The Sound of Surprise (the loudspeaker/stand interface) Page 5

This tied in with my auditioning of the AE1 on the various supports while setting the pair up for my review auditioning. With the Blu-Tack interface on the Celestion stand, the low frequencies were the tightest and the most tuneful, the lower midrange the most transparent.

Using no interface, the speaker just sitting on the stand, slightly lowered the amplitude of the main resonance but brought up the level of a number of others, the one at 344Hz in particular. That in the upper bass also shifted higher in frequency.

The situation was similar for the accelerometer measurements of the AE1's top panel. Again, all the interfaces increased the amplitude of the main mode at 484Hz, compared with the cones. Blu-Tack raised it the least, however. Fig.6 shows the waterfall plot for the AE1's top panel with the speaker supported on cones: note the 484Hz mode and the strong modes in the upper bass, all ringing until the 75ms edge of the plot. Fig.7 shows the effect of the AudioPrism feet in damping the upper-bass resonances.

Fig.6 Acoustic Energy AE1 top panel, Celestion Si stand, three German Acoustics brass cones, cumulative spectral-decay plot (8Hz-2kHz, 75ms time window).

Fig.7 Acoustic Energy AE1 top panel, Celestion Si stand, three AudioPrism Iso-Bearings, cumulative spectral-decay plot (8Hz-2kHz, 75ms time window).

Boom, chick!
Whereas the stand used was always the same in the Table 1 tests, Table 2 shows a more detailed analysis—using the resonant behavior of the ProAc's side panel—with a smaller set of interfaces but now with the three different stands. Again, the absolute and relative level of each resonant mode is noted.

Table 2: ProAc Response Two, side-panel resonant modes

InterfaceResonant mode amplitude in dB
Resonant mode Freq in Hz55164258305359586664758
German Acoustics Cones-19.1-12.4-15.0-4.2-18.2-17.4-16.0-14.2
Target Stand0.
German AcousticsCones-17.7-12.5-13.0-2.5-16.1-14.7-14.6-12.3
Celestion Stand+1.4-0.1
German Acoustics Cones-20.3-20.8-14.7-1.0-16.0-16.2-14.8-13.9
Wooden Stand-1.2-8.4+0.3+3.2+2.2+1.2+1.2+0.3
Blu-Tack pads-19.1-*-20.1-5.2-17.4-17.3-16.5-14.4
Target Stand0.0<-17*-5.1-1.0+1.2+0.1-0.5-0.2
Blu-Tack pads-20.5-22.3-15.2-1.5-14.6-15.3-15.5-12.6
Celestion Stand-1.4-9.9
Blu-Tack pads-19.6-*-14.6-1.9-16.1-15.9-14.3-13.4
Wooden Stand-0.5<-17*+0.4+2.3+2.1+1.5+1.7+0.8
½" urethane foam-18.1-*-17.7-4.9-18.3-17.2-15.4-14.6
Target Stand+1.0<-17*-2.7-0.7-0.1+0.2+0.6-0.4
½" urethane foam-20.4-21.4-15.7-2.1-16.9-17.3-15.9-14.1
Celestion Stand-1.3-9.0
AudioPrism Iso-Bearings-18.9-*-15.1-5.5-19.2-17.4-16.0-13.1
Target Stand+0.2<-17*
AudioPrism Iso-Bearings-18.0-22.8-15.6-1.1-15.0-14.4-15.4-11.9
Celestion Stand+1.1-10.4-0.6+3.1+3.2+3.0+0.6+2.3
Navcom sheet-19.6--16.1-3.9-17.6-17.4-16.4-14.6
Target Stand-0.5<-17*-1.1+0.3+0.80.0-0.4-0.4
Navcom sheet-21.2-17.6-15.3+0.1-14.2-16.3-16.1-14.4
Celestion Stand-2.1-5.2

* Resonant mode has been suppressed below the waterfall plot's -36dB floor