The Compositions home theater speakers are the first Infinity products to reflect
the input of Laurie Fincham, the company's new senior vice president of engineering.
Mr. Fincham was formerly at KEF, where he pioneered computer-based speaker
testing. In addition to the P-FR full-range sys tem reviewed here (which I
tested as stand alone stereo speakers, not as part of a home theater setup),
the Compositions Prelude series includes the P-CC center-channel and the P-QPS
surround speakers. These will soon be joined by other series of Compositions
speakers.
The P-FRs have a striking and distinctive shape: A column, 3 feet high and 8 inches deep, houses all but the woofer of this four-way system; that column sits atop a bass en closure that's much deeper than the column but only 7 3/8 inches wide. All drivers are magnetically shielded, so as not to affect nearby video screens.
The column, which has no amplifier of its own, houses seven drivers in a vertical array. At the center of the array is a 1-inch, soft-dome tweeter with a neodymium mag net. Its dome is surrounded by a molded-in elliptical waveguide, to smooth the response and control its directivity. Just above and below the tweeter are the two 4-inch upper-midrange drivers, which have polypropylene cones. They are driven in parallel and are mounted in small, individual sealed cavities. The four lower-midrange drivers are 5 1/4-inch long–throw units, wired in series-parallel, that use the internal volume of the column as their en closure. That enclosure is vented by four small port tubes, 1 inch in diameter and 0.6 inch long, with flared ends; they tune the box to about 100 Hz, below which signals are handled by the woofer.
The column itself is heavily contoured, front and rear, to minimize diffraction and improve strength. It is made of metal, with a molded plastic front panel and a snap-on grille.
The base forms a small (2/3-cubic-foot) sealed enclosure for the beefy 12-inch woofer; it also houses the 350-volt-ampere power amplifier that drives the woofer. The P-FR's base is so narrow that the woofer's magnet actually protrudes through the opposite wall of the base and is covered by a metal magnetic shield. Though the woofer is mounted on only one side of the base, matching grilles are provided to cover both sides.
The woofer itself is a long-throw unit with a large magnet in a heavy cast frame. Its molded plastic cone has a foam surround, and the voice coil is 2 inches in diameter. The driver's impedance is a low 1.8 ohms, but the built-in amplifier is optimized for that impedance.
The woofer's small enclosure raises the driver's resonant frequency to a high 80 Hz. This causes a 12-dB/octave rolloff below that frequency, which is compensated by equalization in the power amplifier. In part because of the bass boost from this equalization, the system includes protection circuitry for the driver and amplifier. This circuitry makes the amp soft-clip before the woofer can exceed its maximum safe excursion level.
The amplifier is controlled by switches on the bottom of the base.
By using these switches, you can turn the amplifier on or off, activate or defeat its auto-sensing (which puts the amp in standby when there is no signal), select one of three bass out put levels, and adjust the grounding configuration. (You will need the grounding switch only if there's hum or noise from the bass amp.) The auto-sensing system turns the amp on just about instantaneously when signal is present and goes into the low-power standby mode after about 10 minutes without a signal. A two-color LED on the top front of the base turns red when the amp is in standby mode and green when it is operating.
A passive crossover network is mounted inside the column. The tweeter is driven by a second-order high-pass filter, the two upper midranges are driven by second-order high- and low-pass filters, and the four lower midranges are driven by second-order high- and low-pass filters. Impedance compensation is included for all drivers. The lower mids are connected with the same polarity as the woofer, whereas the tweeter and upper mids are reverse-connected.
Input connections go to two five-way binding posts, which are spaced to accept double-banana plugs and have large enough holes to accept cable up to 0.15 inch in diameter (AWG #8). These binding posts are mounted to a heavy-duty assembly on the rear of the base.
Measurements
Fig. 1-One-meter, on-axis frequency response.
Fig. 2-On-axis phase response, group delay, and waveform phase.
Fig. 3-Horizontal off-axis frequency responses.
Fig. 4-Vertical off-axis frequency responses.
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Drivers: 12-in. cone woofer, four 5 1/4-in. cone lower midranges, two 4-in. cone upper midranges, and 1-in. soft-dome tweeter.
Frequency Response: 35 Hz to 20 kHz, ±2 dB; +0,-6 dB at 25 Hz.
Sensitivity: 96 dB at 1 meter, 2.83 V rms applied.
Crossover Frequencies: 110 Hz, 350 Hz, and 3 kHz.
Impedance: 6 ohms, nominal.
Recommended Amplifier Power: 10 to 150 watts per channel, above 100 Hz.
Power of Built-In Woofer Amp: 350 volt-amperes.
Dimensions: 54 1/2 in. H x 7 3/8 in. W x 19 3/8 in. D (137.5 cm x 19.4 cm x 49.9 cm).
Weight: 78 lbs. (35.4 kg) each.
Price: $3,000 per pair; available in char coal gray only.
Company Address: 20630 Nordhoff St., Chatsworth, Cal. 91311; 818/407-0228.
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Fig. 5-Impedance phase (A) and magnitude (B).
Fig. 6-Three-meter room response.
Fig. 7-Harmonic distortion for E1 (41.2 Hz).
Until now, my anechoic speaker measurements for Audio have been taken outdoors not too pleasant or easy in the winter. From here on, though, I'll be using Electro-Voice's large anechoic chamber. That's because I recently rejoined Electra-Voice (after a 20-year hiatus) as a senior research engineer at the company's Mark IV Audio division. (E-V makes only professional audio products, so I will not have a conflict of interest.) Figure 1 shows the P-FR's on-axis anechoic frequency response, for all three positions of the bass switch.
With the switch set at maximum and the column's grille removed, the curve is flat and smooth, fitting a tight, 5.5-dB, window from 32 Hz to 20 kHz. Except for the slight droop above 10 kHz, the curve fits a commendable 3.5-dB window (-0.5,-3 dB) from 36 Hz to 10 kHz. Each successive switch position shelves the bass-5 dB be low 70 Hz, with a hinge point at about 150 Hz. With the switch at "Max," you might hear excessive bass when the P-FR is near a room's reflecting boundaries. The grille causes major response deviations above 7 kHz, with a significant dip at 9 kHz, a narrow peak at 12 kHz, and roughness at higher frequencies. Average sensitivity from 250 Hz to 4 kHz measured a very high 94.2 dB. Figure 2 shows the P-FR's phase and group-delay responses referenced to the tweeter's arrival time.
Also shown is waveform phase, which indicates whether wave-shapes will be preserved in specific frequency ranges. The phase curve is well behaved but rotates 305° be tween 1 and 10 kHz. The group-delay curve, averaged from 700 Hz to 2 kHz, indicates an offset be tween drivers of about 0.25 milliseconds, the upper midrange delayed behind the tweeter. As is typical, the waveform phase curve indicates that waveshapes will not be preserved in any frequency range, because the phase values are not at or near 0° or ±180° over any frequency band.
Fig. 8-IM distortion For A4 (440 Hz) and E1 (41.2 Hz).
Fig. 9-Maximum peak input power and sound output.
Figure 3 shows the P-FR's response over a range of horizontal angles (the bold curve at the rear of the graph is the on-axis response). The uniformity from curve to curve is excellent, with only slight loss of high frequencies off axis above 10 kHz.
The P-FR's vertical off-axis response is shown in Fig. 4 (on-axis response is the bold curve in the center). Within ±10° of the axis, the curves are very uniform. Even at ±15°, there is a dip of only 5 dB (not clearly seen) in the upper most crossover region. Though it's hard to see the curves behind the on-axis response ( far below the axis), there is good up/down symmetry. At extreme angles, a sharp dip develops at 1.1 kHz.
Figure 5 shows the phase and magnitude of the P-FR's impedance. Note that the phase (Fig. 5A) approaches -90° at low frequencies, which shows that the impedance is capacitive in nature. Within the woofer's range of operation, he impedance magnitude (Fig. 5B) shows a rapid upward slope as frequency drops, reaching 100 ohms at 5 Hz. This rise is due to the series capacitors in the high-pass filters in the column's crossover network; without the influence of that net work, however, only the bass amp's even higher input impedance would be evident at these frequencies. Aside from that rise, the impedance's highest peak is 12.4 ohms (at 160 Hz), while its minimum is only 4 ohms (at 1.1 kHz). However, since the impedance is 27.2 ohms at 20 Hz, the max/min impedance variation between 20 Hz and 20 kHz is a fairly high 6.8 to 1 (27.2 divided by 4). To keep cable-drop effects from causing response peaks and dips greater than 0.1 dB, cable series resistance would have to be limited to a maximum of about 0.054 ohms. For a typical run of about 10 feet, that would mean using low inductance cable of AWG #14 or larger. Yet because of its high impedance at low frequencies and its reasonable impedance minimums, the P-FR will be an easy load for most amplifiers. For amplifiers that have low damping factors, such as tube models, the capacitive impedance rise at low frequencies may lead to bass boost.
The cabinets were quite rigid. When the system was subjected to a high-level sine-wave sweep, side-wall resonances were minimal. When the Compositions P-FRs arrived, one of the woofers had a moderate "tick," caused by the rubbing of a mis aligned voice coil. After I replaced that woofer with a new one from Infinity, I had no further problems.
Below the woofer system's closed-box resonance of 80 Hz, the driver's motion is controlled by stiffness, chiefly the stiffness of the small volume of air sealed into the enclosure. You can tell how stiff this is by trying to push the woofer's cone in. However, when the woofer is out of the enclosure and operated in free air, its diaphragm is quite easy to move.
I tested the amplifier's power-limiting threshold by noting the input voltage at the point where limiting occurred for several frequencies and settings of the bass switch. The higher the setting, the lower the limiting threshold. At the "Max" bass setting, the limiting thresholds at low frequencies occurred at quite low input levels, in the range of only 3 to 4 volts rms. At inputs above this threshold, distortion increased rapidly be cause of the amplifier's clipping and the driver's reaching its displacement limit.
This limit was only about 0.33 inch, peak to peak, at frequencies below 80 Hz and high input levels above threshold. (The woofer did not exhibit dynamic offset distortion at any frequency or level.) Interestingly, without its enclosure, the woofer could be driven to maximum excursion of about 1.1 inch, peak to peak-the largest excursion capability I've yet measured. In other words, the power limitations of the bass amplifier and the stiffness imposed by the small enclosure limited the woofer's throw to about one-third its natural excursion capability! Figure 6 shows the 3-meter room response of the P-FR, with both raw and sixth-octave-smoothed data. The system was in the right-hand stereo position, with its bass switch in the "Max" position (as it came from the factory), and aimed directly ahead, as per Infinity's recommendations.
The measurement microphone was at ear height (36 inches), at the listener's position on the sofa. Between 380 Hz and 17.5 kHz, the averaged curve is very well behaved and fits a very tight, 5-dB, window. There are room-effect dips at 210 and 320 Hz and a bass elevation between 100 and 200 Hz. Slight treble rolloff is evident above 17.5 kHz. For another test of room response ( not shown), made with the speaker canted in and aimed toward the test microphone, the results were essentially the same as those when the P-FR was aimed straight ahead.
Figure 7 shows E1 (41.2-Hz) bass harmonic distortion with the bass switch in its middle position. At this frequency, power is actually being supplied by the woofer's internal amplifier; Fig. 7's indications of apparent power are calculated from my test amplifier's output voltage and the speaker's rated nominal impedance of 6 ohms. My test amp was actually delivering much less power than this.
The second harmonic reaches 15% at full power, after rising to an intermediate peak of 25% at about 12 watts. The third harmonic rises to a very high level, actually 2.7 dB above the fundamental, for a calculated distortion of 136%! The fourth harmonic reaches a level of about 20% at full power, while the fifth rises to an even higher 37%. The high third- and fifth-harmonic distortion values indicate that the woofer's displacement was limited symmetrically in both directions. Subjectively, the distortion rose quite rapidly above 10 watts and then leveled out at about 25 watts, with neither the fundamental nor the distortion getting any louder at higher input power levels.
It was quite clear that the bass amplifier was being worked very hard in this test, be cause the rear of the base unit (where the bass amplifier is mounted) was quite hot to the touch, and the system exhibited a moderate "hot electronics" odor. The Infinity did not sound as bad as these high distortion readings would suggest. In fact, it sounded rather mellow at these levels, which indicates low levels of high-order harmonics. At apparent input power levels above 25 watts, it was clear that the internal amplifier was simply self-limiting at its de signed protection point.
At A2 (110 Hz), bass harmonic distortion at full power (not shown) rose only to 3.0% second harmonic and 1.4% third; higher harmonics were below the floor of my test gear. The A4 (440-Hz) harmonic distortion (also not shown) was quite low, reaching only 0.4% second harmonic and 1.1% third at full power.
Figure 8 shows IM versus power for 440 Hz (A4) and 41.2-Hz (E1) tones of equal level. After reaching 2% at about 16 watts, the distortion levels off at about 3% above 30 watts. At 100 watts, you can see that the IM rises only to 3%.
Figure 9 shows the short-term peak-power input and output capabilities of the P-FR as a function of frequency, with the bass switch in its "Min" and "Max" positions. (Peak input power was calculated by assuming that the measured peak voltage was applied across the rated 6-ohm impedance. Because of the system's high impedance at low frequencies, actual input powers levels were much smaller at low frequencies than calculated.) The measured peak power levels were for moderately clean-sounding acoustic outputs.
Note that the peak input level in the bass range depends on the gain setting of the bass amplifier. Maxi mum low-frequency power handling is achieved with the bass switch in its mini mum position, and vice versa. With the bass switch in the "Max" position, the input power starts very low, only 2 watts at 20 Hz and 5 watts at 40 Hz. But the input power rises very rapidly thereafter, leveling out at a high 4,000 watts above 400 Hz.
With room gain, the maximum peak output SPL of the P-FR starts at a usable 93 dB at 20 Hz, rises very rapidly (reaching 100 dB at 32 Hz, 110 dB at 48 Hz, and 120 dB at 78 Hz), and then rises to the very high range of 127 to 130 dB SPL at all frequencies above 93 Hz. Note that the maximum peak acoustic output doesn't depend on the position of the amp's bass switch.
The P-FR's maximum acoustic output in the upper bass, midrange, and treble is very high, in the top 15% of all speakers I have tested. Its maximum low-bass output, how ever, falls only about in the middle of the speakers I have tested. On the other hand, its maximum output from 40 Hz up-very important in this speaker's home theater target market-has few equals.
Use and Listening Tests
The Compositions P-FR speakers come in quite large boxes with relatively complicated internal packing. Detailed unpacking instructions are included in the owner's manual. Before the systems can be re moved from the car tons, four adjustable-height glides must be threaded into two bracket assemblies on the bottom of the speakers (supplied spikes can be substituted for the glides). Each of my test samples, however, had one improperly threaded bracket, which made it quite difficult to at tach two of the glides to each system. The front glide bracket protrudes about 2 1/2 inches beyond the sides of the woofer cabinet, but an attractive molded plastic cover hides it.
The P-FRs are quite good-looking, even in their basic charcoal gray (the color of many TV sets) and present a striking narrow and tall appearance when set up-definitely not your usual column-style systems.
Infinity has paid a great deal of attention to design, including such details as the appearance of the molded plastic front panel and the individual drivers, which are visible when the grille is removed.
The 16-page owner's manual is very comprehensive, with an emphasis on home theater and multimedia setups. Much useful information is included on operation and setup of the woofer and its controls. The speakers were quite easy to hook up. I listened to them with gear that included Onkyo and Rotel CD players, a Krell KRC preamp and KSA250 power amp, Transparent Audio MusicLink Reference interconnects, and MusicWave Reference speaker cables. I also used B & W 801 Matrix Series 3 speakers for comparison.
The P-FRs were set up in my usual speaker locations, about 8 feet apart and far from the rear and side walls. Listening was done from the sofa, about 10 feet away, both with the speakers facing straight ahead (Infinity's recommendation) and with them angled in toward the listening position. I slightly preferred the sound with the Infinities angled in. All listening was done with grilles removed.
For my initial listening, I used African Variations, a promotional sampler disc of African music (Rykodisc RCD-PRO-AFR), which emphasizes percussion, rhythms, and drums. On this material, the P-FRs exhibited a very dynamic, clean, and wide-range sound. They were very smooth and could actually play louder and cleaner than the B & W 801 speakers.
Most listening was done with the bass level control set to its middle position.
With the switch set to "Max," the bass was somewhat emphasized as compared to the 801s. In the middle position, the bass level was slightly less than the 801s'. The Infinities are among the very few systems I have evaluated whose maximum bass output can match that of the B & Ws. The P-FRs also kept up very well with the 801s in bass cleanliness, level, and smoothness. Only on material that had high levels of very low bass did the P-FRs come up short.
There was no room-shaking bass from 20 to 30 Hz; the presence of such bass in the signal was sometimes accompanied by a sudden change of bass tonality when the level was turned up beyond a certain point. On loud rock 'n' roll bass and kick drum (which is mostly 35 Hz and up), the P-FR's bass quality and quantity matched or bettered that of any other speaker I have reviewed.
The P-FR's dynamic range capability was very impressive. This speaker could be played very loudly and cleanly on live sound effects, rock 'n' roll, and full sym phonic music with percussion. I had to attenuate the signal a full 8 dB to match the Infinity P-FR's sensitivity to that of the B & W 801! Switching from speakers of average sensitivity to the extremely sensitive P-FRs is like multiplying your amplifiers' power by about six.
On my old favorite, Ein Straussfest (Telarc CD-80098), the P-FRs turned in one of the best performances I have heard; the rifle and percussive sound effects were re created with extreme realism. The synthesizer sequence on track 1, "Ascent," of Don Dorsey's Time Warp (Telarc CD-80106) was quite impressive. This disc also demonstrated the Infinity's impressive capabilities on "movie-style" material, such as the main theme from Star Trek With pink noise, the P-FRs did quite well on the stand-up/sit-down test. They did exhibit a significant change in sound when I stood up, but the change was mostly a balanced reduction in level of mids and highs rather than the change in tonal character through the midrange that some other systems exhibit. When I sat, the Infinity P-FRs were just as smooth as the B & W 801s, with a very similar tonal balance. On most pro gram material, it was hard to tell the difference between the P-FRs and the 801s in casual listening.
On band-limited pink noise, the Compositions P-FRs generated no usable bass out put in the 20- and 25-Hz third-octave bands but produced some usable output at 32 Hz and had strong and powerful output in all bands from 40 Hz up. In the three lowest bands (20, 25, and 32 Hz), the P-FRs overloaded, suddenly sounding very distorted when a specific threshold was reached. Fortunately, the upper-bass and lower-midrange content of normal, wide-range program material effectively masks the woofer's distortion.
The P-FRs could handle a wide range of material-from symphonic music to male and female voice and from live jazz to loud dance music-with equal ease. In general, the P-FRs consistently presented a crisper, more up-front sound, with less room effect, than the 801s. Presumably this occurred be cause of the P-FR's restricted vertical cover age pattern. Speaking voices were particularly well reproduced, with a quite vivid center image. These latter traits are exactly what's required in a good home theater speaker.
The Infinity Compositions P-FRs' sound and appearance are competitive with those of the best home theater and stand-alone stereo speakers available. They should be very seriously considered by anyone who needs a speaker system that performs very well in both applications.
-D. B. KEELE, JR.
(Audio magazine, Mar. 1993)
Also see:
Infinity 9 Kappa Loudspeaker (Auricle, Jan. 1988)
Infinity SERVO STATIK 1A speakers (ad, Aug. 1975)
Infinity 1001 Speaker System (Equip. Profile, Apr. 1973)
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