EM Vs PM Speaker












1












$begingroup$


Modern Speakers have permanent magnets and are called PM speakers.Permanent magnet materials technology has improved a lot over the last 80 years .Around WW2 EM speakers were common because permanent magnets were not as good as they are today .The old school EM speaker had the usual voice coil and a wound electromagnet where the permanent magnet is today .The electromagnet wasted a lot of power .5 to 10 watts being typical .This DC power burn was often more than the audio output of the radio .Mains radios had electromagnets wound from many turns of very thin fragile copper wire giving a coil DC resistance of about 1000 to 2000 ohms .These coils would fail open circuit meaning that you wont see many of these today .Car radios would also use EM speakers with low resistance EM coils to match to the 6V battery .The car radio EM speakers were more reliable despite the high temps encountered in a car .The Audio output power of these old radios was often lousey by modern standards like 3Watts.The old radios with EM speakers sounded loud despite the low Audio power .Finaly my queation is '' Are EM speakers more efficient in terms of dB per watt than PM speakers ? ''






vintage







share|improve this question









$endgroup$








  • 1




    $begingroup$
    They may be better in terms of dB per watt applied to the voice coil if the field generated by the field coil is stronger than the permanent magnet would produce, but the field coil is a static power consumption, so overall efficiency of the system would still be lowered by that, especially at low outputs.
    $endgroup$
    – Phil G
    5 hours ago










  • $begingroup$
    On the radios with EM speakers that I have encountered the EM power Exceeds The voicecoil power .If a PM speaker is installed in place of an existing EM speaker that has died how much more audio power is needed for the same sonic result?
    $endgroup$
    – Autistic
    4 hours ago






  • 1




    $begingroup$
    If you copy over your text into your favorite word processor, can you see it underlines every single period? This is because space comes AFTER period.
    $endgroup$
    – winny
    3 hours ago
















1












$begingroup$


Modern Speakers have permanent magnets and are called PM speakers.Permanent magnet materials technology has improved a lot over the last 80 years .Around WW2 EM speakers were common because permanent magnets were not as good as they are today .The old school EM speaker had the usual voice coil and a wound electromagnet where the permanent magnet is today .The electromagnet wasted a lot of power .5 to 10 watts being typical .This DC power burn was often more than the audio output of the radio .Mains radios had electromagnets wound from many turns of very thin fragile copper wire giving a coil DC resistance of about 1000 to 2000 ohms .These coils would fail open circuit meaning that you wont see many of these today .Car radios would also use EM speakers with low resistance EM coils to match to the 6V battery .The car radio EM speakers were more reliable despite the high temps encountered in a car .The Audio output power of these old radios was often lousey by modern standards like 3Watts.The old radios with EM speakers sounded loud despite the low Audio power .Finaly my queation is '' Are EM speakers more efficient in terms of dB per watt than PM speakers ? ''






vintage







share|improve this question









$endgroup$








  • 1




    $begingroup$
    They may be better in terms of dB per watt applied to the voice coil if the field generated by the field coil is stronger than the permanent magnet would produce, but the field coil is a static power consumption, so overall efficiency of the system would still be lowered by that, especially at low outputs.
    $endgroup$
    – Phil G
    5 hours ago










  • $begingroup$
    On the radios with EM speakers that I have encountered the EM power Exceeds The voicecoil power .If a PM speaker is installed in place of an existing EM speaker that has died how much more audio power is needed for the same sonic result?
    $endgroup$
    – Autistic
    4 hours ago






  • 1




    $begingroup$
    If you copy over your text into your favorite word processor, can you see it underlines every single period? This is because space comes AFTER period.
    $endgroup$
    – winny
    3 hours ago














1












1








1





$begingroup$


Modern Speakers have permanent magnets and are called PM speakers.Permanent magnet materials technology has improved a lot over the last 80 years .Around WW2 EM speakers were common because permanent magnets were not as good as they are today .The old school EM speaker had the usual voice coil and a wound electromagnet where the permanent magnet is today .The electromagnet wasted a lot of power .5 to 10 watts being typical .This DC power burn was often more than the audio output of the radio .Mains radios had electromagnets wound from many turns of very thin fragile copper wire giving a coil DC resistance of about 1000 to 2000 ohms .These coils would fail open circuit meaning that you wont see many of these today .Car radios would also use EM speakers with low resistance EM coils to match to the 6V battery .The car radio EM speakers were more reliable despite the high temps encountered in a car .The Audio output power of these old radios was often lousey by modern standards like 3Watts.The old radios with EM speakers sounded loud despite the low Audio power .Finaly my queation is '' Are EM speakers more efficient in terms of dB per watt than PM speakers ? ''






vintage







share|improve this question









$endgroup$




Modern Speakers have permanent magnets and are called PM speakers.Permanent magnet materials technology has improved a lot over the last 80 years .Around WW2 EM speakers were common because permanent magnets were not as good as they are today .The old school EM speaker had the usual voice coil and a wound electromagnet where the permanent magnet is today .The electromagnet wasted a lot of power .5 to 10 watts being typical .This DC power burn was often more than the audio output of the radio .Mains radios had electromagnets wound from many turns of very thin fragile copper wire giving a coil DC resistance of about 1000 to 2000 ohms .These coils would fail open circuit meaning that you wont see many of these today .Car radios would also use EM speakers with low resistance EM coils to match to the 6V battery .The car radio EM speakers were more reliable despite the high temps encountered in a car .The Audio output power of these old radios was often lousey by modern standards like 3Watts.The old radios with EM speakers sounded loud despite the low Audio power .Finaly my queation is '' Are EM speakers more efficient in terms of dB per watt than PM speakers ? ''






vintage




vintage






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 5 hours ago









AutisticAutistic

7,44021533




7,44021533








  • 1




    $begingroup$
    They may be better in terms of dB per watt applied to the voice coil if the field generated by the field coil is stronger than the permanent magnet would produce, but the field coil is a static power consumption, so overall efficiency of the system would still be lowered by that, especially at low outputs.
    $endgroup$
    – Phil G
    5 hours ago










  • $begingroup$
    On the radios with EM speakers that I have encountered the EM power Exceeds The voicecoil power .If a PM speaker is installed in place of an existing EM speaker that has died how much more audio power is needed for the same sonic result?
    $endgroup$
    – Autistic
    4 hours ago






  • 1




    $begingroup$
    If you copy over your text into your favorite word processor, can you see it underlines every single period? This is because space comes AFTER period.
    $endgroup$
    – winny
    3 hours ago














  • 1




    $begingroup$
    They may be better in terms of dB per watt applied to the voice coil if the field generated by the field coil is stronger than the permanent magnet would produce, but the field coil is a static power consumption, so overall efficiency of the system would still be lowered by that, especially at low outputs.
    $endgroup$
    – Phil G
    5 hours ago










  • $begingroup$
    On the radios with EM speakers that I have encountered the EM power Exceeds The voicecoil power .If a PM speaker is installed in place of an existing EM speaker that has died how much more audio power is needed for the same sonic result?
    $endgroup$
    – Autistic
    4 hours ago






  • 1




    $begingroup$
    If you copy over your text into your favorite word processor, can you see it underlines every single period? This is because space comes AFTER period.
    $endgroup$
    – winny
    3 hours ago








1




1




$begingroup$
They may be better in terms of dB per watt applied to the voice coil if the field generated by the field coil is stronger than the permanent magnet would produce, but the field coil is a static power consumption, so overall efficiency of the system would still be lowered by that, especially at low outputs.
$endgroup$
– Phil G
5 hours ago




$begingroup$
They may be better in terms of dB per watt applied to the voice coil if the field generated by the field coil is stronger than the permanent magnet would produce, but the field coil is a static power consumption, so overall efficiency of the system would still be lowered by that, especially at low outputs.
$endgroup$
– Phil G
5 hours ago












$begingroup$
On the radios with EM speakers that I have encountered the EM power Exceeds The voicecoil power .If a PM speaker is installed in place of an existing EM speaker that has died how much more audio power is needed for the same sonic result?
$endgroup$
– Autistic
4 hours ago




$begingroup$
On the radios with EM speakers that I have encountered the EM power Exceeds The voicecoil power .If a PM speaker is installed in place of an existing EM speaker that has died how much more audio power is needed for the same sonic result?
$endgroup$
– Autistic
4 hours ago




1




1




$begingroup$
If you copy over your text into your favorite word processor, can you see it underlines every single period? This is because space comes AFTER period.
$endgroup$
– winny
3 hours ago




$begingroup$
If you copy over your text into your favorite word processor, can you see it underlines every single period? This is because space comes AFTER period.
$endgroup$
– winny
3 hours ago










2 Answers
2






active

oldest

votes


















5












$begingroup$

Permanent magnet materials were expensive, and not all that permanent, back in the 1930s, capable of losing their magnetic strength under shock or other abuse, or even heat - which was common in a valve radio. This made the electromagnetic field generator a cheaper and more reliable option.



But that's not the real reason they were so ubiquitous.



The HT power supply for the radio (about 250-350V at 50-100mA) needed low pass filtering after rectification, to eliminate mains hum (ripple voltage). And large value high voltage electrolytic capacitors were expensive.



The solution was a choke - a large inductor in the 10 to 100 Henry range, forming a low pass Pi filter between 2 relatively low value (10 to 30 uF) capacitors.



And the most economical place to wind that choke was ... the loudspeaker's field coil, where the DC component of the rectified current also provided the speaker's magnetic field.



So, far from being wasteful, the EM loudspeaker could do 2 jobs at once.



(Oh, and don't underestimate 2 or 3 watts in a nice large 8 or 10 inch paper cone loudspeaker. They still are plenty loud enough)






share|improve this answer











$endgroup$





















    0












    $begingroup$

    An old AM radio had no bass sounds and had no high frequency sounds so they made the speaker shriek noises at a high sensitivity.






    share|improve this answer









    $endgroup$













    • $begingroup$
      This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
      $endgroup$
      – mkeith
      36 mins ago











    Your Answer





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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    5












    $begingroup$

    Permanent magnet materials were expensive, and not all that permanent, back in the 1930s, capable of losing their magnetic strength under shock or other abuse, or even heat - which was common in a valve radio. This made the electromagnetic field generator a cheaper and more reliable option.



    But that's not the real reason they were so ubiquitous.



    The HT power supply for the radio (about 250-350V at 50-100mA) needed low pass filtering after rectification, to eliminate mains hum (ripple voltage). And large value high voltage electrolytic capacitors were expensive.



    The solution was a choke - a large inductor in the 10 to 100 Henry range, forming a low pass Pi filter between 2 relatively low value (10 to 30 uF) capacitors.



    And the most economical place to wind that choke was ... the loudspeaker's field coil, where the DC component of the rectified current also provided the speaker's magnetic field.



    So, far from being wasteful, the EM loudspeaker could do 2 jobs at once.



    (Oh, and don't underestimate 2 or 3 watts in a nice large 8 or 10 inch paper cone loudspeaker. They still are plenty loud enough)






    share|improve this answer











    $endgroup$


















      5












      $begingroup$

      Permanent magnet materials were expensive, and not all that permanent, back in the 1930s, capable of losing their magnetic strength under shock or other abuse, or even heat - which was common in a valve radio. This made the electromagnetic field generator a cheaper and more reliable option.



      But that's not the real reason they were so ubiquitous.



      The HT power supply for the radio (about 250-350V at 50-100mA) needed low pass filtering after rectification, to eliminate mains hum (ripple voltage). And large value high voltage electrolytic capacitors were expensive.



      The solution was a choke - a large inductor in the 10 to 100 Henry range, forming a low pass Pi filter between 2 relatively low value (10 to 30 uF) capacitors.



      And the most economical place to wind that choke was ... the loudspeaker's field coil, where the DC component of the rectified current also provided the speaker's magnetic field.



      So, far from being wasteful, the EM loudspeaker could do 2 jobs at once.



      (Oh, and don't underestimate 2 or 3 watts in a nice large 8 or 10 inch paper cone loudspeaker. They still are plenty loud enough)






      share|improve this answer











      $endgroup$
















        5












        5








        5





        $begingroup$

        Permanent magnet materials were expensive, and not all that permanent, back in the 1930s, capable of losing their magnetic strength under shock or other abuse, or even heat - which was common in a valve radio. This made the electromagnetic field generator a cheaper and more reliable option.



        But that's not the real reason they were so ubiquitous.



        The HT power supply for the radio (about 250-350V at 50-100mA) needed low pass filtering after rectification, to eliminate mains hum (ripple voltage). And large value high voltage electrolytic capacitors were expensive.



        The solution was a choke - a large inductor in the 10 to 100 Henry range, forming a low pass Pi filter between 2 relatively low value (10 to 30 uF) capacitors.



        And the most economical place to wind that choke was ... the loudspeaker's field coil, where the DC component of the rectified current also provided the speaker's magnetic field.



        So, far from being wasteful, the EM loudspeaker could do 2 jobs at once.



        (Oh, and don't underestimate 2 or 3 watts in a nice large 8 or 10 inch paper cone loudspeaker. They still are plenty loud enough)






        share|improve this answer











        $endgroup$



        Permanent magnet materials were expensive, and not all that permanent, back in the 1930s, capable of losing their magnetic strength under shock or other abuse, or even heat - which was common in a valve radio. This made the electromagnetic field generator a cheaper and more reliable option.



        But that's not the real reason they were so ubiquitous.



        The HT power supply for the radio (about 250-350V at 50-100mA) needed low pass filtering after rectification, to eliminate mains hum (ripple voltage). And large value high voltage electrolytic capacitors were expensive.



        The solution was a choke - a large inductor in the 10 to 100 Henry range, forming a low pass Pi filter between 2 relatively low value (10 to 30 uF) capacitors.



        And the most economical place to wind that choke was ... the loudspeaker's field coil, where the DC component of the rectified current also provided the speaker's magnetic field.



        So, far from being wasteful, the EM loudspeaker could do 2 jobs at once.



        (Oh, and don't underestimate 2 or 3 watts in a nice large 8 or 10 inch paper cone loudspeaker. They still are plenty loud enough)







        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 3 hours ago

























        answered 4 hours ago









        Brian DrummondBrian Drummond

        47.7k138108




        47.7k138108

























            0












            $begingroup$

            An old AM radio had no bass sounds and had no high frequency sounds so they made the speaker shriek noises at a high sensitivity.






            share|improve this answer









            $endgroup$













            • $begingroup$
              This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
              $endgroup$
              – mkeith
              36 mins ago
















            0












            $begingroup$

            An old AM radio had no bass sounds and had no high frequency sounds so they made the speaker shriek noises at a high sensitivity.






            share|improve this answer









            $endgroup$













            • $begingroup$
              This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
              $endgroup$
              – mkeith
              36 mins ago














            0












            0








            0





            $begingroup$

            An old AM radio had no bass sounds and had no high frequency sounds so they made the speaker shriek noises at a high sensitivity.






            share|improve this answer









            $endgroup$



            An old AM radio had no bass sounds and had no high frequency sounds so they made the speaker shriek noises at a high sensitivity.







            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 47 mins ago









            AudioguruAudioguru

            42413




            42413












            • $begingroup$
              This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
              $endgroup$
              – mkeith
              36 mins ago


















            • $begingroup$
              This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
              $endgroup$
              – mkeith
              36 mins ago
















            $begingroup$
            This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
            $endgroup$
            – mkeith
            36 mins ago




            $begingroup$
            This may be more related to the audio bandwidth of the AM channel and the other effects caused by modulation/demodulation, etc. Also, it is not an answer to the question as far as I can see. I am fearing you may receive some down-votes because of that.
            $endgroup$
            – mkeith
            36 mins ago


















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