Cheap but good 2ch amp and 1ch mono

chodecz · Post by **chodecz** » Wed Mar 29, 2006 1:30 pm

Glasswolf, I just tested the voltage using a digital voltmeter.

It read 14VDC. This was with the engine at idle and music playing a moderate level. It dropped very slightly when I turned my lights on and volume full.

I took the measurement at the battery. 14VDC isn't going to my amp, is it?? If it is not, how do I measure what is???

PLease help.

Bwcad1 · Post by **Bwcad1** » Wed Mar 29, 2006 1:41 pm

yes most likely your amp is geting 14 v go to the amp and measure it at the terminals. and my lights dim if it drops below 13.5

Post by **GlassWolf** » Wed Mar 29, 2006 2:26 pm

measure at the distribution block and ground, or at the amp's power and gnd terminals.
14 volts isn't a problem though. as long as you're at 12 or more, you're good.

chodecz · Post by **chodecz** » Sat Apr 01, 2006 7:19 am

OK guys.

I measured at the amp... with engine off its just over 12VDC, and engine on (idle) its just over 14VDC.

I've been looking at amps specs, and they usually quote at 12.5VDC and 14.4VDC. So I will just run my system with engine on at all times so I dont have to buy bigger amps (or provide less current to my speakers).

One question though... for example a MTX amp states 2 x 90w RMS @ 12.5 VDC,, then Dynamic power (no mention of RMS) 2 x 125 @ 14.4VDC.

If i'm running this amp at around 14.4VDC, what will the RMS power be???

Thanks in advance.

JeremyC · Post by **JeremyC** » Sat Apr 01, 2006 8:05 am

You don't have to worry about "Just running the stereo with the car running" unless you plan on cranking it for extended amounts of time. You won't get the full RMS wattage out of an amp till you have your radio turned all the way up (right before the amp enters clipping).

Any other time, and the amp will be putting out less than rated power, so it won't really matter if you have 12 or 14.4 volts pushing it.

chodecz · Post by **chodecz** » Sat Apr 01, 2006 1:28 pm

Thanks JeremyC!

One question though... for example a MTX amp states 2 x 90w RMS @ 12.5 VDC,, then Dynamic power (no mention of RMS) 2 x 125 @ 14.4VDC.

If i'm running this amp at around 14.4VDC, what will the RMS power be???

Thanks in advance.

Post by **GlassWolf** » Sat Apr 01, 2006 2:22 pm

that is RMS.
they mean dynamic in this case because power fluctuates with voltage. unregulated power supply.
basically take the RMS power (say 90 watts) and divide by the voltage (12.5)
the result is the amperage drawn.
multiply that amperage by the new voltage (14.4V) and you have your wattage (RMS) @ 14.4VDC.

example, my amp is rated at 1000 watts @ 4 ohms @ 12VDC
that's 83.33333 amps
so, with an unreg'ed power supply @ 14.4VDC, the amp puts out:
(83.33333*14.4 =) 1200 watts RMS
(rated anyway.)

chodecz · Post by **chodecz** » Sat Apr 01, 2006 2:38 pm

Thank you Glasswolf (yet again) :) .

Ok so I do 90 / 12 = 7.2 amperage drawn, then 7.2 x 14.4 = 103.68w RMS @ 14.4VDC.

So why does the manual state "Dynamic power = 2 x 125 @ 14.4VDC"???? When you said that this was the RMS??

chodecz · Post by **chodecz** » Sat Apr 01, 2006 4:10 pm

I have also just looked at a Kicker manual for the kx350.2

It states 2 x 70w RMS @ 4 ohms @ 12.5VDC, and 2 x 110w RMS @ 4 ohms @ 14.4VDC.

If i do the calculation you said... 70 / 12.5 = 5.6, 5.6 x 14.4 = 80.64w RMS!

What am I to believe now?? Do Kicker print false (exaggerated) specs???

Post by **GlassWolf** » Sat Apr 01, 2006 6:04 pm

I'm not sure what they're thinking then, but also remember as you go up in power (higher voltage, lower load, etc) you lose more to heat, so the calculation is never exact, and you still need to figure for efficiency which can affect input power to output power by as much as sixty percent.

Keep in mind when you talk about RMS power ratings though, you're talking about continuous power at full volume with a non-reactive load, and a tone generator running 20-20,000Hz pink noise. In short, the power you'll actually put to speakers at normal listening volumes with music playing is a small fraction of that power rating in reality. The rest is just dynamic headroom.

With that in mind, it's easier to talk about percentage differences when talking about power differences of an amp with an unregulated power supply at 12 or 14 volts than it is to ask about "how much power" you'll really get.

If you have such an amp, you'll get 20% more power (approximately) at 14.4VDC than you will at 12VDC.

That's what you really want to know.

Then you can figure that twice the actual power to a speaker yields a +3dB increase in volume. This is the same increase as adding a second identical speaker without increasing the power at all.
A +10dB increase in output is equal to double the audible volume, or increasing power by a factor of ten.

The result of a 20% increase in power is barely audible, if at all, especially when considering the dynamic nature of music to begin with.