Nov 29, 2004 02:48 am oops... i just realized i posted this in the wrong forum...feel free to move it db. thanks
power from amp to speakers
Posted on Nov 28, 2004 10:43 pm
drake
Member Since: Apr 13, 2004
i have an amp sending 300W/chan @ 4ohm into 4 150W rms (250w peak) 8ohm speakers (2 on each chan.)
S - - - S - - - AMP - - - S - - - S
150W 150W 300Wx2 150W 150W
8ohm 8ohm @ 4ohm 8ohm 8ohm
so i understand that if i chain the speakers like that, it turns it into a 4 ohm load rather than 8ohms, that is why i give you the amp wattage at 4ohm. now my question is this:
is this giving each speaker 150W (like i want)each or 300W each?? is this setup ok??
Thanks guys :)
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Nov 29, 2004 02:48 am oops... i just realized i posted this in the wrong forum...feel free to move it db. thanks
Nov 29, 2004 06:25 am It cuts the ohm load in half if it's run parallel, what you are showing is daisy chaining, which would double the ohm load...making it 16 ohms.
Nov 29, 2004 09:22 am Drake,
You are inadvertently asking a lot of questions. The topic of power delivered to speakers is unfortunately made complicated by manufacturers of audio equipment. I don't want to bore you with a lengthy math lesson, however I surely don't want you playing "smoke in the studio" the last version.
First is power. Expressed in watts. Amps will deliver a maximum amount of power. Speakers will tolorate a maximum amount of power. Make sure that all of your speakers and amp are expressed in RMS. Some manufacturers use peak or peak to peak power ratings to boost their claimed wattage.
Power or watts is expressed in terms of W=V*A or watts equals Volts times Amps. Just like looking at a waveform in an editor, if the waveform is calibrated in volts, Watts expressed using a peak to peak voltage in the formula would use the very highest and lowest voltages in the signal as a voltage for calculating power. So if the signal goes up to +100V and down to -100V the Voltage used to calculate the wattage would be 200V. Now say the amp is delivering or the speaker is accepting 2 amps the power would be 400W (peak to peak). Usually manufacturers that do this do not specify the (Peak to peak), they just kinda omit that. The next way to expres watts is peak. In the above case the voltage would be measured from center or zero reference of the wave form and the voltage used would be 100V. Now we have a 200W rating; peak. Now there is RMS or DC equilivalent. Here they use the peak voltage measurement 100V per above and multiply it times 0.707. This yeilds 141W RMS.
Now we have all of the equipment expressed in the same terms we can look at loads.
If a amplifier is rated at 400W into an 8 ohm load. That amplifier will deliver 800 Watts into a 4 ohm load and 200 watts into a 16 ohm load. Every amplifier has a minimum load rating. Often that is 2 ohms. If the load is diminished to a load rating less than that minimum; Smoke! The amp is working harder than designed to trying to pump out too many watts. Conversely a speaker can handle only so many watts and smoke. More than one speaker hooked to an amplifier changes the load. If the speakers are hooked up in parallel, that is the hot side of the speaker wire out of the amp to the first speaker's hot terminal, then looped to the second speaker's hot terminal and the negitive wire looped in the same fashion this is parallel. In this case to total load is about half of the smallest load rating of the speakers. If two 8 ohm speakers are wired in parallel then the total load of the system is 4 ohms. If one 8 ohm and one 4 ohm speaker are connected this way the total load would be 2 ohms. The wattage of the speakers can simply be added. So if one speaker will handle 100 watts and the second will handle 200 watts, the speaker system will handle 300 watts. So in the scenerio of the 8 and 4 ohm speakers, if the amplifier will work with as little as 2 ohms and delivers 300 watts per channel at 2 ohms you have a system that will probably not produce smoke regardless of how high you turn up the volume.
The other way to wire speakers is series. Here you connect the hot terminal of the amp to the hot side of the first speaker. Take the negitive terminal of the first speaker and run a wire from it's negitive terminal to the positive terminal of the next speaker and then run a wire from the negitive side of the second speaker to the negitive terminal on the amp. In this scenerio you can simply add the loads of the speakers. With this arrangement the 8 ohm speaker and 4 ohm speaker would handle 300 watts at 12 ohms. Now the amplifier used in the parallel example would be delivering about 60 watts at 12 ohms. Obviously much safer for the speakers and amp, but with greatly diminished volume overall. Another consideration with serial wiring is phase. Eack speaker in line in a series wiring format will shift the phase delivered to the next speaker down the line. Depending upon the speakers this can cause greatly diminished quality of sound.
Last consideration is continous power vs peak power. Here our marketing geeks can really have a ball. Big bold letters say 500 WATTS PEAK PROGRAM POWER! This translates to a statement that says that the equipment will handle a surge of power of up to 500 watts. What they don't say is for how long. Could be a second, could be a micro second. Best to disregard this number when setting up a system.
Good luck! I wish you a smokeless Christmas!
Nov 29, 2004 09:26 am hehehe, well, I purposely avoided the long version :-)
Dec 03, 2004 06:43 pm I love it when Walt gets all Mr. Wizard. He is like the mad scientist we have grown to know and love.
Good shout Walt, that should keep some peeps' from torching their speakers and such.
Dec 04, 2004 12:05 am Gad, can I babble from time to time. It's working out good to late. My routine is now get up around 6:30 A.M. and try to gain consiousness prior to leaving for work at 9:00. These kind of questions make me think back to pre Noah times when I was in college and thought big thoughts about electronics. Kinda like Brain-er-size with morning coffee! It truely is fascinating stuff. I just discovered that CP has a little routine in it for generating sine waves of any frequency you so desire. Oh my! Now I can have some fun with my dB meter ringing out the room. That should make Sandy nuts for a while!
Boys and their toys!
Dec 04, 2004 05:00 am Whoa...Walt...its gonna take me a few days to assimmilate all that...but very interesting stuff.
Cheers,
BM :-)
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