Aug. 26, 2015

Mixers and Equalizers, Part I

What distinguishes an organ, what separates its sound from all other musical instruments, is its incomparable range larger than a symphony orchestra, its tremendous scope of color and volume, its glorious fire in its mid and upper ranges, and its incredible, earth moving bass.  In pursuit of this sound, when adding external amplification to a self-contained electronic organ in a residence and it's been determined that factory organ speaker cabinets will not work in this application due to limited floor space, one solution would be to connect each divisional output jack in the back of the instrument to the input channels (blue input plugs in the photo, channels 1-6) of a power mixer.  If the instrument has, for example, 6 separate divisional outputs, then a minimum of 6 independent channel inputs on the front of the mixer will be needed.  Standard audio "gig" cables with 1/4-inch phone plugs on both ends are typically used to connect the ouputs from the console to the inputs of the mixer.

The mixer is used to amplify the signal, adjust the proportional volume of each channel, adjust certain frequency bands of each channel, add effects such as artificial reverb, and convert everything into one main stereo output signal.  Before that signal is sent to the main right and left stereo speaker cabinets it also helps to loop that output signal from the mixer by means of an output jack and plug with a split cable (small black plug in the photo) on the front of the mixer to the right and left balanced input jacks of a dual band graphic equalizer where further adjustment to certain frequency bands may be made. Standard RCA plugs are typically used for this.  For production of organ sound this equalizer should be equipped with at least 15 bands X 2.  The two balanced output jacks from the equalizer are then used to return the equalized signal back to the mixer by means of "power amp 1 in" and "power amp 2 in" jacks (small orange and gray input plugs in photo) on the front of the mixer.

Then, using the main output jacks from the back of the mixer, the equalized stereo output signal is then sent via standard 1/4-inch phone plugs on two separate lines to the largest subwoofer (which captures the most extreme low frequencies) and from there, by means of its "subwoofer out" jack on the back of the sub, to any other subs (if used) and on to the remainder of the external stereo speaker system.

For production of organ music the best results are obtained if the external speaker system receiving the main signal has a crossover network which breaks up the entire stereo signal range into several segments, sending only certain frequency widths to certain sized drivers.  It's also important to remember to keep the main output volume knob on the mixer turned to 0 db gain (12:00 o'clock), so that the external speaker system is never over driven (if distortion or bleedover is detected, this knob should be turned downward up to a maximum of around -10 dB gain to help prevent over driving of the speaker system.  WARNING:  Commercial right and left stereo speaker cabinets equipped with drivers designed for reproduction of sound should not be used for this purpose whenever their rated output is far less than the power output of the amp driving them.  For example, stereo speaker cabinets each rated at only 50 watts max should not be used with a 600 watt power mixer or damage to the drivers may result.  Using a 600 watt power mixer the stereo cabinets receiving the main channel output from the mixer should be rated at least at 150 watts apiece, 200 watts max, the volume knobs on the power mixer should always be kept at a low setting, and the original drivers should be removed and replaced with new, heavy duty drivers specially made for this purpose, i.e., for production of sound, in order to minimize the risk of damage.  It's best here to seek a professional audio technician for this type of renovation and to follow their guidance. 

Depending upon how the external stereo speaker system is configured, how many amps and speakers there are, and where they're positioned in the room, the results obtained this way can be much more realistic and makes full use of whatever limited floor space may be available for a practice instrument in a residence [See blog, Step Up Instruments, Part V].

(con't in Part II)