71 Radio Speakers (AM/FM)

[Jack H.]

Re: 71 Radio Speakers (AM/FM)

WAY too much is made of the impedance characteristics of speakers!!!

The reason you want to 'match' impedance is to achieve optimum power transfer from the radio's audio drive circuit to the speaker(s). Use of an 8-ohm impedance speaker to substitute for the factory original 10-ohm speaker(s) won't result in 'diddly' in terms of difference(s) you can detect!

Plus, modern speakers are MUCH more efficient than those of yesterday (magnet & speaker cone technology) resulting in typically increased electrical input to acoustic output efficiency... So, who cares if the impedance isn't 'perfectly' matched?

Now, it's a COMPLETELY different story for C1/C2 Corvettes where major component of the radio itself (the final acoustic drive matching network) moved OUT of the radio chassis and onto the speaker frame (the 'transformer' some refer to...actually, it's an RL filter circuit that just uses one side of the transformer to create the inductor portion of the RL circuit). Without those components in the circuit, you WILL get terrible sound quality AND you'll pretty quickly burn up the DS-501 audio drive transistor.

But, by Shark era, the audio drive components were moved OFF the speaker and back into the radio chassis. The DS-501 audio drive transistor moved out of the radio chassis onto a separate heat sink (the 'convector') making it effectively part of the radio's wiring system for Corvette. So, with these C3 cars, you can freely substitute speakers without fear of 'frying' the radio...

[Joe L.]

Re: 71 Radio Speakers (AM/FM)

WAY too much is made of the impedance characteristics of speakers!!!

The reason you want to 'match' impedance is to achieve optimum power transfer from the radio's audio drive circuit to the speaker(s). Use of an 8-ohm impedance speaker to substitute for the factory original 10-ohm speaker(s) won't result in 'diddly' in terms of difference(s) you can detect!

Plus, modern speakers are MUCH more efficient than those of yesterday (magnet & speaker cone technology) resulting in typically increased electrical input to acoustic output efficiency... So, who cares if the impedance isn't 'perfectly' matched?

Now, it's a COMPLETELY different story for C1/C2 Corvettes where major component of the radio itself (the final acoustic drive matching network) moved OUT of the radio chassis and onto the speaker frame (the 'transformer' some refer to...actually, it's an RL filter circuit that just uses one side of the transformer to create the inductor portion of the RL circuit). Without those components in the circuit, you WILL get terrible sound quality AND you'll pretty quickly burn up the DS-501 audio drive transistor.

But, by Shark era, the audio drive components were moved OFF the speaker and back into the radio chassis. The DS-501 audio drive transistor moved out of the radio chassis onto a separate heat sink (the 'convector') making it effectively part of the radio's wiring system for Corvette. So, with these C3 cars, you can freely substitute speakers without fear of 'frying' the radio...

Jack-----


I once connected 4 OHM speakers to my original radio for a VERY short period of time. I just did it for a trial and would not have left them connected for very long, anyway. However, even if it had not been a trial I wouldn't have left them connected. The sound was absolutely horrible.

[Jack H.]

Re: 71 Radio Speakers (AM/FM)

And, did I say to cut the impedance by 60%??? That's the effect of going from 10 ohms to 4 ohms... No, I said you'd not see diddly in terms of replacing a set of 10-ohm speakers with 8-ohm units. That's a modest 20% mis-match.

[Joe L.]

Re: 71 Radio Speakers (AM/FM)

And, did I say to cut the impedance by 60%??? That's the effect of going from 10 ohms to 4 ohms... No, I said you'd not see diddly in terms of replacing a set of 10-ohm speakers with 8-ohm units. That's a modest 20% mis-match.

Jack----


I didn't say you said one could cut the impedance by 60% and all would be well. I just reported on what happened when I tried 4 OHM speakers.

[Paul C.]

Re: 71 Radio Speakers (AM/FM)

I know your can get the passenger's side speaker out without rmoving the dash--I have done that. I have also accessed the driver's side speaker to change wires by pulling the the instrument bezel forward--but can you remove the driver's side speaker without removing the dash pad? Would like to stay away from removing it if possible.

[Jack H.]

Re: 71 Radio Speakers (AM/FM)

Mille scuze, Joe! I thought your reply was a critique rather than an enhancement. Guess I need a thicker skin!

Yes, I would expect what you observed... It's the degree of impedance mis-match that dictates the result. When 'perfectly' balanced, output power divides evenly between the radio's speaker drive circuit and the target speaker(s).

When you have an impedance mis-match, audio power begins to divide unevenly. If the mis-match is excessive (like your case of using 4-ohm speakers in a 10-ohm environment), you lose audio output and begin to dissipate too much power in the radio's drive electronics.

That can result in electrical component overheating, distortion, and if taken too far, damage to the radio. But, 'minor' degrees of mismatch fall within design tolerance limits and aren't noticeable. Typically, tolerances are designed in the 5-25% range and that's why the use of 8-ohm speakers in a 10-ohm environment isn't a big deal...

[Jack H.]

Re: 71 Radio Speakers (AM/FM)

Yes, you can drop the steering column, remove the speedo/tach instrument cluster and get to the LH speaker that way. But, some consider that route more labor intensive than lifting out the upper dash panel...

[Paul C.]

Re: 71 Radio Speakers (AM/FM)

Do you have to remove the dash pads to replace the speakers? I have replaced the passenger side without removing the pads and have accessed the driver's side speaker wires by pulling the instrument cluster forward--but am not sure if I can replace the speaker that way. Don't want to remove the dash pads if I don't have too--worried about them cracking. Thanks Paul

[Joe L.]

Re: 71 Radio Speakers (AM/FM)

Do you have to remove the dash pads to replace the speakers? I have replaced the passenger side without removing the pads and have accessed the driver's side speaker wires by pulling the instrument cluster forward--but am not sure if I can replace the speaker that way. Don't want to remove the dash pads if I don't have too--worried about them cracking. Thanks Paul

Paul-----

I think there may be a confusion of terms here. The dash pads include both the UPPER dash pad (the one that is directly below the windshield and which extends the full length from A-pillar to A-pillar. The LOWER dash pads are those pieces which, on the driver side, includes the tach and speedo and on the passenger side includes the map pocket.

We have been discussing various way to replace the speakers requiring different combinations of pad removal.

[John H.]

Re: 71 Radio Speakers (AM/FM)

HOLD ON TO YOUR HATS, FELLAS.
I can personally tell you to stay away from Tony Mac Crutchfield
also known as Wonder-Bar-Man. He has a very slick web site so please
dont get sucked in. Tony is a NCRS member only to get free advertizing
and busines who dont ask first and find out the hard way, like me.
I used Tony to check out my 72 radio and recore one speaker.
Ieven was super stupid and sent him the full amount $350 ALL IN ADVANCE. After being cused out over the phone on more than one occasion when I asked for my money back and radio 4 months into the
ordeal. He said I hate you NCRS corvette nuts, but the radio is now his
to fix when ever he gets to it. I have several e-mails that will back this
all up. He even said it was a extra $125 cause the radio was in a fire
and had exstinghser power all over it. He also said the radio speaker
wire was to short. Now fellas PLEASE PAY ATTENTION HERE.
I AM THE ORIGINAL OWNER OF THIS 72 CAR, RADIO AND SPEAKER.
The story even gets better. I had the 72 radio removed in 1977
and saved it in my closet until this episode with Tony in 2004.
When I first contacted Tony I asked him "If a car radio could cause
a fire if is shorted out?" His response was it would be very unlikely
due to inline fuse and low amperage, etc.
My car did catch on fire in 2004 due to a LIVE 20AMP wire that was
pinched when a shop was installing a new heater core. The radio in
the car at the time was a after market model from 1977.
Well when Tony put this line of B.S. on me four months later he forgot
which radio he was sent, and he proceeded to extra charge for his
line of B.S.. Fellow NCRS MEMBERS DO NOT USE WONDER-BAR-MAN
If you want more information you can call me or e-mail me.
happyappy@bellsouth.net John O'Haire #38127
I along with several other NCRS members had a very good discussion
with the DriveLine/Restorer staff while in St.Charles at the National
Convention. WE NEED TO BLACKBALL THESE TYPE OF FAKES.

[John H.]

Re: 71 Radio Speakers (AM/FM)

P.S. From Big John the previous poster.
Just as a reminder if you send off your radio, DO NOT include the
radio knobs. Any repair shop has plenty of knobs, but yours are the
originals. Just explain in a note that you dont need replacement knobs.
Or yours will end up with Tony the forked tongue......
There are a few other vendors out there that are first class I helping
you with your radio needs.

[Norman S.]

Re: 71 Radio Speakers (AM/FM)

Thanks for the tips, Paul. I agree with you re radio/speaker quality but I just want the speakers operate without crackling so my XM radio sounds better.

[Norman S.]

Re: 71 Radio Speakers (AM/FM)

Hi Paul-- thanks for all the valuable info. Would've got back sooner but went to the Bend Regional.
Best regards, Norm