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Aug. 25, 2015
(con't from Part I)
Compared to the sound of real organ pipes, electronic organ stops playing through speaker cones (drivers), while some are quite fine in effect, just do not match up. This is due in part to the effects such drivers can have on frequency ranges in relation to the higher harmonics (overtones) of organ stops and their contribution to organ tone. Cones which cause slight disturbances of reproduction in the region of those same higher harmonics, where certain frequencies are subdued or taken out altogether, greatly affect whether an organ voice going through that driver sounds something like the real thing or whether it sounds plastic and flat.
While the subject remains controversial, it's been reported that experimentation with cone drivers and a frequency analyzer shows that reproduction of frequencies in 1kHz-2kHz range can be compromised, and that boosting these bandwidths using a graphic equalizer gives an interesting sound, without which it sounds lifeless. Other experiments are reported to refute this claim. The fact remains however that any graphic equalizer looped into a power mixer and external speaker system of an electronic organ has to have its bandwidths adjusted in a way that not only brings out the best in the incoming signal stream but also keeps a happy household among all the speakers in use to where they can deliver to the ear all that they were designed to do [See blog, Mixers and Equalizers, Part I].
This can pose an issue however when speaker pipes are used [See blog, Conn Speaker Pipes]. Since these are strictly treble units designed to work from 200Hz on up, boosting bandwidths in this range will swamp the subtle harmonic and pneumatic effects the speaker pipes are designed to contribute to the overall sound. At the same time certain frequency bands in the signal stream always work best when they receive equalization. This can be done at the power mixer using built-in equalizers for main and monitor channels [photo] with more precise adjustments being possible with the addition of a separate 31-band graphic equalizer. Bandwidths in the 20Hz range can be given a +12 decibel (dB) maximum boost and perhaps a +3dB boost @ 31.5Hz. If speaker pipes also are receiving manual signal, and the goal is to use them to full audio advantage, then it's advisable to keep frequencies in the 40Hz-630Hz bandwidths flat and begin to introduce negative boost of -3dB @ 800Hz and -6dB @ 1kHz. In such a scenario a maximum negative boost of -12dB is advisable for all other higher bandwidths up to and including 16kHz, possibly backed off to -6dB @ 20kHz, if desired. The idea would be to provide full boost for the very lowest bandwidths arriving at the subwoofers, keep the lower midrange flat, and gradually taper off the highest treble frequencies in strength starting at around 800Hz. Midrange fundamental frequencies from 200Hz on up arriving at the speaker pipes will then find their own pipes and cause them to resonate in a way that the listener can actually pick up their effects with the ear.
Many ways to configure these settings might present themselves, every situation is different, and the ear has to be the final judge, but this overall approach has been tested using the ear with all types of organ music on a large electronic organ supplied with speaker pipes and is very solid. When speaker pipes are not used it's advisable to give those frequencies between 1kHz and 2kHz special attention with the idea of boosting them to some extent, if needed, to improve the sound.