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nuub
Dodge Dakota
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4/17/2004
19:34:03
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 Subject: Amp Volt question
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Hello i'm very new at the car audio stuff. I want to get an amp but i got a question. I have been looking at amps and it has two sets of numbers one with 12.5 volt and other with 14.4 Which one do i look at?
Example
Thunder 304 Amplifier
--------------------------------------------------------------------------------
RMS Power measured at 12.5 Volts DC:
37.5 Watts x 4 into a 4 Ohm load with less than 0.1% Thd+N
75 Watts x 4 into a 2 Ohm load with less than 0.3% Thd+N
150 Watts x 2 bridged into a 4 Ohm load with less than 0.3% Thd+N
Dynamic Power (IHF-202 Standard) measured at 14.4 Volts DC
90 Watts x 4 into a 4 Ohm load
165 Watts x 4 into a 2 Ohm load
325 Watts x 2 bridged into a 4 Ohm load
Thank you very much
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Jim Z
GenI
4/17/2004
20:27:51
|  RE: Amp Volt question
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well, the 12-12.5 volt number is likely to be closer to real world conditions. The electrical system of most cars runs from 13.5-14.2 volts. Assuming you have good power cabling which is sufficient for your current draw, you can probably take the 12 volt rating as the minimum you're likely to see.
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nuub
Dodge Dakota
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4/17/2004
20:39:00
| RE: Amp Volt question
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Thanks Jimz.
So does the amp power vary. If i get a pair of speakers with is 40 watts rms will it blow??
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Jeff
Dodge Dakota
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4/18/2004
13:10:01
| RE: Amp Volt question
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12.5 volts is from the battery (while the truck is off)
14.4 is the voltage while the truck is on, the alternator makes a bit more than the battery.
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Levey
Dodge Dakota
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4/18/2004
22:18:21
| RE: Amp Volt question
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Volts is the power going to the amp..powering the amp. Watts are what are going to the speakers, From the amp. You wont blow your speakers as long as you choose an amp that matches your speakers RMS Watts. Watts RMS is the number you should look at, Watts MAX is kind of irrelevant. Choose an amp that has a rated RMS watts thats as close to (without going over) the stated RMS watts of the speakers. If you follow this and hooked everything up correctly it is virtually impossible to blow your speakers.
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Jim Z
GenI
4/18/2004
23:38:27
| RE: Amp Volt question
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Volts is the power going to the amp..powering the amp. Watts are what are going to the speakers, From the amp.
Volts are volts, not power. the amp takes power in (the supply voltage multiplied by the current draw), and outputs power to the speakers.
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Levey
Dodge Dakota
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4/20/2004
21:48:05
| RE: Amp Volt question
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Your right, I was just tryin to be simple, clearing up the fact that the input volts an amp is measured at is different than the watts it puts out.
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JMII
Dodge Dakota
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4/21/2004
16:58:07
|  RE: Amp Volt question
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Volts X Amps = Watts.
So, for example...
12V X 30A (fuse rating of the amplifer) = 360 watts.
This how you can easily tell if a company is BSing about the power their amp puts out. In the above example if the amp says "500 watts" you'll know it's physically impossible, the fuse would blow every time.
Dynamic or Max power is what the amp can do in short bursts, almost all amps will double their power but for only a split second. Thus as mentioned this spec is nearly useless. Just look at the RMS @ 12V since that's what will happen in the real world vs a test bench. If you hook up a multimeter up to the 12V+ on you amp while the truck is running you'll see it hop around between 14 and 11V as the music changes or as you turn on the A/C & headlights. If it drops below 10V then your wires are too small to pass the needed current.
- John
http://www.blueoceanpress.com/~storage/truck/index.html
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Levey
Dodge Dakota
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4/22/2004
01:10:09
| RE: Amp Volt question
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Now thats some good info! Thanks.
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nuub
Dodge Dakota
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4/22/2004
02:34:19
| RE: Amp Volt question
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Thank you jim and everyone
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nuub
Dodge Dakota
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4/22/2004
02:55:54
| RE: Amp Volt question
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I got one more question. The specs on my reciver says it reproduces signals from 40htz and up. Does it mean that if i connect to an amp it will not go any lower than 40 htz?
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Jim Z
GenI
4/22/2004
18:18:37
| RE: Amp Volt question
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That might only be for the speaker outputs. Some high-power receivers will high-pass the speaker outputs, most likely to protect speakers which can't handle low frequencies.
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Roy Germer
Dodge Dakota
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4/23/2004
02:10:56
| RE: Amp Volt question
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Im running a Mtx rt4240 for bass. why, I have no idea i guess i wass a victim of a sales man, any way. Im running this amp with some bazookas that deliver 200 rms at 4 ohms. my question is in what way sould i bridge the amp so that i get the max out of this sistem. The way i have it now is at 4ch low pass (lefth-top pos, to lefth-bottom neg) and right-top neg, to rigth-bottom pos)its workin berry good but if there is a way to make this convination improove i woul berry much like to know how. Im getting verry intrested in car sistems and so far i have heard only good things about this amp. I would like to thakns in advance for your time
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POSTAL24060
Dodge Dakota
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4/24/2004
09:22:16
| RE: Amp Volt question
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The formula above volts x amps = watts is correct but should not be used to calculate amplifier output
1. fuse rating is max that amp can draw before overload ( internal short cicuit or component failure)not what the amplifier can draw on continuous basis.
2. no electrical circuit or component is 100% efficient so the amplifier will always use more current(amps) on the power (volts) side that it can put out on the speaker side.
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JMII
Dodge Dakota
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4/26/2004
13:25:12
|  RE: Amp Volt question
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POSTAL24060 - true... I was just posting it to keep people from getting ripped off by those cheap amp compaines that claim 500 watts but only have a 20 amp fuse on thier products.
Most amps are only about 60-70% effeicent I'd guess... maybe even less - this is why they get so hot. Thus in my example above an amp with a 30A fuse will put out around 260 watts in the real world at 12 volts. Class D amps are better at around 80% effeicent (once again a rough guess) but they are only good for subs due the switching distrortion inherent in their design.
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Jim Z
GenI
4/26/2004
15:09:06
| RE: Amp Volt question
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Most amps are only about 60-70% effeicent I'd guess...
Class AB amps are about 65% efficient at full output. Efficiency goes down as output power is reduced. Class D amps can be up to 90% efficient.
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