speaker enclosure A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often rectangular box-shaped) in which speaker drivers (e.g., woofers and tweeters) and associated electronic hardware, such as Audio crossover, crossover circuits and, in some ca ...

using a

passive Passive may refer to: * Passive voice, a grammatical voice common in many languages, see also Pseudopassive * Passive language, a language from which an interpreter works * Passivity (behavior), the condition of submitting to the influence of ...

radiator usually contains an "active

loudspeaker A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...

" (or main driver), and a passive radiator (also known as a "drone cone"). The active loudspeaker is a normal driver, and the passive radiator is of similar construction, but without a

voice coil A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. Th ...

and magnet assembly. It is not attached to a voice coil or wired to an electrical circuit or

power amplifier An audio power amplifier (or power amp) amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspeakers or headphones. Audio power a ...

. Small and Hurlburt have published the results of research into the analysis and design of passive-radiator loudspeaker systems. The passive-radiator principle was identified as being particularly useful in compact systems where vent realization is difficult or impossible, but it can also be applied satisfactorily to larger systems. Logitech Z4 satellite 1

In the same way as a ported loudspeaker, a passive radiator system uses the sound pressure otherwise trapped in the enclosure to excite a resonance that makes it easier for the speaker system to create the deepest pitches (e.g.,

bassline Bassline (also known as a bass line or bass part) is the term used in many styles of music, such as blues, jazz, funk, Dub music, dub and electronic music, electronic, traditional music, traditional, and classical music, for the low-pitched P ...

s). The passive radiator resonates at a frequency determined by its mass and the springiness (compliance) of the air in the enclosure. It is tuned to the specific enclosure by varying its

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

(e.g., by adding weight to the cone). Internal air pressure produced by movements of the active driver cone moves the passive radiator cone. This resonance simultaneously reduces the amount that the woofer has to move.

Design considerations

Passive radiators are used instead of a reflex port for several reasons. In small-volume enclosures tuned to low frequencies, the length of the required port becomes very large. They are also used to reduce or eliminate the objectionable noises of port turbulence and compressive flow caused by high-velocity airflow in small ports. In addition, ports have pipe resonances that can produce undesirable effects on the frequency response. To a first-order approximation, the passive radiator works identically to a port. Passive radiators are tuned by mass variations (M_mp), changing the way that they interact with the compliance of the air in the box. The weight of the cone of the passive radiator should be approximately equivalent to the mass of the air that would have filled the port which might have been used for that design. If the passive radiator's acoustic mass equals that of the port, and the passive radiator's compliance is negligible, then the frequency response behaviour of these two types of systems will be virtually identical. Although the frequency response of a passive radiator will be similar to that of a ported cabinet, the system low-frequency roll-off will be slightly steeper (5th-order rather than 4th-order), due to a notch (dip) in the

frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and Phase (waves), phase of the output as a function of input frequency. The frequency response is widely used in the design and ...

caused by the V_ap (compliance or stiffness) of the passive radiator. This notch occurs at the passive radiator's free-air resonant frequency and causes slightly poorer transient response. Despite this, perhaps due to the lack of vent turbulence and vent pipe resonances, some listeners prefer the sound of passive radiators to reflex ports. Passive radiator speakers are only slightly more complex to design and are generally more expensive as compared to standard bass reflex enclosures.

Applications

Passive radiators are used in

Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is li ...

speakers, home stereo speakers,

subwoofer A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies, known as bass and sub-bass, that are lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range that is ...

cabinets and

car audio Vehicle audio is equipment installed in a car or other vehicle to provide in-car entertainment and information for the occupants. Such systems are popularly known as car stereos. Until the 1950s, it consisted of a simple AM radio. Additions si ...

speaker systems, particularly in cases where there is not enough space for a port or vent system. While most studio monitor speakers are either ported bass reflex designs, or closed-back without a vent or passive radiator,

Mackie Mackie may refer to: Organizations * Mackie (company), American manufacturer of professional audio equipment * Mackie International, a textile machinery engineering plant and foundry in Northern Ireland * Mackie Academy, a secondary school in Sto ...

's HR824 and HR624 monitor speakers have a passive radiator installed on the rear of the cabinet. Focal also sells a studio monitor with a passive radiator called the SM9.
Respective examples of a

smart speaker A smart speaker is a type of loudspeaker and voice command device with an integrated virtual assistant (artificial intelligence), virtual assistant that offers interactive actions and Hands-free computing, hands-free activation with the help of o ...

and a portable Bluetooth Speaker utilizing passive radiators are

Apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...

HomePod mini The HomePod Mini (stylized as HomePod mini) is a smart speaker developed by Apple. It utilizes Apple's Siri digital assistant. Roughly a 10 cm sphere, it was released on November 16, 2020 as a smaller and less expensive version of Apple's Home ...

and

Ultimate Ears Ultimate Ears is an American custom in-ear monitor (IEM), Wireless speaker, speaker, and earphone manufacturer based in Irvine, California, Irvine and Newark, California, United States. It was founded by Mindy and Jerry Harvey (inventor), Jerry H ...

' UE Boom.

References

{{Reflist , refs= {{cite journal , first=R. H. , last=Small , title=Passive-Radiator Loudspeaker Systems Part 1: Analysis , journal=Journal of the Audio Engineering Society , volume=22 , number=8 , pages=592–601 , year=1974 , url=http://www.aes.org/e-lib/browse.cfm?elib=2739 {{cite journal , first=R. H. , last=Small , title=Passive-Radiator Loudspeaker Systems Part 2: Synthesis , journal=Journal of the Audio Engineering Society , volume=22 , number=9 , pages=683–689 , year=1974 , url=http://www.aes.org/e-lib/browse.cfm?elib=2731 {{cite journal , first=D. H. , last=Hurlburt , title=The Complete Response Function and System Parameters for a Loudspeaker with Passive Radiator , journal=Journal of the Audio Engineering Society , volume=48 , number=3 , pages=147–163 , year=2000 , url=http://www.aes.org/e-lib/browse.cfm?elib=12074 Loudspeaker technology Audio engineering

Design considerations

Applications

See also

References