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Sound Pressure Level


Piston area of a speaker.




A measurement of the sound output of a speaker or speaker system's output relative to the power put in. Typically measured in dB at 1 watt of input, 1 meter away.

Series Sixth Order Enclosure

An enclosure consisting of a vented box with its port firing into another vented box.

Series Wiring

A circuit where components are wired sequentially, dividing the voltage between them.


A circuit where there are components wired in series and in parallel to get the desired result. This is often used in multi-woofer systems to optimize the impedance seen by an amplifier.

Short Circuit

The situation that occurs when there is an alternate path created between the positive and negative portions of a circuit, bypassing some or all of the components of the circuit and preventing operation.

Small, R.H.

A pioneer in the study of the relationships of speakers and enclosures. Along with A.N. Theile, Small spelled out what is still the basis for speaker enclosure design.


Acoustical energy in waves generally accepted to be between 20 and 20,000 cycles per second.

Sound Pressure Level

Acoustic measurement for sound output. Measured in dB, the readings are often "weighted" to reflect how human ears work.


The part of the speaker attached to the junction of the cone and voice coil that keeps the voice coil aligned in the gap and helps suspend the cone.

Stray Field Containment Geometry

A speaker motor assembly designed to reduce stray magnetic fields around the speaker and focus the energy in the voice coil gap. Proprietary to JBL, this method is used in high-end products such as the GTi competition series.


A speaker or speaker/enclosure system designed to reproduce only bass frequencies. Generally used only below 80Hz.

Symmetrical Field Geometry

A speaker motor assembly design that maintains equal magnetic force throughout the travel of the voice coil. This improves bass response and substantially reduces distortion.