Amplification and Audio
The low-frequency drivers in the X-800C are powered by a two-channel proprietary Meyer Sound amplifier with MOSFET output stages. The audio signal is processed with an electronic crossover, correction filters for phase and frequency response, and driver protection circuitry. Each channel has peak and rms limiters that prevent driver over-excursion and regulate the temperature of the voice coil.
 |
X-800C Rear Panel (with NEMA L6-20 AC Connector)
The X-800C rear panel includes audio connectors for Input and Loop output, as well as an Input Polarity switch. The X-800C is also available with an optional RMS module. For more information,see X-800C RMS Remote Monitoring System.
Audio Connectors
The X-800C includes female XLR Input and male XLR Loop output connectors.
 |
X-800C Audio Connectors, Input and Loop Output
Input Connector
The female XLR Input connector accepts a balanced audio signal with an input impedance of 10 kOhm. The connector uses the following wiring:
Pin 1 — 220 kOhm to chassis and earth ground (ESD clamped)
Pin 2 — Signal (+)
Pin 3 — Signal (–)
Case — Earth (AC) ground and chassis
Pins 2 and 3 carry the input as a differential signal. Pin 1 is connected to earth through a 220 kOhm, 1000 pF, 15 V clamped network. This circuitry provides virtual ground lift for audio frequencies while allowing unwanted signals to bleed to ground. Make sure to use standard, balanced XLR audio cables with all three pins connected on both ends.
Telescopic grounding is not recommended, and shorting an input connector pin to the case may cause a ground loop, resulting in hum.
Tip
If unwanted noise or hiss is produced by the loudspeaker, disconnect its input cable. If the noise stops, there is most likely nothing wrong with the loudspeaker. To locate the source of the noise, check the audio cable, source audio, and AC power.
Loop Output Connector
The male XLR Loop output connector allows X-800C subwoofers to be looped from a single audio source. For applications that require multiple X-800Cs, connect the Loop output of the first unit to the Input of the second, and so forth.
Note
The order in which loudspeakers are connected when looping audio signals is unimportant. The Loop connector is wired in parallel to the Input connector and transmits the unbuffered source signal even when the X-800C is powered off.
To avoid distortion when looping multiple X-800Cs, make sure the source device can drive the total load impedance of the looped loudspeakers. In addition, the source device must be capable of delivering approximately 20 dBV
(10 V rms into 600 ohms) to yield the maximum peak SPL over the entire operating bandwidth of the loudspeakers. Most professional audio equipment can transmit these source levels.
To calculate the load impedance for the looped loudspeakers, divide 10 kOhms (the input impedance for a single
X-800C) by the number of looped loudspeakers. For example, the load impedance for 10 X-800C loudspeakers is 1000 ohms (10 kOhms / 10). To drive this number of looped loudspeakers, the source device should have an output impedance of 100 ohms or less. This same rule applies when looping X-800C loudspeakers with other self-powered Meyer Sound loudspeakers and subwoofers.
Note
Most source devices are capable of driving loads no smaller than 10 times their output impedance.
Caution
Make sure that all cabling for looped loudspeakers is wired correctly (Pin 1 to Pin 1, Pin 2 to Pin 2, and so forth) to prevent the polarity from being reversed. If one or more loudspeakers in a system have reversed polarity, frequency response and coverage will be significantly degraded.
Limiting
The X-800C employs Meyer Sound’s advanced TruPower® limiting. Conventional limiters assume a constant loudspeaker impedance and set the limiting threshold by measuring voltage alone. This method is inaccurate because loudspeaker impedances change as frequency content in the source material changes, and as thermal values for the loudspeaker’s voice coil and magnet vary. Consequently,
conventional limiters often begin limiting prematurely, which reduces system headroom and dynamic range.
 |
X-800C Limit LEDs
In contrast, TruPower limiting anticipates varying loudspeaker impedances by measuring both current and voltage to compute the actual power dissipation in the voice coil.
This improves performance, both before and during limiting, by allowing the driver to produce the maximum SPL across its entire frequency range. TruPower limiting also eliminates power compression at high levels over lengthy periods, which helps regulate voice coil temperatures, thereby extending the life of the driver.
Note
Since TruPower limiting only reduces signal levels to keep voice coil temperatures under a safe margin, signal peaks remain unaffected.
Sub Limit LED
The two low-frequency drivers for the X-800C are powered by separate amplifier channels that are routed to a single limiter. When a safe power level is exceeded in either channel, limiting is engaged for both channels and the SUB Limit LED lights.
When engaged, the limiter not only protects the drivers but also prevents signal peaks from causing excessive distortion in the amplifier channels, thereby preserving headroom and maintaining smooth frequency responses at high levels. When levels return to normal, below the limiter thresholds, limiting ceases.
The X-800C performs within its acoustical specifications at normal temperatures when the SUB Limit LED is unlit, or if the LED is lit for two seconds or less and then turns off for at least one second. If the LED remains lit for longer than three seconds, the loudspeaker enters hard limiting where:
Increases to the input level have no effect
Distortion increases due to clipping and nonlinear driver operation
The drivers are subjected to excessive heat and excursion, which will compromise their life span and may eventually lead to damage over time
Caution
The SUB Limit LEDs indicate when a safe, optimum level is exceeded. If an X-800C begins to limit before reaching the required SPL, consider adding more subwoofers to the system.
Note
The X-800C subwoofer uses an optical limiter that adds no noise and has no effect on the signal when the limiter is not engaged and the SUB Limit LED is not lit.
Excursion Clamp LED
The X-800C drivers are protected from over-excursion by an Excursion Clamping circuit, indicated by the Exc Clamp LED. The circuit does not have attack or release time constants and provides instantaneous braking for the drivers without the pumping effects commonly exhibited by compressors and limiters.
The Excursion Clamping circuit uses sophisticated filters to minimize the distortion normally caused by clamping and clipping. As the X-800C’s input signal is increased beyond the clamping point, the output signal remains at a fixed level, protecting the drivers and minimizing negative sonic effects. The X-800C operates normally and safely when the Exc Clamp LED is on for no longer than two seconds, and off for at least one second.
Input Polarity Switch
The X-800C includes an Input Polarity switch on its rear panel that toggles the polarity of the source signal. When the switch is in the UP position, pin2 is hot relative to pin3, resulting in a positive pressure wave when a positive signal is applied to pin2. When the switch is in the DOWN position, pin3 is hot relative to pin2, resulting in a positive pressure wave when a positive signal is applied to pin3.
 |
X-800C Input Polarity Switch
Note
The Input Polarity switch does not affect the signal coming from the Loop output connector. The Loop output connector is wired in parallel to the Input connector and transmits the unbuffered source signal (even when the loudspeaker is powered off).
Amplifier Cooling System
The X-800C uses a forced-air cooling system with two fans (one variable-speed, ultra low-noise primary fan and one reserve fan) to prevent the amplifier module from overheating. The fans draw air in through ducts on the front of the cabinet, over the heat sink, and out the rear of the cabinet. Because dust does not accumulate in the amplifier circuitry, its life span is increased significantly.
Airflow for the X-800C
Caution
To keep the X-800C from getting too hot, allow for proper ventilation, 6 inches, behind the loudspeaker.
When the X-800C heat sink temperature is below 42° C, the variable-speed primary fan runs continuously at its slowest speed with an inaudible operating noise. The primary fan increases speed when the heat sink temperature reaches 42° C; the primary fan reaches full speed at 62° C and is barely audible near the cabinet, even without an audio signal. If the heat sink temperature reaches 74° C, the reserve fan turns on. The reserve fan turns on if:
The primary fan has failed (check status immediately)
High source levels are encountered for extended periods
Dust has accumulated along the cooling path
The reserve fan turns off when the heat sink temperature lowers to 68° C.
Note
In the unlikely event that the reserve fan does not keep the X-800C heat sink temperature below 85° C, the unit automatically shuts down until AC power is removed and reapplied. If the X-800C shuts down again after cooling and re-applying AC power, contact Meyer Sound for repair information.
Dust and the Amplifier Module
Operating the X-800C in dusty environments, or for pro- longed, intensive periods, may cause dust to accumulate along its airflow path, thereby preventing normal cooling. Under these circumstances, it may be necessary to periodically remove the air intake foam and use compressed air to clear the dust from the foam and air ducts.
In addition, if the amplifier gets unusually hot, remove the amplifier module and use compressed air to clear any dust from its heat sink.
Caution
Make sure to unplug the AC power from the X-800C before cleaning its amplifier.