This is going to be a bit big, unfortunately, because I need to take the original message point by point and comment on it. Please forfive the size!
----- Original Message ----- From: <[email protected]> To: <[email protected]> Sent: Thursday, March 02, 2006 11:47 PM Subject: Re: [Phono-L] Victrola VE 15-1: Electrola Hyperion > You folks are using terms that might confuse some readers, if they were not > versed in terms that are still heard, but used with slightly different > meanings. In a modern context, a "dynamic" speaker is any speaker that uses > a cone, > a permanent magnet, and a voice coil. Among collectors of audio gear from > the so-called "Golden Age" of Hi-Fi, dynamic speakers with large, permanent, > alnico magnets are very desirable. Many, if not most of those speakers were > shipped off to the pacific rim, while the Japanese sold us rack-system junk. > > I think the speakers you are referring to as being "dynamic" speakers are > now referred to as "Electro-dynamic" speakers, or "Field coil" speakers. > They > use a magnet that is powered by an external power supply. This allows those > speakers to have an enormous advantage in efficiency, especially woofers, > which require long, heavy throws of the voice coils. In the beginning, all dynamic speakers had to have a field coil to generatet the magnetic flux. The higher the magnetic energy in the voice coil gap, the more efficient the speaker. These later became known as electro-dynamic to differentiate between those with a field coil and a and those with a permanent magnet. The type of magnet is the difference.Today, they are abbreviated thus: "EM" is Electro-Dynamic, and "PM" is permanent Magnet. I'm referring to dynamic speakers, only. > > Amplifiers used with "dynamic" speakers have to generate all of the power > required to move the cones in modern dynamic speaker systems. That's been true from the beginning. The voice coil is driven by an amplifier. (It's true for any type of speaker used, be it magnetic, electrostatic, dynamic or whatever). That is one of > the reasons I have a dedicated circuit for my stereo. I use two stereo > amplifiers that are large enough, if driven to full power, as a pair, to > trip a 15 > amp circuit breaker in my house's main fuse panel. > Field coil speakers do not need amplifiers with that kind of power. They > require amplifiers that are only powerful enough to excite, or modulate the > magnetic field that is generated by the power supply. I have not run the > numbers, > but I would guess that this can mean the difference between a speaker > needing 5 watts for a given SPL (sound pressure level), and 500 watts. Electro-dynamic speakers require some kind of field supply. Some had rectifiers that used the AC line with rectifier stacks, as the RCA Loudspeaker 106. Other companies such as Jensen, Rola, and Magnavox also sold a speaker with field supply for use with radios that had no built-in speaker. That era was chiefly 1929-29. The sets with built-in dynamic speakers used current from the set's power supply to excite the field coil. The reason for all that was that they were about 10 years away from magnetic material that had enough flux and retentivity to be used in a dynamic speaker. There were early attempts at PM dynamic speakers. I have a 1932 vintage Majestic radio with two big iron magnets for the voice coil magnetism. They were far short of efficient. Philco had a couple in in battery sets. They worked, but.......... > > Field coil speakers were abandoned, mostly because they were expensive to > make, and relatively complicated. As permanent magnet technology improved, > field > coil speakers were phased out. However, a small, but highly vocal, and > dedicated fringe of modern Audiophiles still seek out old field coil > speakers, and > get a kick out of what those speakers can do with miniscule amounts of > amplifier power. They are especially popular with fans of amplifiers that > used > single-ended, triode output tubes, like 2A3's 300B's, etc. As magnetic materials improved, just before WWII began, Electro-dynamic speakers began to fade out. At first, the PM speakers could perform camparably well, and eliminated the need for a field power supply. Early PM dynamic speakers were more expensive than EM speakers. Check the catalogues from those years. I remember them very well. That changed after the war. When WWII ended, and Alnico 5 became common, the energy level in the voice coil gap was higher than could be had by even a gigantic field coil. Later, ceramic magnets surpassed Alnico. The higher the magnetic level in the voice coil gap is, the more sensitive and efficient the speaker will be. My Electro-Voice Patrician speakers are a good example. The woofer is an 18 inch PM speaker, with other PM drivers for mid range and tweeters. A transistor pocket radio can drive those speakers to decent sounding room volume. (I use a Fisher receiver with about 35 watts per channel to drive them). You need to remember that in those big arenas and stadiums, though the amplifiers have high power capability, the typical power to drive the systems in them is a couple of watts in a typical program. Another important item to remember that the majority of power in sound is in the low frequencies. You don't hear many low frequencies in a stadium! Now, I consider myself an audio nut of sorts, I would prefer to avoid contact or discussion about single ended amplifiers and the stuff mantioned above. Much of it is against engineering principles. I'm a graduate electrical engineer, and most of the audiophools are not. > > I believe there is one company left in the world that makes uses > high-quality, field-coil drivers. I think it is a French company, but I'm > not sure. > Google it, if you are curious. Thanks, but I'm not! > > One easy way to spot a field coil speaker is to look at the number of wires > going to the unit. If there are more than four wires connected to the > speaker, > it is probably a field coil unit. And, in many cases, the field coil of the speaker is open and visible. The nicer and more expensive speakers had a cover pot over the field, be it PM or EM (Electro-Dynamic). As Randy says, look for the extra wires. > > Randy Minor Thanks, Randy , Doug. Houston > > _______________________________________________ > Phono-L mailing list > [email protected] > > Phono-L Archive > http://www.oldcrank.org/pipermail/phono-l/ > From [email protected] Fri Mar 3 19:02:30 2006 From: [email protected] (Ron L'Herault) Date: Sun Dec 24 13:11:27 2006 Subject: [Phono-L] Early Pickup Repair In-Reply-To: <000b01c63ee7$416f2b90$af9bb...@vaio> Message-ID: <000801c63f38$13c5b3c0$2f01a...@ronlherault> Where is Mr. Epple located? Ron L -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bruce Mercer Sent: Friday, March 03, 2006 12:24 PM To: [email protected] Subject: [Phono-L] Early Pickup Repair The ONLY person I would trust with my pickups is George Epple gke(at)verizon.net. _______________________________________________ Phono-L mailing list [email protected] Phono-L Archive http://www.oldcrank.org/pipermail/phono-l/
