Rauna Balder loudspeaker Measurements

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.)

688Raunafig1

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.

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

688Raunafig2

Fig.2, Rauna Balder, modulus of impedance in ohms vs frequency in Hz.

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COMMENTS
Timbo in Oz's picture

Hi John, As you may recall I own 3 pairs of Audiosphere speakers. They are cast in two halves and glued together in off-white concrete. They do have a small amounnt of diffraction as the circular front baffle meets the spherical enclosures. But they do manage to disappear as sources when you close eyes.

One pair of the 'sort-of phase-linear' model 2s that use a Coral Flat 5 WR 5" driver with the paper dustcap being a continuation of the pressed paper cone. ? They're a little less edgy than those with a shiny metal dustcap.

And, two pairs of the Model 3s which use a 35MM Foster dome which gets a notch for an impedance peak, and a 3rd oder HP @ a bit abobve 3.3Khz. The mid-bass are Foster/x FW202s which die off naturally to match in. I call the 'sphere 2s poor man's QUAD 57s, and the 3s are poor-man's 63s. But they go deeper, being able to do 32 Hz Pedal reeds in-room and adjusted as per Allison's unequal distances/ratios idea. 1 to floor, X 1.5 to one wall and 2.25 to the other near wall.

I've sold QUAD 57s in an audio shop, and own a pair of 63s. They really do need subs, but integrated and eq'd well (after optimal positioning.) I'll be going with a Duke leJeune Swarm, with two of the subs getting down to 2O Hz or lower.

As a fan of Tony Faulkiners coherent recordings, the spheres are worth having. Especially the 2-ways. Which are not a disappointment against 63s with subs, exceot for big pipe organs.

You may recall that I'm an ex Cathedral Chorister via the RSCMusic (a leader in *the 1sts). Soooo, and I realise I've never asked you!? But can your stand excess vibrato and shrillness from female singers? I just can't!

;-)

Tim Bailey

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