GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: “Why horns”, years later.

Post Subject: Power-to-weightPosted by jessie.dazzle on: 10/1/2010

Romy wrote:

"...a chassis designer told me. It is now possible to buy normal efficiency drivers with low mechanical loss..."

Sure it might exist, but I question the application.

First, a bit of the obvious:

Consider only the driver; not the amps and related gear.

What is necessary to make a high-efficiency driver?

There is only one answer; a high power-to-weight ratio; i.e., a strong motor as compared to the weigh of the parts it must move.

If drivers now exist offering "low mechanical loss", but are still of average efficiency, then logically they have an average power-to-weight ratio; meaning one of the following:

      1) Weak motors with light-weight moving mass
      2) Strong motors with heavy moving mass

Both would result in what we might call "average performance".

One might argue that N° 1 (low moving mass with a weak motor) is better, but if the motor is weak, the mass won't move.

Mother nature cannot be cheated.

To understand why a good Power-to-weight ratio is desirable, consider the following automotive analogy (for some, this too will be obvious):

Think of the wheel of a large truck rolling on a cobblestone street at 50 mph. Because it is heavy, the wheel will follow the major (large-scale) variations in the road surface, but will bridge across or average out the minor variations. Also, having greater inertia, this wheel will tend to continue reciprocating against the vehicles suspension, which because of this, will have to incorporate more substantial damping; thus further impairing the wheel's ability to "react" and accurately follow the surface of the road. Heavy wheels tend to "write" their own road. The vehicle itself must also be heavy, or it will simply not offer a stable reference point against which such a suspension can work, in which case the entire assembly would shake to pieces whatever it might be carrying (occupants or freight). This in turn implies stiffer springs, further impairing the wheel's ability to "react".

Why is it desirable that a wheel remain in constant contact with the surface of the road? Because it will at some point be necessary to slow (apply the brakes), accelerate, or alter the course of the vehicle in motion, all of which require that the wheel remain in contact with the road.

Now think of a wheel on a normal passenger car, which by comparison is light-weight; this wheel will follow the finer irregularities, and because it has far less inertia, will not require excessively stiff springs or overly firm dampers.

To bring this back to drivers:

The irregularities in the road are analogous to detail in sound.
Wheel mass is analogous to the moving mass of a driver.
Vehicle weight is analogous to mass and robustness of driver enclosure and driver chassis.

Horn-loading:

If high-efficiency drivers are desirable, horn-loading takes it all one step further. Horn-loading is literally a series of physical levers wich allow getting work done via reduced effort. Translation: Low-excursion, small-diameter diaphragms; two things that contribute significantly to low moving mass. Getting the same work done via direct radiators is possible, but it requires working the lever from the other end; either by increased effort (excursion), which unfortunately automatically implies much higher piston speeds and the consequent need for greater damping, and loss of detail, or by breaking the work down via increased surface (greatly multiplying diaphragm area; i.e., multiple drivers), which unfortunately means multiple point sources.

To bing it back to automobiles:

A horn-loaded driver is analogous to a small-displacement automotive motor coupled to a multi-ratio gearbox, wich is in turn coupled to the driving wheels.

A direct radiator is analogous to an internal combustion automotive motor, having its crankshaft directly coupled to the axle of the driving wheels. A vehicle of this sort using a small-displacement motor would have dismal performance. If good performance is the objective (good acceleration and good top speed without a gearbox), the vehicle would have to work the lever from the other end, by using either a very large motor (inefficient and heavy), or by assigning the work to multiple, small-displacement motors (very large and expensive vehicle).

In automotive applications, electric motors, having constant torque regardless of rpm, are able to directly drive the wheels while offering good (even blistering) acceleration and top speed, but the acceleration comes at the expense of energy debit, which in the case of an automobile translates as reduced range. Most still do use a gearbox of some sort.

jd*

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