If you ever wondered about the electrical analysis of amps, speakers, and pickups then here's a good Grok AI explainer

[dubbmann]

Please note that the context added by respondents to this post addresses inaccuracies in the AI text cited - ED.

Hi all,

I've long wondered about the *exact* electrical connections between amplifiers and speakers, and also the reverse with guitar pickups. I sent a set of questions to Grok and here's its response. I thought it was good and it clarified the matter greatly for me, not least the reason impedance is used to rate speakers rather than resistance despite both using Ohms as their unit of measurement. Hope this is useful. The first paragraph is the prompt and after it are the responses.

Cheers,

d

is it correct that loud speakers are powered with AC current? how are the frequencies of the original (analog) signal modulated into the current sent from amplifiers to speakers? are the frequencies encoded in the frequency of the AC current, using multiple frequency signals for the harmonics in the analog source? do guitar pickups generate DC or AC current? discuss how impedance affects the power delivery for speaker systems.

### 1. Are loudspeakers powered with AC current?

Yes, that's correct. Loudspeakers are driven by alternating current (AC) from the amplifier. The audio signal is inherently AC because it represents sound waves, which are oscillations that alternate in polarity (positive and negative excursions). A direct current (DC) would only push the speaker cone in one direction without returning it, leading to no sound production or potential damage. The amplifier outputs an AC signal that varies in voltage and current over time, causing the speaker's voice coil to move back and forth in the magnetic field, which vibrates the cone to produce sound.

### 2. How are the frequencies of the original (analog) signal modulated into the current sent from amplifiers to speakers?

The process isn't "modulation" in the sense of radio frequency modulation (like AM or FM, where a carrier wave is altered). Instead, it's direct amplification of the analog audio waveform. Here's how it works:

- The original analog signal (e.g., from a microphone, guitar pickup, or audio source) is a low-level voltage that varies over time, representing the sound's amplitude and frequency content.
- This signal is amplified by the amplifier circuit, which increases its power (voltage and current) while preserving the waveform's shape.
- The amplified signal is sent as AC current to the speaker's voice coil. The current's variations directly correspond to the audio waveform: peaks and troughs in the signal cause the coil to move proportionally, reproducing the sound.

In essence, the amplifier acts as a power booster, delivering the audio signal's frequencies as-is in the time domain, without encoding them onto a separate carrier.

### 3. Are the frequencies encoded in the frequency of the AC current, using multiple frequency signals for the harmonics in the analog source?

Yes, the frequencies are directly represented in the AC current's waveform. The AC current oscillates at the same frequencies as the original audio signal. For a simple sine wave tone (e.g., 440 Hz A note), the current would alternate at 440 cycles per second. For complex sounds with harmonics (overtones at multiples of the fundamental frequency, like in music or speech), the current waveform is a composite: it's the superposition (sum) of multiple sine waves at those various frequencies and amplitudes.

This is based on Fourier's theorem, which states that any periodic waveform can be broken down into a series of sine and cosine waves (harmonics). The amplifier doesn't "encode" them separately; it simply amplifies the combined waveform, and the speaker reproduces it mechanically. No separate carriers or modulation schemes are used—it's all in the time-domain variations of the single AC signal.

### 4. Do guitar pickups generate DC or AC current?

Guitar pickups generate AC current (or more precisely, AC voltage that can drive current in a circuit). They work on electromagnetic induction: the vibrating metal strings disturb the magnetic field around the pickup's coils, inducing a varying voltage according to Faraday's law (voltage is proportional to the rate of change of magnetic flux). This induced voltage alternates in polarity as the string vibrates back and forth, producing an AC signal at the frequency of the string's vibration (plus harmonics). A DC output would require a steady, unchanging field, which doesn't occur with vibrating strings.

### 5. How does impedance affect power delivery for speaker systems?

Impedance (Z, measured in ohms) is the AC equivalent of resistance, accounting for resistance, inductance, and capacitance in the speaker's voice coil and crossover networks. It affects power delivery in several key ways:

- **Power Transfer Efficiency**: For maximum power transfer from amplifier to speaker, the amplifier's output impedance should ideally match the speaker's impedance (though modern solid-state amps have very low output impedance for damping control, and matching isn't strict). Mismatched impedance can lead to reduced power output or distortion. For example, connecting an 8-ohm speaker to an amp rated for 4 ohms might halve the power delivery.

- **Power Calculation**: Power delivered to the speaker is given by P = V² / Z (where V is RMS voltage) or P = I² * Z (where I is RMS current). Lower impedance allows more current to flow for a given voltage, increasing power—but it demands more from the amp (higher current capability). Higher impedance reduces current draw but may limit maximum power.

- **System Design and Safety**: Speakers are rated at nominal impedances (e.g., 4Ω, 8Ω), but actual impedance varies with frequency (dipping low at resonances). If impedance is too low (e.g., wiring multiple speakers in parallel drops total Z), the amp may overheat, clip, or shut down due to excessive current. Too high, and the system underperforms. Crossovers in multi-driver speakers manage impedance to ensure even power distribution across woofers, tweeters, etc.

- **Practical Impacts**: In pro audio or home theater setups, impedance matching prevents voltage drops over cables and ensures consistent volume. For guitar amps, tube designs often use output transformers to match high-impedance tubes to low-impedance speakers, optimizing tone and power.

Overall, proper impedance management ensures efficient, safe, and high-fidelity power delivery.

[Wonks]

For guitar amps, tube designs often use output transformers to match high-impedance tubes to low-impedance speakers, optimizing tone and power.

There may possibly be some rare esoteric guitar valve amp designs out there that don’t use an output transformer for the power amp section, but I’ve never come across one. So ‘often’ is rather an understatement here.

[James Perrett]

While much of it is correct, it has made a big mistake near the end. Can you spot it?

[Sam Spoons]

Crossovers in multi-driver speakers manage impedance to ensure even power distribution across woofers, tweeters, etc.

[James Perrett]

Crossovers in multi-driver speakers manage impedance to ensure even power distribution across woofers, tweeters, etc.

That wasn't the one that I was thinking of but that's also not exactly right.

[zenguitar]

impedance matching

Is this the fella James?

Andy

[Wonks]

impedance matching prevents voltage drops over cables and ensures consistent volume.

Definitely isn't correct. Voltage drops over cables depends on the cable resistance and the current flowing, nothing else.

And consistent volume?

What has this AI been smoking?

[James Perrett]

The impedance matching isn't exactly right either - but the one I'm thinking of is where it gets it completely the opposite way round to reality.

[Wonks]

Oh, the speaker impedance dipping at low frequencies, when in reality the resonant peak of maximum impedance is at a low frequency, typically in the 50-80Hz area. Then dropping back and rising slowly as the frequency increases.

[Tomás Mulcahy]

I can't see a reversal, but I do get that kind of thing a lot when using AI like this. It gets confused about L/R X/Y often. I see some odd things though, for example "managing impedance" is a typical weird AI take. In a passive crossover there is interaction with impedance, but this is a side effect, that might be carefully managed in some designs but in most it is accepted. It does not occur with active crossovers. Question 3 is a very odd question, but it was asked by a human The answer is a bit confused at the start, but is clearer by the end.

[Hugh Robjohns]

The impedance matching isn't exactly right either - but the one I'm thinking of is where it gets it completely the opposite way round to reality.

My vote is:

"...but actual impedance varies with frequency (dipping low at resonances)."

Which is the inverse of reality since the impedance peaks to a very high value at resonance.

Eg.

[James Perrett]

My vote is:

"...but actual impedance varies with frequency (dipping low at resonances)."

Which is the inverse of reality since the impedance peaks to a very high value at resonance.

Eg.

Yes, that was the one that leapt out at me when first skimming through. I wonder what it was trained on in order to reach that conclusion?

[Wonks]

It's also a very AI response in that it answers a question in the way it was written rather than in the way a knowledgeable person would. For example for #3, you wouldn't go into Fourier analysis, which has nothing really to do with the answer,

are the frequencies encoded in the frequency of the AC current, using multiple frequency signals for the harmonics in the analog source

The answer is that nothing is encoded. The incoming signal is simply amplified by the power amp and sent out to the speakers.

If the amplifier doesn't have the frequency bandwidth to fully replicate the incoming signal in full, then the upper frequencies will be lost, which is then where Fourier analysis can be mentioned.

[Tomás Mulcahy]

Agreed Wonks, well expressed about that particular answer.

Yes, that was the one that leapt out at me when first skimming through. I wonder what it was trained on in order to reach that conclusion?

IME all of them mix up these kinds of complex opposites in this strange way. IME with audio stuff I've seen it mix up XY90 with XY120 and claim 120 has the wider SRA, or mix up vertical with lateral mod in vinyl cutting, claiming vertical is for mono. I tried telling it that it had reversed them and to rewrite accordingly, and it still came back with the same mistake.

[ef37a]

It is a very nuanced subject. We don't "match" audio kit any more.
Then there is a difference between the application such as valve output stage being used for high fidelity amplification and music instrument work (factory PA is yet another can of worms but who would use valves theses days!)

The hi fi amp should have a very low source impedance just as solid state device do. The speaker tappings, 16 Ohms, 8 Ohms are really just changes in the voltage the amp can deliver. A really good valve hi fi amp might have a source impedance of around 0.5 Ohms giving an 8 Ohm "damping factor" of 16.

A guitar amp such as the venerable Vox A30 on the other hand has an OPZ of 30 to 50 Ohms and it is this lack of damping which makes a good contribution to the sound. Indeed, some solid state designs employ feedback tricks to attempt to emulate this high source impedance.

Both amplifier types can be destroyed by running them hard with no load. The guitar amp is especially vulnerable because it is very often driven hard into clipping. It is therefore important to set a G amp to the right speaker impedance although even when properly "matched" some makes are more feeble than others!

Solid state amplifiers don't like low or shorted loads but be warned! They are not totally immune if you run the nuts off them into an open circuit!

These points come up almost weekly on a mainly guitar based forum I infest.

Dave.