valve amp power is directly proportional to speaker Impedance
    therefore power increases as the speaker Impedance rises.

    Solid-state power is inversely proportional to speaker Impedance
    therefore power decreases as the speaker Impedance rises. "

  4. #4
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 4,261
    I'm Lawrence.


    Doesn't that assume that amplifiers are perfect voltage or current drivers, which is just not true? There's the output impedance to consider if nothing else.

    Sent from my HRY-LX1 using Tapatalk

  5. #5
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 1,614
    I'm Dennis.


    My conception is that voltage drive was always the aim even with valve amps, but they were compromised because of O/P transformer characteristics, and the presence of the O/P transformer is because of the inherently higher O/P Z of valves.

    When transistors evolved, much lower O/P Zs were obtainable and so the ccts functioned more towards the voltage drive ideal, and they were also transformerless, then going direct coupled thus removing the O/P caps.

    There are still some who espouse deliberately designed current drive, saying that it has other advantages.

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