Speakers and Tone Chambers


Most speakers deteriorate. The main elements are time, environment, and usage. Large diameter speakers designed to reproduce the lowest frequencies (woofers) usually have a cone suspension of foam, which disintegrates into a pile of gummy goo in the bottom of the box after about fifteen to twenty years. Many of the smaller full-range speakers have foam suspensions, too. The organ voices will have a faint "edge" at first, progressing into severe distortion and a "rattling noise". If this condition is not corrected, fried amplifiers will be the special of the day!

Also, an internal mechanism called the "spider" keeps the cone centered as it moves, and limits the cone excursions. The spider can break from wear, or by overdriving the speaker. A rattling noise will be heard, and sometimes the harmonics are transmitted into the midrange speakers, causing distortion in the normal playing range anytime a Pedal note is played.

James Baysinger, (left) and #3 son, Jonathan, after replacing 25 speakers on a 1975 Saville organ

Two photos of a thirty inch Electro-Voice subwoofer that was used in some 1980's models to reproduce the 32' Pedal stops. Two of my kids, Jonathan (left) and Jeremy (center), and their neighbor, Michael, posing in 1986. This one had just been rebuilt by Advanced Sound right here in Knoxville - one of only a handful that have training & actual experience rebuilding these monsters. The cone is heavy paper with another Styrofoam(tm) cone glued to the back for lightweight support. The area of this cone is equivalent to almost five 15" woofer cones, to give you an idea of the volume of air it can move.

Most speaker cones are made of paper. If a speaker cone gets wet or even damp, especially on one side, it can warp, causing the voice coil to be off center from the magnet it surrounds. Only a few thousandths of an inch separate the two. Eventually, the coil will rub against the magnet enough to wear through the insulation and short the coils of wire out, again blowing the amplifier.

In the fifties, sixties and seventies, many church organ manufacturers used various mechanical speaker systems to create a more realistic pipe organ sound. Silver oxide commutator brushes, mercury contacts, motors, rotating speakers (on horizontal and vertical axes), belts, pulleys, relays, and bearings are all tucked away in these speaker boxes. Regular maintenance is essential for proper operation and normal service life.

This Allen Gyrophonic Projector employs silver oxide brushes, commutator rings, pillow blocks, brass bushings, a motor, rubber grommets for vibration damping, a belt, and relays to control the rotation of the two speakers mounted on the round baffle. It also houses a powerful amplifier and high-voltage power supply.

The silver oxide brushes wear down after many years and lose contact with the commutator rings, causing the sound to sporadically cut out. The motor and bearings need oil periodically, and the belt will stretch, and eventually fray. The rubber grommets harden with age, transmitting motor noise into the wooden cabinet...and the beat goes on...

Custom Speaker and Tone Chamber Design

Sometimes it is necessary to change the speakers and/or chambers. Among the variety of possible situations is: relocation of speaker chambers, consolidating several individual speaker enclosures into one, installation of antiphonal speaker(s) in a constricted or uniquely-shaped area, and tuned exponential bass ports several yards long.

Organtek designs and installs custom sound systems, and modifies existing systems for sound enhancement. Examples of our work include tone chambers, grille covers, built-in tuned bass ports, trumpet-en-chamade exponential horns, and subwoofers. The frequency response and power requirements are balanced to room acoustics and volume, in the most aesthetic design possible.

 

 

Dr. Joe Clark of Maryland purchased this 1-owner Rodgers 820 from me, and employed my services to deliver, install, tune, and voice it to his living room. The five speaker units fit nicely in an unused closet (left photo).

 

For the best speaker rebuilding and repair, I use only Advanced Sound. Audiophile-quality - custom speakers - sales - installation - service - www.advancedsound.com, or email Bob Craton at speakerdoctor@icx.net.

Would you like to see what a difference new grille panels can make? Grille cover replacement - Beaver Creek Cumberland Presbyterian Church - Powell, TN.


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