beyerdynamic MMX 300 PRO and MMX 330 PRO both say 96 dB — closed and open, one number, no unit
«Nominal sound pressure level: 96 dB» with no reference, on a closed 48 Ω headset and on an open one. Per milliwatt a Focusrite Vocaster One arrives with +2.6 dB; per volt it is 10.6 dB short. beyerdynamic names the unit on its PRO X pages, and that is the evidence.
Signal Chain Compatibility Matrix
Select gear and parameters for live gain, impedance and SPL calculations.
Input Equipment Setup
PASS: Optimal Signal Chain
Requires minimum +60dB of clean pre-amp gain. Most budget entry interfaces max out at +50dB to +56dB and introduce hiss at max pot. An inline preamp booster (Cloudlifter CL-1 / FetHead) is strongly recommended.
The interface preamp provides sufficient headroom.
$538
$405
-25%Tonal & acoustic characteristics: Flat, wide-range frequency response for clean music and speech. Smooth, warm acoustic character with air-suspension shock isolation.
Technical advisory: With +69dB max gain, the Gen 4 Solo can drive demanding dynamics like the Shure SM7B natively without requiring an external inline booster.
Physical Interconnect Topology
Shure SM7B
Direct Cable Connection (No Intermediate Box)
1x Shielded Balanced XLR Cable (3-Pin XLR Male to XLR Female)
Focusrite Scarlett Solo (Gen 4)
Host: Apple MacBook Pro (M1/M2/M3/M4)
One figure serves a closed gaming headset, an open one, and — on a third beyerdynamic sheet — three impedance versions of a studio closed-back. It cannot be a measurement of any of them.
The MMX 300 PRO page prints «Nominal impedance: 48 ohms» and «Nominal sound pressure level: 96 dB». The MMX 330 PRO page, for the open model, prints exactly the same two lines. Focusrite publishes for the Vocaster One «Maximum Output Level @ 0dBFS +6.5dBu» — 1.64 V — and 5 Ω output impedance.
Read per milliwatt, which we store. S_V = 96 + 10·lg(1000/48) = 109.19 dB/V. A 110 dB peak needs 1.098 V, 22.88 mA and 25.12 mW. The Vocaster's 1.64 V across 5 Ω into 48 Ω delivers 1.485 V: 112.6 dB SPL, +2.6 dB, verdict «enough, without headroom». Damping ratio 9.6, just past the rule of 8. The MMX 330 PRO, carrying identical numbers, returns identical results.
Read per volt. The peak would need 5.012 V, 104.41 mA and 523.31 mW. The same interface would reach 99.4 dB SPL, −10.6 dB, too quiet. Thirteen decibels of ambiguity — 10·lg(1000/48) — separate «it plays, tightly» from «buy an amplifier».
How to judge. beyerdynamic spells the unit out on its PRO X pages: «100 dB SPL (1mW/500Hz)». The house convention is per milliwatt, so we read 96 the same way. Physical plausibility agrees: 96 dB/V at 48 Ω would be 82.8 dB/mW, a figure no 48 Ω headphone of this class measures. If the PRO X convention of 100 dB/mW applied to the MMX as well, the same Vocaster would give +6.6 dB — which shows how much four decibels of driver efficiency are worth here, and how little they are worth next to the thirteen the unit decides.
The pearl: the same 96 dB appears on the DT 770 PRO sheet that covers the 32, 80 and 250 Ω versions. One number standing for five products with three impedances and two enclosure types is a driver specification, not a measurement of a finished headphone — and an open back cannot produce the same sound pressure as a closed one at the bottom of the range, whatever the driver does. Use the figure to size an amplifier, which is what it is good for. Do not use it to choose between the MMX 300 and the MMX 330: on this interface both answer +2.6 dB, and they must, because there is only one measurement behind them.