Will it work? Original radio, more modern speaker with extra resistor

[Julien Abrahams]

Hey guys, my original radio works, but the original speaker is dead. I have a good speaker lying around (which I presume will fit). However, if I'm not mistaking, these old radios were built to work with speakers that have a resistance of 8-10 Ohms. The speaker I have has a resistance of 4 Ohms. Will it work if I put an extra resistor (say 5 Ohms) between the radio and the speaker? Was wondering if this will work and make it a small project over the summer.

[J. Gomez]

Julien,

Not to go into a complicated mumble jumble technical answer on impedance matching, etc., the simpler answer is;

Adding a 4 ohm resistor in series with the speaker would provide the 8 ohm across the radio output. One note, there would be a loss of sound quality, but it should be fine if you keep the volume in the low range.

The resistor would need to be about 4-5 ohms and would need to be a high power 10W should be fine or higher if the radio amp rate is more than 10W.

One alternative if you want to keep the sound is to hook up two 4 ohm speakers in series that would split power between both, again this is just an option if you have two speakers and if both can be installed.

Good luck..!

[TJ Hopland]

Is this in your 67?     I don't know the details of the specific radio/amp but in general using a resistor in series would work.   So 4 ohm speaker and a 4 ohm resistor with adequate power capacity in series with the speaker would look like 8 ohms to the amp.   Series would be radio + to speaker +.  Speaker - to resistor.  resistor to radio -.   

Down side is the resistor will be consuming as much of the power as the speaker.    Guessing a stock radio to be maybe 5 watts so you would want a 5 watt resistor.  This means you will be down to 2.5 watts for the speaker.   If its a older speaker they tended to be efficient because amps were expensive so it should still be able to get to a reasonable level.    In the 80's amps got bigger and cheaper so the speakers got less efficient.   If you have the specs for the speaker sensitivity is the one that tells you how loud it will be with how much power.  Car audio and a lot of other consumer audio is often missing that spec and on 'pro' gear they play games with how they measure that.

Other option would be to run it direct which would put a heavier load on the amp.  This extra load may or may not be more stressful than doubling the load with the resistor.    Doubling is twice the load but still at what we assume is the rated impedance (ohms) so it will have to work hard but should survive.   Maybe running direct you would be pushing it less because of the reduced load but depending on the actual amp design is if that will stress it more because of the lower than rated impedance. 

With tube amps the risk is in burning out the output transformers which I don't believe are reproduced and are too complicated for a DIY person to repair or rebuild.    With solid state it would usually be the output transistors which are pretty much in the same boat as the output transformers.   The technology has changed enough now that the older devices are no longer made.    Any amplifier that is more than about 10-15 years old is likely suffering anyway because of aged electrolytic capacitors to some degree.   Those overall tend to be available so someone that knows what they are doing can replace them.  Some may not be physically the same as originals but function wise they can usually be duplicated.       

[Julien Abrahams]

Yes, this is my '67. I am certainly not an expert with regard to electronics. Learning as I go along. To prevent frying my radio, I'm asking all the help I can get .

[bcroe]

Hey guys, my original radio works, but the original speaker is dead. I have a good speaker lying around (which I presume will fit). However, if I'm not mistaking, these old radios were built to work with speakers that have a resistance of 8-10 Ohms. The speaker I have has a resistance of 4 Ohms. Will it work if I put an extra resistor (say 5 Ohms) between the radio and the speaker? Was wondering if this will work and make it a small project over the summer. 

A good fix is to get a line to voice coil transformer, with taps for 4 and 8 ohm speakers.  Insulate
the line wires; connect the radio to the 8 ohm and the speaker to the 4 ohm tap.  The return wire
will be common to the radio, transformer, and speaker.  Bruce Roe

[Julien Abrahams]

Well, first I want to see if I can find out why the speaker does not work anymore (probably not, but hey, its a nice Sunday 'project'). I've read on other forums that it is a bad idea to use an external resistor as the resistance of the speaker varies with regard to the response frequency. Another option is to wire two 4 Ohm speakers in series. Then the total resistance is also 8 ohms, and it should be good to go. Just need to figure out a way to do this without cutting holes in dash or door panels (as I think that ruins the car). Thanks for the suggestions.

[n2caddies]

Why not have the original speaker reconed? There are vendors In Hemmings that offer this service. If you are keeping the original radio it may make the most sense. JMHO.
Randy

[76eldo]

I have not had to buy a radio speaker for a long time but is an 8 ohm speaker that hard to find?

When I'm looking for solution to something like this I usually do a google search or search on YouTube.

Brian

[Julien Abrahams]

It is not that hard to find these speakers. The only problem is that I am wondering if I want to spend over $100,- for a brand new speaker for those few occasions in which I listen to the original AM radio. I just think it would be cool if it would work, especially the signal seeking feature is a neat trick. As I have fixed the power antenna, it would be cool if I could get the old radio fully operational. As other projects are taking op some time now, I'll postpone this fun project for later. Thanks for the tips though. .

[Andrew Trout]

Why not have the original speaker reconed? There are vendors In Hemmings that offer this service. If you are keeping the original radio it may make the most sense. JMHO.
Randy

My Dad and I had the radio and speaker out of his '61 convertible reconditioned. We went with Precision Stereo Repair. They're in Utica, NY. https://plus.google.com/115109975884684820572/about?gl=us&hl=en

You can read about their operation on the Hemming's website as well: https://plus.google.com/115109975884684820572/about?gl=us&hl=en

They reconditioned the radio, and also added an auxiliary input so we can plug in an iPhone. The cord is long enough that we can hide it inside the dashboard and have the jack in the glove compartment. 

[mgbeda]

I have done this in the past.  It "works", i.e. you get sound and you don't blow up the radio.  But the volume level goes way down.  T J has now explained to me why that happens.

-mB