DIYAPASON-L Digest #596 - Monday, July 8, 2002
 
Re: Tremulant Placement and windline
  by <TheGluePot@aol.com>
Re: Releathering stoppers
  by <TheGluePot@aol.com>
 

(back) Subject: Re: Tremulant Placement and windline From: <TheGluePot@aol.com> Date: Mon, 8 Jul 2002 14:23:06 EDT   I have posted on the Physics of tremulants in other lists and had articles=20 printed on the subject. To paraphrase and shorten the blather, the tremulan= t=20 is a tuned system. The regulator should be a spring type with pallets to=20 work best. It is tuned to the oscillation period of the trem rate. Since i= t=20 is a forced oscillation caused by the dumping of wind through the tremulant,= =20 it must be adjusted for the best response. Adding a great amount of weight=20 on the regulator is NOT a good way to make adjustments. The tremulant too=20 must be adjusted by use of the gates and weights on the moving tremulant top= =20 (for a book type tremulant). The internal air volume of the system is=20 another factor that is entered into the design. The air also acts as a=20 spring to form a standing wave in a properly operating tremulant system. =20 Elbows and other "organ legends" are of little use to make a system function= =20 properly when it is not all synchronized; and, flexible windlines can=20 sometimes keep any good tremulation from occurring by dampening out the=20 oscillation. Unfortunately there is limited room and graphics capability of= =20 list posting for the whole system design to be laid out here.   Suffice it to say that a tremulant system is like children skipping rope. =20 The child on one end represents the regulator, the rope represents the air=20 inside the system, and the other child represents the tremulant. Both=20 children on the ends must be at the same frequency for the rope to oscillate= =20 in a stabile periodic wave. If one child wants to go fast while one wants t= o=20 go slow, the rope responds by making odd meanderings with no large open=20 oscillation. Length of the rope affects the rate and the children must=20 adjust accordingly to get the large jump loop.   Al Sefl, Ph.D. If he tried jumping rope we'd have the next great California quake... Not to worry since he only uses his 20 foot jump rope for a belt... ;-)         =A9reserved - 2002 -      
(back) Subject: Re: Releathering stoppers From: <TheGluePot@aol.com> Date: Mon, 8 Jul 2002 14:27:14 EDT   Dear Bob:   Just a quick note to say that a good felt underlayment is what most organ technicians use on stoppers before the leather goes on. It will compress down nicely for a good fit yet allow the stopper to move without excessive =   force when tuning.   Good luck,   Al Sefl