Polk Audio LSi M 704C Center Channel Speaker

Driver Technology

Performance Objectives of the Polk Audio LSiM Series Loudspeakers:

  • The LSiM series loudspeaker is Polk Audio's best high-performance loudspeaker.
  • Polk Audio designed the LSiM series loudspeakers to create a sound that virtually transports you to the scene of the recorded performance.
  • It was engineered & created with the following performance objectives in mind.
  • Pleasing tonality, even during extended listening at performance levels.
  • Crisp, lifelike impulses, transients & coherent detail without any unnatural ringing or decay.
  • Natural reproduction of complex low frequency instruments & special effects.
  • Uniform sonic representation within the listening area & immersive spatial impression.
  • Reproduce concert/theater levels while maintaining linearity and accuracy.
  • Compatibility with a wide array of electronics both past, present & future.
  • Work as promised for many years of enjoyment (5 year parts & labor warranty).

Dynamic Balance:? 

  • Dynamic Balance is a proprietary Polk Audio technology using laser imaging to determine what combination of speaker materials create the least amount of resonance.
  • Eliminating resonance in speakers results in a wide, smooth response, & low distortion.

3-Way Driver System: 

  • The Polk Audio LSiM series center channel loudspeaker employs a 3-way driver system for crisp, detailed highs; natural, lifelike midrange; and accurate, dynamic midbass.
  • The center channel houses a 1" (diameter) Dynamic Balance Enhanced Ring Radiator Tweeter, a 3.25" (diameter) Dynamic Balance Super Cell Aerated Polypropylene cone midrange driver, & two 5.25" (diameter) Dynamic Balance Super Cell Aerated Polypropylene cone midbass woofers.

Enhanced Ring Radiator Tweeter: 

  • The ring radiator tweeter was a vital element in the success of Polk Audio's original LSi Series.
  • Polk Audio engineers have made some nuanced improvements in the design of this tweeter.
  • First, they reshaped the tweeter's bullet-shaped phase plug, allowing it to move farther out of the baffle, improving dispersion and eliminating horn-loading. Next, they opened up the tweeter's face-plate, then redesigned the tweeter's diaphragm roll to make it more efficient and improve dispersion even more.
  • Finally, they gave the new ring radiator tweeter its own tuned enclosure (Dynamic Sonic Engine).
  • This new ring radiator tweeter boasts higher power handling, extended dynamic range, improved dispersion and extended top-end response.

Super Cell Aerated Polypropylene (APP) Cone Woofer:

  • If the perfect cone material is lightweight (for faster, more efficient action) and stiff (for less distortion-causing flex), with enough internal damping to suppress and offset any limitations of its lightweight stiffness, then the Super Cell APP Cone Material is about as perfect as cone material gets.
  • Aerated Polypropylene (APP) is a mineral-filled polypropylene material that's been "puffed up" with injected air to form a honey-comb structure.
  • Polk Audio's original APP cone approached the ideal balance of lightweight stiffness with high damping, along with good resistance to moisture, UV and temperature extremes.
  • Next generation LSiM series loudspeakers employ Polk Audio's next generation of APP Super Cell.
  • In Super Cell APP, the "puffed cells" are larger, for a thicker cone material that actually has less mass than the original APP material. Super Cell APP has larger cells, for lighter weight and more inherent damping, plus uncompromised stiffness, for unsurpassed transient response and resonance suppression.

Butyl Rubber Surrounds: 

  • Durable, soft, injection-molded butyl rubber surrounds are tuned to absorb and suppress unwanted cone resonances.
  • Polk Audio's butyl rubber material is impervious to UV, extreme temps & humidity, for a lifetime of smooth, reliable sound.

Extended Linear Motion Voice Coils:

  • Allowing lots of movement in a limited space, ELM Voice Coils power the LSiM series speaker's mid-range & mid-woofer drivers to extend their higher-frequency response with much less impedance.

Cast Aluminum Baskets: 

  • These lightweight, cast aluminum baskets provide a rigid structure for precise alignment of the speaker's active parts, for flat response & low distortion, with no mechanical resonances or ringing. The open design provides ample venting for unobstructed linear movement.

Orth Crossovers: 

  • The Polk Audio LSiM series center channel speaker employs proprietary engineering, designed and patented by Polk Audio to maintain a lower order crossover design & increase power handling.
  • Orth Crossovers feature Mylar/polypropylene capacitors for sparkling highs & Air Core Inductors for superior transparency.
  • Notch Filters and sophisticated Zobel circuits smooth the impedance curve of the system for more efficiency & better high frequency response.
  • Tweeter/Midrange Crossover: 2.5 kHz, 18 dB/oct
  • Midrange/Midbass Crossover: 280 Hz, 12 dB/oct

Timbre-Match Series: 

  • You can achieve incredible realism & seamless surround effects when you build a complete Polk Audio LSiM series speaker system.
  • All LSiM series speaker models feature the same components & tuning for perfect timbre-matching.

Frequency Response Note:

  • The overall frequency response is 40Hz to 40kHz & the -3dB frequency response is 70Hz to 30kHz.

Enclosure Design

Real Wood Veneer: 

  • The Polk Audio LSiM loudspeaker is finished in a real, natural, furniture-grade wood veneer.

MDF Enclosure: 

  • The enclosure is an integral part of the sound design of the Polk Audio LSiM series loudspeaker.
  • All LSiM cabinets are made of .75" MDF, with wide-radius baffles of robust 1.25" MDF. Substantial internal bracing (each driver has its own separate non-parallel chamber) increases efficiency and banishes internal resonances & standing waves, for high power handling and incredible smoothness.
  • Wide-radius baffles, along with zero-diffraction magnetic grilles, help stabilize imaging for a very wide, well-defined soundstage.

Dynamic Sonic Engine (DSE): 

  • At the heart of the Polk Audio LSiM series center channel speaker is an enclosure-within-the-enclosure design (known as the Dynamic Sonic Engine) that houses the mid-range driver & the ring radiator tweeter.
  • Molded into one rigid piece, the DSE enclosure tapers to a "turbine" that reduces back-wave reflections.
  • The DSE combines its two speakers in an aligned, optimized array for wide, uniform dispersion in the critical 200Hz-2kHz midrange, improving transient response.
  • The combination delivers exact timbre-matching, improved high-frequency dispersion and greater horizontal off-axis response.
  • The ring radiator tweeter & midrange driver are housed in a separate internal sealed enclosure from the ported enclosure which houses the two midbass woofers.

PowerPort Bass Venting:

  • PowerPort Bass Venting is a Patented Polk Audio technology that uses a specially designed "cone" at the mouth of the bass port to direct moving air as it exits the port. Air moving out of a bass port creates turbulence, which can result in boomy distortion & "port noise", especially at high volume.
  • This distortion can cause bass output losses up to 3dB, wasting lots of amp power.
  • To eliminate bass-stealing turbulence at the mouth of the port, Polk Audio engineers designed the PowerPort. It's unique shape promotes "laminar" airflow even in short tube ports by mimicking the properties of longer, flared port openings.
  • No turbulence means no wasted power, which means more efficient bass response.

Zero-Diffraction Magnetic Grille: 

  • The super thin (1mm), zero-diffraction grille has no measurable effect on the speaker's response. Completely unobtrusive, stylishly sheer; the grille locks into place magnetically.


Gold-Plated Binding Posts: 

  • The center channel loudspeaker has one set of gold-plated binding posts. The binding posts will accept bare wire (16-12 AWG), pin connectors, spade connectors, & banana plugs (single only).


  • The center channel speaker's binding posts are color-coded (red/black) for easy identification between positive & negative.

Mounting Options


  • With today's modern flat-panel TVs, the most popular placement, and our recommendation for your center channel speaker, is beneath your TV screen.
  • You may also place the center channel speaker above your TV, should you choose.
  • The LSiM center channel loudspeaker is very heavy (27.8lbs) and we do not recommend wall mounting it, unless placed on a sturdy shelf.
  • The LSiM center channel speaker is not magnetically shielded.
Rubber Feet: 
  • The center-channel speaker comes with 4 self-adhesive rubber feet so it will sit securely on your stand or shelf.
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