Speaker magnets are argued about almost entirely in adjectives. Alnico is "smoother," "sweeter," "compresses earlier." Ceramic is "punchier," "tighter," "louder." None of that is wrong exactly. It is just untested, because the comparison usually puts two different speakers side by side and gives the magnet the credit for every difference.
The way to isolate the magnet is to find a maker that sells the same speaker twice, once in each magnet, and read both spec sheets. Jensen does. So does Weber.
The Controlled Comparison
Jensen's Vintage line names its magnet in the first letter of the model. P is alnico. C is ceramic. The suffix letter is the model. So the P12R and C12R are one speaker design with two magnets, and Jensen's own copy calls the C10R "the ceramic version of the P10R."
Figures below are the 8-ohm versions, from Jensen's product pages. Diameter, voice coil diameter and gap depth are identical within each pair.
| Pair | Magnet | Magnet weight | Rated power | Sensitivity (1 W, 1 m) | Resonance (Fs) | BL (T·m) | Moving mass (Mms) |
|---|---|---|---|---|---|---|---|
| P12R | Alnico | 200 g | 25 W | 93.7 dB | 80 Hz | 5.53 | 25.2 g |
| C12R | Ceramic | 270 g | 25 W | 92.3 dB | 88.3 Hz | 6.24 | 29.5 g |
| P12Q | Alnico | 300 g | 40 W | 94.4 dB | 90.5 Hz | 5.88 | 26.8 g |
| C12Q | Ceramic | 426 g | 35 W | 93.2 dB | 87.5 Hz | 6.03 | 29.7 g |
| P10R | Alnico | 200 g | 25 W | 94.2 dB | 97 Hz | 5.83 | 15.2 g |
| C10R | Ceramic | 270 g | 25 W | 93.6 dB | 96.6 Hz | 6.42 | 17.6 g |
| P8R | Alnico | 200 g | 25 W | 91.8 dB | 135 Hz | 3.99 | 8.8 g |
| C8R | Ceramic | 270 g | 25 W | 93.0 dB | 126 Hz | 4.70 | 9.0 g |
Note the Q pair is not perfectly clean — the alnico P12Q is rated 40 W and the ceramic C12Q 35 W. The three R pairs match on every stated figure except the ones the magnet could plausibly change.
Read the sensitivity column across the pairs. Alnico louder by 1.4 dB, 1.2 dB, 0.6 dB. Then ceramic louder by 1.2 dB. Read resonance: the ceramic is 8.3 Hz higher on the 12R, 3 Hz lower on the 12Q, 0.4 Hz lower on the 10R, 9 Hz lower on the 8R.
There is no direction. Whatever "alnico versus ceramic" does to these speakers, it is not a consistent shift in either of the two figures that describe output and low-frequency reach.
The Part I Had Backwards
I expected the ceramic versions to be louder. Every ceramic in this table has the stronger motor — BL, the force the magnet and coil produce per amp of current, is higher on all four ceramic models, by 3 to 18 percent. A stronger motor pushing the same cone should move more air per watt.
It does not, in three of four pairs, and the spec sheet says why. The ceramic models also carry more moving mass — 17 percent more on the 12R, 11 percent on the 12Q, 16 percent on the 10R. Only the 8-inch pair breaks the pattern, with a 2 percent mass increase against an 18 percent BL increase.
A speaker's reference efficiency scales with BL squared, divided by voice coil resistance and by moving mass squared. Cone area cancels within each pair, so the published BL, Re and Mms predict the sensitivity gap on their own:
| Pair | BL change (ceramic vs alnico) | Mms change | Predicted sensitivity change | Published change |
|---|---|---|---|---|
| 12R | +13% | +17% | −0.8 dB | −1.4 dB |
| 12Q | +3% | +11% | −1.0 dB | −1.2 dB |
| 10R | +10% | +16% | −0.5 dB | −0.6 dB |
| 8R | +18% | +2% | +1.1 dB | +1.2 dB |
Computed from Jensen's published BL, Re and Mms using the simplified efficiency relation; this ignores inductance and measurement tolerance, which is why the magnitudes are close rather than exact.
The direction is right in all four. Here's the data, then: the loudness difference between Jensen's alnico and ceramic versions is explained by the moving assembly, not by the magnet material. Jensen's ceramic versions are heavier where it counts, and the extra mass eats the extra motor force. Jensen publishes no cone part numbers, so I cannot say which part of the moving assembly gained the weight. But the magnet itself does not move, and it is not what made them quieter.
Weber: The Cleanest Pairs, the Fewest Figures
Weber names its magnets the same way in a different letter. Its own naming page says alnico is "designated by the letter A," and F is ceramic, from strontium ferrite. The number is the voice coil diameter. So the 12A125 and 12F125 are a 12-inch with a 1.25-inch coil in each magnet.
From Weber's product pages, prices as listed on tedweber.com in October 2026:
| Model | Magnet | Power options | Voice coil | Cone (as listed) | Speaker weight | Price |
|---|---|---|---|---|---|---|
| 12A125 | 11 oz alnico | 20 / 30 W | 1.25 in | seamed, ribbed | 4.85 lb | $145 |
| 12F125 | 30 oz ceramic | 20 / 30 W | 1.25 in | seamed, ribbed | 7.8 lb | $129 |
| 12A150 | 40 oz alnico | 25 / 50 W | 1.5 in | ribbed | 6.75 lb | $265 |
| 12F150 | 40 oz ceramic | 25 / 50 W | 1.5 in | ribbed | 8.1 lb | $144 |
| 10A125 | 11 oz alnico | 20 / 30 W | 1.25 in | seamed | 5.35 lb | $139 |
| 10F125 | 30 oz ceramic | 20 / 30 W | 1.25 in | seamed | 6.65 lb | $118 |
Weber's pairs match on cone, coil and power — the magnet is the only listed variable. The catch is that Weber publishes no sensitivity, resonance or Thiele-Small figures at all, so these pairs isolate the magnet perfectly and then tell you nothing about output.
What they do tell you is weight. The 12A125 is about three pounds lighter than the 12F125. In a 4x12 that is roughly 12 pounds off the cabinet, for $64 more across four speakers at Weber's listed prices. That is the most reliable difference in this entire article, and it is a logistics number, not a tone number.
What a Spec Sheet Cannot Show
The case for alnico is not about any figure in these tables. It is about compression at high power: the claim that an alnico magnet's field sags when the coil is driven hard, which softens the attack and evens out the level. Weber's own Q&A describes alnico as "smooth, compressed and fattened at higher volumes, less headroom," and notes the effect "is not permanent."
Every number above is a small-signal measurement. Thiele-Small parameters are taken at low drive, where the speaker behaves linearly. Power compression is by definition what happens when it stops behaving linearly. So the published figures neither confirm nor refute the alnico claim — they are measured in the wrong regime to say anything about it. Eminence's FAQ goes further, saying that at equal flux "you probably won't notice a difference in tonality," and putting any difference down to the magnet's position and the resulting flux rather than the material.
That has a direct consequence for anyone on a modeler.
On a Modeler or IR Loader
An impulse response is a linear snapshot of a speaker, cabinet and microphone at the level it was captured. Linear means it keeps the frequency response and discards anything that changes with level. Large-signal compression changes with level. So whatever alnico does at high power, it is absent from every IR of an alnico speaker — on a Helix, a Quad Cortex, a Fractal or a pedal IR loader alike. The background is in our impulse response guide.
What an IR of an alnico speaker does carry is its small-signal response, and in the matched pairs above that differs from the ceramic version by about a decibel of level and a few hertz of resonance. If an alnico cab and a ceramic cab sound strongly different in your modeler, the cause is almost certainly that they are different speakers — different cones, different cabinets, different mic positions — not the magnet.
How to Decide
- Choosing between the P and C version of the same Jensen: expect up to 1.4 dB of level difference. That is the alnico P12R needing 28 percent less power than the C12R for the same level — real, but under half of the 3 dB that doubling your amplifier's power buys. Do not buy either version expecting a different voicing on the strength of the magnet letter alone.
- If weight matters: this is the one argument the figures fully support. Alnico saves 70 g of magnet per Jensen R-series speaker and about three pounds per Weber 12A125.
- If you want the alnico compression: the only way to evaluate it is to drive the speaker hard in the room, because no spec sheet and no IR contains it. Buy where you can return.
- If you are comparing across makers: stop at resonance and sensitivity. Jensen's published Qts values run 1.5 to 2.5; Eminence's run near 0.6 for comparable guitar speakers. Those are not two different physics. They are two different test methods, so Thiele-Small figures only compare within one maker's sheets.
For what a speaker's size changes with the magnet held constant — the same Jensen alnico line in 8, 10 and 12 inches — see what diameter actually decides, and for what any of these speakers pass below 100 Hz, the low-end rolloff post. The four-way Celestion comparison is in the Celestion speaker showdown — none of Celestion's alnico and ceramic models share a power rating, which is why they are not in this article.
