Monolith III

The Power of Sound

The Monolith III stand alone. Powerful. Imposing. Thrusting you into a world of harmony and purity discovered only by a chosen few.

It all began with this reference speaker project. Since its emergence in 1982, the Monolith has represented the culmination of reference level ML electrostatic technology and exhaustive crossover and dynamic driver research, providing dynamics, precision and bandwidth comparable at any price range. This system combines lush woodgrain and black satin composite finishes into a strikingly beautiful cabinet, as elegant to behold as its sound reproduction is to experience. The Monolith III requires the addition of an external crossover. You can choose the superb Monolith IIIp passive crosover ($1000 US retail), or the Monolith IIIx (EXOS - $3500 US retail) active crossover.

Launched in 1990

Price when discontinued:



Specifications are subject to change without notice

Frequency Response

28–24,000 Hz ±3dB

Recommended Amplifier Power

20‒500 watts per channel

Horizontal Dispersion


Vertical Dispersion

48" (121.92cm) line source


89 dB/2.83 volts/meter


IIIp High-pass: 4 Ohms, 1 at 20kHz
IIIp Low-pass: 4 Ohms
IIIx (Exos) High-pass: 47,000 Ohms
IIIx (Exos) Low-pass: 100 Ohms . Compatible with 4, 6, or 8 Ohm rated amplifiers.

Crossover Frequency

IIIp: 125 Hz. IIIx 125Hz 12dB/octave low-pass, 18db/octave high-pass

High Frequency Transducer

48" (121.92cm) CLS™ electrostatic transducer

Low Frequency Transducer

12" (30.5cm) high excursion, super light, high rigidity cone with extended throw driver assembly. Non-resonance chamber format.


Monolith III: Glass epoxy boards, Custom wound audio transformer, polypropylene capacitors, air core coils.

IIIp Passive Crossover: Glass epoxy boards, polypropylene capacitors, 100% oxygen free copper coils, wire-wound resistors.

IIIx (Exos) Active Crossover: Glass epoxy bards, metal film resistors, polypropylene capacitors, hand picked J-FETs, TIFFANY input/output connectors.

Audio Controls

IIIx (Exos) Active Crossover Frequency: 30, 35, 40, 45, 50 Hz
IIIx (Exos) Active Crossover Boost/Cut: -4, -2, 0, +2, +4 dB


30-amp gold plated 5-away bi-wire binding posts


120 lbs. (54.5 kg)


73.75" × 26.75" × 11.75"
(187.3cm × 67.9cm × 29.8cm)

Compatible Products

IIIp Passive Crossover, IIIx (Exos) Acticve Crossover

Customer Reviews For Monolith III

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  • Wednesday, November 12, 2014

Oldie but a Real Goodie 4.6 stars
I purchased my Monolith IIIx,p in 1992. They were a floor demo, since the small dealer only has 1 pair! I received a decent discount since they were 1 year old at the time. I have both the passive and active crossovers. I now use Pass Labs X3 pre and X350.5 amp ('stats) and Parasound HCA2200 II amp (woofer). The ultra high quality passive crossover only requires one stereo amplifier to drive the speaker system but like ALL passive crossovers, it really gets in the way (slightly colors) the sound when directly compared to the awesome XOS electronic crossover (IIIx version) and using a pair of great SS amps. I was advised against using my beloved tube power amps due to their high Damping Factor which causes an obvious roll-off of high frequencies in the 'stat panels. For similar reasons, tubes usually do not promote tight bass. Anyway, since excellent, powerful and musical SS amps are abundant, why not? I have used a bi-amp configuration for over 15 years now. I also use a digital room bass correction system on the woofers only. Automatic room-speaker mode (peaks) correction really helps clean up the bass and make it much more crisp and defiend - and way less boomy. I have new Peerless aluminum 500W woofer cones also, this helps bass definition also. I also have new factory buit 'stat panel since about 2009. These were built to the latest standards and do sound better than the origonal panels. BTW, the panels will eventually (15+ years) lose volume (1-2dB) and high frequency extension, even if you keep them clean and dust free. So replace them if M-L still provides that service. The sound: overall, the sound using Pass X350.5 on the panels is awesome: big, clean, clear, tight, fast, musical, detailed, dead quiet background and very 3 dimensional. However, a small region the mid bass is still a tiny touch muddy and the highs above about 5kHz are a bit subdued - but still very clean. It's as if the cymbals and triangles are 10-15 feet farther away that the rest of the musicians. But vocal clarity and depth, or solo instruments, be it guitar, saxophone, piano or drums are just amazing - they float in front seamlessly in crystal clarity across from left to right in glorious and delightful 3 dimensions. Airy, effortless and realistic sound floats on the soundstage in front of and behind the actual speakers. Wow. As a minor owner of s hifi store (no names) for the last 30 years, I periodically bring home a pair of the latest (non electrostatic) speakers for a few days of "home demo". Invariable they go right back into the store demo stock. Electrostatics are magical even if they are not perfect in their ESL-to-woofer blending - they still beat the pants off of almost everything else. They spoil you too. The soundstage they present, the clarity is just addictive its so realistic. Tiny midranges and tweeters just cannot convey this sense of size and openness. The Monolith have one feature that the latter-day M-L designers simply missed is their separate speaker inputs for the raw woofer and for the electrostatic sections. Thus bi-amplification is possible. Active bi-amping is very desirable (implying the use of an electronic crossover and/or separate digital room-bass correction while the stats are driven with pure analog signals). Active bi-amping capability allows the User to try all sorts of individual control measures on both the woofer and separately, the 'stat panels - this opens up a whole new world now that digital speaker correction is becoming commonplace. In a few yearsa, audiophile grade full spectrum automatic digital control / speaker compensation will be possible, so even the 1992 Monoliths III can be made to sound as good as anything on the market. Almost twenty-five years on, a good condition used Monolith III system can cost you $3k, if you can find one. A new Summit pair is $15k. Is the Summit 5 times better?

Jeremy Searles

  • Saturday, May 25, 2013

Love all over again
I have had these Monoliths in my life for quite some time. First, they were my Uncles, but after his passing, I was graced with them. With the help of the customer service dept, I was able to change out the panels a little over a year ago. Since then, they sound like they did when new. The sound is so clear and pure. It's like listening to a song again for the first time so times. Currently I am using Harman Kardon amps. These speakers really bring vinyl to life. If you come across a set, worth a look. You won't be sorry.

Peter Yeanacopolis

  • Thursday, October 21, 2010

My Monoliths
I have owned my Monoliths since they came out in 1990 and have enjoyed them ever since. I originaly powered them with Macintosh pre-amp C22 and MA 75 and they sounded the best with tubes sending highs thoughout the room delivering all frequencys with utter clarity. I have since changed to Adcom Limited Edition matched amps and wish I stayed with Mac. I also use the Monolith IIIx active crossover which allows me to customize my listening and would not do without it. I have not heard the newer products offered by ML however with the correct cables, amps and pre-amp, (I use Transparent)these are what I continue to enjoy for thier reproduction capability.