More Calibration

Nagging doubts still existed about the matching of the old and new sets of drivers. It all looked fine on the REW graphs but there was an asymmetry in the EP2500 channel settings. The older drivers were still not matching the newer ones below 20Hz. There was also a deep trough at the crossover point and above. More obviously needed to be done before I could be completely satisfied that I had plumbed the full potential of the 8 x 15".

The first thing which needed doing was to extend the boost to the old drivers to the full 120B/W on the BFD. The other settings, for the older drivers alone, remained at +16dB boost @ 20Hz. I ran some new sweeps and noted the old drivers response had lifted nicely to match the newer drivers around the 13.8Hz room induced peak. The graph hinged from this point to run just above the newer drivers.

By a combination of adjusting the level controls on the EP2500 and fine tuning with BFD filters I was finally able to match the response levels of both sets across a wide frequency band. This still left the combined response overpowering the speakers. Now that the asymmetry was gone on the power amp control knobs so I could safely reduce the combined levels to better match the speakers. This occurred at 20 on the EP2500 control scales. At the 26 setting I had the IB good and hot for action films. Now I no longer needed to remember the differential between the control knobs. Then I added some gentle boost filters around 90Hz to try and fill the crossover trough. This required further filter adjustment on each driver channel to keep the combined response from humping at 100hz.

Note the closer matching between the two sets of drivers over a much wider power band than before:

The film setting runs rather hot compared with the main speakers:

And the graph showing both the film and music settings including the greater subwoofer output for film watching. The (third from the bottom) blue line arrowed is the music response curve. The two lower curves are each driver set alone. The smaller difference in level for music does not rob the music of bass. Far from it. Though there is considerable variation in bass levels between different CDs I can now adjust bass levels far more easily.

There is still room for improvements. A house curve would be nice to overcome the natural roll-off of my rapidly ageing ears. it started with target shooting in the ATC at school without ear protection. Then weekly rock concerts at a local dance hall in the SPL unlimited 60s and regular attendance at motorsports have all damaged my HF hearing beyond repair. Many a week passed with tinnitus in my youth and, more irritatingly, much later.

Ear syringing can return me a few more kHz but the procedure is not completely without risk. All of this this does not mean I cannot judge the SQ of my system. I seem to be just as sensitive to bright speakers at the dealers and AV shows as I ever was. I can still hear very nasty resonances in very expensive, electrostatic, panel speakers despite the protestations of their owners on the more upmarket forums. :-)

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