Radio Speakers

[Harmon C.]

I found some Delco 4 OHM speakers at a swap meet they are 4X6. They are the same size magnets and all as the originals. Is their any way to make them 10 OHM as was in my 73 with the original radio?

[Jack H.]

Re: Radio Speakers

Yes and no.... You can trim the speaker drive magnet of HIGHER impedance speaker with external load components to reduce impedance, but you lose sound transfer efficiency in the process. If you add series impedance to pump the impedance up, you also suffer power transfer loss. It's a no-win situation and in the end, one has to ask why you want to do this....

Impedance is simply one aspect of the speaker's electrical characteristic. When the speaker is 'matched' to the output impedance of the driving source (radio's electronics), you achieve maximum power transfer. When you're 'mis-matched' you simply lose 'some' output power.

The 'trick' to most Corvette applications (pre-shark) era was obtaining a speaker whose frequency response characteristics were 'matched' to the radio's drive electronics. This was dictated, primarily by the use of a DS-501 germanium power/speaker drive transistor. On early Corvettes, the speakers had a matching transformer installed on the speaker itself to save space inside the radio chasis. Without this transformer being present, the sound was highly distorted (the transformer acted as filter to 'color' the sound) and substituting high quality (flat response) speakers without the companion matching transformer resulted in low volume output with a very 'tinny' sound AND you ran the risk of BLOWING the DS-501 drive transistor via electrical overload with the matching transformer being absent....

But, in conventional passenger car applications and in later Corvette radios, the matching transformer was built into the radio chassis itself. So, there you 'could' substitue speakers pretty freely with good results. Original Shark era, 4x6, 10-ohm speakers aren't that hard to come by anyway. So, I guess I'm missing the reason/need for matching impedance....

[Harmon C.]

Re: Radio Speakers

I only paid $1.00 per pair for them new in the box and he had cases of them so I was looking to see if they would work. I never use the radio with the top down and exhast noise old radios are a little weak.

Thanks