ajlelectronics
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You haven't explained how an input of 40W can generate an output of 150W though?
- Thread starter JOEPRO
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You haven't explained how an input of 40W can generate an output of 150W though?
why on earth would you think it could ,,,, ? you asked why a separate amp would be better , so there are a few reasons.
ajlelectronics
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I beg your pardon, it was someone else who made the comment, not your good self.
MetalMonkey
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In what way?
2 channel amp 150w RMS a channel, fused at 40 amps, seems quite plausible to me.
Compare that to 4 channel head unit rated at 18W per channel with a 5A fuse.
Generally the advice if you want a quick and dirty way to see if an amp is actually likely to be capable of putting out its claimed numbers is to look at the fusing.
Plenty of cheap and nasty ones claiming 400 jiggawatts fused by a 10A, which are obviously fake numbers.
You aren't trying to tell me you expect this sort of thing is run from the output of a headunit are you?.....
ajlelectronics
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You cannot get more than 40W from a 40W input, even at 100% efficiency. You can have 100A fuses and cables the size of your leg, but the physics tells you that 13.8V driving a 4R load equals 40W regardless.
MetalMonkey
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Why on earth do you think there is a 40w limitation?
The only thing you feed into the amp from the head unit is the pre out signal. The amp is powered directly from the battery and charging circuit, which is capable of delivering 100s of amps.
Much of the groundwork irrespective of if you are going SQ or SPL is on making sure the power delivery is there, that includes upgrades to charging, batteries, cabling to reduce voltage drop etc.
This is all well established principles.
ajlelectronics
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Ohms law. At 13.8V, a 4R load can only draw 3.45A, regardless of the hundreds available. 13.8V at 3.45A is a tad over 40W. The ONLY ways to get more power out is to reduce the impedance (tricky) or increase the Voltage. I imagine that there must be amplifiers with inbuilt inverters, however I have never seen one. Every iteration that I have seen uses deceitful figures in an effort to sell refrigerators to Eskimos. Ye cannae change the laws of physics cap'n.
MetalMonkey
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I think you are either getting confused or on a wind up!
The supply voltage to the amplifier might be at 13.8v DC. The output voltage to the speaker will be AC and peak significantly higher.
For the 150w example you would have an output of about 24.5V RMS or about 70v peak to peak, actually likely higher as output won't be pulled all the way.
Its also fairly normal to parallel loads to drop the impedance even lower.
ajlelectronics
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Where does it come from? Perpetual motion doesn't exist. If you modulate a DC signal, you get slightly less AC output, there being no efficiency figure of 100%.
You can dress the figures up all you like, but you cannot take out more than you put in. Yes, you can parallel speakers to give you 2R and I have seen it done, although it introduces issues of its own. However even using 2R as the load, you are still only going to have a true power output @100% efficiency of (13.8/6.9) of 95.22W, a long way short of 150W. Unless of course you use the nonsense PMPO figures.
lots of single subs now run multiple voice coils on the same former in the same gap too ,,, ie 2x 2 ohm or 4 x 1 ohm loads to maximise the efficiency of amps that will load down to 1 ohm ,,,, scares me , but thats how they do it. as for the power ,, isnt that why they used to put big capacitors in amps , now its all electronic stuff that is over my head ,,,, I just plug it in and use it ,,,, but in the pro world 3u amps are getting fed three phase supply and delivering kw / channel into subs ,,,,
MetalMonkey
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I was hoping you were on a wind up given your moniker!
This is, err, year one electronics I’m afraid. I really don't know how else to say it.
You take 13.8v or whatever your supply DC voltage is, at say, 40 odd amps at peak because that's what it draws, and that goes into your amplifier at one end.
At the other end you get out about 25v RMS into a 4 ohm load which will dissipate around 150W.
You will actually draw a lot more than that from the supply because of the losses in the amplifier and associated mechanics of converting electrical energy into sound.
Class AB amps are only about 50% efficient, class D, more like 80%.
I don't know what tree you are attempting to bark up here, but I can say its most certainly the wrong one.
Its has nothing to do with perpetual motion, far from it. Look into class A amplifier design if you want to understand just how far!
No offence meant - I just always assumed you were into electronics.
If amplifier design is not something you are familiar with then that's fair enough, but this is really really basic stuff mate.
ajlelectronics
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but this is really really basic stuff mate.
Quite. Ohm's law and physics cannot be denied.
MetalMonkey
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Nowhere is it.
You are putting in about 550W of power and getting out 300. Tops.
cos they are like better ,,,, one better than just ten.
owas
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I fitted speakers into the headlining above the doors in my Landy which was the closest I could get them to my ears to give me a fighting chance of hearing anything over the noise of the engine, transmission, etc.
I've got 4 6x9s,2 6.5s, 4 tweeters and a slim sub in mine
I've always found just replacing the speakers for decent ones more than adequate in my w201/124s.
My_Teenage_Self
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I have an amp capable of 1000w @ 1ohm (@12.4v). It powers a Subwoofer with an impedence of 1 ohm (actually about 1.2 at rest). With the gains set correctly, and with it at near maximum output playing a 60hz sine wave (speaker disconnected!) it outputs over 30v - I measured it. it's a decent quality amplifier (helix) and they (and many others - search youtube for Amp Dyno) have been independently verified to put out over 1000W.
this isn't made up - this is my actual setup. Amplifiers do output a higher voltage than they are supplied.
It's installed in a car that is built for sound quality (and as sad as it sounds, yes, I have competed) it's built for quality, not volume. It's not easy to reproduce the feeling of church organs at 10hz, and takes a lot of power/speaker area.
JOEPRO
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I got a rare couple of hours late last night so I finished the heater box. Therefore I plan to re install the dashboard tomorrow or Thursday night, sooner than expected but all good.
I ordered these speakers which from measuring will fit in the front dash recesses and get covered by the original grills so won't be seen, seem decent spec for the £:
I ordered these speakers which from measuring will fit in the front dash recesses and get covered by the original grills so won't be seen, seem decent spec for the £:
