• also, "nominal impedance" is usually 125% of Zmin of the conventional woofer in a speaker - Mart 01:59:08 05/02/06 (0)
  In Reply to: What is the term "nominal" impedance in speaker lit? posted by Duilawyer on May 1, 2006 at 07:24:10:

  That's because current demand is most often the dictating concern. Bass frequencies with their long periodic signals drain PS capacitors & are most often responsible for burning up amplifiers due to I²×R heating. This is why hybrids like Logans ignore minimum impedances as low as 1Ω @ 20kHz.

  
  ... just my 2¢

  ♪ moderate Mart £ ♫

  ☺ Planar Asylum

  
  
  

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• "For Practical Purposes" - Ripple 13:30:39 05/01/06 (0)
  In Reply to: What is the term "nominal" impedance in speaker lit? posted by Duilawyer on May 1, 2006 at 07:24:10:

  Since a speaker's resistance constantly changes with frequency, you can view "nominal" as meaning an average, practical value. For example, my Martin Logan Aerius speakers have a nominal 4-ohm rating but at the upper octave frequencies resistance drops to about 2 ohms. This is the main reason a high-quality amp is needed for this design. The lower the resistance, the more control is required of the amp.

  Ripple
  
  

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• Well, just off the top of my head... :) - grantv 09:32:21 05/01/06 (3)
  In Reply to: What is the term "nominal" impedance in speaker lit? posted by Duilawyer on May 1, 2006 at 07:24:10:

  The term nominal impedance in electrical engineering or audio has a number of different meanings. It refers to the approximate designed impedance under certain conditions. The actual impedance may vary from this nominal figure. The term is used when the exact value of impedance is not important to the operation of the circuit or system.

  Nominal impedance refers to the impedance of the speaker at a defined low frequency in free air. The impedance will change with loading and frequency. In the days of valves, most loudspeakers had a nominal impedance of 16 Ω. Valve outputs require an output transformer to match the very high output impedance and voltage of the output valves to this lower impedance. These transformers were commonly tapped to allow matching of the output to a multiple loudspeaker setup. For example, two 16 Ω loudspeakers in parallel will give an impedance of 8 Ω.

  Since the advent of solid-state transformerless outputs, these multiple-impedance outputs have become rare, and lower impedance loudspeakers more common. The most common nominal impedance for a single loudspeaker is now 8 Ω. Most solid-state amplifiers are designed to work with loudspeaker combinations of anything from 4 Ω to 8 Ω.
  
  
  
  

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  • Re: Well, just off the top of my head... :) - Fixertony 17:32:03 05/01/06 (1)
    In Reply to: Well, just off the top of my head... :) posted by grantv on May 1, 2006 at 09:32:21:

    "The most common nominal impedance for a single loudspeaker is now 8 Ω"

    Not in this part of the Asylum.

    When was the last time Magnepan made a speaker that didn't have a nominal impedance of 4 Ohms?

    A large percentage of cone speakers made in the last 5 years are probably around 4 Ohms also.

    How many ELS go to 2 Ohms (or below) approaching 15 KHz and above and 30 Ohms or higher approaching 100 Hz and below? More than likely quite a few as was noted elsewhere in this thread.

    I hope this post was not offensive in any way, it is just a sanity check - mine.

    - Tony
    
    
    

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    • I should have noted from the start.... - grantv 06:54:23 05/02/06 (0)
      In Reply to: Re: Well, just off the top of my head... :) posted by Fixertony on May 1, 2006 at 17:32:03:

      I just did a quick google search and came up with that explanation. Hence the smile after my post title. Copied and pasted it. Saved some time, got a quick answer.
      I didn't write it and do agree with all as noted by you.
      
      
      

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  • I should add: - grantv 13:57:51 05/01/06 (0)
    In Reply to: Well, just off the top of my head... :) posted by grantv on May 1, 2006 at 09:32:21:

    In reply to Duke's reply below, I copied and pasted this from the link below. It goes into more detail.
    
    

    • Quick google search turned this up   (Open in New Window)

    
    

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• Re: What is the term "nominal" impedance in speaker lit? - Duke 09:25:41 05/01/06 (2)
  In Reply to: What is the term "nominal" impedance in speaker lit? posted by Duilawyer on May 1, 2006 at 07:24:10:

  That's a good question - the term is something I've used for years but never really known the precise definition of.

  I've taken the term "nominal impedance" to mean the "face value" impedance, or perhaps the "ballpark rounded-off practical average" impedance. It's usually not the minium impedance, but rather seems to be the impedance that the speaker can be reasonably considered to have as far as amplifier matching goes.

  Well there we still don't know what it really means, so hopefully someone who does really know will post.

  Duke
  
  

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  • Is there any reason to use the 4 ohm taps on the amp? - Duilawyer 10:30:22 05/01/06 (1)
    In Reply to: Re: What is the term "nominal" impedance in speaker lit? posted by Duke on May 1, 2006 at 09:25:41:

    Or, if the 8 ohm sounds noticeably better, is 8 ohm the right set of taps. And is this what the Moodies refer to when they say the lost chord is "Oomm"
    
    

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    • Re: Is there any reason to use the 4 ohm taps on the amp? - Duke 13:32:58 05/01/06 (0)
      In Reply to: Is there any reason to use the 4 ohm taps on the amp? posted by Duilawyer on May 1, 2006 at 10:30:22:

      I think Grantv's explanation of nominal impedance is a lot better than mine was.

      I'm in favor of experimenting with which set of output taps sounds best on a tube amp. My parents have a JoLida integrated, and the 16-ohm speakers I built for them sound best on the 4-ohm taps.

      I re-read your comment about the Moodies and Ooom a couple of times, and even tried standing up on my chair but it still went over my head...
      
      

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