I use the Avantone Mixcube on every mix

The Avantone MixCubes ($139 each) are a replica of an old studio standard the Auratone. 

The MixCubes are manufactured by Avant Electronics who also makes microphones. These speakers are extremely useful as a real world reference due to their limited frequency response and if you can get the mix sounding great on these speakers it will usually translate to most computer speakers, portable radios, MP3 players, iPods/iPhones and factory car systems. I use these speakers on every mix I do. One of the first projects on which I used the Mixcubes (the passive version) was Amy Winehouse' "Back To Black" album with producer Salaam Remi. The speakers emphasis on the midrange frequencies will let you hear any discrepancies in your mix immediately and I consider them essential for balancing vocals. I use only one speaker and monitor in mono to ensure the mix will translate to all mediums including radio and TV. Nowadays every TV is stereo capable but the broadcasts are not always in true stereo. One of the reasons these work so well for mixing is that they provide a single point source and they are pretty much flat across the entire midrange spectrum. There are no phase issues or frequency dips in the upper midrange due to the fact that there is no crossover in the signal path. As for the low end use your mains or subwoofer to check the extreme lows but make sure you can hear the kick and bass on the mixcubes.

Features

• 5.25" Shielded Passive Full range 8 ohm drivers
• 6 1/2" Cube Cabinet with multiple coats of "Retro-Cream" High Gloss lacquer finish
• Precision-milled high-rigidity MDF cabinet sides & baffle for low resonance
• Radiused corners & edges reduce edge diffraction for better imaging
• Custom Cone is crafted using New Zealand pulp with mica fibers added for light weight & rigidity
• Cloth surround made in Japan to uniform thickness tolerances
• Top Plate and T-Yoke of driver are made of Sumitomo 1008 low carbon steel
• The 43oz. low distortion motor structure magnets are Y- 40 GRADE (MIL-SPEC)
• High-Rigidity DIE-CAST Aluminum frame with polished mounting bezel
• Nickel Plated "high-end" binding posts (properly spaced for dual banana plugs) - insulated for CE compliance
• Anodized aluminum milled terminal plate
• 1/4" soft Neoprene Pad is recessed into the cabinet base to serve as a non-skid acoustic isolator
• Standard size (5/8"- 27 threading) female microphone stand mount is built into the cabinet base

The MixCubes are available in a powered version. ($239 each)

Specifications

System Type

Active (Self-powered) shielded full-range stereo pair

  Frequency Response
  90Hz - 17,000Hz (useful musical range)

  >Driver Impedance
  Nominal 8 ohms

  Max SPL
  104db @ 1 meter = 1%THD (PINK NOISE)

  Amplifier Type
  Class A/B

  Amplifier Power
  60 watts RMS@ .005% THD (1KHz)

  Amp Frequency Response
  22Hz-50KHz +0dB/- 3dB (90Hz-50KHz +/-0dB)

  Noise
  S/N -113 dB

  Sensitivity
  0dBu (.775VRMS) input at maximum volume (+6dB) = 104dB SPL

  Driver
  Proprietary design 5.25" cast aluminum frame / paper cone / shielded

  Cabinet
  sealed / 18mm MDF / Dacron acoustical stuffing

  Inputs
  XLR & TRS (COMBO JACK) +4/Balanced and -10 unbalanced

  Weight
  7 lb 5 oz (per speaker)

  Dimensions
  165mm x 165mm x 165mm (6 1/2" x 6 1/2" x 6 1/2" in)

Also available in black.

The Avantone MixCubes can be purchased at Little Fish Audio.