|   does bridgeing affect the impedence? | perk
Jul 9, 2001 9:54 AM | | My amp warns me not to use anything less then 4 ohms when bridged, and i was wondering why? I would think useing two amps would allow you to drive even more difficult loads. Does anyone know how bridgeing affects the amplifier's workload/impedence and power output? |
| big time. | Markw*
Jul 9, 2001 10:22 AM | | First off, understand that speaker's impedance readings are nominal values. It can dip well below the rated impedance at times.
When you bridge an amp, it "sees" the (nominal) impedance of the speaker hooked up to it as one half of what it is. It will "see" an 8 ohm speaker as 4 ohms.
Likewise, it will "see" a 4 ohm speaker as 2 ohms and since that's only a nominal reading in the first place, it will almost certainlty dip to below 2 ohms at times. That's dangerous for almost any amp. |
| Bridging: doubled voltage swings and quadrupled power | Kursun
Jul 9, 2001 3:17 PM | | When bridged, the outputs of the amplifier channels are effectively in series. In this configuration, provided the amp has a perfect power supply, the voltage swing available is doubled, and the power is quadrupled, into the equivalent load.
So, suppose a two channel amp that has a power output of 100W/8 Ohms/channel. If it had a perfect power supply, when bridged it will produce a mono output of 400W. Into 4 Ohms this will be 800W, and to 2 Ohms the output will be 1600W. Remember, all these assumptions are true if the amp has a perfect power supply and the output stages are beefy enough to handle the required powers. (P.S.: W=V2/R : output voltage doubled=>output power quadrupled, speaker impedance halved=>output power doubled - IF there is a perfect power supply)
Now, think of yourself as an amp designer. You are designing a two channel amp powered 100W/8 Ohms/channel. It is a bridgeable design. What is the probability that someone is going to use it in bridged mode? Probably not much more than 10-20%. So you are going to design an amp that is rated for 100W/8 Ohms/channel, but it also has to handle 1600 Watts just in case somebody decides to use it in bridged mode with 2 Ohm speakers. This is just unreasonable. All this is not the whole story. Just like speaker building being full of compromises amplifier design work is also full of compromises.
An amp that handles 4 Ohms when bridged is reasonable. |
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