REL Acoustics ‘Q’ range User manual
21
TECHNICAL
The ground switch (if fitted) provides a physical mains earth connection to the Sub Bass System if
required. When the unit is connected up and switched on, listen for any ‘hum’ from it, if ‘hum’ is
present then change the ground switch position from in to out (on to off for US market) or vice versa.
In the in (on) position the mains earth is connected, in the out (off) position the mains earth is
disconnected.
The “Q” range models use an unusual method of bass loading. They are designed to operate below
normal system resonance, at least over some of their operating range. This has been achieved
without the normal form of bass boost or electronic equalization. Instead of a constantly increasing
bass equalization response, we simply ensure there is sufficient amplifier gain to drive the speaker
unit to its maximum excursion level at whatever the designated lowest operating frequency is, (25
Hertz for the “Q” range models), and then cut the bass at a controlled rate of 12 dB per octave above
this frequency. Although this may at first seem identical to boosting the bass, it is actually quite
different and ensures that the timing of transients is far improved compared to the usual bass
equalization used. We call it Zero-Q loading. The main benefit is no obvious boom or bloom to the
bass. Bass will sound cleaner and faster. For maximum performance we believe the electronics,
cabinet and the drive unit should all be designed to work together.
The amplifier is fully DC coupled to avoid phase shifts and compromises in its low end performance.
The three filter stages, each operating at different frequencies, are Sallen and Key two pole
(l2db/octave) using high quality components. The filter capacitors are the highest quality 1%
tolerance nitrogen filled polystyrene types with an indefinite shelf life. This means they are inherently
stable and will retain their characteristics over very long periods of time - important in a unit designed
for an exceptionally long working life. The Q400 has six high current output devices, the
Q150E/Q200/201E has four high current output devices and the Quake/Q108 has two high current
output devices to ensure maximum current delivery and long term thermal stability. These amplifiers
are designed to withstand reasonable abuse and overloads.
As with all other REL units, care has been taken to deliberately over engineer it to withstand up to
300 Volts mains input. This ensures a robust, long lasting device.
OVERLOAD PROTECTION
All REL Sub-Bass Systems are designed as true sub-bass speakers. They are designed to
reproduce those exceptionally deep notes that are felt rather than heard. This it will attempt to do at
whatever volume level you set. If set too high no damage should result because the built-in
electronics will limit the cone movement. This electronic control is called set-safe. It constantly and
instantaneously monitors the output from the power amplifier and is totally transparent in operation
until required. This means it has absolutely no effect on the sound quality of your REL until an
overload is detected.
Ordinarily an overload would cause the power amplifier to go into clipping with resultant loss of
control over the drive unit. This can cause drive unit damage and always sounds nasty. Set-safe
detects the point of incipient clipping and gently soft clips the waveform of the signal to ensure actual
clipping does not occur. This is a necessarily simplified version of what actually happens, but it
effectively controls the amplifier and ensures there is minimum risk of amplifier and driver damage
caused by over-driving.
A thermal overload device is fitted to Quake/Q108. If the unit is deliberately overdriven this device
will sense the temperature rise and cut the output, recovery time is approximately five minutes. If this
happens it is a warning that the unit is being overdriven and the gain control should be reduced to a
safe level.
Although everything possible has been done to minimize risk of thermal overload
failure, there can be no defense against those individuals who deliberately abuse
the device. Such damage is NOT covered by Warranty. Please remember your
REL is there to supplement your main system, not overwhelm it.
