Impeadance adding external speakers

[Hydrolastic]

Hello guys, experts. So I am trying to understand the proper way to match speakers to a tube amp. various places I have read that matching speaker impedance is necessary on a tube amp as the speakers draw power based off of the impedance of the speakers / horns.
On the CG the internal speakers are 5844140 and 5844130 both 8 ohm. The horns are the 580053 8 ohm. as far as I can tell the SO 43 is the correct external speaker. this is a 584037 woofer 4 ohm and a 580050 horn 16 ohms
to clarify the biamped setup means that channel 1 sees a 8 ohm woofer and a 8 ohm horn AND a 4 ohm woofer and a 16 ohm horn wired in parallel. Using a speaker impedance calculator I get 2.67 ohms on the low and 5.33 ohms on the high.
Can someone explain to me whats happening here ? I understand that the lower the impedance that the louder the speaker will be on the same power. What I want to understand is when is it harmful to the amp to run different impedances.

[electra225]

I'm no expert, Hydro, and try not to think too hard.....

First off, I try to let the engineers do the thinking, then I try to renew or repair parts like they were when they left the factory. My thinking on this would be that if you have the correct speakers, the ones specified in service literature or what was there when it left the factory, I'd say you are good, regardless of what impedence they measure. My understanding on tube amps is that as long as there is a "reasonable" load on the output transformer, you shouldn't do damage. Having the exact specified impedance of the speaker is unimportant. There might arguably be some performance degradation, but many ears couldn't hear it.

Secondly, Magnavox speaker wiring is bizarre. They use speakers of various impedance, wired in series and parallel. The CG has two different size speaker magnets, and my Imperial has a bell cover on one speaker, none on the other one. Wires run every which direction, external speaker connections and the unusual "Channel 2" connections are hard to figure out and even worse to troubleshoot. Another problem with mathematical equations that figure speaker impedance is that you start with DC resistance. That may put the calculations off to start with.

Another thing I should mention. I think the external speakers for a CG will also work with an Imperial. The cabinet might not be the same but the speakers will work. I had a set of external speakers designed and in the works by a man in Missouri a few years back. He was killed in an auto accident. The project, about half done, and, more importantly, the plans, disappeared. He was building the cabinets out of cherry-veneered ash. I had the speakers found and the wiring made. External speakers for a CG are half the size of the CG cabinet. These were to be on casters. Losing those plans put a halt to the project. I was going to use front-fired 15" and 12" woofers with a 4 X 10 horn. They weren't Magnavox speakers, per se, but should have worked well. I have no idea what the impedance was. I still have the speakers, and recently blew up the horns when I was working with the Imperial chassis.

[TC Chris]

Hello guys, experts. So I am trying to understand the proper way to match speakers to a tube amp. various places I have read that matching speaker impedance is necessary on a tube amp as the speakers draw power based off of the impedance of the speakers / horns.

My understanding is that impedance matching mostly affects damping factor, which is basically the interaction between the amp's power output and the speaker's back-flow to the amp caused by the voice coil moving in a magnetic field, generating some power. Too much mismatch can cause flabby bass or inadequate bass. The effects are pretty minor in most cases. And measured impedance and advertised impedance often differ. Stereophile often suggests in speaker reviews, "this speaker will sound better on the 4-ohm tap of a tube amp." In any event, it's mostly unimportant except as impedance mismatches may affect sound in minor ways. It may affect performance of the crossover network, and if you are unhappy with the balance, maybe try different values of capacitors in the crossover.

A mismatch is not going to cause harm to equipment or burn anything up. Most speaker damage is caused by too little amplifier power, which results in "clipping" of the output signal when people try to crank up the amp to stadium-concert sound levels. Read about it here:
https://en.wikipedia.org/wiki/Clipping_(audio)

So basically, feel free to play around with values to see how they affect the sound you hear. Don't worry about hurting the equipment. It's not like plugging 115 VAC device into a 220 VAC outlet.

Chris Campbell

[hermitcrab]

I get confused by this subject as well , I was told you can use 4 ohm on a 8 ohm amp as long as you are not playing it full blast , otherwise it stresses out the outputs , I have a portable player from Monkey wards ... it uses 32 ohm speakers ... try to find some of those ... I hooked up 4 ohm car speakers to it , it sounds good , but am I destroying the amp?

[electra225]

I don't understand all I "know" about solid state equipment, but my understanding is that some circuits use the 32-ohm speakers are a part of the output circuit. I don't believe I would eliminate the 32-ohm speakers. Replacing them with 4-ohm speakers might not work out well long term. Just my two cents, YMMV......

[TC Chris]

I get confused by this subject as well , I was told you can use 4 ohm on a 8 ohm amp as long as you are not playing it full blast , otherwise it stresses out the outputs , I have a portable player from Monkey wards ... it uses 32 ohm speakers ... try to find some of those ... I hooked up 4 ohm car speakers to it , it sounds good , but am I destroying the amp?

Greg is right. If the speakers are 32 ohm, then they are likely in an older transistor circuit that needs the unusually high impedance. You could run 2 16-ohm speakers in series, or 4 8-ohm ones.

My Heathkit AA-22 from the early '60s has a 4-ohm wirewound resistor in the 4-ohm tap circuit. They were worried about too-low a load. But for most modern designs and just about any tube amp, exact impedance matching is unimportant except as it affects sound at the margins.

Chris Campbell

Chris Campbell