Latest on C1 Speakers

[Dennis C.]

I am looking for some input from others that have used reproduction speakers for C1's. I have read the threads in the archives and have visited Wonderbar Man's web site and I am left wondering if the reproductions work ok or cause problems?

Thanks in advance.

Regards,

Dennis

[Dennis C.]

Re: Latest on C1 Speakers

Wanted to bump this up to the top and see if someone can offer some advise on a radio speaker for a '61.

I added pictures of a speaker I purchased from one of the supply vendors. I also tried placing an ohm meter across the terminals and a digital meter bounces from 0 - 7 ohms and an analog meter reads 0 ohms. The analog meter also makes the speaker crackle (sound).

Based on information from the Wonderbar Man's web site, I am thinking that this speaker may not work. Does anyone have any experience using a reproduction speaker?

If the one I have isn't going to work, can someone suggest a vendor who carries a speaker that will work?

I am hoping I will only have to do this once......

Thank you.

Regards,

Dennis

I am looking for some input from others that have used reproduction speakers for C1's. I have read the threads in the archives and have visited Wonderbar Man's web site and I am left wondering if the reproductions work ok or cause problems?

Thanks in advance.

Regards,

Dennis

[Jack H.]

Re: Latest on C1 Speakers

Placing an ohm meter across speaker terminals is NOT the way you measure impedance! You're measuring resistance.

What's the difference? Impedance is the 'effective' resistance a given load poses to an AC signal. Resistance is the DC characteristic of the load.

When speaker mfgr's specify impedance, they also define the specific frequency (or frequency band) they're quoting. Industry norms are for impedance to be measured with respect to a 1004 Hz tone, but there are other definitions.

So, to properly measure the impedance of a speaker, you'd have to have a tone generator to produce the driving AC waveform and know/measure its RMS voltage level. Then, connect the tone generator to the speaker and measure the RMS value of the AC current that flows.

Divide the RMS voltage by the RMS current and you get the speaker's impedance. If this isn't the way you obtained your numbers, you're working with 'trash'...

The issue about reproduction speaker 'compatibility' is MUCH more complicated than simple impedance. The thumbnails on various web sites/blogs (like WonderBar Man), grossly over-simplify the situation...

[Dennis C.]

Re: Latest on C1 Speakers

Jack,

Thanks for replying. While I understand there is a difference between impedance and ohms, I didn't know about needing the tone generator.

Here is the verbage from Wonderbarman's web site:

"Corvette Radios 1961 to 1967 use a speaker mounted loading coil with out this coil bias on speaker goes from the normal 1.5 Volts D.C. to 12 Volts D.C. burning out the voice coil in the speaker and, the DS-501.12 Volts on the speaker leads tells You Your radio needs the coil or the DS-501 is shorted on radios that do not use the coils. I find new speakers being sold that are said to be for 1961 through 1967 CORVETTES but have a .5 ohm coil IN PLACE OF A 1.5 OHM. This will cause bias on speaker terminal to drop to .5 Volts D.C. [IT SHOULD BE 1.5 Volts D.C.] overheating radio in about 15 minutes sound becomes fuzzy. Along with slowly over heating wiring harness all the way back to battery. Drain is not enough to blow fuse only to slowly break down insulation on wiring that could cause a short that would burn car to ground?"

"The yellow aftermarket coil should be checked for proper impendeance of 1.5 ohms and are bad untill proven good! I see a lot of them that are .6 of an Ohm.

If you have recently replaced your Corvette speaker and have this symptom simply ring out speaker and if it reads less than 1.5 Ohms, or less than 1.5 Volts D.C. across speaker leads. Then return to vendor and tell them they sold you the WRONG speaker. [This speaker over heats RADIO, WIRING AND, COULD? CAUSE CAR TO BURN TO GROUND] "

Is this hype? Should I go ahead and install this speaker or look for something else?

Thanks for all your assistance.

Regards,

Dennis

[Jack H.]

Re: Latest on C1 Speakers

Sigh!!!

Looks like I'm talking to myself, so this is the last input I'll offer on this thread...

(1) I said I knew about the various mis-information that was presented on different web-sites/blogs including that of Mr. Wonderbarman. I don't need to read it again.

(2) See how he's intermixing the terms resistance and impedance? You can't do that! They're specific and different definitions in electrical engineering.

(3) To measure impedance, you HAVE to do so at a pre-defined AC frequency. That IS the definition of impedance.

(4) He concludes that all 1961-67 Wonderbar radios have the same circuit topology for their audio output stage and use the same speaker. WRONG!!!

(5) That's telling you something about his technical skills compared to a design engineer or a tech who has all the factory original Delco schematics, parts lists, and service bulletins. Nobody with that skill set/knowledge would make the statement(s) he makes!

(6) As a result of this kind of trash talk, people have gone 'runamock' talking about the vital needs of the impedance profile of their speakers.

(7) GM/Delco used at LEAST four different PN's for these speakers over time and each had different characteristics but all were downward compatible for the application.

(8) Each WB radio has a potentiameter associated with the final acoustic drive circuit to adjust the bias on the 2N273 (DS-501) transistor. That HAS to be set properly or you'll get all kinds of (*&^ happening.

(9) Many prior owners either 'blew' or damaged their DS-501 transistors by connecting the radio to an ordinary, off-the-shelf, speaker that lacked the flyback protection circuit components that were built onto the factory original speakers.

(10) These components changed over time with the original design using a series RL filter and the improved later radios using a parallel RLC filter with only the 'L' or transformer out on the speaker. That's why the components mounted on early vs. mid vs. late Corvette speakers differ visually.

(11) His memo says to check the aftermarket coil for proper impedance and it ought to be 1.5 ohms. Another 'dumb' move. He meant to say check the resistance profile of the inductor/choke (it's accomplished by using half of a transformer and leaving the opposite side 'hanging in the breeze').

(12) Since the later style speakers (and their radio chassis) use a parallel RLC flyback protection circuit, if you simply put an ohm meter across the speaker terminals, you're measuring the winding resistance of the inductor/choke/transformer in PARALLEL with the native windings of the speaker's voice coil. OF COURSE you're going to get flakey readings if you do it that way!!! He specifically said to measure the TRANSFORMER. So, you have to de-solder the transformer from the voice coil to make that measurement.

Look, I'm obviously upset because this (**&&^ has been floating around for years just SCARING people who don't understand diddly about radios and electrical design.

But, take a pro like Charlie Sigfried who does impecable WB restoration work. Does he warn of the sky falling if you connect his restored WB radio to an aftermarket speaker?

The answer is, no. If the radio has been repaired/restored properly and the aftermarket speaker agrees with GM's design profile (either early, middle or late), it will work, mon.

[Dennis A.]

Re: Latest on C1 Speakers

I installed the a speaker w/ transformer to 8-ohm from Paragon with my original wonderbar and it works fine....except the old wonderbar isn't the greatest, but with the top down....who cares

[Dennis C.]

Re: Latest on C1 Speakers

Thanks, Dennis

Regards,

Dennis

I installed the a speaker w/ transformer to 8-ohm from Paragon with my original wonderbar and it works fine....except the old wonderbar isn't the greatest, but with the top down....who cares