M&K Bookshelf-75 Speaker System Review

Miller & Kreisel Sound Corporation (M&K) has a well-established reputation as a manufacturer of high-quality loudspeakers for serious audiophiles. Like the high-fidelity industry as a whole, the M&K product line has expanded considerably in recent years to meet the demands of the growing home-theater market.

Traditionally, most M&K speakers have been priced well above the range of more popular, broader-market audio components. However, the rapid growth of home theater has spurred the development of affordable, high-quality components for that application, such as the Bookshelf-75.

The Bookshelf-75 is a two-way speaker that can be used for either the left/right front or surround channels in a music or home-theater installation. The companion Center-75 speaker is designed to be acoustically compatible with the Bookshelf-75 in a home-theater setting, as are several of M&K’s powered subwoofers.

As its name suggests, the Book-shelf-75 is a compact speaker. It has a nominal 6 Vi-inch woofer (actual effective diameter is 5 inches) and a 1-inch soft-dome tweeter, the same that is used in M&K’s more expensive speakers. There is a port on the speaker’s front panel, but it comes blocked by a removable plastic-foam plug.

With the plug left in place, the Bookshelf-75 effectively operates as a sealed (nonvented) system, and M&K says that in this mode the speaker will deliver the best transient response, tightest mid-bass, and flattest overall frequency response. It is the recommended operating mode for systems that include a subwoofer. When the plug is removed, the speaker operates as a vented system, adding about 2 dB more output in the range around 80 Hz. This mode is suggested for systems without a subwoofer. Nevertheless, the manual suggests experimenting with the plug, which can be removed or inserted as often as desired, to obtain the best overall sound.

To insure compatibility with home-theater video components, the Book-shelf-75 is magnetically shielded. Additional installation flexibility is provided by a threaded insert on the back of the cabinet that can be used with an optional OmniMount 53-RST bracket ($80 a pair) for mounting the speakers on a wall or on M&K LDM series stands ($250 a pair).

The cabinet exterior, including the front panel, is finished in black ash woodgrain vinyl. The curved black metal grille is easily unsnapped for access to the drivers or the removable vent plug. Despite the speaker’s relatively light weight, our knuckle-rap test suggested that its construction is exceptionally rigid.

The Bookshelf-75 has a rated impedance of 4 ohms and is recommended for use with amplifiers rated between 50 and 200 watts output. Although the sensitivity rating was not stated in the otherwise comprehensive installation and operation manual, we measured the sensitivity as 89 dB sound-pressure level at 1 meter, a typical figure for this category of speaker.

We measured the impedance with the vent plug both inserted and removed. With the plug in place, the maximum impedance was just over 13 ohms at 75 Hz, reaching the rated minimum of 4 ohms between 150 and 300 Hz and returning to the vicinity of 5 or 6 ohms at the lowest audio frequencies. The impedance rose at higher frequencies into the range of 7.5 to 9 ohms between 1.5 and 20 kHz. This combination of moderate impedance characteristics and good sensitivity indicates that the Bookshelf-75 can easily be driven by any properly functioning amplifier.

With the plug removed, the most significant impedance change was the characteristic double-humped curve of a vented speaker, with the single bass resonance replaced by two peaks, 16.5 ohms at 28 Hz and 13 ohms at about 100 Hz. The rest of the impedance curve was unaffected.

The corresponding acoustic effects were equally distinct, though perhaps not as obvious as the impedance changes. With the plug inserted, the close-miked woofer response was ±3 dB between 55 Hz and 200 Hz. Removing the plug slightly increased the output below 100 Hz, which confirmed the manufacturer’s statement that the principal effect of the vent is to add a couple of decibels of output in the mid-bass region around 80 Hz.

When the system is used with a subwoofer, however, the manufacturer strongly urges that the Bookshelf-75’s plug be left in to provide the smoothest transition between the bass and middle frequencies, and our measurements confirmed that, too. The averaged room response of the left and right speakers, with their vent plugs in, was very smooth, with a +2-dB variation over the range of 100 Hz to 15 kHz, although the typical response above 2 kHz was 2 or 3 dB less than at lower frequencies. The room response dropped about 15 dB between 10 and 20 kHz, presumably because of absorption by the room surfaces and furnishings (that effect is typical for this measurement).

The horizontal dispersion was also typical of systems using 1-inch tweeters, with less than 2.5 dB total variation in output up to 8 kHz over a +45-degree horizontal arc. Above 8 kHz the on-axis response increased by 4 dB up to 20 kHz, while the off-axis response fell off steeply above 10 kHz, to about -15 dB. It is important to note that this behavior is quite typical of virtually every conventional (forward-facing) speaker we have tested, even though the response deviations might seem large compared with, say, typical amplifier measurements.

Our MLS quasi-anechoic frequency-response measurement, which minimizes the effect of room boundaries, was made at distances of 1, 2, and 3 meters on the forward axis of the speaker. These tests showed an overall response variation of less than +4 dB from the lower measurement limit (300 Hz) up to 20 kHz.

These and other measurements can serve to verify the qualities of a speaker, but it is surprisingly difficult to evaluate the sound of a speaker from any (or all) measurements. As always, the ultimate proof is in the listening. Although there is little in its appearance, size, price, or driver complement to distinguish the Bookshelf-75 from a number of comparable systems we have used and tested, like every other speaker it has a character of its own, which can only be appreciated by listening to it. What I can tell you, without hesitation, is that this M&K speaker fully lived up to its pedigree. Not often do we encounter an unassuming and affordable product whose performance belies its price and modest exterior as unequivocally as this one.

It became obvious after only a short period of listening that the speaker’s components (specifically, its drivers and crossover) were thoroughly optimized in the development process. With most program material whose low-frequency content was above 50 Hz or so, the Bookshelf-75 held its own against far costlier speaker systems we had on hand for comparison.

In a marketplace presently blessed with a number of excellent small speakers, don’t be misled by the plain Jane appearance of the M&K Bookshelf-75. If you’re shopping for speakers in the under-$500 range, be sure to consider a pair of Bookshelf-75's.

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