While the Gibbon 88 is nominally specified as an 8 ohm speaker, if you already haven’t I would strongly suggest trying them with the 4 ohm output taps of your amp. For a couple of reasons:
1)The 4 ohm tap will have a significantly lower output impedance than the 8 ohm tap, and I suspect that the Gibbon 88 has a significant impedance rise in the upper mid-range, in the vicinity of the crossover point between drivers. The interaction of high amplifier output impedance and that kind of speaker impedance characteristic will result in increased emphasis of that part of the spectrum.
2)The measurements section of Stereophile’s review of the DiaLogue Premium HP states that "... the lowest mid-frequency distortion was obtained when the 4 ohm tap was used to drive 8 ohms.... These graphs suggest that the 4 ohm tap is best used with loudspeakers whose impedance ranges from 4 to 16 ohms, as long as this tap can provide sufficient gain."
Also, if you already haven’t it might be worthwhile trying whichever output stage operating mode (triode or ultra-linear) that you haven’t been using.
Good luck. Regards,
-- Al
1)The 4 ohm tap will have a significantly lower output impedance than the 8 ohm tap, and I suspect that the Gibbon 88 has a significant impedance rise in the upper mid-range, in the vicinity of the crossover point between drivers. The interaction of high amplifier output impedance and that kind of speaker impedance characteristic will result in increased emphasis of that part of the spectrum.
2)The measurements section of Stereophile’s review of the DiaLogue Premium HP states that "... the lowest mid-frequency distortion was obtained when the 4 ohm tap was used to drive 8 ohms.... These graphs suggest that the 4 ohm tap is best used with loudspeakers whose impedance ranges from 4 to 16 ohms, as long as this tap can provide sufficient gain."
Also, if you already haven’t it might be worthwhile trying whichever output stage operating mode (triode or ultra-linear) that you haven’t been using.
Good luck. Regards,
-- Al