Don't understand why you think they would not be in phase. Each identical amp fed by the same input would have negligible output phase shift difference between them.
Exactly - simply wire the speakers in series/parallel - it's standard practice (fears of damping factor problems are just that, totally ungrounded fears).
As for worrying about phase problems with different amplifiers, that's nonsense as well - PA systems commonly use dozens of different amplifiers with no such problems.
Still don't understand why you are "sure" there's a phase shift between amps. If it's intuition you are using, that's generally not reliable when determining the operation of electronic amplifiers.Actually I am sure that there would be an out of phase at the final outputs by using independent amplifiers, though I do not know if it is negligible or not.
Anyway If I do not find another solution I will use the independent amplifier method.
Is the output of 2 independent amplifiers connected to 2 independent speakers side by side just 2x power of each? For instance what about using 2 LM3886 each delivering 68W?
If you have 10 speakers and play 50W from each one then obviously the amplifiers must provide a total of 500W.
An amplifier rated for an 8 ohm load might blow up if the load is 4 ohms or less because it is almost a dead short and the current will be much too high. You could use 5 amplifiers spec'd for 100W into 4 ohms and connect two 8 ohm speakers in parallel to each amplifier.
The LM3886 has an output of 68W into 4 ohms when its has a 56V total supply. If you connect two 8 ohm speakers in parallel then each gets only 34W.
With a 70V supply the output into 4 ohms is 130W which will destroy the IC.
None of the graphs show a supply more than 56V when the load is 4 ohms and the output is 68W.
If you connect two speakers in series then each one gets only 1/4 of the output power.
I have desired to design and make a line or planar sound source using 10 or more (if needed) common 4 ohms speaker (I have more than 20 of them).
Either I really don't understand what ypu're asking here, or you're just plain being ridiculous.
As I understand it, you have:
- At least 20 4 ohm speakers, other characteristics unknown, and
- At least 12 LM3886 power amplifiers.
You want to drive those speakers (10 or more, according to your original post) with at least one of those amplifiers.
What's the problem? Just wire 16 of the speakers in series-parallel. Specifically,
- wire 4 sets of 4 speakers in series
- wire the 4 sets in parallel
Voila! You have a total impedance of 4 ohms, perfect for your 3886s.
You haven't told us:
- How much total power you require
- What the power-handling capacity of each speaker is
- What you're trying to accomplish here
If you need more power than one 3886 will provide them, then run two or more in bridged mode. They're made so you can do that. (Check the datasheet.)
I don't see what the problem is.
I think that I respond almost all of your questions in my previous posts.
How do you want me to put the speakers in series/parallel and use a single LM3886 yet get the MAX power out of the speakers???!!!
Suppose I put 2 of the speakers in series, Now I'll get 8 ohms of load, I have to increase the voltage of the LM3886 by a factor of 2 (i.e 112V) to get the same power as using a single speaker. It is not possible. Hope that makes sense.
As stated by others, you put the speakers in series-parallel. Thus you have two sets of two speakers in series and then parallel the two sets. That puts you back at the original impedance of 4 ohms. Now you will get the same total power at the same amp voltage as you would with one speaker. Of course, the power is now shared between 4 speakers but that's to be expected.Suppose I put 2 of the speakers in series, Now I'll get 8 ohms of load, I have to increase the voltage of the LM3886 by a factor of 2 (i.e 112V) to get the same power as using a single speaker. It is not possible. Hope that makes sense.
I don't know where you got a signal that is 56V p-p into 4 ohms because it is 100W but an LM3886 has a max output of 68W when its supply is 56VDC. An applications note for the LM3886 IC explains that its SPIKE protection circuit turns on when the output is 68W into 4 ohms which is is 16.5V RMS which is 46.6V p-p.Please can you tell me how much of voltage a single 4 ohms speaker sees by 56V total supply while using LM3886?
As stated by others, you put the speakers in series-parallel. Thus you have two sets of two speakers in series and then parallel the two sets. That puts you back at the original impedance of 4 ohms. Now you will get the same total power at the same amp voltage as you would with one speaker. Of course, the power is now shared between 4 speakers but that's to be expected.
No, it does not make sense.
It sounds like you're saying you won't be satisfied until you can get the "maximum power" (i.e., the 68 watts that the 3886 is capable of providing) out of each speaker. Meaning that if you have 10 speakers, you are demanding 680 watts of power?!?!?
Which is why I asked what you're trying to accomplish here. It's possible you have some strange application where you simply must get the maximum possible power out of each speaker.
Do you even realize how much power 68 watts is? And are you going to be running this whatever-it-is at maximum power, wide open?
Generally speaking, audio amplifiers (with some exceptions) are not expected to be run at their full rated power.
The solution I offered you--wiring your speakers in series-parallel--will work with what you have. It's up to you to explain to us why that is not an acceptable solution. I still don't get it.
As stated by others, you put the speakers in series-parallel. Thus you have two sets of two speakers in series and then parallel the two sets. That puts you back at the original impedance of 4 ohms. Now you will get the same total power at the same amp voltage as you would with one speaker. Of course, the power is now shared between 4 speakers but that's to be expected.
Perhaps you need to review ohms law of parallel and series circuits.
WE whole now that by using the speakers in series/parallel Each speaker does not see the max power needed for it because it does not see the voltage of while used lonely.
I don't know where you got a signal that is 56V p-p into 4 ohms because it is 100W but an LM3886 has a max output of 68W when its supply is 56VDC. An applications note for the LM3886 IC explains that its SPIKE protection circuit turns on when the output is 68W into 4 ohms which is is 16.5V RMS which is 46.6V p-p.
Simply use one LM3886 for each speaker and use a 56VDC supply or plus 28VDC and minus 28VDC. The phase of the sound from a speaker will be identical to the others (unless a speaker is connected backwards).
Carl, I'm certainly not a mind-reader, but I get the feeling the O.P. somehow wants/needs/requires/fantasizes about getting the "maximum power" (the 68W of the LM3886) out of each speaker. Of course, since they haven't told us what they're trying to do with this project, there's really no way of knowing.
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