ef37a
Joined: 29/05/06
Posts: 5625
Loc: northampton uk
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Why 15 Ohms?
#958270 - 10/12/11 11:56 AM
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Way back any loudspeaker with pretensions to quality or power (PA) was 15Ohms.
Those found in lesser equipments, radio/tv were alway 3 Ohms. The advent of the
transistor saw 8R speakers emerge (but those daft, DIN continentals went 4R nuts) but what
technical reason if any, led to the original 15R impedance? Was it just an expediant
optimum re coil size, wire gauge and other factors?
I note also that early
microphones were 30 Ohms and in fact I still have a Geloso dynamic which is 16R!Is that
moot at all?
Dave.
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Hugh Robjohns
SOS Technical Editor
Joined: 25/07/03
Posts: 18373
Loc: Worcestershire
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Re: Why 15 Ohms?
[Re: ef37a]
#958280 - 10/12/11 01:30 PM
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I would image the 15 ohm thing came about because of the practicalities of valve amp
output transformer ratios and the need for an appropriate reflected impedance.
Hugh
--------------------
Technical Editor, Sound On Sound
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ef37a
Joined: 29/05/06
Posts: 5625
Loc: northampton uk
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Quote Hugh Robjohns:
I would
image the 15 ohm thing came about because of the practicalities of valve amp output
transformer ratios and the need for an appropriate reflected impedance.
Hugh
Yes but that is a sort of chicken
and egg argument? There was never a problem in making any reasonable transformer ratio,
6volt heaters, 100:1 mic traffs? So where did 15Ohms come from originally?
Dave.
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Martin Walker
Watcher Of The Skies
Joined: 28/02/01
Posts: 16381
Loc: Cornwall, UK
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Re: Why 15 Ohms?
[Re: ef37a]
#958403 - 11/12/11 01:13 PM
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Perhaps they wound the voice coil with the thinnest enamelled wire they could find, kept
going until they couldn’t fit any more in without chafing in the gap, and then measured
the impedance?  Martin
-------------------- YewTreeMagic
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ef37a
Joined: 29/05/06
Posts: 5625
Loc: northampton uk
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Quote Martin Walker:
Perhaps they
wound the voice coil with the thinnest enamelled wire they could find, kept going until
they couldn’t fit any more in without chafing in the gap, and then measured the
impedance?
Martin
Heh! I think you are playing the QI paddle "Nobody Knows"!
Dave.
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Folderol
Joined: 15/11/08
Posts: 2551
Loc: Rochester, UK
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Quote Martin Walker:
Perhaps they
wound the voice coil with the thinnest enamelled wire they could find, kept going until
they couldn’t fit any more in without chafing in the gap, and then measured the
impedance?
Martin
That might not actually be so far from the truth. There was a lot of {ahem} empirical
design in the early days of electronics.
--------------------
It wasn't me!
(Well, actually, it probably was)
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Martin Walker
Watcher Of The Skies
Joined: 28/02/01
Posts: 16381
Loc: Cornwall, UK
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Re: Why 15 Ohms?
[Re: ef37a]
#958577 - 12/12/11 03:37 PM
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There we are - I'm being taken seriously again!  Martin
-------------------- YewTreeMagic
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