MANUFACTURER'S SPECIFICATIONS
Enclosure Type: Aperiodic suspension (highly damped vent).
Woofer: 10-in. (25.4 cm).
Tweeter: 1-in. (2.54 cm).
Impedance: 8-Ohms, nominal.
Power Handling: 50 Watts.
Size: 20-in. (50.8 cm) x 11 1/2-in. (29.2 cm) x 10-in. (25.4 cm).
Weight: 25 lbs. (11.34 kg).
Price: $109.00.
The Dynaco A-25XL loudspeaker system is a diminutive reproducer that can fit almost anywhere. Measuring 508 mm (20 in.) by 292 mm (11.5 in.) by 254 mm (10 in.), this walnut enclosure houses a 254 mm (10 in.) woofer and a 25 mm (1 in.) non-rigid dome tweeter. Although the speaker can be placed on any bookshelf (it weighs only 11 kg (25 lbs.), Dynaco provides wall brackets and screws for hanging the speaker directly on a wall.
The system is rated at 8 ohms and speaker connection is made to well-marked terminals in a recessed well on the rear of the enclosure. Also provided is a three-position, rotary tweeter level control with the center station marked Normal. Rotating the control adjusts the tweeter level a calibrated amount with clockwise rotation for increased tweeter output. A short but reasonably complete brochure accompanies each speak system so do-it-yourselfers should have no problems in hooking the system up.
Technical Measurements
The magnitude of terminal impedance measured for the three rear-mounted switch positions of Hi, Normal, and Low is shown in Fig. 1. The lowest impedance presented to a power amplifier occurs at near 7 kHz with the clockwise, or Hi switch position, and is approximately 5 ohms. This is a low enough value that I would recommend against connecting two A-25XLs in parallel if the Hi switch position is chosen.
The A-25XL is a vented cabinet with a high degree of acoustic damping in the vent. This gives the unusual looking low frequency tail on the bass resonance peak. The single bass resonance peak at 70 Hz is quite normal, as is the second resonance peak at 1200 Hz which is presumably due to the crossover network. But the subsidiary impedance peaks at 220 Hz and 560 Hz, and the dip at 7 kHz warrant some closer scrutiny.
Fig. 1-Magnitude of terminal impedance for three positions of the equalizer.
Fig. 2-Complex impedance for Normal equalizer position.
Fig. 10-Intermodulation distortion of A4 or 440 Hz by E1 or Hz mixed one to
one.
Fig. 11--Energy-time response.
The polar impedance plots for normal equalizer, and for clockwise, or high, control positions are shown in Figs. 2 [...]
Horizontal or vertical enclosure mounting is equally good, I found that I quickly preferred a mounting configuration with the long axis placed vertically.
My impression was of good spectral balance for stereo listening, but a mild polar fingering caused me to prefer rotating the enclosures slightly toward the listening area.
The A-25XLs are moderately efficient and can kick up quite a fuss with a reasonable amount of amplifier power.
However, I had the subjective impression that the sound was ever so slightly compressed, not distorted, but just a bit compressed on dynamic peaks.
The super low frequencies are absent, and in my opinion there was a slight midbass peak. But the top end is superb.
High frequency transients are reproduced very cleanly. After extended listening, I found that I preferred the treble control in the Low position for symphonic music, while some vocals gave a more accurate sound with the Normal, or occasionally, the High equalizer position.
The reproduction of piano music is moderately good but I felt that it was a bit bright and somewhat compressed on strong dynamics. The stereo imagery is good in lateralization, and there is reasonable depth to the image. Not perfect, but quite good for the price.
-Richard C. Heyser
(adapted from Audio magazine, Nov. 1976)
Also see:
Dynaco A-35 Loudspeaker System (Jun. 1973)
Design Acoustics D-12 speaker (Apr. 1973)
University "Project M" Speaker System (Apr. 1970)
Electro-Voice Interface:A speaker (Mar. 1976)
Dynaco AF-6 AM/FM Tuner (Equip. Profile, Sept. 1974)
Dynaco Stereo 70 Series II Tube Amp (Nov. 1992)
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