Totem Acoustic Forest loudspeaker 2005 Measurements

Sidebar: 2005 Measurements

The Totem Forest's sensitivity is low, at an estimated 86dB(B)/2.83V/m, but its impedance graph (fig.1) reveals it to be an easy load for the partnering amplifier, dropping below 8 ohms only in the lower midrange, and then to 7.2 ohms. In the measurements sidebar that accompanied LG's 2001 review, I mentioned the presence of various high-Q cabinet resonances; these affect the impedance plots by producing small glitches in the midrange, at 270Hz, 520Hz, and 700Hz. Fig.2, a waterfall plot calculated from the output of a plastic-tape accelerometer fastened to the Forest's front baffle below the woofer, clearly reveals the presence of these resonances, as well as some pumping of the cabinet wall at the port tuning frequency, though these are all quite low in level. Adding the sand and lead shot to the cabinet's lower chamber reduced the amplitude of the two lower resonant modes, but not the one at 700Hz, suggesting that it is actually an air-space mode.

Fig.1 Totem Forest, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

Fig.2 Totem Forest, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the front baffle beneath the woofer. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

The quasi-anechoic response of the 2005 sample, serial number FC3320 (fig.3, red trace), is very similar to that of the 2001 sample, serial number MI-195B (fig.3, blue). The bass is flat down to 45Hz and the mid-treble is shelved up by a couple of dB. The metal-dome tweeter's ultrasonic diaphragm resonance lies at a high 26.5kHz, but produces a 20dB-high peak at that frequency. As I wrote in 2001, this resonance is too high to be heard and will not be excited by restricted-bandwidth CDs. But it will ring with SACDs and DVD-As having content at that frequency, as well as with LPs played back with an MC cartridge. In these cases it might have an unpredictable effect on sound quality. It is fair to note, however, that I didn't hear any problems with hi-rez digital media.

Fig.3 Totem Forest, anechoic response on-axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer and port responses plotted below 300Hz: 2001 sample (blue), 2005 sample (red).

Fig.4 shows the spatially averaged 1/3-octave response produced by the pair of Forests in my listening room. It correlates nicely with my listening impressions: extended low frequencies coupled with a slightly excessive mid-treble, but otherwise impressively flat overall.—John Atkinson

Fig.4 Totem Forest, 1/3-octave, spatially averaged response in JA's listening room.

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