Shure KSM8 Review: Two Diaphragms and a Number That Disagrees

The Shure KSM8 has two diaphragms, and it's the only microphone in this set of 28 dynamics that does. Shure calls the construction Dualdyne and the claim attached to it is specific. A second diaphragm plus reverse airflow cancels most of the proximity effect, the low-frequency rise a mouth brings on as it closes on a cardioid capsule.

$439 is what that costs, but one number on the retail page can't be trusted. The listing gives sensitivity as "1.85 mV / −51.5 dBV/Pa": two values for one quantity, and they disagree by 3.1 dB.

Two figures for one sensitivity

Sensitivity in dBV/Pa converts by one formula and nothing else. Ten raised to the decibel figure divided by twenty gives volts per pascal. There's no weighting to choose, no reference to guess and no rounding convention that moves the answer three decibels. Run −51.5 through it and 2.661 mV comes out. Run 1.85 mV backwards and −54.66 dBV appears. The listing prints both, side by side, with a slash between them.

The manufacturer's guide settles it at −51.5 dBV/Pa, with the conversion spelled out in brackets as 2.66 mV. The figure used everywhere below is the manufacturer's. Where the 1.85 mV came from isn't obvious, but it's not a neighbour's value either. Shure's guides give the SM58 −56.0 dBV/Pa (1.6 mV) and the Beta 58A −51.5 dBV/Pa (2.6 mV), so neither of the two handhelds a shop is most likely to have open in another tab produces 1.85. And the value doesn't match anything in the line it sits beside.

This matters beyond one page. A shop that mis-states a converted value by 3 dB is a shop whose specification table can't be normalised without checking every line against the maker, and normalising is exactly what a comparison across 28 microphones requires.

2.66 mV/Pa, third highest of seventeen

Against the 17 dynamics with a convertible sensitivity figure, 2.66 mV/Pa comes third from the top, where the median is 1.8. Only two Sennheiser handhelds sit above it, at 2.7 and 2.8, though the Beta 58A ties it exactly. A hot dynamic is a quiet channel. Every decibel a capsule produces on its own is a decibel the preamp doesn't have to add, but preamp gain arrives with preamp noise. The SM7B at 1.12 mV/Pa sits 7.5 dB below this microphone, and on a cheap desk those decibels separate a clean vocal channel from a hissy one.

330 g, the exact median

27 dynamics here publish a weight, and the middle of them is 330 g. The KSM8 weighs 330 g. Of all the ways a specification can land, landing on the median precisely is the least interesting and the easiest to verify.

But what the weight does say is that the second diaphragm cost nothing in mass. A handheld that adds a mechanism and stays at the class average has spent its engineering somewhere other than the scales. Shure's guide names the body as cast aluminium, where the SM58's guide names enamel-painted die-cast metal. The two microphones nonetheless weigh the same 0.33 kg, so the housing material is a durability and finish decision rather than a weight one, and the second diaphragm arrives without a penalty that any published figure records.

What the second diaphragm is for

Proximity effect isn't a fault to be fixed. It's what a directional microphone does. A cardioid works by comparing pressure at two points, and as a source gets closer the comparison exaggerates low frequencies. Singers use it deliberately, engineers cut it with a high-pass filter, and both are working around the same physics.

Shure's claim is that this microphone removes the need to work around it. The guide describes two ultra-thin diaphragms and a reverse airflow path, and states the result as greater output with the proximity effect minimised, though it names no figure for either.

And two things about that claim are worth naming plainly. It's Shure's, not ours, and nobody publishes a comparable proximity-effect figure, so no ranking of this property exists anywhere. What can be checked is the output half. 2.66 mV/Pa is real, verifiable and third of seventeen.

The Beta 58A is the sharper comparison for it. Shure's own guide gives that microphone the same −51.5 dBV/Pa on a supercardioid capsule for $190 less, so the output the KSM8 is praised for isn't what the extra money buys. So what the extra money buys is the second diaphragm and the claim attached to it, which is the one thing on the page nobody can rank.

Die-cast aluminium, in black or nickel

A die-cast aluminium body under paint or a brushed-nickel finish, 330 g, cardioid, with nothing on it to switch. Shure's Model Variations section lists the two finishes as the same microphone, KSM8/B in black and KSM8/N in brushed nickel. Output impedance is 300 Ω, which the shop page omits. Frequency response runs 40 Hz to 16 kHz and no measurement level is stated, so the pair states no claim a rival's sheet could contradict. There's no maximum SPL on either page.

Spare parts carry numbers. Replacement grilles are the RPM266 in black and the RPM268 in nickel. In the box there's an A25E swivel adapter, an AK8C zip case and a thread adapter, and the optional A85WS windscreen is shared with five other Shure handhelds.

Eight ratings at $439

Seven fives and one four, averaging 4.9 across eight ratings. Eight isn't a sample, and one unhappy owner would take the average to 4.4.

And the count follows the price. A $439 handheld dynamic sells to fewer people than the Shure SM58 at $109, which has 165 ratings on the same site. But neither number says anything about how the two perform.

Shure's own store shows a perfect score, though it's worth seeing what that score rests on. One rating, five stars, 100 per cent of respondents recommending, and that single review carries Shure's own label: submitted as part of a promotion. A hundred per cent of one is a sentence rather than a statistic, but it's printed in the same typeface a shop uses for a hundred per cent of a thousand.

$439, and where that sits

The median across 28 dynamics is $169. The KSM8 at $439 has four models above it and twenty-three below, and the two nearest neighbours at that money are a Sennheiser MD 421-II and an Electro-Voice RE20, both broadcast microphones rather than handhelds. Among handhelds this is the top of Shure's wired dynamic range, at four times the SM58 and two and a half times the Beta 58A that matches its output figure. What the extra buys, on the sheet, is the second diaphragm and the aluminium body.

What the sheet answers about the KSM8

Three specification lines cover most of what gets checked on a handheld at this price. Those are the published range, the finish options and the output.

What is the KSM8's frequency response?

40 Hz to 16 kHz, with no tolerance stated. That's wider at the bottom than the SM58's 50 Hz and the same at the top as the Beta 57A's 16 kHz, but none of the three states a measurement level.

What is the difference between the KSM8/B and the KSM8/N?

The finish. B is painted black, N is brushed nickel, and Shure lists them under Model Variations as one microphone in two appearances.

What is Dualdyne?

Shure's name for the two-diaphragm construction in this model. The guide describes two ultra-thin diaphragms with reverse airflow, and attributes both the higher output and the reduced proximity effect to it.

Does the KSM8 need power?

No. It's a moving-coil dynamic with no electronics, so there's no phantom power, no battery and nothing to switch on.

Where a $439 dynamic makes sense

A close vocal on a loud stage is the case the numbers describe. The output is third of seventeen, so the desk works less. The pattern is cardioid, so the monitor goes behind. And if Shure's proximity claim holds, a singer who eats the microphone gets less of the bass hump that a high-pass filter would otherwise remove.

But a first microphone is where the price stops making sense. Four SM58s cost the same as one of these, though the specification differences that can be verified come to 10 Hz at the bottom, 1 kHz at the top and 4.5 dB of output. The rest of the case rests on a claim about proximity effect that no comparable figure exists for.

Price and specifications

Sources

1. Shure KSM8/B Dualdyne Dynamic Handheld Vocal Microphone, product listing at B&H Photo Video: price, rating count and its star distribution.
2. The product markup on that same listing: polar pattern, element type, frequency range, connector, thread and weight, and the sensitivity line carrying two values that disagree.
3. KSM8 user guide at Shure: the dual-diaphragm type, output impedance, sensitivity with its conversion, net weight, housing, the Model Variations section on the two finishes, and the A25E, AK8C, A85WS, RPM266 and RPM268 part numbers.
4. Medians and positions come from listings of 200 audio products collected the same way. How those are converted and compared.

The figures from the shop were collected on 20 August 2026 and have not been updated since.

What we did not do

This microphone has never been in our hands. The proximity-effect claim above is Shure's and no comparable figure exists to test it against; what we add is the arithmetic on the sensitivity line and the ranking of the figures that can be normalised.