Integrated Amplifiers

Harman Kardon HK 990 Stereo Integrated Amplifier with Digital Room Correction and Dual Subwoofer Bass Management – Part I


Deep Dive to Examine the EQ 2 Setting

Figures 7 – 19 explore the problem with the EQ 2 setting. I am going to spend some time with this issue even though Harman says they can correct it with the software fix because I have seen it in other room EQs that offer the option to limit the frequency of correction.

Figure 7 is set up like Figure 2. Again, the Infinity C336 is used, but in a different position. Now the EQ 2 curve (red) does not match the uncorrected curve (black) above 2 kHz. Instead, the entire curve shifts down 2 dB. Looking at the electrical correction curve makes it clear why this happened: the red curve of the electrical correction plot has not returned to the black curve (0 dB insertion), but stays 2 dB down.

Figure 8 shows the electrical correction curve alone with more annotation on the problem.

Figure 9 refers to a competitive high-quality speaker, which I call P. I am not identifying it because the single shoot measurement at one-third octave smoothing belies the speaker's true performance. It is in position 3 in the larger test room. Now the red curve in the acoustic measurement (EQ2) above 2 kHz is above the black curve by about 1 dB. The speaker brightens with this offset above 2 kHz and is clearly less flat with EQ applied. Again, the electrical correction curve shows the problem: above 2 kHz it is 1 dB above the 0 dB insertion curve (black).

Figure 10 illustrates the electrical correction curve alone with more annotations.

Figure 8 had signal attenuation above 2 kHz, but on Figure 10 for the different speaker in another part of the room, there is lift. Figure 2 illustrated the unit's proper operation with no loss or gain above 2 kHz. The electrical correction curve for this case is repeated in Figure 11.

Figures 11 – 15 reveal why the EQ2 curve above about 2 kHz (it slightly different for each speaker-room combination) is not always at the 0 dB reference level. These electrical correction curves involve three different speakers in two rooms with multiple placements. The EQ2 curve above about 2 kHz takes on the amplitude of the correction curve at about 2 kHz. This is about flat for the graph in Figure 11, so the red curve remains at the 0 dB line.

In Figure 12, note the electrical correction curve which is up more than 3 dB at 2 kHz and the EQ2 curve remains 3 dB hot above 2 kHz.

Figure 13 highlights a 1.5 dB shift above unity gain. The level of the correction curve is matched at 1.2 kHz. The respective lifts of Figures 12 and 13 brighten the speaker.

Figures 14 and 15 are electrical correction curves where the correction curve is below unity gain at 2 kHz. The EQ2 curve above 2 kHz now shows a loss of about 3 dB for both cases. The cut in gain in Figures 12 and 13 dulls the speaker.