Charlie Jones

I have read in several threads here that original Delco radios from the sixties must use 10 OHM speakers. Or the output driver will be damaged.
I have an original AM/FM radio in my 63 Dynamic 88 , and the speakers are toast.
The Parts Place offers new 8-10 OHM speakers for $49 .
My question is , are these just 8 OHM speakers that they HOPE will work in a 10 OHM application ? Are they safe to use with my original radio ?

MDchanic

1. Yes, they should be 10Ω, and it is possible that 8Ω could damage the output transistor(s).
They have a reputation of being sensitive to this.

2. Good question. I have no idea whether their their speakers have the correct impedance.

- Eric

cdrod

If you want to be certain, use a VOM meter and measure the resistance across the speaker terminals. That's what I would do, I would not trust PP to know the products they sell.

Rocketbrian

S&M Electro-Tech Inc. in Minnesota may have what you want. Their email is
turnswitch@turnswitch.com. I bought a 10 ohm front speaker for my 71 Cutlass from them and am pleased with it.

firefrost gold

I too used them they were great to deal with and got my Rallye 350 am working for me. They have the mold and tooling to make new speakers .
Took me in the back and showed me all kinds of old radios and how they differed from mine . They do have a web site also .

rocketraider

Worst to worst you can have your originals reconed, especially if there's an oddball bracket or dash seal involved- and IIRC 63-4 FSC front speakers have a weird moulded rubber seal. Jackson Speaker Service in Jackson MI has done a few for me and Pontiac friends.

You can also put a 2 ohm resistor on the speaker + and jack up the resistance, but that may affect sound quality. Not that those speakers were excatly hi-fi!

Charlie Jones

That is exactly what I was going to do . I took them to some jerk in Orlando that just closed up and left for parts unknown . With my original speakers.

RandyS

A 2 ohm resistor will have no effect whatsoever on the quality of the sound, merely a small effect on the total volume. You can find 10 ohm speakers on eBay at a fair price. If you go with 8 ohm, add the resistor. 2 ohm at any wattage will work for a car radio.

Indy_68_S

Remember though; A typical VOM/multi meter is reading resistance...not impedance. You can get close with a meter, but IIRC, the reading will be lower than the impedance. A 8 ohm rated speaker will read like 6-7 ohms. A 10 ohm speaker will read around 8-9 ohms.

MDchanic

This is true.
Resistance refers only to the way in which a substance resists the flow of electrons.
Impedance includes this quality, as well as the resistance caused by inductance and/or capacitance, and tends, therefore, to be related to the frequency of the current it is exposed to, so impedance is very relevant to audio systems.

- Eric

plonka

I too, have used these guys. They know what's up.

Fun71

Right. Essentially resistance is a DC measurement and impedance is an AC measurement.

bluecab

IIRC impedance varies with frequency.
If an amplifier is designed to drive a 10 ohm speaker at lower frequencies the impedance will be lower.
I believe that an 8 ohm speaker would probably be ok in that application.
Problems occur when a low impedance speaker is used where it should not be and the speaker presents itself as a dead short to the output transistors of the amplifier.
This will typically happen when connecting 4 ohm speakers in parallel which results in a 2 ohm static impedance that most amps are not made for.

MDchanic

I wouldn't go so far as to compare it with a dead short.

A current passing through a conductor induces a magnetic field.
You need voltage to drive the current, more so as resistance increases, but it is the current that creates the magnetic field.

Loudspeakers work by having a current, from the radio / amplifier, run through a coil in the base of the speaker cone (the part that moves), which is resting inside of a recess in a permanent magnet (the big, round one mounted rigidly on the back of the speaker frame). As this current varies, it creates a varying magnetic field, which pulls the cone toward or away from the permanent magnet, which moves the cone, which compresses the air, which makes sound.

Because of this, the more current you can drive through the speaker's voice coil, the more sound you can get out of the speaker. If you exceed the capabilities of the speaker, you will either deform the weakest physical components (the cone or the cone surround), or you will burn up the voice coil with excessive current, exactly like blowing a fuse.

On the other end of the equation is the amplifier. Obviously, you want the speakers to be able to withstand as much current as possible, without making their moving parts so heavy that they cannot respond quickly enough to make clean sound, while you want the amplifier to be able to produce as much current as possible, with enough voltage to push that current through whatever impedance the voice coils that you are driving are presenting.

As with automotive engineering, the principle "Speed costs money - How fast can you afford to go?" applies - it is cheaper to make less current and to make speakers that can handle less current.
Therefore, as with cars, all audio is an exercise in aspiration meeting reality.
In the case of factory radios / stereos, it is in the car company's interest to make a system that sounds "pretty good," but costs very little, so the capabilities of their components are very limited when compared to what you would buy yourself.

To get (finally) to my point: Output transistors, like wires, switches, and other components, are designed to to be able to pass a certain amount of current without damage, but if too much passes through them, they will overheat and be damaged.
As stated by others, according to Ohm's Law, if you decrease resistance (or impedance), current flow will increase. If the design of the output transistors is just barely adequate for the rated impedance, then reducing the impedance just a bit may be enough to blow them if you turn up the volume high enough (probably not, if you don't, as there won't be that much current flowing). If the design is extremely robust, as with many high-end components, then reducing speaker impedance will do no harm, and, by allowing increased current flow, will permit louder sound to be produced (though the transistors will likely need to shed more heat, thus requiring larger heat sinks or cooling fans).
For instance, I have a set of four Adcom GFA-565 amplifiers powering my stereo, each of which is rated for 300W into 8Ω, but about 450W into 4Ω, and is stable down to 2Ω (putting out 600W or more that way). It can drive a high current through a low resistance without harm, and does so with a high voltage of about 80-100V, meaning that if you were to run your speaker wires inside of walls, the building code would require you to run them as though they were household wiring. The internal output circuitry is extremely robust, and, because of its high current capacity, bears some resemblance to an arc welder, which, in some ways, it is.

The factory radios that GM made in the sixties and seventies are not robust in this way, and require only a small excess of current to fry them, which does not have to even approach being a dead short.

- Eric

radioburningchrome

This topic comes up often and the information in this thread should be made into a sticky.

radioburningchrome

Excellent explanation.

Why 4 Adcom monoblocks? Is your house an auditorium?

After years of marriage (sold the Hafler DH200, Scott 101 and Fisher 500B)all I have left is one Adcom GFA-535 II, with a set of pioneer floor speakers. Sufficient in my "old" age. (off topic)

MDchanic

Welllll... I used them to bi-amp a pair of Infinity QLS-1s, which are power hogs, plus I have them in my wife's shop, which is a 75x25 foot room.

But, yeah, you could pretty much use them to address the fans at Wrigley Field.

- Eric