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Nanbakat Unregistered guest | Glasswolf: In another posting you wrote the following: "I'd stick with CDT for rears, and if you do amp them, use a 4 chanel amp, and bridge it for the rear two channels to run them in mono (in series) to help maintain your stereo imaging in front." OK. I have a four channel amp, Alpine MRV-F545, and I currently have four speakers running from each of the channels. I am planning on upgrading my speakers from 4 coaxials to 2 component speakers in the front and 2 mid-range woofers in the back. Since I'm spending a lot of money on speakers and would like the best imaging and sound quality possible, I am going to do what you recommend and send mono-sound to the rearfill speakers. My amp can put out: 500 watts RMS x 1 (When channels 3/4 are briged) or 125 watts RMS x 1 (When channels 1/2 are bridged) or 125 watts RMS x4 I assume that I'd want to bridge channels 1/2 for the rearfills and use channels 3/4 for the front speakers, right? If I wire the rear-fill speakers in series the total resistance from both speakers would be 8 ohms (4 ohms + 4 ohms). Would the higher resistance pose any kind of danger to the amplifier, eg overheating? How should I set my gains if my rear-fill speakers are 80RMS? Thanks. |
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Gold Member Username: CarguyPost Number: 5322 Registered: Nov-04 | Whether your amp can handle 8ohm load will depend on the manufacturer. Why don't you just leave the amp in 4 channel mode and send mono signal to the 2 rear channels instead? That way, you don't have to worry about ohm matching. As for gain/level setting, it's not used to match ohms nor is it a volume control. Set it correctly and leave it. |
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Platinum Member Username: GlasswolfWisteria, Lane USA Post Number: 11160 Registered: Dec-03 | any amp can do 8 ohms.. however, you'll have a bridged amp so it'll see 4 ohms.. same power output as if you just ran unbridged stereo and put one speaker on each channel. |
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Nanbakat Unregistered guest | You're correct, as always, Glasswolf. Thank you for the reply. I did a Web search and I determined that an 8 ohm load in series to a bridged amplifier is exactly the same as two 4 ohm speakers wired to two channels. Pasted text from http://www.bcae1.com/bridging.htm 2 Ohm Stereo vs 4 Ohm Mono Loads [or in my case, 4 ohm stereo vs 8 ohm mono load] There seems to be some confusion as to why a 4 ohm mono and a 2 ohm stereo load are the same, as far as the amplifier is concerned. When two 4 ohm speakers are connected to each channel of a 2 channel amplifier, the amplifier is capable of driving the speakers with half of the total power supply voltage. If the amplifier has a power supply which produces plus or minus 20 volts, it will not be able to drive the speakers on a single channel with any more than 20 volts at any point in time. If we have a 2 ohm load on each channel, at the highest point on the waveform the amplifier will apply 20 volts to the speaker load. Remember that we are only considering a single point in time for this example. If we go back to ohms law... I=V/R I=20/2 I=10 amperes If we take a single 4 ohm speaker and bridge it on that same amplifier, the amplifier will be able to apply twice the voltage across the speaker. This is because while one speaker terminal is being driven positive (towards the positive rail), the other terminal is being driven towards the negative rail. This will allow the entire power supply voltage to be applied to the speaker's voice coil. It will now be able to drive the 4 ohm speaker with 40 volts instead of 20 volts in the previous example. Back to Ohm's law... I=V/R I=40/4 I=10 amperes The same amount of current flows through the output transistors whether the amplifier is driving a 4 ohm mono load or 2 ohm stereo load. As far as the amplifier is concerned, they are the same load. NOTE: Some people say that when an amplifier is bridged onto a 4 ohm load, it 'sees' a 2 ohm load. While it is true that the same current flows whether the amp is bridged on a 4 ohm load or a 2 ohm stereo load, the amplifier is driving a 4 ohm load across its outputs. A single 4 ohm speaker can never be a 2 ohm load. |
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Platinum Member Username: GlasswolfWisteria, Lane USA Post Number: 11171 Registered: Dec-03 | I use the term "see" because to the layman it makes more sense than trying to teach someone how a multirail power supply works in an amplifier just to explain how a bridged amp works. It was done more for simplicity sake rather than accuracy. |