45 Ohm speaker replacement options?

Discussion in 'The Projects Forum' started by wayneh, Nov 4, 2010.

  1. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    My home intercom/music system uses 45 ohm speakers, with a series pot to control (reduce) volume at the speaker. I have one speaker outdoors that's gone bad, and the OEM replacement is outrageously priced. I can't find one for less than $50. I'm looking for any reasonable solution that saves money.
    http://www.linearcorp.com/product_detail.php?productId=512

    I've tested a normal, lower impedance speaker and it does work, although I'm concerned it would eventually cook the amp. I could eliminate that concern by adding a cheap $20 amp such as:
    http://www.parts-express.com/pe/sho...t&utm_content=310-300&utm_campaign= Flyer_10F

    But I don't have power installed near the speaker. It's not too far away though. Short of adding a power amp, are there other clever solutions to consider?
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    What is the intercom power requirements.

    U can use a cheap LM386 with an 8 ohm speaker :)

    Better yet, post the intercom amp specs
     
    Last edited: Nov 4, 2010
  3. wayneh

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    Sep 9, 2010
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    Huh, that's a thought, change the amp. There is power and a little room in the "command center" cavity in the wall. It'd be easy to lodge a small circuit in there, and run the wires for the outdoor speaker from the new circuit instead of the intercom PCB.

    I haven't been very impressed with the LM358 [correction: LM386] circuits I've played with, but I wasn't really trying something like this. What would it take to have it sound decent? (Intercom decent, not hi-fi decent.) The existing system sounds better than you'd expect, and gives decent volume to the outdoor speaker.
     
    Last edited: Nov 4, 2010
  4. R!f@@

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    Recheck the post.. made a boo boo!!
     
  5. R!f@@

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    The 50 ohm ones are driven with quite a power and sounds pretty descent.

    why don't u try a 16 ohm one with a series resistor
     
  6. Kermit2

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    Feb 5, 2010
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  7. wayneh

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    Well, that's almost so simple as to be cheating!

    I might even have a workable transformer already in my parts box. I suppose internally this thing has a turn ratio of ~2.5:1, so that the impedance ratio is roughly 2.5^2 = 6.25:1 (45Ω versus 8Ω)?
     
  8. R!f@@

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    Impedance matching should be 45Ω primary to 8Ω secondary if 8 ohm speaker is to be used.

    Byfar this is the simplest method

    If mismatch occurs power will be reflected back into the amp.
    This cause excessive power being dissipated by the amp. If the amp has poor heat dissipation, it will burn quickly
     
  9. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Here's the follow up and my successful solution.

    To recap, the OEM speaker from Linear Corp. couldn't be found for less than ~$45 delivered.
    http://www.linearcorp.com/product_detail.php?productId=512

    http://www.discounthomeautomation.c...base&cvsfa=1970&cvsfe=2&cvsfhu=4d4d534e523850

    Since it's really just a cheap speaker, I didn't want to pay that much for it and started looking for options. I didn't want to use just any "normal" 8Ω speaker for fear of burning up the intercom amp. Thanks to this forum and especially Kermit2's slap-the-forehead-simple suggestion, I went looking for a 8Ω speaker+transformer to replace the 45Ω speaker.

    I found one here:
    http://www.parts-express.com/pe/showdetl.cfm?&DID=7&Partnumber=300-020

    It's perfect, a speaker and transformer sold together for less than $20 delivered. The speaker fit the existing enclosure exactly. The transformer offered several wiring options.

    And. it works fine! Maybe a hair less loud at a given setting than the OEM, but fine.
     
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