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Sennheiser MM 400-X

Bluetooth® stereo headset with aptX® high-fidelity wireless audio capability

Item #: 143MM400X

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Bluetooth for wireless music and talk

Going somewhere? Don't forget your Sennheiser MM 400-X portable headphones. They're fantastic for enjoying your music and managing your phone calls without getting tangled up in cords. These headphones include built-in Bluetooth technology for a hassle-free wireless connection to compatible devices, such as many cell phones, laptop computers, tablets, and MP3 players. You can use the integrated volume, track skip, and call answer/end buttons built into the right earcup for convenient operation while your phone or music player remains safely in your pocket, purse, or backpack. The MM 400-X headphones even support the latest aptX technology — a sophisticated audio circuit that delivers true high-fidelity stereo sound wirelessly over Bluetooth with aptX-enabled sources.

Great comfort, sound, and convenience

The MM 400-X's soft padded ear cushions and adjustable headband provide a comfortable fit for hours of relaxed listening, making these 'phones great to have on long trips. The headset's folding design makes for easy storage when you travel. Sennheiser's patented Duofol™ diaphragms provide detailed, crystal clear sound. And just in case you need it, Sennheiser includes a cable plus an airline adapter for a direct wired connection in situations where Bluetooth isn't permitted, or you want to make use of in-seat entertainment and other wired sound sources.

Product Highlights:

  • portable, folding, on-the-ear design
  • padded, closed earcups and adjustable headband
  • Bluetooth® wireless operation with advanced aptX audio circuitry for streaming high-quality stereo sound from aptX-enabled devices
  • built-in microphone and wireless earcup controls for hands-free conversations using compatible Bluetooth cell phones
  • integrated controls on the right earcup for track, volume, and answer/end call functions
  • rechargeable lithium-polymer battery included
  • single battery charge gives you:
    • up to 20 hours Bluetooth talk time
    • up to 10 hours Bluetooth listening time
  • advanced Duofol™ drivers for outstanding sound quality
  • frequency response 15-22,000 Hz
  • 60" detachable audio cable with stereo mini plug included for wired listening options
  • airline adapter, USB charging cable, multi-country wall charging adapter, and carrying case included
  • weight: 3.7 oz.
  • warranty: 2 years
  • Our 60-day money-back guarantee

Hands-on research

What's in the box?

Download owner's manual

  • MM 400-X Wireless headphones
  • BA 370 PX Lithium-Polymer rechargeable battery pack (installed)
  • Wall charging power supply
  • US power plug adapter
  • EU power plug adapter
  • UK power plug adapter
  • AU power plug adapter
  • Airline adapter (single female 3.5mm-to-dual male 3.5mm)
  • 50" USB charging cable (Type A USB on one end and proprietary USB on the other end)
  • 5' Audio cable (male 3.5mm miniplug on one end and male 2.5mm sub-miniplug on the other end)
  • Zippered storage pouch
  • Instruction Manual on CD-ROM
  • Quick Guide
  • Safety Guide
  • Compliance statement
  • "Replacement of the Mains Unit" sheet

Features and Specs

Fit Style On-ear
Earcup Type Closed
Noise-canceling No
Bluetooth Yes
Frequency Response 15-22k Hz
Sensitivity 107 dB
Impedance N/A
Weight 3.7 ounces
Cord Length 60"
Airline Adapter Included Yes
iPod Control Yes
Volume Control Yes
Built-in Microphone Yes
Parts Warranty 2 Years
Labor Warranty 2 Years

Product Research


Overview: The Sennheiser MM 400-X headphones are an accessory that allows you to enjoy your digital music files on your mobile phone or portable music device, including those equipped with Bluetooth technology. The MM 400-X can be used wirelessly, or in places where Bluetooth isn't available, you can plug them in and use them as wired headphones.

Bluetooth Wireless Reception/Transmission: The MM 400-X features Bluetooth v2.1 wireless reception and transmission with a built-in microphone for cable-free use with select Bluetooth enabled phones and audio devices. Supported Bluetooth profiles include A2DP (Advanced Audio Distribution Profile), AVRCP (Audio/Video Remote Control Profile), HSP (HeadSet Profile), and HFP (Hands-Free Profile). The MM 400-X saves the connection profiles of the last eight devices with which it was paired; when turned on it automatically tries to connect with one of those devices.

Note: Not all Bluetooth enabled audio devices will be compatible.

apt-X: The MM 400-X headphones are equipped with apt-X, an audio coding technology that works within Bluetooth to wirelessly deliver CD-quality audio from your portable music device to the headphones. With apt-X, you can listen to your digital music files in crisp, pure, and full stereo sound. The following 3rd party devices / configurations have built-in apt-X support (as of 7/18/2012):

  • Apple Mac OS X Snow Leopard and Lion Operating Systems
  • Apple Mac Mini (latest generation with latest OS update)
  • Apple Macbook Air (latest generation with latest OS update)
  • Apple Macbook (latest generation with latest OS update)
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Controls: On the right ear-cup there are integrated controls for your connected phone or audio device. Audio controls include volume, skip forward or backward, fast forward or rewind within a song, play, and stop. Phone controls include volume, accept call, reject call, end call, redial, voice dial, and mute.

Note: All control functions must also be supported by the connected device.

Battery Pack: The MM 400-X has a removable BA 370 PX Lithium-Polymer battery pack (3.7 volts DC/1 Wh) which provides up to 10 hours playback using Bluetooth reception. A power supply with US, UK, European, and Australian plug adapters is included to charge the battery pack; charging time is approximately three hours. The headphones can also be charged using a computer's USB port.

Collapsible Design: These headphones feature a collapsible design with metal-reinforced headband to ensure portability and durability.

Cord & Adapter: The MM 400-X will also work as wired headphones, useful when Bluetooth connection is not an option. The headphones come with a 60" mini-jack cable terminated by a 3.5mm connector for a wired connection. An in-flight audio adapter (dual mono 3.5mm) is included for added convenience.

Carrying Case: A nylon carrying case is included to protect the headphones during storage or transport.

Specifications: The MM 400-X has the following specs:

  • Frequency Response: 15-22kHz
  • Nominal Impedance: 590 Ω active mode; 100 Ω passive
  • SPL (1 kHz/1 Volt): 107 dB
  • THD (1 kHz): < 0.1%
  • Connectors: 3.5mm, 3.5mm double mono plug in-flight adapter
  • Weight: 3.7 ounces (105 grams)
  • Bluetooth:
    • Version: 2.1 + EDR
    • Range: up to 33' (10 meters)
    • Transmission Frequency: 2.4 GHz
    • Transmission Power: 8 dBm
    • Profiles: HSP, HFP, A2DP, AVRCP
    • Codec: SBC, apt-X

Our Product Research Team

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Sennheiser MM 400-X Reviews

Average Customer Review:

2 reviews
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I thought they were great.

Written By Mike, New Braunfels, TX on Friday, January 10, 2014

Crutchfield Customer Review (What's this?)

  • "Coolness Factor"
  • Build Quality
  • Comfort
  • Noise Reduction
  • Sound Quality

I purchased these Sennheiser MM400-X as a Xmas present for my daughter. She had mentioned the Beats Solo as a present. So I did my research and read many reviews and felt the MM400-X was a better product. On Christmas day she opened her present and was disappointed they were not Beats in drenched blue. I explained how the Sennheiser had a better balanced sound, were wireless and bluetooth compatible with the iphone, lighter in weight and build quality was superior. She listened for a few minutes then put the headphones back in the box and said they were nice but she wanted the Beats. It did not matter that the Sennheiser was better. Beats has done a better job marketing to the young people and making groovy colors. We sent the Sennheiser back to Crutchfield, who makes returns really simple and easy. Now my daughter has the drenched blue Beats and is happy. Not because they are a better quality overall, or provide a balance sound, but because she now has what all the other young people and her friends have.

Pros: Light weight, wireless and bluetooth compatible, works great with the Apple products.

Cons: Lack marketing to the youngster and do not come in fun colors.

Great little Bluetooth headphones

Written By DB Dan, Diamond Bar, Ca. on Monday, December 16, 2013

Crutchfield Customer Review (What's this?)

  • "Coolness Factor"
  • Build Quality
  • Comfort
  • Noise Reduction
  • Sound Quality

Overall, very nice & progressive audio gear. I got these primarily to use with my new Ipod touch. The sound, depth & bass is great , especially for the on the ear style. The only downside is that they don't stay in place on your head unless there in the exact right spot on your head. Even then they can still slide off rather easily. I think the headband should have been a little wider. They fit better & stay on when wearing a ball cap.

Pros: Looks, Sound & Quality

Cons: Comfort & Fit