Feb 2, 1999 5:28 PM, By Hunter Pipes

MIDFIELD STUDIO MONITORS

The Professional Monitor Company's PMC IB1S midfield studio monitors provide one of the most sensational listening experiences I have enjoyed. I found it practically heartbreaking to have to return them to the manufacturer after the evaluation.

Retailing for $4,500 a pair, the IB1S measures 29.1x13x18.3 inches (HxWxD) and occupies a little more than four cubic feet of studio space. Weighing in at a hefty 79 pounds apiece, these monitors provide a usable frequency response of 25 to 25k Hz and pack a mighty wallop. Peak SPL is listed at >116 dB @ 1 meter; sensitivity is 89 dB (1W/1m). Recommended power handling is up to 500 watts, and for this review, I used Bryston's 4B-ST stereo power amplifier, providing 455 watts into a 4-ohm load.

THE BOTTOM LINE IS TRANSMISSION LINE
How do you design a loudspeaker to achieve at least one more octave of low-frequency information while providing higher SPLs, lower distortion and a more sonically transparent delivery than an equivalently powered ported loudspeaker? PMC's answer is Transmission Line loading, which makes these speakers extremely accurate at both high and low SPLs, and provides uncolored sonic clarity across the frequency spectrum.

Behind the front grille is a flat, extremely rigid, piston-type low-frequency driver. Constructed of a carbon fiber and Nomex sandwich, this 8-inch planar woofer is driven by a 24.6-pound (!) magnet, with a ferrofluid-cooled, edge-wound 3-inch Kapton voice coil. Working in tandem with this driver is the transmission line. A polyurethane-lined port—which occupies the same surface area as the woofer itself and folds to an effective length of 14 feet—allows the speaker to perform more efficiently. The integration of this port provides accurate and punchy bass-end balance at nearly all listening levels.

The mid driver (crossed at 380 Hz) is a 3.5-inch doped fabric dome. After the 3.8kHz point, highs are handled by a 1-inch silk-dome tweeter, said to offer response to 25 kHz. The 25 elements in the fourth-order Linkwitz-Riley crossover include matched, high-quality components such as high-current air core inductors and low-loss caps. Multi-stranded oxygen-free copper wiring is used throughout.

Speaker inputs comprise three pairs of 4mm gold-plated terminals that are strapped together with gold-plated banding that's removable for active bi-amping and tri-amping. Other options include matching speaker stands, mag shielding and film curve filtering; the IB1S is also available in a self-powered configuration.

HEARD BUT NOT SEEN
For the critical listening tests, I selected five CDs in various styles and genres, from rock to jazz to classical to techno, and a few masters that I had mixed myself. First out of the bag was the techno: rich and heartily textured with great analog synth sounds and sweeps, pounding low frequencies and shrill highs. The sound of this modern mixture of old and new was like a breath of fresh air. It was as if my control room had been transformed into some sort of supercharged listening environment. I quickly ran down the hall and summoned everyone in the facility, saying, "You gotta come hear these things!"

As the day wore on, I realized I was hearing things that until then had been imperceptible to me. For example, when listening to a jazz trio that had been recorded in what sounded like a fairly large tracking room, I was amazed to discover that I could hear the rustling of a musician's clothes before he performed. Further listening revealed the slightest buzz of an antique organ speaker and the switching of channels in the bass part as the take was going down.

Next came classical scores: Beethoven, Vivaldi, Wagner, Brahms. The width of the image was completely uncompromised. I could close my eyes and point to each musician, as if they were all seated in the studio in front of me. French horn in the middle of the third row, oboe in the last seat of the last row on the left-hand side and a bass drum booming right down the middle with the intensity of a freight train.

When I concentrated on mixing, I noticed the amount of depth that was opened up within my own mixes. I was working on an animated series, and it seemed as if each element of the show—dialog, music, Foley and SFX tracks—occupied its own pocket within the mix. There was more "airiness" within the mixes, and the depth of field was something that I had not previously experienced using my standard monitor system. The director kept saying, "Wow, this is great. It sounds so much better than last season." I just smiled and bit my lip. I did not want to tell him that it was more likely the speakers that he was appreciating instead of some radical advancement of my sound design techniques.

The IB1S system reminded me of a finely tuned racing car. The speakers were great fun to zip around at low level and everything sounded wonderful, but when you started to apply a little gas, it really got exciting. I noticed that as I applied a little more power, the cabinets seemed to open up; at SPLs around 85 to 90 dB, the speakers really started to punch. I pulled out the techno again and started to apply the gas. I slowly started to increase the monitor levels past 85 dB, onto 90 and then to 95 and up to the point of clipping the Bryston. The amazing thing was there was no audible distortion within the cabinets. Actually, I was barely able to see any excursion on the low-frequency driver: The speaker handled everything I could throw at it.

Due to the physical constraints of my control room, I was forced to place the speakers on a shelf behind the console and I was certain that I would have problems with the studio furniture creating low-frequency resonance, but the IB1S proved me wrong. Even with the most earth-shaking low-frequency information fed to them, there was barely a hint of any external vibration when I put my hand on the surrounding surface. This was also true when I felt the outside of the speaker enclosure.

In closing, I was completely impressed with the IB1S. I've been mixing in one environment for an extended amount of time and I'm very comfortable with the sound of the room, so I didn't think that another pair of speakers could make much of a difference. Boy, was I wrong. The PMCs let me hear information that I didn't know was present in program material that I had been familiar with for months. They provided an extremely wide and deep stereo image with little to no distortion or resonance, and a silkiness and sheen among the mid and high frequencies the likes of which I had not imagined. If I only had a few more square feet in front of my console, I would be adding a pair to my ensemble.

PMC Monitors, www.pmcloudspeakers.com.

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Lab Analysis: PMC IB1S Monitor
By John Schaffer and Rob Baum

The PMC IB1S is a three-way system. The 1-inch Vifa soft-dome HF tweeter is driven by a 1-inch-diameter voice coil and is mounted to a 4-inch-diameter, horn-loaded faceplate. The pole piece is vented into a sealed plastic enclosure. The unshielded driver is supplied with two 0.11-inch male connectors. The midrange driver, a Vifa 3-inch dome unit with a 3-inch diameter voice coil, has a 6-inch diameter shallow, horn-loaded plastic faceplate. The design uses a central slug of either neodymium or Alnico magnet, so it is inherently shielded. The motor case is vented into a sealed plastic tube rear enclosure and there are two 0.11-inch male connectors.

The 10-inch woofer has an 11/44-inch-thick flat diaphragm and is constructed from textile skins on either side of a honeycomb diaphragm, which is attached to a half-roll butyl-rubber surround. Flat diaphragms permit shallow baskets or frames and consume less volume inside the enclosure than cones; hence, the popularity of flat woofers in car audio where space is at a premium. The cast-aluminum basket is powder-coated black and the surround is attached by screws into the main body of the basket. The woofer's top plate is 18.5mm thick and the 3-inch diameter voice coil is underhung, i.e., the voice coil is shorter than the top plate. The unshielded woofer uses a 7-inch-diameter cupped (as opposed to flat) spider. The one-piece backplate and pole piece are forged. The conventional ceramic (ferrite) magnet is 811/42 inches in diameter and 1-inch-thick. The wire terminals are spring-loaded barrel terminals.

The PMC IB1S cabinet uses a slot-loaded scoop design, is built of 1-inch-thick MDF and is finished in black-textured paint. T-nuts are used for all threaded fasteners, and the enclosure is heavily stuffed with polyester foam. All the drivers are recessed, as is the crossover panel. The crossover uses three pairs of gold-plated five-way binding posts on an MDF rear panel, allowing for tri-amped or full-range use.

TEST RESULTS
The on-axis frequency response is fairly flat above 500 Hz, except for a shallow dip between 1,200 and 3k Hz. The frequency response rises by about 5 dB from 1.8 to 20 kHz. The off-axis response smoothly tapers down by 5 dB from 500 to 11k Hz, and then decreases rapidly above 11 kHz. The PMC exhibits a fine transient response, particularly for a three-way system. The drivers are generally in good acoustic alignment with each other.

Harmonic distortion measured well, and was approximately 0.2% for the two decades from 100 Hz to 10k Hz, rising only at the frequency extremes. The spectral contamination-distortion test is a measure of the speaker's nonlinear distortion (i.e., the generation of frequencies not harmonically related to the original input frequencies and therefore very objectionable). The PMC generated spectral contamination (or self-noise) at a level of about 45 dB below the input test tones.