Th 1551
Sound for the Theatre


An electro-mechanical device for converting varying audio voltages into corresponding sound waves.


Amplifier sends alternating voltages to a voice coil that moves within a magnetic field. Magnet that surrounds voice coil moves voice coil and paper or synthetic diaphragm which creates sound waves.


Damage Control

Excessive heat in voice coil due to volume or low frequencies.
Tweeters particularly susceptible.
Fuses in house wiring.

Excessive excursions (volume)
Bottoming - clacking of voice coil hitting back plate
Rattle - voice coil pops out of slot and does not properly reenter.
No sound - coil jammed in slot.

Characteristics of Dynamic Loudspeaker
Higher fidelity
"Sweeter" sound

Compression Drivers
Thin metal diaphragm that compresses air into a pressure chamber that leads to a horn-type radiator.
Excellent for high-frequencies.
Less capable of recreating low frequencies.
More volume
More directionality


All sound waves should have same exiting point from the speaker so acoustic waves are in sinc

Acoustic Demands
Speakers are designed for assumed acoustic environment

Backwave Considerations

Infinite Baffle Speaker Cabinet

Infinite Baffle

Cabinet Proportions
Depth = A
Width = A x 1.73
Height = A x 2.46
Lower frequencies boosted when large sealed enclosure such as an adjoining room is used.

Bass Reflex (or Vented Box)
Open port for bass backwave to be added to resonant frequency. (Only very low frequencies move easily around corners).

Bass Reflex Speaker Cabinet

Folded Horn
Baffles used to lengthen the backwave path.

Crossover Networks
Separates frequencies into overlapping ranges that are routed to speaker designed best for that particular range.

JBL Control 1 Pro Loudspeaker
JBL Control 1 Pro Loudspeaker

Passive Crossover
Frequency Range: 80 Hz to 20 kHz
Power Capacity: 150 W
Crossover Frequency: 4.2 kHz


Active Crossover
Compressed Driver Domeo Tweeter: 3-16 kHz
Compressed Driver Horn Midrange: 200 Hz-5 kHz
Folded Horn Woofer: 16-300 Hz

OAP T-102
Passive Crossover
Frequency Range: 78 Hz - 16 kHz
Power Capacity: 300 W

JBL 18" Subwoofer
JBL MP418 18" Subwoofer
Powered - send line voltage signal to onboard amplifier
Bass-reflex enclosure
600 watts

Dispersion Angle
Angle at which there is no more than 50% drop in Db
Higher frequencies are more directional than low frequencies
Cellular cones may limit beaming.

Electrical resistance speaker presents to amplifier (16, 8, or 4 ohms). Divides by half each time an additional speaker is introduced in parallel.

Frequency Response
Range of frequencies particular speaker reproduces. Generally linear, unless more of particular frequency is desired.

Nominal Power Handling
Maximum power (measured in watts) that can be handled over long period of time without damage to the speaker.

System Configurations