Description
Offered for your consideration is a vintage pair of RCA MI-6234 Alnico magnet “free cone” 7 inch full-range speakers, USA-manufactured c.1943. These remarkable permanent magnet drivers were engineered in the late 1930s by Harry Olson, RCA’s head of acoustical research, with an innovative “free cone” design to enhance the low-end response of this modest-size platform. The cones are not glued to the basket flanges here. Instead, theyre freely suspended above the voice coil/spider they’re attached to, which allows low frequencies to vibrate their entire length without the reluctance of conventional suspensions. They were called rolled-edge accordion cones and their edges are protected by the multi-stacked hard paper flange gaskets. In my research for this listing, I found the MI-6234 in RCA’s Broadcast Equipment catalog from 1941. The next closest RCA period catalog I could find was from 1945, but the driver had been renamed MI-6234-A by then. So, please see my large photos and read the remaining description to decide if this rare pair of RCA free cone speakers should be yours. This pair of RCA MI-6234 speakers is in relatively clean, very good condition for being some 80 years old. Most crucially, the original ribbed paper cones are amazingly well-preserved with no cracks, holes, or even stains, just some color fading from the decades. Plus, the felt voice coil covers are perfect. In addition, the steel baskets are finished in enamel the catalogs referred to as “umber” gray and they have no dents, notable dings, or scratches, only some minor, expected chipping to the paint. Whats more, the cast iron magnet pots have thin metal plates that rusted, which darkened the paper product labels attached to them, and a small weld dot on one had gone missing at some point. I also noticed that one spider is a bit misshapen. And, the +/- input terminal spades measure the standard .205”, are marked for polarity (small paint line next to positive), and have been de-soldered for the new owner’s convenience. Most importantly, I’ve auditioned these WWII-era speakers and they are both playing nicely with clear, well-detailed midrange, pronounced treble, and adequate bass (as tested without cabinets). I did note some popping distortion, but only during heavy bass passages and at volume beyond the limitations of their 3-watt rating. Otherwise, I was surprised and delighted that speakers this old were both playing well at all. It’s a testament to RCA engineering back then, and the quality work of their employees! And even though these speakers were categorized as “full range” by 1940’s standards, the published peak is only 7kHz. I’d also seen 8kHz when four MI-6234 speakers were used in the MI-6222 cabinet, but that figure might be a catalog misprint. In those days, the conventional wisdom was that listeners preferred a ceiling of no more than 5000 cycles (5kHz), which Olson attributed to the upper-frequency distortion with 78 rpm records and AM radio broadcasting of the era. He felt that with improved source signals, listeners would welcome speaker reproduction at higher range, and he was right. Lastly, I tested the speakers’ DC resistance at a closely-matched 5.1 and 5.2?, respectively, consistent with a nominal 6 ohm published driver rating. And, the baskets measure 7” across, they stand 3?” tall, and the four-corner mount holes are spaced 4 5/16” adjacent / 6 3/16” on the diagonal apart, c-t-c. As pictured and described, this pair of RCA MI-6234 free cone, full-range Alnico 7 speakers is offered at a competitive price. Terms of Sale: I encourage interested parties to ask any questions they may have about this listing before committing to purchase as there are no cancellations, returns, refunds, or claims considered. Payment is due at checkout by PayPal or other accepted methods. U.S. mailing addresses will pay $19.95 for very carefully packed shipping via U.S. Postal Service, FedEx, or UPS with tracking, delivery confirmation, and insurance. International purchases accepted only from those who are able to pay with PayPal or other forms, including shipping by U.S. Postal Service Global Priority Air Mail. Thanks for looking!
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