Specifications

(4) Flying the APL-10/12

For many applications, the APL-10/12 subwoofer may need to be flown. This

commonly occurs with television award shows, political conventions, and

other events where the audience is located too close to the stage to allow

the subwoofers to be placed in the typical side or front-of-stage position.

APL-10/12 speakers perform perfectly well when flown; in fact, the sound

quality is often perceived as being superior when the speakers are in the air

as opposed to on the ground. This is usually because they integrate better

with the flown full-range speakers when they are in close proximity to them,

although it can also be because of the acoustical characteristics of a given

room, or a combination of both. However, be aware that the same number

of units that performed satisfactorily on the ground or in a corner will have

to be doubled or tripled to achieve the same power output level when they

are flown.

The APL-10 and -12 are equipped with four rigging points – two on the top

and bottom of the APL-10 – and two on either side for the APL-12. These

points are supplied with either Apogee nutplates or Aeroquip pan-fittings, as

specified at purchase (fitting types can be changed easily in the field to accom-

modate changing requirements). If the rigging fittings are to be changed, always

use the screws that are supplied from the factory – never use generic screws

purchased at a hardware store because they are unsafe for this application!

Nutplates are circular steel plates with a welded 3/8-16 threaded fastener in

the center, designed to accept 3/8-16 threaded bolts (also available in Metric

M-10 version). Each nutplate can sustain a straight-line-of-force load of 2500

lb. (1136 kg) before failure. An APL-12 weighs 214 lb. (97 kg), so if only two

nutplates are used to suspend the speaker, the safety factor is 23:1 (NOTE:

OSHA requires a 5:1 safety factor, whereas most theatrical rigging shops have

voluntarily adopted a 7:1 safety factor.).

It is vitally important that all hardware used to suspend the APL-10/12 be of

the highest grade materials and construction. All bolts must be SAE Grade 7

or better. The American bolt-grade rating system is often depicted by a num-

ber of linear hash marks on the head of the bolt – five marks mean Grade 7,

six marks mean Grade 8.

If eyebolts are used, they must be forged and of the shoulder-type. Eyebolts

are designed for a straight-line-of-force. They de-rate rapidly and become

unsafe as the load angle deviates from the 0 degree axis (in line with the

length of the threaded bolt).

All bolts must be tightened securely, but not over-tightened (5-7 ft. lb. of

torque is generally sufficient for 3/8" bolts). Over-tightening can cause much

of the tensile strength of the bolt to be used up, before any external load is

placed on it. An exception to this rule is when the bolt is used in sheer, such

as when rigging plates are attached to the side of a speaker. In sheer, the fric-

tion provided by tightening and preloading the bolt actually increases the

strength of the joint and decreases cyclic failure of the fastener.