Harman-Kardon 120.3SE Power-Handling Limitations, Connecting A Subwoofer System, I = w1 + w2 + w3

POWER-HANDLING LIMITATIONS

CONNECTING A SUBWOOFER SYSTEM

The power-handling capability of any subwoofer is related to both its ability to dissipate heat and the maximum excursion limits of its cone. Once the subwoofer’s voice coil moves outside the magnetic gap, power can no longer be converted into motion and all the amplifier’s power is con- verted into heat. This is the most significant detri- ment to subwoofer longevity, so overexcursion should be avoided. Since cone excursion is differ- ent for each type of enclosure, expect power han- dling to be different for each enclosure as well.

EXCURSION IN A SEALED ENCLOSURE Sealed enclosures exert the most control over the motion of a subwoofer because the air inside the box acts like a spring against the motion of the subwoofer cone. Larger boxes allow for more excursion, thus providing more low-frequency out- put for the amount of power used. When a sub- woofer is placed in a sealed box much larger than its associated Vas , it will perform as if it were in an infinite-baffle installation. We do not recom- mend this application.

EXCURSION IN A PORTED ENCLOSURE

Vented and bandpass enclosures have the lowest amount of excursion for the amount of sound out- put. This is a result of port output reinforcing the sound output from the subwoofer. The mass of the air contained in the port provides an acoustic

OTHER CONSIDERATIONS

• Voice-coil overheating and burning due to

overexcursion are often caused by overdriving

an amplifier into “clipping.” A severely clipped

signal, or square wave, contains nearly twice

the power of a clean sine wave at the same

level. Bass that sounds broken up and distorted

at higher volumes is usually indicative of an

amplifier that is clipping and being asked to

deliver power beyond its ability.

• Infinite-baffle or “free-air” mounting applica-

tions allow for greater cone excursion than

subwoofers mounted in an enclosure. For this

application, power handling should be reduced

to half of its published specification.

• Study the excursion curves on the enclosed

Kappa Series data sheet and note the differ-

ences for different enclosure applications. The

type and size of box used will produce different

excursion demands on the subwoofer and, con-

sequently, different levels of power handling. As

long as the recommended enclosure parame-

ters are used, the subwoofer will perform prop-

erly in its enclosed environment. However, any

design deviation may result in less than opti-

mum performance, and may also subject the

subwoofer to overexcursion (i.e., where the

voice coil leaves the gap) that can eventually

damage the speaker. For additional help with

IMPEDANCE CONSIDERATIONS

To achieve maximum amplifier output, you should design a subwoofer system that provides

the lowest impedance that your amplifier can drive safely. Here are some design tips:

•Don’t mix different subwoofer or enclosure types in the same system. For example, use only all single-voice coil woofers or all dual- voice coil woofers.

•Connect a dual-voice coil subwoofer in series, but NEVER connect separate subwoofers in series. Because the amplifier’s damping factor (i.e., the amplifier’s ability to control the motion of the sub- woofer) is expressed as a ratio of

terminal impedance (i.e., the sum of speaker impedance, wire resistance, and the direct- current resistance of any crossover coil connected to the subwoofer) to amplifier output impedance, connecting subwoofers in series reduces the damping factor of the amplifier to a value less than one. Doing so may result in poor system damping.

•You must use both coils of a dual-voice coil subwoofer either in series or in parallel.

•Most amplifiers deliver exactly the same amount of power bridged into a 4-ohm load as they do running a 2-ohm stereo load.

•The formula for total system impedance of voice coils connected in parallel is:

I = 1⁄(1⁄ w1 + 1⁄ w2 + 1⁄ w3 ...)

where I is the total system impedance in ohms, and w is the nominal impedance of a voice coil in ohms.

•The formula for total system impedance of voice coils connected in series is:

I = w1 + w2 + w3...

CONNECTIONS

The following illustrations show parallel and series speaker connections.

Figure 1. Parallel connection

ENGLISH

load on the subwoofer’s cone at the tuning fre- quency, and this added mass decreases sub- woofer-cone excursion. However, vented boxes do not provide adequate subwoofer control when driven below the tuned frequency (Fb), so proper design is important. A vented bandpass box will have the lowest overall cone excursion, provided a subsonic filter is used.

this issue, please contact your authorized

Infinity dealer.

Figure 2. Series connection

POWER CONSIDERATIONS

To design a subwoofer system that maximizes available amplifier power, keep the following rules in mind:

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