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18SOUND 8NMB420

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18SOUND (Eighteen Sound) 8NMB420 — 8" / 8 inch · Midrange with Lower Midrange (ML) · Midrange · Neodymium
2" voice coil · 8 Ω
Part no.: 42A-CHS-MT-18S-0023

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  • Impedance (Ω)
  • Power handling (W)
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  • Frequency from (Hz)
  • Frequency to (Hz)
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  • Mounting depth (mm)
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  • Re (Ω)
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  • BL (Tm)
  • Mms (kg)
  • Sd (m²)

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18SOUND 8NMB420 — 8" · Midrange Driver

280 W AES · 95 dB Sensitivity · Frequency range 60 Hz – 5500 Hz

Technical data

  • Diameter: 8 "
  • Voice coil: 2 "
  • Power handling: 280 W AES
  • Sensitivity: 95 dB
  • Impedance: 8 Ω
  • Magnet: Neo
  • Weight: 1.7 kg
  • Mounting depth: 99 mm
  • Frequency range: 60 – 5500 Hz

Datasheet (PDF) · Manufacturer page

Series: NMB · Part no.: 42A-CHS-MT-18S-0023

18Sound 8NMB420: lightweight 8" mid-woofer with neodymium, 95 dB and 5.8 mm Xmax

The 8NMB420 from 18Sound's NMB series is an 8" midrange with lower midrange capability, and it weighs just 1.7 kg. The neodymium motor drives a 2" voice coil, sensitivity 95 dB, power handling 280 W AES, working range 60 Hz to 5,500 Hz. Moving mass is only 14.9 g. Together with BL 10 Tm that makes a motor that responds quickly without needing a heavy cone.

What sets it apart within the category are the parameters for the lower midrange: Fs 61 Hz, Qts 0.28, Vas 33 l and Xmax 5.8 mm. In a vented box it reaches noticeably lower than a pure midrange and can handle the low-mid section alone in a compact 2-way system, as long as a subwoofer covers the rest or the level demands stay moderate. The mounting depth of 99 mm is kept short.

Use and enclosure

Two concepts suggest themselves. First, a small 2-way top with a 1" compression driver in which the 8NMB420 works as the mid-woofer: the guideline here is a vented box of around 13 l, tuned to 81 Hz, with a lower cutoff around 94 Hz. The EBP of 197 confirms that the vented alignment is the right one. Second, as the midrange in a 3-way system, in which case a sealed midrange chamber of about 6.1 l with an in-box resonance around 154 Hz. Both values are approximations; fine tuning is done in our enclosure calculator.

In vented operation, protect the driver with a high-pass below the tuning frequency; in a midrange chamber, cross well above 60 Hz. Going up it carries to 5,500 Hz. For the high-frequency partner, a 1" compression driver from the 18Sound range is a natural choice, and the matching horn is in the same manufacturer's category.

What to look out for

  • This version: 8 Ω, Re 5 Ω; the model is also offered at 4 and 16 Ω.
  • Only 1.7 kg and 99 mm mounting depth: for columns and lightweight tops.
  • Xmax 5.8 mm with 33 l Vas: real lower midrange, but not a subwoofer.
  • Le 0.35 mH: low inductance, easy to handle in the crossover up to 5,500 Hz.
  • Datasheet PDF and TSP in the 42.audio driver database.

Frequently asked questions

Is the 8NMB420 enough in a 2-way top without a subwoofer?

For speech, monitors and small rooms, yes: in a vented box of around 13 l it reaches a lower cutoff around 94 Hz. For music with deep bass content you should plan a subwoofer, which keeps the 5.8 mm of excursion free for the midrange.

Which amplifier suits the 8NMB420?

Power handling is 280 W AES at 8 Ω. A channel in that class with a limiter is the sensible choice. With 95 dB sensitivity you reach solid levels with less power as well.

How does it differ from the 8NMB750?

The 8NMB750-8 sits at Fs 88 Hz, Qts 0.27 and Vas 6.9 l, so it needs a much smaller box and reaches less deep. The 8NMB420 with Vas 33 l and Fs 61 Hz is the choice when lower midrange in a somewhat larger volume is wanted.

At 42.audio you get the 18SOUND 8NMB420 with datasheet PDF, all key data in the driver database and the enclosure calculator. More drivers from this manufacturer: Atlas 18Sound.

Thiele-Small parameters

Nominal impedance8 Ω
Resonance frequency fs61 Hz
Total Q Qts0.28
Electrical Q Qes0.31
Mechanical Q Qms4
Equivalent volume Vas33.0 l
Moving mass Mms14.9 g
Cone area Sd230 cm²
Linear excursion Xmax5.8 mm
Force factor BL10 Tm
DC resistance Re5 Ω
Voice coil inductance Le0.35 mH

Enclosure suggestion

The EBP of 197 suggests a bass-reflex enclosure. EBP = fs / Qes = 61 / 0.31

Sealed (Qtc 0.707)

Enclosure volume Vb
6.1 l
System resonance Fc
154 Hz
Cut-off frequency F3
154 Hz

Bass reflex (QB3 after Small)recommended

Enclosure volume Vb
9.9 l
Tuning frequency Fb
89 Hz
Cut-off frequency F3
104 Hz

Vb is the required net internal volume, Fb the tuning frequency of the reflex port and F3 the frequency at which the level has dropped by 3 dB. Calculated approximation after Small. A starting point for simulation, not a finished build plan.

Comparable drivers

Same size, same type, Qts within ±30 %.

Specifications

Allgemein
Manufacturer 18SOUND
Category Mid Frequency
Series NMB
Magnet Neo
Impedance (Ω) 8
Power handling (W) 280
Sensitivity (dB) 95
Frequency from (Hz) 60
Frequency to (Hz) 5500
Abmessungen & Korb
Diameter 8
Voice coil (inch) 2
Mounting depth (mm) 99
Weight (kg) 1.7
Thiele-Small-Parameter
Re (Ω) 5
Le (mH) 0.35
Fs (Hz) 61
Qms 4
Qes 0.31
Qts 0.28
Vas (l) 33
Xmax (mm) 5.8
BL (Tm) 10
Mms (kg) 0.0149
Sd (m²) 0.023