Dayton Audio B652 loudspeaker Measurements
Sidebar 3: Measurements
The $39.80/pair B652 is by far the least expensive loudspeaker ever to be reviewed in Stereophile. I examined its performance with DRA Labs' MLSSA system, using a calibrated DPA 4006 microphone to measure the speaker's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield responses. The B652's voltage sensitivity is specified as 87dB; my estimate was a little higher, at 88.4dB(B)/2.83V/m. The Dayton's nominal impedance is 8 ohms, which my measurement confirmed. Fig.1 shows that the impedance remains between 4 and 8 ohms throughout almost all of the audioband, rising to 12 ohms at the woofer's sealed-box tuning frequency and to 9 ohms in the mid-treble.
There are small discontinuities in the impedance traces between 200 and 300Hz and between 600 and 1200Hz. These indicate the presence of some kind of resonances in these regions. The enclosure was very lively when tested with the traditional knuckle-rap test; examining the vibrational behavior of the panels revealed very strong resonances at 273, 344, and 488Hz (fig.2). I detected no resonance at higher frequencies, however.
The 6.5" polypropylene-cone "woofer" is tuned to just over 100Hz. Most of the response rise in this region in fig.3 will be due to the nearfield measurement technique, but the B652's low-frequency alignment does appear to be a little underdamped. The farfield response on the tweeter axis rises throughout the midrange, with then a somewhat peaky output throughout the treble. (I removed the grille for the measurements; leaving it in place had surprisingly little effect on the B652's behavior, other than filling in a little the response dip at 2kHz.) This peakiness leads to the higher-than-specified sensitivity, but whether or not it is heard as brightness will depend on the speaker's dispersion.
Fig.4 shows the B652's lateral dispersion, referenced to the tweeter-axis response. The speaker is quite directional between 2 and 7kHz, which will work against the on-axis peakiness in the same region, though the use of a small-diameter (5/8") tweeter results in a wider-than-usual radiation pattern in the top octave. In the vertical plane (fig.5), a suckout at the crossover frequency develops immediately above the tweeter axis. Tall stands will work better than short stands with this speaker, especially as the mid-treble output drops a little just below the tweeter axis, which will work against the tendency to brightness.
Turning to the time domain, the B652's step response on the tweeter axis (fig.6) indicates that both drive-units are connected in positive acoustic polarity, the decay of the tweeter step blending smoothly with the start of the woofer step. This blending suggests optimal crossover design. The cumulative spectral-decay plot on the tweeter axis (fig.7) shows a surprisingly clean decay over much of the audioband, but with strong ridges of delayed energy at 1.4kHz (the frequency of one of the wrinkles in the impedance graph) and 4.8kHz. The former will add hardness to the B652's balance, the latter a somewhat steely character.
While the Dayton B652 has some severe measured problems, it actually performed much better on the test bench than I was expecting, given its price. When you consider that the build budget of a speaker selling for less than $40/pair will be no more than $8 for both speakers, assuming the usual 5:1 ratio of retail price to parts cost, the B652's measured performance is actually quite remarkableand certainly better than the plastic squawkboxes sold for use with computers.John Atkinson