4 ohm vs 8 ohm

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plugger340

plugger340

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Are the radios on the 2nd GEN a-bodies 8ohm? If so, is it possible to run a single 4 ohm speaker or do I have to run two 4 ohm speakers in series?
The reason that I ask is that I have a single 4 ohm 4x10 that I’d like to install in the dash.
 
IIRC, (I am assuming that you are talking about 1970ish +/-), the speakers were 8 ohm with the factory radios. You do not want to use the 4 ohm on it's own as it is hard on the output transistors. Just like revving an engine with no load. You need an 8 ohm sinlge, or two 4 ohm in series.

@moparmat2000 made and supplied a nice little speaker frame that fits the original dash bolt pattern, only it holds two 3 inch speakers.....A nice piece.
 
CFD244 said:
You need an 8 ohm sinlge, or two 4 ohm in series
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You can put a 10w (probably 5 watt would do) 4 ohm resister in series with the 4 ohm speaker.

It's not 100% the same as an 8 ohm speaker but it should protect the output transistor.
 
You can use a mismatched speaker [ different ohms ] but the volume will be less & you could get some slight sound distortion.
 
Bewy said:
You can use a mismatched speaker [ different ohms ] but the volume will be less & you could get some slight sound distortion.
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Wouldn't be more ? A 4 ohm speaker on a 8 ohm amp should make more wattage, so if the components can handle the extra wattage/heat it may work or just burn our over time, doubt the OP gonna crank it so it might work. I'm not sure better with aftermarket amps.
 
I'm a retired Electrical Engineer and had done a lot with early audio, the CFD244 is giving you good advice, use a 8 ohm speaker, the radio's from Bendix will not tolerate 4 ohms the transistors of that time are not that robust, if you really want 4 ohms speaker there are mods to make it work, but that would require changing the output amplifier stage or a 2:1 output impedance matching transformer. A modern I/C Amp it would increase easily increase output power and wouldn't care what speaker impedance is, they're designed to handle it.
 
Speedy Pedi said:
I'm a retired Electrical Engineer and had done a lot with early audio, the CFD244 is giving you good advice, use a 8 ohm speaker, the radio's from Bendix will not tolerate 4 ohms the transistors of that time are not that robust, if you really want 4 ohms speaker there are mods to make it work, but that would require changing the output amplifier stage or a 2:1 output impedance matching transformer. A modern I/C Amp it would increase easily increase output power and wouldn't care what speaker impedance is, they're designed to handle it.
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Okay, thanks. Why are many modern car speakers 4 ohms instead of 8 ohms?
 
Bewy said:
You can use a mismatched speaker [ different ohms ] but the volume will be less & you could get some slight sound distortion
Click to expand...
The output transistor is looking for an ohm range to work within its parameters. 4 ohm is closer to a dead short than 8 ohm so the transistor has to work harder and can lead to early failure.
 
Some Sub amps can go down to 1/2 ohm, My guess back then they weren't looking to make a lot of wattage and probably with the components of the time 8 ohm made sense, 4 ohm may been a better compromise when people wanted a little more juice out of there stereos.
 
The number of ohms the speaker presents directly affects the amount of amps needed to be supplied to drive the speaker. A 4 ohm speaker will cause the power supply to provide double the number of amps and will result in burning out your amplifier. Current x ohms = voltage.
 
Germanium Transistors were not intended nor designed to be high current devices, 8 ohms was the standard in that time period. The new systems trade high fidelity for higher power using lower output impedances. Your radio is a class A amplifier continuously conducting in that mode. The newer systems are I/C's Class A/B at best most often Class B conducting 70% of the time, causing distortion.
 
Rather than use a series resistor, I'd just find another 4 ohm and wire the two speakers in series. Mount it remotely somewhere, like ?? LOL ?? the rear deck.
 
If you measure the resistance of the voice coil of a 4 ohm speaker, it is not 4 ohms. That is because with speakers, the term 4 or 8 is the IMPEDANCE of the voice coil, not the resistance. To complicate matters, impedance is also quoted in ohms. The actual resistance [ impedance ] varies with frequency; impedance is the resistance to alternating current [ AC ], resistance is the resistance to direct current [ DC ]. The quoted impedance of a loud speaker is the nominal impedance.
What I said in post #4 is correct. In electrical theory there are 'theorems & laws', such as Thevenim's. Another one is the 'Maximum power transfer theorem', which states that the output of a device will transfer maximum power to the load when the input of the load has the same value [ or load ] as that of the output device. If the car radio has an output impedance of 8 ohms, max volume & clarity will be obtained with an 8 ohm speaker. Using a 4 or 16 ohm speaker will result in max volume not being as loud & some possible distortion...but it will work ok.
 
Every car amp I've ever heard of you lower the speaker impedance you gain wattage.
But like I said I've more experience with aftermarket stereos, my Punch 150HD is rated 180w mono @ 4 ohm but makes 300w at 4 ohm and 600w @ 2 ohm not rated to run 2 ohm but many do especially for competitions.
 
273 said:
Every car amp I've ever heard of you lower the speaker impedance you gain wattage.
But like I said I've more experience with aftermarket stereos, my Punch 150HD is rated 180w mono @ 4 ohm but makes 300w at 4 ohm and 600w @ 2 ohm not rated to run 2 ohm but many do especially for competitions.
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The issue is, whether the old transistors will put up with the load. These things are OLD. I don't know when the last germanium transistors were used
 
67Dart273 said:
The issue is, whether the old transistors will put up with the load. These things are OLD. I don't know when the last germanium transistors were used
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I totally agree, I have no idea if they can. Just never heard of less volume going with less impedance.
 
You could always cut a board to fit the speaker size and run like 2 3.5" 4 ohm wired for 8 ohm.

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antiqueradios.com

replacing speakers with higher impedance

I've got a philco AA6 am/fm radio with a scratchy sounding speaker. This set has dual speakers paralleled together. DC resistance on these two measures 2.3 o…
antiqueradios.com antiqueradios.com

This thread has some good info. Scroll to about halfway down the page and there's a handful of posts there and on the next page that are educational.
 
The bottom line is you need to do some math if you want to be certain. The amp is rated to put out a maximum current. The speakers the system came with meet the design criteria of the radio manufacturer. You should be careful when you “load the system” ( connect the speakers) the impedance of you load should match what the system cam with. If you put 4 ohm speakers on an 8 ohm system in a one for one swap and then crank the volume you will burn out your amp. It is no more complicated than that, understand that I’m recently retired form doing this for a living.
 
plugger340 said:
Thanks, that’ll be plan B if I can’t find a second reasonably priced 4x10 4ohm speaker
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I have the one from Retrosound. It wasn't exactly cheap, but I bought it before the inflation run-up of the past few years. So the price today may be out of your definition of reasonable.
It works well with my old radio.
 
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