Bridging
It is often said that when bridging an amplifier the amplifier sees half the ohms. The more correct statement is each CHANNEL sees half the ohms. A 4 Ohm load bridged is approximately equivalent to 2 ohm loads in stereo. Typical 400W Amplifier:
- 100×2 @ 4 Ohms
- 200×2 @ 2 Ohms
- 400×1 @ 4 Ohms
- 800×1 @ 2 Ohms (Probably not supported (Otherwise it would be an 800W amp), each channel sees a 1 Ohm load, good chance of going into protection)
Or Perhaps:
- 50×2 @ 4 Ohms
- 100×2 @ 2 Ohms
- 200×2 @ 1 Ohm
- 200×1 @ 4 Ohms
- 400×1 @ 2 Ohms
Gains
Everyone seems to use the “gain” as a volume control. The gain on an amplifier has one primary and one secondary purpose. The primary purpose of the gain is to match the amplifier output to the input voltage. The secondary goal is to match amplifier output (volume) between amplifiers in mulit-amp systems. People are constantly saying “the gain is only half-way” or “the gain is only about a quarter”. These statements are often used to imply that somehow the amplifier is able to push speakers to their maximum output. This is incorrect. While the volume outputted may be sufficient increasing an amplifiers size will always yield more volume (considering they really are not being pushed beyond their peak). The distortion heard is often the AMPLIFIER’S signal not the speakers. Adjusting Gain:
- Turn all gains/level controls to zero or just above zero.
- Ensure all enhancements are off or at their flat positioning. These can include bass boosters on amps, loud settings (off), bass and treble or full blown EQs (flat). Doing gain adjustments with these settings enabled (or increased) will most likely cause a signal to clip at a lower level.
- Turn the head-unit to about ¾ of full volume. This should be high enough to get a sufficient output signal without clipping and allow head room for “lower” recorded material.
- Staring at the head-unit follow the signal to the amplifier. In simpler setups they may just be an amplifier gain. However, in others you may have an in-line converter or an EQs or crossover gains. Boost each gain at each step of the signal until distortion is heard then turn back. In systems will high voltage outputs an amplifier may be able to produce its full power with a gain at or nearly at zero.
- Note: The source used for the test is very important. Using a source recorded at low volume will yield in-fluctuated gains cause the large majority of tracks to be distorted at ¾ volume. General rule: use a sine wave recorded @ 0db at median of the frequency range. For instance for a sub amplifier that plays notes from 80Hz-20Hz. 50Hz would be an appropriate frequency. Generally you can use 50Hz for sub amps and 1 KHz for highs.