Mission 707 Bookshelf speakers
In size and price, the Model 707 lies roughly in the middle of the Mission speaker line. It is a compact, two-way bookshelf system based on an 8-inch woofer operating in a ported enclosure. The woofer cone is plasticized, with a foam-plastic surround. At 2,200 Hz the system crosses over to a 3/4-inch-dome tweeter whose voice coil is damped and cooled by Ferrofluid in its magnetic gap.
The Mission 707 has a nominal impedance rating of 8 ohms and a relatively high rated sensitivity, 92-dB sound-pressure level (SPL) at 1 meter when driven by 1 watt. The speaker is recommended for use with amplifiers rated to deliver from 20 to 100 watts per channel. Its rated frequency response (under unspecified conditions) is from 50 to 20,000 Hz ± 3 dB.
The cabinet of the Mission 707 is 18-1/2 inches high, 9-7/8 inches wide, and 10-5/8 inches deep. Each system weighs 16 pounds. The cabinets are available finished either in walnut or in black. Removing the black cloth grille reveals an off-white front panel with a vertical alignment of the woofer at the top, the tweeter just below the center, and the bass port at the bottom. The front panel is actually made of plastic, about 1 inch thick, and is designed to be much more rigid than conventional chipboard panels. The insulated hinding-post connectors in the rear can accept stripped wire ends, lugs, and single or dual banana plugs. The Mission 707 is sold in pairs for $449 per pair.
Lab Tests
The averaged room response of the Mission 707 was very uniform over a large part of the audio range, from 1,000 to 20,000 Hz. While there were the usual irregularities caused by room resonances and multiple signal paths from the speakers to the microphone, the 3-dB overall variation of the smoothed curve through that range of more than four octaves was exemplary. For this measurement the speakers were mounted about 18 inches in front of the wall and 25 inches from the floor. The same placement produced very satisfactory listening results and was in general accordance with the manufacturer's suggested procedure.
The measured response between 130 and 1,100 Hz was also very smooth and flat, but it averaged 2 to 3 dB higher than the output at the higher frequencies. We measured the woofer response separately, with close microphone spacing, and the combined cone and port response (the effective acoustic crossover between the two was at about 90 Hz) was at maximum between 100 and 250 Hz, dropping off at higher frequencies to about -6 dB at 1,000 Hz and at lower frequencies to -6 dB at 45 Hz. There was some ambiguity in splicing the woofer response to the room response to form a composite response curve. Our final curve showed a ±4.5-dB variation between 35 and 20,000 Hz. The actual response of the Mission 707 in the bass and lower midrange (and, thus, its overall response flatness) is likely to be greatly affected by how the speakers are placed in a specific room and by the room's dimensions.
Quasi-anechoic response measurements with the IQS FFT analyzer showed an axial response (1 meter from the speaker) of ±5 dB from 180 to 20,000 Hz. Much of this variation was caused by a dip at 5,000 Hz that was apparently caused by unavoidable reflections from room boundaries (it did not show up in the room-response measurements).
Discounting this anomaly, the anechoic response was an impressive ±1.5 dB from 180 to 15,000 Hz. A comparison of the response measured on the speaker's axis with that 45 degrees off axis showed typical differences between the two curves of no more than 3 dB up to and beyond 10,000 Hz, and only about 10 dB at 20,000 Hz, confirming the excellent horizontal dispersion of the dome tweeter. The speaker's phase linearity was also very good; the group delay varied only ±0.2 millisecond over the tweeter's range, with occasional excursions to about 0.5 millisecond down to about 500 Hz.
The sensitivity of the Mission 707 was even higher than rated. An input of 2.83 volts of pink noise in an octave band centered at 1,000 Hz produced a 94-dB SPL at a 1-meter distance. The system's impedance curve had maxima of 25 to 35 ohms at 23, 95, and 1,500 Hz, minima of 7, 6, and 5 ohms at 55, 200, and 8,000 Hz, respectively. Given this performance, the impedance probably should have been rated as 6 ohms, but the manufacturer's 8-ohm figure is not unreasonable.
We measured the woofer distortion (separately at the cone and port) at frequencies from 100 Hz down to 30 Hz. The drive level was maintained at 1.8 volts, corresponding to our reference midrange-output SPL of 90 dB. The harmonic distortion was about 1.3 percent at 100 Hz, 2 percent at about 70 Hz, and a very respectable 8 percent at 30 Hz.
Finally, we drove the speaker using single-cycle sine-wave tone bursts, with duty cycles of 1 on and 128 off, to establish its short-term (dynamic) power-handling ability. By simultaneously viewing the amplifier's electrical-output waveform and the speaker's acoustic-output waveform on a calibrated oscilloscope, we determined how much voltage could be applied to the speaker before its output became distorted. In many cases the amplifier clipped before the speaker did.
We ran the tone-burst test at frequencies of 100, 1,000, and 10,000 Hz. For each measurement, the RMS voltage of the single-cycle input was squared and divided by the measured speaker impedance at that frequency to derive an equivalent power in watts. Since there are no accepted standards for this sort of measurement, we have developed our own somewhat arbitrary procedure. For example, we decided to use the measured impedance at each test frequency, instead of the speaker's nominal rated impedance, because we felt it was more realistic. In fact, however, the actual "dynamic" impedance of a speaker (the voltage divided by the current) during a short energy burst may be much lower than any steady-state value. In any event, the Mission 707 was able (somewhat to our surprise) to absorb the full output of the amplifier at the two higher frequencies. At 1,000 Hz the amplifier clipped at 477 watts, and at 10,000 Hz it clipped at 1,560 watts! Only at 100 Hz did the woofer cone reach its excursion limits, with audible distortion at 134 watts input.
Comments
The Mission 707 proved to be an exceptionally balanced and clean-sounding speaker. While its apparent bass was not as strong as our measurements might imply (remember, bass response is strongly affected by a speaker's acoustic environment), it was certainly not lacking in any substantive respect. The smoothness and wide range of the speaker's output was evident from first listening, and these qualities more than compensated for any real or imagined limitations in the lowest audible octaves.
The Model 707 is not only an exceptionally efficient small speaker, but it is one that can handle huge dynamic-power inputs without damage or serious distortion. This quality implies that it can be played quite loud-and, more important, that it can produce the high peak levels of CD's and the best LP's.
From its externals, there is little to show that the Mission 707 is more than "just another bookshelf speaker." It is light in weight, low in price, unpretentious in styling and finish (we thought our black-finished samples had a rather utilitarian appearance), and hardly unique in its specifications. However, a few minutes of listening (before making any measurements) left us with a strong impression that this speaker had been designed by someone with definite goals and the ability to realize them in practice. Although the Mission 707 is rather low priced by today's standards, it has the smoothness and balance of a far more expensive speaker. A lot of things have been done right in its creation, and the proof is in the listening.
