Handbook for Sound Engineers

1362 Chapter 35

35.2.1.2.2 Modeling by Means of a GLL Data File

While trying to solve the same problems, technically the
GLL concept^34 takes a different path compared to the
DLL philosophy. Based on the experience with many
loudspeaker manufacturing companies and the imple-
mentation of simulation and measurement software
packages, the generic loudspeaker library (GLL) was
developed as an object-oriented description language to
define the acoustic, mechanical, and electronic proper-
ties of loudspeaker systems, Table 35-1. Since for each
physical entity the GLL language has a representation in
the software domain, there is no need to make artificial
assumptions in order to comply with rigid, reduced data
structures. Basically, in the GLL philosophy every
sound radiating object should be modeled as such and
every interaction possible between engineer and loud-
speaker in the real world should be imaged in the soft-
ware domain. In this picture, transducers, filters,
cabinets, rigging structures and a whole array or cluster
are present in the GLL with their essential properties
and parameters, Fig. 35-25.

Typically, the GLL model of a loudspeaker consists
of one or multiple sound sources, each with its own
location, orientation, directivity, and sensitivity data.
These sources can be simple point sources but also
spatially extended sources, such as lines, pistons, etc. In
addition to that, a complex directivity balloon based on
high-resolution impulse response or complex frequency
response data on a spherical grid describes the radiation
behavior. With the sources representing the acoustic
outputs of the loudspeaker on the one hand, the builder
of a GLL defines the electronic inputs of the loud-
speaker on the other hand. A filter matrix provides the
logic to combine inputs and outputs, see the example in
Fig. 35-26.

It can include multiple sets of filters, including IIR
and FIR filters, crossover, and equalization filters. The
loudspeaker box is mechanically characterized by
means of a case drawing and data for center of mass

calculations. Boxes can be combined into arrays and

clusters. Available configurations are predetermined by

the loudspeaker manufacturer according to the functions

available to the end user. Additional mechanical

elements such as frames and connectors allow speci-

fying exactly which configuration possibilities exist.

Once all the data is assembled, the GLL is compiled

into a locked, distributable file, Fig. 35-27. In fact, the

end user of a compiled GLL can only see the loud-

speaker system as he would see it in the real world. The

user can apply filters to the electronic inputs of the

loudspeaker and he can calculate (= measure) the

acoustic output of the loudspeaker. He can look at the

loudspeaker case as well. When modeling arrays he

may change the arrangement of boxes as allowed by the

manufacturer.

It is obvious that the GLL format provides a natural,

straightforward way to describe loudspeaker systems.

By means of a GLL model any active and passive multi-

way loudspeakers, digitally controlled column loud-

speakers, line arrays, or loudspeaker clusters can be

accurately represented with regard to their acoustic,

electronic, and mechanical properties. Nonetheless the

GLL model will fail due to its very nature, when artifi-

cial algorithms are to be implemented that do not have a

counterpart in the real world.

35.2.1.3 Background of Simulation and Measurement

This section reviews simulation methods and measure-

ment requirements as well as their theoretical basis with

respect to both DLL and GLL modeling approaches.

Figure 35-25. Some elementary objects of the GLL descrip-
tion language.

GLL Box Type

Sources

Filter Groups

Input Configurations

GLL Line Array

Frames

Connectors

Limits

Box Types

Figure 35-26. Typical GLL input configurations and filters

for a two-way system.

Figure 35-27. Compilation to create a GLL.

Active System Passive System

HF XO

LF XO

HF XO

LF XO

HF

LF

HF

LF

GLL Project GLL File

Compilation

Creation in

Design Mode

Use in

Run Mode