Shure Beta 58A vs SM58: 4.5 dB and a Tighter Pattern

Seventy dollars buys 4.5 dB and a tighter pattern, but costs you the only rejection figures on either listing. The Beta 58A puts out 2.66 mV/Pa against the SM58's 1.59. And it narrows the pickup to supercardioid, which is what 12 of the 82 microphones here say against 41 that say cardioid. The SM58 is the one whose retail page states how much it attenuates at 60°, 120° and 180°, while the Beta 58A page gives nothing, and neither maker's guide gives a figure at any angle.

For a loud stage where the gain knob is already high, take the supercardioid. For a stage where a wedge monitor sits behind the singer and the engineer needs to know what that costs, the cardioid is the one with an answer on paper.

Side by side

Four rows carry the decision. Those are the pattern, the output, the rejection figures and the price. The bottom limit is identical at 50 Hz. Neither publishes a maximum SPL, and there's no switch, pad or filter on either.

4.5 dB, and what it is worth on stage

−51.5 dBV/Pa against −56.0 is 4.5 dB of extra signal from the same pascal of sound pressure. In the seventeen dynamics here that state it in convertible form, the Beta 58A sits joint third from the top at 2.66 mV/Pa, level with a Shure KSM8, and the SM58 seventh from the bottom at 1.59.

So where that shows is gain before feedback and preamp noise. Every decibel the capsule produces on its own is a decibel the desk doesn't add, and desk gain arrives with desk hiss. Behind a budget desk at the back of a hall the difference is audible. But on a modern interface with clean gain to spare it's not.

But the same 4.5 dB also means the Beta 58A clips a cheap input sooner. Nothing in either microphone limits level, but a loud singer close to a hot capsule can push a budget preamp into distortion that the quieter model wouldn't reach.

Supercardioid against cardioid, which is geometry

A cardioid is quietest directly behind. A supercardioid is quietest at roughly 125° either side of the front, though it picks up a small lobe from directly behind. Eight of the 28 dynamics collected here are supercardioid, though the other twenty are cardioid. On a stage that changes where the monitor goes. Behind a cardioid is the null, while behind a supercardioid is the rear lobe, and the nulls sit off to the sides. Point a wedge at the wrong angle for the pattern and the tighter microphone feeds back sooner than the wider one.

And the trade is positioning tolerance. A supercardioid holds a narrower front lobe, so a singer who drifts off the axis loses more level than the same drift costs on a cardioid.

The rejection figures only the cheaper one publishes

Eleven microphones out of the 82 here carry these angles on their listings, and the SM58 is one of the eleven. Its more expensive stablemate isn't.

Whose numbers they are is worth naming, because it changes what the row proves. Shure's user guides give a polar diagram for both models and no attenuation figure for either, while the SM58's dealer page carries the table and the Beta 58A's doesn't. Shure's own specification sheets couldn't be checked, because the host serving them refuses automated requests. So the difference above is a difference between two retail pages, not between two manufacturers' candour.

This is the part of the comparison that doesn't resolve cleanly. A supercardioid pattern is, by construction, tighter than a cardioid, so the Beta almost certainly rejects more from the sides. But what doesn't exist is a number, and the same gap turns up on the instrument model in the Beta line, where the shop prints no output figure at all.

So a buyer comparing on published specifications is choosing between a figure and an inference.

Different cartridges, again

Shure lists the Beta 58A cartridge as the R176 and the SM58 cartridge as the R59. The grilles are the RK265G and the RK143G. And the Beta grille is shared with two wireless variants rather than with the SM58. That matters for the same reason it matters between the SM57 and the SM58. They're separate capsules with separate part numbers, not one capsule behind different metalwork. And replacements aren't interchangeable in either direction.

46 grams and one kilohertz

The Beta 58A weighs 281 g against 327 g, which is 46 g less in a hand held up for a two-hour set. Its top end runs to 16 kHz rather than 15. Neither figure carries a measurement level, so the kilohertz can't be checked against another maker's numbers. Body dimensions are within a couple of millimetres of each other. Neither shape favours a hand over the other. Both use a 5/8"-27 thread with a 3/8"-16 adapter in the box, so any stand clip fits either.

Fifty ratings against 165

The SM58 carries 165 ratings at 4.9 and the Beta 58A 50 at the same 4.9. There isn't a rating below four stars on either.

The counts differ by more than three to one, and the reason is volume rather than quality. A $109 handheld sells to everyone and a $179 one sells to people who already know what a supercardioid costs them. Two averages that match at 4.9 across such different sample sizes say the same thing about both.

Which one to buy

Take the Beta 58A when the gain structure is tight and the stage is loud. It arrives 4.5 dB hotter, weighs 46 g less, and its narrower pattern holds more gain before feedback if the monitors are placed for it.

Take the SM58 when the monitor position is fixed and behind the singer, when the vocalist moves, or when $70 is better spent on a stand and a cable. The published rejection figures make its behaviour predictable, but the wider pattern forgives a performer who doesn't stay on axis.

Neither choice is a compromise on build. Both are die-cast metal with steel mesh, both need no power, and both publish the same 50 Hz floor.

Sources

1. Shure Beta 58A and SM58-LC product listings at B&H Photo Video: prices, rating counts and star distributions.
2. The product markup on those listings: polar patterns, frequency ranges, sensitivity, dimensions, weights, threads, and the off-axis attenuation figures published for the SM58.
3. Beta 58A user guide at Shure: output impedance, sensitivity with its conversion, housing, and the R176 cartridge and RK265G grille part numbers.
4. SM58 user guide at Shure: output impedance, the spherical steel mesh housing, and the R59 cartridge and RK143G grille part numbers.
5. Medians, positions and the count of microphones publishing off-axis figures come from listings of 200 audio products collected the same way. How those are converted and compared.

Shop data on this page was captured on 20 August 2026.

What we did not do

Neither microphone has been in our hands. Every figure above is Shure's or its dealer's. Where a figure does not exist we say so rather than infer one: the Beta 58A's off-axis behaviour is not published, and this page does not invent it.