Loudspeakers and their specifications

Loudspeaker types

Loudspeakers (including sound transducers) convert electrical audio signals into sound waves. They are designed for both general and specific applications, and therefore have different executions. Loudspeakers for voice alarm systems according to TS 54-24 must be certified according to the EN 54-24 product standard.

Broadband loudspeakers

A loudspeaker that can reproduce at least the main portion of the audible range and therefore also a large frequency range (250 Hz to 6 kHz or higher).

Multiway loudspeakers

Two or more loudspeakers are combined. Each individual loudspeaker is designed for a specific frequency range. The result is that a larger frequency range is covered. Depending on the number of combined frequency ranges, these loudspeakers are referred to as 2-way loudspeakers, 3-way loudspeakers, etc.

Enclosure types

Using a closed loudspeaker box is not problematic. The loudspeaker diaphragm is protected against extreme movements by the back-pressure of the air in the enclosure. A bass reflex loudspeaker can reproduce low frequencies somewhat louder than the closed loudspeaker can. Using a high-pass filter is recommended. Such a filter is installed at the lower end of the loudspeaker’s stated frequency response. This protects the loudspeaker diaphragm against excessive movement at very low frequencies, which can damage the loudspeaker. Some loudspeakers, such as ceiling-mounted loudspeakers, do not have an enclosure. A loudspeaker of this type is designed in such a way that the movement of the diaphragm is restricted in order to protect the loudspeaker against damage.
 

• Closed loudspeakers
• Bass reflex loudspeakers
• Open loudspeakers

Horn loudspeakers

A horn loudspeaker consists of a driver that converts audio signals into acoustic waves, and a horn that focuses and amplifies the sound waves. Horn loudspeakers are highly efficient and can achieve very high characteristic sound pressure levels.

Line array loudspeakers

Line array loudspeakers operate as what is referred to as a line source. The drop-off in the characteristic sound pressure level as a function of distance is less than is the case with ordinary loudspeakers. Line array systems generally have a wide horizontal coverage angle, and a narrow vertical coverage angle. When oriented properly with respect to the audience, only a small portion of the sound will strike reflecting walls and ceilings, meaning that the system generates little reverberation. Line array systems are therefore ideal for reverberant environments.

Rated power

The rated power, measured in watts, indicates the electrical power that the loudspeaker is able to draw in continuous operation without distortions and without being damaged. The signals that typically require processing cause the instantaneous power to fluctuate significantly at times. This is why for low-impedance loudspeakers (without transformers, 4, 8 or 16 ohms) we state a programmatic rating, which should be understood as the recommended power output of the driving amplifier. As a result, amplifiers can accurately reproduce transient signal peaks without damaging the loudspeaker. However, if you need to reproduce sounds at constant amplitude and high power (e.g. alarms), the rated output of the amplifiers in low-impedance systems should not be greater than that of the loudspeaker.

Power tapping

100-volt loudspeakers often allow for the power to be adjusted to values lower than the rated power (tapping). It is frequently possible to tap the power to one-half, one-quarter or one-eighth of the rated power (corresponding to -3, -6 and -9 dB). This is always specified in the technical loudspeaker data. This makes it possible to adapt the volume of the loudspeakers to their surroundings when installing the loudspeakers. In this case, 100-volt loudspeakers draw the power to which they have been adjusted from an amplifier. This makes it possible to connect 100-volt loudspeakers to a 100-volt amplifier until the sum of the powers to which they have been adjusted equals the rated power of the amplifier.

Impedance

The impedance is the AC resistance of the loudspeaker. There are two different kinds of impedance systems: low-impedance and high-impedance loudspeakers. Low-impedance loudspeakers have impedance ratings of 4, 8 and 16 ohms typically. In high-impedance loudspeakers, the impedance depends on the rated input and may vary between a few tens of ohms and a few thousands of ohms.

Sensitivity

The characteristic sound pressure level of a loudspeaker is stated in dB, measured at one watt of supplied power at a distance of one metre and is called sensitivity. No uniform notation has been defined, but the general convention is something like 96 dB (1 W/1 m). Unless otherwise stated, TOA uses the average and not the maximum characteristic sound pressure level.

Frequency range

The transmission range (also referred to as the frequency range or frequency response) is the range that the loudspeaker can reproduce. This information may be provided in writing (e.g. 50 Hz - 20 kHz) or in the form of a graphical representation.

It is apparent from the figure that the sound pressure level varies at the various frequencies. For this reason, the aforementioned frequency response only takes into account the range in which the sound pressure level has not dropped by more than 10 dB relative to the average value, in the example above: 100 Hz – 20 kHz.

Coverage angle

The coverage angle defines the angle at which the sound pressure level has dropped by 6 dB relative to the sound pressure on the main axis of the loudspeaker. Because this angle is frequency-dependent, it is only meaningful when stated together with the frequency to which it refers. A sufficiently high level of speech intelligibility is insured within the angle of radiation at 4 kHz. Some loudspeakers have asymmetric radiation. For these types of loudspeakers, the angle of radiation is stated horizontally and vertically relative to the main axis of the loudspeaker. Most ceiling-mounted loudspeakers have symmetric radiation. In this case, only one value is stated.

THD

Total harmonic distortion (THD) is defined as the percentage ratio of the sum of the powers of harmonic components to the power of the fundamental frequency. This ratio allows for a rapid assessment of signal transmission quality with regard to non-linear distortions of the transmission path. A harmonic distortion of up to 1% is practically imperceptible to the human ear. Only starting at around 3% is total harmonic distortion perceived as unpleasant.