Manufacturer's Specifications:
Type of System: Acoustic suspension.
Speakers: One 10-in. woofer, one 2-in. midrange and one 1 1/2-in. tweeter.
Nominal Impedance: 8 ohms.
Power Needed: 10 to 60 watts per channel.
Size: 24 3/8 in. H x 13 3/4 in. W x 12 in. D (62x35x 30.5 cm.)
Weight: 35 lbs. (15.9 kg.)
Price: $159.00.
The Audioanalyst Model A-100X is a three-way speaker system using a 254-mm (10-in.), high-compliance woofer, a 51-mm (2-in.) midrange driver, and a 38-mm (1 1/2-in.) wide-dispersion tweeter. The major structure is designed as a sealed enclosure to provide the proper woofer loading for good low frequency response in a moderate sized box.
The external finish on the sides and top of the system is walnut, with an optically opaque, but acoustically transparent, cloth grille covering the front. Measuring 619 mm (24 3/8 in) high, by 349 mm (13 3/4 in) wide, and 305 mm (12 in) deep, the A-100X is designed as a bookshelf unit that can be mounted either vertically or horizontally. However, even though of modest weight, 16 kg (35 lbs.), the smooth sides of this unit cause me to recommend that rubber bumpers, or similar safety stops, be provided on any shelf containing this speaker to prevent the unit from accidentally sliding off, as with any smooth-sided speaker.
Connection is made to well-marked terminals on the rear of the enclosure, and two toggle switches provide simple adjustment of midrange and tweeter acoustic balance if that is desired in a particular listening situation.
A simple, but adequate, instruction sheet comes with the speaker, which even a novice can use with comprehension in hooking up a system for the first time. A welcome addition in the instructions is the inclusion of a cautionary note on the hazards that long term exposure to high sound pres sure level poses to hearing. The long term risk to hearing is a very real hazard if common sense is not used, and I applaud Audioanalyst for their concern.
Technical Measurements
The magnitude of speaker impedance as a function of frequency is shown in Fig. 1. While the rated nominal impedance is 8 ohms, the lowest value of about six ohms is reached at around 120 Hz. There is some change in load impedance with position of the rear-mounted level switches, and the two extremes of this variation are shown in this plot. From the standpoint of amplifier load, a slightly lower impedance is presented at high frequencies when the rear-mounted switches are both set to the upward or HI position. The bass resonance for this speaker occurs at 54 Hz.
Fig. 1--impedance versus frequency for extreme positions of equalizer switches.
Fig. 2--Complex impedance for Mid Hi & Tw Hi equalizer switch
positions.
The polar impedance counterpart of Fig. 1 is shown in Fig. 2 for the same range of frequencies and for the condition when both rear-mounted switches are in the HI position.
Bass resonance is quite well behaved, and the 450 Hz shelf in impedance in Fig. 1 is revealed as a possible diffraction effect. At the higher frequencies, the maximum capacitive phase angle is seen to occur at around 9 kHz, with a transition toward inductive reactance at 20 kHz. Since the magnitude of this impedance at 9 kHz is around 10 ohms, with only about 3 ohms capacitive reactance, most amplifiers should have no difficulty driving the A-100X near clipping level on high frequency transients.
Figure 3 shows the one-meter axial anechoic frequency response for one-watt average drive. This is the plot of the sound pressure amplitude and is made for the two extreme positions of the equalizer switch position. There is the slightest tendency for a low end peak at around 63 Hz be fore the response falls uniformly below that frequency.
From 200 Hz and continuing upward there is a very gradual increase of level with frequency, even for the LO equalizer positions. This indicates that the direct sound will have a mildly bright characteristic with a tendency toward a bit too much top end. Output for this one-watt drive level averages approximately 87 dB above about 50 Hz, showing the A-100X to be moderately efficient for a closed-box system.
From the anechoic standpoint, the tweeter is about a dB and a half hotter than the midrange woofer, and you may want to drop its level by that amount for a better spectral balance. The tweeter keeps right on going at 20 kHz, which is quite good performance. There are enough variations in both midrange and tweeter response to indicate the existence of diffraction effects.
The anechoic phase response is shown in Fig. 4. There are two plots here. One plot is corrected for the path delay of the tweeter, while the other is corrected for the path delay of woofer unit. The tweeter is acoustically the first driver heard, followed by the midrange unit, then followed by the higher frequency components of the woofer. The tweeter is actually 0.28 milliseconds in front of the top end of the woofer and 0.07 milliseconds in front of the midrange.
The actual acoustic crossover between woofer and mid range occurs at slightly above 2 kHz, while the 7.5-kHz crossover for the tweeter is just what Audioanalyst specifies it to be. There is, however, a 180-degree phase reversal be tween tweeter and woofer, so that care should be used when matching this system with ones of other manufacturer for use in quadraphonic systems.
The time scatter of arrival for the three drivers gives a non-minimum phase response around the crossover regions. Small details in response due to each driver considered separately, however, are of minimum phase.
The spectral dominance of the tweeter, coupled with the fact that the tweeter and midrange sound arrived ahead of the components below 2 kHz, implies a bright sound.
The three-meter room response for on-axis and 30-degree left-channel stereo position are shown in Fig. 5. For this test the A-100X was placed against a wall, and the height adjusted so that the tweeter was one meter above the floor with the enclosure long axis vertical. The plots are displaced 10 dB for clarity of presentation.
The better of the two responses is obtained directly in front of the enclosure, in an on-axis position. Severe diffraction dips take their toll off-axis. This measure strongly suggests that the A-100X should be angled toward the listening area for more accurate sound.
Fig. 3--One-meter anechoic sound pressure level for one-watt drive.
Fig. 4--One-meter anechoic phase response.
Fig. 5--Three-meter room response.
Fig. 6--Horizontal polar energy.
Fig. 7--Vertical polar energy.
The equalizer positions chosen for this test were both midrange and tweeter in their LO position, which was the condition experimentally chosen during the earlier listening test and the position the maker recommends in their literature. The drop in response in the octave of middle C shown in this plot for both speaker positions may account for the feeling of thinness which I had earlier when listening to orchestral and piano music. As in the anechoic response, the top end goes right up to 20 kHz with no strain.
The polar-energy response plots are shown in Fig. 6 for azimuth and in Fig. 7 for elevation. For these measurements, the long axis of the enclosure was vertical, with the tweeter above the woofer, as it was placed for the three-meter room test. The four possible combinations of switch equalizer position are shown in these plots. On average, the midrange control gives about a 1 dB variation, while the tweeter control gives about 2 dB variation for the total energy in the 20 Hz to 20 kHz frequency range. It is apparent that there is a definite left-right disymmetry. These plots indicate that if the A-100X is placed in a conventional manner, with the en closures pointing directly out from a wall, the left channel will be slightly stronger than the right channel for higher frequency stereo sound. Some care should therefore be taken in the choice of mounting configuration for these speakers, as there is an azimuth beaming problem within 15 degrees or so of a position directly in front of the enclosure. If the spacing between speakers is wide enough to give a physical angle between them and the listening area of 60 degrees or greater, then the speakers should definitely be rotated toward the listening area for balance. But don't angle them directly toward the listening area or the beaming will be noticeable in terms of a diffuse stereo image.
The good vertical dispersion above the median plane in Fig. 7 shows that the A-100X should be placed reasonably close to a floor for the best timbre. But do not mount the units above ear level or directly under protruding reflecting surfaces.
Harmonic distortion for the musical tones of E1 or 41 Hz, A2 or 110 Hz, and A4 or 440 Hz is shown in Fig. 8. With the exception of the second harmonic of E1, the distortion re mains quite acceptable throughout the dynamic range of most material. Even though the numerical value of such distortion is higher than that found in most power amplifiers, the uniform characteristic of this distortion and its continual reduction to very low values at low drive level will lead to an acceptably good listening characteristic for the A-100X from the standpoint of harmonic distortion.
Intermodulation distortion is shown in Fig. 9. This is the amount of distortion produced on a pure tone of 440 Hz when 41 Hz is simultaneously reproduced at equal drive level. The low frequency produces a rather large effect which infers that low frequency tones can produce distinct muddiness on higher frequencies when sound is played at high levels. At low power levels the intermodulation is almost pure amplitude modulation of 440 Hz by 41 Hz. As the level increases the characteristic of this distortion changes. At ten watts average, there is 6 percent peak-to-peak amplitude modulation and 5 degrees peak-to-peak phase modulation of 440 Hz, larger than I would prefer to see in a loudspeaker of this quality.
Crescendo handling capability for random sounds, such as hand claps and cymbal crashes, is quite good and the full power capability of the A-100X can be used on wide range material without difficulty. For the musical tones of middle C (262 Hz) and low G (98 Hz), the Audioanalyst A-100X was able to handle signal levels of random noise up to 105 volts peak to peak, corresponding to about 150 watts average, without masking inner musical voices.
The conclusion I would draw from these three measurements, harmonic, intermodulation, and crescendo handling, is that the Audioanalyst A-100A should give a brisk, reasonably clean level for most material, but will tend to go muddy if pushed too heavily with frequencies below 100 Hz, such as strong and deep organ pedal notes.
The energy-time response, which is the measure of energy spread in the reproduction of a perfect impulse, is shown in Fig. 10. The first peak in arrival, for the microphone placed exactly one-meter in front of the enclosure, comes from the tweeter at 3.02 milliseconds. The midrange drive contribution arrives at 3.1 milliseconds and is sufficiently close to the tweeter response to give a single peak in energy. The woofer contribution occurs at 3.3 milliseconds, with some longer term "grumbling" extending to 4 milliseconds, where the sound level is sufficiently low that diffractive scatter from enclosure boundaries are all that remain.
The impulse response is quite good, with some mild oscillatory ringing in the drivers, and the midrange and woofer energy scatter in the 3.5 to 4.25 millisecond time range would indicate that physical structure on the front of the enclosure is causing a small degradation of percussive response properties.
Fig. 8--Harmonic distortion for the tones E1 or 41 Hz, A2 or 110 Hz, and A4
or 440 Hz.
Fig. 9--Intermodulation of A4 or 440 Hz by E1 or 41 Hz mixed one-to-one.
Fig. 10--Energy-time response for axial one-meter microphone position.
Listening Test
In order to audition the A-100X, the speakers were placed near a wall and the height adjusted so the position of the tweeter was about one-meter above the floor level. This places the speaker at ear level for normal listening. The included angle between the speakers and the listening location was set to about 60 degrees for stereo.
The first impression I had was that the sound was bright, with a distinct upper register dominance. The rear-mounted switches were then set to LO for tweeter and LO for the midrange for most of the audition material, which are the maker's recommended positions.
My impression then was that was clean but thin, as though the woofers were being driven out of phase.
A momentary phase reversal test performed on one of the speakers convinced me that the drivers were properly phased. Serious listening to wide range material assured me that the bass was there, but was simply down in level for such a speaker placement. Moving the speaker down to the floor, to pick up an extra boundary, might help, as would placing the A-100X's in the corner of the room. But in my opinion this would not be as acoustically proper for this particular speaker as would simply lifting the bottom end with pre-amplifier equalization.
Piano music has good articulation, but tends toward a thin sound, with the octaves below middle C definitely requiring augmentation in the preamplifier to achieve balance. On orchestral music I found that I preferred to lift the midrange switch to HI position, keep the tweeter in its LO position, and pull the top end down slightly to avoid the bright sound on strings which some persons like, but which I find un natural. When I did this the stereo image was quite good, and in fact had a good sense of depth which is so often lacking on speakers in this price range.
The Audioanalyst A-100X can handle peaks on rock music at lease-breaking levels, but I could never quite get proper spectral balance. Choral music and single vocals were quite another thing and the A-100X did an excellent job of reproducing both.
This is a darn good machine for general listening, considering the low cost of the loudspeaker. Most listeners should appreciate the sound reproduction of the system, particularly with vocal selections, though there are obvious exceptions such as rock enthusiasts who will prefer a stylized sound for their specialized listening needs.
-Richard C. Heyser
(Audio magazine, Sept. 1976)
Also see:
Audioanalyst Model A-200 loudspeaker (Jan. 1974)
Celestion UL-10 Loudspeaker (Jan. 1977)
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