Sidebar 2: Measurements
The frequency response was measured in the listening window—spatially averaged to minimize room standing-wave problems—using a 13-octave warble-tone generator, which is said to be a little more analytical than the filtered pink-noise signal I have used in the past; in addition, the nearfield low-frequency response of each speaker was measured with a sinewave sweep to get an idea of the true bass extension relative to the level at 100Hz.
The most outstanding feature of the Rauna's spatially averaged room response (fig.1) was its flatness through the midrange: with the exception of a slight lack of energy in the 400Hz 1/3-octave band, ±0.6dB limits sufficed from 125Hz to 2.5kHz, a range of over four octaves! This is about the best I have ever measured in my present room. The treble had a slight excess of energy in the 4–6kHz region, perhaps due to the horn—it didn't sound resonant in this region—but then rolled off a little prematurely, being almost 8dB down at 20kHz. (Being an averaged room response, 0dB at 20kHz is not what is required, which would necessitate a rising on-axis response, but the Balder had too little energy in the top octave to sound flat on-axis.)
The in-room bass was a little uneven compared with other box loudspeakers of similar extension—I suspect the rear-facing port has something to do with this in my room—indicating that a position farther away from the rear wall would be a good thing. Unfortunately, they were already about as far out in the room as possible. (This aspect will vary according to the listening room in which the Balders are used.) Measured in the nearfield, the –6dB point for the woofers was a high 50Hz. This figure does not take into account the reinforcement of the low bass from the port, however, which was giving useful output down to 30Hz, suggesting that the loading is more akin to a reflex than a true transmission line.
This was reinforced by the modulus of impedance curve (fig.2), which has the characteristic double-hump in the bass of a reflex-loaded design. The port/line appears to be tuned to 35Hz. Apart from that, the impedance rarely falls below 8 ohms. The voltage sensitivity, measured with 1/3-octave pink noise centered on 1kHz, was a little below spec at 89.5dB, but this is still above average, suggesting that, in conjunction with the easy load, just about any amplifier will be able to drive the Balder to reasonably high levels without strain.—John Atkinson
Fig.1, Rauna Balder, spatially averaged 1/3-octave response in JA's room.
The treble response laterally off-axis was well-controlled, revealing the speaker to have wide, even dispersion. It is essential with the Balders not to have side walls near if the stereo imaging and midrange tonal balance are not to be compromised.
Fig.2, Rauna Balder, modulus of impedance in ohms vs frequency in Hz.
