External speakers and Ohms ?

[Hydrolastic]

Hello All, Been messing around since 2019 with magnavox stereos. Not knowing anything about them I have experimented (and blown up a couple) of stereo's Its been a mystery why and I want to figure this out.
without a long drawn out history it comes down to this. I have two external speakers cabinets they are both S-37 units. They come with a 3.7 ohm 583 962 speaker and the 580050-1 horn . The magnavox speaker PDF says that's the correct for a S-37. The S-43 is the speaker that comes with the concert grand it has a similar wiring (Bi-amped three wire) and the same horn but the woofer is a 584 037 speaker also 3.7 ohms but a much heavier magnet I want to convert a external speaker (S-37 to S-43) to run on the concert grand but the speakers it uses internally is the bigger 8 ohm woofers. I am also wondering why the external S-43 GG speakers are not 8 ohms ? Hydro

[TC Chris]

Impedance matching is not a crucial issue for most speakers and amplifiers (except some early transistor amps). The effect of mismatching may be some bass-range issues (too flabby or boomy). It's usually a question of damping factor. Just hook 'em up and see how they sound.

Note: as mentioned, some early transistor amps were picky. My old Heath AA-22 amp has a 4-ohm resistor in series with the speakers on the 4-ohm tap. I observe that one carefully.

Chris Campbell

[Hydrolastic]

Hello Chris, Thats good to know on the ohms. I read somewhere that the ohms had to go equal or smaller. Or larger...
So there were various size magnets on the Magnavox speakers. Does that effect the amp? or the transformer on the amp? Here is a photo of the speaker selection from magnavox. I am wondering if the 7.5 watt amp 175 can be damaged by driving a big magnet speaker or do you need the larger AMP182 or 8102 to run those? that's what I was doing when the AMP 175's stopped working.

[TC Chris]

One of the issues with magnets is back-EMF: the electric current generated by the voice coil moving in a magnetic field, feeding back to the amp. It doesn't hurt anything but it can affect how things sound. Magnet sized may affect a speaker's efficiency--how much noise it makes for a given power input. Basically, the rule here is try it and see how it sounds. The differences are mostly fairly subtle

On old transistor amps that are picky about speaker impedance, you're safer with a higher impedance speaker.

The is not problem using a small amp to drive a big speaker, as long as you are not using it at a party with a bunch of drunks who want to turn it up. Your tweeter can be damaged if an amplifier is overdriven into a form of distortion called clipping. But that's usually audible, or at least something that reasonable people avoid. And it only happens when you turn it up way too high. It's not the low powered amp that's the problem. It's asking the amp to put out more power that it can deliver. A small amplifier and a big speaker can be very happy together.

When I was a kid I played my one-tube RCA portable phono through a 12" Zenith console radio speaker. Makin' do with what was at hand.... You can see the RCA in my YouTube video here:

https://www.youtube.com/watch?v=zrc0enXp8AY&t=57s

Chris Campbell

[electra225]

What Chris said.....

I don't think you would have a problem using any speaker Magnavox put into their equipment. Remember, also, that the speakers Magnavox used was matched to the cabinet and also to the amplifier. Mixing speakers may not damage the electronics, per se, but it might not sound the best, either. It is generally good practice to use the speakers and electronics in the cabinet Magnavox provided at the factory.

With consideration for not derailing your topic, Concert Grand used two sizes of magnets on their 15" woofers. A 50 oz. magnet in channel 1 and a 35 oz. magnet in channel 2. I believe the speakers in S-43 speakers have the same size magnets.