Full coil 16 ohm vs 8 ohm partial coil - matching speaker

[pjd3]

Hello,

Has anyone actually done an A/B test of say, the full secondary 16 ohm coil with a 16 ohm speaker and then a the 8 ohm secondary tap on the same model of matching 8 ohm speaker? And if you did, were there any notable differences in fidelity, or freq response, etc...?

I have been curious of this for quite a while but more specifically, my kids are picking up a pair of G10 Vintage speakers for my stereo amp and I forget to tell them whether to get the 16 ohm or 8-ohm version. I did mean to tell them the 16 ohm as I've only heard that it is better to use the entire secondary coil of the amps output transformer. I had to wonder if they got the 8 ohm speaker by accident and I used the 8 ohm tap, is there anything I would have compromised at all in tone as opposed to a 16 ohm speaker using the full 16 ohm full coil tap?

Not a big concern but, I am curious if there has been a notable difference for anyone who has tested this.

thanks,
Best,
Phil D

[Stevem]

A voice coil being a coil of wire with a magnetic metal in its center has inductance just like a choke does in a power supply.

The differing amounts of inductance from speaker to speaker makes for a differing sound and responce between speakers .

A 16 ohm driver has more coil windings then a 8 ohm driver for example.

The inductance also changes when speakers are wired in series or parallel

The magnet type will make a difference also.

For example, a Alnico magnet speaker wil compress a good amount before a ceramic or Neodymium magnet speaker will and this fact gives a Alnico magnet driver more sustain to it when power going into the voice coil overwhelmes the magnetic flux of the Alnico magnet.
It also makes for a looser bottom end response at that point.

[TUBEDUDE]

Given both options, I would go with 8:8. Less coil wire on both sides. This would seem to be less reactance involved. But intuitive doesn't mean correct.

[Stevem]

When using the highest impedance secondary tap that a given OT has your then also getting the best coupling that can be had between the Output transformers primary and secondary.

[flemingmras]

This is an absolutely pointless and frivolous argument, and I wish whoever came up with this fallacy would stop coming up with these falsehoods.

16 ohm and 8 ohm variants of the exact same speaker will not sound identical. How can one draw the conclusion that "it's because you're not using the full secondary" from that?

Output transformers are just power transformers for speakers. They work the exact same way and do the exact same thing as power transformers. A push-pull output section is a full wave center tapped rectifier circuit flipped upside down and backwards. The output tubes are just modulating DC back into AC through the output transformer primary windings. The transformer steps it down to a lower voltage that the speakers can work with within their rated power handling.

If I feed 120VAC into the primary of a 100 watt Marshall transformer, I will get 11.65VAC on the 16 ohm tap, 8.24VAC on the 8 ohm tap, and 5.82VAC on the 4 ohm tap. Using the different taps just sets a different voltage for each speaker load impedance so that the proper load is reflected back to the tubes and the same power transfer occurs regardless of speaker load. The tubes don't know any different.

[martin manning]

Some transformer data sheets include frequency response curves for each secondary tap. I took a shot a measuring that here: https://ampgarage.com/forum/viewtopic.p ... 95#p440495

[flemingmras]

Some transformer data sheets include frequency response curves for each secondary tap. I took a shot a measuring that here: https://ampgarage.com/forum/viewtopic.p ... 95#p440495

I'm not arguing that different taps may/may not have differing frequency responses. I am, however, debunking the "16 ohm sounds best because you're using the full secondary" and the "If you're using the 4 or 8 ohm tap when there is a 16 ohm tap available, you're not using your transformer to its full potential" argument. This is the garbage that gets circulated by people who know nothing of electronics, thus they believe every "article" they read because they don't know any better. Most of these "articles" from "reknowned trusted sources" are the epitome of cork sniffing at its finest.

Like what if the secondary were only a 4 ohm secondary? Would it sound worse if we added another secondary in series to make it 16 ohm, but only used the 4? Like where do we draw the line here?

I'm of the long held belief that if you take "articles" at face value and can't tell fact from bullshit written in the tube amp "article" that you're reading, you probably should not be working on tube amplifiers.

[Stevem]

Flemingmras we're not having a argument as you precive by your responce in post 65, we're having a discussion, your the one who seems to be in need of having a argument to assert your superior knowledge.

Output transformers other than some Partridge models are wound /made with the concideration ofthe highest impedance tap first and foremost that they need to have, and that as Martin's info shows does make a difference between the availabile taps .

[pdf64]

Hammond info shows that with some multi tap models, the frequency / phase response gets worse with each higher tap, eg https://www.hammfg.com/files/parts/pdf/ ... 1697661946

[didit]

To the initial question posed assume we all broadly agree that it depends.

Output transformers are just power transformers for speakers. They work the exact same way and do the exact same thing as power transformers.

I trust we'd also agree this is a serious oversimplification. The power transformers we use are designed to provide cost-effective and efficient coupling of the primary to secondaries in a stable narrow band from 50-60Hz with relatively stable operating transfer. Design objectives for output transformers also involve cost and efficiency, but get complicated by goals of wide bandwidth of up to three decimal orders of magnitude (roughly to 10 octaves) and relatively linear performance for over 100dB+ of dynamics all while meeting the damping requirements of the upstream speaker load, etc., etc., -- so not really exactly a power transformer.

Best ..

[Helmholtz]

Hammond info shows that with some multi tap models, the frequency / phase response gets worse with each higher tap, eg https://www.hammfg.com/files/parts/pdf/ ... 1697661946

Interesting.
Of course something like 0.3dB difference at 20kHz looks rather insignificant.
Hanmond uses a source resistance of 3.2k here, too low for pentode mode.

With my own measurements I use an Rs of 22k, but then I have to boost the signal using a SS power amp.

[pjd3]

Flemingras,

This is why people like me generate posts like this, to get beyond any rumour or misgnomer about, well, anything. I'm certain we have all been subject to misguided information and I take that as a normal development of finally arriving at the correct theory on things. You have refuted the "full secondary" crap but have not offered any explaination of "why" it is bull shit and what the real situation is. Kind off a waste of post space.

I brought this up to one of our principal EE engineers here at work who was the main design engineer for the new flagship defib/monitoring unit from one of the most well known companies. He;s a pretty "fart smeller" who has been up the ass of all of this for decades. He explained that if not using the entire secondary coil that the primary to secondary coupling may not be as full or complete as with say, a full 16 ohm tap, and could possibly make for some inductive leakage due to less used interleaved portions of the coils. He couldn't speak for how it would effect measured or perceived tone but, it wouldn't surprise me if he knew that could happen as he's been dealing with transformers directly in life saving equipment for a very long time, and little things all matter in these devices. That's why I think in my original post I asked if anyone had actually done an A/B comparison of 8/8 ohm tap-to-speaker, and then a 16/16 ohm tap-to-speaker, as that may provide a very apparent perception of difference if there even was a notable difference.

If my daughter had accidentally ordered me the 8 ohm versions of this speaker, I just would have hooked them up to 8 ohm taps and be done with it, and I'm confident I would have lived fine with it. But I always would be wondering what I would have experienced with the 16 ohm speakers to the full secondary tap. You know how that stuff goes.

Thanks everyone for coming around.

Best,
Phil D.

[pdf64]

I think that his point, that the difference between 8 and 16 ohm versions of the same speaker model are likely to be rather more significant than differences between the 8 and 16 ohm OT taps of any given transformer, is valid.

[Helmholtz]

I think that his point, that the difference between 8 and 16 ohm versions of the same speaker model are likely to be rather more significant than differences between the 8 and 16 ohm OT taps of any given transformer, is valid.

Not sure.
The measurements of Martin Manning do show significant difference, e.g. 3dB at 10kHz.
I don't agree that frequencies above 5kHz don't matter with a guitar speaker, as that's where most of the "chime" happens.

[flemingmras]

To the initial question posed assume we all broadly agree that it depends.

Output transformers are just power transformers for speakers. They work the exact same way and do the exact same thing as power transformers.

I trust we'd also agree this is a serious oversimplification.

Um...no we wouldn't.

The power transformers we use are designed to provide cost-effective and efficient coupling of the primary to secondaries in a stable narrow band from 50-60Hz with relatively stable operating transfer.

Um...who said that?

The size of the iron is dictated by its lowest operating frequency. The lowest operating frequency vs the power needed to be transformed is their primary concern. The lower the frequency, the greater the iron mass necessary to transform it efficiently. This is because you're transforming less energy per second the lower the frequency.

This is the whole premise behind SMPS power supplies. Because they step the operating frequency much higher (250kHz and up), the transformer transforms more energy per second, and thus doesn't need near the iron mass as a 50-60Hz transformer would given the same power. This allows for drastic downsizing of the transformer to transform the same amount of power, thereby dropping the size and weight of the device for the same amount of power.

Design objectives for output transformers also involve cost and efficiency, but get complicated by goals of wide bandwidth of up to three decimal orders of magnitude (roughly to 10 octaves) and relatively linear performance for over 100dB+ of dynamics all while meeting the damping requirements of the upstream speaker load, etc., etc., -- so not really exactly a power transformer.

Best ..

Again, disagree. See above.

Output transformers are anything but flat and linear. They're actually rather imperfect.

No matter how much y'all want to think otherwise, amplifiers know zilch about "sound", or the extremely dreaded word..."tone". From the moment the transducer on the guitar (i.e. the "pickup") converts the mechanical/acoustic energy of your guitar string into electrical energy, to the moment the transducer in the speaker cabinet (i.e. the speaker) converts that electrical energy back into mechanical/acoustic energy (i.e. sound), your signal is pure electricity. An amplifier is just a power supply for speakers. Speakers are just a reciprocating motor. You're using the signal from your guitar pickup to modulate DC from a DC electrical energy reservoir back into AC. The resultant output ends up as an amplified version of your original guitar signal (abeit with some frequency shaping through filter networks in the preamp as certain harmonic frequencies receive more amplification than others). That AC power generated from a DC source by your guitar pickup is what drives that reciprocating motor we call a speaker.

There is no "mystique/mojo/voodoo hoodoo" about them.